Patents

for several days and calcined. The end-product was a cont inuous layer of ZSM-5 zeolite; the thickness was about 250 microns.

Mobil has now patented the use of such a material in gas and liquid separat ions Including oxygen / nitrogen, hydrogen /ca rbon monoxide, hydrogen/methane , linear paraf f in /branched par~mn and para-xylene / ortho-or meta-xylene mixtures.

The membrane can incorporate catalytically active metals such as pla t inum or silver, or can have its own intrinsic catalytic activity suppressed by the incorporation of alkali or a lka l~e ear th metals.

Patent number: US 5069794 Date: 3 December 1991 Inventors: W.O. I-I~g, J.G. Tslkoyannis Applicant: Mobil Oil Corporation

Pervaporation with optimum permeate flow Conventional industrial pervaporatlon systems employ plate-and-frame modules to retain the membrane and subject it to a partial v a c u u m or sweep one aide of it with a carrier gas. Membrane Technology & Research are the proponents of a spiral-wound pervaporation module which employs an apparent ly anomalous mass t ranspor t phenomenon.

The key attr ibute of the module, which in general details is otherwise a conventional spiral-wound membrane construction, is the permeate spacer. It might be thought that a design which packs as m u c h membrane area as possible into a given cylindrical volume would be optimal. Instead, it is found that pervaporation capacity rises as the thickness of the permeate spacer is Increased to an opt imum value, beyond which it begins to decrease. This effect more than compensa tes for the reduction in membrane area consequent on increasing the

thickness of the layers which are rolled up to form the module.

The membranes used in these modules are multflayer s t ructures with very thin permselective layers. They are typically 0.15-1m wide and 1-5 m long. To form an envelope, the membrane is folded on its short side, with spacers on the feed side and the permeate side. The permeate spacers are made from net or other large-dimermlon porous material. In one example, 32-mil netting with a porosity of 70% was used as both feed and permeate spacer. Other examples successfully used a net of thickness up to 120 mils: beyond that, the membrane area reduct ion does begin to take effect.

Patent number: US 5069793 Date: 3 December 1991 Inventors: J. Kaschemekat, R.W. Baker, J.G. WiJmans Applicant: Membrane Technology and Research Inc.

Enantiomers separation Stereoisomers are those molecules that differ from each other only in the way in which their a toms are oriented in space. Enant iomers are a subset of this large group: pairs of molecules are mirror images of each other. There are some established techniques for separating these isomers: a chiral molecule in a chromatography column will interact more strongly with one enantlomer than the other so giving a longer residence tlme, hence a separation will occur and in some cases, if the mode of interaction is known, the elutlon order can be predicted.

This is not a commercial proposition for large-scale synthesis, a l though it is a regular tool for the preparative scale synthetic chemist. If the chlral aspects of the chromatographic stat ionary phase can be used as a chlral carrier, then the prospect of a continuous, large-scale separation process becomes

possible. A liquid membrane, in conjunct /on with a sere/permeable barrier, is a possible candidate for such development and has been used for tha t purpose. Many schemes have been devised, bu t most have only a low resolution of the two stereoisomers.

In this invention, a supported liqu/d membrane contains a chiral carrier which forms a stable complex with one of a pair of en~ntiomers. The complexation is aided by temperature control of that part of the system. The stable complex is then rapidly t ransported away from the initial mixture, and is dissociated hack to the carrier and the corresponding enantlomer at a point where min/mal contaminat ion with the other enant iomer can take place. If one enantiomer is removed, the proportion of the other in the remaining mixture is also enhanced: thus a subtracUve process can result in the non-reactive enantiomer nevertheless being concentrated.

The system in this invention relates to the separation of the enant iomers of N-(3,5- dlnltrobenzoyl)amino acid esters: the chlral carrter is the (L)-N-( l-naphthyl)leuclne structure.

The liquid membrane is supported in m/croporous material such as hollow fibres, for example of polysulphone or silicone rubber. The liquid membrane itself is a Cio-Cl4 mlkmne such as dodecane (C12H26). The receiving solution for the separated enant/omer is an 80% methanol:20% water solution sa tura ted wlth dodecane. The enantlometr/c e~cess in the receiving phase was 57.3% (the start ing solution, with equal enantiomers, has a zero value for this measurement) .

Patent number: WO 9117816 Date: 28 November 1991 Inventors: W.H. Pirkle, E.M. Doherty App/ican~ Research Corporation Technologies, Inc

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