1
l l Patents the developed world. Ithas important properties which include providing bulk and sweetness. Artificialsweeteners do not provide bulk or {as do sugars in some products) initiate the Maillard browning reactions. Bulking agents such as alginates or carageen sometimes failto provide manufacturer- or consumer-desired attributessuch as 'mouth-feel'. Polyethylene glycol {PEG) has previously been tested as a new low-calorie food component, as a partial sugar replacement and as an emulsifier to reduce egg and shortening content. The material used was a (US) National Formulary grade which merely limits ethylene glycol + diethylene glycol content to 0.25% maximum. PEG has been purified by cation/anion exchange; this does not, however remove the PEG oligomers. This invention purifies PEG of molecular weight 400-15,000 with, as the major impurity, oligomers of the alkylene oxide and active hydrogen compound initiators.Itemploys a membrane with a molecular weight cutoff of at least 150 daltons. In the examples given in the patent, the membranes used are FilmTec NF-20 and NF-40, and Osmonic SEPA SX01 cellulose acetate membranes, usually with a membrane area of 0.25 ft z.The PEG was diluted by the addition of a minimum of 2g water/g PEG, typically 10-25 g water/g PEG, and in these examples was subjected to 100 Ib/in2g for a period of 425 mins. The results show that low-molecular-weight glycols up to pentaethylene glycol were totallyeliminated from the raffinatein all tests.In one longer test over a period of 73.5 hrs, using a larger membrane of 25 ft 2 area, all glycols up to decaethylene glycol were rejected to below I ppm in the PEG raffinate. Patent number: US 4946939 Date: 7 August 1990 Inventor: F.H. Murphy, R.T. Jernigan, J.G. Grierson, W.G. Wessels Applicant: Dow Chemical Co. III IIIII Hill IIIIIII Compartmented hollow-fibre gas separator This arrangement uses hollow fibres in such a way as to give improved separation efficiency by allowing a shorter path of permeate gas compared to the non-permeate gas. This is achieved by dividing the interior of the vessel into compartments, each compartment having an individual outlet for the permeate. The separation takes place in a conventional hollow fibre membrane separation system which has been modified internally by means of 10 or more gas-tight partitions. These convert the vessel into a series of compartments each with its own outlet for the permeate. The outlets are arranged to give generally countercurrent flow of permeate and residual gas within each compartment, and are connected by a manifold to an exhaust pump. This arrangement increases the overall permeation rate by changing the average ratio of partial pressures of the permeate on either side of the diffusion membrane. Patent number: GB 2228427 Date: 29 August 1990 Inventor: M.E. Garrett, J.B. Gardner Applicant: BOC Group PLC Membrane separation in semiconductor manufacture Polycrystalline and epitaxial silicon metal used in semiconductors is produced by reducing or decomposing volatile silicon compounds such as silane, silicon tetrachloride or chlorosilanes. Silicones manufacture involves similar reaction steps. There are drawbacks to these processes. The chlorinated compounds are mixed with hydrogen at elevated temperatures so that elemental silicon is formed. The remaining gas mixture consequently contains unreacted silanes and hydrogen, and corrosive hydrogen chloride as a reaction product. Refrigeration techniques to recover unreacted silanes consume large amounts of energy. Where silane is pyrolysed, the exhaust gas is sometimes flared rather than any attempt made to recover the unreacted silane. An economical manufacture and recovery process is the object of this patent; an asymmetric membrane which can resistattack by these reaction mixtures is employed to recover silanes and silicon tetrachloride.The same process can also be used to recover other Si-H-halogen compounds. The membrane substrate is preferably a polysulphone, in a hollow-fibre configuration, but polyolefins, polyphenylene sulphide and polyether ketones were also tested at room temperature for periods of up to 14 days at room temperature and also showed satisfactory resistance to attack by silane.The separation layer can be any of these materials: sulphonated polysulphone, cellulosic polymers, cellulose acetate, natural or synthetic rubbers, polysiloxanes, polysilazanes, polyesters and polycarbonates. The separation layer thickness is 0.05-10 microns. Hydrogen passes through the membrane to be recycled, so leaving a concentrated silane or chlorosilane raffinatewhich requires less energy to refrigerate and recover itfrom the admixture of hydrogen chloride. Patent number: US 4941893 Date: 17 July 1990 Inventor: S.-T. Heish, G.E. Keller Api:ilicant: Union Carbide Chemicals & Plastics Co., Inc. Membrane Technology 15

Membrane separation in semiconductor manufacture

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l l P a t e n t s

the developed world. It has important properties which include providing bulk and sweetness. Artificial sweeteners do not provide bulk or {as do sugars in some products) initiate the Maillard browning reactions. Bulking agents such as alginates or carageen sometimes fail to provide manufacturer- or consumer-desired attributes such as 'mouth-feel'.

Polyethylene glycol {PEG) has previously been tested as a new low-calorie food component, as a partial sugar replacement and as an emulsifier to reduce egg and shortening content. The material used was a (US) National Formulary grade which merely limits ethylene glycol + diethylene glycol content to 0.25% maximum. PEG has been purified by cation/anion exchange; this does not, however remove the PEG oligomers.

This invention purifies PEG of molecular weight 400-15,000 with, as the major impurity, oligomers of the alkylene oxide and active hydrogen compound initiators. It employs a membrane with a molecular weight cutoff of at least 150 daltons.

In the examples given in the patent, the membranes used are FilmTec NF-20 and NF-40, and Osmonic SEPA SX01 cellulose acetate membranes, usually with a membrane area of 0.25 ft z. The PEG was diluted by the addition of a minimum of 2g water/g PEG, typically 10-25 g water/g PEG, and in these examples was subjected to 100 Ib/in2g for a period of 425 mins. The results show that low-molecular-weight glycols up to pentaethylene glycol were totally eliminated from the raffinate in all tests. In one longer test over a period of 73.5 hrs, using a larger membrane of 25 ft 2 area, all glycols up to decaethylene glycol were rejected to below I ppm in the PEG raffinate. Patent number: US 4946939 Date: 7 August 1990 Inventor: F.H. Murphy, R.T.

Jernigan, J.G. Grierson, W.G. Wessels

Applicant: Dow Chemical Co.

III IIIII Hill IIIIIII

Compartmented hollow-fibre gas separator This arrangement uses hollow fibres in such a way as to give improved separation efficiency by allowing a shorter path of permeate gas compared to the non-permeate gas. This is achieved by dividing the interior of the vessel into compartments, each compartment having an individual outlet for the permeate.

The separation takes place in a conventional hollow fibre membrane separation system which has been modified internally by means of 10 or more gas-tight partitions. These convert the vessel into a series of compartments each with its own outlet for the permeate. The outlets are arranged to give generally countercurrent flow of permeate and residual gas within each compartment, and are connected by a manifold to an exhaust pump. This arrangement increases the overall permeation rate by changing the average ratio of partial pressures of the permeate on either side of the diffusion membrane. Patent number: GB 2228427 Date: 29 August 1990 Inventor: M.E. Garrett, J.B.

Gardner Applicant: BOC Group PLC

Membrane separation in semiconductor manufacture Polycrystalline and epitaxial silicon metal used in semiconductors is produced by reducing or decomposing volatile silicon compounds such as

silane, silicon tetrachloride or chlorosilanes. Silicones manufacture involves similar reaction steps. There are drawbacks to these processes. The chlorinated compounds are mixed with hydrogen at elevated temperatures so that elemental silicon is formed. The remaining gas mixture consequently contains unreacted silanes and hydrogen, and corrosive hydrogen chloride as a reaction product. Refrigeration techniques to recover unreacted silanes consume large amounts of energy. Where silane is pyrolysed, the exhaust gas is sometimes flared rather than any attempt made to recover the unreacted silane.

An economical manufacture and recovery process is the object of this patent; an asymmetric membrane which can resist attack by these reaction mixtures is employed to recover silanes and silicon tetrachloride. The same process can also be used to recover other Si-H-halogen compounds.

The membrane substrate is preferably a polysulphone, in a hollow-fibre configuration, but polyolefins, polyphenylene sulphide and polyether ketones were also tested at room temperature for periods of up to 14 days at room temperature and also showed satisfactory resistance to attack by silane. The separation layer can be any of these materials: sulphonated polysulphone, cellulosic polymers, cellulose acetate, natural or synthetic rubbers, polysiloxanes, polysilazanes, polyesters and polycarbonates. The separation layer thickness is 0.05-10 microns. Hydrogen passes through the membrane to be recycled, so leaving a concentrated silane or chlorosilane raffinate which requires less energy to refrigerate and recover it from the admixture of hydrogen chloride. Patent number: US 4941893 Date: 17 July 1990 Inventor: S.-T. Heish, G.E. Keller Api:ilicant: Union Carbide

Chemicals & Plastics Co., Inc.

Membrane Technology 15