A perfectly designed process for producing ethanol from ethylene would be the catalytic hydration method developed based on direct hydration technology. This method has very fewer bottleneck factors when compared to other methods like indirect hydration technology. Direct catalytic hydration method posses optimized energy consumption and material balance. Equipments used in catalytic hydration are lesser than the old process in practice.
A petrochemical industry that has a high source of ethylene stock prefer to select this method. Ethylene with 95% concentration is the best raw material quality that this process can handle. Designing a plant that handles catalytic hydration has high scope in modern continuous processes. The project of ethanol production has much more important in most petrochemical industries due to its growing demand in the international market. Engineers who can improve the existing process and bring out high performance by rectifying the problems are in demand for a process industry.
Process description of catalytic hydration of ethylene:
A catalyst like diatomaceous earth will support the phosphoric acid. The surface of diatomaceous earth is coated with phosphoric acid so that it acts as an acid catalyst. The concentration of H3PO4 should be around 85-90%.
Water is vaporised and added to the vapours of ethylene at pressure 65-70 atm and then heated to the reaction temperature 300 oC. The reactant mixture is fed to the reaction tower from top. A catalyst solution of H3PO4 is also fed to the top of the tower as makeup when required only. The concurrent flow pass through the packing material of catalyst and following reaction takes place.
H2O + CH2=CH2 → H3PO4 → CH3CH2OH
The impurity that is present in ethylene would be mainly acetylene (C2H2). This will also participate and react to produce acetaldehyde by the reaction.
C2H2 + H2O → CH3CHO (acetaldehyde)
The product mixture containing ethanol, unreacted ethylene, water and acetaldehyde are sent to a separator. Ethanol and water are separated from the bottom and unreacted ethylene removed from the top and scrubbed with caustic soda to remove the trace of acid. A high-pressure stripper separates acetaldehyde and sends it to a hydrogenator to produce ethanol with the help of nickel catalyst. The reaction is.
CH3CHO + H2O → N2→ CH3CH2OH
Finally, ethanol (C2H5OH) is produced at a different concentration as per the requirement in separators with a yield of 95-97% ethanol.
Other production methods: