A connecting fitting includes a body having a cam surface and an inserting assembly which is pivotally connected with the body. The inserting assembly includes an inserting member and at least one expandable member mounted between the body and the inserting member. The expandable member includes an expandable portion and a lip portion extending from the expandable portion. A compressible space is defined by the expandable portion and the lip portion, and the expandable portion has a plurality of snap portions. When the body is axially turned relative to the inserting assembly at a certain angle to generate a push force, the snap portions will be expanded outwardly by the push force.

1. Field of the Invention
This invention relates to a connecting fitting, and more particularly to a connecting fitting for furniture installation, which is able to be used repeatedly.
2. Description of the Prior Art
Connecting fittings can be used for furniture connection. Such techniques have been disclosed, such as U.S. Pat. No. 5,611,637, titled "Furniture Fitting", which comprises at least one dowel 6 to be inserted into a hole 22 in one furniture part, an expansion member 10 disposed in the dowel 6, and a holding member 8 connected to another furniture part. The expansion member 10 has an expansion surface and is movable relative to the dowel 6 between a relaxed position, enabling the dowel 6 to be inserted into the hole 22, and an expanded position. The holding member 8 is connected to an end of the expansion member 10 with a shaft for pivotal movement about the shaft. The holding member 8 has a cam surface 9 which is adapted to abut against a surface of the dowel 6, such that pivotal movement of the holding member 8 causes the cam surface 9 to abut against the surface of the dowel 6, and the holding member 8 drives the expansion member 10 to move axially. With the expansion surface to expand the dowel 6, the dowel 6 is able to be secured in the hole 22.
The dowel 6 is substantially formed with plural teeth around its surface. The inner surface of the hole 22 of the furniture part can be bit by the dowel 6 when the dowel 6 is inserted into the hole 22 and the holding member 8 is turned for the expansion member 10 to expand the dowel 6. However, once the holding member 8 is released, the expansion member 10 will return to its original position, so that the dowel 6 will be released and the teeth will be disengaged from the inner surface of the hole 22. When the teeth engage with or disengage from the inner surface of the hole 22, it will leave marks at the same positions each time. After many times of usage, the marks will influence the retaining effect of the conventional connecting fitting.


There is disclosed, for use in video text analysis system, a video processing device for searching video streams for one or more user-selected image text attributes. The video processing device comprises an image processor capable detecting and extracting image text from video frames, determining attributes of the extracted image text, comparing the extracted image text attributes and the user-selected image text attributes, and, if a match occurs, modifying, transferring, and/or labeling at least a portion of the video stream in accordance with user commands. The invention uses the user-selected image text attributes to search through an archive of video clips to 1) locate particular types of events, such as news programs or sports events; 2) locate programs featuring particular persons or groups; 3) locate programs by name; 4) save or remove all or some commercials, and to otherwise sort, edit, and save all of, or portions of, video clips according to image text that appears in the frames of the video clips.

The present invention is directed, in general, to video processing systems and, more specifically, to a system for analyzing and characterizing a video stream based on the attributes of text detected in the content of the video.
The advent of digital television (DTV), the increasing popularity of the Internet, and the introduction of consumer multimedia electronics, such as compact disc (CD) and digital video disc. (DVD) players, have made tremendous amounts of multimedia information available to consumers. As video content becomes readily available and products for accessing it reach the consumer market, searching, indexing and identifying large volumes of multimedia data becomes even more challenging and important.
Systems and methods for indexing and classifying video have been described in numerous publications, including: M. Abdel-Mottaleb et al., xe2x80x9cCONIVAS: Content-based Image and Video Access System,xe2x80x9d Proceedings of ACM Multimedia, pp. 427-428, Boston (1996); S-F. Chang et al., xe2x80x9cVideoQ: An Automated Content Based Video Search System Using Visual Cues,xe2x80x9d Proceedings of ACM Multimedia, pp. 313-324, Seattle (1994); M. Christel et al., xe2x80x9cInformedia Digital Video Library,xe2x80x9d Comm. of the ACM, Vol. 38, No. 4, pp. 57-58 (1995); N. Dimitrova et al., xe2x80x9cVideo Content Management in Consumer Devices,xe2x80x9d IEEE Transactions on Knowledge and Data Engineering (Nov. 1998); U. Gargi et al., xe2x80x9cIndexing Text Events in Digital Video Databases,xe2x80x9d International Conference on Pattern Recognition, Brisbane, pp. 916-918 (Aug. 1998); M. K. Mandal et al., xe2x80x9cImage Indexing Using Moments and Wavelets,xe2x80x9d IEEE Transactions on Consumer Electronics, Vol. 42, No. 3 (Aug. 1996); and S. Pfeiffer et al., xe2x80x9cAbstracting Digital Moves Automatically,xe2x80x9d Journal on Visual Communications and Image Representation, Vol. 7, No. 4, pp. 345-353 (1996).
The detection of advertising commercials in a video stream is an also active research area. See R. Lienhart et al., xe2x80x9cOn the Detection and Recognition of Television Commercials,xe2x80x9d Proceedings of IEEE International Conference on Multimedia Computing and Systems, pp. 509-516 (1997); and T. McGee et al., xe2x80x9cParsing TV Programs for Identification and Removal of Non-Story Segments,xe2x80x9d SPIE Conference on Storage and Retrieval in Image and Video Databases, San Jose (Jan. 1999).
Recognition of text in document images is well known in the art. Document scanners and associated optical character recognition (OCR) software are widely available and well understood. However, detection and recognition of text in video frames presents unique problems and requires a very different approach than does text in printed documents. Text in printed documents is usually restricted to single-color characters on a uniform background (plain paper) and generally requires only a simple thresholding algorithm to separate the text from the background. By contrast, characters in scaled-down video images suffer from a variety of noise components, including uncontrolled illumination conditions. Also, the background frequently moves and text characters may be of different color, sizes and fonts.
The extraction of characters by local thresholding and the detection of image regions containing characters by evaluating gray-level differences between adjacent regions has been described in xe2x80x9cRecognizing Characters in Scene Images,xe2x80x9d Ohya et al., IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 16, pp. 214-224 (Feb. 1994). Ohya et al. further discloses the merging of detected regions having close proximity and similar gray levels in order to generate character pattern candidates.
Using the spatial context and high contrast characteristics of video text to merge regions with horizontal and vertical edges in close proximity to one another in order to detect text has been described in xe2x80x9cText, Speech, and Vision for Video Segmentation: The Informedia Project,xe2x80x9d by A. Hauptmann et al., AAAI Fall 1995 Symposium on Computational Models for Integrating Language and Vision (1995). R. Lienhart and F. Suber discuss a non-linear red, green, and blue (RGB) color system for reducing the number of colors in a video image in xe2x80x9cAutomatic Text Recognition for Video Indexing,xe2x80x9d SPIE Conference on Image and Video Processing (Jan. 1996). A subsequent split-and-merge process produces homogeneous segments having similar color. Lienhart and Suber use various heuristic methods to detect characters in homogenous regions, including foreground. characters, monochrome or rigid characters, size-restricted characters, and characters having high contrast in comparison to surrounding regions.
Using multi-valued image decomposition for locating text and separating images into multiple real foreground and background images is described in xe2x80x9cAutomatic Text Location in Images and Video Frames,xe2x80x9d by A. K. Jain and B. Yu, Proceedings of IEEE Pattern Recognition, pp. 2055-2076, Vol. 31 (Nov. 12, 1998). J-C. Shim et al. describe using a generalized region-labeling algorithm to find homogeneous regions and to segment and extract text in xe2x80x9cAutomatic Text Extraction from Video for Content-Based Annotation and Retrieval,xe2x80x9d Proceedings of the International Conference on Pattern Recognition, pp. 618-620 (1998). Identified foreground images are clustered in order to determine the color and location of text.
Other useful algorithms for character segmentation are described by K. V. Mardia et al. in xe2x80x9cA Spatial Thresholding Method for Image Segmentation,xe2x80x9d IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 10, pp. 919-927 (1988), and by A. Perez et al. in xe2x80x9cAn Iterative Thresholding Method for Image Segmentation,xe2x80x9d IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 9, pp. 742-751 (1987).
The prior art text-recognition systems do not take into account, however, the non-semantic attributes of text detected in the content of the video. The prior art systems simply identify the semantic content of the image text and index the video clips based on the semantic content. Other attributes of the image text, such as physical location in the frame, duration, movement, and/or temporal location in a program are ignored. Additionally, no attempt has been made to use video content to identify and edit video clips.
There is therefore a need in the art for improved video processing systems that enable a user to search through an archive of video clips and to selectively save and/or edit all or portions of video clips that contain image text attributes that match image text attributes selected by a user.
To address the above-discussed deficiencies of the prior art, the present invention discloses a video processing device for searching or filtering video streams for one or more user-selected image text attributes. Generally, xe2x80x9csearchingxe2x80x9d video streams refers to searching in response to user-defined inputs, whereas xe2x80x9cfilteringxe2x80x9d generally refers to an automated process that requires little or no user input. However, in the disclosure, xe2x80x9csearchingxe2x80x9d and xe2x80x9cfilteringxe2x80x9d may be used interchangeably. An image processor detects and extracts image text from frames in video clips, determines the relevant attributes of the extracted image text, and compares the extracted image text attributes and the user-selected image text attributes. If a match occurs, the video processing device may modify, transfer, label or otherwise identify at least a portion of the video stream in accordance with user commands. The video processing device uses the user-selected image text attributes to search through an archive of video clips to 1) locate particular types of events, such as news programs or sports events; 2) locate programs featuring particular persons or groups; 3) locate programs by name; 4) save or remove all or some commercials, and to otherwise sort, edit, and save all of, or portions of, video clips according to image text that appears in the frames of the video clips.
It is a primary object of the present invention to provide, for use in a system capable of analyzing image text in video frames, a video processing device capable of searching and/or filtering video streams in response to receipt of at least one selected image text attribute. In an exemplary embodiment, the video processing device comprises an image processor capable of receiving a first video stream comprising a plurality of video frames, detecting and extracting image text from the plurality of video frames, determining at least one attribute of the extracted image text, comparing the at least one extracted image text attribute and the at least one selected image text attribute, and, in response to a match between the at least one extracted image text attribute and the at least one selected image text attribute, at least one of: 1) modifying at least a portion of the first video stream in accordance with a first user command; 2) transferring at least a portion of the first video stream in accordance with a second user command; and 3) labeling at least a portion of the first video stream in accordance with a third user command.
According to an exemplary embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is one of: scrolling horizontally; scrolling vertically; fading, special effects and animation effects.
According to one embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is one of: a name of a person; and a name of a group.
According to another embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is part of a commercial advertisement.
According to still another embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is text appearing at one of: a start of a program; and an end of a program.
According to yet another embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is part of a program name.
According to a further embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is part of a news program.
According to a still further embodiment of the present invention, the at least one extracted image text attribute indicates that the image text in the plurality of video frames is part of a sports program.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9cprocessorxe2x80x9d or xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Additionally, the term xe2x80x9cvideo clipxe2x80x9d may mean a video segment, a video sequence, video content, or the like. Definitions for certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

Method and system for analyzing video content using detected text in video frames


A method of installing a telescopic shelf in a cabinet comprises installing a pair of facing guides, each guide having first and second brackets fixed at opposed ends of the guide and each bracket having either a planar lug or a hook for engaging with a series of mounting holes. When the guides have been installed, a telescopic shelf can be slid into the facing channels. As the brackets are fixed to the guide and, the fixing of the guides within the cabinet is carried out purely by engagement of parts of the brackets with the mounting post, there is never any need for loose pieces to be used within the cabinet. The brackets are telescopically adjustable to accommodate guides and shelves of different dimensions.

1. Field of the Invention
The present invention relates to a method of assembling a cabinet, particularly the type of cabinet having at least one telescopic shelf.
2. Description of the Related Art
In certain types of cabinet with telescopic shelves, the guides for the telescopic shelves are fixed to the cabinet by brackets having a pair of vertically spaced lugs which diverge in a vertical direction. In this case, a respective bracket is provided at each end of the guide and each bracket is fixed in place by inserting one or other of the lugs into a mounting hole and then forcing the other lug so that it fits into a vertically spaced mounting hole, whereupon the two lugs hold the guide securely in place.
Such an arrangement is not suitable for use with electronic equipment, as when the shelves are extended telescopically from the cabinet, the bending moment on the rearmost brackets is considerably exaggerated, so that the vertical force acting on the rearmost bracket tends to cause this bracket to pop out of engagement with the mounting holes.
Therefore, for such applications, it is necessary to bolt each bracket in place to ensure that it remains engaged with the mounting post. Such an arrangement has a disadvantage that each bracket has several loose pieces which can easily be dropped inside the cabinet, and also in that the brackets are time consuming to install which is particularly a problem in installations which require numerous cabinets, each of which has numerous telescopic shelves.
U.S. Pat. No. 3,110,536 discloses a method of installing a telescopic shelf in a cabinet comprising an opening at one side and being substantially rectangular in plan, a pair of rear mounting posts extending vertically in the two corners of the cabinet remote from the open side, and a pair of front mounting posts extending vertically in the corners of the cabinet adjacent to the opening, mounting holes being provided in each pair of mounting posts, the method comprising the steps of installing a guide into the cabinet, the guide comprising a longitudinally extending channel portion for receiving a respective edge of the telescopic shelf, a first bracket fixed at the rear end of the guide and a second bracket fixed at the front end of the guide, the first bracket being provided with a first lug, the second bracket having a second lug; the steps of installing the guide comprising fitting the first lug in a mounting hole in a rear mounting post and moving the guide longitudinally until the first lug is secured in the mounting hole, and twisting the guide about a longitudinal extending axis, so as to insert the second lug into a mounting hole in the front mounting post, the engagement of the second bracket with the front mounting post preventing movement of the guide longitudinally sufficient to release the first bracket from the rear mounting post; installing a second guide in a similar manner so that its channel portion faces the channel portion of the first guide; and sliding the opposite edges of a telescopic shelf into the facing channels.
With this arrangement, when the shelf is extended and loaded vertically thereby transmitting an upward vertical load to the first bracket, the first bracket cannot be disengaged from the rear mounting post as to disengage the hook from the mounting hole requires movement of the guide longitudinally in the horizontal direction, which is prevented by the second bracket. As the brackets are fixed to the guide and, the fixing of the guides within the cabinet is carried out purely by engagement of parts of the brackets, with the mounting posts, there is never any need for loose pieces to be used within the cabinet.
In practice, it has been found that, with this arrangement, the telescopic shelves can be installed 95% quicker than with guides which must be bolted in place. This represents a enormous time saving for installations where numerous cabinets are used. It also allows unskilled operators to install shelves without tools, allowing an operator to adjust the position of the shelves without difficulty. Access for the installation is only required from the front, so that there is no need to remove the side panels of the cabinet.
There is a growing need within electronic cabinets to mount equipment of various xe2x80x9cmounting standardsxe2x80x9d and of various front to back (depth) dimensions. Some of this equipment requires that the front mounting posts and the rear mounting posts are set at depths which are specific to that equipment. In some cases, these centres will not match the fixing centres of side rails or telescopic slides. In such cases, extra pairs of vertical mounting posts are required to accommodate these various depth requirements. In densely populated cabinets, it is often impossible to fit these mounting posts.
According to the present invention, the method disclosed in U.S. Pat. No. 3,110,536 is characterised in that at least one of the brackets for each guide is telescopically adjusted to set the position of the guide relatively to at least one of the mounting posts in the depth and/or width directions of the cabinet.
This arrangement enables great versatility in mounting the shelf guides at appropriate positions in the cabinet to meet operational requirements. For example, short guides can be fitted in deep cabinets by using the brackets to bridge the difference in depth.
The range of application is therefore dramatically greater than fixed centre versions of this type of quick fit assembly, and is a unique, and cost effective solution, for populating a densely packed cabinet with equipment of widely varying depth or width measurements, whilst preserving the quick fit characteristics of the design.
For depth adjustment, at least one of the brackets may be telescopically adjustable relatively to the guide in the longitudinal direction of the guide. For width adjustment, both brackets will need to be adjustable and two parts of each bracket may be telescopically adjustable relatively to one another in the width direction of the cabinet.
The present invention also includes a cabinet comprising an opening at one side and being substantially rectangular in plan; a pair of rear mounting posts extending vertically in the two corners of the cabinet remote from the open side; a pair of front mounting posts extending vertically in the corners of the cabinet adjacent to the opening; mounting holes provided in each pair of mounting posts; a pair of guides being mounted at opposite sides of the cabinet and having facing channel portions between which the telescopic shelf is slidably received; each guide being attached within the cabinet by a first bracket fixed at the rear end of the guide and a second bracket fixed at the front end of the guide, the first bracket having a first lug mounted in a mounting hole such that it must be moved by a certain amount in the longitudinal direction of the guide to be disengaged from its mounting hole, the second bracket having a downwardly inclined second lug fitted in a mounting hole, and engaging with the lowermost edge of a mounting hole, the engagement of the second lug with its mounting hole being such as to prevent the movement of the first lug by the certain amount; and a telescopic shelf slidably supported between the facing channel portions; characterised in that at least one of the brackets for each guide is telescopically adjustable to set the position of the guide relatively to at least one of the mounting posts in the depth and/or width directions of the cabinet.
If the first lug is planar and extends rearwardly from the first bracket, the lug is engaged by movement of the guide in the direction in which the shelf is retracted. On the other hand, if the first lug is a hook, the open portion of which faces the front of the guide, the hook is engaged by being fitted into a mounting hole in a horizontal direction and pulled forwardly so that the bottom of the hook abuts against a vertically extending edge of the mounting hole. This second approach has been found to provide a more rigid support for the guide. Further, the hooks can be fitted into mounting holes which face across the cabinet, rather than mounting holes which face the front of the cabinet. This is advantageous with cabinets for electronic equipment in which the front facing mounting holes are conventionally used for mounting other equipment.
In order to provide a more rigid connection the first bracket preferably has two or more elevationally spaced first lugs. Although some vertical movement of the first bracket can be tolerated, another way of improving the rigidity of the brackets is for the height of the or each first lug to be substantially equal to the height of the mounting hole in which the or each first lug is fitted. This prevents movement of the first bracket in a vertical direction. Furthermore, a pair of vertically spaced second lugs may be provided and which diverge in the vertical direction, such that the uppermost lug engages with the top edge of a mounting hole. The width of the or each second lug is preferably substantially equal to the width of the mounting hole in which respective lug is engaged, to prevent movement of the second bracket in the direction in which the shelf is retracted and extended.
As the load on the second bracket is almost exclusively a downward vertical load, it is preferable for the uppermost lug to extend vertically by a greater extent than the lowermost lug to prevent the first bracket from being dislodged by a vertically downward load. When such a bracket is installed the longer uppermost lug is firstly inserted into a mounting hole and the guide is lifted slightly in order to force the second lug into its mounting hole.

Method of installing a telescopic shelf in a cabinet


An electrically short, omnidirectional antenna formed with a strip conduc helically wound about the outside of a cylindrical ground plane. A layer (ideally, a very thick layer) of a nonconducting material preferably with a low dielectrical constant (i.e., .epsilon..sub.r .perspectiveto.1.0) separates the microstrip from the ground plane.

This invention relates to antennae and more particularly, to omnidirectional microstrip antennae.
A short, vertical rod is the classic omnidirectional antenna. It is omni-directional in a plane perpendicular to its longitudinal axis, vertically polarized in that plane, and may be easily matched with the impedance of ancillary equipment stages. Characteristically, a vertical rod is inefficient, does not remain tuned when placed in different media of radiation, and is particularly sensitive to nearby sensors, oscillators, and transmitters. While two orthogonal vertical loops may be used to provide the proper pattern (i.e., omnidirectional) and desired polarization, interactions between loops detracts from the performance of the antenna. Also, efficiency is low when loops are small compared to the operating wavelength. The noun "ground plane" denotes a conducting or reflecting plane functioning to image a radiating structure.

The United States of America as represented by the Secretary of the Navy


This invention concerns a boiler fitted with a burner suitable for wall heaters or built-in kitchen heaters in which a mantle-shaped heat exchanger made of pipe elements connected in parallel and/or series divides the boiler chamber into a combustion chamber and an exhaust chamber. The heat exchanger has openings for hot flue gases distributed over its mantle. The burner head disposed in the combustion chamber is suitable for burning oil and has a flame tube with an axial flame opening and a flame baffle element disposed at a distance from the flame opening which is constructed so that the flame is diverted into the space between the flame tube and the heat exchanger. In addition, a fire chamber mantle can be disposed between the heat exchanger and the flame tube to protect the heat exchanger from direct contact with the flame.

1. Field of the Invention
The present invention relates to a boiler or water heater equipped with a burner, including a housing surrounding a boiler compartment, a cylindrical heat exchanger, which divides the boiler compartment into a combustion chamber, and an exhaust chamber; whereby said heat exchanger comprises passages distributed across its surface for the hot exhaust gas, and a burner head positioned in the combustion chamber.
2. Review of the Prior Art
Such a boiler or water heater is disclosed in the French Patent document No. 93 00498, and is incorporated herein by reference. It contains a number of boiler designs, which exhibit the above-mentioned design features. These boilers are designed to accommodate gas burners and comprise a cylindrical casing with the sides closed off, and a plurality of flame openings distributed across the surface area. Such a gas-fired boiler or water heater is space-saving in its design and does not require a separate furnace room.
It has been a long-standing desire for such a space-saving furnace to be capable of being operated with fuel oil. The disadvantage of using gas as fuel is the more complex fuel storage requirements as compared to oil. As a result, the gas furnace has to rely on either an expensive pressurized tank or on a connection to a gas distribution network. Oil, on the other hand, has been stored in sufficient quantities in tanks located at the site of the furnace in thousands of installations without any problems. Additionally, the supply and filling of the tanks with oil is substantially simpler and less dangerous as compared to gas.
It is therefore the purpose of the invention to provide a furnace, which can be operated by an oil burner without making it larger than a comparable gas furnace. Furthermore, the furnace should be capable to be operated with a gas or an oil burner. Additionally, it is an objective of this invention to provide a furnace characterized by low exhaust emissions, reduced heat loss, and low noise levels.
The objectives are met, in accordance to the intent of this invention, by adding a fire tube comprising an axial flame opening and a flame deflection piece positioned at a distance to the flame opening to the burner head; whereby, the fire tube is designed in such as manner that the flame between the fire tube and the heat exchanger is deflected.
One of the advantages of a furnace designed per this invention is that it can be operated by burners, which produce a lance-shaped flame. Such a flame usually requires a very long combustion chamber. A flame deflection piece, designed in accordance to this invention, allows the length of the combustion chamber to be significantly reduced. The deflection piece turns the flame back to its origin and, as a result, reduces the length of the combustion chamber by xc2xd. This allows the combustion chamber to be almost fully saturated by the flame exiting the fire tube which is subsequently being deflected into the opposite direction. The deflection of the flame to its origin has the further advantage that very hot gas is present around the fire tube very soon after the flame is initiated, enhancing the cold start characteristics of the furnace. Another advantage of deflecting the flame in the above-described manner lies in the fact that the combustion chamber can be utilized much more effectively and, therefore, can be designed in a more compact fashion as compared to those systems that produce a long, thin flame. More specifically, because of the burner head being surrounded by the flame, the entire length of the combustion chamber is more thermally uniform and therefore better-suited to exchange heat energy to the heat exchange medium.
It is advisable for the heat exchanger to comprise a blocking plate, which effectively limits the combustion system in lengthwise direction. In addition to the exhaust chamber, this creates an additional chamber into which exhaust gas flows from the exhaust chamber. The exhaust gas is cooled by the heat exchanger and is partially re-circulated back to the fire tube in order to cool the flame, and partially exhausted through the flue. A preferred blocking plate design separates the discharge chamber from the boiler compartment at its side facing away from the combustion chamber, whereby said discharge chamber is connected to the flue. Such a discharge chamber resides axially inside the boiler. This allows a uniform flow of the exhaust gas from peripheral the areas into the discharge chamber. This avoids non-uniform thermal loading issues of the heat exchanger. It is preferred for the blocking plate to separate a re-circulation chamber from the boiler compartment. Cooled exhaust gas can then re-circulate through this re-circulation chamber into the fire tube in order to cool the flame. The re-circulation chamber can also serve the function of a discharge chamber. It would be preferred, if the discharge chamber and/or re-circulation chamber (separated by the blocking plate) were surrounded by the heat exchanger. This allows additional cooling of the exhaust gas entering these chambers prior to leaving the furnace. As a result of the dual contact with the heat exchanger, the exhaust gas is cooled to approximately 80 degrees C., at continuous operation under full load. This allows for the exhaust gas to be piped directly into a flue (made of a plastic compound) upon exiting the boiler.
Further, it would be preferred that the blocking plate between the combustion chamber and the exhaust discharge chamber is shaped in a curved manner in such a way as to allow an increase in the length of the combustion chamber while minimizing the space requirements of the exhaust discharge chamber. Such a design feature results in a relatively large ratio of the heat exchanger surface surrounding the exhaust discharge chamber with respect to its volume.
In order to reduce the number of required parts, the flame deflection piece should form the blocking plate. In doing so, the position of the deflection piece in relation to the housing wall has certain acoustic advantages. The domed surface should point towards the exhaust discharge chamber. The purpose of this domed surface is to deflect the flame without the participation of any heat exchange elements, permitting the use of the entire heat exchange area since the deflection piece does not obstruct any passages for the hot exhaust gas. A preferred flame deflector design comprises a flame separator, positioned along the centerline of the flame and a ring-shaped deflector dish, which surrounds the flame separator. The flame separator divides the flame, and the deflector dish reflects the flame in order to change the flame direction by 180 degrees. The deflector dish should be made circumferentially uniform in order for the flame to retain a uniform shape after its deflection.
The casing of the heat exchanger consists of pipes positioned adjacent to one another with clearance between the pipes; whereby, said pipes are positioned to surround the combustion chamber and are connected to a supply and a return line. The heat exchange pipes should be wound in a screw-like manner. Such a heat exchanger unit is easy to manufacture; it comprises a large surface area and provides for passages between the pipes. Additionally, pipes can be made to thinner wall thicknesses as compared to castings, and therefore offer a more dynamic heat transfer characteristic which is reflected by higher performance at reduced space requirements. It would also be beneficial if this heat exchanger were assembled from a plurality of heat exchanger units. The individual heat exchanger units have the advantage of using shorter pipe lengths, as compared to a single unit having one long pipe system, resulting in higher through-flow velocities.
The heat exchanger units should be connected to the supply and return in parallel. Heat exchanger units using individual elements disclosed in the French Patent No. 93 00498 are applied successfully. The units described in said documents are characterized by a flat cross-sectional area of the pipes, resulting in an increase in the heat exchange area compared to typical pipes with round cross-sectional areas. Furthermore, an essential advantage of these heat exchanger units is due to the fact that these units are in series production for gas furnaces, and are therefore readily available in the marketplace at excellent quality levels.
The burner should be equipped with exhaust gas re-circulation in order to exceed the current regulated emission values, especially during cold starts.
Even if gas burners are applied to the boiler described by this invention, it is still preferred to use oil burners, simply because oil can be stored in inexpensive tanks, which can be readily refilled. The dependence on a supply distribution network can thus be avoided. Furthermore, the handling of oil is much less hazardous as compared to the handling of gas, which must be stored under pressure in appropriate tanks, in cases where it is not supplied through a gas distribution network.
It would be of benefit, however, to have the capability of the burner to operate on both fuels, oil as well as gas. If the burner head is designed to accommodate oil as well as gas, both fuels can be used in the same furnace alternatively with only minimal effort. This has the advantage that price changes and supply shortages can be dealt with in a more proactive fashion, or in a case of having to wait for a hook-up to be in place to provide gas to the furnace, oil can be used as a temporary means to power the furnace until the gas supply is secured.
For oil operation, an injector sprays oil into the exhaust gas being re-circulated into the fire tube; the inlet openings into the fire tube for fresh air as well as exhaust are designed so that fresh air and exhaust are mixed together inside the hollow cylinder or the hollow truncated cone making up the turbulent zone. As the oil mixes with the exhaust, it fully evaporates prior to its mixing with air. This assures very low exhaust emission values and an excellent starting behavior of the burner.
For gas operation, an air supply passage is used for introducing the gaseous fuel. The inlet openings into the fire tube for the fuel/air mixture and the re-circulated exhaust gas, respectively, are designed so that fuel/fresh air mixture and the exhaust are mixed together inside the hollow cylinder or the hollow truncated cone making up the turbulent zone. Because of these similar methods of introducing the fuels, the same fire tube can be applied to both fuels, gas and oil. It is feasible, to leave the oil injector in place during gas operation and to leave the gas supply system in place during oil operation, in order to provide a dual-fuel furnace with a single burner. A system, such as the one described above, is capable of achieving exhaust emission values of below 60 mg Nox per KW when operating on oil and under 20 mg Nox per KW when operating on gas. The CO values also lie under 20 mg Nox per KW at a very low level. In addition to these very low emission levels, the furnace is capable of performing very well under cold start conditions.
In the combustion chamber, in the area between the fire tube or deflected flame and the heat exchanger, resides a cylindrical combustion chamber shroud, comprising openings for the hot combustion gas. This combustion chamber shroud provides a uniform distribution of the hot combustion gas to the heat exchanger and also serves as an ash collector. It protects the heat exchanger from direct contact with the flame. This allows the distance between the flame and the heat exchanger to be very small. Additionally, this combustion chamber shroud has a positive influence in terms of noise suppression. The openings are arranged so that the combustion gas exits the combustion chamber shroud tangentially in order to facilitate the flow of the gas through the heat exchanger casing to also occur in a tangential direction. This improves the heat transfer as compared to a system that utilizes a radial through-flow direction.
The housing of this unit should be proportioned to be similar in size of a wall heating unit or a xe2x80x9cplug-inxe2x80x9d kitchen unit. The housing, including the air supply line and exhaust line, should have a length of approximately 50 cm. A short design should be able to operate with a boiler length of 30 cm. This means that a separate room for this furnace is not required. It can be stored in a cabinet. The air supply line should surround the exhaust gas line in a counter-flow arrangement in order to pre-heat the incoming air by the warm exhaust gas. The blower should be placed next to the housing with the air supply line leading from the blower to the end face of the housing and the burner head, in order to minimize the length and depth of the unit.
It is practical to line the end faces of the combustion chamber with fireproof tiles with a labyrinth-like inner structure. These protect the underlying metal parts, isolate the housing from the heat of the flame, and dampen the sound emissions of the burner. It is furthermore appropriate to provide one end face of the housing with a removable cover. It would be advantageous to mount the burner on this cover because this allows easy access to the boiler compartment and the burner.
It is further advisable to use austenitic stainless steel, which resists the aggressive exhaust gas and condensates.

Process and fuel burner with exhaust-gas recirculation


A ceramic-supported polymer membrane is disclosed where a porous ceramic membrane support of average pore size no larger than 500 xc3x85 is activated by attaching a vinyl terminated lower alkoxy silane to the surface of the ceramic membrane pores. The resulting membrane retains at least 10 micromoles of the vinyl terminated loweralkoxy silane per square meter of the ceramic membrane surface. A method for optimizing the amount of vinyl loweralkoxy silane reacted with the ceramic support surface is also disclosed. The large amount of vinyl terminated loweralkoxy silane which is chemically bonded to the surface of the ceramic porous support produces activated ceramic membrane support surface which is useful for graft polymerization of vinyl monomers onto the porous ceramic membrane support surface. A vinyl monomer is then graft polymerized onto the activated membrane. The resulting ceramic-supported polymer membrane is useful for pervaporation separation of liquids mixtures that are sufficiently different in their vapor pressure.

It is suggested in the art that separation of liquid mixtures is feasible by the process of pervaporation. Pervaporation is a separation process whereby a liquid mixture is separated based on the preferred solubility and diffusivity of the components of the mixture through an active polymer membrane phase. On the permeate side of the membrane the partial vapor pressure of the species to be removed is maintained at a level much lower than its value under ambient conditions by maintaining vacuum or using a sweep gas (for example, air or nitrogen). The permeating species undergo a phase change (from liquid to vapor) as they diffuse through the membrane and the permeating species are condensed in a cold trap. The process of pervaporation can be used effectively to separate mixtures of close-boiling point components and it is suitable for the removal of volatile compounds from aqueous as well as organic liquid mixtures. Application of pervaporation technology include dehydration of alcohol-water streams, removal of organic pollutants from dilute aqueous wastes, and separation of close boiling point mixtures and isotropic mixtures.
To date, most pervaporation studies have involved pure or asymmetric composite polymer membranes. Well-documented drawbacks of polymeric pervaporation membranes include lack of physical stability and chemical vulnerability to various industrial solvents. Conversely, ceramic membranes are known to have excellent structural integrity and high chemical and thermal resistance (Charpin, et al., 1991). The benefits of ceramic membranes are largely offset by poor selectivity and a limited selection of pore sizes. Such shortcomings are overcome in my invention by surface modification of the ceramic substrate with grafted polymer chains, forming an asymmetric covalently-bonded polymer surface layer. This thin polymer layer provides the desired chemical selectivity and allows controlled reduction of pore size near the membrane surface. The resulting grafted asymmetric ceramic-supported polymer (CSP) membrane possess polymer layer stability far superior to membranes which are simply coated or pore-filled with a polymer phase (Sakohara, et al., 1990).
Polymer modification methods of membranes include the filling of porous polymeric membranes with a gel, made consisting of cross-linked polyvinyl alcohol, for use in fractional liquid extraction [Hongbing, D. and E. L. Cussler, Fractional Extraction with Hollow Fibers with Hydrogel-Filled Walls, AICHE J., 37, N6 (1991) 855-862.] The membrane proposed by Hongbing and Cussler is different from the present invention because it deals with a polymeric membrane and the modifying polymeric gel is not chemically bonded to surface of the membrane.
Modification of a ceramic membrane by solution coating of preformed polymer was reported by Rezac and Koros [Rezac, M. E. and W. J. Koros, Preparation of Polymer-Ceramic Composite Membranes with Thin Defect-Free Separating Layers, J. Appl. Polymer Sci., 46 (1992) 1927-1938.]. Polymer-ceramic composite membranes were prepared by solution deposition of a thin selective polymer layer onto a microporous ceramic support. This membrane was formed by physical adsorption of pre-formed polymer onto the surface of the membrane. Thus, the polymeric phase is not a stable phase, thus polymer attrition will occur upon exposure to a good solvent. The present invention, in contrast, consists of a ceramic membrane support with polymeric chains chemically attached to the ceramic support.
Another example of a polymer-coated membrane was reported by Song and Hong [Song, K. M. and W. H. Hong, Dehydration of Ethanol and Isopropanol Using Tubular Type Cellulose Acetate Membrane with Ceramic Support in Pervaporation Process, J. Membrane Sci., 123 (1997) 27-33.] for the dehydration of isopropanol. A tubular-type cellulose-acetate membrane was formed on either the inner or outer surfaces of a porous ceramic support by the dip-coating and a rotation-drying technique. The Song and Hong membrane consists of a ceramic support physically-coated with a dense polymeric phase. Such a membrane will be unstable when exposed to high concentrations of the permeating species or good solvent for the polymer. In contrast, the present invention consists of a polymeric phase which is covalently bonded to the ceramic surface.
Another example of a polymer-coated membrane was reported by Song and Hong [Song, K. M. and W. H. Hong, Dehydration of Ethanol and Isopropanol Using Tubular Type Cellulose Acetate Membrane with Ceramic Support in Pervaporation Process, J. Membrane Sci., 123 (1997) 27-33.] for the dehydration of isopropanol. A tubular-type cellulose-acetate membrane was formed on either the inner or outer surfaces of a porous ceramic support by the dip-coating and a rotation-drying technique. The Song and Hong membrane consists of a ceramic support physically-coated with a dense polymeric phase. Such a membrane will be unstable when exposed to high concentrations of the permeating species or good solvent for the polymer. In contrast, the present invention consists of a polymeric phase which is covalently bonded to the ceramic surface.
A polymer-coated ceramic membrane for pervaporation was also proposed by Zhu et al. [Zhu, Y. R. G. Minet and T. T. Tsotsis, A Continuous Pervaporation Membrane Reactor for the Study of Esterification Reactions Using A Composite Polymeric/Ceramic Membrane, Chem. Eng. Sci., 51, No. 17, (1996) 4103-41]. The membrane was prepared by dip-coating a xcex3-Alumina ceramic support tube with polyetherimide solution. The membrane is intended for in situ water removal from reaction systems. In this membrane the polymeric phase is physically coated onto the ceramic support. As a result, such a membrane has a short life-time due to polymer attrition when subjected to good solvent conditions. Such a membrane cannot be effectively used for organic-organic separations. In a later study Zhu and Chen [Zhu, Y. and H. Chen, Pervaporation Separation and Pervaporation-Esterification Coupling Using Crosslinked PVA Composite Catalytic Membranes on Porous Ceramic Plate, J. Membrane Sci., 138 (1998) 123-134.] reported on a pervaporation membrane prepared by crosslinking a PVA dense active layer was coated on the porous ceramic plate. Then, Zr(SO4)2.4H2O, an inorganic solid acid which was used as the esterification catalyst in the experiment, was immobilized on the dense active layer. This membrane belongs to the class of coated polymeric membranes with cross-linking to improve membrane stability. However, the polymeric phase is not chemically attached to the porous ceramic support. In contrast, in the present invention the polymeric phase is chemically attached to the support surface.
Another example of a polymer-ceramic composite pervaporation membrane was proposed by Goldman et al. [Goldman, M., D. Fraenkel and G. Levin, A Zeolite/Polymer Membrane for Separation of Ethanol-Water Azeotrope, J. Appl. Polymer Sci., 37 (1989) 1791-1800.] who added a fine zeolite to a solution of dissolved poly(vinyl chloride), with the final membrane formed by subsequent casting of the mixture followed by a drying step. The membrane was used for ethanol/water azeotropic pervaporation. The above membrane differs from the present invention in that it deals with a powdered ceramic dispersed in a polymeric phase. In contrast, the present invention is a ceramic membrane with a polymeric phase of single chains chemically bonded to the ceramic membrane surface.
A ceramic membrane modified by pore-filling with acrylamide-based polymer was reported by Sakohara et al. [Sakohara, S.: F. Muramoto; T. Sakata and M. Asaeda, Separation of Acetone/Water Mixture by Thin Acrylamide Gel Membrane Prepared in Pores of Thin Ceramic Membrane, J. Chemical Engineering of Japan, 23, N1 (1990) 40-45.] A thin polyacrylamide gel membrane was formed within the pores of a thin porous ceramic membrane of silica-alumina by copolymerizing acrylamide type monomer and N,Nxe2x80x2-methylene-bis(acrylamide) as a crosslinking agent. This membrane consists of a gel phase which is physically held in the pores of the ceramic silica-alumina membrane. In contrast, the present invention consists of a ceramic support membrane with a layer of terminally and covalently bonded polymer chains. Therefore, the present invention does not suffer from instability caused by exposure to good solvents, or at elevated temperatures above the glass transition temperature of the polymer phase.
Hautojxc3xa4rvi et al [Hautojxc3xa4rvi, J., K. Kontturi, J. H. Nxc3xa4sman, B. L. Svarfvar, P. Viinikka, and M. Vuoristo, Characterization of Graft-Modified Porous Polymer Membranes, Ind. Eng. Chem. Res., 35 (1996) 450-457.] modified porous poly(vinylidene fluoride) membranes via radiation-induced grafting of acrylic acid. When the grafted membranes were characterized by measurements of convective permeability, diffusion and ion exchange properties, they showed variable membrane permeability with respect to the solvent and also ionic semi-permeability. The present invention is different from the above membrane in two ways. First, the present membrane is a modified ceramic membrane (and not a polymeric support membrane). Second, the present surface modification is based on liquid-phase free-radical graft polymerization whereas the above process requires radiation-induced grafting.
A strictly ceramic pervaporation membrane was developed by Van Gemert and Cuperus [Van Gemert, R. W. and F. P. Cuperus, Newly Developed Ceramic Membranes for Dehydration and Separation of Organic Mixtures by Pervaporation, J. Membrane Sci., 105 (1995) 287-291]. In their approach xcex3-Alumina was used as the membrane support onto which silica is deposited as a dense top layer by the sol-gel technique. The resulting membrane was tested for methanol, ethanol and 2-propanol dehydration by pervaporation. This membrane is a purely ceramic membrane, whereas the present invention is a hybrid ceramic-polymer membrane consisting of a ceramic porous support with a chemically-bonded polymeric surface phase.
Modification of a silica membrane for organic/aqueous pervaporation was reported by Kitao and Aseda [Kitao, S. and M. Asaeda, Separation of Organic Acid/Water Mixtures by Thin Porous Silica Membrane, J. Chemical Engineering of Japan, 23, N3 (1990) 367-370. ] A thin porous silica membrane was formed at the surface of an xcex1-alumina substrate by dipping in an inorganic silica sol-gel mixture. The solution was prepared by hydrolyzing tetraethoxysilane with a small amount of nitric acid. The above membrane is a silica membrane whereas the present invention is a ceramic membrane onto which a modifying organic polymeric phase is covalently attached via graft polymerization.
An approach where a membrane is prepared from a mixture of silica particles dispersed in a casting polymer solution was reported by Ulutan and Nakagawa [Ulutan, S and T. Nakagawa, Separability of Ethanol and Water Mixtures through PTMSP-Silica Membranes in Pervaporation, J. Membrane Sci., 143 (1998) 275-284.] Asymmetric poly[1-(trimethylsilyl)-1-propyne] composite membranes having silica on one side were prepared by mixing silica particles with a polymer casting solution. The higher density of the silica during casting caused the formation of a silica enriched membrane surface. The above approach is based on depositing a suspension of silica particles and organo-silane to form a dense membrane surface. The present invention is different since it does not require a mixture of silica particles and a pre-formed polymer which are casted from solution. The present invention is a surface modification method whereas the Ulutan and Nakagawa membrane process is a bulk-casting process.
Pasternak and Kokturk [Pasternak, M. and U. Kokturk, Membrane and Method of Separation, U.S. Pat. No. 5,171,449, Dec. 15, 1992] disclosed the details of membrane prepared with non-porous membrane separating layer of cross-linked polyvinyl alcohol cast on a porous alumina ceramic support. Organic nitrogen compounds (i.e. ethylene diamine) may be separated by this pervaporation membrane. This membrane differs from my proposed invention because the polymer layer is coated on the ceramic support and then crosslinked. Thus, the active polymer phase is not chemically bonded to the support, unlike my invention in which the polymer is chemically grafted onto the membrane surface. A similar approach by Pasternak et al. [Pasternak, M., U. Kokturk, M. S. Najjar and R. D. Malouf, Novel Membrane and Method of Separation, U.S. Pat. No. 5,141,649, Aug. 25, 1992] reported that aqueous mixtures of organic oxygenates may be separated by pervaporation through a membrane assembly containing a porous ceramic substrate which supports a separating layer of cured polyvinyl alcohol which has been cross-linked with glutaraldehyde. This membrane differs from the proposed invention in that the polymer layer is coated on the ceramic support and then crosslinked. Unlike my invention, Pasternak et al. membrane lacks the chemical bonding between polymer and the support.
The use of polyphosphazene as the active membrane phase was reported by Soria et al. [Soria, R. C. Defalque and J. Gillot, Membrane for a Filtration, Gas or Liquid Separation or Pervaporation Apparatus and a Manufacturing Method for such Membrane, U.S. Pat. No. 5,066,398, Nov. 19, 1991]. In the approach of Soria et al., a membrane for filtration, gas or liquid separation or pervaporation apparatus was formed from at least one porous layer of an inorganic material selected from sintered ceramic, sintered metal, sintered glass or carbon and a separating layer of organic material (polyphosphazene). The patent of Soria et al. does not overlap with the current invention because the claim only deals with polyphosphazene as a separating organic layer. Also, the patent claims specify that this polyphosphazene is dissolved in a solvent prior to application to the porous support, making it a polymer coating rather than a chemically grafted layer.
The coating of a polymeric membrane with a polymer phase for pervaporation application was disclosed by Bruchke [Bruchke, H., Multi-Layer Membrane and the Use Thereof for the Separation of Liquid Mixtures According to the Pervaporation, U.S. Pat. No. 4,915,834, Apr. 10, 1990.] The above patent describes a multi-layer membrane having a porous backing layer of polyacrylonitrile, polysulfone or the like, and an active separating layer of poly(vinyl alcohol) or cellulose acetate. The membrane is suitable for the separation of water-alcohol mixtures by pervaporation. This membrane differs from the proposed invention in that it claims an active polymer layer crosslinked onto a flat porous polymer support. In contrast, the proposed invention contains an active polymer layer chemically bonded to the surface of a ceramic support.
All of the articles cited above provide, to those skilled in the art, information about the preparation of modified ceramic and polymeric membranes by physical attachment of a polymer phase onto the membrane surface and/or filling the membrane pore completely or in part with a preformed polymer. There have also been studies that reported on polymer-based and ceramic-based membranes prepared by filling a support membrane pores with a monomer and polymerizing the monomer inside the pores. It is known in the art that polymer chains can be grafted onto the surface of polymeric support membranes. Various techniques for modifying polymeric membrane supports are known to those skilled in the art and therefore no detailed exemplification thereof will be given herein.
It is important to note that none of the articles or patents disclose or suggest that any of the authors have actually grafted a polymer onto the surface of a ceramic membrane. To date, ceramic membrane modification studies and patents have focused primarily on physical coating with a polymer layer and by the pore filling technology. The drawbacks of these polymeric/ceramic composite membranes include their lack of chemical resistance and thus longevity in demanding applications. All previous membrane modifications, in which the polymer phase is not chemically bonded to the support, suffer from the drawback that modifying polymer phases which are completely miscible in the liquid mixture to be separated or one of its ingredients cannot be used; cross-linking of the polymer phase is then required to impart mechanical stability to the membrane at the expense of reduced flux and selectivity. Drawbacks of polymeric-ceramic composite membranes in which the polymer phase is not chemically bonded to the support membrane also include their lack of thermal stability and poor chemical resistance to many solvent. In a good solvent or solvent mixture, the polymer phase can swell, detach from ceramic (or polymeric) support and thus result in loss of performance.
My invention overcomes the difficulties discussed above by creating a class of ceramic-supported polymer (CSP) membranes in which covalent bonding of polymer chains to the ceramic substrate results in stable membrane. In my invention the entire amount of polymer, which modifies the ceramic membrane support, is chemically grafted onto the membrane surface as well as the membrane internal pore surface. The CSP membranes have an important advantage in that a variety of different polymers can be graft polymerized onto the surface of the membrane. Finally, the active membrane phase is essentially a single macromolecular layer keeping membrane resistance at a minimum. The chemically bonded polymer phase is useful in converting a ceramic porous membrane support into a membrane capable of separating mixtures of organic compounds from liquid solutions by pervaporation. The chemically bonded polymer phase is stable and the membrane retains its effectiveness even under conditions that result in swelling of the chemically grafted polymeric phase.
The present invention is predicated upon a number of surprising findings. First, using the method of the present invention, ceramic support membranes or filters having surface hydroxy group can be surface activated with vinyl loweralkoxy silane. It should be noted that when I refer to a vinyl lower alkoxysilane I mean a compound having the following formula:
wherein R is an organic group, R1 is an organic group containing at least one vinyl functional group, R2 is lower alkyl, m is 0, 1 or 2, n is 1 to 3, p is 1 to 3 and the sum of m, n and p is 4. It is preferred if R1 is a loweralkylene (e.g., alkyl) which may contain oxygen (e.g., lower alkyl oxide). It is also preferred if R is a lower alkyl or oxygen or chlorine containing alkyl. Since vinyl loweralkoxy silanes are well known in the art, no detail exemplification thereof will be given. Examples of vinyl loweralkoxy silanes include diallyl dimethoxy silane, allyl triethoxy silane, ethyl vinyl dimethoxy silane, divinyl diethoxy silane and, preferably vinyl triethoxy silane and vinyl trimethoxy silane.
Prior to chemically bonding the vinyl loweralkoxy silane to the membrane support surface, the membrane surface is exposed to an atmosphere of controlled humidity in order to maximize the surface yield of the chemically bonded vinyl loweralkoxy silane. The surface yield of chemically bonded loweralkoxy silane displays a maximum with respect to the surface water content of the ceramic membrane support. For a silica substrate, for example, surface coverage by vinyltrimethoxy silane as high as 80 micromoles per square meters of silica surface can be obtained at water surface coverage equivalent to about 2 monolayers of water. For zirconium oxide and xcex1-alumina surfaces, coverages of up to about 23 and 40 micromoles of vinyltrimethoxy silane per square meter of the support surface, respectively, can be achieved corresponding to surface water content equivalent to 3 and 15 water monolayers for the zirconium oxide and xcex1-alumina substrates, respectively. Subsequent modification of the surface of the ceramic support with water insoluble polymers does not require any additional surface treatment. However, for subsequent modification of the ceramic support surface with water soluble polymers which are graft polymerized onto the surface in an aqueous mixture, the loweralkoxy groups are hydrolyzed to produce a surface with restored wettability, thereby allowing for high graft polymerization yield on the surface when utilizing water soluble vinyl monomers.
The ceramic porous supports used as the membrane support in the present invention are well known in the art and therefore no detailed exemplification thereof will be given herein. Such ceramic support membranes or filters will have surface hydroxyl groups for chemically bonding the vinyl loweralkoxy silane to the surface of the ceramic membrane. Generally speaking, the membrane support can consist of silica, zirconia, alumina, or any other inorganic oxide support whose surface possesses surface hydroxyls or a surface that can be hydrolyzed to create surface hydroxyls. These surface hydroxyls provide the active sites for chemically anchoring vinyl-silane molecules. The preferred vinyl activators are vinyl loweralkoxy silanes. The starting pore size of the ceramic support membrane that can be used will vary but in general will be from about 20 Angstroms to 500 Angstroms. The geometry of the porous ceramic support can be in a circular disk form, rectangular, tubular or multi-channel array. The ceramic membrane support can be either homogenous (i.e., the entire support is made of the same material and of the same pore size) or asymmetric. An asymmetric porous ceramic support can consist of a thin or thick ceramic layer with small pores on top of an underlying ceramic support with larger pores. The said thin ceramic support (which I refer to as xe2x80x9cporous ceramic membrane supportxe2x80x9d) can exist on either side or both sides of the supporting larger pore ceramic support layer. At present, commercially available ceramic support membranes have porosities (i.e., pore volume fraction) that are about 30% or higher. In general, it is preferred to utilize ceramic membrane support with a porosity (i.e., void fraction) equivalent to 30% or higher.
As noted previously, the compound used to activate the surface of the porous ceramic membrane support is a vinyl loweralkoxy silane. In order to achieve sufficiently high surface coverage (i.e., so that said vinyl lower alkoxysilane covers the surface of the ceramic membrane support, in an amount of at least 10 micromoles of vinyl silane per square meter of said ceramic membrane support surface). I discovered that it is necessary to optimize the surface moisture of the ceramic material (prior to its modification with the vinyl loweralkoxy silane) in order to maximize the amount of vinyl lowralkoxy silane which is chemically bonded to the support surface. For example, as noted earlier, the optimal surface water coverage (prior to the silylation reaction with the vinyl loweralkoxy silane) is about 2-4 equivalent water monolayers for a silica substrate, about 3 water monolayers for a zirconia substrate and about 15 water monolayers for an xcex1-alumina substrate. Also, for the chemical bonding of the vinyl loweralkoxy silane, it is necessary to utilize as a solvent, lower alkyl benzene such as toluene, phenylpropane, ortho, meta or parazylene, etc. When using this type of solvent, high surface coverage of the ceramic surface is achieved by the vinyl loweralkoxy silane, such yields being, from about 10 micromoles per square meter to as high as 80 micromoles per square meter of the ceramic membrane support.
The temperature of the silylation reaction is not critical; however, higher temperature increases the speed of the reaction. Generally speaking the reaction can be carried out up to the boiling point of the solvent abut it is preferred that the reaction is above the boiling point of the lower alkyl alcohol formed by the reaction. For example, if xylene and vinyl trimethoxy silane are used, the preferred range would be between about 80xc2x0 C. and 137xc2x0 C.
The resulting surface vinyl groups are the active sites from which polymer molecules are grown. The ceramic substrate provides the required mechanical support-frame while the chemically anchored polymeric phase is used to control pore size and pore surface chemistry, thereby imparting chemical selectivity to the CSP membrane.
The silylation reaction is achieved by contacting the membrane surface with the solution of lower alkyl benzene and vinyl loweralkoxy silane. The reservoir for the feed solution is fitted with a reflux condenser and the mixture is heated above the boiling point of the thus produced alcohol but slightly below or at the boiling point of the solvent. The reflux condenser is so arranged that the displaced alcohol is removed but the vapors of the vinyl loweralkoxy silane and lower alkyl benzene are condensed and returned to the reaction mixture. For tubular membranes, the surface of the membrane on tube-side and/or the outside surface can be modified by contacting the membrane with the flowing solution in a standard housing module. Modification through the entire depth of the membrane is accomplished by pumping the solution through the tube-side of the tubular membrane under sufficient transmembrane pressure to allow for passage of the solution of vinyl loweralkoxy silane in the lower alkyl benzene solvent through the porous membrane support layer. Modification of the surface of flat sheet membranes or disk membranes is accomplished by immersing the membrane (being held in a stainless steel basket to prevent movement of the membrane) in the reaction solution for a prescribed period of time. After the membrane is chemically modified with an adequate amount of vinyl terminated loweralkoxy silane, the resulting surface activated membrane is washed with the lower alkyl benzene and allowed to dry.
Thereafter, if the membrane is to be graft polymerized with a water soluble polymer in an aqueous reaction mixture, the remaining unreacted lower alkoxy groups are hydrolyzed. Such hydrolysis can be accomplished in a number of different ways known to those skilled in the art. For example, the hydrolysis step may be performed by immersing the membrane in water to which a base has been added to adjust the pH to between about 8 and 12. A pH range of 8 to 10 is suitable for silica while pH as high as 10-12 is suitable for a zirconia-based membrane. The hydrolysis step may be performed under ambient temperature and the membrane is allowed to remain in the alkaline water for a sufficient period of time to complete the hydrolysis of the loweralkoxy groups (e.g. one to five days). After the hydrolysis step, the membrane is more hydrophilic as opposed to being more hydrophobic prior to the hydrolysis step. The base used for the hydrolysis may be any base either weak or strong, inorganic or organic. For example, basic compounds useful in the present invention include sodium hydroxide, calcium hydroxide, potassium hydroxide, etc.
Once the membrane surface has been modified, by chemically bonding onto the surface vinyl loweralkoxy silane in an amount of at least 10 micromoles per square meter, the membrane is then ready to be graft polymerized. Graft polymerization allows for chemically bonding the resulting vinyl polymer onto the activated membrane surface (either side of the membrane or throughout the membrane matrix). It should be noted that by xe2x80x9cgraft polymerizationxe2x80x9d I mean the growth of polymer chains from surface active sites (i.e, surface vinyl groups) by step or chain polymerization. This is to be distinguished from polymer grafting which involves the bonding of previously synthesized polymer chains from a bulk phase to the membrane support surface. Polymer grafting is not satisfactory in this invention because polymer molecules must diffuse to the solid surface and therefore diffusional limitations and steric hindrance severely reduce the degree of surface coverage and graft yield obtained. In complete contrast thereto, in graft polymerization, diffusional limitations and steric hindrance effects are substantially diminished due to the smaller size of the monomer molecules and therefore a higher surface concentration and a more uniform surface coverage is possible.
In general, any polymer which can be formed by the polymerization of vinyl monomers via addition polymerization can be utilized in the present invention. Vinyl monomers are well known in the art and include both water soluble and organic solvent soluble monomers. Water soluble polymers include but are not limited to acrylic acid, acrylamide, vinyl heterocyclic compounds such as vinyl pyridines and vinyl pyrrolidone such as N-vinylpyrrolidone. Other suitable vinyl monomers include but are not limited to styrene, vinyl acetate, methyl acrylate, acrylonitrile, methyl methacrylate. Although any one of several reactions methods, which are well known in the art, can be utilized for polymerization of vinyl monomers, the preferred polymerization is via free-radical polymerization due to the ability to synthesize polymers under relatively mild reaction temperatures.
When utilizing the surface activation method in the present invention, I obtain a surface coverage of the polymer in the range of about 1 to 6 milligram of polymer per square meter of ceramic support surface. Generally speaking, polymer surface coverage corresponding to about 2 milligram per square meter or higher are desired for effective pervaporation membranes when the initial membrane pore size is about 500 Angstrom or less. The graft polymerization is preferably performed in the absence of oxygen which is believed to lengthen the polymerization reaction time and result in a lower polymer graft yield. In as much as the preferred reaction is a typical free-radical reaction, it is necessary to have an initiator such as diazo compounds or a peroxide. Example of peroxides include hydrogen peroxide, t-butyl hydroperoxide, diacetyl peroxide. Other type of initiators that can be used include diazo compounds such as 1,4-dimethyl-valeronitrile, xcex1,xcex1xe2x80x2-azobis(isobutyronitrile) and azodisulfonic acid. The temperature of the reaction affects the speed of the reaction and may range from about 50xc2x0 C. to about 90xc2x0 C. Higher temperatures may be used as long as the temperature is not above the boiling point of any of the ingredients in the polymerization reaction mixture which is brought into contact with the ceramic membrane support. The rate of reaction is, to some extent, governed by the initial concentration of the vinyl monomer in the solution. For example, I have found that little as a 10% weight of the vinyl monomer in solution is satisfactory but higher initial vinyl monomer concentrations of up to about 40% may be used. The amount of polymer grafted onto the surface will typically increase with higher initial monomer concentrations. However, as well known in the art of polymerization, high viscosities, which result when polymerizing from a solution of a high initial monomer concentration (greater than about 30% by weight), can make it difficult to mix the reaction mixture and in the case of tubular membranes may also make it more difficult to circulate the reaction mixture through the membrane tube- or shell-side. Therefore, the optimal concentration has to be determined for each selected vinyl monomers. For example, I have found that initial vinyl monomer concentrations in the range of 10% up to 30% by weight are preferred.
The polymerization reaction time may also vary greatly depending on the temperature and the concentration of the vinyl monomer. Generally speaking, the reaction to obtain the desired graft yield will take from about two to ten hours.
The ceramic-supported polymer (CSP) membranes of the present invention are useful in a number of ways. First, they are excellent for separating volatile organic compounds from water. For example, alcohols such as methanol, ethanol, isopropanol, aromatic compounds such as benzene, toluene and xylenes, chlorinated compounds such as trichoroethylene, vinyl chloride, chloroform and ethers such as methyl-t-butyl ether can be separated from water using a pervaporation operation. The process of pervaporation is well known in the art and therefore no detailed exemplification thereof will be given herein. The permeating species (i.e., the compound to be removed from a solution mixture) has to have a greater solubility (or partitioning) in the grafted polymer relative to the solubility of the other components of the mixture. Generally speaking, chemicals which can be separated by the present invention are those which are attracted to the graft polymer on the ceramic membrane support. For example, when trichloroethylene is to be removed from water by pervaporation, poly(vinyl acetate) is a suitable polymer for the active membrane separation layer. In its pure form (i.e., not bonded to a surface) poly(vinyl acetate) is soluble in trichloroethylene while being completely insoluble in water. Selection of the appropriate polymer for a specific pervaporation task can be performed with a homopolymer (i.e., polymer not chemically bonded to a surface) using a variety of test methods well known in the art. It is emphasized that once the polymer is chemically bonded to the membrane support surface, it can swell with the chains extending away from the ceramic support surface but the polymer chains remain chemically attached to the support surface.
Separation by pervaporation can be carried out under ambient conditions but higher temperatures will results in a higher separation factor (concentration of target compound in the feed/concentration fo target compound in the recovered permeate). The flow of the feed solution past the membrane feed-side can also affect the separation factor. It is known in the art that, as the velocity of the feed increases, higher separation factors can be obtained. With the present invention enrichment factors, defined as the ratio of the target chemical concentration in the feed to its overall concentration in the collected permeate, are typically in the range of 100 to 400 at operating temperature of about 23xc2x0 C. It is well known in the art of pervaporation that higher operating temperatures will result in higher enrichment factors. It is also known in the art that enrichment factors will increase by increasing the feed-side flow rate. Enrichment factors, as discovered in the present invention, will also increase with increasing polymer graft yield. For example, the separation of trichloroethylene from water using a tubular poly(vinyl acetate)-silica membrane with an inside diameter of 0.5 centimeters, 20 centimeters in length and a porous wall thickness of 0.5 millimeters would result in enrichment factors that can range from about 70 to 850 for a polymer graft yield ranging from about 1 to 3.5 milligram polymer per square meter of membrane support surface.
The present invention allows the attachment of a polymer phase covalently to ceramic support. Thus, the problem of loss of membrane stability due to swelling by the permeating species is avoided. The polymer layer can be created at varying degrees of surface density thus controlling the level separation.
Given below are presently preferred embodiments, which are set forth solely in order to full illustrate the invention, being understood that such examples are not to be considered limiting.

Ceramic-supported polymer (CSP) pervaporation membrane