Control system for multistage chemical upgrading

A continuous catalytic process for converting olefinic feedstock comprising ethylene and C.sub.3 + olefins to heavier liquid hydrocarbon product comprising the steps of:

• prefractionating the olefinic feedstock to obtain a gaseous stream rich in ethylene and a first liquid olefinic stream comprising C.sub.3 -C.sub.4 olefin;
• passing the C.sub.3 -C.sub.4 liquid olefinic stream to a first accumulator vessel;
• contacting a major stream portion of the C.sub.3 -C.sub.4 olefins from the accumulator vessel with shape selective medium pore zeolite oligomerization catalyst in a distillate mode catalytic reactor zone at elevated temperature and pressure to provide a heavier hydrocarbon effluent stream comprising distillate, gasoline and lighter hydrocarbons;
• fractionating the effluent stream to recover distillate, gasoline and a second C.sub.3 -C.sub.4 hydrocarbon stream containing isobutane;
• further reacting a stoichiometric excess of isobutane from the second C.sub.3 -C.sub.4 hydrocarbon stream with a minor stream of C.sub.3 -C.sub.4 olefin from the first accumulator vessel in an alkylation reactor zone in the presence of acid alkylation catalyst to produce an effluent stream containing C.sub.7 + alkylate;
• fractionating the alkylate reactor effluent stream to recover C.sub.7 + alkylate product, a C.sub.3.sup.- light hydrocarbon stream, a stream rich in normal butane and a stream rich in unreacted isobutane;
• passing unreacted isobutane to a second accumulator vessel;
• recycling isobutane to the alkylation reactor zone at a predetermined rate;
• sensing C.sub.3 -C.sub.4 liquid level in the first accumulator vessel;
• generating a first control signal representative of said first liquid level;
• adjusting fluid flow control means in response to the first control signal to increase flow rate for the major C.sub.3 -C.sub.4 olefinic liquid stream from the first accumulator to the distillate mode oligomerization reactor zone with increased liquid level in the first accumulator vessel;
• sensing isobutane liquid level in the second accumulator vessel;
• generating a second control signal representative of said isobutane liquid level;
• and
• increasing flow of the minor C.sub.3 -C.sub.4 olefin stream from the first accumulator to the alkylation reaction zone in response to the second control signal indicating increased isobutane liquid level in the second accumulator.