Process for the preparation and recovery of maleic anhydride

A process for the preparation and recovery of maleic anhydride comprising:

• reacting a hydrocarbon having at least four carbon atoms in a straight chain with molecular oxygen in a reactor containing a vanadium-phosphorus-oxygen catalyst for the catalytic oxidation of the hydrocarbon to maleic anhydride to produce a reaction product gas comprising maleic anhydride;
• cooling said reaction product gas;
• contacting said cooled product gas with a substantially water immiscible, maleic anhydride-absorbing solvent in an absorption zone, thereby absorbing maleic anhydride from said product gas into said absorbing solvent, and producing an exhaust gas substantially free of maleic anhydride and an absorption liquor comprising said absorbing solvent, maleic anhydride and contaminants comprising polymeric tars;
• stripping maleic anhydride from the absorption liquor to produce a stream comprising maleic anhydride and a regenerated absorbing solvent substantially free of maleic anhydride comprising said absorbing solvent and said contaminants;
• contacting at least a portion of said regenerated absorbing solvent in an agitated extraction zone with an aqueous liquid extractant that is substantially immiscible with said regenerated absorbing solvent to hydrolyze polymeric tars present in said regenerated absorbing solvent and transfer water-soluble contaminants to said aqueous extract phase, thereby producing a mixture comprising an aqueous extract phase containing water-soluble contaminants and an organic raffinate phase comprising regenerated absorbing solvent having a reduced concentration of polymeric tars;
• separating said aqueous extract and said organic raffinate phases;
• and
• recycling said organic raffinate phase to said absorption zone for absorption of maleic anhydride from said reaction product gas, said organic raffinate phase recycled to said absorption zone not having been distilled for removal of polymeric tars;
• the portion of regenerated absorbing solvent introduced into said agitated extraction zone and the conditions of temperature, agitation and contact time between said regenerated absorbing solvent and said aqueous extractant in said extraction zone being controlled such that, at an acceptable level of tars in the recirculating solvent, the rate of removal of polymeric tars by hydrolysis and extraction is substantially equivalent to the rate of introduction of tars into the absorbing solvent by absorption from said cooled product gas and generation within said solvent.

A process for the preparation and recovery of maleic anhydride comprising:

• reacting a hydrocarbon having at least four carbon atoms in a straight chain with molecular oxygen in a reactor containing a vanadium-phosphorus-oxygen catalyst for the catalytic oxidation of the hydrocarbon to maleic anhydride to produce a reaction product gas comprising maleic anhydride;
• cooling said reaction product gas;
• contacting said cooled product gas with a substantially water immiscible, maleic anhydride-absorbing solvent in an absorption zone, thereby absorbing maleic anhydride from said product gas into said absorbing solvent, and producing an exhaust gas substantially free of maleic anhydride and an absorption liquor comprising said absorbing solvent, maleic anhydride and contaminants comprising polymeric tars;
• stripping maleic anhydride from the absorption liquor to produce a stream comprising maleic anhydride and a regenerated absorbing solvent substantially free of maleic anhydride comprising said absorbing solvent and said contaminants;
• contacting from about 15 to about 75 percent of said regenerated absorbing solvent in an agitated extraction zone with an aqueous liquid extractant that is substantially immiscible with said regenerated absorbing solvent to hydrolyze polymeric tars present in said regenerated absorbing solvent and transfer water-soluble contaminants to said aqueous extract phase, thereby producing a mixture comprising an aqueous extract phase containing water-soluble contaminants and an organic raffinate phase comprising regenerated absorbing solvent having a reduced concentration of polymeric tars, said extraction zone being maintained at a temperature between about 60.degree. and about 80.degree. C., said mixture of said organic raffinate and said aqueous extract phases in said extraction zone being agitated with a power input of between about 3.times.10.sup.-4 and about 2.times.10.sup.-3 horsepower per gallon of said mixture and said regenerated absorbing solvent being contacted with said aqueous extractant for at least about 15 minutes;
• separating said aqueous extract and said organic raffinate phases;
• and
• recycling said organic raffinate phase to said absorption zone for absorption of maleic anhydride from said reaction product gas;
• the portion of regenerated absorbing solvent introduced into said agitated extraction zone and the conditions of temperature, agitation and contact time between said regenerated absorbing solvent and said aqueous extractant in said extraction zone being controlled such that a stable emulsion is not formed in said extraction zone and, at an acceptable level of tars in the recirculating solvent, the rate of removal of polymeric tars by hydrolysis and extraction is substantially equivalent to the rate of introduction of tars into the absorbing solvent by absorption from said cooled product gas and generation within said solvent.

A process for the preparation and recovery of maleic anhydride comprising:

• reacting a hydrocarbon having at least four carbon atoms in a straight chain with molecular oxygen in a reactor containing a vanadium-phosphorus-oxygen catalyst for the catalytic oxidation of the hydrocarbon to maleic anhydride to produce a reaction product gas comprising maleic anhydride;
• cooling said reaction product gas;
• contacting said cooled product gas with a substantially water immiscible, maleic anhydride-absorbing solvent in an absorption zone, thereby absorbing maleic anhydride from said product gas into said absorbing solvent, and producing an exhaust gas substantially free of maleic anhydride and an absorption liquor comprising said absorbing solvent, maleic anhydride and contaminants comprising polymeric tars;
• stripping maleic anhydride from the absorption liquor to produce a stream comprising maleic anhydride and a regenerated absorbing solvent substantially free of maleic anhydride comprising said absorbing solvent and said contaminants;
• contacting from about 15 to about 75 percent of said regenerated absorbing solvent in an agitated extraction zone with an aqueous liquid extractant that is substantially immiscible with said regenerated absorbing solvent to hydrolyze polymeric tars present in said regenerated absorbing solvent and transfer water-soluble contaminants to said aqueous extract phase, thereby producing a mixture comprising an aqueous extract phase containing water-soluble contaminants and an organic raffinate phase comprising regenerated absorbing solvent having a reduced concentration of polymeric tars;
• separating said aqueous extract and said organic raffinate phases;
• and
• recycling said organic raffinate phase to said absorption zone for absorption of maleic anhydride from said reaction product gas;
• the conditions of temperature, agitation and contact time between said regenerated absorbing solvent and said aqueous extractant in said extraction zone being controlled such that, at a polymeric tar concentration of between about 0.6 and about 3.5 percent by weight in the regenerated absorbing solvent stream entering said extraction zone, at least about 6.5 percent by weight of the tars in the regenerated solvent stream entering said extraction zone are transferred to said aqueous extract phase.