I/EC A
COSTS
W O R K B O O K
F E A T U R E
by Walter L. Hardy, Foster D. Snell, Inc.
Plant to Produce 2,4-D Acid and Isopropyl Ester To compete commercially, plant must make base materials, 2,4-dichlorophenol and monochloroacetic acid
N 1944, the problem of weed conIdichlorophenoxyacetic trol was first attacked when 2,4acid (2,4-D) was discovered. This pioneer herbicide operates by absorption in the plant, where it disturbs the biochemical balance and causes death. To be useful, of course, a herbicide must be selective. 2,4-D is used to control broad-leaved weeds and is a silvicide as well. It is sold as the acid, as butyl, propyl, octyl, and other esters, and as amine salts. The esters are used in oil sprays and oil-water emulsions. The amine salts are used in water solutions. Sales of 2,4-D acid in 1955 were 34,100,000 pounds. Sales of 2,4-D esters and salts exceeded 28,000,000 pounds. A second herbicide, 2,4,5-T (2,4,5trichlorophenoxyacetic acid), is finding increased use, both alone and in combination with 2,4-D. It is superior to 2,4-D in some respects, in particular for basal bark spraying and destruction of mesquite. The manufacturing process for 2,4,5-T is almost identical to that for 2,4-D. The only basic difference is the substitution of trichlorophenol for the dichlorophenol used in 2,4-D manufacture. 2,4-Dichlorophenoxyacetic acid is manufactured by reaction of 2,4dichlorophenol and monochloroace-
tic acid in the presence of sodium hydroxide. The reaction is: CUCeOH + ClCH 2 COOH + XaOH - * Cl 2 C 6 H 3 -0-CH 2 COOH + NaCl + H 2 0 The required amounts of dichlorophenol, chloroacetic acid, and caustic soda are charged into a jacketed agitated reactor and heated until refluxing starts. While the kettle is maintained at reflux temperature, the reaction is allowed to proceed for approximately 3 hours. At the end of the reaction period, the reaction mixture is run into an acidifying tank, where it is treated with hydrochloric acid to decompose the sodium salt of 2,4-D. From the acidifying tank, the reaction mass is sent to a crystallizer, where 2,4-D acid separates. The resulting sludge is centrifuged to recover crude 2,4-D crystals. Excess dichlorophenol is removed from the mother liquor by distillation. The crude 2,4-D may be recrystallized from benzene to obtain the pure product. Benzene is recycled. Pure 2,4-D crystals are washed, dried, classified, and packaged or sent directly to ester manufacture after drying. 2,4-D ester is manufactured by
reaction of the pure acid with an appropriate alcohol. A typical reaction for the isopropyl ester is: Cl,C 6 H:rO-CH 2 COOH + C 3 H 7 OH - * Cl 2 C 6 H 3 -0-CH 2 COOC 3 H 7 +
H20
The isopropyl ester of 2,4-D is manufactured by a typical procedure. The esterification plant consists of a jacketed, agitated glasslined reactor fitted with a vapor takeoff, vapor condenser, condensate decanter, and condensate return. A charge consists of 2,4-D acid, isopropyl alcohol, methylene dichloride entraîner, and sulfuric acid catalyst. The acid catalyst and methylene chloride are mixed with the alcohol in a primary charge tank and charged into the reactor. With application of low heat and slow agitation the solid 2,4-D crystals are charged into the alcohol mixture and dissolved. The reaction mass is then heated to reflux. Initially, vapors are pure isopropyl alcohol. As the reaction proceeds and water is found, the water is carried over by the entrainer, condensed, and separated from the entrainer-alcohol layer by décantation. The reaction is complete when no more water is removed. V O L . 49, NO. 3
·
MARCH 1957
55
A
I/EC
COSTS
A Workbook Feature
The acid reaction mass is washed with water and dilute carbonate solution. The entraîner is removed by distillation and the ester remaining is drained into containers. Costs of a plant for the manufacture of 4000 pounds per day of 2,4-D acid, with conversion of 2000 pounds per day of this acid to the isopropyl ester, are presented below. If dichlorophenol and monochloroacetic acid are purchased at current carload rates, the cost of raw materials alone would be 41.5 cents per pound of 2,4-D acid produced. Raw material cost per pound of 2,4-D isopropyl ester would be 40 cents. This compares unfavorably with current bulk rates of 37 cents per pound of technical 2,4-D and 39 cents per pound of isopropyl ester. It is evident that no 2,4-D plant can compete which does not also manufacture the base materials 2,4-dichlorophenol and, possibly, monochloroacetic acid. More significant are the estimated production costs, exclusive of raw materials. Processing costs are approximately
6 cents per pound of 2,4-D acid and 4 cents per pound of 2,4-D ester. If all intermediates are purchased, total production costs would be 47.6 cents per pound of 2,4-D acid, and 44.1 cents per pound of 2,4-D ester. To complete successfully in today's mar-
Raw Material Cost Raw Materials
Process charge tanks (2) Reaction vessels (2) Acidifying vessels (2) Crystallizer Centrifuge Recrystallizer unit Tray dryer Caustic soda and acid storage tanks Process pumps Product size reduction and packaging Piping Instrumentation Engineering Contingencies Fixed investment (exclusive of building and site)
56 A
2,4-D acid Isopropyl alcohol Lost methylene chloride Sulfuric acid
2000 640 50 4
1134.60 420.00 55.44 49.00 S1659.04
0.2836 0.1050 0.0139 0.0122 $0.4147
0.4147 0.0670 0.1500 0.0250
829.40 42.88 7.50 0.10 879.88
0.3765 0.0195 0.0034 0.0001 0.3995
Per Day $ 20.00 16.80 12.80 24.00 14.72 $ 88.32 $ 10.00 21.25 0.15 $ 31.40
Maintenance cost, including maintenance labor at 5%/year of total erected cost $ 35.20 Depreciation at 10%/year of total erected cost $ 70.40 Other (to cover taxes, insurance, etc.) at 3%/year of totaj erected cost $ 21.12 $246.44 Daily processing cost Processing cost per lb. 2,4-D acid Total production cost per lb. 2,4-D acid based on purchased intermediates
12,500 5,000
S
0.0616
$
0.4763
2,4-D Isopropyl Ester Plant, 2200 Pounds per Day, 250 Days per Year as Adjunct to 2,4-D Acid Plant
3176,000
$
3660 2000 3960 3500
$/Lb. 2,4-D
Utilities Power, 500 kwh. at $0.02/kwh. Steam, 25,000 lb. at $0.85/1000 lb. Water, 3000 gal. at $0.05/1000 gal. Total utilities
2,4-D Isopropyl Ester Plant, Capacity 2200 Pounds per Day Ester reaction vessel Isopropyl alcohol charge tank Process pumps Product packaging Piping Instrumentation Engineering Contingencies Fixed investment (exclusive of building and site)
2,4-Dichlorophenol Monochloroacetic acid 50% caustic soda 18° hydrochloric acid
S/Day
2,4-D Acid Plant, 4000 Pounds per Day, 250 Days per Year Labor Skilled, 8 man-hours at $2.50 Semiskilled, 8 man-hours at $2.10 Unskilled, 8 man-hours at $1.60 Supervision, 8 man-hours at $3.00 Reserve at 20% Total labor
3,000 20,000 14,000 10,000 8,500 10,000 7,500
10,000 40,000 8,000 12,500 15,000
«/Lb. 2,4-D Acid 0.310 0.210 0.014 0.014
Estimated Production Cost
Erected Cost S
Lb.
2,4-D Isopropyl Ester
Estimated Investment Cost 2,4-D Acid Plant, Capacity, 4000 Pounds per Day
ket, it is evident that dichlorophenol must be made available at below the market price. This can be accomplished by captive production. Larger plant capacity would further increase the possible profit margin by reducing unit processing costs.
Labor Skilled, 8 man-hours at $2.50 Unskilled, 8 man-hours at $1.60 Reserve at 20% Total labor Utilities Power, 300 kwh. at $0.02/kwh. Steam, 20,000 lb. at $0.85/1000 lb. Water, 3000 gal. at $0.05/1000 gal.
8,500
S 20.00
12.80
$
6.56 39. ,36
$
6. . 0 0 17..00 0. .15 S 23..15
800
2,000 7,000 10,000 3,700 3,000 5,000
Maintenance cost, including maintenance labor at 5%/year of total erected cost $ Depreciation at 10%/year of total erected cost Other (to cover taxes, insurance, etc.) at 3%/year of total erected cost Daily processing cost $ $
0.0415
S 40,000
$
0.4410
INDUSTRIAL AND ENGINEERING CHEMISTRY
Processing cost per lb. 2,4-D ester Total production cost per lb. 2,4-D ester based on 2,4-D acid produced with purchased intermediates
8. 00 16.,00 4. 80
91.31
