This invention provides for a process for the alkylation of an aromatic hydrocarbon stream having impurities in which a hydrocarbon feedstock is contacted with a first molecular sieve comprising Linde type X molecular sieve and having a Si/Al molar ratio of less than about 5 to remove at least a portion of said impurities and to produce a partially treated aromatic hydrocarbon stream; and then contacting said partially treated hydrocarbons stream with a second molecular sieve comprising a zeolite Y and having a Si/Al molar ratio of greater than about 5 to remove substantially all of the remaining portion of said impurities to produce a fully treated hydrocarbon feedstock having a reduced amount of impurities. The fully treated hydrocarbon feedstock is contacted with an alkylating agent in the presence of an alkylation catalyst having a cycle length and under alkylation conditions to produce an alkylated aromatic hydrocarbon stream.