AU5268898A - Apparatus and process for electrodialysis of salts - Google Patents

Description

I 1 Regublian 1 2

AUSTRALIA

Parcnfs Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S.

Name of Applicant: Actual Inventor: Address for service in Australia: Invention Title: ARCHER DANIELS MIDLAND COMPANY K. N. MANI CARTER SMITH BEADLE 2 Railway Parade Cam be rwell Victoria 3124 Australia APPARATUS AND PROCESS FOR ELECTRODIALYS[S OF SALTS The following statement is a full description of this invention. including the best method of performing it known to us APPARATUS AND PROCESS FOR ELECTRODIALYSIS OF' SALTS This is a Contifluatiofliflpart of Serial No. 08/787,899, Filed January 23, 1997 Field of the Invention This inVention relates to apparatus and nrdc-sses for electrodialysis of salts and more particularl! Lo apparatus an processes that incornorate'at least one of three distinct etue: a nanofiltration unit combined with ant elecrodialysis 1 unic, ion exchange column connected to and in commrrunication wih the base loon of afl electrodialvs-lS cell, and the use of certain types of cation membranes in said electrodialysis cells.

Thil electrodial-yris apparat-us can, be used in a :numbe- of large scale process applicationls. Spec if cally, it, may be'used ito r t'hae recovery of lactic acid from farraertati-l nerivred ammonium lactate in a twoconpartmerit cation cell. There may he either a n an_1o f11t e r or an ion exchange column (or b-ozh) in, comtmunication with the base loop: of the eleczrodialysis cell.

The column contajins a weak acid cation exchange resin.

For more information on the-background of the inventive structure, reference may be made to ray co-pending applicati onS having the followig identifications: Process for- the Recovery of orgallic Acids and Ammonia from Their Saltsi S.N. 0S/G39,83!, filed April1 92, 1996- The invention includes an apparatus and its related method using an electrodialySiS cell cells) in ccombinatic- with a naniofiltration unit for filtering ani Lncoming monovalent salt solution in order to minimize the level of multivalent impurities- The apparatus may also include an electrod~alysis; cell (or cells) fin comabination with an ion exenanue CcolU71 in communication with a base loop of the said electrodiaiy5si cell.

The pH of the bae product from the apparatus maybe in the range of 5-11 and preferably i the range of 7 to about 13 The anp.'aratus and urocess are particularly well suited to the urodliction o f acids, espe2cially arganic a cid s, In C~juncticrn with weak bases su ch as a-tmtonia, or the, salts weak acids sucon *as sodium caronate orbr sulfite. -The electrodialysis cells of: t h -invenition may employ membranes, such as bi-olar m ermbr anes, or assemblies for splitting water., Alternatively the spl1Itting of waepo cibs roducionl may be accomplished 14i.h a set of electrodes.

.BackaroUfld o the :1nveto ermentation processes for producing organic acids, such as 1-5 acetic and la c tic aci;ds,. go_ through an intermedi.ate product ion of salts, such as ammnoniulm acetate or lactate. Hence, salts are the byproducts or intermediate products of a nurfber of chemical processes. For example, regernerablOf~lue gas desulf-urization *processes use a sodium alkali to absorb the SO 2 thus resulting in a soluble bisul-Fite salt, NaP7SO 5 Production of soda ash (NaCO,) requires the processing of the raw material salt viz.., trona(acO.Nai'CQ.2- O) .or. the naturally occurring brines. in magneoyroYai poe eeation process the ptassum carhop-ate seed material absorbs SO, in the fuel and 's ccnvert-_ed to a byproduct potassium sulfate.

Electrodialveis (ED) may be used to convert these annd ot-her soluble saltsidirectly into their acid and base COMPontnts. For example, such a procedure na-bles a direcc recoue-ry nf a reclatively pure form of the organic acid from its orcanic Saltthe co-prodUct base Cammoniai for example) may be reccverea o reuse in the f ermentiation process for pHI adjustment, thus ermittiflg an economical and environmefltally superior otion for producing organic acids. T-1- other instances, such as wit'- sod~iume hisuillite, trona _or-potassiumr sulfate, the electroda'-st offers i0 an envaron-mentally superior route for recovering or recycling h e acid, bases components.

Electrodialysis uses direct current as a means for ca-using a movement of ions in the solutions o f the rprocessiilg screams or salt starting material. Electrodialysis processe s are usuallyv carried out in an arrangement. comprising a.stack where a plt~rality of lat sheetL ion exchange. Membranes and. gasket s'h -eCrtS ar-e camne-ad together. -These sheets:-orovidE flow~ paths for)containin4 salt. materials that produce acids and bnases. The process unit reg'aire3 a means for splitting water into nvoxrdog=ri and hydroxyl (OW)1ons Two useful means for splitting water are: ft()Ab-ioclar membrane or a bioolar -module fiormed by a I comb-nto fcto n no membranes which functions as a bipolar membrane- Suitable bi-polar membrar-es are a-vailable -From kalytics, a o~iv-s3 on of Graver water, and from Tokuvama Soda, *and from the Form ic.Corboration; a-nd 1' xN:3. %33-I3 An electrode set comorisirig an anode and a carn-ode.

The electrodes, narticularly the anodes, are coated for chemical stabil ity, fcolr. ini nizing power consu motio., ando for the *form- aticn of bvoroducts other than hydrogen (at cathode) and S oxygen (at the anbde), among other things-. Suitable elecdtrodes are available 'rom the Eltech Corooa. n the Elect-coderdut Inc-, and from others- A hydrogen depolarized ano de can also generate HU ions 2Jn al aqueous solutionl or an el1e c t cc: s t-r-ea m next to the ano de.

i~o As described in my above-identified co -pendinig ao~aif the stac'k contains electrodes (anode and cathode', at either end and a series of, membranes and' gaskets which have open -active areas in their middl~e to form a mnulti-plicity of compartments which are s eparated by. teMembranes. UsuallY, a senarate -i's solution (an electrode stream) i s also supplied to eacl, o f r te compartments containing the electrodes. Soecial membranes may be placed next to the electr odes to prevent a mixing of te process streams with the electrode streams- The maajority of the. stack between tne elect-rode comuartm-nts *comp-rises a repeataflg series of units of diff erent inemoranes wit-h.

*solution comcartments between. adjacent membra-nes. Each of the reoeatina units is called the "unit dell" or simply ac 1 The solution is suoolied to the comaoartments by intern-al Mani-folds formed as part of the gaskets and me-mbranes or by a inat ion of internal and e- ternal manifolds. The_ staccs~ can i nclude more than. one type of unit cell.

4 Streams of ;Drocessincr fluids may be fed from one stack to another in order to ontimize process erir2caency. A7 fter one pass through the stack, if the change in the ccmmosi.tior. of -a orocess *scream is relatively small, the process ltoncaberyld by ibeing pumueacct and.from recycle -anks. Anaddition of fresh *prccess solution to and withdrawal o f orocu-ct ftrc rath e r ecy Cle lonca b mde -iher cntinuously or zper4.od_ c'n 1 y~ n order :0 miaint a in the concent-ati-Or of Droducts withi4n a desired range.

Wh-en bioar membranes ar e used to form acid or base from the salt, in order for the membrane. to function. as a water.

solitter, the component-ion exchange lavers must be ara gd so that the anion elcielayer of each membrane is clos er to the anode than the cation selective layer. A direct current pssed tnrouah the membranes in, this con:-ua- o cue ae 1 splitting With. OF- ions being produced. on the anode side anda corresnondin& number of F- ions being produced onz.Che cat_hode_ side of the mecibranes., The dissociated salt- anions move toward the 'anode. Tne'dissociated s al~t -c at ions move toward the cathIode The electrolysis process works in a s m i a r ma nn er with the ~0 water splitting occurring at the two electrodes. When a dairect current anerwater molecules are converted to-oxygen gras at the anode along with t-he introduction of H- ions 4 ntc h acqueous solution. At the cathode, the water molecules are converted to hydrogen gas along with the introduction of 0i4' ions into the acuaeous solucton. T- the hydrogen depolari zed aanode basenelectrolysis unit_, ions are releaseC: it tre ac-ueous Solution nex to the cathode. While released, tehdoe a is forwa~~~d~d to the catalytic hydroger. depoaie nd o i4of gefleratio-0f Electrod ialys a' ecui-oment for acid/base uroductico may have three com.Lartraent cells cornoriSing7 bipolar, catlcr, and an-Jon -memorfls two coiuar. tlfen, cells containin;~ hiz.clar and c=ation (or anion) rmouranes; multiichamber two comoartment- *electrodialvsis calls comorlising bipolar anda Lwo cor more cat--o= mmbranIs The tem T"binolar mermorane" also includes bipclar eq-ivalant structures, such as the use of electroc-es a-nd com-oosite bioolars. Fig. i. shows the unit cell for the zhr-e e most- iIse'u! configurationls.

Specific references are: "Electrcdia>vsS Water SV liltinlg Technology"l byK.'.~n;u Merabra-flae Sci. (1991), .53, ll3-1l38 Patents 4,082, E35; 4,10701S; C4,592,617; L-636,289; 4,S&3t,077- 4,390,402; and 4,536,2!G9.

Inaccrnafoc ithan aspect of t sinventicf,ar *electrodia-Y52. acparatus i~s improved thro~agh t-he addiztion of a 0 njanofi-ltrat-Jon uni-t -upstream of an elccrodialvsis cell orthrough the use of- a downstream icon exchanue column in combination w-ith the electrodialysiS cell and in co-Lmmn i cat ion with the base loopD of the cell. Or, bothn nanoffiltration and an ioni exchange column may be useo.

I oterasicc of the invention, the use of moznovalent *selective ca-.Io mem-,branes in combination- with adecuate d:ilutionofthe base nrcduct a~lcws reliable non-f ou-,ing ooera-4c a:th *electrodialyis cell to produce acid and base frmSalgrief Descriotiofl -f thE Dra~iO The jnvenzio2-Of mnay, be umderstood best by readinu rhe S followinga Specificatiofn ccnnect-40fl -With17 the a-ttached drawings, in which: :iUs. Sc'ematCai 50WcS ite -Un cells for two and three compartment electrodiasi5s cells nosinag binolar mambr anes; 0 Figs. 2(b) schemaicaly -,nw ccns!truc!-lon cf Lthe uni cells -for twc and three c oum-a r L n t cells usi-la a ser: of electroCCes; **Fi 3 sch-ematically zshows a two cc martmenI cell using a hydrogen depolarizinlg electrode; Fi- and 4 are block diaarafl5 whicli Snow Lnre inventiofl using an electrodialysis syst4zem Jnaving, an ur'stream Figs. 5()S()are block diagrams which show another appDTaratus of this incventioi co-m-orsing an electrodialysis cell in comrbifazibf with an ion exchange coluzn in comnmunicatiofi with th-e base loom of the electroaialysis cell; Fi.~i ceatic diagran showina th.e canstruc-ofl o' the two-com-oartm.ent cell used to de-monstrate the iutility of :z invention; Fig. 7 is a block diaaram snowln ic-sse uc o -,estiplg a-n a7nparaU'S oL thi s inventiOZI; Fia S s raph suzmmar zi;ng h so'lub3.ltv da of calciu=fl and magnesiurn as,,a function off base p-H; 9 is a block diagram which shows the use Of tnis ~netf n the urcduction Off ora~c acd v a feme -aion; FiU. 1 0 a n bloc'. diaa.ams which shows aspac-s ~Off this inet~ nthe production =gra~nic a~ "fermnftat IOn ar-e bl ck diagrams show2.nu E:ue cas desulfurizat-ofl r-ocess systems using the apnaratus cf Ehnls invent -Op.; Fi. 2 is a lckdiagram whi ch deoi cts t aplicab'lkty o f the inventioni to the,-recoverV Of: sodf'I-m carbonate

C.M.

carbriate/bicarbolnate containiflo maineral 5ourc es, Fig. 3 is ablock iagram, which shows a systemusig c ri 1 vetif i4 n conjunction with both a nanoffiltered inc1-ut Leed ant an ion exchange column at an cutnun.- of said system;an -Fig-1, JA is a flow chart showing a p-rocess ffor protucing :osodium hydroxide anId h-vdroc~l-oric acld.

cell Conszr-uct2iof *Fin.- I(a) sh-ows atwo comppartment cel 20 comnr. .SOC biol ar (desianated as embranes 22, 22 and anion (designated as rnetaranes 2 2. A salt/base comparzmelt (S,3 loae beweenthe anion surface off the bipolar ebae22ante anion membrane 24. an acI coraoartment oae ewr the cacion surf ace of 1:he bicolar membrane 22 and ancther anion mrembrane 26. 7hF cc- biin of the-se two cc ra '3 an-: A)and of: the -,embranes 42- is ctermed a "n7 1 S a '1cell. 'Then. trie cell compart-ments repcat, as at and contanuina on.- smi as two hundred or more suca cells m-Lay _re asmldbetween an anode 2± 28 an a a c atnoh C d 3C The satou~n32 process fe ed sr e a r hic iJ -S b ac'di:Hied, a _.atat~e Sclutiofl 10, for example, is e ote Salt/base compartment S13, while. a l ii cortprais-s wae 3 a b e, s-u pi a- to the acid co-m-art-meat. Under a orrect Curren- 11 drving forqe, the binoIa r membrane 2S soi s t acer, oener F a:Id OH- ions as s~hown (zF'ic. irf~~~u 1 the X anions r esultin fror-n the dissociation of the Salt Streamis Mx -rarnsotd across the ar'o' ebrn to the aciomzpartmenz, wnlere they comnbine with thie ions to form ae ac.-.d The process may be reeetosnmtclvas follows: *(Salt/base Compartments) IX On X, MCB{ *(Ac id compartment. S) -t- The process has been detailed full1y in m.ry earlie cc-pendng patent applicati.ons. T-his process is beSt utd oruoes salts of weak bases, uarticularly -for orocessina ammonium salts.

Th icCOMnCenrat-iof Of th aci-d croducL that ca-n !e p.ade in thl e order of 1-G, N, with the higher concentrations heing feasible f=r organic acids XpK ofaot2.e~cater) The _zeed s alt Concurretly~ b3ecomes alkaline; wit-I" te -oF beiriz ahCo't 10-11 fr ammonia rroduction.

Ei~.1C~s-cws a -wn omaneocli3corsn i~ and cation memhraneS (-designate ase cnaton

B

located betwee- t~he cat: cn surface ~c of heoila z n an' anot:.her ca rcnmeroorane2 Th cmna-of c -1 t 0 onfe s and ewoc cm-,-ar t~mEri cz det a 1. Toh'~ o- rore suco cel 7.-y he as~~btenar anode =n'd a catho-e.

-Th e salt sol'.tcon to acii-fed (an oranic saltz sclut:2.cm -Ix -ocr examole) i:s fed to th 2 saitacid compartment £,Awhilea icidcomrising water may De Sa olicd to ch base Coz oarnt U. toer- a diriect curre= driving force the bi-o3- ar mprL-rarte enr-te a O 4 sowz eb otir Mcazoi re su 1 ti1 a rc-m thne SSO~iat-ion. of a sa IN~ are aiasotcross~ the ca- o inr- e=n r. 0 'n ase c zo:ar "mnt, wore Lhy Co~ w' r 1 C u u-naLMO n" cess mayv be reuresented as-.

(Salt/Acid com-oar"rnents) 4 (Base corm-artments) The contversionl the s al1t Inat can he carrie:d efficilen- by this arrangement is dets--rmiiied by thle amount of *curr-ant uSan (Couicm!Ds), the ccettonof the salt scolutio-n andarrtnl, by the Paof the acid involvead. For wal dissociatLed thA a~ u-x geate rhan about 2.5 he ccnvers--ion cant he from. abciut EC0. tCo about 97-. MoSt- oranic acids 5-uco as atcacet~ic, citric, foric and 07ner acras into this cate'-ar::. The zrzisidna! catic: conitent 4z, the arid croduct can then be removed, if n ecessary, via a c o o2 aI cation exang resin..

S 71 cire CartmC t Cell '14 us nz zo al s G, cation 483 and anion 50 memn'nrames- Three cotrcartment-s, a id a bs e( ar d s a I t re_ ccae -e::Wsetnhre- ~raembranes, as Szhowm. The entirec ia onc*-rne en comnarment erued a "Cell)' As war.te zo *cells of Fig.I many ce, ls may he plIacedi between a sne sez.

=0 elecurode5. ThI-Ls tl-e ccmnartme: cell arranseern LS e most genric fcr the pocrtion of acds am bases, prcai s sronq acras, sucn. s hvci chor:c a- n'irc acics, ant srrcona ~S eS s u c' as so d;um rvroxicde vo- a'L hdroide Th 'Sa1 Oliti4f r5 n t cL the S cmcarn IfLen- ccate.d: b'etween thie cation 4-tE and a ni4on 5O emLnrarles. 1 i ac con-or s7lc warer a-s red to t~he acid and b a se co ens> loaed on either side of t-e bioolar memrar-e- dner a do;reczm currenz dv' ng fo~e the 11 and ions generated a" he boclar: *mebran are transorted to the acid A and,-- baseS 0 comna--"mntS, resoect--veiv Concurrently, to i1 cr.S are zrar soo LeQ across the cation. membrane 48S to the boase comna rent E, whie te X- ions are transorzed across the an.-o- meanbrane t theb acid cmnartment ThQ net effect is th- crozducztiof: rela~ilrelv pure acid and base products frcm the sa--t?

MX

Ocher cell arrangements inivolvina bipolar membranes in cjunction wth two or mnore catio benranes or too mr aan membanes may also busdi oesnri salts where the pK of the product acid or base is in the intermediate range. Such cell arran.gemen-t s convert the salt to an aci*d and a base at a higher current efficiency, as comp~ared to the conversion of the twocO~atmnCcelsshwnin Fis. 1(a) an ~Vbut it i also at higher" capital and:.operatinag costs.

The operation oE the procass using electrodes as the source ja~ oF' and 0H- ions isoentemed electrolysis which ivle the co-production oft 0, and H, at the anode and cathode, re civl.El ectr olysis operation is similar to the oeration *of the bipolar membhrane electrodialys-'s described. above. The main difference between these two operatiosi the membranes Which aDDcar. between an anode and a cathode. W i th e a ch cell containing a set of electrodes, a number of cells may be assembled into a sinigle process-unit, The electrical and hydraulic connections between the cells...may be made in either sera-es or a -Darallel combination in order to form a compaact coim'ercial process unilt. Exemplary references are: -Meliere, K.A. et. -Descripotiof and Oeration of Stone& Webster/loflics SO, removal and recovery" US5 NTIS REnort, PS-242 573, (1974), 1109-26- US_ Fateant 3,,175,122.

Figs. 2 -2 show. two of the possi'ole cell arrangements.

More particularly, Fig. 2(a) shows a cell S6 using two cation 12 -S Ck3- .87Z membranes 52, 60 and three compartments located between an anode C)and a cathode The oneration of the orocess is similar to the oneration of the two-cortoartrnent cation cell shown. in gig.

and is particularly applicable to the production of weak 5 acids from theiJr salts. 'A separate acidic streamnrmay be circulated in the compartment which is a buffer comrpartment next to the anode 62. The salt p~rocess streanm which is co be -processed is circulated in the compartment between the two cation membranes 58, 60. The buffer compartment A' -and cation -meziirane 10 60 are used to contain the salt stream. While the buffer *compartment is oref err-ed, -it is riot essential to the czerar-ion ot the two compartment cell.

IA stream comprising water is circulated in the B compartment n ext: to tHe 'cathode 64. Under a direct current driving force, H' -and OH- ions are generated at the anode and cath-ode, repcivl~ along -with oxygen and hydrogen which are cov roducts fr~om the dissociatio n of water. Simultaneously, the Hions are transported across the first cation membrane S8 to the intermediate salt/acid compartment where it combines with the anion X- to f orm the acid FX. The M' cation is t-ransported across the second cation membrane Go to the S compoartment to form the base IMOH.

The reactions may he summarized as follows: (uerA' compartment) 14,O 5O, 2R- 2etransported out across the first caticn membrane) *(Salt/acid. compartment) 2RX .2 H' 2M- 2 F-4 (Base compartmenlt) 2H,O 2e- H 211 20H 2NO01i (overall) 2MX 3HzO 2FL 2MKCH E O^ *Fig. 2(b) shows an.otner version of a four comPartmernt cell 66 *Using two catiLon m e-branes 8,7andl one anion Membrane 72 10 between an anode 7Y4 and a cathode 76. The opeiration of this cell sG is similar to the oceration of the three comp~artmient cel-l shown in Fig._ 1Cc) The, cell 6G is capable of generating relatively 'Cure acid and base. The salt 'L1: Is fEed to the comL~ar tment 'S between the anion mernrane 72 and the second cation membrane 70. The anion membrane separates the acid product from the feed sa!l- Otherwise, th~ o n eraton o the cell is simiilar to the overat ton of the two-compartment cell shown in Fig. 2 When cells 56, 66 of Figs. 2a,,2b are comnared with the bipolar membrane based cells 20, 36, 44- (Figs. the co-production of hydrogen and oxygen at the electrodies along with the acid arid 'base products reauires an additional onereyv nrut to the process of about 1.2V/cell. One oDtion that car: reduce this power load is the use of a hydrogen depolarmized anode in place or a conventional anode.

Fig. 3 shows the construction of 'a cell 78 with a hydrogen depolarized anode,. which is conceptually identIical to cell 56 of Fig. 2 (all in such a cell, the hnydrogen gas produced at the C cathode 800 is returned to the anode 52 where it is oxidized to *14 IP--J...ASPCSU3O.I3,-..R2 pro tons at a gas diffus ion electrode. The F- ions are released into the aaueO'45 solution next to the gasdifSOelcre82 This technique can lower the-cell volitagre by about I ot/e thus reducing the Power cornsu-mptiofl level to be somiewhat nearer to that obtained wIth a cell using a bibolar membrane (Merrrafle &SenaratJ-01 Technnology News, (199e), 15(2), other cell configurations employing the gas diffusion anodes can b visualized by those skilled in the art.

For purposes of this disclosure, the cells employ bi-polar .0 membranes, a combiniation of cation and anion me-noran"es that behave together 'as a bipolar membrane. The cells may also emiploy bizolar membrane ecauivalents, such as structures using electrodes and composi.te bipolars,'. The cells that have a set of electrodes generating and icns, a hydrogen depolarized anode based In cell that collects ,the hydrogen gas at the cathode and injects it.

into the* companion porous catalytic electrode to generate may be conmsidered. equ.ivalenlt, The term "bipolar maembrane' or its equivalent will be used herein to denote any one of these opotions.

Desvite the -usual filtratiocn/ultrarl-iltrati-Ofl and carbon treatment steps, a major problem in u-sing the electrodialysiS cells in the water splitt-ing applications, is that the feed salt contain-s a signif icant amount of divalent metal, ions, narticula-rly calcium. and magnesium- W-hen the feed s tream 2-s processed, the metal ions are transported to the base locp of the electroaialysis unit- Due to their -ocor solu'oility, the metal I EC 2 330-13c.R! ions are precipitated in the base locv. The, Prec40-tation Of teeions inside the base lopplugs the CellSt and damages the *membranes triereby decreas .ing th e Icurrent* throughput and, in the extreme, causing a mechanical -Faihl-re resulting from an overheatinlg anda, perhaps, a mieltdownl.

Aresinl based ion exchange is a standard technicue used to reduce t h e-',1cai u and magnesium levels in the feed stream to the low levels required for the proper operation of thel *electrodialysis cells.. A problem With this apprcacf is thatth pl: of the feed stream has to be raised to through an addition o:f a base material. The feed stream is filtered one more time (to remove any precipDitates formed) in order for -the. ioneoxchap-ge step to be effective. Such a step Ii s practiced,' for example, I P the ourificatioa of .NaCl screams in the production uf caustic soda via electrolysis.

Many of the salts f rom the commercially important -processes *are acid or neutral. These salts may result from a fermentati~on of dextrose to organic acids- -lactic, citric, acetic, 2-keto gulonic, and the'like. These salts have a pH ranige of 4 to 7 arid contain signaif icant amnounts of free acids as well as calcium or magnesium whlich had been added as nutrients during> the -Irmentation step. Such~salt solutions requpiire en ad~itol of considerable quantities of alkali in order to raise the pH to a 0 Moint where an effrectiv .e ooeration of the _on. exchange column c an be assured- The added base w'ould then have to be recovered in the electrodialYsis unit at an added cost in terms o h aia cost of the membrane area and electrical power c fs~ito r Aknother application where acdl -1t: r~Le 5i flue gas desulfurization. in tbhe proeS h ufrdoiei h flue qas isabsorbed in a solution of so dium sulfite (Pa or 11) result nQ anT acidic salt solution of sodium bisulfiJtP

(PH-

A The bisullfite stream can then be crocessed3 in the electrodialySis units to recover "he S0 2 product and the alka±l! which mlay be-recycled to the absorber. Patents 3,475,1 22 4,082,83S) oeea problem is that the, -flue gas, which is derived If r om the combustion of fcssil fue ,contains flyash.

derived im-ouritieS, usually including calcium and magnesium compounds. and_ possibly, corrosion'broducts (iron from thze ductr work through which the iflue gas passes.- The presence of these impiuritieS make the proces sing of the bisl estra in e water splitter iather difficult, i.not impossible.

A A similar, situation exists in the processi~ng of impure alkaline sodiu-m brine streams used to make sodium -carbonate or s o dium hydroxide. The brine stream may be from certain surface sources (such as Searles Lake in California) or-from a m Jne ralI *source such as trona (sodium sesquicarbonate), derived via m! ni -q at'Green River, Wyoming. nawte pttf9ProeS h m ine ralI is acidified to liberate carbon dioxide in the acidA loop.- Depending on the process choice, the acidified product may be reactled with an additional sodiumn mineral either in an above 17 uwCS3ground reactor or !71 an under ground mine (so1utiofl mining) tO librat CD and a neutral sodium salt eg.sodium sulfate)- Conurenly,3.'-the base loop sium carbonateispoue by reacting, the caustic soda product with a corci~no7. G thIIe bicarbonate feed or by absorbing the carbon dioxide ~nthe sodiumO hiydroxide generated in the base loop. U.S. -natenlts 4,584t077, 4,.592,517 and 4,,636,28 contain exarnlas of such processes. -n addition to containincg auantities of Sodium sulfate, sodium bjcarboinate, sodium chloride, and-sodiut carbonate, the minerals also contain, among other things,-snme calcium arlo macnesumf compounds which- could hamper their direct processing via electrodialrs is.

in the above described and other similar applicationis 1 i t would be highly desirable to have improved apparatuses and is procescs that can trean an acidic or near-neutral pH salt to yield the co6rre SponfdJ acid and an alkali at a pH, of9-, without the need for an upstream -PH adjustment and ion-exchange.

.*An earlier of my co-p Iending patent. applications, Serial No: 08/639,831 discloses a-'use of a nanofEiltration step to reduce-zhe calcium and magnesiu-m levels in solutions containing ammonlium salts of monovalent organic acids. Subsed:uently, such solutions are processed in a 'two compartment electrodlialYsis cell containing bipolar and anion, memb~ranes. This process generates an ammonlacal organic salt solution at a pH of about 10 andl a concentrated solution of the organic acid. While effective in reducing oreliminating the precipitate formationl at the bip~olar mmbrne urfce the cc-pendinlg appli~cation does not, address eithe theoroducizion Of: concentrated alka~le ouitSo *o-roduction of mult~i~el acids.

A need exists f or superior au-paratuses tor procucirng S concentrated alkaline stre ams; ammonia, sodium sulfite, sod'ium carbonate, sodium hydroxide and other -materials in the p4_ range of 14.A and caor processes which produce sucfl streamshnocher n~eed exists for an' i apro-ved Croc3 ess that can conv,;ert Salt solutionrs without the need fo= eeither mht ad~justme7.t or an upstream ion exchange: rea based sof teniLng step, -ih-ile acnievang a reliable lo-ng ter-ir oneration of the electrodialVsis cell-and the product'ion o' con qentratedalkaiine solutions.

Yet, another need also exists for a process that:ca concurrently generate r-elatively pure acid co-uroo-ucts.

IS Still aniother need also exiLsts for a novel aooaratus -and *process thrat canc directly process rrltered/ ultrarailtered solutions OfL ammoniumr or alkali metal salts of organic or inrai Jd to yield a cocntrated ar1rao k yielding a relatively pure acid or a substantially acidified salt *O stream.

*Sum~iary of_ he Invention The' inventlon orov:ides improved apparatuses.. methods, and orocesses for convertiT.g a variety of salt streams into relaively pure acids and alkaline orodiucts. The alkaline may be almost any o~,but -For many applicationas the p~n' is vrefEerably in the ranige of 7 to about 13 The ivninge out of a-nutfler of findings- when Drocessinlg salts of certain organic acids, the murt'a1 lnt catiole appa--rntly bind With the organic anionr. This substantially reduces their n ras~r ut. of tile gait or the salt/acid solutiol. W i th the appropriate cation membiranes and whben dealing wihweak *acids, a vortioni of; the divalent- metal cations rnav be retained in.

the feed salt loopo. The balance of these cations are to the base loop without causing a oli of the catlon membrane~s. The transported divalent metals have a low hut finiite solubility in the alkaline product solution.

By devising suitable app)-aratuses th-at can azttaif anoc m.airtair- a su-Jficiently low concent-1ation of the di-valent metals in the base loo., the-.precipitat-ofl c tneEe metals either does not occur or is not a serious oroble~z- Ma-intaiflina low *concentrations of the di'valent metals in the base looP, thereby averting their precipitation, has suroprisingly beneficial effects such as a high and steady current throughput and the -elirmiatiol of shunt and stray currents. related heating and melting problems.

Long term trouble-free opceration of the electrodialysis cell hard ware, me-ianranes and the process are thereby achieve.

One aspect of the invention resides in processing Salts of weak, low4 molecular weight monovalent acids. in this, the feed lur~n nim latateor aetat) is subjetdt so-u~ g. amcmonunltaeo jeedo 25 nanofiltration. The nanofilter that is most effectl-ve has a ratina in the order of- about 200 Daltons. Thus, th',e molecular weight Of the acid that can be efficintL rcessec lssta a-bout 150 DaitonS. The feed may be at almost: any nH, b~ut preferably i-s in tre ange of 4-.0 he nanof il trat ion step produces.-a filtrate, w ,eieifl the divalEnt muetals, content in the sat steamis less than an roxJ-mately 25 puf total.

The purinied- salt stream is z'nen Drocessea in a two cot Dart-meflt cell coritai.nlig bipolar metaran-ies (or eauivalent) and cation membranes. The feed salt st-rear, is fedto *the salt/acid coapartmaft cornaiie betweenl the clation ~ide C: io the bipolar membrane and the cation. selective membrane while a *st-ream of water is ed into the base compartment between the *cation membrane and the anion side of the.bDinole-r memL-brane.

*Under a direct curn driving force, the feed salt is acidiified in the cell to the extent that is tech-ically a-nd econom-ically t fesbea ~eu~ fte H' ions generated- by the bipla membtrane.- ***Concurrently, the salt cation is -transvcrted to the base lonwvr-it combine with the OH- ions generated by the ioa *membrane to forrt the base -oroduct. The extent of the conversionl of the salt to an acid in the acid 1.6~ is detarmined or-imarily bv the amount o. current (coulombs) passed through and by the -pK, o E the acid. !For- weak acids having pKa's greater than there is a conversion of 80-97%-, Man,; organic acids fit this category- This inventicn can. be used tor base Drcducts in the niF range of ueferably in the range o-f 7-13-5, and more oreterably inth r~ ange of 8-i1. When the feed stream conta s an additionl salt of a st=ronger aidwt Csaecio (eg amoiu ac--e and amw11,cniut su, fate), the additional saltbecomes a sun-0ortiflg electrolvte. The formal cornvars.on of the weak acid can be in the order of 100j%. some ti mes, other r-arts of the system may contain weak acidwhc was n" part of t~his original feed, in whichl case the weak acid conversi on!av be greater- 'par. lQ% of the weak acid in-the feed. -_he uroduct acid.

tnenmayhav soe eces ~{ions. The prccduct base -Stypically at a strength of 1-15 N_ A seco-,d asoect of the invention. c subject~r.u the salt' of the monovalent acid (molecular weight less than anorox2.rtaelv 150) to rnanofiltration, fEollowed by processing in athree cornarw~nt el which contais a bi nolar- mmbnan (oit iS1 ecn-ivalent), cation memb rane S and anion. metmbaaes. f te r n ano f11t r tio n in.-order to reduce, its multivaet c aticr. content to below about 25 OppL, the feed salt solution mpay be at any urH peerablY in the range of q-10). Th,-e sqolutior, is fed nto a salt cornoartmeflt contained b et w e e cation. aad anion -memrores.

.20 Liouuids contai.ning water are fed to the acid and base comnar-tments. The acid compartmen1t is contained between the 4 cationr. side of the binolar membrane and the anion memlbrane. Th e base comzartmoenlt is contained between tht- anion sid~e oE the -bicolar -membra; ne and the cation mkTembLrane. The .~dsclution, is depleted of issalt con-tent in the process, w..hie 'a relatively 22 2kAA5PECI

ZR

oue rout acid and base at concer ratior.s atllS strength.

are generated.

The inveto car, be used to generatebe Prcdt in the pH range of 5-14, preferably in the nH rarlae of 7-1i3.Sj and more p referably jin the p-H range of S-1i. Tn contrasrt wth th e twocompartmentr versionl, the thrlee-cornpattmen"t cell can in- lsc S dor_ producing strong or weak low m-,olecula-r weighr-t mcnovale"nt aci ds.

Aknother asoect of the inventionl is a nvla-paratus and urocess tnat incoruora.ces an ion exchnange column in commun'caticOn 10 with the base loop of the electcrddialysis cell. The feed salt_ *solution, whiLch hav'be'at any p-H, but typically in: the range ofE about 4-10, i-s suitably filtered to remove inolbl atter and_ then orocesse. in an electrodialysi's cell conta~ning bipolar membranes or their eacuivalent.

The base compartmnef orF the cell, contained between the anIon: side of the bioolar membranze and the adj;acent monozolar membrane, is con-nected to an ion exchange c ol1umun The base solutior. circulates through both the cell- and the column. Tine I-on exchange column contains an. iorn exChanae resin canable of :20 removina substantially all of the multi'valen--t metal Lo-s that -may enter the loon, either, across the cation membrane or from the =aqueous reed solution to the loop. The base -oroduct may ha at any pT- in the range par-ticalanl'/ when- base loaop z)s cont-ained between a cation -wemb'rane and the anion side of- the bipolar membrane- For an -fcent removal o1.emltvln cations, (pa-ticularly calcium and magnesium) the pH in the base loop is pr!efarably in tne range Of aot7-14; ano MOstm Dretferably alout81 The eiectro2aaL Vsis cell "ay be ttypCCP~e ~e, 1; membraneCs, Cr a t-nree .comarnmaflt call contar.nltrg rlar, oatic.

aria anion membranes. nultichamber cells conzuJ-Bin two o- r or r,,oovlar inerifObrafles of the sam,-e tycpe as detaile n P aJ t e nt S 4,53G,2L-1 rz082 .l ay alIse -s e as Dart of the ipoe process andc aDoparatus.

The inventive nrOcess ana ancarn-tus has been found- co be oarticularly efLceV When the base comoartment c-E the electrod-Ialvs. cell, iLs ccnt a .i ne netween te cat300 memobrane anc *the anion suIrfacelof the birolar -membrane. This arrancemenit is *uset because acidition~al senarat-ion and retent ioan fror th.e mult-ivalenz mtetals are vrovided by the cation tmembranes which reduces the amount ofF these metals in the base loopu, thereby saving on the cost of i'solatinor utnem- Conscaue-' 1 Vl i0n exchance load f or these sreciesmay be subustanti al ly reduced and heonexchanzge coluimn can be made suabstanzially smaller in relation to the amonunt otmulti4valent cations in Lroe feed strea.m heinoi proce ssed.

I n anr.othe r aspect of this. invention th1-e feed:al solutaion nas relati.vely low levels of hardness or can be pur1 47i V-a *.convenltional~ adjustment fil1tration ste-os in order to reduce the total 'hardness to their- solubility l eve]ls. Tis ves so has the advantage hat it car rrocess salts orE mono- or exchange columnk in co iain vihteeetclls- s cell and in omun~aion with zthe base loop Of "i'e cell.

ihe zmproved apparatuse5 can be better unrto -From Figsia.(b,5a)-55 c) .Ot'her kinds of cells r cel desicuns can' 5 be visualiz- b-Y Personis skillec in' t~n art. F i gs 4 a) a nd 4 (b) shc-4 the aoo)arat:us ofthis invent-on that tises a ranoilzer iLn conjunctio n -4ith an elec tro di a Iysis unir.ts su U s clIa S s w- ~n Figs. 13 F ig.. shows a naznofilter 90 operat ing unstrea:mz of a twocompartmnent cat-ion cell 52-. The cell may of the tcyoc shown in or similar to Figs. 2,1a) 3 or wnJIcn may e-mploy two or more cation memhanfes. Teaoilte-r has a typical mosecular weighnt ct L of Lo about 200- Suitable fLilters are availabcle from Desalination Szystemns, Filmtec and oth-ers.

The feetd stream> may be a salt of a rnonovalent cation and monovalent a-nion, may be at almost any pH, but usuall y is at a of 4to 10. The feed stream nay contain multivalent cation, impurities-ann is initially procelssed in the nano-filtration unit containir 9lt S to obcain a filtrat nit a aivalen.mea content of about 25 ppm total. The filtered stream i.s red through pipe 9tohesalt/acid comoartmflt 99 of the cell 92when processing salts Of low molecular weiaht less than abozut 150) weak acids, this reduced level of multivalent cations has been founld to be adeauate for ensu-ring a long tetrm, troublefree oneratiOn of the electrodialysis cell.

The-nahofiltered feed stream in the salt/acid(/A compartment 96 the tw4o c-ompartment cell. 92, is usually a weak acid such as laccic, acetic, formic and the like, and is acidified by the protons generated by the bipolar memorane (or its equivalent) .The salt cation M- is tranSpartec. across the cation membrane 98 to base compartment 100. The pH4 of the base is Produced by the in-put of Oz U ions from a bipolar membrane in the base compoartment 96. The PH of the base is controlled to be in- the range of about 5-14 and preferably in the oIH ranqe cf 7-13.5 in order -to ensure a- trouble-free operatioO of the electrodialysis cell. The latter pH range is naturally achieved *when a weak base, such as ammonia, is produced.

Alternatively, the pH--ay be kept within a, target ran~ue by an'addition of a neutr-ali'zing comb o und, :such" as C 2 sodlium bicarbonate (NaFiCO,) odium bisulf ite (NaIISO) or SO,> The *resulting basic salt is a marketable product (as Is tnhe case with sodium carbonate) or a reusable chemical (such as sodium,. sulfite, NaSO, for- use in flue gas 'Scrubbing, for example).

As opposed to the use -of nanlofiltrationi in conjunrction with 2- 0 the two-compartment anion cell disclosed in. my earlier co-pjending *Application (Serial No. 08/639,831), the ap-paratus off Fig. 4 (a) has a significant advantage.- With certain cation memibranes, the monovalent cations are transported more effectivelv over multivalent cations, even at the high current densities i- the order of 70-100A./ft2. The cation mem branes so-called monovalent favoring or monovalent selective type are nor- readily fouled by S7 the multivalent cations over a broad pH range. The apparatus of Fig. 4(a) takes advantage of this phenomenon to further reduce the multivalent ion concentration in the base loop of the electrodialysis cell, thereby ensuring that they do not precipitate in the loop.

Fig. 4(b) shows another version of the apparatus, comprising a nanofilter 102 and a three compartment electrodialysis.cell 104. The salt feed stream of the low molecular weight monovalent acid and a monovalent base is processed in the nanofilter and then supplied to the salt loop 106 of the cell. Once again, the nanofilter is able to reduce the multivalent cation content of the feed to about 25 ppm. As with the two-compartment cation apparatus 92 of Fig. the cation membrane 108 in the three compartment cell reduces the multivalent cation transport to the base loop i10, thereby further improving the long term reliability of the process. However, in contrast with the two compartment cation cell 92, the three compartment apparatus -104 has an extra anion membrane 112 to isolate the acid generated in S. the process. The three compartment apparatus 104 is capable of processing salts of strong or weak acids, while producing a relatively pure acid product. Feed streams containing salts of weak and strong acids can also be processed via this route. Once again the pH of the base product may be in the range of 5-14, but is preferably controlled to be in the range of 7-13.5 for many applications.in order to ensure trouble-free operation of the electrodialysis cell.

28 IRWSPECSu -1M''.R Figs. 5 show another inventive apparatus thbat uses an ion exchange column 114, in commulicti-on,- with the base loop of *the electrodiaiYSis cell. This apparatus has an advantage because it can process salts o f 'multivalent acidsion exchange coliamn 114 ccntains a cation exchange resin cpaoe of removing the. multivalent ions, and particurl the divalent ions, from the base loot) solution. Since the ion exchange co lumn can in principl e maintain very low levels of *multivalent (mostly divalent: Ca and Mg) cations in the base io loop 1 the prr of the generated base product can cover the ent-ire reutral gamut, i-e- np- 7-14. With a proper i on exchange column operation, dilute 'solutions (o is1 wt~k) of a strong base, (e.g.

sodium or potassium hydroxide), can be -produV--ed. In this PH range, a weak acid cation exchange res .in is p rtiOt. I ry dsial and effective, but strong acid or chel~ating type cation resins may also be used. _In one preferred mode; the pR in the base loop is maintained in the 7-13-5 rangelso as to provide a cransolubility buf'Fer for the divalent. cations. It is desirable, but not necessary, that the ion exc'nangeresinf be in* :*iO th e appropriat onvetcation fort. prior to use in the processing overation.

.*.Three versions of the apparatus using an ion exchange columnI are shown in Figs. -Other versions may he easily visualized by persons skilled in the art.

Fig. 51a) shows the ion exchange columnu 114 in communication with. the salt/base loop) !16 of a t .fo-compartrnent anion cell 11ie- 2 9 1 A P 3 R This loop is preferably operated in a feed and bleed mode so that the pK in the loop is maintained at the 7 level which is needed for an efficient operation of the ion exchange column. A feed stream of a salt solution is "fed to the salt/base(S/B) loop 116.

The product base is withdrawn at 120, so as to achieve a requisite conversion of the feed salt. The product acid 122 is withdrawn from the acid loop 124.

The ion exchange column 114 maintains the multivalent cation concentration in the base loop 116 at a level that is low enough to obtain long term trouble-free operation of the process. When the ion exchange column has been- sufficiently loaded with the multivalent cation species, particularly Ca" and Mg-2 the column is taken out of. the salt/base recycle loop and is regenerated with acid in the conventional manner, and then put back into service. The apparatus of Fig. 5(a) is best suited for processing salts of weak bases, such as ammonium nitrate or ammonium lactate.

Fig. 5(b) shows the ion exchange column 114 in conjunction with a two-compartment cation cell 126. This configuration is 0 useful for processing salts of weak acids, particularly organic acids derived from fermentation and related processes. The feed stream supplied to the salt/acid(S/A) loop 128 of the cell may, for example, be an ammonium or sodium salt of the organic acid at about pH of 4-7 and contain significant cuantities about 5 ppm each) of calcium and magnesium.

S 30 lR:V.WASPECS3-t37.Y2 Undr adirct urrent driving force, the salt isa: dft in the S/k loop 128, while the ammonium or sodium ions arc transported to the base loop 130%. The cation membrane 132 may retain a substantial bortion of the multivalent cationls in the feed loop 12G., However, depen4ng on the acid b~ing processed, the cation membrane 132 that is used,-. and the extent-,of the conversionl of th e feed stream to the product acid, a significant amournt of te mutvlent.cations~ may get transported. across membrane 132.

the absence of the Ion exchange column, tnE- transported Multivalent cations. will pre cipitate in the high pH ein'lronmelt of the base loop 130, thereby -preventing a -reliable operation of the electrodialysis process, Howeve with the ion exchange columni. 114 in polace, the multivalent cations are selectively arnd subs tant ially removed from the base loop 130, thereby dramnatically improving the apparatus and process operation.

Since the ion exchange column 114 can maintain very low' levels of the divalent metals in solution, the base loop 130 may be at any neutral or alkaline pH, i.e. pH 7-14.

0.The one constraint is that some- cation membranes 2.32, such as the AQ cation membranes, and the Naf ion® cation membrane (DuPonit) exhibit signif icant levels of calcium transport, and are somewhat easily fouled at a high pH of about 14 by the tran'sported calcium. For this reason, one preferred pHr range for 25 the base. uro~duct has been found to be a pH in the range ofE about 7to 13.5. For weak bases such as ammonia, this limitation 3 1 WAPs1' occurs naturally. However, when dealing with sodi um arid potasium salts, mixtures thereof or miXtures of these salt s with ammnum salts, a suitable neutralizing com pound -such as So,, NaHCO3 arid the like, may be~addOd to obtair a bse oro-duct S Withn-fl the -target. pH range. An additionl of a licquid comPrlSIflg Water may be-required in the base loop 130 in order to maintain the product base concentration at certain target levels. once again the pH in the base loop should be maintained i the 7 range i norder to ensure reliable op eration of the ion exchange colun 11,1, for removing the nultivalent cations- Fig. 5(c) shows a third version of the inventive a-pparatus.

Here a three compartmen-It cell 136 is. used, with the ion exchange jclumn 1i4 once again in communlication with the base loop) 138.

*This is thue most -versatile apparatus in the Series of FEigs. 5 5 s ince one can process the salts, of. either s It ron7ig or weak acids, while yielding relatively -pure acid and base products.

Once again, 'in order to obtain reliable operation of the ion *exchange column 114, the pH- 'in the base loop is maintained at-pR *7 or higher. As with the two compartment cation cell 128 (Fig.

the, cati on membrane 140 may retain a signif icant portion of the multivalent im-ourities in the original feed, sal-t, thereby reducing the load on the ioni exchange, column' 114 in the base loop Many-of the commercially useful products such as ammonia, 25 sodium carbonate, potassium carbonate and sodium' slfite have a pH in the range of 9-11. Therefore, this p.4 range for the base C.:32 *loop is -a creferred r ange for this apparatus. Weak acid ion exchangers have the best performance inte4so see vty, capacity, stability anid cost in.this pH range and, therefore, are also preferred.

the feed salt- solution has relatively lower- levels of calcium and 'Magnesium, the use of the ion exchange column in the base loopD is not required if the elect rodialvs is were to0 use.

cation membranes that are particularly selective to monovalent *cations and sufficient dilution water containing stream Added to 0 the base looo in order. to -maintain the calcium, and magnesium concentrations below -their solubility level in the base product.

The inventive aparatus and process are better understood from the following examples.. All experim~ents were carried out using an eight cell, pilot, electrodialysis stack 149 that was 5 assembled as, shown in Pig_ 6 All1 of the experiments were conducted in the two compartment cation cell using salts of weak acids to demonstrate the app aratus and process.

The stack 149 included end plates ISO and 152 to which the electrodes 154, '156 are -attached and through, wh i ch solutions were :2 £0 fed into and. removed from~ the stack. Gaskets used to separate *the membranes arid fLorm7 the solution compartments A and s were 0.716 mm thick. Each gasket, had an open central area of 465 cm 2 (0 .5 fL 2) through which current could pass. T he open central areas are filled with an open mesned screen to keep the membranes 1 25 separated as well as supported, and to promote good flow turbulence.. H~oles punched in the gaskets are aligned to form 33 tFUMSPECS1338-2&R internal manifolds. Slots (ports) cunnecting the manifold with the open central area provide a flow of the solution into and out of each compartment.

The stack employed a coated metal (rutheniumn) oxide anode -15l4, supplied by Electrode Products Tnc.; an eledtrode rinse compartment (ER) 158, Sybrorn Chemicals MC 3475 cation membrane 16o (used because of its added strengnh) and seven' repeating -cells. Each cell (for example- 162) includes acid co-mpartment

A

64, andia CKV, AQ, CIMS, or CTTcatiol membrane 266. The AQ membrane is available from, Aqualytics, *a diVi's ion ofr Oraver Water, CMS membrane from Tokuyama Soda, while other membr anes are Products of the Asahi1 Glass Company. Each cell also includes base compiartmenr B 168 and birolar -memoranq 170, available from~ Aqrualytics.

The last .172 of seven bipolar membrane in the stack-14.9 was *followed by an acid compartment A 174, a c at ion m e-mbrane (the saetpe as in cells 1-7) 17G. a base compartment 5 178, another bipolar, membranfe 180, an electrode rinse compartment (EI)S2 *and a stainless steel cathode !S6.

The assembled stack 149 wa~ ulaced in the system shown schematically in Fig. nodrt ar out the electrodialVSis .experiments. Three pumps (P1-P3) were used to circulat-e *solutions ton the acid (190), base (192) and electrode rinse Compartments from their respective recycle tanks 204, 202, 194 at a rate of 2-3.5 1/min. The acid loo 196 was ooerated in a batch mode,. while the base loon 198 was run in a feed and bleed -mode.

1 -MV5P EC SIY137 9 During op0eratiofl, either fresh water or a salt Solution may be addd va aDU~ 24fro a akeuQ tank 203, as neeed- The base aad the elec-rode rinse tanks 202, 194 each had a nomin al volumte of 5 liters, while the acid recycle tank 204 had the capacity to S process as much as !So liters per batch. A cooling water coil in the acid tank controls the temperature.

In SOMwe experaments, an ion-exchalge column 206 contailiing a *weak acid resin, IRC 84 from the Rohm Eaas Company, was used in the base recycle loop 198. Cartridge filters 210, flow meters 212 and pressure gauges 214: were used in each loop to ensure a flow of clear fluids at known flow rates and pressure drops in the three loops. A separate pDump (not shown) was used to supply the feed salt solution to- the acid recycle tank 204. A DC -power supply (not shown) was hooked up to the anode and cathode- 1s terminals 216, 218 of the stack. The -eauisite controllers for *providing and controlling the electrical current input and voltage are located in. the power supply itself. Conductivity meters 220 were used in the acid and base loops to monitor the progress of the electrodialysiS operation.

20, The system was initially charged with the reqjuisite quantity of the f ilte-red salt solution which was fed into the acid tank 204. A dilute alkaline solutionl along with a small amount of salt solution was added to 'the base tank 202 to provide the req.uisite electrical conductivity- The, electrode rinse tank !94 was filled with about 5 wt-* sulfuric acid- Recirculatina oumps P1-P3 -were started and the flows were adjusted in order to get an sr31~ inlet p-essure drop 0Ot 4- Dsi -in each of the loons. The DC current was turned on and tie amperage adjusted to obta-4n about I 40~A (80 A/=t: 2 current density) at the start cf h btn As the batch progressed, the conductivIty of t-he acid solution decreased due to the transport of the mtonovalentc cation (N-Fij, K' or Na-) across the cation membran-es 222, and the concurren formation the acid in the acid loop. Conisequenliy, *the cell voltage increased as thE batch progre, sed, until a set: voltage limit of about 38V is reached (re-presenting a ult cell voltage of about-4V, allowing 6 volts for the electrodie rinse locus).- The orocess continued with a decreasing current throughput.

The process is deemed complete when a target. adoI conductivity, typically 2OmS/cm, is reached. in the basc 1S comoartment 192,, the monovalent cation cc-mbines with the OH' ions to for-m the base product. The electrical conductivity in the base loon was maintained at lOmrS/cm, for most exzeriments through an addition ofL -a salt solution, if needed. The addiLtion Of CO, was also made to the base loop when p-rocessing sodium lactate in order to maintain the pH in the loon at <13.5.

Examples Three' different salt feeds were orocessead to demonstrate the *usefulness of this invention. The salts, ammonium lactate, sodium lactate and ammaonimur 2-keto levo gulonate (DFH,-2KLG) were Droducts from the fermentation of dextrose. The n-H of the salt PC3-~R solutioni rang~ed from 4.5 to 9, th ~cr~lcornductivity of and a salt conte-nt of 70 t-o about: 200 97/1. ;0-1 of the experimeants -were carried out at or near aarnit tem'oeratures 3V~ C).

Exainolh 1 The noilot. cell was assembled w~ith AQ binolar me,,branes and.

CMV cation membranies. One hundred and six liters of ul-tra Ilt ered ammoniumr lactate solution was charged into the acid recycle tank 204- The con- ersion to acid was monitored conductivity and pH measurements. The base loo 198 did not have an ion exchange column 206. The base 'tank 202 was initially charged with dilute ammoniumn hydroxide solution, and as the ED orocess ocerated, the product ammonia solut ion overflowed frnm the base recvcle tank 202. Small amounts of dilute NaCL, soluio were added to the base loop 1.98 to improve its conductivity. The process was deemed co)mplete when the -acid loop conductivity fell to around about 7 mS/cm.

The trial lasted approximately 15 hous aleofci and base were collected and analyzed for lactic, ammonia and divalent metals. The results were as follows: .:37 LP1nNISPC 'lL!3 Voltase urrent onucivy or t Ai Aci;d omp. Ease acmp..

Tim A rmS/c m A _id Voume. gM il gm/I mm Acid Base L atc N-N.

mi- -T 3.1 1, G 0 42.37, 23.3 _1 7 I1.

2 .5 4 42.45 _7235 542___ 2 3~ q0 41.74 24.2 4.56 -To6 1.3 t7- i 18 4 -0 j T .3 23- 4.5'4 10 .6 81.4 .87 61 T 13.4 B.1. 1 .0 8 .71 7T 5.2.3 IL 34~ 40.1 .2.4 a7 1011 61338.1. 33.14 1. 3 48 .5 8 5 1.

Y 381 .38.1 13. 2.59.2. 8.3 2- 6 11.

24 893.6 4 .1 7. I 2 89 oH n -h acdioo 16- eraesa h lcae at4 co5-rt1 40o 26. aci 8o5 h vrc uretioct n 7. 4rcs 2was 15l-1te 8a. 49.4 84.Z/t) aci ls h 3 oo 6.44 /aU.01~dt abu Oeal ur C..8 errcint (i5e8, eouvltt3o m-5 a rnsotdocaaa memoraf1e. Dui tets 1 8=he 75 aad lvl i h OZ themoercen remnoa thas ions in 8the b ae beo seen. thea 0runcton o= cesiuale a-'no~ concentraton z2nLaci loo. T:he bas loo 38 a acltda but!Sr vrl ilr retention fligur.es are shown cumulative, t7rcm s'art or the process.

TABLE 2 Run NH U, addc. Acid anaiyzis, lime,

PPM

9r,1911 0% Con.r Na Ca M~g 3 -T 0 t65 2 -0 T o I~ E3.2 24.

O3 1 13o 53 10 5l.2 243 1T48 7-1 7 196 14.6 24.

315 1.9 1.48 2- 1 4 22 15 v 17.2 6-4 E 189 152 2237 613 -Y.89 1 7 1 4. 155 .5 48 10 138 4 .7 480~ .4 1 20 889 2.18 7 1 0 O 22J Fe Base arialysis, Ca Mg

F.

%RelenticniTV acid loco Na Ca M 9 c 1I J3 N D 1 1,21) 1 1 nil 1 1,10 0.5s 18 N.O. 95.5 SY.6 0. 57 0 .52 0.8 0.D 17.8 13.1 11.3 7.

9~773 52.1 N -100 -1~ b- I4.6 :86. 92.6 81- 91.2 65.2518, R~l 4 N. t The vH in, the base loop 224 was about 10-l015. The solublit oZ the divalent metals in the base loo 192 i-s estimated at 8-2 p-M rfor calcium and 4-10 cm !:or magneim she hc rres, the decreasing~ levels of Ca arnd Mg in the base loco indicates a tendency fo the prec-icptat-io of these metals in the base loop with tinne. it can be seen that the CML-V cation membranes retain :signif icant amounts of tne multivalent metals, particularly magneslum, and iron. in specific termas about of the iJron, about 63% or-: the macnesium, ancl about S:S of th-'re calcium are retained in the acid loon.

At the conclusion ofF the exneriment, the CHMV. membranes were visiblv in excellent ohyvsical condition and. wei-e not fcl b the divalent cations.

3 9 The 2 amnolE 1 was repeated after replacing zhe CL-V cation membranes with AQ cation membranes. A hundred six arid-6ne half liters of the ammonium lactate feed were processed-ove Sr Minutes to yield a p~rcducrt acid containing 1.58 qr/l ZVK at an aveiage- current in-out of 33.2 A(66.

4 A/ft 2 Amm~nonia removal was about 92. TheI-" lactic loss via dif fusion to the ammonia loop was -about 2_8%i. The Overall current efficiency for the process was about G8~ 63 However, metals analysis showed that the retention of" the. -divalent metals was lower than ~for CKV; about 4V- for magnesium, and about 37-. for calcium. Therefore, the ammonia solutiona f r 0- the test had higher levels of dissolved metals: about 10-19 popm calcium an& 5-31 ppm mag nesium. ANt the end Of the experimenlt, the AQcations were somewhat-mottled in appearance, indicating possible fouling by the divalent_ cations- E ight hatches, o-f ammonium lactate feed containing 70-92 9-m/ 1 .lactate, with an initial conductivity of 28 to 42 mS/cm, were processed in the pilot cell. The cell contained AQ bipolar 20 memtibranes, and CMV7 cation membranes that were used in Example 1.

The input reedl streams were subjected to ultrafil-tration (200,000 Daitons cutoff)- There was no ion exchange column 206 in the base loop0 198". Ammonium hydroxide was at a concentration of 6 g/l and c onductivity of 11 to 32 oS/cm was generated in the 25 base loop !96. A diff'usion of a small amnount of lactic anion int~o the base loop 19.8 provided the requisite conductivity in the loop.~ No water or-salt solution Addition was made during these oper -ations. The batches were of varying size and lasted from 6.35 to 40.3 hours. Each batch was terminiated when. the acid 1ooD conducti-vity had decreased to about 7-10 mS/cm. During the batches, the ammonlum ion concentrato int Acid loop 196 dropped f .rom 7-12 g-m/l to 1.173.~ 6 -rg/I.

The total cell voltage was limited at about 38 Volts for each batch- The current input, which was limited at 0L A '(representfrlgf :initial current density of 80 A/f decreases as the batch progresseK FPr 'each batch the average current -inpu wa clulated. The results were as follows: TABLE 3 atch No. eaSf eeatchf uration.. Average Values -PPM Hours Current. Voltage ICa Mg, A

V

20 _7 3 43 3 34 3 4 4 1. 31.4 520 45 18.7 30 39- *.20 24 46 263 7-0o .6 15 233 10.5 38 The cell was opened and inspected at the conclusion of the operations. The bipolar membranes and GIV cation membranes were in good cendition, wihno physical evidence of fouling.

However, there was a certain amount-Of precipitates in the base compartments 192, which was easily washed off. The precipitate was analyzed and found be 16.4%, Ca, 25.S Mg, 0.52 Na, 0.1%.K and 41 LFLVSPECS3W-A 3 aTl 350 ppm Fe. These operations demonstrate the progressive decrease in the current throughput, arising from presence of the divalent metals in the feed stream and their transport to the alkaline environment in the base compartments 192. A plugging of the base compartments 192 and a blockage of the bipolar membrane surface by the divalent cations had decreased the cell performance.

Example 4 Four batch experiments were carried out using a sodium lactate feed stream derived via fermentation. The ultrafiltered feed solution which had a pH of about 5.4, contained about 105 gm/l of lactic in the form of its sodium salt as well as about 21 ppm Ca, and 62 ppm Mg. The feed salt had a sodium content of gm/l. The pilot cell. contained eight AQ -bipolar membranes, seven CMV cation membranes (one new and six of them from earlier Examoles 1, and one new AQ cation membrane. The cell voltage was once again limited at 38 Volts. Water was added to the-base loop 198 at the rate of 10 ml/min in order to keep the product alkali concentration below about 2.5N. There was no ion exchange 0 column 206 in the base loop 198. Carbon dioxide was bubbled into the base loop in order to maintain the pH therein below about 13.5- During the electrodialysis process, the feed conductivity decreased from about 34ms/cm to about 9.5mS/cm, with the residual sodium content in the acid being 3.5-4.0 gm/l.

'25 Details on the cell performance follow: 42 R:

PECS

TABLE 4 Batch ura ion Avefage values Acid batch FConvers ion acMtl NO: min. voltage Current volume oF lactate to retained in acid V A L acid Ca Mg 1 290 38 26 28-25.2 85

JTF

21 38 26 109- 8 -85- 1 9 31. 38 26 17221 4 -1478 38 25. 1 -18 88 The retention Of the, diva.14nt metals by the cation membranes in the se operations, was sunerior to' that observed with ammonium lactate in Example 1. :This is probably due to the relatively higher concentration- a the of the monovalent cation. (sodium in this instance) and higher current efficiency f or sodium vs.

~0 Ammonium (th-le absence. of back diff usion losses), the use of dilution water to keen the cransuorted divala nt ions in solution as well as the lo wer-,conversion of the lactate salt.

IThe cell was opened and inspect'ed. The bloolars and CMV *cation membranes were in excellent condition without any physical evidence of fouling. The AQ-cation membrane was cloudy/opaqrue and appeared to be fouled- The int ernal narts of the cell were clean, because the high retention of the divalent cations by the (COW) cation membranes resulted -in low- levels of divalent metals *in the base loop) 224 ppm Mg and <20 ppm Ca) The :20 precipitation problems will undoubtedly occur with higher levels Of the divalent metals in the feed stream, lower feed concentration, or higher process conversions.

43 pc31

T

Example A test on the conversion of arnmonium-2 keto gulonic acid *.(NH,-2KLG) to the free. acid 2 keto gulonic acid (2KLG) was carried out in the pilot cell 'Containing AQ birolar and AQ cation membranes'. The starting solution was obtained by neutralizing a, fermentation derived sample off 2KLG with iammonia, containing 170 gtn/l 2KLG and 12-99 gm/l N14, equivalents., and having a Oil o f *about 9. Twenty eight liters of the feed was processed i n the eleotrodialysis cell, with the conductivIity decreasing from-i 35.liTnS/cm to 8.6mS/cm due~tc acidification and the concurrent tranisport of ammonia out of' the feed loop extending to feed tank 200. The NaC. solution'-was added,t ao the base loop 198 during the process in order to'maintain a conductivity therein of 16-- Once againi, there Was no -ion exchance _column 206' in the *base loon 1598.. The result. were as -follows: TAB jE Ru: n -time Voltage Current Acid Acid loop analysis acid .Base lop min. V A Conductivity -2KLG pH NH, Ca Mg volurne analysis, ppm 'mS/cmn gil .gmdl PPM ppm L Ca-: Mg ~W ~1 9.1 1Y9 21.9 5.62 28 F01 T'F 35.1 40 7r._2 7~ _5 -6 1 17 -2 3 4.8 27 0.

'IN 32._7 40 35,1 2732.3 4 38 ._T4 4.74 10. 19 -4-52 -28 2901 .18 32.3__ 40 3 4_ 37 40 28 178 6.0 W 16.3 -3.44 27. 40.1 54 118 3& 40 23. 1T 4. 13.2 2.67 -aT -975 3.2 M3 34.9 40 19.2 1j8 1 2f. 73 -3.35 10. 22.04T 1.

38.1 40 11T5 212 -i 1.40 .63 7_7 -79- -T 255T 38.1 382 .6 2.~Y0.1 2. T 9 _3 _37:9 1 .6 190 1 0.73 173_ 91.7 177 44 R W SEia The final product contained 190 -9m/ I 2KLG and only, 73 0 ppm Ni., representing about 95k removal of the cation from the salt. The current efficiency was about 40%. It can be. seen that substanial alo6f the calcium and magnesium values in the feed salt have. been tran sorted across the AQ cation membranes. This j.0 1s in drdmaLuic contrast with the results obt-ained wit-h the sodiu.m lactate test in Example 4. At leastin part, the high levelJ-of *divalent, cation -transuort is likely,-,due to the- lower retention by the AQ cation membranes '(see Example but may also occur.

either because 2KLG is an acid ,which is a much stronger acid than l5 lactic or 2KLG was not7'-able to bin d very well with the divalent catlons. This large transport substantially increas'ed the concentrations o f the metals in the base loop 20 2 The metals, about 20 ppm f cr Mg and abo ut 100 ppm f orCa remained inl solution, since the ioH in the 'base laoO'24 was only in the range Of 10-11.

Solubility Data for vaei ion P ae a function of PH Thirty seven batches of ammoniumn and sodium' lactate and NN, 2KLG feeds, were processed in the pilot assembly, with the processing of -each batch lasting from G to >24 hours. The lactate feeds were from the f ermentation of dextrose. The 2KLG feed was obtained by neutralizing the acid with ammonia. Each of th eeds wer e subjected-t6 simple flrto rt ultrafiltration prior to processing in the electrodialysis cell- The feeds had 20-1S0 ppm Ca and 6-60 ppm Mg. When processing the 4 5 PC~l-]? sodium lactate salt, the pR of the sodium alkali base product was limited by the addition of gaseous CO 2 Samples of the product base were analyzed for both their divalent mretal content and their D14. There was no ion exchange column 200- in the base loop 198, so that the measured concentrations of these ions represent their solubility in the base loop. The CMVr% or CMT cation membranes were used in these processings. The C 4V membrane was used in the first eighteen. and the CMT membrane in the later nineteen tests. Both catJin membrane remained in excellent condition after the processings,:,, withi- no- visible evidence of fouling by multivalent cations in che feedq.

The results of the study on solubility-as a function o f 1D;% are plotted in Fig. When producing ammoniacal base solutions is the ranged from 9 to about 11.4, While the sodium alkali solutions had a pr!ranige of about 12 to 13.4. The data could be divided into two sections for eachl- of calciuta and magnesium. One setl of data represents the sojlubility limit, while the second set of data repre'sents a supersaturated state where the alkaline 0 solution can hold significantly higher levels of the divalent Howeerthere is always the potential for spontaneouis precipitation and the consequent plugging-of the base loop of the electrodialvsis cell. It should be pointed out thar- the base loop could be cleaned and the cell performanice restored, as had been done on occasion in the laboratory.- The cleaning was 4 6 M.jy.p EC 3 =22 j17. Robtained by washing the loop with -a dilute solution of a strong acid, preferably HCIl. 1-~er s uch -a-steo _nvolves unscheduled downtime and reduced process throughput with the potential for mechanical damage to cell hardware due to heating, meltdown etc.

There is also 'a potential long term damage to the bipolar membranes as a reS'ult of heavy surface precipcitar-iofl blistering, The inventive apparatuses and processes enable a long term *-trouble fAree operation of the, electodialysis cell by maintaining the divalent metal concentrat ions in thu base loop, either-below or near their solubil'ity limits. In- one pr;f erred pg. range 11 of this invention,, the target levels are about 2-25 porn for Mg and about 20-100 ppm-for Ca. For a prolonged trouble-free -oueration of the ED cell, one needs to maintain the divalent -metal at a somewhat -lower,level., say 2-10.ppm M~g and 10-25 ppm Ca, this being governed by the dynamics of the process, since the anion surr-acei of the bipolar me-mbrane hihgenerates the OHions is at a p.4 of about 14.- By maintainPig adequate fluid Velocity within the base compartmenlts, there is a sustained reliable, longq term operation at high current throughput.

-it is important to note that the data shows a solubility of utom for calcium at A Pa~ value of 14. if, such low levels or calcium can. be maintained In the base loono, the extended-term rod uction of dilute al:.<alis (0-15 wt~k) such as.sodlium or potassium hydroxide can be achieved.

47 aM ~xamrle 6 Ammonium lactate made in a erment-er was f ilrered byuina *nannfiltratiOn unit. The filter Desal 5-DK-made bv Desalination Ssesas u sed for this purpose. The poduct frm- his filtration steo)had about go gm/l of lactaze, 10-13 qc-/l ammonia as ammoniUrn cation, 11 ppm calcium and 9 ppm magnesium. The faeed, at a ulH o f a bo ut 5, was theff processed in the pilot cell as described in Thcamnple 1. The pilot -cell contained eicht AQ bipolar membranes and sxCMV cation membrZane taken~ from Example 1 and two new AQ-cation membranes. Six consecutive batches of about 120 liters of feed per batch were processed if a manner similar to Example 1. The results are summarized below: TABLE.6 atch Duration, Average values Acid conc. Acid loop Ammonia in acid. gnVIi number hr. *jCurrent Voltage TM.'l conductivity Star, End A V Intial Final mS/cm 1 8121 .79 94 35- 8 10.44 2,7 38 82 87- 4 37 28 38 92 951-5 137.9 1.14 524.7 27 8.5 38 93 9 91-. 1. ct 12. 28 38 Not measured it Can be seen, that the batches were o-uite reproducible in terms of current Tho-.ut, voltage drop and cves o F the salt to acid.-A the conclso of the study of si;;x batclhes thne cell was Soened. nh arzs were clean. and ffree of precipzitates, demonstrat i that z:-e use or nancrilraton, ccun~ed with the retertic-i of toe .ltvalent catLons afforded bv h cation P w- VR *membran-es was effective in maintaining s :able long tserm operformnce.

The useof nanofiltration results in a generation of. a concentrate (termed retentate) stream that contains a n)ortion of 5 the feed salt as well the bulk of the divalent metals. The stream may be disposed of after suitable treatment. This disposal represents a lost resource. However, in many instances,I *such as in a fermentation Operation, the stream may be returned back into the front end and recovered.

lxamvpl e 7 Apilot system was setup in the mode-shown in Fig. 7 with

F

*the ion exchange coluriuii 20,6 in place. The electrodialysis cell contained eight AQ bipolar membrazies and eight CMT cationl membranes. Both types of membranes were taken from the lo trm is studies detailed earlier. The ion exchange column 206 in the base loop 19% was filled with IRC 681 resin,(a weak acid. cation *exchange resin) from Rohm and Haeas and c onverted to the amnmonium form prior to the trials.

Feed ammonium lactate for the trials had been ultrafiltered in a unit rated at about 200,000 Daltons and contained typic ally 40-150 Dpm Ca and 45-65 ppm Mg. Lactate content in the feed ranged f ro-m G0-100 gm/i.

Th irtyv batches of the feed ammonium lactate were processed J r L a manner analogous to the processing in Examples detailed before. Each of the batches lasted 6 to 24+ hou-rs with each 4-

.CM-

batch being- terminated. when the acid 1000O co-nductivityv dropped below .about l0-rS/cm. Detailed measurements showed the CMT and CMvi nembranes had similar levels of retention -for inulivalelt S, The ion exchange column was e4 fectiVe in mnaintainijng the divalent metal concentrations at low levels in the base loop.

Du ring theili tial batch following a regeneratiozn of the colum -the levels of calcium andjmagnesutf in the base loop were in the order of 0-2 ppm each. The-levels gradually increased during subsequent batches, principally because o f the kinetic limitations of a Irelati.vely short column k~ 2 feet deep) and a high service flow rate. When the divalent metal concentration reached about 10 ppm_ total, after about four batches off 140-18.0 liters each, the column was regenerated- and reused in the subsequent batches. in this-manner a stable long term operation o the electrodialysJ.s cell was achieved, with steady current throu hputs and voltage drops.

'..The appoaratus combining the electrodialySis cell with an ion *exchange column in the base loop enabled the electrodialysis cell to operate over extended periods -e~ihout the need for routin~e acid cleaning of the base loop. In fact, a certain amount of buffer ca-cacity exists within the, improved app~aratus. The ion exchange columnu is able to clean the base !coo simply by having the base solution circulatinu in the apparatus with the *25 electrical power turned off.

*.0 For the inventive apparatuses an ,d processes,, cation membranes that have a high level of retention for the divalent cations are -preferable because they reduce the level of these -ions in the base loop. Therefore, they reduce the load on the on exchange column The hiaher retention. membranes CM' and CMT have been found to be not prone to fouling by the div,;alent cations. it is beli eved t hat- these membranes are prepared by using cross-linked polvmerization of styrene ana nlx'inyi benzene onto a suitable subhstrate. These and similarly made cation 10 membranes, which we will term the "monavalent fzav oring type" are the preferred ones for the inventive az aratuses of thiks invention- in this context, the, "monovalent selective" tvoc membrane (such* as the CMS memrane from Tokuvama Scda) are the most -oreferable.

The apparatus of this. invention cani be used to improve many processes r Iovina the -;roduction of acid s and bases from salts.

Three such applications are shown schematically in Figures 9 through 12.

9 shows the use of one version of the -inventive 0 apparatus in the production of, low molecular weight monovalent organic acids. A hank- 230 of fermenters may be operated in a batch mode to produce the organic acid in its salt form. For .*optimum productivity the fermentatior is conducted atl a -nH of about 4-7. The pl= is maintained through an addition of an 2-9 alkali. Ammonia is a preferred alkali because Qf its low cost 51 1: 51%%SPECS13-

.R

and the ease of its recovery in a downstream electrodialysis operation.

Th -e produ ct organic. salt-is then filtered at 232 to remove.

any insoluble cell mass and,. suabsecruently nanofiltered at 234.

i a retentate from the nanofiltracion unit is rec:ycled at 235; to the f ermernters. Th- nanof iltrate may he f urther concentrated via conventional evamoration at 238 if desired and fed to the acid, recycle tank 246 of the electrodialys2is cells.

One or-oeelectrodialysis process units 242, each Containing two hundred or more electrodialysis cells may' be mtplayed to obtain the requisite prodluct-6 throghput. T-he electrodialysiS cells are ofthe' twCo-corpartcle:, cation tyoe, such as-shown in Fig s. 1 2 or.3. The acid looD 244 ~s operated in a batch mode, with the product acid being pumped .15 out. of the aciLd recycle tank 2,16 when the target -conversion is realized- Afresh batch of feed 4s then added to the acid recycle tankc and the. process continue-.

V.Ammoniu= hydroxide is generated in the base lIoop 2418 of the ED cells. The base loom may be operated in a preferlred steady .20 state feed and bleed mode or in a batch mode., Dilution water and a small amount of a salt solution may be added to the base loom, -if necessary, in order to maintain the nroduct ammoi .:concentration and conductivitv at certain target levels- The orocess is sui4table -for processing a nuntber of crganic acids such 25 as. acetic, and lactic.

.:52 A three compartri-enzt cell such, as sh~own in Figs or C 2 may used in place o E the two com-oartment cation cell for producin~g higher purity acids or processing salts of sc-roncer acids.

Fig- 10 shows another vex-in -of the- process emplo'vinq another of the inventive anparacus. in this examule, the oroduct 0organic. salt from the rermenters 250 is once again filtered to rroe the cell-mass and theisoulimriisvaacre ultrafilter 252 _(typically 200,000 Daltons, rating) The filtrate usually contains 70-,110 gm,/I of organic. salt- The organic salt may optionally be concentrated further via conventional evarcoration 254 aprior to processing in the two co-mpartment

ED

cell 256. The concentration step has the advantage that- It stabilize-s the feed organic salt against fEurther m-icrohlial -growth, as well as impDroving the product recovery and process efficiency of the ED recovery step.

The ED cell 256 has. an ion exchange column 258 in co-miunication. with the base loop 260. During the pr-ocessingc operation, the ion Exchange colurmn, containing a weak acid cation 2~ 0 exchange resin, keeps the multivalent cation levels in the base loop 260 at or below their solubility limits (occasional excursions above the solubility may be tolerated because orthe built-in buffer of the ion exchange colu-mr.

Deuending on the acid being produced and the product p;:urity .2S desired n ~o h el hw in igs -3 (or similar ones) may be used. in place of the two compartment cell 25G that is 33 shown. The apparatus incorporating the ion exchange columnn 258 in communication with the base loop -260 of the ED cells 256 is geaeric and versatile. The apparatus can process salts of either weakc or strong, monovalent or multivalent acids. Examples of acid that can-, be processed by the apparatus include acetic, lactic, formic, citric, gluconic and 21MG.

Pics. show the applicability of the inventive *apparatus in the recovery of sulfur dioxide from flue gases. The basic process is described in some of the patents cited earlier arid marketed by the Allied Signal Corporation as the SQXAL 3 process. In, the process., sul-fur dioxide from the ;"lue gases of power plants or other sources is absorbed in a solution of sodium sulfite and sodium hydroxide (pH 9-12) to yield a salE' -sodium hisulfite. !I the process a-certain portion of the feed sulfite is oxidized to suIf ate.

in the recovery process shown in Fig- a portion of the bisulfite product, which may have some unconverted sulfite, usually at a DH of about is fed to the acid compart~ment 2G4 of a two compartment cation cell (as for examrzple Fig. I 266 while the remainder of the bisulfite product is fed to the base loop 263. The bisulfite product also tends to have *significant amounts of dissolved. calcium, magnesium and other -i -Fo h fu a multiv-alent metal species.derived _ro th-legssource.

These metals precipitate in the base loop 2G8B of the ED cell 266, '2 5 thereby ca using significant operational problems- 54 VZAVA P 54S3--13 in the ED cell 266 of pig. 11(a), in adidition to. the sodium i ons, a ~o Irtion of the divalent cations are transported across th caio me aes 7270 to the base loop- The divalent cations, along with those cations added with the makeup bisulfite are removed fromr the base !coo 2-48 by the ion exchange column 27-2.

*The use of thea inventive apparatus and process shown in Fig.

1(a) eliminates or greatly mitigates this problem so that long termpreliable operation of the process can be achieved. The divalent catioris retained in the acid loop 274 are removed along with the sulfate after removing the, So. product in a s-tripper 276. Potassium or-ammnonium or mixtures of monovalent cations may be used ip lace of sodium if desired.

The sodium, sulfate solution from the S0, stripper may be processed in a three compartmpent cell after a su-itable pre- .treatment to re-MOVE-the mul tiv.a lent metals in order to-generate *additional alkali and byproduct silfuric aci d In a oreferred mode the suilfate solution has a certain amount.. of free sulfuric acid to enanl susan6l-acmplete -reco ve.ry of d i h -*stripper. As a result-, the sulfate stream would' be-acidic, -in thepH range of; Fi.11,_h) shows the use: of an impr oved apparatus __n recovering the acid, base values-from-the acidic sulfate stream.

*The sulfate stream Is,- fed to a three compartment cell. 28,0 *incororating an ion exchange coluum 262 in communoation with .~2S the' base_-loon 284,. A portion o f the _sodium suit ate is..converted.

to a by-product sulfuric ac id and a base which is suicable for recycling to the absorber. A portion of the unconverted sulface values, along with the multivalent metals present in itj may be discharged as a purge from the salt loop, while the balance is recycled., As a further option,. the base loons of the two and three compartment cells in Figs 11(a) and 11(b) may be set in *communicatiofl with a common ion exchange column i t desired.

Fig. 12 shows the. application of the inventive apparatus for *processing imp~ure bicarbonate/carboftate/sui.L~ate containing s treams to produce sodium carbonate. Commerciallv available Sodium alkali minerals often have impurities; such as sodium sulfate, sodium chloride' and -a'certain amount -of calcium and *magnesium salts. In the ED process the mineral is acidified in the acid loon 286, thereby liberating carbon dioxide, while sodium hydroxide is generated in the base loho _p284. The base loop product may be acidified with a carbon dioxide containing isorce tc gene-rate-sodum carbonate or- a similar alkaline product. once again the us e afi ion, exchar qe_ -column 282 in communicatlon' with the-base loop 284 of the ED cell removes the, multivalent ions, ,thereby; assuring long term reliable operation of the overall process. Potassium sulfate streams may similarly **be.Drocessed to yield- potassium carbonate.

SFla. 13 shows a process system that uses nanofiltrac-ion at *230 to remov e asubstaitial part of. the multivalent metals. prior to a processing bf the feed-in the electrodialysiS unit 292. The ion exchange column 294 is 'in the base loop) i n order to remove S6 R* .LSP ECSMC1337.R any residual metals that might enter the base loop, thereby enhancing the reliability of the overall process.

The combined apparatus of Fig. 13 is used with salts containing monovalent anions, sodium, potassium or ammonium chloride, lactate, acetate et. Also, the process using both nanofiltering and an ion exchange column is better suited for use in a two compartment cation (Shown in Fig. 13) cells or in three compartment cells. For two compartment anion cells, where the feed enters the salt/base loop, and the'ion exchange column also located in the same loop, the benefit would appear to be less valuable.

Example 8 Briefly in review, the foregoing description shows that suitable apparatuses can attain and maintain a sufficiently low concentration of the divalent metals in the base loop. Hence, the precipitation of these divalent metals either does not occur or is not a serious problem, if it does occur. By maintaining low concentrations of the divalent metals in the base loop, their precipitation is averted, which has surprisingly beneficial 20 effects such as the maintenance of a high and steady current throughput.

SAlso, the use of a cation membrane reduces the ratio of divalent metals relative to the amount of monovalent metals in the base loop, thereby reducing the cost of isolating the divalent metals. Moreover, the use of certain cation membranes 57 RJVASPECS1330-136T.R2 allows transport of monovalent cations in preference to the multivalent cations, thus reducing the multivalent cation concentration in the base loop to a point where they do not precipitate in the base loop. The monovalent selective cation membranes(e.g. CMS from Tokuyama Soda) are most preferred for use in the apparatuses and processes of this invention.

Fig. 8 shows the solubility targets for calcium anid magnesium for a base product of a given pH. A long term trouble free operation of the electrodialysis cell is obtained by maintaining the divalent metal concentrations in the base loop either below or near their solubility limits. The concentration targets are -2-5 ppm for magnesium and 10-15 ppm for calcium in the high pH region of 12-14, Higher levels of Calcium and Magnesium can be present in the pH range of 9-11.

The pilot system described above was set up in the mode shown in fig. 7, with the ion exchange column 206 in place. The electrodialysis cell contained eight AQ bipolar membranes and eight CMS cation (monovalent selective) membranes. The ion exchange column was regenerated with hydrochloric acid and placed in the ammonium form.

The ammonium lactate feed stream was ultrafiltered as in the earlier examples and was concentrated by evaporation to provide a -250 gm/l lactate content prior to processing in the electrodialysis unit. The calcium content of the feed stream was higher than normal, possibly due to a dissolution of scale material from the evaporators.

58 1R:iW ASPECS\30-8I?.R2 Four batches were processed with the results summarized in the following Table 7. From tank 209, de-ionized -water was added to the base loop at a rate of 8 ml/min. The slightly higher level off lactic diffusion tib the bas e boon provided an adequate conductivity mS/cm) for producig areliable cell stack oeration. The base loop product contained -S-6S giu/l of-ammonia and produced a PH ranging from 9.5 to -1I.

TAMLE 7 Average Metalm in VaJIUC3 Alverage 3flet,13 acid,' M wa Current Current ?teta13 retention content In base t-aio PPM 11 erv Voltage Efficiency (overall) Ir% acid. W product, PPM Ihr. Ca A' 'r t Ca aP I 1 31.2 1310 1.43 93 4S 23 56, 32 >99 1.5 0.3 2 34. 1.331 141 3 45 21.4 S9 95 '99 3.0 0.6 3 51.6 1250 179 45 22-5 -50 .98 ,99 0 -5 1.0.0 3_ 20 102461. 99 '39 10 The excellent retention shown by the monovalent selective cation membrane significantly reduced the load on the ion exchange column. The combination of this cation memrbrane andithe ion exchange column was able to totally eliminate membrane and cell fouling problems; and this, in terms, results in surprisingly high current throughput, low cell voltage, as well as reproducible cell operation; despite the relatively high Clevels Of Calcium in, thei feed lactate.

-J SPCX0IA. -p 5Exqmp1e 9 -The pilot cell was set up in the mode shown in Fig. 7 with the ion exchange column removed from the- base loop. The concentrated Ammonium lactate feed stream used in the previous example. _was diluted wIth. de-jionized water to reduce its lactic and multivalent metals concentration. Nine batches were processed as shown in the following Table. 8. An aqueous solution was added to the base loop at -a rate of 10 mi/nir- for the first 8 batches and 16 mi/min for the last' batch-9 (due to the higher metals concentration *in the last batch 9, feed sideb, The lactate in the feed stream ranged from 120 to 155 gmr/i for the first 8 .batches and was 244 gin/l for batch 9. The base loop product once again contained 35-65 gm/l of ammonia with a pH range from 9S to -11. The base lIoop conductivity was maintained at a-15 mS/cm at a minimum through addition of-dilute' ammonium sulfate or sulfuric acid if necessary.

TABLE 8, Meoa vaue Metals retent.ion Average metals acd.t~monia Current Current (overall) in aci;d, content in bane Batch flura ion o~m removal, Voltage Efficiency ~pout g U hr. Ca Mg I A VC CH Mg 1 31. so 9 45 2.5 52 9*7 99 92.3 3.821 2 35.E Sac 94 90.5 49 26 S4 3 9 g 3.

*3 31 SID. 94 90.5 45 2E 51 93 >59 9. a 2 S.o50 94.6 91 45 25.5 53.4 .37 99 97.5 4.2 S 3g. 2 503 94 .4 0.9 4 5 2 6 62.2 5.5 >39 99.4 a 27 420 '75 87 45 27 523 9S ,.39 94 1.

7 27 4 10 164 99.9 49 2 aS2 0* 26.9 397 I 62 993 26 46 9. S 77 4 92 AS 1251 97 9 3.7 R~'~~~.SEC5I33-1,5GO S The average metals content reported in the last column of Table 8 was calculated from the average retention for calcium and mag-nesium f or the 9 batches and the total volumetric outout from *the base I00P. it cani b, 'seen that in-term s of current throughput., voltage and ~urnthe-efficiency of the cell, performance was- quite reproducible.

At the conclusion of-the'nine.-batches, the cell was opened and the internal structures* were examined. All41 of the membz'anes were in excellent -condition,, showing no evidence of fouling.

There were small amounts of calciurpe-iae in the base loop. Evidently,- this is because-the base lopcalcium concentration-was 87 9765 ppm in the above. trials, which is above its solubility levels of 20 -45 Ppm in the pH range-of operation (Pig- 8).

'A use of larger amounts of dilution water to the base loop and/or a reductionjin the amou~nt of calcium in the feed stream *salt would ;essentially eliminate the preci ittion MrberS.

Therefore, A n the present example, assuming no further dilution *of the base product, the feed containing 150 gm/l lactate should coi-.:ain no more than -125. ppm c alcium and -90 ppm magnesium- 5 Those levels of 'the divalent metals are, readily realized in actual fermentation operations. Hence, a process following this **guideline would opDerate, over very long oerating periods withoutan~y fouling problems., -Ii n this and other examples,.the multivalent metals 0 Concentrations and their retention by the monovalent selective aEl RU SPECSIQ3.1387.R2 cation membrane have been stated in somewhat absolute terIms. -in reality, any given process solution contains a varietv off car-Ions, all of which -will be transported across the cat'ion 4m~entbranes in Proportion to the membrane's selectivity (or S tranisport number) f--or the various cations.

Hence, a more accurate definition of the feed stream purity target is the ratio of the multivalent to monovalent metals *content in th~e feed stream. In the present 'example, the feed has 150 gm/i of lactic as lactate; i.e. 1.67 gram eouivalents/iiter.

Therefore, at a near neutral pH of the feed has 1.67 gram, equivalents/liter of ammonium-ions. As a result the target divalent ,etals,,concentrations can be restated as -75 ppm and ppm of magnesium per gramequivdlent of ammnonium ions in the feed solution.

a similar fashion, the retention ability of 'the cat-ion membrane is'a function.-of the ratio of the monovalent to multivalent cations in the feed salt- As the feed :Salt gets depleted of monovalent cation, content in the electrodialysis .t feed decreases. The term relative traaspoort number (RThq) is often used to define the performance of the cation membrane: 62 rR._&WSPECSuaO.13aTF RTNHCa, CM/cC wherein: M- monovalent ion N-H,Na, K or their total concentration Cl transport number of M ion in the cation membrane tca,: transport number of Ca ion in the cation membrane concentration of M ion in solutiin concentration of calcium ion in solution A suitable monovalent. selective membrane f or the process of this invention should exhibit an RTN relative to calcium of 6 or higher, vref erably 8 or higher, and should yield the >9o.

retention, as shown in the above examoles. CrIS, a monovalent selective membrane made from polymeric materials satisfies this criterion. In, reality 'the monovalent selectIve membranes may be made of organic or inorganic materials or combinations -thereof.

For example a ceramic membrane made of sodium super ion conductor (NaSICON) made by Ceramatec (Seuaration Science and Technology, 321((1 4),,pp 557-572, 19-97) has-the ability to transport of *monovalent cations (sodium) and exclude the transport of multivalent' cations or even' large monovaleat cations such as cesium; and would therefore have a large RTN. By way or comparison, a typical monovalent favoring membrane such as CMV 4has a. RTN of while other cation membranes such as the AQ cation have even lower RTN values.

shows the use of the two compartment cation cell usinig the monovalent selective cation membranes in the production of lactic acid, from ammonium lactate, The lactate salt from the fermenter contains -95gm/i of lactic, as the lactate salt, and JVPC.OfRZ -12-17.gm/i ammonia. The ammonium lactate is suitably f iltered to remove the insoluble (cell mass) material. The lactate from the fermenter would typically~ contain <50 ppm calcium and 25-50 ppm magnesium in the form of soluble salts.

filtered lactate solution is optionaly co ncentrated via *evaporation to >l80-gm/il-actic cont ent and processed in the two Compartment electrodialysis cells. Dilution water optionally containing small amounts of -sulfuricacid (typically -0.1 wt-.

acid concentration) or somne other suitable salt for providing conductivity is added to the base loop in order to pick up the ammonia that is produced. The ammonia-solu-tion from the base loop of th ealectrodialysis cells is collected-in an NH3 storage tank for possible reuse in the fermenter.

The acidified product from the electrodialysis cells typically contains <2.5 g-ru/l of ammonia equivalent and has zH of 2.7-2.9; represencing 90; or-a higher, level of ammonia remnoval.

This acidified product is further purified via a cation exchange (CMX to remove the remaining ammonium and multivalent cationis.

*The product from CIX is then treated in an anion exchange column (AIX) to remove substantially all the extraneous anions (e.g.

sulfate, chloride, phosphate), and further concentrated as needed .go for sale.

Example The utility of the process and apparatus using monovalent selective cation membranes is generic to all soluble salt feed stream solutions containing specific low levels of divalent metals contaminants. Such levels maybe obtained via a simple pR adjustment and a polishing filtration. For example, in the production of dilute sodium hydroxide and hydrochloric acid from salt sodium chloride or sodium sulfite, other salts of monovalent cations), the feed stream salt solution can readily be purified via pH adjustment to about 10 with sodium hydroxide/carbonate and then filtered to yield a 10-25 wt% solution containing less than about 10 ppm calcium and s 1 ppm magnesium. In prior arg, this feed stream is further treated via a chelating resin ion exchange to further reduce the calcium content to 0.5 ppm or lower, prior to processing in the electrodialysis cell.

The improved process and apparatus disclosed in this application makes it feasible to eliminate the ion exchange pretreatment step and to directly process this feed in a two Scompartment cation cell or-a three compartment cell that uses .monovalent selective cation membranes.

Fig. 14 shows a flow sheet of a process for producing tons/day of sodium hydroxide (typical) and 36.5 tons/day of hydrochloric acid. The feed stream salt containing 10 ppm calcium and 1 ppm magnesium is fed to the salt loop of a three compartment cell. The bulk of the salt feed is converted into RJU WSPECS 13B7.

o e• the acid and base components i.n an elec Itrodialysis call that.

Contains the monovalert select;ive cation membranes These metnbraner, retain the bulk (ty-PiCally -95-c or higher) of Ithe divalent cations in the salt loop. These cationis are purqged from t-he-salt loop as r art of a depleted, salt soluichjo in the example, show.n in Fig- 14, the depleted salt solutioni cOntains 961; of the divalent cations present in the original reed screamn, which translates to. abouz 55 ppm- calcium in the deplcz;-e salt solution.

If des ired, this depleted salt solution can -be saturated with solid salt and Qurif ied via _a pHl adjustment and f iltration.

to remove Lhe excess multivalent metals. Then the purified solution is reused in the electrodialysis cell. Dilution water is used in the base loop to pick up the sodium hydroxide generated there.

This combination o f monovalent selective membranes and the use of dilution water r-educes the concentration of calcium in the base loop to <I ppm [and a much lower concentration of magnxesium), thereby ensuring an -operation of the process and membranes in a non-fouling manner.

Exa~mle 11.

Five batch tests were carried out by using ultra-Filtered V. ammonium lactate feed solutions, The batch lasted a total of hours. The lactate feed stream was relatively low in divalent The feed lactate was processed- in a two compartment cell containing AQ bipolat' membranes and CM4T cation tnembz-anes. The cationl mermrbxanes are of the "monovalent favoring"~ type (as oposed to Cm1S cat':ion membranes Which are a "mOnOvalent selective" ty-pe) A steady stream of make up lioiriid was maintair-ed in the base loop helps retain the transported metals sudbstantially i solution as twell as facilitating thei-Jr removal with the o-verflow.

The make up liquid was 10 mlim of dilute amnmonium Sul'fale for *the tirst four batches and DI water for the f iZF t h batch. The results are summarized below: TA BL~ _V9 qa:tccanubetio n ta h omiaiV Lac a lo cneLaio Q Szlet e t.s in r thn fe d acid~ h seo i2un liui iI the_. ,ZaZopws betogeesnjal snIt cant esenspot o the dvab~nant meaI oot of ah aowico Thcr woui kild in the-ae1C'wsbl at gi411 eadntiy rev e hw o dib chel inventormn hre, he aeed cesmlam areotoducbe cosI e o cove all eiinl farccte whic fllwitinthetre sl- a ed s ooirit o theric that Sntio X2 Fhor te puroseso this speiiction incldin the a, the tperm e co laiimi"salb taken to have the meaning 'including" IR .PCS6. E3.~

Claims (34)

1. 2- Th e aP ara t us of Claim 1 .wherein the. cation membrane is selected from a group cconsisting of a Tmo novalIent-favoring mem. rane Ian," a monovalent selective membrane. An apparatus- comprising an electroidialysis cell- *having a salt compartment and a -base compartrentwi h a binolar membrane between said salt, an ase compartments,. saidhioa memranie having a cation side and:an ani on side, a cation membrane, an anion membrane, s aid salt corr-artiment being located between the cation side of the bipolar memrbrane *and the anion exchange membraes nanofiltration means, an icln excnan-ge :column packed wich a cation excHange medium, LVSE~O7P means for -de-livering an input strea inoadsal-t compartment Via said nanofil tration means in order to filter said' i~fiput- stream, and mean -ordelivering an.-outpu. which is -said input stream-after it has pas sed through said noil-aonmnsan has been r ecirculated a t least. in p'at bysaid apparatus.
2. 4.The appar atus of" Claim: 3 -wherein the cation membrane is- s.elected from a- group consisting of a monovalent favoring membrane anid a monovalent s(Kl-Ctive__memnbrane. ni apparatus comprising an eletoilsscl having ac least- a bipolar membrane and at least one membrane take -ar agroup Consisting- of cation and anion exchange mebans- said bipolar membrane. havingT a cation side and an ano ie adeectrodialyi cell having at, leas.t~ base lcop,-an ion exchange-column in communication-with the base loop-of said~electrdialysis cell, said colun beiag packed with a cation exchange r2 es and mneans for discharging at least part of an output stream after passing through said base loop. The apparatus of Claim S wherein the cation membrane is selected from a group. conasisting 0. a monovalent-favoring membrane and a monovalent selective juembranie.
3. 7- -The apparatus of claim 5 where the electrodialysis .c cell comprises a bipolar membrane, a cation membrane and an anion membrane.
4. 8. A process for converting an incoming feed of a salt -of a monovalent cation and a low molecular weight monovalent weak acid anion into an acidified product. stream reduced in its monovalent cation content, said process comprisingte 1teoS of: subjecting, the feed to nanofiltration to obtain a f iltrate having a-total divalent metal content which is less *than about 25 parts per Millioni passing the filtrate through a salt/acid compartment of a two compartment electrodia-ysis -cell containing at least a bipolar membrane and a cation membrane, said biiolar membrane having a cation side and an anion side, said salt/acid compartmenft being located between said cation selective side o he bipolar-membrane and a cation membrane, the other of said two compjartments being a base compartment coupled in a base 2loop; s Iupplying a liquid including water to the base I compartient;of the cell, said base compartment~being located etween_ said anion side of-the bipolar membrane and a cation memblranej passing a direct Current through the electrodialysis cell for causing an acidification' of the feed salt and the concurrent transport 'of the monovalent cation to the base loop; *7 I I producing a base product through a combination of the transported cation with a hydroxyl ion generated by the bipolar membrane in the base loop; maintaining a pH in the base loop in the range of 7 to about 13.5; and withdrawing the acidified feed and the base products.
5. 9. A process for converting an incoming feed stream of a salt with a monovalent cation and a low molecular weight monovalent anion into an acid product stream and a base product stream, said process comprising the steps of: subjecting the.incoming feed stream to nanofiltration so as to obtain a filtrate having a total divalent metal content which is less than about 25 parts per million per gram equivalent per liter of salt content; passing the filtrate of step through a salt compartment of a three compartment electrodialysis cell containing at least a bipolar membrane, a cation membrane, and an anion membrane, said bipolar membrane having a cation side and an anion side, said salt compartment being located between the cation membrane and the anion membrane, the other two compartments of said three electrodialysis cell being an acid compartment coupled to an acid loop, and a base compartment coupled in a base loop; supplying a liquid including water to tne acid and S0 base compartment of the cell; 72 sP EC *III ,-it. passing a direct current through the electrodialysis cell for causing a conversion of at least a portion of the feed salt into its.acid and base components; maintaining a pH in the base loop in the range of 7 to about 13.5; and withdrawing the feed depleted in its salt content, the acid and the base product. A process for converting an incoming feed of a salt of a monovalent cation and a weak acid anion into an acidified product stream which is reduced in its monovalent cation content, said process comprising the steps of: obtaining an input feedstream which is freed of suspended solids; passing the feed of step through a salt/acid compartment cf a two compartment electrodialysis cell containing at least a bipolar membrane and two cation membranes, said bipolar membrane having a cation side and an anion side, said salt/acid compartment being located between said cation side of the bipolar membrane and one of said cation membranes, the other of said two compartments being a base compartment coupled in a base-loop, said base compartment being located between said anion side of the .bipolar membrane and the other of said cation membranes; supplying a liquid including water to the base compartment of the cell, said base compartment having an output stream in communication with an ion exchange column in *7-3 ""^seCl s **72 *l Se 3 *l said base, loop, said COlurmn being packed with a mat-erial capable o.4 removing multivalent cations that may enter the base loop, passing a direct current through the cell for causing an acidification of the feed salt and a concurrent transnorc of monovalent cat-jons to the base loop; producing a base product through a combination of the transported cation with a hydroxyl. ion generated by the biuclar membrane in the base loop; and withdrawing.the aciLdified feed and the base product.
6. 11. The process ofE Claim 10 wherein the acid is an organic acid.
7. 12. The process of Claim 10 wherein the produced base is selected from a group comprising ammo-nia, sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium sulfite, potassium sulfite, or mixtures thereof. 1.A zrocess for converting an incoming feed of a salt a weak base monovalent cation and an anion into a basified n roduct stream which is reduced in its anio n content, said Cprocess comprising the steps of:- obtaining a feed which is free of suspended solids; passing the feed through a salt/base compartment of a two, compartment electrodialYSis cell containing at least a 74 bipolar mem-b-rane and an anion membrane, said bipolar membrane having a catiOn' selective side and an anion selective side, said salt/base compartment being located between said anion selective. side of the hbi.0oar membrane anrd an anion membrane; said salt/base compartment being coupled mina base loop, the other of said-Itwo com~partments being an acid compartment, said saIL/base ooprmn~ eirig in communication with an ion exchange column capable of removing the multivalent cations :.that may ezqte-i the acid loop; supplying a liquid including water to the acid *compartmenrt of the cell, said acid compar tment being located *between said cation selective side of the bipolar membrane and an, anion membrane; passing a direct current through the e-lectrodialys 5 cell for cadsing.a basification of the feed salt and a corncurrent transoort of the anion to the acid loop; -producing an acid product through a combination of the transported anion with a hydrogen ion generated by the bipolar membrzane in. the acid loop; and t: withdrawing the basified feed and the acid product-
8. 14. The process of Claim 13.wherein the salt which is processed, is an- ammonium salt, selected from a group consisting of an organic and an inorganic acid, said acid being at least partially water soluble. The process of Claim 13 where the acid which is produced is an organic or inorganic acid and the base which is produced is ammonia.
9. 16. The process of any one of the Claims 3, 9, and wherein the cation membrane is selected from a group consisting of a monovalent favoring membrane and a monovalent selective membrane.
10. 17. The process of any one of the claims 8, 9, or wherein the cation membrane is selected from a group consisting of a monovalent favoring and a monovalent selective membrane and the step of maintaining the pH in the range of about 5 to about 14.
11. 18. A processes for converting an incoming feed of a salt of a monovalent cation and an anion into an acid product stream and a base product stream, said process comprising the steps of: obtaining a feed which is free of suspended solids; passing the filtrate of step through a salt S compartment of a three compartment electrodialysis cell containing at least a bipolar membrane, a cation membrane, and an anion membrane, said bipolar m:i nhaving a cation selective side and an anion selective side, said salt compartment being located between the cation membrane and the anion membrane, the other two of said three compartments being an acid compartment and a base compartment coupled with their respective acid and base loops; eIRo PeC3 7.R2 supplying a liquid including water to the acid and base compartment of the cell, said acid compartment being located between said cation selective side of the bipolar membrane. -arid said anion membrane, said base comnpartment being located between said anion selective side off the bipolar membrane and said cation membrane, said base compartment being in communication with an ion, exchange column packed with a material cap'able of removing multivalent- cations that *may enter the loop); passing a direct current through the, electrodialysis cell for causing-a c onversicn. of at least a portion of the feed salt to its acid and base components; and withdrawing the feed depleted in its salt content, the acid, and the base Product.
12. 19. The process9 of either one of the claims !0 or 18 where the acid is a water soluble .acid selected from a group *consisting of monoorganic, diorganic, and trivalent organic acid- T he Process of. Claim 18 wherein the. salt which is processed, is a salt selected from a group consisting of -Sodium sulfite, sodium bisulfite, sodium sulfate, sodium carbonate, sodium bica'rbonate, potassium carbonate, potassium bicarbonate and mixtures thereof.
13. 21. Thne process of \either-one of thc-laiffis 10 or 18 wherein an acidifying agenit--'s, added;;i'nto the base loop\ to maintain the pH in the range of 7-13.5. .77 1 RZU VAS P CSW3I.137. R2
14. 22. The process of either one of the Claims 10 OrT1 wherein an acidifying agent is added to the base loo to maintain the pR in the range of about 8-11 within the base -loop).
15. 23. The process of Claim 18 where the salt that is processed is selected 'from a group consisting a sodium potassiumn, or an arnronium salt. 24 A process for the production of organic acid, said process comprising the steps of: fermentation of a suitable substrate to generate a feed scream of a monovalent cation salt of the organic acid; tiltering said fermentation feed to remove solids suspended therein;- supplying the filtered ferm~ntatf~on feed of step o an acid compartment; supplying a liquid includinrg water to a base *compartment, said acid compartment and said base compartment together forming a two compartment cation cell apparatus, said apparatus having an-ion' exchange column, in communication *with the base compartment; passing a direct current through the two Tpartment cation cell for producin~g the organic acid and a ase product; and withdrawing said organic acid And base products. 00 78 The process of Claim 24 wherein at least some of the base product output from said process is recycled to fermentation for pH adjustment
16. 26. The process of Claim 24 where the organic acid is lactic acid.
17. 27. The process of Claim 24 wherein the base product that is produced is selected from a group consisting of ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate and mixtures thereof
18. 28. A process for recovering sulfur dioxide from gases, said process comprising! absorbing from a feed stream selected from a group consisting of a sulfite or hydroxide containing a solution of a monovalent cation for forming a mixture of bisulfite and sulfite; dividing a solution derived in step into two parts and feeding one of said divided parts into a salt/acid S loop and feeding the second of said parts into a base loop of a two compartment cation cell; transporting said part in said base loop through an ion exchange column packed with a material capable of removing multivalent cations that may enter the base loop; passing a direct current through said feed stream to convert the bisulfite/sulfite values to sulfur dioxide in the salt/acid loop and concurrently producing a sulfite rich alkaline solution in the base loop; and 7 9 withdrawing the said acid and base products from said feed stream after it is p~rocesse hruh
19. 29- The Process off claim 28 where the cation membrane is selected from a group cosisting of a monovalent favoring ora monovalent selectlive type. he roces o Clim 28 where the monovalent cation is selected from a group consisting of sodium, Potassium and ammonium, or mixtures thereof..
20. 31. The process of Claim 28 where the base product is selected from a group consisting of sodium sulfite and.a mixture of sodium sulfite and sodium hydroxide.
21. 32. The-process of Claim 28 and the added step ot stripping the acid product of its sulfur dioxide content bv an application of'heat, with a co-prodi~ction of a sulfate purge stream.
22. 33. -The process of Claim 23 and the added ste-o of1 stripping the acid product of its sulfur dioxide content by an application of a vacuum, with a co-production o f a sulfate purge stream. The process of one of the Claims 32 or 33 where the purge sulfate stream is further processed in a three compartment cell to produce *a sulfuric acid containing v roduct and a base stream. The process of claimC28 where cation membrane is selected from a group consisting of a monovalent fav-oring or a monovalent selective type. 3G. The Process of one of the Clams 28 or 34 where the base product is recyclied to anl SO, absorber- A p0rocess for the production sodium alkali- from impure sodium mineral -sources containing carbonates. said process compri-sing the steps of: WaS filtering a sodiuma minera! feed solution to remove insoluble materials; acidifying a portion of the Feed of step with a portion of an acid product fr~m a two compartment cation electrodialysis cell, the two compartment cell having an acid compazrtnmert and a base coMvartment in communication with an ion exchange column packed with j material for removing multivalent cations that may enter the, base comopartment; separating carbon dioxide formed in sterp and forwardina salt- comnrising an' anion of acid to the acid compartment of. the electrodialysis cell; dYfeeding a liquid including water to the as (d e bas r compartment in order to reaulate the concentration of the base rroduced;, an-d withdrawing acid anid base products produced by said process.
23. 38. The process of Claim 37 wherein the process produces sodium alkalilin a form of sodium carbonate.
24. 39. The process of Claim 37 wherein the process produces sodium alkali in a form of sodium hydroxide. The mrocess of Claim 37 wherein :he tlwo comoartmenru cell has a Cation membirane selected from~ a a-our, ccnjsisting of a monovalent favoring type and a ironovalen: s=elective type.
25. 41. A process for producing monovalent oraanic acid, said process compr ising the steps of: f e rment ing a substrate to gen~erate a salt solution of an orgaan acid;- subjecting the salt solution of step to nanofiltration to reduce its divalent metals content to a level below appr-oximately 25 ppm per gram equivalent/liter of salt content; c) supplying the nanofiltered salt solution of step to an acid compartment of a two compartment ,cation cell and supplying- a licmuid incluIn wazer to a base compartment of said two :orrartment cation cell; passing a ditect current through the. two compartment cation cell f or pr6cing; an~o rganic acid And a base product.; and e) withdrawing said organic acid and base products as' an output of said
26. 42- The process of Claim 41 wherein the base product and a retentate -rom the nanofiltration step are recycled to a fermentation of step
27. 43- The process of Claim 41 wherein the two compartment cell dontains a monovalent favoring cation memnbrane. :82 'AUN%%SPC%3-@72
28. 44. The Process Of Claim~, 4 whereir. th-.-e two COMnartment cell contain~s a monovalerit selecting cation memnbran.e. -A Docess for producing organic aci6, said vrocess comprisincr zhe sters Of: ferientibga a substrate to generate a salt solution of oruanic acid- sub-jecting the salt solution of sten to -nanofiltracion to reduce its divalent metals cointent to below a predetermined level; c)splying the nanofiltered salt solutio o se to an acid compartment of an electrodialysis cell and supplying a liid including water to a base coriinartmenril of said cell, said base -compartment having an ion exchange column in com-munication with. a base loop oF the cell, said ion exchange column capable of removing-the multivalent. cat-*on entering the loop; passing a direct current through the cell for producing an organic acid and a base product; and withdra-wing said organic acid and base produicts as an output of said process. S546. A process for qonverting a salt of a monovalent cation and anion into an acidified product stream reduced in its monovalent cation content, said process comprising the steps oil: a)filtering a feed stream to free it of susnended solids; 83, passing the feed stream through a salt/acid compartment cell of a two compartment electrodialysis cell containing a bipolar membrane and a monovalent selective cation membrane, said salt/acid compartment being located between a cation selective side of the bipolar membrane and said cation membrane; supplying dilution liquid comprising water to the base compartment of the cell, said compartment being located between an anion selective side of the bipolar membrane and a monovalent selective cation membrane, said dilution liquid being sufficient to maintain -the concentration of the multivalent metals in the base loop solution at a level which is no higher than the solubility levels of the metals; passing a direct current through the electrodialysis cell for causing an acidification of the feed stream salt and a concurrent transport of monovalent cations in substantial preference to the multivalent cations and their combining with the hydroxyl ions generated at the bipolar membrane to form a base product; and withdrawing an acidified feed stream and base. solutions from their respective compartments, said acidified feed being enriched in its multivalent cations content.
29. 47. The process of Claim 45 wherein the feed stream contains no more than about 75 ppm of calcium and 55 ppm of magnesium per gm equivalent per liter of the monovalent 84 IspEC3s S; IR UlWASPECEL330*T387.P2 cations present in the feed stream and the pH in the base lopP is maintained in the range of about
30. 48.. The process of either one of the Claims 45 or 4,6 wherein t-he feed stream is selected from a group consisting of an ammonium, sodium, potassium salt or mixtures thereof.
31. 49. he poces ofClai 46wherein the feed stream is primarily- an ammnonium salt of an organic acid- The process of Claim 45 wherein the feed stream is an organic salt selected from a group consisting of amimonium, sodium, potassium or mixtures thereof. The process of Claim 46 wherein the pl -of the feed stream salt solution is adjusted to a value !4reater than about 9- and is filtered to remove precipitated multivalent comoounds prior to processing in the electrodialysis cell. S2. The process of Claim 51 wherein the feed stream salt is selecced 'from a group consisting oiF Sodium chloride, potassium chloride,.sodium sulfate;- potassium sulfate,: sodium. nitrate,* potassium nitrate or mixtures thereof.-
32. 53. Aprocess of converting a salt of a monovalent cation and an anion into an acid product stream, a base product stream and a depleted salt stream enriched init multivalent metals content, said process comprising the steps .of: filtering a salt solution feed stream in order to free it of suspended solids- passing the filtrate through a salt Voormrta a three compartment electrodialysis cell containina a bipolar memb2 ane, a monovalent selective cation memabrane and an anion membrane, said salt compartment beligloae between the cation membrane and the anion menhrane;, SurPlying a liquid comprising water thr, acid compartment, said acid compartmnent being located'etween a cation -selective Side of the bipolar membrane and the anion membranre; adding a dilution liquid comprizing water to the base compartment, said base compartment being located between. an anidi selective side of-the bipolar membrane and the cation membrane, said dilution liquid being -suf ficient to maintain the concentration of the divalent metals at a lev el which is no higher t h an at their solubility limitsi passiLng a direct. current'through the eletroialsiscell, said direct current causing a preferential. transpqrt of monovalent salt cations across the *cation membranes to 'a base compartment where said salt *cations comdbine with the hydroxyl. ions generated by the .:bipolar membrane to form the base, and a concurrent transport of salt anions across the anion membrane to the acid *compartmaent wherein the salt anions combine with the hydrogen. ions generated at the bipolar membr-ane to form' the acid; and f w ithdrawing the acid, base and the derleted salt solutions from their respective compartments. 86 IR**WAPES G167R 4JThe process of Claim 53 wherein 'the R~ of tefe stream salt solution is adjusted to a value greater than about 9 and filtered to remove DPrecipitated multivalent compoundS to processing in the electrodialysis cell. 1The prccess of Claim 54 wherein the salt is selected frzom a group consisting of sodium chloride, potassium chloride, sodium. sulfate, potassium sulfate, sodium nitrate, Dotassium nitrate, sodium phosphate., potassium phosphate, or mixtures, thereof. So. The proces sof Claim 53-wherein. the feed is selected from, a group consisting of an ammonium, sodium Qr potassium salt.
33. 57. The process of Claim 53 wherein the feed stream contains no more than about 7 5:ppm of calcium and 55 ppm of magnesium. per gram equivalent of the monocvalent cation presen.t, in, the feed stream and the pH in th e base loop is 'in the range of 7 to about 11. *58. The process'of claim 53 wherein the depleted salt solution from the tlectrc~dialysis. cell is resaturated with a *solid salt and recycledrt-o the pH adjustment step- The Drocess of'Claim.51 whereinl the: feed stream is taken from a group consisting of an ammonium, sodium or *potassium salt or mixtures thereof. Apparatus comprising anclectrodialysis ccll, substantialIV aS hercinbefore described with reference to the exaniples and/or accom~panying drawings.
34. 61. Processes for converting an incoming feed or a-salt, producing an organic acid recovering sulfur dioxide from gases, producing sodiumn alkali from impure sodium mineral sources, containing carbonates or producing mronovalent organic acid, substantially as hereinbefore described with reference to thle examples and/or accompanying drawvings. DATED: 21 January 1998 CARTER SMITH BEADLE Patent Attorneys for the Applicant: ARCHER DANIELS MIDLAND COMPANY DAfl:TNIP:27512ARC CLA- 8 88 It bvur, TINS