A process for producing an alkylated aromatic compound stream from an at least partially untreated alkylatable aromatic compound stream having catalyst poisons and an alkylating agent stream, wherein said alkylatable aromatic compound stream is treated to reduce catalyst poisons, the process comprising the steps of: (a) contacting said alkylatable aromatic compound stream having said catalyst poisons with a treatment composition in a treatment zone separate from an alkylation reaction zone under treatment conditions to remove at least a portion of said catalyst poisons and form a treated effluent stream which comprises treated alkylatable aromatic compound and a reduced amount of catalyst poisons, wherein said treatment composition has a surface area/surface volume ratio of greater than 30 in -1 (12 cm -1), said treatment conditions include a temperature of from 30°C to 300°C; and (b) contacting said treated alkylatable aromatic compound in said effluent stream and an alkylating agent stream with a catalyst composition in said alkylation reaction zone separate from said treatment zone under at least partial liquid phase catalytic conversion conditions to form an alkylated effluent stream which comprises additional alkylated aromatic compound, wherein said catalyst composition comprises a porous crystalline material having a framework structure type selected from the group consisting of FAU, BEA, MOR, MWW and mixtures thereof, wherein said at least partial liquid phase catalytic conversion conditions include a temperature of from 100°C to 300°C, a pressure from 689 kPa to 4601 kPa, a molar ratio of treated alkylatable aromatic compound to alkylating agent of from 0.01:1 to 25:1, and a feed weight hourly space velocity (WHSV) based on alkylating agent of from 0.5 to 500 hr -1, wherein step (a) further comprises intermittently supplying an alkylating agent stream to said treatment zone at intervals from at least 1 hour up to 24 hours or more and then interrupted for periods of 10 days to 15 days or more to produce a temperature increase caused by an exothermic reaction between said alkylating agent and said alkylatable aromatic compound in the presence of said treatment composition under said treatment conditions, whereby said temperature rise indicates the ageing of said treatment composition. (a) contacting said alkylatable aromatic compound stream having said catalyst poisons with a treatment composition in a treatment zone separate from an alkylation reaction zone under treatment conditions to remove at least a portion of said catalyst poisons and form a treated effluent stream which comprises treated alkylatable aromatic compound and a reduced amount of catalyst poisons, wherein said treatment composition has a surface area/surface volume ratio of greater than 30 in -1 (12 cm -1), said treatment conditions include a temperature of from 30°C to 300°C; and (b) contacting said treated alkylatable aromatic compound in said effluent stream and an alkylating agent stream with a catalyst composition in said alkylation reaction zone separate from said treatment zone under at least partial liquid phase catalytic conversion conditions to form an alkylated effluent stream which comprises additional alkylated aromatic compound, wherein said catalyst composition comprises a porous crystalline material having a framework structure type selected from the group consisting of FAU, BEA, MOR, MWW and mixtures thereof, wherein said at least partial liquid phase catalytic conversion conditions include a temperature of from 100°C to 300°C, a pressure from 689 kPa to 4601 kPa, a molar ratio of treated alkylatable aromatic compound to alkylating agent of from 0.01:1 to 25:1, and a feed weight hourly space velocity (WHSV) based on alkylating agent of from 0.5 to 500 hr -1, wherein step (a) further comprises intermittently supplying an alkylating agent stream to said treatment zone at intervals from at least 1 hour up to 24 hours or more and then interrupted for periods of 10 days to 15 days or more to produce a temperature increase caused by an exothermic reaction between said alkylating agent and said alkylatable aromatic compound in the presence of said treatment composition under said treatment conditions, whereby said temperature rise indicates the ageing of said treatment composition.