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550 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 41, No.

40 50 00 70 80Conversion, yoFigure 11. Thermal Conductivity of UnventedLatex against Per Cen t Conversion

Tomp., * C. Symbol28.1 038.6 h

where 1 = temperature in The data of Smith ( la) , basedon the work of Bridgman (6 ) and Daniloff (8) gree with thisexpression within 5.1yoat 30' @. but lie about 55y0 higher a t75 " C. The present calibration da ta on ethano l lie from 7.9 to8.3% above this equation throughout the temperature range of28" to 48' C.

The data, of bates, I-lazzard, and Palmer on methanol are re-presented b y the eq uation:

C

K t = 0.00064 - .00000150 1 cal./sec., cm., ' ,Smith's data on methanol agree with this equation exactlyat 30"C. but lie about 14% higher a t 75" C. In the present work,the value obtained for methanol a t 33.3' C. mas about 7yobelow

the equation. Therefore the present ap paratus gives results

th at agree within ab out + 7 % with the data of Bates et al. Tlatt er are probably the best available a t present, judging frotheir completeness and the reproducibility reported.

The thermal conductivity of stripped latand th ree samples of v ented latex between 51.0 and 75.5% coversion over a temperature range of 28' to 48" C. have been otained and are shown in Table II and Figure 10. The coductivity of the 5 1~ 0 % ample is constant over the given teperatu re range within the experimental error; for the 69.9 a75.5% conversion samples, the conductivity increases about 10over this temperature range. In Figure 11, the thermal coduct ivity of unve nted latex is plotted against per cent convesion for three temperatures. Conductivity increases abou t 50at all temperatures between the conversions of 50 and 75.575.

Data on Latex.

LITERATURE CITEDBates, 0. K.+ ND.KG .CRBM~,5, 431 (1933).Ibid., 8, 494 (1936).Bates, 0. X., Hazzard, G., and Palmer, G. , I N D .E m , CHEANAL. D. ,10, 314 (1938)-Bidvell, C. C., Ph y s . Rev . , 56, 594 (1939).Bridgman, P. W., Proc. Am . A d . Ar t s ScL, 59, 141 (1923)Daniloff, M., J.Am. Chem. Soe., 54, 1328 (1932).Drucker, C., "O~stwald-Luther's Hand und Hilfsbuch zAusfuhrung physiko-chemische IlIessungen," K ew YoDover Publications, 1944.Dwyer, 0. E. , personal communication, Sept. 8, 1944,Hammann, G. , Ann. Phvsik, 32, 593 (1938).Jakob, M. , Ib i d . , 63, 37 (1920).Kaye, G. W. C., and Higgins, W. F., Proc. Roy. Soc. (Londo

A117,459 (1928).Meyers, C. H. , S c o t t , R. B., Brickmedde, F. G., and RandR.D., Jr., report t o the Office of the Rubber Director (Ju30 ,1943) .(13) Smith, J. F. D., Trans . Am. Soc. Xllech. Engra., 58, 71 9 (1936)(14) White, W. P., "The Modern Calorimeter," Ax . CHEM.SOMonograph No. 42 , N e w York, Reinhold Publishing Co., 192(15) Winding, C. @., IWD. XG. HEW,7, 1203 (1945).

RECEIVED ctober 4. 1947. This investigation was carried out under tsponsorship of the Office of Rubber Reserve, Reconstruction Finance Cporatio n, in eonxiection with th e government's synthetic rubber program

Production ProcessesPa M e KARIPhIEYER A N D E. E. STAHLY

M e l l o n I n s t i t u t e of Industrial Research, P i t t s b u r g h , P u .T h e American process for production of butadiene fromethyl alcohol, as developed by the Carbide and CarbonChemicals Corporation, was operated w ith a 2.75 to1molarratio of ethyl alcohol to acetaldehyde feed for optimalyields of butadiene. Two improved methods utilizingdifferent over-all feed ratios have been devised; these givehigher yields tha n do th e conventional plant operations.First, it has been demonstrated t ha t injecting an auxiliaryside stream, rich in acetaldehyde, into the catalyst bedet or above th e midsection, where th e aldehyde is rapidlydepleted, leads to yields of 64 o 68 mole % an d conversionsof 35 t o 37 mole % per pass. These results compare with63 and 34mole %, respectively, fo r calibration run s withoutthe side stream , An increased total throughpu t, henceincreased production, is also realized. Th e second novelmethod of operation comprises an auxiliary feed of ethylalcohol added a t or below th e mid point of the catalystamtion; th is affords consistent yields of abo ut 76 mole %.

Preliminary work on a two-step process with ethyl alcohoacetaldehyde feeds has been found promising bu t furth estud y is required. Carbon deposition is no t prohibitivin these procedures.

RODUCTION of butad iene from ethyl alcohol, as deveP ped by th e Carbide and Carbon Chemicals Corporation (is a two-step process represented by the following equations:

CtHaOH + HaCHO +He (CaHbOH +CHzCHO --+ C4Hs +2H20 (

Th e investigations of the present project were concentrated othe second step of this process because th e first step gave a yieof 92y0acetaldehyde whereas the best over-all yield of bu tadie nfrom the two steps was 65 % of theoretical. The outlook whopeful for improvement in view of the fact that an increaseonly 1% in the yield of but adien e would represent an enormousaving in both time an d money in the emergency rubber program

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March 1949 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 55The major efforts of the program were assigned to the better mentof th e catalyst employed in the second step. Two or more SUC-cessive reactions are involved in this ste p and the method of plan toperation was a limiting factor for obtaining optimal conditionsfor these several reactions. Some atten tion therefore was de-voted to devising new methods of operating th is second step.The present paper records only the studies relevant to methodsof operation-studies initiated with the idea of controlled varia-tion of the ratio of reactant s in the butadiene reactors. Becauseof the early termination of the project, this work was not carriedto an entirely conclusive end, bu t the results are reported hereto demonstrate improvements obtainable in the ev ent that futurerequirements will justify further refinements in the process. Alogical continuation of thi s work would involve establishing opti-mal partial pressures of reactants as well as the optimal ratiowhich should be maintained in various portions of the catalystbed.

COMMERCIAL PROCESSEarly in th is work it was confirmed t ha t two or more successive

reactions occur during th e formation of butadie ne from acetalde-hyde and e thyl alcohol according to th e proposal of Quattlebaumet al . (6). The optimal plant operating conditions for carryingout these successive reactions in one reactor as established byCarbide and Carbon Chemicals Corporation were as follows:Temperature 325-350' C.Pressure Essentially atmosph ericFeed RateFeed FZ.atio"

0.4 t o 0.5 vol. liquid feed per vol. of catalyst per2.75 moles ethyl alcohol per mole acetaldehyde

5 Feed ratios refer to moles of ethyl alcohol per moles of acetaldehyde.hour (liquid hourly space velocity)

The optimal feed r ate is believed t o bc 0.6 liquid hourly spacevelocity (i?)nstead of the s,bove rate.

In the s tandard commercial process (7 ) for producing butadienefrom ethy l alcohol the initial step comprises the passingof t he ethylalcohol vapors over a suitable catalyst to produce acetaldehyde.Ethyl alcohol and acetaldehyde are then mixed in 2.75 to 1 to3 to 1 mole ratio, t he vapors of this mixture passing over a suitablecatalyst (about 2% tant alum pentoxide on silica gel) a t 325' to350" C. and 0.4 to 0.5 space velocity t o produce butadiene inabout 62 to 63 mole yoyield based on total ethyl alcohol feed. Re-generation by burning off in situ at 400' C. is necessary at inter-vals of 100 to 120 hours. With fresh or new catalyst, mole con-versions of 28 to 30% are obtained per pass; after prolongedoperation conversions of a bou t half this amount are realiaed. Amolar ratio of e thyl alcohol to acetaldehyde of 2.75 to 1 o 3 to 1gives the optimal initial feed composition. Somewhat higher ratiosof ethyl alcohol to acetaldehyde may give rise t o slightly higheryields bu t lower conversions per pass. Higher concentrations ofacetaldehyde lead t o higher conversions but shorter periods ofoperation between catalyst regenerations because of excessivecarbon deposition on the catalyst. (Standard laboratory runswith fresh catalyst showed abou t t he same over-all yield as thecommercial plant bu t th e laboratory mole per cent conversion perpass was higher-about 33% against 28 to 3070.)

Variations in plant reactor composition thus were limited tothose resultant from a fixed initial feed. Restricted conditions oftemperature and feed rate likewise had been established foroptimal yields in the current plants. The problem of improvingyield and/or conversion seemed to be one of finding new methodsor systems of operation which permitted controlled variati on ofreaction compositions in various sections of the catalyst bed.A stu dy of variation of catalyst and temper ature in the fore andafter parts of the reaction system was begun but not completed.

OPERATING METHODS INVESTIGATEDThe methods investigated are based on the need of controlling

the ratio of reactants in the reactors as well as in the feed. A

TABLE. COMPARISONF OPERATION ROCEDURES(Temperatures 350 C.: commercial tantala-silica catalyst; initial feeratio 2.75)

reed Rate , Molar Feed to CbHa,L.H.S.V.0 Ratio Mole '%636668760.40 2.10 38 67

Standa rd conventionaloperation 0.40 2.75 34l b 0.40 1.76 312A 0.58 2.12 372B 0.50 4.07 283 .. Nil ..Acetaldehyde feed 0.40 . . Nil . .thy l alcohol (92%) feed 0 .40

5 Liquid hourly space velocit6 Auxiliary acetaldehyde fee8'added a t four points.

factor usually ignored in discussions of optimal conditions foplant operation was the gradual change in feed ratio throughouthe 17.6-foot length of catalyst bed. A n entering feed ratio o2.75 to 1might be accompanied by a n effluent having an 8 oratio of ethyl alcohol to aldehyde. Therefore any assumption implying one optimal concentration of ethyl alcohol and acetaldehyde throughout the reaction chamber appeared highly improable; it would be fortuitous if the same operating conditions, thsame concentrations of reactants, and the same catalyst weroptimal or the several reactions involved.

Three variations in operating methods were included in thistudy:1. Multiple-point addition of an auxiliary feed2. Spot addition of an auxiliary feed: ( A ) enriched acetaldehyde feed as a side strea m; and (B) high ethanol feed as a sidstream3. Two-stage process with cthanol-acetaldehyde feedsThe d ata for the third operating method show promise but thi

phase of t he work was no t carried to a conclusive point.A comparison of these operating procedures under the ~011mercial optimal conditions (other than reactant ratios) is seforth briefly in Table I. Data for conventional operations anfo r ethyl alcohol alone and acetaldehyde alone as feeds are included for comparison.

From th e standpoint of yield of butadiene the best procedurappears to be that in which alcohol is added &s a side stream

FE,ED FEED , 4

OF F GA S - ,, WASTEFigure 1. Multiple-Point Injection Test Unit

A - eeder 111 mixture; B - feeder 2.75:1 mixture; 6 - Commabellows pump; D = feed prebeater (steam); E =needle valves; F -valvem; G - manifold. H - orifice housing; I = feed preheate(steam); J 3 urnace &lock; K = thermocouples; L - water oondenser; M = valves; N = wet test meter; 0 = receiver flask; P -300 CC . of eatalyst; Q = inert paeking; R - urnace shell and insuletion; S - topcooks; T - heating element

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552 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 41, No.(method 2B) a t or below the midpoint of thc catalyst bed. Acombination thereof with th e operation (method 2A) in whichacetaldehyde-rich feed is added above the midpoint might showfurthe r improvcmcnt, but available time did not permit an assess-ment of this combination. Fur the r work on the two-stage pro-cedure (method 3) is desirable to establish optimal catalyst andconditions for the initial crotonaldehyde condensation in view ofthe high conversions obtaine d.

Figure 2. Laboratory U n i t with Rlultiple-Point FeedSystem

Equipment. Th e reactoi and assembly evolved for flexibleoperations are illustrated by a flow diagram, Figure 1,and photo-graph, Figure 2 .

The reaction chamber comprised an insulated electrically-heated 3-inch stainless steel block, 36 inches long \vith a 1-inch holedrilled centrally. A series of six 0.625-inch holes a t 4-inch inter-vals were connected with side arms equipped with needle valvesfor control of auxiliary feed flows. (T he cataly st bed comprised azone 24 X 1 inch inside diameter.) Seven thermocouples andauxiliary devices for recording and controlling catalyst-bed tem-peratures were provided. Temper ature was controlled so as tohave a spread of only a few degrees along the entire length of th ecatalyst section of the furnace block.

Th e top flange plate closure was connected to a feed steam pre-heater with standard fittings, The bottom plate was joined inlike manner to a water condenser followed by a product-collectionsystem. Th e side stream or auxiliary feed entered first a steampreheater and then an electrically-heated manifold (maintainedat about 165" C.). Feeds were pumped from buret reservoirs bymeans of bellows-type pumps ( 1 ). Other details of the assemblyand equipment a re clearly shown in Figures 1 and 2The reactor wa s charged as follows:50 cc. of an inert packing (Ca rborundum ) w as followed with 300cc. of % to 12-mesh catalyst; finally 65 cc. of t he sam e ine rt

Operating Procedure.

packing was added to serve as the preheat section. Th e catalywas flushed with nitrogen while bringing up and adjusting ttemperature to 350' C.

After charging the feed reservoirs with the desired feeds tnitrogen flush was discontinued and the bellows pumps westarted. Operation for 1 hour constituted the prcrun duriwhich final adjus tmen ts in tempera ture and feed rates were madThe effluent was shunte d to th e waste-product receiver. Alduring t'his int'erval, the product receiver flask was attached the condenser and packed in dry ice. Just prior to completionthe prerun th e feed reservoirs were refilled. Imme diate ly a t tend of the prerun the flow t o the product receiver was sta rtea t the same time th e ent,ry to th e waste-product receiver wclosed.A t the end of th e 4-liour run th e product flask was weighed astored in a dry-ice chamber to await analysis. The net, weightthe product divided by the weight of the total feed gave tliquid weight recovery; the amount of gas was of the order ofliter per 100 grams of feed. At the beginning of the project tsame charge of catalyst was employed in a series of runs eploying only a nitrogen-flushing period between runs. Cont rato previous information this practice was found inadequatemaintaining consistent cataly tic activ ity. To obtain consistenconiparable data fresh catalyst was rirwssary in cach run.Analytical Proce dure. The analyti cal procedure consisted ofinitial distillation through a n 18-plate packed column and colltion of the following fractions : initial boiling point to 13" C13" o 30" C.; and 30 " to 95' C. These fr actions were analyzas follows: the first fraction for butadi ene and acetaldehydc; tsecond fraction for acetald ehyde; and the third fraction for ethalcohol acetaldehydc, and acctal. Butadicne was dctermined an aldehyde-free gas sample by the Koppers-Hinckley malanhydride method ( 6) acetaldehyde and acetal were determinby an hydroxylamine-hydrochloride method; and ethy l alcohwas found by phthalic anhydride esterification according tomodificalion of a Incthod of Elving e t al . (3).Acetaldehyde (Niacet Chemical Company) ofleast 99% purity and ethyl alcohol (Commercial Solvents Cporat,ion) of 92 weight 7@ere employed in preparing the ethalcohol-acetaldehyde feed mixtures. Crotonaldehyde, from Cbide and Carbon Chemicals Corporation, was fractionated about 99% pur ity . Commercial tantala-silica catalyst was usas received from the Koppers, Kobuta, Pa., but>adienepla(mostly 3 to 10 mesh). Commercial silica gel cat,alyst was otained from the Davison Chemical Company. Alkaline-set silgel was prepared by the group on catalyst preparation (8).The yield values were calculatedfolloa-s:

Materials.

Calculation of Results.

Yield (or efficiency), mole yo=moles of C4Heformed X 200moles CHaCHO consum

0.92 _-oles C~HKOHonsumed -I-Acetaldehyde (o r ethyl alcohol) efficiency, mole 70 =moles C4H6 formed? 100

moles CHaCHO (or CeH50H)consumTh e moles of acetaldehyde consumed were divided by 0.92

cause the commercial dehydrogenation of ethyl alcohol gave abo92y0 yields of acetaldehyde, The yield data in this paper thefore refer t o an over-all efficiency of t he process based on ethalcohol in conformity with plant practice. For conversion. tfactor 0.92 is not employed, again because of the p lan t practice.

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March 1949 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 55 3Reproducibility of Results. Preceding this stud y 16 duplicate

experiments were made on fresh commercial catalyst as received,at 350" C., 2.75 to 1 feed ratio, 0.4 iquid hourly space veloc-ity , and 8-hour dura tion . Knowledge of reproducibility is es-senti al to avoid misinterpretations of inhe rent vagaries of the in-trica te sequence of t he st eps of t he operation an d reaction.

StandardMean DeviationOver-all efficiency, '%Conversion, %Ethyl alcohol efficiencyAcetaldehyde efficiency

6 3 . 6 1 . 63 5 . 6 2 . 55 5 . 1 2 . 18 2 . 7 4 . 2

MULTIPLE-POINT ADDITION OF AUXILIARY FEEDDuring nornial plant operation the acetaldehyde concentration

decreases throughout th e cat alys t section of each pla nt reactorwhile the alcohol to aldehyde ratio increaEs. To determinewhether a sustained 2.75 to 1 or lower feed ratio is actually opti-mal, runs were made with and without t he addition of auxiliaryacetaldehyde simultaneously through the lower five jets (Table11). Improvement in u ltimate yield, but not conversion, was ob-tained as a result of multiple-point addition with jets 2 to 6, butnot with jets 2 to 6 . Although it is probable that these resultscould be improved bv use of fresh or regenerated catalyst for eachrun, considerations of the mechanical and economic factors in-volved in providing multiple-point addition to each of the manytubes in a commercial jacketed reactor led to investigation ofsimpler methods of operation employing spot-addition of anauxiliary feed. In all subsequent work fresh catalyst was used ineach run to obviate an y question of comparability of dat a.

SPOT-ADDITION OF A N AUXILIARY FEEDEnriched Acetaldehyde Feed as Side Stream. In a series offive 8-hour standardization runs using commercial tantala-silica

catalyst at the o ptimal plant conditions (350"C. with 2.75 to 1

TABLE1. PROCEDURE-MULTIPLE-POINT ADDITION OFALDEHYDEEEDCommPraial tantala-silica catalysts. 350' C ' 0.4 average liquid hourlyspace velocity; and maierial balaze e 99 to 100%)Over-all ConversionType of N o. of Molar Feed er Pass, Yield, Av.Operation Runs Ratiob %ole % Mole %

1 C (Jets 2-6) 3 1. 89 :l 26 681 0 jets 2-5) 1 1 . 76 : l 31 66Standardd 3 2 .7 5: l 34 63Regeneration of cataly st was no t effected between runs.b Over-all feed ratio as used throughout this paper is not descriptive ofratio of reactants a t any point in the reaction zone but applies only to themole ratio of total reactan ts (ethyl alcohol :acetaldehyde) fed during thet e s t via top and jet feed streams.

C Food to top 2.75 t o 1; multiple-point addition of 1 to 1 feed a t jetsindicated.d Feed to top of cata lyst bed 2.75 to 1; no auxiliary feed.

T A B L ~x1. PROCEDURE 2A-sPOT-ADDITION O F AUXILIARYFEED(Commercial tantala-silica catalyst. median temperature 350' C . 2.75 to 1feed to top: 1 to 1 feed to jet indjcated. about 20 % of total fe:d: 4-hourruns preceded by 1-hour prerun' material balances 99 to 100%; averageliquid hourly aia ce velocity about 0.58)

1 : l Av. EthylFeed Over-All Conver- Yield, Alcohol Aldehyd eto Jet No. of Mole Rat io sion, Av. Av. Efficiency, Efficiency,No. Runs Et0H :Ac H Mole % Mole % % %2 . 0 7 : l2 . 1 8 : l2 . 1 7 : l2.12:l2 . 1 2 : l2 . 1 8 : l2 . 7 5 : l3 . 4 3 : l

3535363734313428

6264606867626360

5258596160 '535547

83808182807983904 Standardization rune (with no jet feed) a t 0.40 liquid hourly spaceb Et hyl alcohol instea d of ace taldeh yde : thyl alcohol feed to jet 2 (0.40velooity.liquid hourly space velocity).

TABLEv. PROCEDURE:B-EFFECT O F INCRBASEDTHYL(Commercial tantala-silica catalyst; 350' C. ; 2.75 to 1 feed t o top*wt. % ethyl alcohol t P jet indicated. material balance 98.1 to 1.00%; 'a!:'average liquid hourly &ace velocity abou t 0.57)

Ethyl Alde-E th 1 Je t Feed Cqn- Alcoholffi- hydeffi-Alcogolto Jet No. of Ratio of Tot al Av Yield ciency, ciency,No. Runs Et 0H :Ac H Feed Mole'% Mole % % %

ALCOHOL ONCENTRATION

Over-.All aa Vol. $7 version,

2'3456b

3 . 4 3 : l2 . 8 4 : l4 . 0 7 : l4 .00 : l3 . 9 6 : l2 .76

16.324 .02 7 . 426.72 5 . 90

282328282634

606076706663

475066625955Liquid hourly space velocity was 0.40.b Standardization runs rat 0.40 liquid hourly apace velooity with no jetfeed.

TABLE . PROCEDURE ZB-EFFECT O F INCREASED ETHYL(Standard tantala-silica catalyst, 350' C . 2 : l feed to top; 92 wt. %ethyl alcohol to jet indicat ed; rnkterial bal'&ce 99 to 100%; and av. over-all feed ratio 2.9:1)

ALCOHOLONCENTRATION

E t h 1 Alde-Je t for Liquid Feed as Con- AlcoZool hyd eAux- Hourly Val. % version, Yield, Effi- Effi-iliary No. of Space To ta l Av. Av. ciency, ciency,Av. Av. Je t

Feed Run s Velocity Feed Mole % Mole % % %3 2 0 . 4 8 2 5 . 3 28 67 62 804 2 0.56 24.2 31 66 61 795 2 0.5 7 25. 1 33 69 67 770 58 25. 1 31 03 59 74!? 0 .40 0 40 60 59 69

4 Calibration run with 2 : 1 feed and no side stream.

feed at 0.4 liquid hourly space velocity) the average mole ratio ofethy l alcohol to acetaldehyde varied from 2.75 to 1 (in feed to thetop of the catalyst bed) to 7.83 to 1 (in the exit product). In-vestigation of spot-addition was initiated to establish th e portionsof the reaction zone where higher acetaldehyde concentrations arebeneficial-that is, where auxil iary acetaldehyde should be added.A stream of feed enriched in acetaldehyde (1 to 1 mole ratio ofethyl alcohol to acetaldehyde) was passed in to the c atalyst bed atvarious side entrances. The dat a are shown in Table 111 alongwith the findings in standard runs and in one run with ethylalcohol side stream (the latiter demonstrated the adverse effect of ahigh feed ratio in the forepart of the reactor). Yields and con-versions were both enhanced by addition of acetaldehyde in th eforepart of the system; ethyl alcohol efficiencies were likewise im-proved.High Ethyl Alcohol Feed as Side Stream. Following the in-vestigation of spot-addition of feeds enriched with acetaldehyde,the effect of increasing the ethyl alcohol concen tration at variousparts of the catalyst bed was studied. A series of runs wm madein which 2.75 to 1 eed was led t o the t op of the catalyst bed witha side st ream of 92 weighh '% of ethyl alcohol entering at eachside arm in tu rn. The results are presented in Table IV . Al-though the over-dl liquid hourly space velocity was differentfrom the standard runs owing to the side streams, it has beenconcluded th at th e effect of thi s difference was minor, first becauseof results from other studie s (S), nd secondly because this liquidhourly space velocity was net a weighted value to correct for thefact that th e side stream did not transverse the whole cataly stbed.

Highest yields as well as highest aldehyde and ethyl alcoholefficiencies were obtained with the ethy l alcohol side stream enter-ing at or below th e middle of the catalyst bcd. I t is apparent tha twith this method of operation conversions were markedly lowertha n when using a 1 o 1 eed as the auxiliary feed strea m (or whenoperating in the standard manner passing 2.75 to 1 feed to the t opwithout auxiliary feed). Actual production rate, however, wasstill high as result of the high average over-all liquid hourly spacevelocity.

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554 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 41, No.With the object of maintaining the high yields v i t hou t in-curring this decrease in conversion, runs were made in which ad-

ditional ethy l alcohol was fed a t intermediate points h u t a 2 to 1feedwas substituted forthe2.75 t o 11Eecdpreviouslyemploged. Theresults of these runs shown in Table V are t o be .compared withdata for 2.96 t o 1 feed i n Table PV. The 2 to 1 feed raised theaonvorsion level but lolTered the yield and aldehyde efficiency incomparison with 2.75 to 1 fced. Longer operations, preferably ina pilot plant, would be necessary t o cat,ablish the rate of carbondeposition and length of operating cycle for 2 to P feed relative tostandard operalions (tho eflieacy of 2 to P instead of 2.73 to 1feed in thi s type of operation would depeiid on considerations ofoperable cycle length atid urgency of increasing production ratewith a sacrifice in over-all yield).

Operation with th e addition of a n auxiliary feed stream, as de-hned shove, might be carried out commercially rTith only rela-tively slight altcration of existing equipment. Two of the presentreactors might bo connected in series, auxiliary ethy l alcoliol beingadded t o t,he eflucnt product from the first reactor t o make thefeed ent,ering th e second.

D P SC U SSI O N OF KESUETSReaction Mechanism. From TabIes 111, IV , and V i t iu clear

bhat high conversions arid yiclds are favored by methods ofoperation in ~vhic h elatively high aldehyde concentrations obtainBn the foreparl of the catalyst be d with relatively high ethylalcohol concentrations in t,hc lower soetion. This conclusion i s inaocord with the mechanism represent r d lip th e equation pro-posed by Quattlebauni E a l . ( 4 ,6 ) ,

2CH3CI-ao+ H3aCH=-h:1B--- CikO 4- 1 - 1 2 0 (3)

En vie\\ of fiiitliiigJ from LL J L U C I ~ OI I th e mechanism of this I'D-action ( 4 , 6) Equations 3 and 4 appear t,o be well verified succes-dve reactions of th e process. Reaction 4 tself may involve twoOH"more reactions. If aldol is fornied it must be rapidly de-hydrated to crotonaldehyde because crotonaldehyde, but not&Idol, has been identified in the reaction products. (I n otherwork ( 4 ) it was demonstrated that free erotyl alcohol is not nmajor intermediate, but that a cn t,alysh complex involving cro-tonaldehyde and/or crotyl alcohol is a possible intermediate.)To determine$he action of coinmercial tantala-ail; ca catalyst on ethyl alcohol at350' C . , runs were made in which 92 ncight yo ethyl alcohol W ~ Fpamedover the catalyst at 0.4 liquid hourly ~paot?elocity. A b o u t3.5% acetaldehyde n.ith n o mo r e than D. trace of butadiene m-aFproduced and only slightly more noncondensable gas resulted thanwhen passing 2.78 to 1 feed . Weight recoveries were good butgthyl alcohol in the liquid products amounts .t o only 82% of the$mount fed. (Part of the alcohol consuined was att,ributed t oeth-er format ion.) 'This demonstrates IL definite loss of ethyli~lcohol o by-products independent of the butadiene reaction,

Lilren-ise acetaldehyde alone was passed over the samc ca,talystst 925' C . and 0.4 liquid hourly space velocit,y; no butadiene wasformed-only aldehyde eoadensation products (crotonaldehyde,higher aldehydes, etc .) and unreaeted acet'aldehyde mere re-aovered. Crotonaldehyde mas identified via 2,4dinitrolpheny l-hydrazone. There resulted about 63% recovery of acetaldehydeand a 15y0 conversion to crotonaldehyde. Apparently anequilibrium meil toward th e acetaldehyde side of the crotonalde-hgde formation is approached i n t he absence of ethy l alcohol.

T o test reaction 4 ofthe postulated mechanism, runs were made in which ethylalcohol-crotonaldehyde mixtures were passed over th e com-mercial tantala-silica catalyst a t 350' C. Good yields were ob -Mne d, as shown i n Table VI . It appears from these data that

Ethyl Alcohol QE Acetaldehyde Alone as Peed.

Ethyl ~cohol-CrotonaldehydeFeed.

TABLE I. BOTADIESE ROJI ETHYL~ c o ~ o ~ - C n o ~ALDEHYDE

(Four-hour runs; stan dard tantala-silica catalyst. 850O C: 0.4 l ~ ghourly space velocity ; materia! balance 69 to l 0Oc Li

Pa3

2. 02 . 4 50 . 0364548

50 0 . 8 056 1.1070 1.80moles C d l s X 100_II ___.rnolea CJ feed consumed f moles Cz feed oozsF=dT2-Z Yield % -

crot,onaldchydc is a logical intermediate in the e th y l alcohoprocess. The high conversions indicate rapid reaction of crotonaldehyde n i t h ethyl alcohol; probably t h e cTotonaldehydformation is the slower rate-controlling step of the process. Relative eficiencies of aeet,aldehyde and ethyl alcohol as effected bfeed ratio throw furtlier light on th e interpretat,ion.Feed Ratio and Efficiencies. T h e effect on eEeiencies othe individual reactants, due t,o variation of the initial feed ratio(\Then no adjustment of subsequent ratios of reactants is made) ie h o i ~ nn Tablo VII.

TA%LE VI'I. EFFICIENCIES QP REACTANT5(Four-hour runs: 350' C, ; 0.40 liquid hourly space velocity; at,andartantala-silica catalyst)Initial Partial Yo Efficiency----Iressure, A t m .I -Pnitial ~ c e t - ~ t h y lConversion, yield , Ethy l .keet-Feed Ratm aldehyde Alc ohol Nole % Mole % Alcohol aldehyd e

0.1800.2130.2450,2900.31543.40

0 .2 2 80.660.6430.6280.61213.580,5550.20

28303433403736

5 9626407606248

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92908380696540-The trend toward increasing efficiency of acetaldehyde utiliza-

tion and decreasing efficiency of ethyl alcohol utilization ~v i thn-creasing ethyl dcoholl to accfaldchyde ratio in the initial iced ireadily apparent.

Conclusions. There is t h u s no single optimal feed ratio forYimuItaneously maintaining optimal ethyl alcohol and acetalde-hyde eficiencies. A conipromise must,be struck to att ain optimalover-all. yields. The data obtained by spot-addition of eitherreactant a t varying points of the reaction sy5tem indicate thatLhe o p i h a l ratio in the forezone is different f rom thaL in t,helatter part of the reactor. The so-called optimal feed ratio in thestand ard process is fictitious a n d ineaningless as far as the ratioof partial pressures of reaetm t,s throughout t he reactionconcerned. Th e inlet ratio of 2.75 to 1 has changcd progressivelyto 8 to I at the outlet, and actual partial pressures of th o re-actant s have fallen to relatively l o v values because of dilution byproducts of both thr. main and side reactions. Evidcncc ohh ine dby diluting the feed with mater (4)ndicates that too low partialpressures of reacta,nts decreases the over-all efficiency or yield,meaning that the ratio of formation of products to by-products islowered. Th e predominating reaction in t,he lorepart of thereaction zone leads to depletion of acetaldehyde which can heprofitably counlered by adding aldehyde-rich fced n.bcre a higheroptimal partin! pressure appears t o exist. (Tho sl,anda.rd initialmole fraction of acetaldehyde of 0.223 decreases to 0.08 at themidpoint,) The effect of dilution can he minimized by addition ofeither OP both reactants. Increasing the ethyl alcohol partial prea-sure, hence ethyl alcohol t.oaldehyde ratio, in the hind part of thereaction zone is interpreted as serving tw o purposes: more nearlycompletely reducing the crotonaldehyde to butadiene; and moreefficiently effecting this reduction by offsetting the cont.inua1 de-

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March 1949 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 555crease in partial pressure of the eth yl alcohol while at the sametime decreasing the c onta ct time. Th e first point is possibly oflesser importance; the partial pressure of crotonaldehyde ineffluent from standard runs is about 0.006 to 0.007 atmospherewhereas with add ed ethyl alcohol near the midpoint of the reac-tion zone the corresponding partia l pressure is 0.003 atmosphere.

At this point it seemed expedient to postpone further study ofoptimal partial pressures in various parts of a one-step reactionsystem unti l optimal conditions of each individual reaction hadbeen established.

TWO-STAGE PROCESSFirst Stage. To investigate the role of tantala-silica gel in th e

condensation of acetaldehyde to crotonaldehyde, acetaldehydewithout ethy l alcohol was passed over the commercial tantala-silica catalyst, over a commercial silica gel, and over allraline-setgel prepared in this laboratory (8). The yields of crotonaldehydein these exploratory runs are set forth in Table VIII. Th e silicagel appeared advantag eous in these runs; the alkaline-set gelwas the best.

TABLE III. EFFECT F CATALYSTN ACETALDEHYDE(Three-hour runs; 0. 4 liquid hourly space velocity)

Temp., % Conversion to:c. Catalyst Crotonaldehyde By-productsStandard tantala-sili ca 12 15Standard tantala-silica 16 22Standard tantala-silica 20 302 80 Silica gel (commercial) 22 13280 Silica gel (alkal ine-se t) 30 15350 Silica gel (commercial) 26 16

Second Stage. In an investigation of the second step of thisprocess, effluent from a run with 1 to 1 feed over the commercialtantala-silica catalyst (this first stage employed approximately0.4 liquid hourly space velocity at varying temperatures) wasstripped of any butadiene and diluted with 92 weight % ethylalcohol to make an over-all feed of 2 to 1or 3 to 1 ratio. This re-sul tan t feed then was passed over more of the tantala-silicacatalyst a t 350' C. at 0.5 liquid hourly space velocity in the secondstage. Da ta for three exploratory runs are presented in Table IXfor comparison with the usual standard runs at 350" C .; for230"6. the yield is good (67% against 60% for one-stage process).

TABLEX. COMMERCIAL ANTALA-SILICA ATALYST-TWO-STAGEOPERATION(Becond stage, 350 C. and 0.4 liquid hourly space velocity. first stage,0. 4 liquid hourly space velocity; and 1 to 1 feed ratio)

Ethyl Acet-Temp. for Alcohol aldehyde1st Stage, Over-All Conversion, Ultimate Efficiency, Efficiency,O C. Feed Ratio Mole % Yield, % % %205 3: l 30 62 63 67230 2 : 1 38 67 74 66275 3:l 22 60 58 64

Normal One-Stage Operations3 : l 30 62 51 90. . 2 : l 40 60 59 69

Since a t 205' an d 230' C. in the first stage both a high con-version and yield were realized, it was attempted to accomplishthe two stages more efficiently in one reactor (with tantala-silicacatalyst and 2.75 to 1 eed) by employing a temperature gradient:230" C. at the inlet and 370" C . at the outlet. However, theyields were the same as obtained conventionally with 350" C.throughout the reactor.As alkaline-set silica gel appeared better than the tantala-silica catalyst at 230"C. for the first step (crotonaldehyde forma-tion, Table VI II ) the two-stage operation (Table I X ) was re-peated with this type of silica gel a t 230' C. for the first stage.

TABLEX. PROCEDURE 3-TWO-STAGE OPERATION(Over-all feed ratio 2 to 1. First stage: 1 to 1 feed. 23OO.C . 0.45 liquidhourly space velocity. Second stag e: 3 50 C ' 0:4 liquid 'hourly spaoevelocity; 2% tantala-silica c;t(talyst)cop- Ethyl Acet-version, Yield, Alcohol aldehydeCatalyst in Av. Av. E5ciency, E5ciency,Operation First Stage Mole % Mole % Av. '% Av. %Two-stage Si02 gel (alka-line-set) 36 65 59 79Two-s tage 2% TazOs-SiOp 38 67 74 66One-stage(2: l feed) ........ 40 60 59 69

The effluent was stripped of Cd hydrocarbons plus lighter ma-terial and t hen diluted with 92 weight yoethyl alcohol to give anover-all feed of 2 to 1 ratio for use in th e second stage with thecommercial tantala-silica catalyst a t 350" C. In four runs made,butadiene, in trace quantity, was found in the first stage productof only one run. This finding was in marked c ontra st to resultsfor the commercial tantala-silica catalyst in the low temperaturefirst-stage operation (Table IX ). Average results of these runeare given in T able X in comparison with tantala-silica cataly st ilptwo-stage operations and stand ard operations for 2 to 1 feed ratio.

The se results are considered encouraging in view of t he follow-ing facts: the first-stage operation was carried ou t at th e notnecessarily optimal temp eratur e of 230 O C. ; practically no searchwas made for a better catalyst for formation of crotonaldehyde;and the 2 to 1over-all feed ratio is not expected t o be the opitmalfeed rat io (Table VII) . Th e reversal of order of efficiency of theethyl alcohol and acetaldehyde consumptions by use of silica gelcatalyst is worthy of further study.

The extent of carbonization of the standard catalyst whenpassing 1 to 1 feed a t approximately 0.4 liquid hourly spacevelocity at a temperature of 230" to 240' C. was not found pro-hibitive. In a tes t comprising a 40-hour period of continuousoperation the silica gel catalyst was still white in contrast to thedarker color of t he commercial catalyst afte r 40 hours in con-ventional operation. However, burn-off of the silica gel didindicate about one third more high molecular weight materialthan with the commercial catalyst (2.2%against 1.6% apparentcarbon).

Furthe r work on a two-stage process was curtailed because of 8change in the program.

ACKNOWLEDGMENTThe authors wish t o acknowledge the aid of J. Voss in c,on-

struction of the reactor, of J. Lieblich in operation of th e a pparatus, of J. A. Hinckley, J. F. hliller, L. J . Lohr, M . Jaskowski,and co-workers in analysis of t he products, of G. H. Young andB. B. Corson in advice and guidance, an d of t he Office of RubberReserve in obtaining release of this account for publication.

LITERATURE CITED(1) Corson, B. B., and Cerveny, W . J., IND.ENO. EEM.,ANAL. D,,(2) Corson, B. B., Stahly, E. E., Jones, H. E. , and Bishop, H. I o ,14,

899 (1942).IND.ENQ.CHEM.,n press.(3) Elving, P. J., and Warshowsky, B., Anal. Chem., 19, 1008 (1947).(4) Jones, H. E. , Stahly. E. E., and Corson. B. B.. J . Am . Chem.SOC.,n press.(6) Quattlebaum, W. M., Toussaint, W . J., and Dunn, J . T.,Ib i d . , 69, 593, (1947).(6) Rubber Reserve Company, Analytical Method L.M.2.1.1.7 (or2.1.1.9); Shepherd, Thomas, Schuhmann, and Dibeler,J . Research Natl. Bur.Standards, 39 , 435 (1947).

(7 ) Toussaint, W. J., Dunn, J. T. , and Jackson, D. R., IND. NG.CHEM., 9, 120 (1947).(8) Welling, Stahly, Jones, and Corson, Ib i d . , in press.RECEIVED ovember 19, 1947. A contribution of the multiple industrialfellowship of the Reconstruction Finance Corporat ion, Office of RubberReserve, published by permission of the latter.