Ethyl en e CIxide
Glycols and
D. GRAY WEAVER, Associate Editor in collaboration with
JOHN L. SMART, Dow Chemical of Canada, Limited, Sarnia, Ontario, Canada
First stage of triple-effect evaporator, in glycol-finishing operation runs at 10-atm. pressure
Cm.m.&’s
first glycol plant went on stream 11 years ago at’Dow Chemical of Canada’s site at Sarnia, Ontario. This was the second Dow operation north of the border, the first having been a-polystyrene unit opened the year before. And just two years ago, Dow opened its 13th facility a t that same location-to make ethanolamines. Together the glycol and ethanolamine plant units form a closely knit petrochemical complex. During World War 11, Canadian consumption of ethylene glycol-supplied by the United States-had risen sharply. I t reached a peak of about 60,000,000 pounds per year in 1944, due in con-
894
siderable part to the need for antifreeze solutions in cooling systems of military vehicles and to the use of its dinitrate derivatives as a freezing inhibitor for nitroglycerine dynamites ( I ) . Production in the U.S.that year totaled some 400,000,000 pounds (5). Immediately after the War, U. S. production tapered off only slightly but Canada’s peacetime requirements for ethylene glycol dropped to half the level of 1944. And, of this, about 20,000,000 pounds went into automobile antifreeze (6). Today Canadian consumption of monoethylene glycol (MEG) approaches 90,000,000 pounds, more than three fourths of which is for automotive use.
INDUSTRIAL AND ENGINEERING CHEMISTRY
To this, some 3,000,000 pounds of diethylene glycol (DEG) and triethylene glycol (TEG) are for uses other than antifreeze. By 1963, the Canadian market for MEG is expected to reach 109,000,000 pounds, with another 4,500,000 pounds of DEG and TEG. U. S. production is now in the billionpound-per-year bracket. The ethanolamine market is much smaller, though highly developed. Major use today for Canadian monoethanolamine (h4EA) is in Western natural-gas processing. The Canadian market for MEA depends largely upon this natural-gas development, and shows excellent grow-th potential. About half
of Canadian MEA production currently goes to this market. Other important processes using MEA include manufacture of syndets, production of ammonia and dry ice, and purification of refinery gas. Diethanolamine (DEA) goes chiefly into synthetic detergents (60Y0 of the market), textile specialities, and various organic intermediates. Triethanolamine (TEA) is used in toiletries and cosmetics (50%), syndets, and rubber chemicals.
Ethylene Oxide Production
#
There are several practical methods of preparing glycols; the most efficient of these (75% or higher over-all yield) involves catalytic hydrogenation of a glycolic acid ester ( 4 ) . I n this process, the acid is prepared in about a 90 to 95oj, yield by reaction among formaldehyde, water, and excess of carbon monoxide, at 200" C. and 700-atm. pressure: CHOH f HzO
+ CO
CHzOH. COOH
+
ROH -+ CH2OH.COOR
+ HzO
Then the ester is reacted with hydrogen, using a chromite catalyst at 200" C. and 30-atm. pressure. This step, too, gives a 90 to 9570 yield. Where pressures above 100 atm. are preferred, a
Pumped to a mixer maintaining the pressure, the fluid meets a stream of chlorine which reacts with the lime to form an unstable intermediate, calcium oxychloride: CaO
HzC
- CHz
'h
$- H z O
The ethylene oxide is absorbed in a scrubber and hydrated to the glycol, with about a 7oy0yield ( 3 ):
i;'
+ HzO
+ HOHzC.CHzOH
Other processes involve preparation This is converted to glycol directly by hydrolysis or indirectly through intermediate forrnation of ethylene oxide which is then hydrolyzed to give the glycol. One method for making chlorohydrin requires ethylene, at ambient temperature, to be mixed with a slurry of hydrated lime under pressure of 200 atm.
of ethylene chlorohydrin.
Dow Chemical Makes Progress Since 1950, the petrochemical industry has grown faster in Canada than any other place in the world. Canadian plant investment for petrochemicals i s approaching half a billion, and end products of about a quarter of a billion are being produced annually north of the border. Reflecting this dynamic growth i s Dow Chemical of Canada, Limited., in Sarnia, Ontario. Born in 1942 t o build and operate a styrene unit for Polymer Corp.-the Canadian Government's wartime syntheticrubber plant next door-the firm drew upon know-how developed in the parent Dow organization in Midland, Mich. After the War, Dow of Canada built a continuous polymerization plant, adjacent to Polymer, for making polystyrene. DOW, which continued to manage Polymer's styrene plant until the end of 1950, contracted to buy excess styrene monomer, along wiih water, steam, and electric power, from the Crown corporation. During these early postwar years, Polymer had excess ethylene from its light-ends recovery unit. Dow saw a good future for Canadianproduced ethylene glycol, and arranged-even before the polystyrene plant was finished-to purchase all of Polymer's surplus ethylene. Construction began late in 1946 on the Dow Canada glycols plant, and the first shipment of Canadian ethylene glycol was made early in 1948. Dow Chemical of Canada has so far placed over a dozen plants on stream at Sarnia-better than one a year. Latest in production are methyl chloride and methylene chloride units which shipped their first orders in the fall of 1958 and a new low-pressure-process-polyethylene plant completed in February 1959. None of these chemicals was ever before made commercially in Canada.
+ Clz
+
CaClOCl
This immediateIy decomposes to give calcium chloride and hypochlorous acid, CaClOCl
+ CL + H2O
-+
CaClz
+ 2HOC1
which then reacts with the ethylene to give a 35 to 40% solution of chlorohydrin : H2CeCH2
H~C-CHZ
+
The glycolic acid is purified by esterification and subsequent distillation: CH2OH.COOH
magnesia/copper oxide catalyst is ernployed. A more direct method involves catalytic oxidation of ethylene with air and subsequent hydration of the ethylene oxide to form glycols. Here, ethylene and air are mixed (1 : 10) and passed over a corundum-supported-silver oxide catalyst. A small amount of ethylene dichloride is usually added to suppress formation of carbon dioxide. At temperatures of 270' to 290' C., with contact time of about 1 second, a t least 60% conversion is usually attained at essentially atmospheric pressure :
+ HOC1
-+
HOHAC.CHzC
Two different routes then can be used to prepare the glycols. For direct hydrolysis, the chlorohydrin solution is treated with the theoretical amount of sodium bicarbonate solution at 70" to 80" C. in a closed, steam-jacketed, efficiently agitated kettle. After 4 to 6 hours, the reaction is complete and evolution of carbon dioxide, which can be used to carbonate fresh caustic solution, ceases:
+
CHzOH. CH&l NaHCO,j 4-HzO + CHzOH.CH20H HzO $. C 0 2 NaCl
+
+
The crude glycol is then concentrated and separated from the brine by distillation. But this salt separation presents engineering difficultieswhich can be reduced by indirect hydrolysis. To get glycols this way, the ethylene chlorohydrin solution is mixed with lime or sodium hydroxide (2) to yield ethylene oxide. This is more easily separated from the brine and can then be hydrated with slightly acidified water under high temperature and pressure to give crude glycols.
Chlorohydrin Process at Sarnia The Dow Canada process is closer to the last of these procedures, with improvements from the parent company's previous experience with the chlorohydrin method a t its Midland, Mich., plant, started in 1937, and from the Dow Texas division, in operation since 1941. I n essence, the operation at Sarnia makes chlorohydrin from ethylene, water, and chlorine. It then neutralizes this to get ethylene oxide which is in turn hydrolyzed to form glycols. From salt deposits some 2700 feet underground, brine is piped from seven wells to either mercury cells or diaphragm cells at the site. Some of the chlorine produced is liqufied for sale; most is piped to the glycol plant. Here, it is sparged, along with ethylene and preheated water, into the chlorohydrin reaction towers, somewhat less than 100 feet in height. The water (15' C. to VOL. 51, NO. 8
AUGUST 1959
895
HANOLAM1NI RIPIT
-! MIXED GLYCOLS WATER
w HYDROLY ZER
DRY MIXED GLYCOLS
IlEC
0 WATER
PLANT PROCESS SERIES
DIETHANOLAMINE
I
TRIETHANOLAMINE
A MONIA ilPPlNG .UMN AQUEOUI AMMONIF ETHYLEh OXIDE
El REACTOR
~~
Flowsheet for the manufacture of glycols and ethanolamines, Dow Chemical of Canada, Ltd., Sarnia, Ont., Canada
896
INDUSTRIAL AND ENGINEERING CHEMISTRY
GLYCOLS A N D ETHANOLAMINE Ethylene oxide, along with some water vapor, is compressed and condensed. This crude contains about 10% EDC and about the same amount of water. These impurities, along with traces of acetaldehyde (“poisonous” for some uses of glycols as intermediates) are later removed in finishing columns 60 feet high. The EDC is neutralized by aqua ammonia. Lighter and heavier components of the crude material are separated by distillation. Finally, bottoms go to rectifier columns which remove “heavies.” This by-product EDC output nicely balances Dow of Canada’s sales of the chemical as an ingredient in tetraethyl lead formulations for motor antiknock compounds.
Ethylene Oxide 4 Glycols
Product finishing columns loom over the five-story ethylene glycol plant at Dow Chemical of Canada in Sarnia. Storage tanks in foreground contain ethylene oxide
40” C.) is also introduced at the base of the brick-lined, acidproof reactors. The gases are only slightly soluble at operating temperatures. Ethylene chlorohydrin (ECH) formation proceeds rapidly and the reaction is nearly complete within the first few feet of travel up the tower : Clz HzO + HOCl HC1 HOCl HzCeCH2 + HOCHz*CHzCl By-products include ethylene dichloride (EDC), Clz HzC=CHz + CICHz.CHzC1
+
+
+
+
and bis-(2-chloroethyl) ether, 20HzCH. CHzCI + CH2ClCHz--O-CHz* CHzCl HzO The dilute chlorohydrin solution from the reactors flows into a gas-disengaging tower. Concentration of ECH runs about 4%. Gases from the reactors and foam tower vent to an overhead acidregistant condenser to recover the EDC. The cooled gases vented from the chlorohydrin reactors are scrubbed with water in acidproof towers which remove the last traces of chlorine before the gases vent into the atmosphere. The dilute ECH solution can now leave acidproof equipment, and it passes into hydrolyzers made of mild steel. Hydrolysis takes place in a weak alkali medium-slaked lime from nearby limestone quarries and kilns or caustic soda
+
from the chlorine cells may be used. The lime reaction:
+
Ca(OH)2 + 2HOCH2. CHzCl 2HzC-CHz CaClz \/
+
+ 2Hs0
6
is the slower. The caustic hydrolysis is considerably faster :
+
HOCHZ.CHzCl NaOH + HzC-CHZ NaCl f HzO
‘d
+
T o produce glycols, the main ethylene oxide product is hydrolyzed in liquid phase under pressure and mixed with 8 parts of water at the same pressure. The mixture, containing recirculated “sweet water” from the continuous system, is preheated above 100” C . to initiate the reaction. This is strongly exothermic and the temperature continues to rise during transit through the reaction vessels which provide ample retention time for the process flow rate. Temperature rises to maximum (165’ C. to 185” C.) as the solution traverses the reactor system. The end of the temperature rise signals the end of the reaction, which gives principally monoethylene glycol (MEG) : HzC-CHz
x
+ HzO
+
HOCHz.CHz0H
Diethylene glycol (DEG) and triethylene glycol, along with “tars”
Working space is important-horizontal run tanks and holding tanks in foreground, finish storage in background serve the glycols operation
Finishing columns in glycols plant
(higher glycols), are present in the crude product. These result from primary MEG reacting further with ethylene oxide : HzC-CHz
‘b/
+ HOCHz.CHeOH
HOCHs. CHZ-O-CH2,
--t
CHZOH,
etc.
Glycol Purification The crude glycols solution is concentrated by a multiple-effect evaporator. The first stage operates at about 10-atm. pressure and takes off about one third of the water. I t then bottoms to a second
Production o f e t h y l e n e glycol starts with chlorohydrin r e a c t i o n towers (right),ends with triple-effect evaporator in batch-finishing columns (center)
similar tower where another one third is removed. The final step runs under vacuum (0.1 atm.), and the resulting crude glycol mixture is nearly anhydrous. A clean-up tower provides final drying. T o separate MEG from the mixture, a finishing column about 60 feet tall pulls a loiv vacuum (25 to 40 mm. Hg) furnished by two-stage steam jets. Bottoms from this still proceed to a DEG finishing column, some 70 feet tall, operating under a similar low vacuum. T o finish the TEG, a 60-foot batch column, drawing an extremely low vacuum (5 to 10 mm. Hg), processes bottoms from the DEG column.
Modern synthetic fibers demand a very pure grade of ethylene glycol to ensure consistent properties and absence of discoloration. Dow of Canada recently has put in a new $100,000 installation, including a column 80 feet tall, having a stainless-steel top to avoid iron pick-up. Taking a side-cut from the MEG column, it gives material with a narrow boiling-point range for this special “Terylene grade” product. Ethanolamine Process Conventionas
The process used by Doiv of Canada to make ethanolamines is basically the
conventional method, a reaction between ethylene oxide and ammonia: HzCCHz
'4
+ NH3
( Monoethanolamine) +
HOCHz.CHz.NHz
+ HzC-CHe
( Diethanolamine)
\d
HOCHz * CHe.NH. CH:!, CHzOH +A
+
Crude amine mixtures are separ a t e d in t h e s e finishing columns for MEA, DEA, and
TEA
H2C--CH*
(Triethanolamine) The company makes its own ammonia, in an adjacent unit on the Sarnia plant site. This employs a conventional highpressure process using hydrogen and nitrogen. The hydrogen is obtained from the two Dow chlorine plants on the site and by treatment of de-methanizer overhead gas from the ethylene plant. Purchases from nearby refineries supplement the supply of hydrogen. Nitrogen is produced in a conventional air-separation plant. A mixture of 75% hydrogen and 25y0 nitrogen is raised to 5000 p.s.i. in multistage compressors. The main gas stream, purified and compressed, passes to converters which do the bulk of the synthesis. Only a small fraction of the gas mixture is combined to form ammonia on a single pass through the equipment, so the product is continuously condensed out and unreacted gas is recirculated. The product is stored, for sale and shipment, as liquid anhydrous ammonia in insulated vessels. For use in the ethanolamines operation, it is dissolved in water to 30y0 content and piped to the primary reaction plant. Here, it is
adjusted in a shell-and-tube absorber by adding 35 to 5070 high-strength anhydrous ammonia from the stripper in the operation, depending upon production rate desired. Concentration of the aqua ammonia is cut back, when required, by adding condensate from the ethanolamines system itself.
Liquid ethylene oxide from adjacent glycols plant and aqua ammonia (both at 500 p.s.i.) are pumped together under enough pressure to maintain the liquid phase. Two reactions in series provide sufficient retention time to complete the ethylene oxide reaction. Excess ammonia is maintained to control the prod-
Y
Ammonia-stripper and water-stripper (center) for purification of ethanolamines and ammonia form a vital part of Dow of Canada's continuous ethanolamines process. Crude amine tank and ammonia storage are in the lower right
HorizontaI tanks in foreground are the heart of the reaction system
VOL. 51, NO. 8
AUGUST 1959
899
Ethylene oxide and aqua ammonia react at 500 p.s.i. in these continuous reactors to give a mixture of ethanolamines by a highly exothermic reaction
uct distribution among mono-, di-, and triethanolamines. The reaction is highly exothermic, so the reactors themselves have temperature controllers to prevent a “run-away.” From these reactors the material is pumped to an ammonia stripper to remove unreacted excess ammonia. This operates at 50 p.s.i. and about 135” C., depending upon composition of bottoms. The bottoms are fed to an evaporator,
running at atmospheric pressure and 1 1 5 O C. The water removed here is recycled to the absorber-as make-up water-to control concentration of the aqua ammonia input stream. Product from the evaporator goes to a dehydrator, 150-mm. H g pressure and 140’ C., which removes the water to conform with specification limits. Bottoms from the dehydrator are pumped to a crude-amine surge tank.
Natural Gas -Big Ethanolamine Market Ethanolamine production in Canada i s being geared to keep pace with availability of natural gas. Ethanolamines are essential for treating crude gas, removing hydrogen sulfide in the “sweetening” process. Most natural gas, as it flows from the wells, contains hydrogen sulfide, and is known as sour gas. It contains about 90% hydrocarbons (most of this methane), 6.5% carbon dioxide, and 3.5y0 hydrogen sulfide, plus a little water vapor and natural gasoline. For fuel use in both home and indusfry, and in applications as a chemical raw material, the impurities must b e removed. The refined pipeline product, or sweet gas, i s essentially free of corrosive and noxious acid gases. Gas processors in Canada are turning more and more to monoethanolamine for sweeting crude natural gas. Here, the sour gas i s scrubbed with monoethanolamine to remove hydrogen sulfide. Dissolved hydrogen sulfide is then removed from the saturated amine and converted to elemental sulfur. The amine i s recirculated. A second major use for boih these amines i s in producing liquid detergents for household and industrial use. A major application for triethanolamine, the weakest base of the three, i s as an emulsifier. Cleaning and polishing compounds take the biggest bite here. Cosmetics and rubber chemicals are two large-volume endproducts using this chemical in their formulations.
900
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The liquid is drawn from here to the monoethanolamine (MEA) finishing column, running under vacuum at less than 10-mm. Hg, provided by threestage steam jets. The MEA product is taken overhead. Bottoms from the column proceed to the triethanolamine (TEA) stripper, operating under similar low vacuum, to separate diethanolamine (DEA) from crude TEA which goes to a hold tank. The separated DEA is piped to DEA finishing column, also working under vacuum below 10 mm. Finished overheads here go to DEA storage, and bottoms cycle back to the TEA stripper. Meanwhile, material from the crudeTEA tank is pumped to TEA finishing columns, operating at the same strong vacuum, on an elevated section of the building. This last step is not continuous and is termed a semibatch operation. I t sends product to TEA storage tanks. The heavier fraction remaining (including tars, other condensation products, and some residual TEA) is not separated further, being salable “as is.” Literature Cited
(1) Can. Chem. Process Znds. 32, 218-20 (March 1948). (2) Faith, W. L., Keyes, D. B., Clark, R. L., “Industrial Chemicals,” 2nd ed., p. 377, Wiley, New York, 1957. (3) Zbid.,p. 378. (4) Ibid., p. 379. ( 5 ) Z6id.,p. 385. (6) Shell Oil Corp. of Canada, Ryerson, Toronto, ”The Canadian Petrochemical Industry,” p. 35, 1956.
