Condensation of Acetylene b-y Molten Salts J
J
PHILIP C. JOHNSON' .4YD SHERLOCK SWdNiV. JR. Vnicersity of Illinois, Urbar-Lu,Ill.
A wetted-wall column with molten salt and gas i n direct contact passing countercurrent to each other proved successful in controlling the highly exothermic reactions involved i n the condensation of acetylene to aromatic hydrocarbon liquids. Numerous salt systems, all of them halides, were investigated over a temperature range of 530" to 625" C. Both pure acetylene and acetylene-ethylene mixtures were studied. Molten systems containing zinc chloride were found to catalyze the reaction as well as to
s e n e as media for temperature control. Distillation of the products obtained under varying conditions yielded nearly identical fractions in every case. These fractionq, furthermore, were similar to those obtained by previous investigators using higher reaction temperatures and carbon catalysts. The results indicate that, in certain cases, fused salt systems could replace to advantage the heat exchange tubes commonly found i n commercial catalyst beds.
A
temperature, the equilibrium lies 99.5% in favor of benzene at 1000°C. Equilibrium is not, therefore, a factor in the choice of operating conditions. The only catalyst found so far for the high temperature polymerization is carbon. It is of particular significance that, in all experiments, heavy layers of carbon are deposited on the socalled catalysts. That it is this deposit of carbon which is the true catalyst has been suggested by both Tiede and Jenisch (20) and Iiovache and Tricot ( I O ) . Tiede and Jenisch, using several different contact material3 with a very carefully controlled temperature of 610" C., obtained oil yields which were identical in amount and gave identical fractions upon distillation. Identical yields were also obtained at a carefully controlled temperature of 600" C. with another series of contact materials. However, similar preliminary experiments in rshich the control was 600" C. * 10% showed erratic results for this same series of materials. Furthermore, these results were not reproducible. This lack of agreement, which was due to temperature alone, could easily explain the differences in apparently similar experiments reported in the literature by different investigators. The actual contact material was probably the same in every case-an adherent type of carbon covering the tube packing. K i t h these facts in mind, the authors considered that a molten salt bath, because of several unique properties, would be particularly desirable as a medium for carrying out this reaction.
STUDY of the polymerization of acetylene was undertaken because of a pressing need for benzene in the war effort The following pertinent conclusions concerning this reaction were reached from a comprehensive survey of the literature. The most suitable reaction temperature lies between GOO700' C., the slow rate of reaction belop 600' C. setting the lower limit, and the spontaneous decomposition of acetylene t o carbon and hydrogen with rapid propagation of P flame setting the upper limit. A series of condensation plus hydrogenation reactions takes place between acetylene and hydrogen a t temperatures up to 350' C. (5, 6). However, the products are principally of a nonaromatic nature, so that the results obtained in this temperature range are not comparable t o those obtained a t higher temperatures. The pnncipal reactions involved are of an extremely exothermic nature. 3C2H2(g) +C G H B ( ~ )
ATIux--~Mo c =
- 1 q O O O g -cal. /$.-mole CBH6
3C,H,(g)
+6C + 3EIz
1H6W--700~ C. = - 162,000 g -tal /3 g -moles C,B.
It is believed t h a t this high heat of reartion is the cause of most of the difficulties encountered in the work carried out so far. Local overheating in the catalyst bed certainly occurs. Lewes (12) actually measured a localized overheating of about' 200" C. in passing acetylene through a silica tube a t 800" C. This local overlieating has two serious effects. It promotes the spontaneous decomposition of acetylene to carbon and hydrogen and favors the formation of the higher polymers. Once started, this decomposition is difficult to control because the heat liberated raises the surrounding gas to decomposition temperature, and, as expressed by several investigators (2, g l ) , the light fluffy carbon which is the main product of decomposit,ion actually catalyzes the decomposition of more acetylene. BerI and Hofmann (2) were, however, able to get a 98.8% yield of liquids by removing this fluffy carbon with water vapor as fast as i t was formed. The water vapor did not affect the layer of graphitic carbon serving as catalyst in their experiments. The free energy change of the reaction 3C1H2 --j CaHs(g) is very negative (18) and, although it decreases n-ith a rise in
FEATURES OF AIOLTEN SALT BATH
lloltcn salts have a high specific heat which affords excellent temperature control. Although data on specific heats of molten salts are not plentiful, an average value of 0.3 g.-cal./gram/" C'. is a good approximation. With a density of 2 grams/cc. the heat capacity of 1 cc. of molten salt is equivalent t o about 3000 cc. of acetylene at GOO" C. The composition of a salt mixture can be varied over a wide range by adding various amounts of fresh salt to a n existing mixture. This eliminates the necessity of repeating a tedious catalyst preparation for each of a series of catalysts being tested. Here the catalyst, preparation is not an a r t where physical structure plays an important role, since all catalysts are prepared by mixing quantities of anhydrous salts and melting them t o a liquid bath. This bath is always reproducible. The molten salt can be circulated through a column and any fluffy carbon which has been formed will be continually washed from it. I n this manner the decomposition of acetylene catalyzed by this t,gpc of carbon can be kept at a minimum. Carbon re-
Present address, Carbide and Carhon Chemicals Corporation, South Charleston, W ,Va.
990
October, 1946
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
moval will also prevent the column from becoming blocked, as is the case with stationary catalvst, beds. The catalyqt d l be the salt rather than the carbon-covered packing material, as in stationary catalyst heds. The carbon \\-aslied from the column rises to the surface af the salt reservoir. By pumping carbon-free salt from the bottom of the reservoir, the column is a l x i y s n e t with pure molten salt.
99 1 WELL
SPHERICAL
APPARATUS
; i,series of
preliminary experiments to determine possible actir-it>-of various salt tctms was curied out i n a stoppercd 38 X 300 nim. test tube equipped with inlet and exit gas tuhes. The test tube v,-m iriinic~racdin a ralliant coil furnace and was half full of molten salt (ahour 200 gram>). Acetylene was admitted through a glass inlet tube to the bottom of the bath. The rcitct ion products were passed through ice and dry ice-isopropanol traps to remove the condensabies. Snrnplea of the noncondeiisable gases n-ere analyzed for unreaeted acetylene, unsaturated and saturated hydrocarbons, and hydrogen. From the preliminary studies it x a s decided definitely that the time of cuntact necessary for appreciable con Riderably exceed that attainable by allowing a gas bubhle t o rise through a layer of liquid. Consequently, a column n-as devised in which the gas arid liquid salt puaed coiiutercurreiit t o each other (Figure 1). In this systeni time of contact %\-ase a d y controlled, since i t is a function of rate of gas input and volume of the column. The eolunin was made by putring tn-enty-five pairs of indentations into opposite sides of a 25-mm, Pyrcx tube, the indentations covering a 50-em. section of the tube. The faces of the indentations were designed so that all surfaces could be mashed continually by the flowing salt t o prevent dcposition of carbon. The molten salt \vas circulated by a bellows pump. The salt was prevented from entering the bellows by an air bulb placed i n the line between the bellows and the salt reservoir. On the buction stroke the air was drawn from the bulb into the bellon-s x-liile the salt entered the bulb. On the compression stroke the air was forced from the bellows back into the bulb and the salt, in turn, n-as forced u p into the lines leading to the top of the column. The valve system, also shown in Figure 1, was made of 6-nim. Pyrex rod enlarged to a 9-mm. ball on one end. The valves fitted into a seat made by shrinking 14-mm. tubing t o approximately 6 mm. Both the hall surface of the valve and the seat were ground with carborundum dust and oil to give a good seal. Very little difficulty \vas encountered once the pump was in operation but it ~ i i often s difficult to start. The products leaving the top of the column turned, upon cooling, to a cloud of small liquid drops in an excess of noncondensable gases. The drops were so small that they were impossible to remove in a 'condenser, in traps, or even by stripping through an oil bath. .4 combination water-cooled condenser and Cottrell precipitator \\-as, therefore, set up. The design of the precipitator n-as similar t o that used by Billman and Cash (5). I n addition to the condenser-precipitator, the exit gases passed through ice and dry ice-isopropanol traps. The pulsation of the salt bath caused by the pump, and the slight increase in pressure drop through the column as the run continued, made it necessary to use a flow system which would give a constant rate regardless of the changes in downstream pressure. Such a flow was obtained by using nozzles with an upstream pressure so great t h a t the linear velocity of the gas through the throat of the nozzle reached the acoustic velocity while the pressure in the throat still exceeded the dov,mstream pressure. L-nder such conditions the flow rate of the gas is a function of upstream pressure and is entirely independent of the downstream pressure so long as this pressure does not exceed t h a t 4 series of nozzles was made in the t'hroat of the nozzle (19). . by collapsing 8-mm. tubing and then calibrating. By using up-
SECTlON SHOWING INDENTATIONS
2 2 CM.
Figure 1.
Reaction Column
stream pressures of 30 to 60 pounds gage, constant flow mteswerr maintained regardless of the changes in pressure in the reaction system. PROCEDURE
Figure 2 shows the complete arrangement of apparatus as used in actual operation. A new column and salt pump were used for each experiment. The purification train consisted of 5.25y0 sodium hypochlorite solution, 50y0 sodium hydroxide solution, 75% by weight sulfuric acid, and a U-tube containing calcium chloride. The salt reservoir was a 64 X 300 mm. test tube. Radiant coil furnaces surrounded both the column and the salt reservoir. The section between the two furnaces was heated by means of a loosely wrapped coil of asbestos-covered resistance wire. The gas leaving the dry ice trap passed through a three-way stopcock which permitted it to exhaust to an aspirator or to enter a sample buret. The total exhaust flow rate was measured a t hourly intervals by means of this buret, and the sample was transferied to an Orsat apparatus for analysis. Experiments were carried out in the following manner: First the column volume was determined by filling it with water and measuring the amount coming from the reaction zone on draining. The column was dried and placed in the furnace. The salt reservoir was lowered and filled Kith salt. Both column and salt were heated to approximately 525' C. During the heating period the flow rate was calculated, based on contact time, column volume, and reaction temperature. The proper nozzle was selected and the gage pressure adjusted so that the desired flow
INDUSTRIAL AND ENGINEERING CHEMISTRY
992
of acetylene, determined by actual measurements, !T-a? obtained. The reservoir was then raised around the column base until it touched the gas entrance tube. The resistance coil was wounJ around the exposed section and brought UP to temperature. The salt Pump started and adjusted to give its maximum flow of aPPoximateb' 250 CC. of salt Per minute. The column was flushed with natural gas and then acetylene admitted to the colurn~i. During Ihe next 20 minutes the column and salt Kere brought to the desired experiment temperature. At' the end of this period (liquid was usually just beginning to drop into the ice bath), the time clock was started. During the next 10 hours the flow rate of the exit gas vas taken every hour and the sample of gas obtained was analyzed. At the conclusion of the run the salt Pump and furnaces 4 w e shut off, the acetvlene was disconnected, and the apparatus was flushed with natural gas. The inlet acetylene rate was checked again, and an arithmetical mean of the two values m s used to compute the total f l o to ~ tile column. The liquid product was sealed in a samplc bottle for later distillation. DISTILLATION AND ANALYSIS OF PRODUCTS
Hourly analyses of the waste gases were made during the course of a n experiment. The samples were analyzed for acetylene and unsaturated hydrocarbons. T h e acetylene absorbent was a solution of 20 grams of mercuric cyanide in 100 cc. of 2 sodium hydroxide. This solution absorbs acetylene without affecting ethylene and other unsaturated hydrocarbons ( I ) . The unsaturated hydrocarbons, mainly ethylene, were absorbed in luniiny sulfuric acid. The remaining gases consisted almost entirely of hydrogen and saturated hydrocarbons. All waste gases remaining after the acetylene was removed were designated as inerts. Periodic analyses of the acetylene and ethylene used showed t h t each contained less than 1% of inert gas. In all calculations, G therefore, these gases were assumed to be 1 0 0 ~pure. The liquid product was fractionated in a column of small liquid holdup. The column vas made by wrapping a 75-cm. length of a/le-inch rod with a spiral of L:s-inch copper tubing. The individual turns of tubing were wound on '/4-inch centers along the entire length of the rod. Thc rod and spiral were then forced into a 14-mm. Pyrex tube. The column was jacketed with a 19-mm. Pyrex tube which was wound with resistance wire. The reflux rate was controlled by the poxer input to this coil. All distillations were carried out a t atmospheric pressure which was approximately 750 mm. Before distillation the specific gravity of the product x a s determined by means of a Westphal balance.
0
n
Vol. 38, No. 10
DISCUSSIOS OF RESULTS
The of the preliminary experiments using the 3-incll layer of molten salt in a test t,ube are given ill Table 1, Althoug)l contact. bet%-een salt and gas was admittedly poor, enough contact resulted to give small amounts of liquid condensation product when salts possessing catalyt,ic activity xvere used. All salt bath conlpositions in Table I are given in mole per cent unless other\vise stated and, in cases TThere the coIlstitution diagram is knolvn, t,he reference is given. The melting points are those at \ylijch a single liquid phase exists having the samp compo;ition as the solid salts making up the bath. -411 chemicals us!:tl were of reagent grade. Studies covering the low melting salts and their binary mixtures shoned that 0111szinc chloride appears to have any catalytic activity for the forlnatiorl of liquid products from acetylene. salt catalyzed the dccompositiol, H ~ , ~in ~the~pure , ~state ~ this , to carbon and hydrogen, ~~~~~~i i,.~lo used zinc chloride on c~larcoal and pumice to catalyze this Same reaction, ohservetl considerable decomposition. All salts except sodium chloride were unsatisfactory as diluents. With SOYG sodium chloride its activity for the decomposition of acetylene, although depressed, was still great. However, the melting point of baths with great,er amounts of sodium chloride were too high for use. Ternary systems \yere next investigated in order to reduce the concentration of zinc chloride still further. The first bat,h, a eutectic of sodium chloride, potassium chloride, and zinc chloride, gave great promis. and \vas used during most of the subsequent work. The two experiments in Table I show t h a t this bath possessed considerable catalytic activity. However, the contact !vas poor and eventually the tube became blocked with carbon. -1wetted wall column was used, therefore, to improve contact and to remove carbon as it mas formed. Table I1 presents the results using pure acetylene gas with various salts in the column. The definitions of the terms used are
Figure 2. Complete Apparatus Assembly
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1946
993
EXPERIMENTS WITH ACE:YLEKE AS INLET Gaa TABLE I. RESULTSOF PRELIMINARY Expt. NO. 2
Salt B a t h
dlIs 8 1 5 . l l B r r 1 9 % NaBr (binary eutectic) 50% .UCIs-50%
SaCl
Bath hJ.P., C. 191
T e m p . of Expt.,
c.
Duration of Expt., Hr. 1
Waste Gas CtHh
Liquid Formation None
Carbon Formation None
1
90
10*250
G H z H I satd.
None
Excessive amounts
Comment N o activity Extremely active for decompn. of CzH2, even at
23
250
250-500
CzHi
Kone
None
90 activity, low vapor
210-250
hyd;oc&hons
Trace
Trace Excessive amounts Considerable amounts Considerable amounts
24.7% c o n v e r s i o n t o liquid
124
13&150
3
CiHz
Sone
Kone
4
318
400-450
1
None
ZnClz
5
318
510
1
CzHz, Hz,s a t d . hydrocarbons CzHz, Hz, satd. hydrocarbons
Excessive amounts Excessive h u t less than a t
ZnCh
6
318
600
1
CzH2, Hz, satd. hydrocarbons
4 g.
70 wt. % ZnClz-30 wt. % FeCll (briars eutectic) 50% ZnClz-50(7o CulClz
3
214
250-400
1
Trace
7
500
0.25
1 . 5 g.
cusc12
8
422
500
...
CZHZ.H z , satd. hydrocarbons CZHZ,H z , satd. hydrocarbons C Z H ZHs. , satd. hydrocarbons
Trace
350
None
Excessive amounts Excessive amounts
5fl% ZnClz-50% NaCl
10
350
5'40
3.5
CzHz, Hz,satd hydrocarbons
11.lg.
Considerable amounts
CzHa, H2, s a t d . hydrocarbons CzHz, Hz, satd. hydrocarbons CzHz Hz satd hyd;ocLrhon$ CzHz, Hz, satd. hydrocarbons CzHz. Ha, s a t d . hydrocarbons
Trace
Trace
Trace
Trace
PbCli
12
501
550
0.5
5% ZnC12-95% PbClz
10
490
600
1.3
50% ZnC12-50% PbClz
18
375
500
1.5
90% ZnCls-lO% PbClz
19
290
550
4.0
12.5% NaC1-59.0% IiCl -28.5% ZnClz (ternary eutectic 12.570 h-aC1-59.0% KCl -28.5% ZnCl2 iternarv eutectcc)
24
402
550
3.5
25
402
600
5.0
given at the end of the article. The results obtained with the different baths will be discussed separately. SODIUM CHLORIDE-POTASSIUM CHLORIDE-ZINC SYSTEM
CHLORIDE
The eutectic bath of 12.5% sodium chIoride-59.0% potassium chloride-28.5yo zinc chloride (8) showed the most favorable catalytic activity of all systems investigated. The bath melts at 402' C. to a water-white, nonviscous liquid which can be pumped with ease. I t s specific gravity varies from 1.95 a t 500" C. to 1.85 a t 600" C. The bath is stable to the atmosphere up to 625" C., but above this temperature fumes of zinc chloride appear. The first seven experiments in Table I1 n-ere carried out with this bath. Let us consider first the conversion to liquid product obtained in a single pass. The data are summarized in Figure 3, where curves are given for both the 10- and 15-serond contact. For the 10-second contact the conversion increases from 12% at 550" C. to 54% at 625' C.; with 15-second contact a 48% conversion a t 550" C. is increased only 7% at 600" C. The slight increase in a n already high conversion by a more drastic condition may be explained by Figure 4,which shows the concentration of acetylene in the exit gases for these experiments. For the 15second contact the acetylene in the waste gas fell only from 74 to 677,, although the temperature was increased from 550" to 600" C. Apparently the diluent effects of the 30% inert gases after 50% conversion, plus the additional diluent effect of the vaporized reaction product, are sufficient t o retard further condensation. This decreased reaction at lower acetylene concentrat'ions eliminates the possibility of successful application of this catalyst to gases containing only small amounts of acetylene. The mean value for the yield of liquid product for experiments 28-33 was found to be 68%. Any divergence from this value shows n o consistent correlation with either contact time or temperature. .4pparently 68% of the acetylene disappearing ap-
CZHI,HI, s a t d . hydrocarbons
c,.
Small amounts 7.0g.
21
ZnClz
58.9% . i l C 1 ~ - ' 4 1 , 1S~a c 1
1000
pressure of AlClr, even a t 550' C. No activity, high vapor pressure of AlCls Carbon blocked reaction tuhe: bath viscous Bath appears more EOtive for liquid formation a t higher temp. Bath active for formation of liquid, too active in decompn. of acetylene Bath unstable, gave off FeCla or FeCL fumes Bath too active in decompn. of acetylene Carbon blocked apparstus immediately, too ECtive 2 ~ conversion 7 ~ t o liquid, hath definitely active for liquid forniation S o t active, ossible dilue n t for Kot active, free metal in bottom of bath K o t active, free metal in hottom of bath Too active in decompn. of acetylene 23.2% c o n v e r s i o n t o liquid
Heavy cloud of drops
ll.6g.
450' C.
Excessive amounts
,
~n81z
peared as liquid product. Combustion analyses of the inert waste gas showed that a n additional 207, of the reacted acetylene was converted to hydrogen and saturated hydrocarbons. The remaining 12% was lost, probably by solution in the salt bath, with subsequent liberation t o the atmosphere. A summary of the data for experiments 26-33 indicates t h a t the yields of products are independent of ,operating conditiona and that, with a contact time of 15 seconds, the conversons are affected only slightly by changes of temperature within the range investigated. E F F E C T O F ZINC C H L O R I D E COXCENTRATIOX
The possibility of changing results by varying the concentration of zinc chloride has been investigated. For this work a binary eutectic of 58y0 lithium chloride-42% potassium chloride having a melting point of 364" C. was used. T o this bath were added varying amounts of zinc chloride. The ternary systems formed a single liquid phase at the temperatures of the experiments. The results are presented in Table I1 under experiments 36-39. The results with these baths were not particularly successful. The lOy0 zinc chloride bath exhibited low activity a t 550" C.19.1% conversion compared to 46.7% conversion under the same conditions using the ternary eutectic. The bath with 2.5% zinc chloride gave off strong fumes of zinc chloride, and gave low yields of liquid product and excessive amounts of carbon and fixed gases. This bath was too active for the decomposition of acetylene to carbon and hydrogen. The unfavorable results obtained with these two baths indicate t h a t other factors besides the zinc chloride content are important in the bath composition. I n the sodium chloride-potassium chloride-zinc chloride eutectic, the sodium chloride and potassium chloride are not serving merely as diluents. The favorable catalytic activity of this bath may be due to actual compounds of these inorganic salts.
INDUSTRIAL AND ENGINEERING CHEMISTRY
994
Erpt. so.
Temp.
c.
Time of Contact, Sec.
Inlet Gas Kate, Cc., Sec.
Expt. Duration, Hr.
W t . of Liquid, G.
Mean Concn.
W t . of Carbon, G.
C?H?in
Waste,
'5
% CzHp Disap-
pearing
yo Conversion t o Liquid
Vol. 38, No. 10
FlC Yield of liquid
C c . Inerts/ G . Liquid1 c c . iC?lI? c;. Di-npprunrigj Curbon
Catalyst, 1 2 . 5 % NaCl-5Ll.070 KCl-28.5% ZnClr 26 30
625 350 5i5 600
8 85 10 0 10.0 10 0 130 15.0 lj.0
5 4 4 4
36 37
550
15 0
600
15.0
3 22 3 01
38 39
550 600
1.i.n 15.0
31: 3 03
,5 0 1 5
34
550 600
15.0 15.0
3,50
5.0
3.18
1,5c
29 2s 32 31 33
530 575
GOO
6.5 4G 29 63 3 0 3 1-1 2 83
12 5 10 0 10 0 10 25 10 0 9 "5 8.25
3; 9 4-1 3 fi6 2
105 58 63 53
6
1 5 4.1
08 7 93 5 83 0
11 .i
3 2 4
8 8 8 2 5 9 5 7
039 i4 68.2 60.3
Catalyst, Binary Eutectic of 5S% LiCl-I?C, KC1 with 5 0 5 0
12 9 33 6
85 2 73.4
1.0 2 4
,.
32 0 33 G 28.G
p
71 5
76 5
12 8 23 8 27 0
1"
66 z 63 0 68 8 60 G9.i 71 6
0 0270 0 128 0.14i 0 ltjl 0 16.5 0.1.57 0 136
8 4 10 8 i 8 12 0 7 1 10 i
72 5 72.5
0 14,; 0 133
I? 9 !4 0
29.2
51 3
0 216
10
12.2 35.6
18.4 56 4
0 . 12.5
8U
0.129
89
i; ; 520 54.8
40
0
9 i
ZnClz Added
3.2 73.8
19 1
53.3
Catalybr, Binary Eutectic of 58CA LiCl-4'2% KC1 with 2 5 5 ZnClz Added 19 4 10.0
7: 8
4.9
57.0
b
Catalyst, 24.0% SaCl-43.070 KC1-33.0r7, CdClz
35
8 9 7.1
96.0 81.8
1.0 0.8
2i.2
63.3
a T h e conversion and yield of liquid product are t o o low i n this experiment because no Cottrell precipirator was used and a large amount of t h e liquiil
e*-
ea ed in the form of a cloud of small droplets.
f
The Cottrell precipitator was used in all subsequent experiments. T h e tube hecame hlocked with carbon after 1 . 5 hours and the erperiinent was ended. One of the furnaces burned out after 1.5 hours of opeiation, and the experiment was ended.
SODIUM CHLORIDE-POTASSIUM CHLORIDE-CAD3TIU31 CHLORIDE SYSTEM
Since zinc chloride exhibited such favorable catalytic activity, it n-as believed that other elements in Group I1 of the periodic system might be active as well. Therefore, a bath of somewhat aimilar composition to the zinc chloride ternary eutectic, but in which the zinc chloride w ~ replaced s by cadmium chloride, was used. This bath, a ternary eutectic of 24.073 sodium chloride43y0 potassium chIoride-33,0% cadmium chloride (a), has a melting point of 386" C. The molten bath was a clear, nonviscous liquid xvith specific gravities of 2.32 a t 500" C. and 2.2-1 at 600" C. The molten salt did not wet the walls of the column but acted like water flowing down a n oily glass tuhe. Two experiments '17-ere carried out x i t h 15-second contact a t 650" and 600" C. The results are given in Table I1 and plotted in Figure 3. The conversions and yields of liquid product were much lower than those obtained using tlie ternary zinc chloride eutectic under similar conditions. The bath had little if any catalytic activity. AIost of the product probably resulted from contact hetwcrn the gas and carbon dcposited on the column walls. The reaction wa3 probably catalyzed by carbon n-ith the added feature of close temperature control by means of molten salt
ylene n-ith itself increases more rapidly n it11 temperatiire than the rate of reaction of acetylene with ethylene. 60
1
50. Y
9 40. J
0
Z
0
30.
II: W
t
20.
v a\"
10-
5 50
575
600
625
ACETYLENE DILUTED WITH ETHYLENE
The possibility that the ternary catalyst 12.5n0 sodium chloride--59.0% potassium chloride-28.5% zinc chloride would act 011 ethylene or mixtures of acetylene plus et liyleiie was consitlcrcd next. The results are presented in Table 111. .4n experiment (not shown here) was carried o u t with pure ethylene with 30-second contact a t GOO" C. =iitc,r 30 minutes of operation the exit gas shoxed 7.5T0inerts, but no liquid product or carbon appeared. The bath vas not active enough to condense pure ethylene. Experiments 41 and 42 viere carried out x i t h I Z - m o n d contact time and a gas containing 25% ethylene and 75y0 acetylene. The conversions of 18% and 41 % arc below those using pure acctylene, but the main point of interest is that slightly o v e r . 2 0 5 of the ethylene entering the column disappeared. The ratio of acetylene t o ethylene disappearing varies considerably x i t h temperature; i t is 4.3 to 1 a t 550" C. and 10.3 t o 1 a t 600" C. These experiments indicate t h a t the rate of condensatiorl of acet-
TEMPERATURE, OC.
Figure 3. Conversion of .icetyleue to Liquid on a Single Pass (aboce) and Amount of Acetylene in T a s t e Gnseh (below) 3
12.5% NaCl-59.070 KC1-28.5% ZnCln a n d 10-second contact 0 12.5% NaC1-59.070 KC1-28.570 ZnCli and 15-second contact 24.070 NaC1-43.0~0KCl-33.0vo CdCli a n d 15-second contact
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1946
995
-
TABLE111. RESULTS USINGACETYLESE-ETHYLENE ~ I I X T C RIS ES RE.ICTIOS CoLunm (Catalyst, 12.5% SaC1-59.0% KC1-28.5% ZnClr) Cc. Inerts/ Time of Inlet con- GasInlet Rates, Expt. Temp., Gas, % tact Cc./Sec. SO. 0 C . C*H* C ~ I I ~~ e c . ' C ~ H , CJG 41 0.78 15.0 2.41 25 550 42 600 2a 15.0 2.28 0.69 ,a 1.52 43 GO0 50 50 15.0 1.52
2;
%lean Conen. 2 :- Liquid, wt. of Wt. of in Waste tion, carbon, Gas, "0
Hr. 5.0
6.0 12.0
G.
G.
12.0 31.4 44.1
1.3 3.3 -1.3
Because of the low conversion n-ith 76% acetylene at 550" C., a singlca i,xprriment with a 50% gas was carried out a t 600" C. and l5-second contact time. The conversion fell from 41%, obtained with the 75% gas, t o 28% for the 50% gas. Onlg 18% of the ethylene was used compared t o 627, of the acetylene, a 3.5 to 1 ratio of acetylene to ethylene. It might be expected that the character of the product in these experiments would differ from that of previous products because of the reaction of appreciable quantities of ethylene. Kozlov and Fedoseev (11) showed that butadiene was formed when acetylene and ethylene were allowed to pass over certain catalysts, including zinc chloride. DISTILLATION OF PRODUCTS
,411 liquid products were fractionated in the column described and the results are given in Table IV. About 1% of phenyl-& naphthylamine was added to each sample before distillation to prevent possible polymerization of styrene or other similar hydrocarbons. The first drop appeared in the receiver a t a vapor tempernture of 40" C. The first fraction was taken off to a final vapor temperature of 90" C. Upon redistillation of some of this material, a fraction representing over 90% of the charge came over between 80-81 C. This fraction had a refractive index of 1.5000 a t 20' C. This compares favorably with the literature refractive index of 1.5014 a t 20" C. given for benzene; therefore the first fraction in these distillations t i l l be called the benzene fraction in the folloving discussion. Only about 1057, of the charge distilled over in the interval 90-150" C.; this fraction probably coiisisted of toluene and xylenes. The fraction from 150-225O C . started to distill over as a liquid; then considerable quasititicbs of a nhite solid, and finally more liquid, appeared.
~70
%
%
cc.
C2H2 C2H4 ConverDis;ip- Disap- sion to C ~ H * c~?& pearing pearing Liquid 20.5 17.6 28.7 70.5 25.4 41.4 23.2 365 (1.9 44.2 2: 8 17.7 62 0 28.4 61.3
+
% (c~H~ G. Yield CZ%) Liquid/ of DisipG. Liquid pearing Carbon 9.2 663 0.118 9.5 69.0 0155 10.3 0.173 71.5
hIolee CtHi Disappearing/ MO~S
CZH4 Disappearing 4.3 10.3 3.5
The solid was identified as naphthalene by its odor and its melting point of 80-81 ' C. It composed roughly half of this fraction. Slight evolution of a noncondensable gas as the vapor tcmperature approached 225' C. gave evidence of cracking of the residue. This residue was fluid a t the still temperature when the distillation stopped, but it set to 8 firm tar upon cooling. Further identification of the individual compounds in the fractions was not attempted. An indication of the types of compounds present may be found in a series of papers by Xeyer (14-17). The product of experiment, 26, in which no Cottrell precipitator was used, showed a small benzene fraction. This was t o be expected and these results are not included in the following discussion. Considering experiments 28-33, the specific gravity of the product increased both with temperature and time of contact. A similar increase is observed in the amounts of the tar fraction. I n both cases, the increase is more noticeable with the 10-second contact time. T o counter this increase in tar a corresponding decrease in the benzene and naphthalene fractions occurs. Although these trends are present, the variation in any fractions over the entire range of contact time and temperature is negligible for all practical purposes. It may therefore be stated that, in addition to the yield, the composition of the liquid is also constant throughout. The fractionation is roughly To 90' C . 50- 150' oC. 150-225 C. Residue
40% 105 20% 30%
The product obtained with the 10 and 25% zinc chloride systems separated into fractions similar in size t o those of the ot,her
TABLE IV. DISTILLATION ANALYSISOF LIQTIDPRODUCT Conditions Expt. KO,
c2h2
c-
c:h
c.
Sec.
(Pressure, 750 rnrn.; crude gravities a t 20') Weight Wt. yo in Boiling Range: Liquid Specific Product, Gravity, To 90125130Grams Crude 90' C. 125' C. 150' C. 225' C.
Residue, Loss, ICt. $3 Kt. %
Comment
Catalyst, 12.57, XaCl-5Q.0% KC1-28.5% ZnClx 26 30 28 29 32 31 33
100 100 103
..
100 100 100 100
,.
530 575 GOO 625
, , , , , ,
GOO
38.37
100
...
550-600
15
38,39
100
,.
550-600
15
,. ,,
?2o
a,a
8 85 100 10 0 10.0 15.0 15.0 15.0
28.2 38.6 57.5 99.1 51.7 55.5 48.7
0.952 0.959 0.964 0974 0973 0.979 0.580
30.8 42.5 38.6 38.2 35.2 38.0 36.6
1.8 3.1 3.5 6.9 5.8 5.4 5.8
10.3 3.1 4.7 4.0 2.3 2 9 3.3
19.8 22.8 21.2 17.4 20.5 21.2 15.9
31.6 22.0 29.6 33.4 31.8 32.2 33.4
5.7
6.5 2.4 0,l 1.4 0.3 1.0
No Cottrell precipitator
..............
............... ............... ................. ................
...............
Catalyst, Binary Eutectic of 58% LiC1-42% IiCl with l o g Z n C h Added 40.1
0.566
39.4
6.0
19.7
2.7
27.4
4.8
........
Catalyst, Binary Eutectic of 58% LiCl-42% KCl with 2 5 7 , ZnCls Added 24.4
0.555
36.0
4.5
7.0
20.8
..
..
36.4
10.9
28.6 25.2
2.3 4.2
Residue lo3t
Catalyst, 24% NaC1-43% I
