Zentrifugalextraktion – Eine Literaturübersicht

Centrifugal extraction – a literature survey . A survey of the different types of centrifugal extractors is presented. The construction details are given both for the common type of extractor and for less well-known designs as encountered in the patent literature. The effect of a centrifugal field on hydrodynamics and mass transfer is also discussed theoretically, together with actual experimental measurements and techniques used in practice.     

Kontinuierliche Reaktionsführung mit löslichen Enzymen

Continuous processes with soluble enzymes. This paper surveys the use of continuously operating enzyme-membrane reactors with enforced flow where the retention of soluble enzymes in the reaction vessel is achieved by means of an ultrafiltration membrane. This technique has been commercialized in the acylase process for the synthesis of L -amino acids on a 200 ton/year level. It is especially useful for the application of multi-enzyme systems with cofactor regeneration. The synthesis of L -tert-leucine from the corresponding α-keto acid has been achieved on a kilogram scale. Coenzymes coupled to water soluble polymers are retained in the membrane-reactor together with the enzymes. Use of suitable conditions prevents loss of enzyme and coenzyme by passage through the membrane or by deactivation. Therefore the costs of enzymes and coenzymes are no longer limitations for economic processes. In the continuously operating enzyme-membrane reactor regeneration of the coenzyme up to 600 000 times was achieved. In continuous peptide synthesis space-time yields of 25 kg/(l d) were obtained. To suppress side reactions very high catalyst concentrations are possible, yielding residence times below 4 min.     

Organosiliciumverbindungen mit funktionellen gruppen und ihre überführung in makromoleküle

By polymerizing unsaturated oligomers of siloxane derivatives (I) and by copolymerizing them with the usual vinyl monomers a variety of soluble polymers can be obtained which possess different organic structural units and di- or polysiloxane substituents. Hereby the siloxane content can vary greatly and in case of some homopolymers may amount to as much as 50 yo, When using polysiloxanes with two unsaturated end groups instead of monofunctional siloxane compounds analogous products are obtained which are however cross-linked and insoluble. Linear organic polymers with Functional silicon-substituents (such as Cl? Si? , HO ? Si? , H ? Si? , CH₂ ? CH? Si? , CH₂?CH? CH₂? Si? , CH?C? Si, n? C₄H₉O? Si? , ClCH₂? Si? groups) are formed by homo-, and copolymerization of silanes and siloxanes which contain a functional moiety besides the unsaturated group. Macromolecules which carry the functional substituents on the ends of the chains instead of exhibiting them as side groups can be prepared by termination of living polymers with chlorosilanes or by initiation of anionic vinyl polymerization with organometallic starter molecules. High molecular weight polymers with two reactive end groups may also be obtained by cohydrolysis or equilibration reactions of the corresponding chlorosilanes or disiloxanes. By these synthetic routes a great number of organic or silicone polymer molecules with functional groups in side or end positions are available by suitable block, graft, and crosslinking reactions in polymer systems with definite structural units, and tailor made micro structures. To achieve this, polymer molecules of different structure are linked together by suitable reactions of their functional groups or one uses polymer molecules with reactive centers as poly-functional initiators for the polymerization reaction. By addition polymerization of organic diisocyanates with oligomer siloxane or silmethylene diols, silicon-modified polyurethanes are obtained. The reaction of the partners in molar ratio 2/1 leads to low molecular weight polyurethanes (degree of addition polymerization m 2) with two isocyanate end groups, which could be employed in the diisocaynate addition polymerization as easily available silicon-containing diisocyanates. Oligomer siloxanes or silmethylenes with two H? Si-end groups (I), (R and R₁?H) and ω,ω′-divinyl- or ω,ω′-diallylpolysiloxanes (I), (R and R¹ ? vinyl-, allyl-) or several other unsaturated molecules, such as p-divinylbenzene and acetylene undergo addition polymerization to give heat stable polysilcarbanes, in which oligomer siloxane or silmethylene groups are linked via ethylene or n-propylene bridges. If the siloxane or silmethylene groups are replaced by ferrocenyl-groups, polyadducts result which are stable up to 400°C for several hours in presence of oxygen. Polycarbonates and polyesters are the condensation polymers of siloxane-containing diphenols and phosgene or terephthalic acid chloride. Polyimides, which are soluble, fusible and stable above 300°C, are the condensation products of silicon-containing dianhydrides and diamines or of organosilicon derivatives of diamines and pyromellitimide, and several organosilicon compounds are also the condensation polymers of dichloro-Si-compounds and N,N′-bis-(3-dimethylhydro-xisilylpropyl)-pyromellitimide, which is a very easily available disilanol. A comparatively lowering of melting points and glass transition points of organic polymer molecules possessing polysiloxane derivatives (approximately 5 wt.-% onwards) is due to the covalent bonds of polysiloxanes. Moreover, one notices also great improvement in solubility as well as in their hydrophobic character. A great improvement in heat stability can be achieved by introducing more siloxane-content (approximately 15 wt.-% onwards).