[1]Patented Feb. 22, 1927. 19618,834 UNITED STATES PATENT. - OFFICE, WALTER A. KUHNERT, OF LOS ANGELES, CALIFORNIA. PROCESS FOR RECOVERY OF SODIUM SESQUICARBONATE FWX BRINES. carbonate for the plirpdse of recovermg soda principally in the forn-1 of sesquicarbonate. Nfy invention lias I)eeii ,ipplied particularly to the brines existing in Oweias Lake, Califorinia, blit is applicable generally to other@ L-rines of the same tvpe containing or consist-ino, of a con-iplex -,oltition of various salts 10 . 1-n the treatment of such brines it has been prop.osed to separate t-he soda therefrom by tr,eatment with carbon dioxide or carboiaating agents so as to produce sodium bicarbonate which separates from the solui@ion 15 on account. of its relatively low solubility. This met-hod is however open to serious objectioins in practical use for the followimg. reasons: The precipitated sodium bicarbonate whicli is. formed in slich operation is 20 generally of an extrpmely @niply divided nat-ure rendering it diflicult to separate froin the solution by fidtration,- centrifuging, or otherwise. The difficuRy of filtration is further increased -by the '!act that colloidal 25. materials, including colloidal silicates and aluminates as wen as organic matter are. generally present in th--,trine aiad products tl-iereof are preciy)itated along with the sodi-am bicarbonate and remaiin @with the same 30 on ffltration. Moreover these impurities are extremely difficiilt to remove from the precipitate'on account of the difliculty in washmg the sodium bicarbo-nate owiiag to its finely divided conditioia. I 35 The main object of the present invention is to separate the soda from such brines in the - form of sesquicarbonate afid in coarse crystalline for-m rendering it readily' amenable to centrifuging or filterin- and wash40 ing. A further advantage of the separation of the soda in thp- form of comparatively coarse erystals of sesquicarboiaate is that the washe(I from. the crystab, thereby min45 i]alizi ng the contamiination of the recovered sodium sesquicarbojiate with other salts such as borax, potassinm ebloride etc., generally @ontained in the mother liquor,. Another object of the in-iention is tlo re@- ce as far as possible the expense of pre.50 du cipitation-of the soda by carbon dioxide by redticing the amount of suclcarbon dio2dde reqtured for such precipitation, it being an additional advantage of the process that's 55 smaller total quantity of carbon dioxide is required for. -precipitati-on in the form of No 3)rawing. Application filed Tuly 27, 1925. Serial No. 46,488. Tllis ini,,ention relates to a process foir se,s4ui carbonate than in the form of bicartreatiii ent of salt brines contabaing@ sodilm -bonate. I - will do'scribe my invention as applied to the precipitation of soda in the form of 60 ses quicarbon6te from t brine su@?,h 'as is fou nd in Owens Lake, California, said brine aft er solar- conceritration being of approximat ely the followiiag composition: Per cent. 65 NA, CO, ----------------------------- 14.60 - Na,B,O,.loH,O-- 8.25 --------- --------- NaCi --------- -------------------- 8.27 KCI --------- ---------------------- 6.66 NA.S O ---------------------------- 3.19 10 Other salts and water -------------- 60.03 Total ---------------------- 100.00 it beiiag understood that the compositionof this brine will chanlre considerably froin 75 time to time owing to -@a'riations in temperature and evaporatiod. The brine is brought bv solar evaporation or otherwise to a conditi@n of saturation or sub tanti ally so as regards its sodium car--- 80 bonate constituent at ordinary lake temperature , which in the summer may be in the neighborhood of 160" F. The saturated brine is then pumped into any suitable receptacle or tank, a-nd is --ubjected to the ae- 85 tion of carbon dioxide obtained in any suitable manner, for 6xample from a lime kiln or from a receptacle containing liquid carbon dioxide under pressure. The gases from the lime kiln conta'm'mg more or less carbon oo dioxide are pumped by - means of any suit-,tble-blower, fa-n, or compressof into contact with the brine. l[n order to provide effective contact, the gas conta may be force(' into 0 pressure so as to c throu-ah the brine an of brine carbo@ dioxide into int ate e mother liquor can - be more thoroughly the brine. The carbon dioxide is absorbed or reacts with the soda i-n its passage through loo the brine while the remaining inert. gas serves to very thoroughly a,-itate the brilae thus facilitating the reaction. This operation may be coiiducted in carbonating towers of the type ordinarily imd for carbonation of 105. stich brines, said towers Ix, ilng @ro@idecl for. example with perforated diaphragms or other baffle means at intervals throughout the height thereof so as to assist in the distribution of the gas and provide the highest 110 degree of agitation of the brine and the most intimate contact between carbon di-
[2]1,618,834 oxide and brine. in soiiie cases lio,",cver I may callse the briiie to percolate dowiiwardI through suitable towers over coke or other Yistributing iiieans, and ciuse the (,ases to pass upwardly throti(rh the t.owei-s so as to provide couiitercurrent flow of tlle brine ,in(I .carbon dioxide beariii(r ga-. Wlieii itiiig tD towers of this lattei- type the bi-ine is rapidlv circulated throii(,-h the toiven by plillipill(r 10 back tl)e soltitio@'n from the bottoiii of the towers to the top iri a Avell-l@no%vn iia,,tnlier. The towers used in the carbonatioii niay be provided with suitable means for coiitrolling' the temperature of the brine; for exalliple 15 ii-ie-,@iis for ad-, eat the I)r!De,. ation of Foda as rine of this character it has been usual to tupply the carbon 20 dioxi.de bearing gas at 1q:@ concentration of about 33@'o or n-iore of carfi.on dioxide by voluine aind to stipply the g@-S at sucli rate, that for a single batch of liq'' r coiitaiiiin@r say VP t@ 18,000 galloiis of brine ati ' oiit 5,000 poiind.s 25 of carbon dioxide will be it'ged, the carbonatiiag operation lastinabout@in'ehours. This represents aii[ absor@'ptioil of approxii-nately 30 pounds of carbon dioxide per hour per 1000@.gallons of brine. In the opei-,,ttion as 30 carried out in this iiianiier usiii(, carbon dioxide bearinlr gas with thp, caiboi'i dioxide concentratioi@' and th6 rate of supply as above stated, th@ precipitation of soda is substantially all in the form of sodium bi35 carbonate and the precipit-ate is extremely fine and therefore difficult to separate fr6m the solution by centi-.iftig ing or filtering and diffictilttowasn. lbii:vefouiidhoweverthat by maintaining a materially lower rate of, ab40 sorption of carr)on dioxide in the brine than that.heretofore employed which inay be aecon-iplished by either stiitably redu@ing the 6oncentrati.on of carbon dioxide in the carb na in a or by redu.ci ng the rate of 45 pp y g g ml I of the carbon dioxide bearing gas to the biine or by reducing both the carbon dioxide c6ntent and the rate of supply of the gas, a-nd@by properly controllin- the teni6 perature, a certain - percentage of the @@6da 50 can be precipitated largelv or wholl iii the @y form of sesquicarboiiate ind in a coTParatively coarse crystallin.e coiidition, which is well adapted for separation by centrifuoin(y or filterin(-r and washinor so as to rei@ove 55 z@ @@- @ rnother,liquor-and otlier iinpuritie from the precipitate. I have obtained good results -by carryin 9 out the precipitation operation in the following manner: The' carbon dioxide b-caring go gas coming froin the Iiine kiln or other tipPI.Y means is if necessary diluted witb air or otherwise -so as to.pre8ent a conce I ntration' of about'23 to 289'o of carbon dioxide and this gas is brought'int6'contact with the so.1--ition in the manner above (lescribed at a teiiip(@t-,tttti,c of tbotit i,7' C. (oi, say froiii 30' C. to 45' C.), the ciiI)oliition of the I)rine iii this itiani)ei- I)ein- condiieted for ,il)ollt 12 liotii@@:, AN-itli Lll(' tlllt a pOrtioii of tlic, ,,-o(Il is lai-(-ely or 70 ivliol]N- iii tl)e fol.iii of aii(I tli(, (@,,irl)oilat(, iii soltitioji is re(Itice(I fi-oiii si-v tl)otit 147o to aboiit 8@lo or less. The i-e(Iii(-tioii of the so(Iiiiii-i ciii-bonate cont(,,,it ol@ 18000 (rallons o-f brine fi-oiii 1470 to 75 81@l,., I)y iiiv I)i-oeess, aboiit 1'100 I)oiiii(l, of clrl)on di-oxi(le, as a(-tiinst 5000 poiin(Is i-e(Iiiii-ed I)v the oi-dinary -iiietliocl ,tbove i-efori-ecl to. The coiicenti-ation of cai-- I)oii (lioxi(l'e in the @-a(.@ ,iii(I the rate of sup- 8( I)IN,ijig !@ris to tlie. I)i-iiie ii-ity therefore I)e'sii(,Ii 2t-,, to I)i-oi,ide aboiit 1706 potiiids of ctrl)on (lioxi(le in 12 lioiii-@,, for eacli 18000 -.illon-.@ of 'k)riiio,. This represents an absorp@ioll'@ of@ oiily aboiit 8 poitiids of cai-bon (ti- 85 ox@,(Ic per liour pei- 1000 ('Yallolis of briiie ii,lii(-Ii is iiiaterially less tlian in the usual pi-acticeasaboveoutlined. Theliquoristlien I)assed tlii@oiigli stiitable 'sepai-ating ineans IS CeDti-iftio-in,)- oi- filtel-ing- apparatus, or 90 I)otli, foi- sel)aratioii of the precipitated so(iiiiiii ses(Iiii(@,ii-bonate along. wi,t,h any so(litim I)ical,bonatewhichiiiaybe precipititted it the qaiiie tiiiie. It is (lesirible however to i-e tilate the conceiitration and rate of .95 9 floiv, of carbon dioxide beai-ing gas,in slich iiianner tliit the aiiiount of sesquicarbonate I)ree ' ipitited ivill be,at a iiiaxin-ium and the aniount of bicarbonate precipitated will be a miniiiiuin. 100 The sesquicarbonate precipitated and separated from the brine as above described is marketable as such, or may be readily converted to alky of the standard soda compoiinds such as sod,,t ash, sodiuioa hydroxide, 105 etc. The'brine from which the p@rtion of sodium carbonate has been, recovered as above doseribed may be then treated further for recoverv @i' other constituents or may be returyied to the main body of brin e in the lal,,e. Instead of reducing the rate of supply of carbon dioxide to the brine by reducing. the concentration of carbon dioxide in the gas I n-iay reduce the rate of flow of stieli cr S' for eximple by reducing the pres- 115 ., a sure or tbe volumetric r'ate Gf flow at which it is supplied, -o as to e-ffect a correspon reduction in t@e rate at which e'arbon ide is broiiaht iiato contact with the soditim t solution and thus tend to pro- 120 carboiaa e in diie-e sodium sesquicarbonate instead of sodium biearbonate. Or, as in the example above given, both the concentration and the rate of flow may be diminished. The carbon dioxide bearing gas used in my process, 125 when produced by -the operation of, a lime kiln will, in aeneral, contain in adclition to the carboii Ai;xide, a lar-e amount of nitr6gen and small amounts of othei; gases. It iii-,iy be stated that in general for produe- 130
[3]1,618,834 tion of about 18@/2 ton@ of carbon dioxide, abotit 30 to-ns of limestone and about 3 tons of eolic (85@lo C.) will be iised and the carbon dioxid.e in the gas is obtained partly from the Iiiiiestone and partly froiii the coke. The carbon dioxide bearifi(t (,as so produced m a contain a higlier coiieehtration of cary bo@dioxide than is desirable for carryin(y out iny iiiiproved process as above describ6d 10 aiid may in such case be diluted 1).y admittin!,r a,ir or other dilutiiicy gas tliereto at any desired sta 'ge of the op(;i@aiion, for exainple after the gas has passed through the orclinary sel-ubbers and before it passes to the 15 punip or blower for forcing it,into contact witli the brine. In addition to the abov4@ mexitioned meclianical - advantages.of my process over the ordinary methods of removing soda by pre20 cipitation as sodi-um bicarboliate, su@h advant,ages resultin-o, pi-incipally from the coarsely crystalline precil)itate obtaine(I b@ mv process, I obtain the further advantaoe oi',i reduction to about one third in the car25 bon dioxide consumptioii.as compared with such otlier iiietliods (for,-,exalnple, a reduc-' tio'n f r.om 5000 pounds to i7OO pounds in the particular case above disetissed). The reason for this redtiction iia the cafbon dioxide 30 required tc, remove a (riv6n aiiiount of soda frbm tlte brine is evident from the followineqiiations, in wltieli the water of ery stallization,is.disregarded for the pufpose of simplification: 35 1. N-,tCO,,+CO,+R,O--2NaHCO, !I. 3Na,CO,+CO,+H,O= 2(Na,CO,,.NalIC03) Equation No. I i-epresents the reaction ordi40 narily obtained in the precipitation of bicarbonate and it will be seen from this equation thdt one molecular equivalent of carbon dioxide-is i-equired for etich molecular equivalent of sodium carbonate removed 45 froiia the brine. Equation No. 11 represents olv the reaction inv ed in the,. precipitati(yu of se.,:quicarbonat6 and it is seen that in this case one niolecular equivaleiat of carbon dioxide is sufficie-nt to convert three molecular 50. equi-s,alents of sodium carbonate:,,-t -the foryn of sesqtiicarbonate in -v@hich pi-ecipitited. By nteans of niy inventid"A""ti .I,erefojre, for a -iven egnsumption of catboi@ dioxide, tliree@ tin-ies as much soda i reriioved 5.5 frc;m tliit@ brine and made available for @ uspor for'.z' a6 as is the case ivith the former method In my proceg4'-.-- as above descri.-bed, tlie. forniation of sesqti , icai,bonate i-nay talt6 I)Iace 60 directly as iiidic' ated in Equation No. 11 above or it niay consist iii t-i-,,o steps: first, bonate. It has been known heretofore to etirbonate complex brines coiitaining sodium carbonate ' in stich inanner as t(> obtlin a precipit.ate ot- bicarbonat'e and then to add the preeil)itited bicarboliate (either iii solid 70 foi-ni or'as a siispeiisioii in water) -to a f iirther quaiitity of sodiuiii carboirtate . solution so as to cause precipitation of sesquicarboiiate. But it lia8 liever been knowil before to iDy kiio%vledge to so cai-ry otit the car- 75, bonation of stieli brines that bot-11 of tliese, operatioiis ire perf,ariiied at the saitie tilile. I ha@,e found liowe-%,er -that by sufficiently redueing the rate of supplyilig cdrbon dioxide to.tlle brine for example as above de- 80 sciibed (thit is to say by supplving. for exaniple,, oijly 1,700 p@ui@ds of eirbon dioxide in 12 li6ui-s, as against 5,000 p.ounds ordinarilv supplied in 9 l@ours for 18,000 gttllons if brili.e) and properly controlling 85 the teiiiperature (tiarin- carbonation, the precipit,ate may be o,blCained principally or in,holly in the follnl of sesquicarbonate and 'if it be assumed that the formation of sesquicai-bonate 'takes place in two steps as above 90 n-ientioned then it ig apparent that the precipitation of sesquicarbonate instead of - carbonate is due to the lower r@,te 6f carbonation -which, in the presence of the other salts in the brine, permits the bicarbonate 9-" as formed, and before reaching a suffi6ent concentration to cause precipitation t-hereof as such, to react with an equi-molecular ioportion of pormal carbonate and form P' sesquicarbonate which precipitates out. 100 I
