Page 62 - Chemical Process Equipment - Selection and Design

34 APPENDIX 2.1

bottoms is pumped to storage. The overhead is cooled in a water oxide and other organic materials go overhead; the bottoms contain
exchanger and proceeds to a separating drum. Condensed water unreacted lime, water, and some other reaction products, all of
and an aromatic oil separate out there. The water is sewered which can be dumped. Operating pressure is substantially
whereas the oil is sent to another part of the plant for further atmospheric. Bubblepoint of the overhead is 60°F.
treating. Separation of the oxide and the organic byproducts is ac-
The uncondensed gas from the separator is compressed to complished by distillation in two towers. Feed from the saponifier
300psig in a reciprocating unit of three stages and then cooled to contains oxide, aldehyde, dichloride, and water. In the first tower,
100°F. Condensed water and more aromatic distillate separate out. oxide and aldehyde go overhead together with only small amounts
Then the gas is dried in a system of two desiccant-filled vessels that of the other substances; the dichloride and water go to the bottom
are used alternately for drying and regeneration. and also contain small amounts of contaminants. Two phases will
Subsequently the gas is precooled in exchanger E-6 and form in the lower section of this tower; this is taken off as a partial
charged to a low temperature fractionator. This tower has a reboiler side stream and separated into a dichloride phase which is sent to
and a top refluxing system. At the top the conditions are 280psig storage and a water phase which is sent to the saponifier as recycle
and -75°F. Freon refrigerant at -90°F is used in the condenser. near the top of that vessel. The bottoms are a waste product. Tower
The bottoms is recycled to the pyrolysis coil. The uncondensed pressure is 20 psig. Live steam provides heat at the bottom of this
vapor leaving the reflux accumulator constitutes the product of this column.
plant. It is used to precool the feed to the fractionator in E-6 and Overhead from the first fractionator is condensed and charged
then leaves this part of the plant for further purification. to the second tower. There substantially pure propylene oxide is
taken overhead. The bottoms is dumped. Tower pressure is 15 psig,
and the overhead bubblepoint is 100°F. Reactions are
4. PROPYLENE OXIDE SYNTHESIS
Draw a process flowsheet for the manufacture of propylene oxide C& + HzO+ ClOH + HCl
according to the following description. C,H6 + Ct, + H,O+ C3H&1OH + HCl ZC,H,ClOH + Ca(OH),
Propylene oxide in the amount of 5000 tons/yr will be made by C3H6 f c& --j %%Cb + 2C3H60 + CaCI, + ZH,O
the chlorohydrin process. The basic feed material is a hydrocarbon C3H,C10H + C,H,CHO + HCI
mixture containing 90% propylene and the balance propane which
does not react. This material is diluted with spent gas from the
process to provide a net feed to chlorination which contains
40mol% propylene. Chlorine gas contains 3% each of air and
carbon dioxide as contaminants.
Chlorination is accomplished in a packed tower in which the 5. PHENOL BY THE CHLOROBENZENE PROCESS
hydrocarbon steam is contacted with a saturated aqueous solution A portion of a plant for the manufacture of phenol from mono-
of chlorine. The chlorine solution is made in another packed tower. chlorbenzene and NaOH is in accordance with the following descrip-
Because of the limited solubility of chlorine, chlorohydrin solution tion.
from the chlorinator is recirculated through the solution tower at a
rate high enough to supplement the fresh water needed for the a. Construct a flowsheet of the process, with operating conditions
process. Solubility of chlorine in the chlorohydrin solution is and the two control instruments mentioned.
approximately the same as in fresh water. b. Prepare a material balance showing the compositions of the
Concentration of the effluent from the chlorinator is 81b
organics/100 lb of water. The organics have the composition process streams in the portion of the plant before the brine
decanter V-103. The amount of phenol in this stream is
2000 lb/hr. Excess caustic (5%) is fed to the emulsifier.
Propylene chlorohydrin 75 mol %
Propylene dichloride 19
Propionaldehyde 6 Process description: The principal reactions in the plant are
Operating pressure of the chlorinator is 30psig, and the C,H5Cl + 2NaOH+ C6H50Na + NaCl + H,O 2C6H,0H
temperature is 125°F. Water and the fresh gas stream are at 80°F. C6H,0Na + HCl + C6H,0H + NaCl 1 + (C,H,),O + H,O
Heat of reaction is 2000 Btu/lb chlorine reacted. Percentage
conversion of total propylene fed to the chlorinator is 95% From storage, monochlorbenzene and 10% caustic are pumped
(including the recycled material). together with diphenyl ether from decanter V-102 into emulsifier
Overhead from the chlorinator is scrubbed to remove excess V-101 which is provided with intense agitation. The effluent from
chlorine in two vessels in succession which employ water and 5% that vessel is pumped with a high pressure steam driven
caustic solution, respectively. The water from the first scrubber is reciprocating pump P-103 at 4000 psig through a feed-effluent
used in the chlorine solution tower. The caustic is recirculated in exchanger E-101 and through the tube side of a direct fired heater
order to provide adequate wetting of the packing in the caustic R-101. Here the stream is heated to 700°F and reaction 1 occurs.
scrubber; fresh material is charged in at the same rate as spent From the reactor, the effluent is cooled in E-101, cooled further
material is purged. Following the second scrubber, propylene to 110°F in water cooler E-102, and then enters diphenyl ether
dichloride is recovered from the gas by chilling it. The spent gas is decanter V-102. The lighter DPE phase is returned with pump
recycled to the chlorinator in the required amount, and the excess is P-104 to the emulsifier. The other phase is pumped with P-105 to
flared. another stirred vessel R-102 called a Springer to which 5% HCl also
Chlorohydrin solution is pumped from the chlorinator to the is pumped, with P-106; here reaction 2 occurs.
saponifier. It is mixed in the feed line with a 10% lime slurry and The mixture of two liquid phases is cooled in water cooler
preheated by injection of live 25psig steam to a temperature of E-103 and then separated in brine decanter V-103. From that vessel
200°F. Stripping steam is injected at the bottom of the saponifier, the lighter phenol phase proceeds [P-108) to a basket type
which has six perforated trays without downcomers. Propylene evaporator D-101 that is heated with steam. Overhead vapor from