Ultrafiltration conversions

In contrast to solid-phase Suzuki couphng, very low amounts of the Pd-catalyst (0.2 mol%) were sufficient and high conversions (87-99%) to biaryls (65) were obtained to yield relatively pure products (>90%, GC/MS, NMR) after ultrafiltration. In some cases most of the polymer supported boronic compound precipitated during the reaction and therefore no further purification was required. Nonetheless, quantitative removal of catalyst traces was not yet possible with either work-up protocol. 

Generally, a distinction can be made between membrane bioreactors based on cells performing a desired conversion and processes based on enzymes. In ceU-based processes, bacteria, plant and mammalian cells are used for the production of (fine) chemicals, pharmaceuticals and food additives or for the treatment of waste streams. Enzyme-based membrane bioreactors are typically used for the degradation of natural polymeric materials Hke starch, cellulose or proteins or for the resolution of optically active components in the pharmaceutical, agrochemical, food and chemical industry [50, 51]. In general, only ultrafiltration (UF) or microfiltration (MF)-based processes have been reported and little is known on the application of reverse osmosis (RO) or nanofiltration (NF) in membrane bioreactors. Additionally, membrane contactor systems have been developed, based on micro-porous polyolefin or teflon membranes [52-55]. 

Figure 9 Conversion of the S-ibuprofen process with and without the ultrafiltration unit.

In the current work, we employed a modified approach, with predeposition of a secondary membrane of yeast (SMY) before starting the filtration of protein. Backflushing was employed periodically to remove the deposited secondary membrane to recover the flux, and a new secondary membrane was deposited subsequently with the start of each new cycle, prior to restarting the filtration of protein. Microfiltration experiments were performed with yeast as the secondary membrane and BSA-only solutions and yeast-BSA mixtures as the feed. Ultrafiltration experiments were performed with yeast as the secondary membrane deposition medium and cellulase enzyme solutions, used in the conversion of biomass into ethanol, as the feed. In this article, we also present direct visual observation images (19) of the formation of the secondary membrane and its subsequent removal. 

A 72-h hydrolysis profile of a 10% acetic acid-pretreated softwood substrate (Fig. 1) represents a typical enzymatic cellulose hydrolysis course with the majority of the cellulose (up to 70%) broken down within the first 24 h. However, the conversion of the remaining cellulose ( 30%) was incomplete, even after another 2 d of incubation. The decrease in the hydrolysis rate in the latter phase is likely owing to accumulation of end products. To demonstrate that the end products played a major inhibitory role, we removed the produced sugar from the hydrolysate through ultrafiltration. Fresh buffer was then added to the retained protein and the residual substrate to attain the initial volume, and the hydrolysis was continued under the same condition. As shown in Fig. 1, significant increases in the hydrolysis rate were observed after the sugar removal at both 24 h and 48 h of incubation, with complete hydrolysis attained after 48 h and 60 h of incubation respectively. 

It is clear from the conversion yield that the biological process was worthy of further development for potential use in the longer term. Work was especially needed to improve the concentration (8 g/liter at the time) and to deal with the slightly different impurity profile (total 0.3% with 0.1% identified as the R-amine VIII). Also, technologies (e.g. ultrafiltration) needed to be evaluated to ensure that proteinaceous material did not contaminate the product. 

Ultrafiltration, 631 applications, 633 membranes, 637-639 Underwood minimum reflux binaty, 387 multicomponent, 397 Units, conversion of, 671, 672 UMQUAC equation, 475 Upflow fixed beds, 609 Uranium recovery, 515 Utilities, typical characteristics, 15... 

Electrokinetic conversion Lactic acid Feimentors Ultrafiltration HF membranes [251]... 

Membranes are being frequently employed in the manufacturing of pharmaceuticals in combination with a bioreactor for enzymatic reactions. In DSM such a combination has been studied for the production of S -ibuprofen, via the hydrolysis of the (R,S)-ibuprofen methylester coupled to a racemization of the unwanted enantiomer. The esterase used for the above conversion is strongly deactivated by the product. To solve this problem, an ultrafiltration membrane unit has been coupled to the reactor, to remove in situ the product formed. The application of the ultrafiltration has led to a twofold increase of the conversion/productivity, as shown in Fig. 11. 

Fig. 11 Ibuprofen methylester conversion as a function of time, with and without integrated ultrafiltration unit. (From Ref.t" l)...

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