Method for the production of butadiene and hydrogen from ethanol in two low-water and low-energy-consumption reaction steps

A process for the production of butadiene from an ethanol feed comprising at least 80% by weight of ethanol, comprising at least:

• A) a step for conversion of the ethanol to acetaldehyde, comprising at least one reaction section supplied with at least a fraction of ethanol-rich effluent obtained from step E1), operated at a pressure in the range 0.1 to 1.0 MPa and at a temperature in the range 200° C. to 500° C. in the presence of a catalyst, and a separation section for separating the effluent from said reaction section into at least one hydrogen effluent in the gaseous form and an ethanol/acetaldehyde effluent in the liquid form;
• B) a step for conversion into butadiene, comprising at least one reaction section supplied with at least a fraction of said ethanol/acetaldehyde effluent obtained from step A), with an ethanol-rich liquid obtained from step C1), with a fraction of the acetaldehyde-rich effluent obtained from step E1), operated in the presence of a catalyst, at a temperature in the range 300° C. to 400° C., and at a pressure in the range 0.1 to 1.0 MPa, the supply flow rates being regulated such that the ethanol/acetaldehyde molar ratio at the inlet to said reaction section is in the range 1 to 5, and a separation section for separating the effluent from said reaction section into at least one gaseous effluent and a liquid effluent;
• C1) a hydrogen treatment step, comprising at least one compression section compressing said hydrogen effluent obtained from step A) to a pressure in the range 0.1 to 1.0 MPa, and a gas-liquid scrubbing section supplied, at a temperature in the range 15° C. to −30° C., with a fraction of said ethanol effluent obtained from step E1) and with a fraction of said ethanol/acetaldehyde effluent obtained from step A), and supplied, at a temperature in the range 25° C. to 60° C., with said compressed hydrogen effluent, and producing at least one liquid ethanol-rich effluent and a purified hydrogen effluent;
• D1) a step for extraction of butadiene, comprising at least one compression section compressing said gaseous effluent obtained from step B) to a pressure in the range 0.1 to 1.0 MPa, a gas-liquid scrubbing section comprising a scrubbing column supplied overhead, at a temperature in the range 20° C. to −20° C., with an ethanol stream constituted by said ethanol feed for the process and/or a fraction of the ethanol effluent obtained from step E1) and at the bottom with said gaseous effluent obtained from step B) and cooled, and a distillation section operated at a pressure in the range 0.1 to 1 MPa, supplied with at least the liquid effluent obtained from said step B) and with the liquid effluent from said gas-liquid scrubbing section, said step D1) producing at least one effluent of gaseous by-products, an unrefined butadiene effluent and an ethanol/acetaldehyde/water effluent;
• D2) a first butadiene purification step comprising at least one gas-liquid scrubbing section the bottom of which is supplied with the unrefined butadiene effluent obtained from D1) and the head of which is supplied with a stream of water which may be a stream of water with an origin external to said butadiene production process and/or a fraction of the water effluent obtained from step E1), said scrubbing section producing a pre-purified butadiene effluent overhead and a spent water effluent from the bottom;
• D3) a subsequent butadiene purification step supplied with at least said pre-purified butadiene effluent obtained from said step D2), and producing at least one purified butadiene effluent;
• E1) an effluent treatment step supplied with at least the water/ethanol/acetaldehyde raffinate obtained from step E2), and producing at least one ethanol-rich effluent, an acetaldehyde-rich effluent and a water-rich effluent;
• E2) a step for eliminating impurities and brown oils, supplied with at least the ethanol/acetaldehyde/water effluent obtained from step D1), and with the water-rich effluent obtained from step E1), and producing at least one water/ethanol/acetaldehyde raffinate, a light brown oil effluent and a heavy brown oil effluent;
• F) a step for scrubbing with water supplied by the effluent of gaseous by-products obtained from step D1), as well as with a fraction of the water-rich effluent obtained from said step E1) and producing at least one alcohol-containing water effluent.