Patents

very pu re solut ion of sod ium chloride, or p o t a s s i u m chloride or su lphate , so tha t mul t iva lent ions do not damage the pe rmeab le membrane . This invent ion is des igned to use an impure solution, with consequen t cost savings.

The invention cons i s t s of an e lectrochemical uni t cell with four channels , several cells forming a bipolar m e m b r a n e s tack. Each uni t cell is formed from a cat ion-select ive membrane , a bipolar membrane , an anion-select ive m e m b r a n e and a cat ion-select ive m e m b r a n e which selectively pa s se s monovalent cat ions.

Brine is fed as shown in the figure, and direct cu r ren t is applied. Base and acid are genera ted and flow through two of the channels . The fourth channe l is ini t ial ly charged with a purif ied sal t solution. In the remain ing channel , the impure feed br ine becomes deple ted of monovalent cat ions.

Patent number: US 5250159 Date: 5 October 1993 Inventor: D.J. But te rwor th Applicant: The Graver Co.

Cleaning spiral-wound cartridges These car t r idges are widely used. They become fouled by ha rd -wa te r salts , which do not a lways f lush away when fluid flow is reversed. The logical s tep t aken here is to remove the filter car t r idge from i ts cas ing and unwind it to expose the whole surface area. Sui tab le chemical compounds can then be u s e d to clean the whole of the m e m b r a n e ' s surfaces . The car t r idge is then r e a s s e m b l e d for reuse.

Reassembly, or r a the r i ts difficulty, is a d d r e s s e d in th is patent . By specifying a ma te r i a l with a 'memory ' - - tha t is, a t endency to r eadop t the shape it held some t ime earl ier - - and by encouraging the memory effect

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Bipolar membrane stack

dur ing r eas sembly by drawing a vacuum on the cent ra l 'p roduct ' tube, the car t r idge in te rna l s adopt their former disposi t ion. In this way the r isk involved in taking apa r t a t ightly wound m e m b r a n e pack is minimized.

Patent number: US 5250118 Date: 5 October 1993 Inventors & Applicants: C.L. Netwlg, D.L. Kronmiller

Elec t rochemica l cell membrane This membrane , though porous, is gast ight when s a tu r a t ed with electrolyte, bu t pos ses se s good ion- t ransfer propert ies . It is made by p repar ing a solut ion of an organic b inder such as a po lysu lphone in a solvent such as N-methylpyrrol idone, add ing a meta l hydroxide or oxide such as zinc oxide or z i rconium oxide, forming a membrane , then extract ing the solvent by immers ion in a l iquid which is not a solvent for the binder.

A pore-forming mater ia l , for example polyvinylpyrrolldone, is a d d e d to the meta l oxide-organic b inder suspens ion a t a concent ra t ion of 0.5-2%. The meta l oxide content of the m e m b r a n e is 65-95%.

The par t i cu la r non-solvent u sed in the extract ion step has been found to affect the proper t ies of the m e m b r a n e

significantly. I sopropanol is the ex t rac tan t of choice in this process .

Patent number: WO 9315529 Date: 5 Augus t 1993 Inventors: P. Vermelren, W. Doyen, W. Adr lansens , R. Leysen Applicant Vlaamse Instenlng voor Technologisch Onderzoek

Membrane washing aid Hollow-fibre m e m b r a n e s become clogged over time, and can be back -washed by revers ing the flow of l iquid th rough them. In this p rocess the p r e s s u r e difference necessa ry to dislodge c o n t a m i n a n t s m a y cause collapse of some of the pores, leading to degrada t ion of the m e m b r a n e ' s sepa ra t ion proper t ies .

The invent ion c la imed here is to coat the outer sur face a n d the pores of the fibre with ceramics, preferably i ron oxides such as ferrite or magnet i te , In this way the adhes ion of par t ic les to the fibre surface is r educed and the pore walls, if they col lapse temporar i ly , are prevented from fusing by the magnet i te coat ing inside them.

Patent number: JP 5168876 Date: 2 Ju ly 1993 Inventor: N. Uetake Applicant: Hitachi Ltd

M e m b r a n e Techno logy No. 49 11