Oligomerization process

A process for oligomerizing propylene to form a Cn, olefin, wherein the process comprises:

• contacting a feed stream comprising X wt % propylene, Y wt % an alkane diluent, and Z wt % a recycle fraction with a solid phosphoric acid oligomerization catalyst under effective oligomerization conditions in an oligomerization reactor to produce an oligomerization effluent;
• and
• fractionating the oligomerization effluent to obtain a product fraction and the recycle fraction, the product fraction comprising the Cn, olefin and the recycle fraction comprising a Cn-3 olefin;
• wherein the recycle fraction comprises at least 80 wt % of the Cn-3 olefin, based on the weight of the recycle fraction;
• wherein X+Y+Z=100 and X is from 25 to 60, Y is from 5 to 50, and Z is from 20 to 70;
• and
• wherein the process comprises:
• at least one period T1 during which n is 9 and X, Y and Z remain constant;
• and
• at least one period T2 during which n is 12 and X, Y, and Z remain constant, wherein at least two of X, Y and Z during period T2 differ by at least 5 from X, Y and Z during period T1.