Suida Process for Acetic Acid Recovery EMERSON P. I'OSTE, P. 0 . Box 51, North Chattanooga Station, Chattanooga, Tenn. uE iiitrrert trjilqy along lines uf ciieiirical
ITH practically the disappearance of the productioii of charcoal iron and the advent of synthetic acctic acid and methanol, the wood distillation indnst,ry siiffmed a serious decline. Ko new plants were constructed. and the future of those which continued in operation was far from hopeful. Radical improvements in the industry were in order if it was to survive. Various efforts to produce acetic acid by direct processes (eliminating the intermediate material, acetate of lime) have ireen made, and many of them have led to results of conrinercial promise. With this encouragement, improvements in wood distillation methods have followed those in byproduct recovery, and the revival of interest hased on these developments will probably twing back to economic importance an industry that. was well on the way to obsolesc'ence. One of the more promising processcs for t,lie direct recovery of acetic acid is that dc+ vised by Hermann Suida of Vienna, which, following considerable success in Europe, has heen introduced into the United States by the Forest Products Chcmical Company, of Memphis, Tenn. The plant a t Memphis was originally an acetate of lime operation. .About three years ago it was converted tu the Suida syst,em without interruption of production. So PUGcessful has heen the outcome that an ~ 9 sociated interest, the Crossett Chemical C'mw pany, of Crossett, Ark., has been put iiito operation based 011 the experience3 at, Memphis. Present developments at Crossett a.nd plans for future expansion along adrlitional lines of chemical activity bring t h k town in the southeastern corner of .Arkansas to the front as one of thr mitrt,anding p i n t s
teclrnology. Crossett is a tiriving cainiiuiriity of about twenty-five hundred inhabitants, which has developed in connection with the activities of the Crossett Lumber Company. The timber liddings of this company involve 4'20,000 acres uf land which are being scientifically cut and reforested. The village is a typical mill t o m of the better type with company st.orr, hotel, community center, hospital, school, a i d play ground. The town is served by the I b c k Island, the Missouri Pacific, and tlre Ashley, Drew, and Northern Railroads, the latter the property of the Crossett Lumber Company. In this environmrnt is taking place what is possibly the most important development in tlre wood distillation industry in the Uniteil States. Because of the close relatirui between tlir: operations of the Forest Products Chemical Company and 'die Crossett Cheniical Coinuanv, . - . the technolow -. of thc two ulants has much in common, and the account being presented covem the essential feat.ures of tlic Suida and related processes as in practice at both plants. WOOD
DISTILI,.4TION
Each of the two plants is equipped for handling 80 curds of wood per day, though the Crossett plant is designed for expansion to a 200 cord daily capacity. The carbonizatiori cycle is the same in both cases. A charge a t Memphis consists of 10 buggies of 8 cords each; at Crossett, 8 buggies of 1 0 cords each. The wood is first treated in a predrier for 48 hours. Heat for this operation is furnished from flue gmps from the retorts, The temperatiires realized range from 150'
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to 200' C., driving off about 8 per cent of the moisture originally containcrl i n the wood. The predriers at Crossett are of an improved down-drait design with automat,ic temperature control realized by admission a i cool air m necded to avoid
retorts are uf the canveutional end-fired type, and light oil froin the plant (supplenirmted by coal) a s f u The improved dmign at the Crossrtt plant is a ritdical dcpart,urc from the usual. The retort gas is suppleinented by natural gas. Thcrc arc four eombimation hnrncri along each side of the setting. Tire flame passcs a c r w under the retort, up the opposite d e , and across the top, ani1 t i l e flue gases are withdrawn through ports in tlie bottiiirr oi the setting. The several units discliargo Aiie xas into a common collecting flue wliicii delimrs to the prrdriert or thi, tttmosphere &s desired. The chargc rcniaiiis in tiit' retorts '24 hours, during which time it is heated gr(ritdual1.yti) :L iriaxiiriuni gas temperature of 400" to 425O C. and iield at that8 temperature for the last 3 or 4 liours. The actual temperature of the charge is from 50' to 7 5 O C. above that ai the
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Cases leaving the retorts pass through water-cooled i q i p i v condensers and the condensed pyroligneous acid is led to :i collecting tank. Noncondensahle gases are conducted to ii copper collecting main, through a scrubbing system, and tiirii t,o a distribut.ing main from which burner connections lend. Ttie gas in this system is aut.omatically held at pressures of 0.2 inch of water above or below atmospheric. The average figures for a series of runs show a noncondoiiof 6780 cubic feet per cord. Ihrioc theentire sable cas .. yield . cycle the gas composition is as iollows:
foul t l w hiiriiers, aiid the scrubbing liqi~orsw-liicli.arc added to the pyroligneous acid increase the alcohol yield about 1 gallon
After being discharged from tlie rctorts, the buggies of diarcoal remain 48 hours in closed coolers and 48 houm in open cooling sheds, following which they pass to a tipple for dumping. The charcoal is carried to the charcoal house for crushing, sorting, and packing. The gas scrubber is 4 feet in diameter and 25 feet higlr. The scmhi>ingoperation produces a clean gas which does not
per cord. Ry the application of the down-draft system to thp prrdriers a i d retorts, only the cooler gases that have given up their heat reach the discharge flue, reducing heat losses to a rninimum. The design of the retort settings makes possible vcry even und accurate temperature control. An automatic recorder registers the temperature of each retort every 10 minutes. A given typical chart shows four retorts starting at somewhat varying temperatures to havc crime witiiin a temperature range of 10' C. after 10 trours a d to have continued witlrin a raiige of 20" C. for 7 hours till a maximum oi 410" C . was rraclied. BY-FHOUL.L.T REC~V~KY The methods of by-product recovery a t both plants center around the Guida process for the direct production of acetic acid. The essential feature is the preliminary separation uf a scrubber oil in which the nretie acid is later dissolved, followed by its extraction and rectification under vacuum. In European practice the alcohol is removed prior to the scrubbing out of the acetic acid. The modification which 118s been in succcssfiil use at MenipIris for three years, and which is in operation at tlie Crossett plant, removes the acetic acid flrst, followed by tire separation of the methanol by simple rectification m e t h o d s . The advantages claimed for the Suida process are that it is continuous, yields an acid of high concentration and purity, involves a small number of separate operations, requires a relativelysmall amormt of ctram, and uses as the
The fractions from the methanol rectification are blended to produce a 94 per cent denaturing grade which makes up about 65 per cent of the output, the balance being marketed as 95 per cent antifreeze and solvent methanol.
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RESEARCH AXD C O S T R O L 997
,4 system of operations a5 complicated as wood distillation and by-product recovery calls for constant study and accurate routine checking. A research and control laboratory is maintained at the plant of the Forest Products Chemical Company and a control laboratory a t the Crossett Chemical Company. In addition to these, control stations in the stillhouses are used for the making of frequent routine tests. At the Memphis research laboratory a pilot plant was carefully studied before the commercial Suida installation was made. The initial full-sized plant involred several modifications of the European process. Based on more than two years experience with this plant, the one at Crossett was designed to incorporate additional improvements, the merit of which has been demonstrated by about six months operation. Certain of the many contributions of these developments to the present status of the industry are presented as of particular interest.
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