Figure 23
Qualitative flow diagram for the manufacture of sodium dodecylbenzene sulfonate.
After removal of aluminum chloride sludge, the reaction mixture is fractionated to recover excess benzene (which is recycled to the reaction vessel), a light alkylaryl hydrocarbon, dodecylbenzene, and a heavy alkylaryl hydrocarbon.
Sulfonation of the dodecylbenzene may be carried out continuously or batch-wise under a variety of operating conditions using sulfuric acid (100 percent), oleum (usually 20 percent SO,), or anhydrous sulfur trioxide. The optimum sulfonation temperature is usually in the range of 100 to 140°F depending on the strength of acid employed, mechanical design of the equipment, etc. Removal of the spent sulfuric acid from the sulfonic acid is facilitated by adding water to reduce the sulfuric acid strength to about 78 percent. This dilution prior to neutralization results in a final neutralized slurry having approximately 85 percent active agent based on the solids. The inert material in the final product is essentially Na2S04.
The sulfonic acid is neutralized with 20 to 50 percent caustic soda solution to a pH of 8 at a temperature of about 125°F. Chemical "builders" such as trisodium phosphate, tetrasodium pyrophosphate, sodium silicate, sodium chlo ride, sodium sulfate, carboxymethyl cellulose, etc., are added to enhance the detersive, wetting, or other desired properties in the finished product. A flaked, dried product is obtained by drum drying or a bead product is obtained by spray drying.
The basic reactions which occur in the process are the following. Alkylation:
Sulfonation:
C6H5 . C12H25 + H2S04 —■» CuHa . C6H4 . S03H + H2O
Neutralization:
C12H25 • C6H4 • SO3H + NaOH-> C12H25 . C6H4 • S03Na + H20
A literature search indicates that yields of 85 to 95 percent have been obtained in the alkylation step, while yields for the sulfonation process are substantially 100 percent, and yields for the neutralization step are always 95 percent or greater. All three steps are exothermic and require some form of jacketed cooling around the stirred reactor to maintain isothermal reaction temperatures.
Laboratory data for the sulfonation of dodecylbenzene, described in the literature, provide additional information useful for a rapid material balance. This is summarized as follows:
1. Sulfonation is essentially complete if the ratio of 20 percent oleum to dodecylbenzene is maintained at 1.25.
2. Spent sulfuric acid removal is optimized with the addition of 0.244 lb of water to the settler for each 1.25 lb of 20 percent oleum added in the sulfonation step.
3. A 25 percent excess of 20 percent NaOH is suggested for the neutralization step.
Operating conditions for this process, as reported in the literature, vary somewhat depending upon the particular processing procedure chosen.
Material and Energy Balance
The process selected for the manufacture of the nonbiodegradable detergent is essentially continuous even though the alkylation, sulfonation, and neutralization steps are semicontinuous steps. Provisions for possible shutdowns for repairs and maintenance are incorporated into the design of the process by specifying plant operation for 300 calendar days per year. Assuming 90 percent yield in the alkylator and a sodium dodecylbenzene sulfonate product to be 85 percent active with 15 percent sodium sulfate as inert, the overall material balance is as follows: Input components:
C12H24 feed = 142.7 lb mol/day
= (142.7X168.3) = 24,016 lb/day 20% oleum in = (1.25X11,145 + 24,016) = 43,951 lb/day Dilution H20 in = (0.244/1.25X43,951) = 8579 lb/day 20% NaOH in = (1.25X43,951) = 55,085 lb/day A1C13 catalyst in = (0.05X11,145 + 24,016) = 1758 lb/day
Alkylation process:
Alkylate yield = (0.9X142.7X246.4) = 31,645 lb/day Unreacted C6H6 = (0.1X11,145) =1114 lb/day Unreacted C12H24 = (0.1X24,016) = 2402 lb/day
Sulfur balance:
Sulfur in = (43,951X1.045X32.1/98.1) = 15,029 lb/day Sulfur out = sulfur in detergent + sulfur in spent acid
= 3915 + 1695 = 5610 lb/day Sulfur out in acid = 15,029 - 5610 = 9419 lb/day
- 36,861 lb/day
The weight of the heavy alkylaryl hydrocarbon is obtained by difference as 3516 lb/day.
The material balance summary made by the design group for the process shown in Fig. 2-3 is given on a daily basis in Fig. 2-4. After a complete material balance is made, the mass quantities are used to compute energy balances
Basis : One operoting doy 16 i
Production of 15» 10" |b/yr ABS with-plant operation of 300 calendar doys per year
Row moteriols
Processing
Products
Production of 15» 10" |b/yr ABS with-plant operation of 300 calendar doys per year
Row moteriols
Processing
Products
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