Technology that made two operations, distillation and chemical reaction combined together and functions as a single unit operation was named as reactive distillation technology. It is well established in manufacturing process like generating acetol from glycerol and large scale production of methyl acetate continuously. The same intention to make process simple and decreased the production cost reactive distillation technology can be used to produce cumene from the benzene and propylene. Even though there are two procedures for catalytic distillation, heterogeneous method was preferred in bulk manufacturing units. Industries like to have their process to be handle in easy way like the separation of liquid reaction phase and solid catalyst. It is effective than the homogeneous system.
Catalytic reactive distillation equipment can be operated in two methods, suspension and fixed bed.
- Suspension catalytic distillation designed in such way that the catalyst particles are fluidized within the liquid phase. It dominates other process by the specialties like, it doesn’t use a packing system, and so for replacing the packing there is no need to shut down the plant. Mass transfer increase at the interface due to complete exposure of surface area of the catalyst.
- In case of fixed bed it simple in operation just a bed of catalyst is installed in the column. The reactants are allowed to flow through the bed and perform the reaction.
Cumene with chemical formula C6H5.CH.(CH3)2 is also called as isopropyl benzene with molecular weight 120.19 and boiling point about 152.5oC. It has demand for production of phenol and acetone. Cumene is unique chemical product obtained by the reaction of benzene and propylene in the presence of Beta zeolite catalyst to support alkylation and transalkylation reactions simultaneously. In a suspension catalytic distillation column propylene is fed at the feed plate where at top of it benzene is introduced and below section of feed plate Diisopropyl benzene is entered from recycle stream for transalkylation. Column is divided into two sections upper for alkylation and bottom transalkylation.
Catalyst is feed to the top of the column along with benzene into the alkylation section where counter flow of propylene will react with benzene to form diisopropyl benzene and isopropyl benzene, due to their high molecular weight and temperature they flow to the bottom section of the column where the catalyst initiate the transalkylation process to convert diisopropyl benzene (DIPB) into pure cumene. Finally the solid and liquid mixture is sent in to the separator and the catalyst is separated for recycle. The liquid stream contain the fraction of benzene, cumene and DIPB is sent to two different consecutive separation column, the first is used to recover the unreacted benzene and recycle it to the reaction section. The second separator produce 99% cumene at the top as distillate and bottom DIPB is recycled to DIPB reacting section.
This technology will save energy and decrease the duration of reaction and increase the production capacity. Overall cumene yield is increased due to high percentage conversion of DIPB to cumene reducing the byproduct formation. Heat energy can be managed without losses by which the heat exchanger equipment count is decreased.
Analysis methods that determine the characteristic of a precursor activity of a catalyst:
- Temperature-programmed reduction
- X-ray powder diffraction (XRD)
- Brunauer–Emmett–Teller (BET )
- Scanning Electron Microscope / Energy-dispersive X-ray spectroscopy
Design a reactive distillation plant to produce 300 Tonnes/ day of cumene
Most chemical industries are in research work to develop cumene production process so that it can produce profitable phenol from it. Selection a project to design to cumene production plant with a capacity 300 tonnes/day can used to adapt the simulation result in present existing plants. By the method of propylene alkylation of benzene, cumene is produced.
So by vary the catalyst and reactor with liquid and vapor phase reaction cumene plant can be optimized for better results. For instant cumene is formed by vapor phase reaction between propylene (CH3.CH=CH2) and benzene (C6H6) at temperature 350oC and pressure 25 atm. By initial guess reactants benzene is available at 99.9 mole% purity and propylene along propane is available with 95 mole% and 5 mole% respectively can be used as feeds but the phase of reactant should be determined based on the reactor type and reaction mechanism so it can handle weather they exist in liquid phase or vapor phase. Pressure can be develop with pump or compressor based on it is in liquid state or vapor state, before the pump recycle of unreacted benzene stream is added. By using a vaporizer or heater reaction temperature is attained.
Now the real part comes, that the catalyst selection shows effect on the cumene yield and conversion of benzene. Due to a side reaction, that is cumene will react with propylene to form diisopropyl benzene which decrease cumene yield. Conversion depends on the molar feed ratio also along with the selection of product selectivity. Vapor with products can be cooled at the same pressure so all the component can exist in liquid phase which will help to separate and purify in a distillation column.
With help of two distillation columns unreacted benzene, propylene and the product cumene and undesirable by-product diisopropyl benzene can be separated based on their boiling points and volatility. To avoid this separation problems reactive distillation column is been studied and research works are in good progress in this view. This is a project which can be designed by chemical engineer, mechanical and instrumentation engineers who can combine their skill on subjects like chemical reaction engineering, control and automation, pressure vessel and machinery designing, heat and mass transfer, etc,.
Factors that influence the reactive distillation process design to obtain the desired products
- Choice of catalysts
- Reactor models
- Process operation conditions
Reactive distillation provide high selectivity design variable and higher value products production on which the profits of chemical industry depends on.