 decomposition of H 2 O 2 by heavy metals occurred. Full bleaching could be realized with a reasonable charge of bleaching chemicals because the organosolv pulp responded extremely well to the oxygen delignification stage. The main weakness of the bleaching procedure was the high NaOH charge in the cold caustic extraction which was necessary to achieve the required low hemicellulose content. The pulp produced had a sufficient degree of brightness and a low hemicellulose content. Compared to literature specifications, the kappa number is slightly too high and the viscosity is only slightly within the specified limits [58]. A more extensive chlorine dioxide bleaching could lower the kappa number with little viscosity losses.

Xylose valorization from hemicellulose
The adsorption of HH with SEPABEADS SP700 resulted in the removal of 94.8% of lignin and other phenolic compounds. The simultaneous losses of hemicellulose, including oligomeric and monomeric xylose, amounted to 8.0%. The adsorption behavior of both lignin and hemicellulose sugar in the multi-component solution is best described by the extended Freundlich isotherm. Hence, multilayer adsorption, with non-uniform distribution of adsorption heat and affinities, seems to be predominant [37]. Figure 3 shows the altered concentrations of oligomeric xylose, monomeric xylose, and furfural versus residence time in the continuous tube reactor at 160, 180, and 200°C during the hydrothermal treatment of HH. The conversion of the oligomeric xylose takes place in the following three steps: (a) hydrolysis of the oligomeric xylose to monomeric xylose, (b) dehydration of the monomeric xylose to furfural, and (c) degradation/condensation of furfural to insoluble humic substances and other hydrocarbons [59]. As can be seen in Fig. 3, a rapid hydrolytic cleavage of the oligomeric xylose takes place, which leads to a rapid increase in monomeric xylose concentration. The higher the process temperature, the faster the hydrolysis. As a result, the maximum monomeric xylose concentration is shifted to shorter residence times with increasing temperature. On the basis of the experimental data determined by Köchermann et al. [12], appropriate process parameters were identified in terms of maximum monomeric xylose yield, minimum oligomeric xylose concentration, minimum furfural concentration, and reduction of residence time. At reaction conditions of 180°C and a residence time of 2.8 min, the above-mentioned criteria can be best met.
Appropriate process parameters for the NF of the hydrothermally treated HH were found to be a transmembrane pressure of 3.0 MPa, a temperature of 35°C, and a crossflow velocity of 1.1 m/s. Thus, obtaining a permeate flux of 38.2 L/(m 2 h) and observed component retentions of 100% for oligomeric xylose, 98.9% for glucose, 96.2% for monomeric xylose, 29.6% for 5-HMF, 19.7% for furfural, and 3.7% for acetic acid. At the determined parameters, the hydrothermally treated HH was concentrated by NF to a volume reduction of 0.6, meaning 60% of the feed solution was transferred into the NF permeate. Thereby, a monomeric xylose concentration of 126 g/L in the retentate and a reduction of the inhibitor-toxylose ratio by 52% were achieved (Table 1).

Malic acid fermentation
Malic acid was successfully fermented on HH from the organosolv process. The oligomeric xylose present in high quantities next to monomeric xylose can be converted to malic acid with identical product formation rates compared to the utilization of technical xylose as feedstock. However, the substrate fraction could not be completely replaced by xylose from hemicellulose (only up to 40% (w/v)) since growth and metabolism were completely inhibited at higher concentrations by the contained inhibitors. The use of HH led to a lag phase at the beginning of cultivation when, among others, 5-HMF was degraded by the fungi. With increased concentration of hemicellulose, the metabolism shifted to succinic acid  production, which reduced the malic acid yield. Overall, the yield of malic acid obtained with HH was still higher than with technical xylose (43%-105% higher) due to the wider substrate spectrum. As a result of HH pretreatment by precipitation, adsorption, and extraction, some of the inhibitors could be removed and the lag phase was shortened. The fermentative malic acid production from xylose by Aspergillus oryzae was successfully transferred from the laboratory-(0.1 L) to the pilot-scale (1000 L). The EDCF was used as the scale-up criterion resulting in a similar pellet morphology of the fungi. A yield of 0.63 mol malic acid per mol xylose and an average product formation rate of 0.15 g/(Lh) could be achieved. A first strategy for the downstream processing of malic acid from the fermentation broth was developed and demonstrated on a pilot scale: consisting of acidification, thermal inactivation, biomass separation by filtration, and purification by cooling crystallization and drying, to obtain the target product. The concentration of the fermentation product malic acid, the by-products succinic acid and fumaric acid, and the starting material xylose, as well as the liquid-phase volume of the piloted fermentation process and the separation and purification cascade, are displayed in Fig.  4. The best yield and purity in cooling crystallization was achieved with a pH of 3.3 and a cooling rate of 5°C/h. However, the amount of malic acid remaining dissolved in the filtrate after crystallization as well as a non-optimized biomass separation and dewatering resulted in a high overall product loss. A malic acid quantity of approx. 15 kg (29% yield) with a purity of 84% was produced.

Lignin depolymerization
Cleavage of lignin via BCD and subsequent separation resulted in solid BCD-oligomers, a liquid BCD-oil, small organic compounds, and gasses ( Table 5). The lignin fragments of the BCD-oligomers were obtained with a depolymerization degree of at least 35% relative to the starting material. The BCD-oil is a fraction containing liquid phenolic monomers and dimers. They were isolated by liquid-liquid extraction of the product solution after solid-liquid separation of the BCD-oligomers. The main monomeric components identified in the BCD-oil were syringol, guaiacol, catechol, vanillin, and phenol. However, their content in the oily phase was low (≤3%). Small organic compounds formed by cleavage of methoxy and ethoxy moieties from the lignin molecules were mainly methanol, ethanol, and their corresponding acids. Formed gasses were mainly CH 4 and CO 2.
As described in Section 2.5, the reference for the design of the BCD-process and the mass and energy balances is the cleavage using 5% (w/w) lignin in a total mass flow of 20 kg/h, achieving a conversion rate of 94.5%. The relatively mild reaction conditions of 25.0 MPa and a temperature of 300°C lead to a depolymerization with good yields of BCD-oil while avoiding repolymerization of the formed lignin fragments [27]. This is necessary to reproducibly obtain the required product specifications and to provide a stable, continuous process.

Costing and environmental assessment
Costing and environmental assessment of the entire LCB presented in Fig. 1 was conducted. As part of a preliminary assessment of the single-process steps, it was found that liquidliquid extraction and subsequent purification of the BCD-oil during lignin depolymerization is not beneficial. In particular, it has been shown that MIBK as a solvent has a considerable negative influence on the costing and environmental impact of the process. Therefore, an alternative approach for assessing the process excluded BCD-oil as a value-determining product and focused exclusively on BCD-oligomers. Hence, the products of the LCB were dissolving pulp, phenolic BCD-oligomers, and malic acid. The results of the assessment include the mass and energy balance from process simulation with Aspen Plus, the economic analysis by determination of production costs, and the environmental analysis using LCA.

Mass and energy balances
The main input and output mass streams of the LCB processing 50,000 dry metric tonnes of beech wood annually are presented in Table 6. It should be mentioned that the examinations carried out in this section have a conceptual character and are based on the experimental work from Section 3.1 to Fig. 4. Concentration of malic acid, succinic acid, fumaric acid, and xylose as well as the liquid phase volume of the piloted fermentation process and the separation and purification cascade Section 3.5. The conversion rates of the starting materials to products, which are described in the individual process stages subsequently, refer to the dry matter of the respective components, meaning water content (w) is 0%.
During organosolv pulping, 46.4% of the beech wood is converted to cellulose fibers, 15.2% to lignin, and 15.7% to hemicellulose sugars (oligomeric and monomeric xylose) in the HH. This process stage is characterized by a high water demand, as water is used in large quantities as a solvent and as wash water for cellulose fibers and lignin. A further reduction of the necessary amount of water has great potential for optimizing the process, due to lower energy requirements and easier access to the hemicellulose sugar. The high