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The technology of po. alcohol warp s mg recovery In t h e t e x U l e i n d u l t r y t h e n e e d t o r e c o v e r raw m a t e d a b , s u c h - - s i z ing , i s b e c o m i n g grea ter as presmzre f r o m publ ic o p i n i o n and enviro-m~tal legillation ~ . Du P o n t S e p a r a t i o n Sys temm o f f e ~ s o m e so luUonm t o t h e s e d e m a n d s u s i n g m e m b r a n e t e c h n o l o g y .

To satisfy the d e m a n d s of envi ronmenta l p r e s s u r e s a n d the need to cu t costs, chemlcal suppl /ers m u s t provide p roduc t s and techn/cal services tha t not only g/ve super /or v a l u e / n thetr p r tmary use bu t also reduce the a m o u n t of chemJcals requ/red, provide pract ical and economical me thods to reuse the chem/cals , and provide technology to d/spose of res /dual cb ~n lca l s in a n env/ronmenta l ly responslble m z / u l e r .

In the case of textile warp s/zing, Du Pont have bel/eved for some t ime tha t the bes t way to sat isfy these d e m a n d s Is to recover and r euse s~ ing chp~mcals, giving super /or weaving performance, e11mlnztmg ch~nJcals f rom waste t rea tment , and saving money. The Du Pont Separa t ion Sys tems group offers Elvanol polyvinyl alcohol (PVA) and caust ic recovery equipment .

Warp s/zing recovery h a s been prac t i sed in the USA for abou t 20 years, a l though only PVA h a s been recovered tn large quantit ies. Initial sy s t em s were installed by Koch Membrane Sys tems (ABCOR) and Gas ton County Dyeing Machine Company, a n d were a tmed pr/marfly at sheet ing mills as a m e a n s of reduc ing the blolog/cal oxygen d e m a n d (BOD) a n d the chem/cal oxygen d e m a n d (COD) loading to was te t r ea tmen t systems.

However, in the p a s t 5 yea rs there h a s been a resurgence in interest in s/ze recovery, becaus e of the increase in envi ronmenta l regulat ions a n d r/sing s~.~ costs. Recent inst-11-tions of recovery sys t ems have been m a d e in the

USA, Germany, Ta/wan a n d Egypt, suppl ied by Du Pont Separa t ion Sys tems and the G e r m a n c o m p a n y GTV.

PVA recovery All of these sys t ems use ultrafil traUon as the m e a n s of separa t ing the PVA from the des/zing I/quor. In add/t /on a few of t hem can recover PVA/ carboxymethy lce .u lose (CMC) blends. In m o s t cases , the ultrafi l tration (UF) sys tem Is installed in a fln/shing mill. The destze I/quor is t aken from the washe r s and sent to the UF system. Th/s I/quor conta ins not only PVA, bu t also otis and waxes f rom the cotton, spin f ln/shes f rom a n y synthet ic components , a n d any other contaminants that have been introduced In the yarn or fabric. The concentra t ion of solids is normal ly between 1.5 a n d 2%.

The weak f eed / s filtered to remove lint a n d other part /cles

before be ing in t roduced to the UF stages, the n u m b e r of w ~ c h varies depending on concent ra t ion of solids, vo lume processed, etc. The concent ra ted I/quor (also known as re~Inl,n, concentrate , or regenerate) ts then sen t b a c k to the s/zing area.

The re-.latin still conta ins a port ion of CoD~mlr~n~, prtmart ly na tu r a l otis and waxes f rom the cotton. I t is no rma l tha t 80-90% of the sol/ds in the r e c l a / m / s PVA, a n d the res t c o n t A m l ~ n t s . The total solids concen/ra t ion depends on sys tem design a n d operat ion, and var/es f rom a r o u n d 8% to approx/mate ly 12%.

U l t r a f f i t r a t i o n Nearly all of the suppl /ers of s/ze recovery equ /pmen t use ultrafiltraUon. The ABCOR sys tems use sp/ral wound m e m b r a n e s , Gas ton County uses ca rbon tubes , a n d GTV has polymer/c sleeves ins/de a s ta inless steel support . The Du Pont Separa t ion Sys tem u s e s a n inorgan/c m e m b r a n e on a s ta inless steel support .

The po rous s ta inless steel tube is m a d e f rom sta inless steel powder w h i c h / s formed under hea t a n d p r e s su re a n d then hea ted in a n inert a tmosphe re to weld the powder f ragments into a r/g/d, po rous tube, the d iameter of wh/ch var /es accord/ng to the appl/cation. In the case of PVA recovery, the tubes a re 1.6 cm (5 /8 inch) In d/ameter. The tubes are p laced tn a larger s ta inless steel housing, and the inorganic

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membrane is formed inside the porous stainless steel tube.

In operation, the weak feed from the desize range is fed into the porous tubes under pressure. The low molecular weight portion passes th rough the membrane and the porous tube. The permeate is collected in the outer housing and is either reused in the washing step or disposed of.

The large molecular weight fraction is rejected by the membrane and stays inside the tube. As the liquor flows through the tube it becomes more and more concentrated. The final concentrat ion is determlned by how long the concentrate is recycled through the membranes .

Most systems use a refractometer to control the final solids concentration. The Du Pont system uses an in-llner viscometer which It believes leads to improved reliability and consistency.

The Du Pont s y s t e m In the Du Pont system different types of membrane are used depending on the appl/cat/on. For the textile indust ry the following are used:

• a microflltration membrane for caustic recovery and indigo dye recovery;

• ultraflltration for PVA recovery; and

• a hyperflltration membrane for dye ellmination/recovery. In all of the Du Pont systems,

the membrane can be easily replaced when it is dirty or has suffered excessive wear. Without having to disassemble the appara tus the membrane can be chemically stripped of fouling chemicals and then reformed in the system.

In actual practice all that is required is a routine flush with water. The membranes need to be reformed once every one or two years.

The reclaimed PVA is not pure PVA, which mus t be compensated for in its use by adding virgin PVA. There are losses in the system, bu t a weil-maintained and operated system in a finishing mill should provide about 80% recovery efficiency.

Reproduced f rom a fea ture in Teo-hnlcal Text i les In te rna t iona l , (Elsevier) February 1993, by permission of George D. Robinson, Senior Technical Specialist, E.L Du Pont de Nemours and Co Inc, 6324 Fab'vlew Road, Charlotte, NC 28210, USA.

An open Du Pont Separation Sys tem (DSS) module, 61 cm in diameter. This particular model is used in a corn processing unit: the technology for PVA recovery is essentially the same but the modules are larger.

P a t e n t s This is a list of recently published patents covering designs and inventions of relevance to synthetic membrane technology. Where the same device has been patented in several countries, we normally give the British patent number. If there is no UK patent, we give the number of an English- language patent, ff one exists.

The patents llst is compiled from international sources by BHR Group's information service. The facility can also be used to carry out retrospective patent searches - - to test the validity, novelty or infringement of existing patents or new ideas. BHR Group, Cranfleld, Bedford MK43 0AJ, UK, will provide free estimates on request.

Countries can be identified by the code in front of the number as follows:

AT Austria AU Australia BE Bclginm BR Brazil CH Switzerland DD East German~. DE West Germany DK Denmark EP European PatentES Spain FI Finland FR France GB Britain HU Hungary IL Israel IR Eire IT Italy JP J a p a n KP North Korea LI Liechtenstein LU Luxembourg NL Netherlands NO Norway RO Romania SE Sweden US United States SU Soviet Union WO World Patent

(Patent Treaty Cooperation publication)

BHR Group does not operate a document delivery service for patents, bu t full copies of the original patent documents can be obtained from the following addresses:

The British Library Patent Express 25 Sou thampton Buildings London WC2A lAW, UK Fax: 071 323 7230

(The British Library will also supply a list of UK libraries

8 M e m b r a n e Technology No. 29