MORTON SALKIND,’ Associate Editor, in collaboration with
E. H. RIDDLE, Rohm & Haas Co., Philadelphia, Pa., and R. W. KEEFER, Rohm & Haas Co., Bristol, Pa.
Acrylates and Methacrylates Raw Materials, Intermediates, and Plant Integration
IN
recent years, acrylate and methacrylate esters and their polymers have found new and growing markets. I t is estimated that in 1959 more than 150,000,000 pounds of monomeric acrylate and methacrylate esters will be produced, representing an output worth over $50,000,000. And this dollar value doesn’t include the much greater figure added when these monomers are converted to a large variety of polymers and copolymers by over 50 polymer manufacturers. Methacrylate monomer and polymer volume started growing with the adoption of poly(methy1 methacrylate) cast sheet for aircraft enclosures during World War 11, and has continued growing during the last two decades with the development of new markets, to be described in Part I1 of this article. Acrylate monomers have been available in the U. S. since 1931, but their use was relatively limited until price reductions made by Rohm & Haas starting in 1953 led to a rapid growth in a variety of new markets. Despite the spectacular increase in monomer requirements, capacity has generally kept ahead of the demand and today there is considerable excess monomer capacity available to support new developments as well as continued growth of present markets. History and Chemistry
Early work in the field dates before 1850 when Redtenbacher prepared acrylic acid by the oxidation of acrolein: CH,=CHCHO
+ HClO
In the meantime, Otto Haas came to the United States and the Rohm &r Haas Co. \vas incorporatrd in this country in 1909, also initially for the manufacture of bating enzymes for thr leather field. The Rohm Pr Hdas Co. in the United States became interested in commercial development of the acrylates for American markets, and in 1931 pilot plant facilities were started at the company’s Bristol, Pa., location to pioduce methyl and ethyl acrylate from ethylene chlorohydrin and sodium cyanide.
-+
CICHzCH20H (2) The reaction of ethylene chlorohydrin with sodium cyanide then gave the ethylene cyanohydrin :
+
ClCH2CH2OH NaCN 4 HOCH2CH2CN
+ NaCl
(3)
Finally the acrylate was formed:
[o1 CH,=CHCOOH
Later laboratory work includes Frankland’s preparation of ethyl methacryPresent address, Molesworth Associates, New York, N. Y .
1 232
CHZ=CH?
.-+
(1)
1
late and methacrylic acid from ethyl CYhydroxyisobutyrate and phosphorus trichloride, and Tollen’s preparation of acrylate esters from 2,3-dibromopropionate esters and zinc. In 1901, Otto Rohm, working on his doctoral thesis ( 7 ) under von Pechmann in Germany, described the structures of the liquid condensation products (including dimers and trimers) obtained from the action of sodium alkoxides on methyl and ethyl acrylate. He also characterized the solid polymeric material formed at the same time, substantiating earlier work by Kahlbaum on polymeric methyl acrylate. Subsequently, Otto Rohm joined with Otto Haas in forming a German company to produce enzymes for the bating of leather. However, Otto Rohm’s interest in acrylates never waned, and after World War I Rohm’s chemists came up with a new acrylate synthesis: they noted that an acrylate is formed in good yield by heating ethylene cyanohydrin with sulfuric acid and an alcohol. The synthesis started from ethylene, which was converted to ethylene chlorohydrin by reaction with hypochlorous acid :
HOCH2CH:CN
HPSO, + ROH +
CH?=CHCOOR
(4)
This technique provided the initial process employed at the German plant in 1927.
INDUSTRIAL AND ENGINEERINGCHEMISTRY
Badger unit for methanol purification
CH,
+ NH, + o1P’,HCN +
+
HI 2H20
(8)
The reaction of ethylene oxide and hydrogen cyanide to make ethylene cyanohydrin was substituted for the chlorohydrin-sodium cyanide step in acrylate manufacture. Since 1953, Rohm & Haas has avoided the ethylene cyanohydrin step entirely-using carbon monoxide, acetylene, and an alcohol as main raw materials for acrylate esters, In addition, methyl and ethyl methacrylate monomers are now produced directly from acetone cyanohydrin and concentrated sulfuric acid by a continuous process involving methacrylamide sulfate a8 intermediate. Plant Integration
Acetylene purification
Researchers logically extended investigations to include the next higher homologs of acrylic acid : methacrylic acid (a-me’thyl acrylic acid) and crotonic acid (p-methyl acrylic acid). Esters of the latter were not readily polymerized, but methacrylic esters gave high molecular weight polymers with greater rigidity and higher softening points than the corresponding acrylate polymers (6). Among the first applications examined for these new acrylic polymers was their use as interlayer for laminated safety glass. Copolymers of ethyl methacrylate with the lower acrylates were found to provide optimum properties, and this led to initial commercial production of ethyl methacrylate in 1933. Acetone and hydrogen cyanide, generated from sodium cyanide with acid, gave acetone cyanohydrin: HCN CHaCOCH3 + (CHa)zC(OH)CN (5)
+
This was converted to ethyl a-hydroxyisobutyrate by reaction with ethyl alcohol and dilute sulfuric acid :
Nowhere is the tremendous expansion of the acrylate and methacrylate monomers more evident than at the Rohm & Haas plant at Houston, Tex. Rohm & Haas, the only producer of both acrylates and methacrylates, has now invested more than $75,000,000 in its Houston operation in the 11 years since the first unit went on stream in July 1948. This plant now includes these production units: Air separation Carbon monoxide Hydrogen Ammonia Methanol Acetylene Hydrogen cyanide (2 units) Acetone cyanohydrin (2 units) Ethylene cyanohydrin Methyl methacrylate (2 units) Higher methacrylate monomers Acryloid oil additive polymers Fatty alcohols Nickel carbonyl (2 units) Methyl and ethyl acrylate monomers (2 units) Butyl acrylate monomer tert-Alkylamines Ammonium sulfate The first units to be installed in Houston in 1948 were the first hydrogen cyanide and acetone cyanohydrin plants,
followed shortly afterward by the ethylene cyanohydrin plant. The next unit was the higher alcohol plant, which started operating in December 1951. The first methyl and ethyl acrylate plant came on stream at the end of 1952. The first methyl methacrylate plant, duplicating a similar unit which had been in operation for several years a t the company’s Bristol, Pa., location, started up in June 1955, followed by the higher methacrylate monomers and Acryloid oil additives in August 1955. During 1958 the plant was completed virtually as it is today, with the addition of ammonia, methanol, acetylene, and second units for the manufacture cf methyl and ethyl acrylate, methyl methacrylate, hydrogen cyanide, and acetone cyanohydrin. A small butyl acrylate unit started up in March 1959. The Houston plant is very highly integrated, as shown in Figure 1, with natural gas and air being basic raw materials for all products made in the plant. Compressed air is separated into oxygen and nitrogen; oxygen is used for the production of acetylene, hydrogen, and carbon monoxide, and nitrogen is used for ammonia production. The natural gas (primarily methane) is reacted with oxygen to make acetylene, carbon monoxide, and hydrogen, and with air and ammonia to make hydrogen cyanide. Carbon monoxide and hydrogen are converted to methanol, while hydrogen is also used with nitrogen to make ammonia and for the hydrogenation of coconut oil and tallow to produce fatty alcohols. Methanol is used to make both methyl acrylate and methyl methacrylate. Carbon monoxide is also used to make nickel carbonyl, which is utilized with additional carbon monoxide in the reaction with acetylene ro make ethyl and methyl acrylate monomer. This pattern continues throughout the plant (Figure 1). The plant site encloses 168 acres of about 1000 owned by Rohm & Haas at Deer Park, a Houston suburb. Employment is over 900, with one supervisor for every five hourly operating
The hydroxy ester was dehydrated with phosphorus pentoxide, producing ethyl methacrylate: PnOr
(CH~)~C(OH)COOCZHI + CHZ=C(CHa)COOCaHs
(7)
By 1936, the methyl ester of methacrylic acid was used to produce an “organic glass” by cast polymerization, and methyl methacrylate was produced initially through methyl a-hydroxyisobutyrate by the same process indicated above for the ethyl ester. Process changes through the three decades that acrylic esters have been commercial have lowered costs substantially. Hydrogen cyanide is now produced catalytically from natural gas, ammonia, and air:
Air plant VOL. 51, NO. 10
OCTOBER 1959
1233
0 3 N
I C
F-! ' I
z w
!
I 7
3NVP13W
I
c
W 5
3NVHl3W
r-
I 234
INDUSTRIAL AND ENGINEERING CHEMISTRY
t
1
I
t
ACRYLATES A N D METVACRYLATES production workers. All of these operations are highly automated, with more than $7,000,000 (nearly 10%) of the total investment being instrumentation (on an installed basis). Because of the complete integration and the consequent difficulty if any one .unit is out of operation, Rohm & Haas has six maintenance people for every ten operating employees; however, actual maintenance costs are quite low (less than 3% of original investment per year), partly because most of the plant is of recent construction but also because of the extensive use of alloys as materials of construction. About 900,000,000 cubic feet of natural gas are used every month on an average. Although 80,000 gallons of water per minute are circulated throughout the plant, this has been no problem as there are three deep wells at the site and extensive use is made of cooling towers with recirculation of water for cooling purposes. A dual feed electrical power system goes into the Rohm & Haas substation; if one fails, the other takes over automatically in a matter of a few cycles. The processing starts with the production of four raw materials. These are: ammonia, produced by a standard Foster-Wheeler package unit (3); acetylene, produced by a BASF-Chemico unit ( 2 ) ; and carbon monoxide and hydrogen, produced by the Texaco process ( 3 ) , purified in a standard Girbitol ethanolamine unit, and separated in a low temperature separation plant engineered by L’Air Liquide ( 4 ) . This was the first commercial-size L’Air Liquide separation plant for carbon monoxide and hydrogen installed in this country. The feed containing carbon monoxide and hydrogen from the Texaco plant is compressed and scrubbed in the Girbitol unit, followed by caustic scrubbing to remove the remaining carbon dioxide. In the low temperature unit, the carbon monoxide is liquified and separated from the hydrogen by distillation. Both carbon monoxide and hydrogen leave the unit at high purity. As the plant is operated so that carbon monoxide is made only as needed, very little intermediate storage is required.
HCN plant ammonia as ammonium sulfate and ammonium bisulfate, which are pumped to the ammonium sulfate plant. An elaborate system of instrumentation is required to maintain the proper flow of the feed gases to the catalyst and to handle the cooling, compression, and recovery of hydrogen cyanide without excessive losses through polymerization. Exit gases from the converter are passed through a two-stage compressor and then cooled by refrigerated water before they enter the water absorber. The main stream consisting of dilute hydrogen cyanide leaves the bottom of the water absorber. Tail gases leaving the top of the column have a low fuel value and are used as fuel for the decontamination furnaces associated with the nickel carbonyl plants. Dilute hydrogen cyanide solution is concentrated in an atmospheric distillation column. Pure hydrogen cyanide from the top of the column is condensed at 25’ C. and stored for further use. Water from the bottom of the distillation column is
Hydrogen Cyanide and Acetone Cyanohydrin
Hydrogen cyanide is manufactured by mixing preheated air, ammonia, and natural gas, and passing the mixture through a platinum catalyst. Conditions for this reaction are critical. I t must take place at a relatively high temperature (above 1000° C.) to maintain a favorable equilibrium in the reaction between methane and ammonia. The incoming air is scrubbed to remove impurities which would tend to poison the catalyst screen. Decomposition of ammonia to nitrogen and hydrogen and of methane to carbon and hydrogen, and the oxidation of methane with oxygen to carbon monoxide and hydrogen are side reactions which occur. Feed gas ratios must be carefully controlled to minimize these effects (Figure 2). Gases leaving the catalyst screen are cooled by means of a waste heat boiler which removes most of the heat from these gases by generating steam. The gases are then scrubbed with a stream of dilute sulfuric acid to remove the
COMPRESSOR
TAIL
Intermediate Manufacture
After producing these four raw materials, five intermediates are made for use in producing acrylate and methacrylate esters-methanol, hydrogen cyanide, acetone cyanohydrin, nickel carbonyl, and fatty alcohols. With the exception of methanol, which is produced by a licensed Foster-Wheeler process (5), all of these intermediates are made by processes developed by Rohm & Haas chemists and engineers.
STEAM
TO REFRIGERATED STORAGE
a
a ACID
=-----I$ Figure 2.
The hydrogen cyanide process VOL. 51, NO. 10
OCTOBER 1959
1235
A Compressors for ammonia refrigeration unit in HCN plant
Acetone cyanohydrin area
acidified and recycled to the water absorber. Acetone cyanohydrin is produced by the reaction of hydrogen cyanide and acetone with an alkaline catalyst in a cooled reaction kettle. The excess catalyst is neutralized and crude acetone cyanohydrin passes to holding tanks. The salt formed by neutralization of the catalyst is removed in a filter press before the crude acetone cyanohydrin is fed to the first stage of a tivo-stage distillation unit. In the first column, most of the water and acetone are removed overhead and partially concentrated acetone cyanohydrin is fed to the second-stage column, Lvhere the remainder of the water is removed at high vacuum from the top and acetone cyanohydrin of over 9801, purity is removed from the bottom, cooled, and stored (Figure 3).
b
argon, nitrogen, and methane, accumulate in the recycled gas and must be vented to maintain the partial pressure of carbon monoxide above 1500 p.s.i. in the reacting gases. The liquid slurry from the reaction goes to waste. Venting of the inert gases provides the major loss of nickel carbonyl, but in spite of this loss the yield of carbonyl based on nickel is high. All of the waste gas streams from the nickel carbonyl operations are passed through a decontamination furnace \\here they are heated to destroy the carbonyl. Gases from this furnace, Lvhich are now harmless, are discharged to the atmosphere through a high stack (Figure 4 ) .
Fatty Alcohols Hydrogen, used mainly for manufacturing ammonia, is also used to make
fatty alcohols for higher methacrylate ester production. The first step in fatty alcohol manufacture is methanolysis of coconut oil and tallow to recover glycerol and give fatty acid methyl esters. In this operation, coconut oil. talloiv. methanol, and sodium hydroxide are fed into a packed column. The main stream, consisting of methyl esters of fatty acids, methanol, and some glycerol comes off the top. The bottoms from the methanolysis column (containing glycerol, methanol: sodium hydroxide and {vater) go through a cation exchange column using Amberlite IR-120 resin and into a settling tank. Fatty acids separate and pass through an esterification vessel where methanol is added to form additional methyl esters. These are recycled to the methyl ester main stream entering the bottom of thr Lvash column.
Nickel Carbonyl Nickel carbonyl is required as a raw material for methyl and ethyl acrylate Solutions containing nickel chloride and sodium hydroxide are pumped through high pressure injection pumps, and carbon monoxide is compressed in a four-stage compressor. Nickel carbonyl is produced by mixing the nickel chloride brine and sodium hydroxide solution with carbon monoxide and a catalyst in a high pressure agitated reactor. At a temperature above 100°C. the nickel carbonyl leaves the reactor with an excess of carbon monoxide and is condensed into a product receiver and stored under refrigerated conditions. Excess carbon monoxide is recycled through the process. Inert gases, such as
1236
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 3.
T h e acetone cyanohydrin process
A C R Y L A T W AND MEVHACRYLATES
,A Gas purification-methanol
4
The bottom layer from this settling tank consisting of methanol, water, glycerol, and traces of fatty acid, passes through a Monobed resin exchanger (a mixture of Amberlite IR-120 and Amberlite IRA-401) to adsorb fatty acid. The glycerol is recovered by evaporation of the water and methanol. The main stream of the fatty acid methyl esters, following passage through a washing column to remove methanol, is distilled in a fractionating tower under vacuum and condensed into a hold tank, where copper chromite catalyst is added prior to hydrogenation. The latter is carried out in a multistage tower under a hydrogen pressure which reaches
Hydrogenation reactors-fatty
t a temperature of 270' to 280' 'C. The liquid level in the last stage of this hydrogenation tower is automatically controlled by a radioactive cesium probe. Low-boiling alcohols from the top of the hydrogenator are condensed, extracted with water to separate methanol, and the remaining low-boiling alcohols recycled to the high pressure reactor through the catalyst blend tank. The main product stream, taken from the bottom of the final stage of the high pressure reactor, passes through a centrifuge to recover catalyst, through a filter press for removal of final traces of catalyst, and finally into a distillation column main-
5000 D. i.
WATER
NICKEL CARBONYL RECYCLE CO COMPRESSOR
Figure 4.
The nickel carbonyl process
and ammonia
alcohol process
tained at a reduced pressure of 30 mm. The 8- and 10-carbon alcohols come off the top of this column. The residue goes to a fractionating column maintained at 10 mm. which separates one cut of 12- and 14-carbon alcohols, and another cut of 16- and 18-carbon alcohols. Throughout the process there are a number of points where methanolwater mixtures are obtained. These are all sent to a recovery unit and the methanol is recycled to the methanolysis column (Figure 5).
Safety First Safety is a vital consideration at Rohm & Ham' Houston operations, and the plant management conducts an intensive safety program. Both hydrogen cyanide and nickel carbonyl are very toxic, with a recommended maximum allowable concentration in the air of 0.04 p.p.m. for nickel carbonyl. Yet the safety record at the Houston plant is outstanding. I n a decade of operations there have been only seven lost time injuries due to exposure to chemicals, with no permanent disabilities. Four of these involved exposure to nickel carbonyl, one each was caused by ammonia, acid burns, and nitrogen. Nickel carbonyl is by far the most dangerous product handled in the plant, and is one of the most toxic materials handled industrially anywhere. Rohm VOL. 51,
NO. 10
OCTOBER 1959
1237
COCONUT OIL AND TALLOW
WATER
1
METHANOLYSIS
METHANOL
SODIUM HYDROXIDE
F A T T Y ACIDS WATER
~i
i
MET~~ANOLWATER TO
Ii
RESIDUE
RECOVERY AND RECYCLE
+ C B / C I O ALCOHOLS
DISTILLATION
WATER
-
EXTRACTION FILTER
CENTRIFUGE
WATER TO RECOVERY AND RECYCLE C 16 / C IB ALCOHOLS
METHYL ESTERS
IC
FATTY ACIDS RECOVERY
GLYCEROL 1
Figure 5. The fatty alcohols process & Haas has already spent over $400,000 on studies of the physiological properties of nickel carbonyl and on methods for its detection in the minute quantities which could be injurious. Urine samples of all employees subject to possible exposure are checked weekly for nickel content. Nickel carbonyl is particularly insidious because it lacks any strong or penetrating odor to warn of its presence and because the most serious symptoms of exposure are delayed for hours or even several days. Safety considerations in the design of the nickel carbonyl installations added over $2,000,000 to the cost of the two acrylate plants. All equipment is housed in rooms or “cells,” each of which is provided with an induced draft fan which changes the air every 2 minutes and maintains the cell under slight vacuum so that the air is drawn in through louvers. These fans, and others used to eliminate any dead spots, discharge directly to the fire box of a decontamination furnace where any nickel carbonyl is immediately decomposed at 1000” F.
1238
and exhausted to a 150-foot stack. Each of the air streams being withdrawn from the cells is continuously monitored by a detector specifically designed by Rohm & Haas for this purpose. I n addition, the air in the control room is checked by a chemical sampling method which will detect concentrations as low as 2 parts per billion. No process streams are brought into the control room, all measurements being made in the field and relayed pneumatically or electronically to the control panel. All process controls and changes are made from this board. The cells are entered for short periods only, each hour, to check equipment, and personnel entering the cells are required to wear fresh air masks. Many details of the methods employed by Rohm & Haas in handling nickel carbonyl are contained in an article by Cummings (7). Hydrogen cyanide, while deadly at low concentrations, is not so difficult to handle as nickel carbonyl because of its higher maximum allowable con-
INDUSTRIAL AND ENGINEERING CHEMISTRY
centration in air (10 p.p.m.) and because of its typical odor. However, this does not mean that hydrogen cyanide is taken for granted at the Rohm 8: Haas plant. Each new employee gets a sniff of hydrogen cyanide and is taught to recognize the odor. Special equipment is provided for obtaining hydrogen cyanide samples. The sample pot in the hydrogen cyanide line has a constant vacuum pull to remove vapor from the pot. The liquid line enters on the back side of the sampling chamber away from the operator; there is also a water line to thoroughly wash the sample bottle prior to withdrawing from the hood. After the operator, who must wear glasses and rubber gloves, takes the sample from inside the pot, he immediately places it in a bucket of ice. The sample is kept cold to reduce vaporization until it can be analyzed under a hood in the laboratory. Another operator always stands by to render assistance in case of an accident. Pumps handling hydrogen cyanide solutions have sealed water at a higher pressure than pump pressure so any leakage is inward. Manual checks are made hourly at various points for detection of hydrogen cyanide leakage. When critical operations go out of range in either the hydrogen cyanide or nickel carbonyl areas, the unit is automatically shut down immediately. Handling of acetylene requires special precautions, involving explosion arresters and rupture disks located at strategic points; as a further safeguard against explosion, specially constructed high pressure lines are used even though the acetylene gas is handled at relatively low pressures. Another important aspect of the safety program has been the installation of two completely separate units for hydrogen cyanide, acetone cyanohydrin, methyl methacrylate, nickel carbonyl, and methyl and ethyl acrylates. The considerably higher cost of duplicating units instead of expanding existing ones was considered worthwhile as assurance against possible explosions or other damage to any one unit. There are even two separate boiler houses providing steam to the plant. literature Cited (1) Cummings, G. H., Proc. of Semi-
Annual Tech. Meeting, Air Pollution Control Assoc., p. 102, Dec. 3-5, 1956. (2) Department of Commerce, Washington 25, D. C., B. D. Rept. No. 4-49--2, Oct. 5, 1959. Fiat Final Rept. No. 988. ( 3 ) Kearny, M. F., Jr., Hrat Eq. 30, NO. 2, 22-9 (1955). (4) Nelson, W. L., Kerry, F. G., presented
before AIChE Meeting, Ohio, December 1958.
Cincinnati,
( 5 ) Petrol. RpJiner 36, No. 11, 261 (1957). (6) Riddle, E. H.: “Monomeric Acrylic
Esters,” Reinhold. New York, 1954.
( 7 ) Rohm, Otto, Ph.D. thesis, Franz Pietz-
cker Publishing House, Tiibingen, Germany. 1901.
