Outline of Cumene Production Process:
Raw material propylene and benzene are used for the production of cumene. These are stored in the respective storage tanks of 500MT capacity in the storage yard pumped to the unit by the centrifugal pumps. Benzene pumped into the feed vessel which mixes with the recycled benzene. Benzene stream is pumped through the vaporizer with 25 atm pressure and vaporized to the temperature of 243oC, mixed with the propylene which is of same and temperature and pressure of benzene stream. This reactant mixture passed through a fired superheater where reaction temperature 350oC is obtained.
The vapour mixture is sent to the reactor tube side which is packed with the solid phosphoric acid catalyst supported on the kieselguhr the exothermal heat is removed by the pressurized water which is used for steam production and the effluent from the reactor i.e., cumene, p-DIPB, unreacted benzene, propylene and propane with temperature 350oC is used as the heating media in the vaporizer which used for the benzene vaporizing and cooled to 40oC in a water cooler, propylene and propane are separated from the liquid mixture of cumene, p-DIPB, benzene in a separator operating slightly above atm and the pressure is controlled by the vapour control value of the separator, the fuel gas is used as fuel for the furnace also.
The liquid mixture is sent to the benzene distillation column which operates at 1 atm pressure, 98.1% of benzene is obtained as the distillate and used as recycling and the bottom liquid mixture is pumped at bubble point to the cumene distillation column where distillate 99.9% cumene and bottom pure p-DIPB is obtained. The heat of bottom product p-DIPB is used for preheating the benzene column feed, All the utility as cooling water, electricity, steam from the boiler, pneumatic air are supplied from the utility section
The reactions for cumene production from benzene and propylene are as follows:
Main Reaction: C3H6 + C6H6 → C6H5-C3H7
Propylene Benzene Cumene
By-Product Reaction: C3H6 + C6H5-C3H7 → C12H18
Propylene Cumene Diisopropylbenzene (DIPB)
Flow sheet of cumene manufacturing from benzene and propylene:
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| 300 Tons/day Cumene production flow sheet |
Well this reaction can occur in liquid and gas phases, but high conversion is obtained at gas phase reactions, the catalyst like solid phosphoric acid are replaced by zeolites and the catalytic conversion reaction are held in shell and tube reactors rather than packed fixed bed reactors. Cumene process reaction is exothermic in nature so a complex shell and tube reactor designs are not sufficient for energy conversion, tremendous research work is involved in design a rector of Cumene production from benzene and propane. For 300 tons per day cumene production outline of the process which uses a solid phosphoric acid as catalyst.
As the flow sheet explains the process of a steady state system which is a continuous process and energy efficient.
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| Temperature, Pressure and Flow rates of the Cumene Process Flowsheet |
The cumene plant consist of the following sections:
Storage and pumping section: Benzene (99.9%) and propane (95%) are stored in a liquid state in storage tanks and propane is stored in the sphere. Benzene excess reactant is mixed in the circulation tank where propane is added to the streamline of the feed inlet to the cascade of heat exchangers.
Preheating and vaporization section: Benzene and propane are mixed with the 2:1 ratio and fed to preheating section where a continuous series of the heat exchanger is used to heat up the feed mixture with the effluents from the Cumene reactor. Finally, after the heat exchanger, a fired heater is used to vaporize and raise the temperature of the mixture to the reaction condition temperature. The pressure is maintained by the compressors from pumping section
Reactor section: A shell and tube reactor is designed as such to withstand the pressure up to 25 atm and 350 degrees centigrade the reactor tube are filled with catalyst and the feed is charged from the top and gas reacts and pass over the catalyst bed with 99% conversion of propylene and outlet stream is sent to the recycle and purification section, where side reaction will generate compounds like di- isopropylbenzene (DIPB).
Separation and purification section: Unreacted benzene is separated in a distillation column from the effluent obtained from the reactor and the recovered benzene is recycled to the feed stream, di- isopropylbenzene which formed as the by-product is separated a sieve tray distillation column which is of 99 percent pure.
Equipment wise Material Balance Sheet
Aluminum chloride catalyst process for cumene production
Phenol Production from Cumene
Phosphoric acid Production Flowsheet
Aspen plus Rplug model simulation of cumene reactor
Disadvantages of using solid phosphoric acid (SPA) Process
1. Lower activity
2. Catalyst non-regenerability
3. Unloading of spent catalyst from reactor difficult
4. Relative high selectivity to hexyl benzene
5. Significant yield of DIPB
Disadvantages of using Aluminum chloride as catalyst
1. High corrosion
2. Environmental hazard
3. Washing step for catalyst removal
Modern Industrial Cumene Production Process:
Cumene is an important chemical in the present industrial world and its uses are steadily increasing. The process followed for the production of cumene is the catalytic alkylation of benzene with propylene and nowadays zeolite based catalysts are used in place of the normal acid based catalysts due to added advantages. Cumene production process has been greatly studied and the reaction mechanism and the reaction kinetics have been specified by many researchers. Both experimental, as well as computer-based simulation and optimization studies, have been carried out by various researchers. |
| Q-Max process for cumene production |
Q-MAX™ Process Description for cumene production:
The Q-MAX™ process provides a very good cumene yield and quality. The QZ-2000 zeolite-based catalyst utilized for the Q-MAX™ process which operates with a low flow rate of benzene and hence investment and utility costs are reduced greatly. QZ-2000 is non-corrosive and regenerate-able. Compared to other zeolite based cumene technologies, the QMAX ™ process provides the highest product quality and great stability. Impurities in the fee have less effect
The alkylation reactor is divided into four catalytic beds present in a single reactor shell. The fresh benzene feed is passed through the upper-mid section of the depropanizer column to remove excess water and then sent to the alkylation reactor. The recycle benzene to the alkylation and transalkylation reactors is drawn from the benzene column. This mixture of fresh and recycle benzene is charged through the alkylation reactor. The fresh propylene feed is split between the catalyst beds and is fully consumed in each bed. An excess of benzene helps in avoiding the formation of poly alkylation and reduce the effect of olefin oligomerization.
As the chemical reaction occurs at the exothermic condition, the temperature increase during the alkylation reaction is controlled by the reactor effluent. The temperature of inlet stream from the catalyst beds is further maintained to the designed temperature by the circuit reactor effluent passing tubes which are cooled by the side stream heat exchangers between the beds. Reacted effluent from the chemical reactor is fed to the depropanizer column which separates the propane and excess water. The bottoms stream of the depropanizer column is fed to the benzene distillation column where excess benzene is collected at top of the column and recycled to the process feed stream.
The benzene distillation column bottom stream fed to the cumene rectifying column where cumene is recovered overhead. The cumene rectifying column bottom product is diisopropylbenzene (DIPB), and fed to the DIPB rectifying column. The DIPB stream is recycled to increase the conversion to the transalkylation reactor. The DIPB column bottom products contain heavy aromatic by-products, which are blended into fuel oil. High-pressure steam is used as the heating medium to the fractionation columns.
The recycle DIPB from the overhead of the DIPB column combines with a portion of the recycle benzene and is charged downflow through the transalkylation reactor. In the transalkylation reactor, DIPB and benzene are converted to more cumene. The effluent from the transalkylation reactor is then sent to the benzene column. The new QZ-2001 catalyst is utilized in the alkylation reactor while the original QZ-2000 catalyst used for the transalkylation reactor. Catalyst lifetime is about 2–4 years.
The Q-Max™ process typically produces near equilibrium levels of cumene (between 85 and 95 mol %) and DIPB (between 5 and 15 mol %). The DIPB is separated from the cumene and is reacted with recycling benzene at optimal conditions for transalkylation to produce additional cumene.
The following reaction mechanism is proposed for the alkylation of benzene for the production of cumene. The major reactions taking place are alkylation and trans-alkylation. Side reactions which take place are isomerisation and dis-proportionation. The reaction mechanism and kinetics may vary depending on the catalyst used. The reaction can occur in the presence or absence of carbonium ion intermediate.
The reaction kinetic data is obtained based on the specific catalyst used for the reaction, for example, a phosphoric acid catalyst and the reaction,
Propylene + Benzene→ Cumene
Specific Rate constant= k= 2.8X10^7
Activation energy = E = 104174 KJ/kmol
Rate of reaction = specific rate constant X Concentration of Benzene and Propylene
= k .Cb Cp
Trans-Alkylation reaction:
The reaction rate constant k = 6.52 X 10-3 exp(27240/RT)
This equilibrium data for the trans-alkylation reaction is obtained for modified Zeolite beta catalyst.
As the chemical reaction occurs at the exothermic condition, the temperature increase during the alkylation reaction is controlled by the reactor effluent. The temperature of inlet stream from the catalyst beds is further maintained to the designed temperature by the circuit reactor effluent passing tubes which are cooled by the side stream heat exchangers between the beds. Reacted effluent from the chemical reactor is fed to the depropanizer column which separates the propane and excess water. The bottoms stream of the depropanizer column is fed to the benzene distillation column where excess benzene is collected at top of the column and recycled to the process feed stream.
The benzene distillation column bottom stream fed to the cumene rectifying column where cumene is recovered overhead. The cumene rectifying column bottom product is diisopropylbenzene (DIPB), and fed to the DIPB rectifying column. The DIPB stream is recycled to increase the conversion to the transalkylation reactor. The DIPB column bottom products contain heavy aromatic by-products, which are blended into fuel oil. High-pressure steam is used as the heating medium to the fractionation columns.
The recycle DIPB from the overhead of the DIPB column combines with a portion of the recycle benzene and is charged downflow through the transalkylation reactor. In the transalkylation reactor, DIPB and benzene are converted to more cumene. The effluent from the transalkylation reactor is then sent to the benzene column. The new QZ-2001 catalyst is utilized in the alkylation reactor while the original QZ-2000 catalyst used for the transalkylation reactor. Catalyst lifetime is about 2–4 years.
The Q-Max™ process typically produces near equilibrium levels of cumene (between 85 and 95 mol %) and DIPB (between 5 and 15 mol %). The DIPB is separated from the cumene and is reacted with recycling benzene at optimal conditions for transalkylation to produce additional cumene.
Reaction Mechanism and Kinetics for Cumene Production:
The following reaction mechanism is proposed for the alkylation of benzene for the production of cumene. The major reactions taking place are alkylation and trans-alkylation. Side reactions which take place are isomerisation and dis-proportionation. The reaction mechanism and kinetics may vary depending on the catalyst used. The reaction can occur in the presence or absence of carbonium ion intermediate.
The reaction kinetic data is obtained based on the specific catalyst used for the reaction, for example, a phosphoric acid catalyst and the reaction,
Propylene + Benzene→ Cumene
Specific Rate constant= k= 2.8X10^7
Activation energy = E = 104174 KJ/kmol
Rate of reaction = specific rate constant X Concentration of Benzene and Propylene
= k .Cb Cp
Trans-Alkylation reaction:
The reaction rate constant k = 6.52 X 10-3 exp(27240/RT)
This equilibrium data for the trans-alkylation reaction is obtained for modified Zeolite beta catalyst.
