Some impurities such as CO and N 2 in particular differ significantly, yet the final purity is identical. The overhead vapour matches very well in terms of total flow. Some differences are observed for the split between methanol and carbon dioxide and hydrogen and methane content. As seen from Table the COCO/COFE model displays higher reaction rate towards methanol / higher hydrogen conversion, likely attributed to the difference in the applied kinetic parameters. A side effect is also an increased heat extraction from the reactor, a sligh reduction in recompression power and a slightly reduced cooling duty required upstream the HP separator. Still, the results are indeed comparable and much alike despite differences in simulation tools, difference in thermodynamic and kinetic models and parameters. For further comparison with the results of Luyben, an optimisation study is performed using the simulation in Figure using a Box-Behnken experimental design for generating model outputs which are used to train a response surface model as surrogate of the actual process simulation e.g. as shown in. The following independent variables / factors are varied: compression/reaction pressure (pressure after K2 compressor), reactor size (via the number of reactor tubes), and the purge/vent percentage. Luyben also investigated the flash pressure in the low pressure flash separator, however, for simplicity this is omitted. For each dependent variable / response, a multiple regression model is built which includes all first order terms, second order terms and linear interaction terms, with backward elimination of insignificant second order and interaction terms. The simulation model in Figure is modified slightly by removing HX3 and setting the outlet of FEHE towards the methanol reactor to 150 • C.