Integrated process for preparing acrolein and 3-methylmercaptopropionaldehyde

A process to produce 3-methylmercaptopropionaldehyde, comprising:

• A and A1) oxidizing a mixture of propylene and inert diluent gases with air over a heterogeneous catalyst in two streams to obtain a first A) and a second A1 gaseous oxidation reaction mixtures comprising acrolein and by-products;
• B) quenching the first gaseous oxidation reaction mixture from A) to obtain a gas stream comprising acrolein and a quench liquid comprising residual acrolein and the by-products;
• B1) quenching the second gaseous oxidation reaction mixture from A1) to obtain a gas stream comprising acrolein and a quench liquid comprising residual acrolein and the by-products;
• C) recovering the acrolein by stripping from the quench liquid in a lower part of the quench B) and returning the stripped acrolein to the quench;
• D) absorbing a first portion of the gas stream comprising acrolein from the quench B) in water to obtain an aqueous acrolein solution and an uncondensable gaseous stream comprising inert gases;
• D1) recycling at least a portion of the uncondensable gaseous stream to the oxidation streams of A) and A1) to supply the inert diluent gases;
• E) distilling the acrolein from the aqueous acrolein solution from D) to obtain an acrolein-free aqueous bottom product;
• E1) condensing the distilled acrolein from E);
• F) reacting the distilled acrolein from E1) and the gas stream comprising acrolein B1) with methyl mercaptan in a mixture comprising at least one of 3-methylmercaptopropionaldehyde and a hemithioacetal of methyl mercaptan and 3-methylmercaptopropionaldehyde to obtain the 3-methylmercaptopropionaldehyde.