Process for preparing linear alkyl benzene

A process for preparing linear alkyl benzene by alkylation of benzene, said process comprising the following steps:

• a) alkylating benzene with an alkylating agent in the presence of an ionic liquid to obtain a first product mixture;
• b) allowing the first product mixture to settle to obtain a first biphasic mixture comprising a first organic phase and a first aqueous phase, wherein the first organic phase comprises linear alkyl benzene (LAB), heavier alkyl benzene (HAB) and unreacted benzene, and the first aqueous phase comprises first partially spent ionic liquid;
• c) deacidifying the first organic phase to obtain a deacidified first organic phase;
• d) fractionally distlling the deacidified first organic phase to obtain a fraction comprising unreacted benzene, a fraction comprising LAB and a fraction comprising HAB;
• e) transalkylating the fraction comprising HAB with benzene in the presence of the ionic liquid at a temperature in the range of 70° C. to 120° C. to obtain a second product mixture;
• f) allowing the second product mixture to settle to obtain a second biphasic mixture comprising a second organic phase and a second aqueous phase;
• wherein the second organic phase comprises LAB and the second aqueous phase comprises second partially spent ionic liquid;
• g) deacidifying the second organic phase, and fractionally distilling the deacidified second organic phase to obtain a fraction comprising LAB and a fraction comprising unreacted HAB;
• and
• h) regenerating the first partially spent ionic liquid obtained in step (b) and/or and the second partially spent ionic liquid obtained in step (f), and reusing the regenerated ionic liquid in the steps of alkylating and/or transalkylating for at least 6 cycles of regeneration;
• wherein the ionic liquid used in alkylation step and translakylation step is at least one selected from the group consisting of fresh ionic liquid, regenerated ionic liquid, the first partially spent ionic liquid and the second partially spent ionic liquid.