Vinyl Chloride from Dilute Acetylene Gases R. EMERSON LYNN, JR.:
AND
KENNETH A. KOBE
hiversify of Texas, Aurtin, rex.
M
ONOMERIC vinyl chloride, although not of itself a useful end product, mmes as a building block far 8 group of plastic resins which are volume leaders in the plastic industry. The annual production of the monomer has grown from 70,000,000 pounds in 1945 t o over 280,000,000 pounds in 1950, and a further growth to 600,000,000 pounds annually has been forecast during the next 5 years (11). Polyvinyl chloride resins are ueed to make such items as tahlecloths, shower curtains, electrical insulation, shoes, phonograph records, food containers, and upholstery material. I n 1951, the industry produced 315,000,000 pounds of polyvinyl chloride plastica valued at $117,000,000 (6). I n addition t o polymerization with itself, vinyl chloride is copolymerbed with many other materials t o give products whose properties vary from elastomeric to rigid and permit fabrication into film, fibers, sheeting, and moldings. Thus, a whole host of products axe available from either vinyl chloride or its copolymers. The forecast increased demand for vinyl chloride resins necessarily calls for an increase in the production of the monomer. At present, approximately 55% of the monomer is produced by the addition of hydrogen chloride t o acetylene and the balance by the splitting off of hydrogen chloride from ethylene dichloride. Increased Produdion of Acetylene from Natural Gas and Hydrocarbons Is Required
Acetylene required for the increased vinyl chloride production will be produced largely from natural gas or other hydrocarbons rather than from calcium carbide. Three proceaees are now available for licensing (Wulff, Sachse, and Schoch processes) which utilize hydrocarbons as the raw material. WuW Process. The Wulff process is a regenerative thermal decomposition process in which a checker-brick furnace is heated to cracking temperature by the combustion of a hydrocarbon gas with air. The air supply is discontinued and the gas is cracked thermally to yield acetylene, other hydrocarbons, csrhon monoxide, and carbon dioxide. Two furnaces are operated as a unit so that one is on the heating cycle while the other is producing acetylene. The Wulff process wm recently described by Gordon Bixler and C. W. Coberly in INDUSTRIAL AND ENGINEERINQ CHEMISTRY, 45, 2596 (1953). Sachse Process. The Sachse, or partial combustion, process is also a thermal decomposition procesa which produces acetylene by burning a portion of the feed stock with oxygen to obtain cracking temperatures. Carbon monoxide, hydrogen, and hydroc&bons other than acetylene are also produced.schoch Process. ~h~ schoch disharge prooess (88) supplies energy to the natural gas in the form Of electrical energy rather than thermal energy. The maximum temperature is aPproximately 265' C . i n - & process, as contrasted to some 1400' to 1600' C. in the other processe8. I
Preaent addrese. B. F. Goodrich Research Cents.,"Brsckavills. Ohio.
April I954
IN
The product gases from each of the three processes contain approximntely 10 mole % acetylene, 40 to 50% hydrogen, and hydrocarbons other than acetylene. Representative gas compositions are compared in Table I. The purification and separation of acetylene should require comparable processing, regardless of which process was used to produce the acetylene. If vinyl chloride is the desired end product, and if it could be produced satisfactorily from the dilute acetylene, its separation and purification should present a more simple problem than the sep* ration and purification of acetylene. Moreover, since d l of the product gases contain hydrogen, the hydrogen chloride required to convert acetylene to vinyl chloride could be pradured in situ by reaction with admixed chlorine.
Table I.
Effluent Gas Compositions of Acetylene Processes
Acetylene H drogen ethane Ethylene Ethane Methylaaetyleoe Pr0pylene
d
10-13 38 40-45 0.8-1.0 3.5 0.4-0.5
12.3 53.6
0.2
0.2
7.1 48.3 28.0 0.9 0.05 0.3
0.1
0.05
Prop*ne
1.3 0.7-1.4 0.2-0.3
Butane
0.210.3 TraOe 0.03-0.3
Diacetvlene Vinylaoetulene Ethylacetylene Butylene Bubdiene Carbon dioxide Carbon monoxide Nitrogen
Benre".e
OXYBen
16.4
5.9
...
...
0.09 0.26 0.03
...
1.8
0.2-0.4
5.6 2.8
0.1
0.43 0.37
...
0.2
0.05 0.07 0.02 ... 0.02 0.07
...
1.25 7.8 5.2 0.3 0.42
7.5-7.8 52-54 4.6-6.1 0.3-0.7
... 3 24-29 1.7-2.9
...
0.4
Bench Scale Experiments Show Process To Be Promising
In order to mcertain whether or not the process was feasible, bench scale apparatus was assembled as indicated in the flow sheet for the process (Figure 1). The hydrogen-chlarine reactor was made from a 12-inch length of borosilicate glass tubing. Chlorine and the gas mixture which contained hydrogen were admitted to this tube through jets. A Nichrome wire coil was placed directly a t the o ening of the chlorine jet t o supply energy for the initiation of &e hydrogenohlorine reaction. The catalyst chamber was constructed of two concentric standard steel pipes. The inner pipe which contained the catalyst, was a standard 1-inch pi e 4b inches in length. The outer pipe was a SGiuoh length of)Linch pipe. A heating coil (20 feet of B & W No. 20 w e e Nichrome wire) wm wound around the lower 12 inches and-& entire reastor"was insulated with 85% magnesia insulation. The annular space wa8 partially filled with a liquid at its boiling p i n t (cumene, boiling point 152' C . ) to ensure a constant temperature within the reaotor.
D VSTRI A L.-A N D E B G I B E E R I N G
c H E M Is T R Y
633
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT The gases from the catalyst chamber were passed through t x o low temperature condensers in series to remove vinyl chloride, then through two caustic scrubbers. From the caustic scrubbere, the gas passed through a sampling manifold and out to the flare.
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SAMPLE BULBS
Figure 1
CAUSTIC WASH
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LOW TEMP. CONDENSERS
go SPACE
VELOCITY
E
HYDROGEN CHLORINE REACTOR
Figure 2.
Catalyst 10 a t approx. 150' C. Space velocity, cu. ft./(hr.)(cu. ft. catalyst)
Flow Sheet of Bench Scale Apparatus
Thc hciich sralc equipmelit n a5 used t o eva1u:ite tht : 1 ( ~ 1 i1t ~T of various ratalyst preparations. Ten recipes (Table 11) 11 P I C evaluated, and on the basis of conrersion, recipe 10 was celc for furthci study. The effect of space velocity (volume oi g standard conditions which f l o w through a unit volume of catalyst in 1 hour) on conversion of acetylene to vinyl chloride n a s studied, and the results are shown in Figure 2. Only small samples of liquid product were recovered, but the boiling point indicated that the product was substantially pure vinyl chloride. Since the beiich scale results were encouraging, a pilot scale unit was built so that process variables could be studied and liquid samples of suitablr size could br collerted and rr:rluatcd. 45-Pound-per-Day Pilot Plant Is Constructed
Effect of Space Velocity on Conversion
The energy required to st)artthc reaction bctwxn chlorine and hydrogen was supplied by a glowing wire. To obt'ain a gastight, electrically-insulated passage into the chamber, two Modcl T Epark plugs were used. Two holes were drilled and tapped for 1!2-inch pipe, one on either side of the chamber. The grounded side of t.he spark plugs wa8 removed and the plugs were screwed into the hole?. (Model T spark plugs were used since these are the only plugs on the market which are threaded with 1/2-inoh pipe threads.) The insulated center poles of the plugs thus gavc two insulated, gas-tight leads into the chamber. A coil of Nichrome wire (R & W No. 24, 8 inches long) was connected to the lcads within the chamber. The external circuit as connected to the out,put of a variable volt'age transformer. Tn order to sce the initiation of the hydrogen-chlorine reaction, a viewing port mas cut into the chamber at, the same height as the nichrome coil. Safety plate glass, backed by a piece of 16mesh xreen, was used to cover the port. Filter. When hydrogen and clilorino wactcd to form hj~irogen chloride in the prescnce of methane, consirlera1)le carbon black was formed. To remove this carhon I)lack irom the gas stream bcfore the gar! was passed through the catalyst chamber, a filter n-as placed in the stream betwccn the hydrogcn-rhlorinc. rractor and the catalyst chtimber.
A pilot plant capable of producing 45 pounds of vinyl chloride per day was constructed. The component parts were somewhat similar to those of the bench scale equipment but were constructed of mild steel. A schematic diagram of the pilot plant is shown in Figure 3 and a photograph of the equipment in Figure 4. The principal components were acetylene purification equipment, The filter was constructed of four bag filtcrs in parallel; this arrangement gave a high surface t o volume ratio with a tot,al flowmeters, chlorine filtei , catalyst chamber, rooler, and lo^ filtering area of 9 square feet. A rule-of-thumb rule in bag temperature condenser. filter design states that 4 square feet of filtering area should be Acetylene Purification Equipment. Many of tlie preliminary provided per cubic foot of gas pes minute. At maximum flow runs were made with a synthetic gas stream similar to that prorates in this equipment, this ratio was 5.5 to 1. The bag filters duced by the Schoch procew. The acetylene used to prepare this simulated Schoch process gas was purified by a SUIFLARE furic acid (707,) ivash, followed b i a 10% caustic wash. The gas was dried over silica gcl and passed through activated carbon. Hvdrogen and natural gas weic metered directly into the plant without purification. The icsults of several iuns showed that mercaptans in the natuial gas were deletciious to thc C activitj of the catalyst IIoiicvei, these hdiinful mercaptans r m be rcmoved h o r n tlie gas fed to the acetylene FILTER generator or from the e u t gas irom the generator by the highei acetylene reHYDROGENCHLORINE moval system. R E A c T o R -J CARBON LOW TEMPERATURE Hydrogen-Chlorine Reactor. The hyFILTER CONDENSER drogen-chlorine reactor is shomn in Figure 5 and the construction details &IC sho\+n in Figure 6. The concentiic CONSTANT TEMPERATURE placing of the pipe for the gas mixOIL BATH ture and the tube for the chlorinc rvas used to ensure adequate mising of the Figure 3. Flow Sheet for Pilot Plant Production of 45 Pounds per Day of Vinyl gas streams. Chloride
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634
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 46, No. 4
PILOT PLANTS were made of a double layer of' standard Fiberglas cloth, Type ECC (continuous filament), with a thread count of 60 by 64. The presence of hydrogen chloride in the gas stream necessitated the use of glass cloth. After over 200 hours of service, the cloth showed no sign of deterioration. The bag filters were mounted in a vertical position and housed in a container constructed of 14-inch light gage pipe, 39 inches in height. Accumulated carbon black dropped from the bag filters into a receiver a t the bottom of the container from which it was easily removed. Catalyst Chamber. The catalyst chamber, Figures 7 and 8, was a multitubular reactor with the catalyst contained within the tubes. The volume of the reactor was approximately 0.25 cubic foot. The tube bundle was placed inside a 46-inch length of 6-inch iron pipe giving a shell-side volume of approximately 0.3 cubic foot. .in absorber oil was ciiculated from a thermostat through the shell of the reactor a t the rate of 3 to 3 gallons per minute. The catalyst was placcd within the tubes and was suppnrted on a Figure 4. Pilot Plant 16-mesh screen cxtended across the bottom of the tubes. A = Constant temperature oil bath E = Differential manometer to indicate *4 '/&ich copper tube extcnded flaw of oil through catalyst chamber down through the center catalyst tube B = Catalyst chamber F = Manometers t o within 6 inches of the bottom of the C = Chlarine and mixture rotameters G =~ ~precooler ~ ~ ~ catalyst bed. This copper tube \vas D = Variable-voltage transformer H = Low temperature bath containing product condenser sealed a t the lower end and emerged from the top collection tube through a gas-tight seal. The upper end of the copper tube was open so that a copper-constantan thcrmoThc. low temperature condenser was also mitdc of a/a-inch couple could be inserted into the tube in order to determine the copper tubing, 20 feet long and formed into a coil 7 inches in temperature a t any height within the catalyst bed. diameter. At the lower end of the coil was placed a rcreiver constructed from a 14-inch length of 2-inrh-inside-diarnet~r copThe thermostat was a heavy-walled 5-gallon tank with a flanged cover. Three 750-watt, immersion-ty e, Chromalox per tube. The capacity of the reccivcr was approximately G80 heaters were placed within the bath. Two of t i e heaters were ml The coil and condenser were immersed in a solid carbon manually controlled, whereas the third was controlled by a diouide-trichioroethylene bath at approximately -80" C. (Tiichloroethylene was used instead of acetone because it is nonFenwal thermoswitch. The temperature of the cirrulating oil could be maintained within *lo C. of the desired temperature flammable.) The gas from the low tempcrature condcnscr was The bath, reactor, and transfer lines were insulated with 85% flared outside the building. magnesia lagging.
Low Temperature Condenser. The gases which emerged from the catalyst chamber were hot (100' to 150' C.), and an intermediate cooler was inserted in the line to cool the gases to about 0" C. before they entered the low temperature condenser. The cooler was constructed of 6/8-inch copper tubing, 20 feet long. The tubing was formed into a coil 10 inches in diameter, and the coil was then immersed in ice water.
Table 11. Recipe
KO.
Agent
1 2
HgClz HgClz HgiClz' HgiC1za HgCh HgClz HgClz HgCIz HgClz BaClz HgCh BaCl?
3 4 5
6 7 8 9
10 a
Catalyst Preparations Catalyst Weight,' g. 23 57
... . . .I
100 50 50 50 10 50 50 50
Prepared using $02 t o reduce HgClp ( 2 0 ) Activated by heating a t 650' F.for 24 hdurs.
April 1954
Carrier (650 Ml.) Charcoal Charcoal Charcoal Silica gel b Silica gel silica gelb Silica gelh Activate3 carbon Activate3 carbon Activated carbon
Air and Moisture Exclusion Are a "Must"
Start-up. Before starting a series of runs, the eiitirc systrm was purged with natural gas (except for the catalyst chamber wliirh was by-passed during the start-up period) for a t least I/. hour. At the same time, the heaters and circulating pump were turned on so that the catalyst chamber could be heated to and maintained a t the desired temperature. Powdered carbon dioxide was added to the low temperature condensers and the gas sampling bulbs were placed in readiness. After the catalyst chamber had attained the desired temperature, the flow of purge gas was stopped and the gas mixture flow started into the hydrogen-chlorine reactor. The voltage W,E adjusted so that the Nichrome coil glowed a cherry red. The chlorine was then admitted into the reactor and, almost immediately, a flame appeared at the chlorine jet. The current to the hot wire was stopped and the gas flow diverted through the catalyst chamber. The apparatus was then on stream. On Stream. The gas mixture and chlorine rates were changed a t intervals so that the effect of space velocity and percentage excess hydrogen chloride (over the theoretical amount necessary to convert acetylene to vinyl chloride) could be determined. After a change of operating conditions was made, a minimum interval of '/2 hour was allowed to elapse before samples were taken so that steady-state equilibrium was attained within the system.
INDUSTRIAL AND ENGINEERING CHEMISTRY
635
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~
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT System pressure, pressure drop across the filters, temperatures of the entering gases, the temperature of the circulating oil, and temperatures within the catalyst bed were recorded a t intervals throughout a series of runs.
Mercuric and Barium Chlorides Are Catalyst
The catalyst used in the present work was a mixture of chlorides supported on 8- to 14-meshactivatedcarboxi(GreenBrothers, Inc., of Dallas), prepared according to the following recipe: 3000 (6.5 liters) 500 500 200 1800
Activated carbon, grams Mercuric chloride, grams Barium chloride, grams Methanol. ml. Water, ml.
The barium and mercuric chlorides were dissolved in the watermethanol solution and the solution was poured, with agitation, over the activated carbon. There was just enough of the solution to wet thoroughly the carbon. The mixture was then dricd over a steam bath for 2 hours and finally in an oven a t 105" e for 24 hours. Four batches of catalyst were prepared according to this recipe and were designated A, B, C, and D, respectivelv. Gas Stream Is Sampled to Determine Feed Composition and Acetylene Conversion
Three sample points (designated X in Figure 3) were used t o obtain gas samples during a run. Analysis of the samples shon ed feed composition, concentration of acetylene in the gas stream entering the catalyst chamber, and the effluent composition which mas indicative of the conversion of acetylene to vinyl chloritlr.. The sample stream was passed through two low temperntuie (-80" C.) condensers in series and through Ascarite befoie i t enterrd the sampling bulbs.
Figure 5.
Hydrogen-Chlorine Reactor (A) and Chlorine Filter (B)
Shutdown. After the completion of the run, the chlorine flow as stopped and the gas mixture flow was shut off. The entire FS stem was then purged with natural gas for an hour. This last purge was required to remove all traces of hydrogen chloride hom the system so that when the equipment was opened for (*leaningthe moisture from the air would not cause severe cor1 osive conditions. Cleanout. After each day's operation, i t was necessary to remove the carbon black which had been formed. The cover of the hydrogen-chlorine reactor was removed and the carbon black removed by a vacuum cleaner. I n addition to cleaning out the carbon black, it was also necessary to clean the chlorine rotameter. The inside of the tube, as well as the surface of the float, was coated with a thin film of abfiorbed chlorine and the float tended to stick if it was not thoroughly cleaned. The rotameter float was removed and wiped nith a dry, lint-free cloth. The inside of the tube was cleaned with a cloth swab. The carbon black filter was cleaned when the pressure drop across it was from 12 to 15 inches of water. This cleanout was accomplished by removing the container which surrounded the filter bags. The carbon black was removed from the carbon collector immediately below the filter bags. The entire filter was vacuum cleaned and reassembled. Testing. After any portion of the equipment had been torn down and reassembled, the entire system was purged with natural gas and then pressure tested a t 3 pounds per square inch gage (the pressure of the natural gas). If the pressure fell more than 0.1 pound per square inch in 10 hours, all bolts were retightened and the equipment again pressure tested.
636
TO VARIABLE VOLTAGE TRANSFORMER
a'
-
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t Figure 6.
STANDARD PIPE
TO FILTER
Hydrogen-Chlorine Reactor
The vapor pressure of vinyl chloride a t -80" C. was estirnaPed by means of an Othmer plot with ethane as the reference gas anti found t o be approximately 0.37 pound per square inch absolute. If it was assumed that the partial pressure of vinyl chloride in the exit gas from the lorn temperature condenser was equal to its vapor pressure, then the exit gases contained ( 0 . 3 i ) (loo)/ (14.7) = 2.5 mole yo vinyl chloride. The gases which entered the low temperature condensers contained about 10% vinyl chloride. Therefore, approximately three fourths of the vinyl chloride was removed by the low temperature condensers All of the hydrogen chloride jvas removed by the Ascarite. Samples from all sampling points were collected by mercury displacement. The flow of the mercury was adjusted so that
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
PILOT PLANTS 2 to 3 minutes were required to obtain a sample. This procedure gave an average sample of the gas stream rather than spot samples. Analysis for Acetylene. Two analytical procedures were used to determine the acetylene concentration of the vaiious streams. One method was used on samples with higher concentrations (10 to 12 mole %) and the other for samples with lower concentrations of acetylene which also contained vinyl chloride. In the first method, a standard Orsat apparatus was used, the acetylene being absorbed in an alkaline solution of mercuric and potassium iodides. This analytical scheme was used by the Bureau of Industrial Chemistry, Acetylene Division, University of Texas. Comparisons with mass spectrometer analysis showed the method was reliable and reproducible. For the other samples. an analytical scheme adopted from Siggia (90)was used. When acetylene is reacted with silver nitrate, 2 moles of nitric acid are liberated for every mole of acetylene reacted, The nitric acid is titrated with 0.02N sodium hydroxide, using a methyl red-methylene blue indicator. Known volumes of gas were injected, by means of a calibrated syringe, into serum bottles containing alcoholic silver nitrate. After the samples were vigorously agitated, they were titrated and the acetylene concentration was calculated in the usual manner. The reliability of this analytical procedure was determined by analyzing samples of known composition, and it was found that the method was accurate to within I%, even though the known sample contained vinyl chloride. Heat of Hydrogen-Chlorine Reaction Produces Additional Acetylene
Before the effect of changes in the various process variablestemperature, excess hydrogen chloride, and space velocity (pressure was slightly above atmospheric)-was determined, a number of preliminary investigations were made. The reaction between hydrogen and chlorine was the first reaction studied. The study showed that the reaction was complete and that all chlorine was converted to hydrogen chloride. Whether hydrogen and chlorine would react in the presence of acetylene was the next question to be answered. Nitrogen, hydrogen, acetylene, and chlorine were metered into the hydrogenchlorine reactor in the following proportions:
Nitrogen Hydrogen Acetylene Chlorine
Flow, Std. Cu. Ft./Min. 0 500 0.400 0.100 0,050
The flame which appeared a t the tip of the chlorine jet was yellow and luminescent. A very small amount of carbon was formed in the flame, which indicated that only a minute fraction of the acetylene was decomposed by the heat of the hydrogen chlorine flame. The effluent from the reactor was passed through .bcarite and analyzed for acetylene content and it was found to be 10.5 mole % acetylene. The acetylene concentration of the entering gas on a hydrogen chloride-free basis was also 10.5 mole %. Therefore, hydrogen and chlorine had reacted in the presence of acetylene with little or no decomposition of the acetylene. To determine the effect of natural gas on the hydrogen-chlorine reaction, hydrogen, natural gas, and chlorine were metered into the reactar at the following rates:
Natural gas Hydrogen Chlorine
Flow, Std. Cu. Ft./Min. 0.600 0.400
0.050
The flame at the chlorine tip was intensely yellow and smoky, much like the flame produced when methane is burned in insuffiApril !354
Figure A = B = C = D =
7.
Pilot Plant
Catalyst chamber Carbon filter Absorber Stripper
cient air, and considerable carbon black collected in the bottom of the reactor and in the carbon filter. An aliquot of the effluent was passed through Ascarite and analyzed for acetylene content. From 0.8 to 1.0% acetylene was found in the off-gas, even though no acetylene had been present a t the start! The absence of free chlorine in the effluent was verified by its failure to liberate iodine from a potassium iodide solution. The formation of hydrogen chloride in the presence of Schorh process gas was next investigated. Schoch process gas (11.2 mole % acetylene) was fed into the reactor a t the rate of 0.925 standard cubic foot per minute, together with chlorine a t a rate of 0.061 standard cubic foot per minute. A sample of the effluent was passed through Ascarite and analyzed for acetylene. The sample contained 12.3 mole % acetylene on a hydrogen chloride-free basis. The inlet gas on the same basis contained 12.0 mole % acetylene; therefore, an increase of about 2.5%, based on the original acetylene content, had resulted. Similar results were obtained when Schoch process gas and carbon monoxide were used as the feed gas. The acetylene concentration increased from 8.1 to 8.34 mole %, an increase of approximately 3%. The following conclusions were drawn from these investigations : Hydrogen and chlorine reacted completely t,o yield hydrogen chloride.
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
637
ENGINEERING, DEStGN, AND PROCESS DEVELOPMENT Figure 8. Catalyst Chamber A = Packing gland B = Oil outlet C = Bolts, 12, I / q inch D = Pipe, 6-inch Schedule 4 0
E = Shellside baffle plates F = Tubes, 19, 3/4 inch, 4 8 inches long
G H I J
K L
Conversion Decreases with Increased Space Velocity
If higher acet'ylenes were the cause of decreased catalyst activity, then Schoch process gas which had been processed through the oil scrubber system ( 2 8 ) should cause no decrease in the activity of the catalyst. Maas spcctrograph analyses showed that the scrubbed gases contained none of the higher acet'ylenes. The of Schoch process gas from thc oil wnsh Mole yo 0 0-0.04 0-0.06 0 0 0 0.05
= Catalyst inside tubes = Thermocouple tube = 85% magnesia insulation = Bolts, 8, l / 2 inch = Oil inlet = Gas inlet
A
A
The heat of the liydrogenchlorine exothermal reaction cawed a net gain of acetylene in the amount of 2 to 3y0 (based on t h r original awtvlrne content). Excess Hydrogen Chloride Has N o Effect on Conversion
The effect of hydroge>nchloiide in excess of the amount theoletically requircsd to conrei t all of the acetylene to vinyl chloride was studied using a mixture of natural gas, hydroL gcn, and acetylene which approximated Schoch proccss gas in its composition. The results are presented in Table 111. For a given set of conditions the percentage of acetylene which was converted to vinyl chloride was not dependent on the amount of excess hydrogen chloride for an excess from 32 to S% over that theoretically required. Therefore, it was decided to operate the equipment with 20% exce,?s hydrogen chloride in the reaction gas. This choice was made because t,he inlet concentration of acetylene w i i s determined by analysis after a rurl had heen completed and the chlorine flow had a tendency to del e because of film fornintion in the regulating valve and required constant attention during the first, hour or so of a run. The use of 20% excess hydrogen chloride \vas a safety factor which ensured that there would al~ynya be some exceds hydrogcn chloi.itlc in rhc, gases that cnlcwd the catalyst chamber.
f
Benzene Methyl acetylene Butane 1J-But'adiene Vinylacetylene Diacetylene Carbon dioxide
Ethanc Propane Carbon monoxide Ethylene Acetylene Methane Hydrogen
Jlole % 2.G 0.18 0.25 0.8 1 0 . 5 -14 42 40
The conversions of acetylene to vinyl chloride a t various space velocities were determined at temperature of 180°, 150", and 125" C. These data are given in Table V and are shown graphically in Figure 10. The yield in grams of vinyl chloride pel liter of catalyst per hour is t'abulated along with thc percentage conversion, and the yields are plotted as a function of space velocity in Figure 11, The yield was calculated by multiplying thc acetylene rate by the percentage conversion and by a constant. The constant lor this particular work was 730 grams of vinyl chloride per lit,er of catalyst per hour for a unit flow of acctylciic expressed as standard cubic feet per minute. This constant the cquation for determining the percentage conversion I , developed on the basis of the perfcrt gas law nrid for a catalyst volume of 0.230 ou. ft.
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Higher Acetylenes Decrease Activity of Catalyst Figure
9.
Effect
of
Higher
to 150" c;. tllali when increased from 150°t0180"c'. Iihen though th(b
increased
Gntreated Schoch process gas \vas used as t,he feocl gas i'or t h e Acetylenes on Catalyst Activity slightly when the, studies of the effect of space veloc9ity. With a temperature of tein p e r at u r e IT a s 150" C. in the catalyst chamber, the spxce velocity was varied Catalyst A at 150' C. from 290 to 395 cubic feet of gas per cubic foot of catalyst per hour. It was noted that Table 111. Effect of Excess Hydrogen Chloride on Conversion the p e r c e n t a g e c o n v e r s i o n Simulated Schoch process gas dropped rapidly the longer the Catalyst C catalyst was on stream. The Temperature 150* C. Acetylme concn.. 10 mole 'X data are presented in Table IT' Space and Figure 9. T o verify these Acetyleno Velocity, Flow Rates, Std. Cu. Ft./Min. Excess in Exit Conversion Cu. Ft./ results, a new batch of catalyst Natural HC1, Gp, of Acetylene, (Hr.) (Cu. Ft. was prepared and placed in the gas Acetylene Hydrogen Chlorine Total 70 70 70 Ca talyst) catalyst chamber. Again the 0,180 0,039 0.141 0.026 0,386 30 0.03 99.8 101 0,180 0,039 0,141 0.024 0.384 22 0.04 99.t 100 activity of the catalyst de8 0.03 99.8 9g 0.180 0.039 0.141 0.021 0.381 creased rather rapidly thc 32 0.16 98.6 151 0.039 0,679 0.211 0,270 0.059 longer the catalyst was on 22 0 . 1 3 9 9 . 0 I50 0 . 0 3 6 0 . 5 7 6 0.211 0.270 0.0513 8 0.22 98.3 140 0.032 0.572 0.069 0.211 0.270 stream. The decrease in ac9F.8 201 0,772 32 0.41 0.281 0.052 0 , 3 6 0 0.079 tivity was thought to be due to 97.0 200 0.768 18 0.38 0.281 0.048 0.079 0,360 the higher acetylenes (vinyl93.5 252 0,964 30 0.84 0.351 0,064 0.450 0,099 acetylene and diacetylene) in 0.460 0.099 0.351 0.059 0.959 19 0.73 94.5 250 the feed gas.
638
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 4
PILOT PLANTS raised from 150' to 180' C., the beet operating temperature was Considered to be 150' C., because a t the temperature there was no indication of mercuric chloride loss by sublimation which might occur a t somewhat higher temperatures.
Table IV.
Effect of Higher Acetylenes on Catalyst Activity Schoch process gas direct from generator Catalyst A Teinperature 150' C.
rioetylene in Feed,
Time,
N o Hot Zone Is Observed In Catalyst Chamber
I t h a s been s t a t e d ( l l , 14, 15, I?, SI, 33) that localized heating is the chief cause of loss of catalytic activity when mercuric chloride is used as the active agent. I n the present work, little or no localized heating was obPerved within the cat-
Hr.
%
2.0 2.2 2.3 2.5 2.7 3.0 3.3 3.5 3.6 3.8 4.3 4.5 4.7 4.9 5.1 5.3 5.5 5.7
12.0 12.0 12.0 12.0 12.0 8.7 9.0 9.2 9.5 9.7 12.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0
.
l?lowRates, Std Cu. Ft./'hlin. Mixture Aoetylene Chlorine Total 0.131 1.092 0.090 1.182 0.131 0.090 1.182 1.092 1,092 0.131 0,090 1.182 1.031 0.124 0,082 1.113 1.031 0.124 0,082 1.113 1.163 0.101 0.070 1.234 1.129 1I199 0.102 0.070 1.086 1.165 0.100 0,079 1.068 0.070 1.138 0.101 1,002 0.067 0.096 1.069 1.407 1.516 0.169 0.109 0.169 1.407 0.109 1.516 0.169 1,407 0.104 1.511 0.160 1,334 0 104 1.438 0.160 1.334 0.100 1,434 0.152 1.267 0.095 1.362 0 , os9 0.144 1,200 1,289 0,085 1.137 1.222 0.136
leased by the exothermal combination of hydrogen chloride and acetylene was readily dissipated by the bulk of the inert gas. The catalyst bed temperature for runs a t 150°, 125", and 180' C. showed that there was a 2 to 3" C. temperature gradient along the length of the catalyst bed and that the catalyst bed contained no localized hot spots, as are present when pure acetylene and hydrogen chloride are combined in the presence of a catalyst. Temperatures of from 240' to 400" C. have been reported (88) in the hot spot reaction zones. The absence of localized heating was thought t o be one reason why the catalyst showed no decrease in activity in somc 37 hours of operation.
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Space Acetyleno ConverVelocity in Exit sion of cu.mi Gas, Acetylene, (Hr.)(Cu. F t . Catalyst) % % 2.4 84 3.2 78 79 3.1 3.0 80 3.1 79 3.4 67 3.5 67 3.6 67 3.3 71 3.1 73 5.7 59 5.3 62 5.4 62 5.2 63 5.3 62 5.1 63 5.1 63 5.1 63
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Figure 10.
Effect of Space Velocity on Conversion
Oil-washed Schoch process gar and catalyst Space velocity, cu. ft./(hr.)(cu. ft. catalyst)
D
Carbon Monoxide Does Not Affect Catalytic Activity
Since \Tiny1 chloride w:ts produced in good conversion frolll Schoch process gas from which higher acetyleneshad been removed, it decided to determine whether or not good yields could be obtailled if carbon lllonoxide were presentin the gas stream. other Rords, could ~ v ~ l f partial f - ~ ~combustionthe feed gas. A series of runs was process aceiylcnc be used made in which a unit volume of Schoch process gas together with 0.3 volumes of carbon monoxide were metered into the apparatus. The resulting feed gas had the following approximate coniposition : Mole % Acetylene 8.2 Carbon monoxide 23 31 Hydrogen 32 Methane 2 Ethane 1SthyIcne 0.6
April 1954
The feed gas was, therefore, of approximately the same coniposition as partial combustion gas and similar to Wulff process gas but contained a higher carbon monoxide concentration (23 as compared to 8 mole %). The results of these runs are presented in Table VI and are compared to results obtained from Schoch process gas in Figures 12, 13, and 14. .4t the conclusion of the runs, the carbon monoxide stream was shut off and a conversion was determinrd for Schoch Process gas only. This value, whcn plotted against space velocity, fell on the percentage conversion curve previously determined for Schoch process feed gas. This fact indicated that no decrease in catalytic activity had been produced by the carbon monoxide in the feed gas. A comparison of the percentage conversion curves showed that less of the acetylene present in the more dilute (8.2 mole % acetylene) feed gas was converted to vinyl chloride than for the more concentrated (11.1 mole % acetylene) feed gas. Two reasons for this phenomenon were possible. According to the data of Frescoln (0), the rate of reaction increased with an increase in acetylene concentration over the range encountered in the present work. The rate of diffusion of acetylene to the surface of the catalyst was less a t the lower partial pressure of acetylene. I n all probability, the lower percentage conversion was a result of a combination of thesc two effects.
INDUSTRIAL AND ENGINEERING CHEMISTRY
639
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT end of t,hedistillationamounted to 5.2 ml. of which 3.1 ml. v a s TTater and the halance (2.1 ml). Oil-washed Schoch process gas Catalpt D was some water-insoluble scbSpacp stance, possibly ethylene diYield, Velocity, Acetylene ConverG. Vi,nyl Cu. Ft./ chloride. The data supported Excess in Exit sion of Chloride/ (Hr.) the assumption ihat all (or Flow Rates, Std. Cu. Ft./hIin. "21, Gas, Acetylene, (L. Cata- (Cu.F t . in Feed, % Mixture Acetylene Chlorine Total % "0 % lyst) (Hr.) Catalyst) nearly all) of the acct,ylene was converted to vinyl chloTemperature, 180" C. ride. 0.029 0.421 0 100 31 110 0,392 0.042 10.6 151 43 0 579 100 0.039 0 10.8 0.059 0.540 Polymerization Rate. The 55 189 0.723 100 0,049 0 11.1 0.075 0.674 225 65 rate of polymerization of niorio0 0.862 100 0,058 11.1 0,089 0.804 0.05 0 992 99.6 259 75 11.1 0 067 0.103 0.925 meric vinyl chloride to poly0 076 0 14 1 126 85 98.9 294 11.1 0.117 1.050 0 24 0 085 1.260 94 98.2 329 0.131 1.175 11.1 vinyl chloride was made a?0 59 0.080 100 0 0.53 0 857 224 10.0 0 804 0 05 99.6 cording to the Raw Material 0.925 0,094 0.081 0.986 59 260 10.3 0 15 98.8 292 0.111 0.070 1,120 80 1.050 10.6 Specification Test of 11Ionsanio 1 253 0 30 97.6 327 0.128 0.078 91 1.175 10.9 0.51 96.0 100 1,396 0.086 364 1.310 10.9 0.143 Chemical Co. (24). The mono1 550 0 79 93.8 109 0.159 404 1,454 0.096 10.9 mer v a s polymerized under 1.702 1 01 9 2 . 0 117 444 0 . 1 7 4 0.105 1.596 10.9 121 465 1.781 1.31 89.8 0.184 0.111 1.670 11.0 s t a n d a r d c o n d i t i o n s , using benzoyl peroxide as initiator. Temperature, 150' C. Both the raw and the dis0.041 0,026 0.418 26 0 100 30 I09 10.4 0.392 39 0.033 29 0.054 0.575 0 100 150 0.540 10.8 tilled monomers were sub54 0.044 19 0 03 99.8 0.074 0.718 187 10 9 0 674 0.053 20 0 08 64 99.4 0.088 0.857 224 11 0 0,804 jected to the polymerization 73 0 20 0.061 20 11.0 98.5 0,928 0.102 0.986 257 rate test, but only the distilled 19 97.3 0.117 1,120 292 0 . 070 0 36 83 1 050 11.1 20 95,7 0.130 0 55 1.253 327 91 11.1 1.175 0 078 monomer polymerized a t a 93.5 0 85 90 1.396 364 11.1 1 310 0.146 18 0 086 0 161 0 046 19 1 06 91.8 1.5.50 403 1 454 108 11 1 rate sufficient t o pass the 48 0.068 0 040 0 100 23 0.649 170 11.1 0.609 minimum specification of 80% 58 20i 0,742 0,080 0.049 0 07 99 5 22 0.791 11.1 0.096 19 98.3 60 0,057 0 22 0 921 240 0.864 11.1 polymerized in the specified 20 0 37 0,110 97.2 1.031 275 0.985 11.1 78 0.066 0.124 0 61 95.4 0.074 1.187 310 1.113 11.1 86 19 time of 7 hours a t 50" C. 0.138 0 85 93 19 0,082 1.322 345 1.240 11.1 93 5 (Of the dist,illed monomer, 1 15 1,380 1 471 91.3 103 0.154 18 0 041 384 11.1 1.527 19 1 29 112 1 608 90.1 0.170 0.101 423 11.1 83% had polymerized, whereas 1.050 I .120 19 %2 202 0 56 95.8 0.117 0.070 11.1 only 48% of the r a x monoTemperature, 125' C. mer had polymerized under 0.042 24 10 9 0.392 0.026 0.418 0 03 99.7 31 100 test conditions.) 0 035 0.059 10 9 0 575 18 0.540 0 14 98.9 43 150 0.076 11.0 0 718 0 33 33 0 044 17 0.674 97.4 187 High Boilers. Tlie amount 0 053 20 0 69 0.857 0 088 224 11 0 0 801 61 94 6 of material which boiled above 0.061 19 1 09 0.925 0.102 11.1 68 0.986 91.5 257 1 0.50 0.070 1.120 0.116 11.1 20 1 46 88.6 75 292 room temperature was deter20 85.2 1 175 1 89 0 078 1 253 0.130 11.2 81 327 1 310 0 145 0.086 82.6 19 2 22 1,396 88 11 3 365 mined for hoth the r a x and 0.026 0 418 0.3'12 0,044 99.1 18 32 11 3 0 10 109 distilled monomeric vinyl chlo0.061 15 0,035 0,575 0,540 0 21 11 3 44 150 98 3 0.076 0 044 0.718 0 671 11.3 16 96.5 54 0 47 187 ride, accordiiig to the Itaw 0.801 0 0;3 0 857 16 0.092 2210 81 62 11.3 94.1 0.061 0,986 1 13 0.925 0.105 91.5 17 11 3 59 2.57 Material Specification Test 1 59 1 050 0 119 0.070 1.120 14 11.3 88.1 76 292 0 078 1.17; 0 133 1 253 18 2 10 11.3 84.4 81 327 Procedure of Monsanto Chemi0.086 0.149 1 310 1.396 17 2 47 11 3 81.5 87 365 cal Co. (WS). Both the raw 1 435 2 72 0.095 1.530 18 0.163 93 400 11.3 79.3 monomer and the distilled monomer contained less high boiling impurities than the Evaluations Show Liquid Product maximum a l h e d by the specification (0.257,). No other Is Essentially Pure Vinyl Chloride tests were made on the liquid monomer, since it was felt that these test3 established adequately the fact that almost A11 of the results discussed have been concerned with gas samples. gOO-ml. sample of liquid vinyl chloride was collected pure vinj 1 chloride had been produrcd from dilute acetylene feed and subiect to various tests, polymerization rate, residue, and gas. fractional distillation. D i s t i l l a t i o n . A 320-ml. sample of monomeric vinyl Table VI. Effect Of Space Velocity on Conversion chloride produced from oilwashed Schoch process gas was Oil-washed Schoch gas pliis 30 mole 70 carbon monoxide Catalyst D distilled. The distillate temTemperature 150° C. Carbon monoxide concn.. 23 mole % perature was in good agreement Kith the data of Dana, yield, Space Velocity hootyiene ~ o n v e r - G . Vinyl c u . ~ t . / ( ~ rC.C) ; ~ . Burdick, and Jenkins ( 7 ) and F l o Rate, ~ Std. Cu. Ft./hlin. in Exit sion of Chloride/ Ft. catalyst) Carbon Gas, -4cetylene. (L. CataTotal Acetis shown as a Function of the 3Iixtiire Acetylene monoxide Chlorine Tohl 0 /O 770 lyjt)(Hr.) ga3 ylene amount distilled in Figure 15. 0.392 0.0364 0 117 0.026 0.535 0 100 27 1i o 5 The first 10 ml. of distillate 0.540 0,0523 0 162 0.035 0.737 0.09 99.0 38 192 13 8 0.674 0 0678 0.202 0 044 0.420 0.17 98.1 49 2a0 17 7 ( a p p r o x i m a t e l y 3 % of t h e 0.804 0.0836 0.241 0.053 1.10 0.37 93.8 5X 287 21 11 0.925 0.0976 0,277 0.061 1.26 0.60 93.4 67 328 23 5 charge) contained a large 1.050 0.111 0.315 0.070 1.44 0.81 91.3 71 375 29.0 1.175 0.361 0.078 0.125 1.60 1.09 88.1 81 417 32.6 amount of dissolved hydrogen 0.392 0.0421 0.117 0.026 0.536 0 100 31 140 11.0 chloride-this aliquot was dis0 0.053 0.857 0.10 99.2 .. 224 0.804 0.0845 carded. The residue at the Table V.
Effect of Space Velocity on Conversion
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640
INDUSTRIAL AND ENGINEERING CHEMISTRY
Yol. 46, No.
4
PILOT PLANTS
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Space-lime-Yield Data Compare Favorably with Other Work
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120
5
The results with Schoch process gas showed that with a catalyst temperature of 150' C., 58 to 59 grams of vinyl chloride was produced per hour per liter of catalyst a t the 100% conversion level. At 95% conversion, about 90 grams of vinyl chloride was produced per liter of catalyst, and a t the 90% conversion level, about 110 grams of vinyl chloride was produced per hour per liter of catalyst. Yields of vinyl chloride reported in the literature varied from as low as 17 grams to as high as 300 prams of vinvl chloride per liter of catalyst per hour. Many of a the patents did not contain suf9 eo ficient data tjo 100 150 200 250 300 350 400 450 SPACE VELOCITY evaluate the 2
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yield Or the perFigure 12. Effect of Added Carbon centage converMonoxide on Conversion sion. Table VI1 Oil-washed Schach process gas and catalyst D gives a comparia t 150' C. Of the A = No added carbon monoxide Percentage conB = 30% added carbon monoxide Space velocity, cu. ft./(hr.)(cu. ft. catalyst) versions, a n d space velocities. The yield of vinyl chloride in the present woik was comparable to the yields obtained by many of the previous workers in the field. However, many of the patents claimed yields considerably higher than those obtained in the present work but all of the high yields were obtained with pure acetylene and anhydrous hydrogen chloride. The only commercial production data which were available for comparison were for the German plants a t Burghausen and Leipzig. The yields obtained in the present work were about two to three times the yields obtained in the commercial installations (20, 34).
F
,
SPACE VELOCITY
Figure 13.
Yield of Vinyl Chloride as Function of Total Gas Space Velocity
Oil-washed Schoch process gas and catalyst D at 150" C. A = No added carbon monoxide B = 30% added carbon monoxide Space velocity, cu. ft./(hr.)(cu. ft. catalyst)
and foremost is that vinyl chloride can be separated more easily and cheaply from the inert gases than can acetylene. The second advantage is that there is no localized heating in the catalyst bed. This localized heating is one of the major factors which lowers the activity of the catalyst and contaminates the product due to sublimation of the catalytic agent. The production of hydrogen chloride in situ by the reaction of chlorine with hydrogen already in the gas has one advantage over the use of hydrogen chloride-namely, that additional acetylene is formed from methane by the heat liberated by the eyothermal hydrogen chlorine reaction. -And
Some Disadvantages
If pure acetylene and anhydrous hydrogen chloride in stoichiometric proportions react completely to give vinyl chloride, the partial pressure of the vinyl chloride would equal the total pressure of the effluent gases and recovery of the product can be readily effected by condensing out the vinyl chloride. However, Process Has Advantages when dilute (10 mole %) acetylene is converted completely to There are two distinct advantages in using dilute acetylene as vinyl chloride, the partial pressure of vinyl chloride in the prodthe feed gas rather than pure acetylene in the production of vinyl uct is only 10% of the total pressure and the recovery of the prodchloride-aside from the fact that acetylene in the dilute state is uct is much more difficult. 4 to 6 cents cheaper per pound than pure acetylene. The first In commercial practice it is often desired to increase the throughput (increased space velocity) for a given catalyst chamber, even though the perTable VII. Comparison of Vinyl Chloride Production Processes centage conversion of acetylene to vinyl chloride is redured. Yield, G. Vinyl Conversion Acetylene Catalyst The vinyl chloride is separated Chloride/(L. of .icetylene, In Feed, Space Tynp., from the reaction products, Catalyst) (Hr.) 70 ?4 Velocity C. Reference and acetylene and hydrogen chloride are recycled to the catalyst chamber. If this procedure were followed with dilute acetylene, then both acetylene and vinyl chloride would have to be removed from the reaction products, with acetylene only being recycled to the catalyst chamber. The recycling of the inert gases would lower the acetylene concentration in the feed to so l o ~ va value (some 4 to 5%) that the process would be uneconomical. Arecovery process which would overcome this disadvantage is presented later. April 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
641
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT For a given yield of vinyl chloride per liter of catalyst per hour, a much greater volume of gas must be moved through the catalyst bed when dilute acetylene is used as the feed gas than when pure acetylene is used. This means that a greater pressure drop across the catalyst bed would result and the power requirements would, therefore, be greater per pound of vinyl chloride produced. It is believed that the advantages of the process far outweigh the disadvantages and that production of vinyl chloride from dilute acetylene is a commercially feasible process (16). Product Can Be Recovered by Adsorption
Since the effluent from the catalyst chamber contain:: about 10% vinyl chloride, recovery by condensation would be incomplete even with strong cooling ( -80" C ) and would undoulitedly bc uneconomical. c
Figure
14. Yield of Vinyl Chloride as Function of Acetylene Space Velocity
Oil-washed Schoch process gas and catalyst A = No added carbon monoxide B = 30% added carbon monoxide Space velocity, cu. ft./(hr.)(cu. ft. catalyst)
D
at 150' C.
that the process will work and that it \vould be economical. A flow sheet of t,he apparatus is presented in Figure 16. The product gas from the catalyst chamber was cooled to about 10" C. by six precoolers; four were wat,er-cooled and the last two were cooled by circulat'ing brine solutions a t -35" C . The gas entered the absorber column, 8, a t a point m a r the bottom of thc column. The absorbent, trichloroethylene, entered the absorbcr a t the top of t>hecolumn a t about 10" C. The bottoms from the absorber, 6600 pounds of trichloroethylene and 310 pounds of dissolved vinyl chloride per hour, left the absorber a t 35" C. and entered a t the mid-point of the crude column, 12, \vhic:li operated under a pressure of 50 pounds per square inch gage. The overhead products from the "crude" column emerged at 30" C., passed through a dephlegmator, 17, from which a portion returned to the column as reflux and the hal:tnce, 530 to ti00 pounds per hour, flowed into storage tanks, IS. d reflux ratio of 3 to 1 iyas maintained in this column and from 20 to 40 cubic feet per hour of gas returned to the absorber column. Thc stripped trichloroethylene passed from the bottom of t,he crude column through a constant-level float valve and then through a heat exchanger, 13, a water-cooled Heliflo exchanger, 14, and H brine cooler: 15, and finally entered the top of the absorbcr column to complete the cycle. A portion, 800 pounds per hour, 01" the trichloroethylene was withdrawn from the cycle and sent to t'he trichloroethylene recovery plant for purification and :t likc amount of fresh solvent was added t,o the absorption tower. This withdra\val and replenishment of solvent prevented tile awuinulation of impurities-e.g., Pthylene dichloride----in I h~ thirhloroethylene stream. The crude vinyl chloride was puinped from tho storage t,anl
