Process for producing methacrylic acid or methacrylic acid esters

A process for producing methacrylic acid or a methacrylic acid ester, comprising:

• a) producing acrolein from a raw material comprising glycerol, wherein the raw material is evaporated and thereafter converted in the presence of a heterogeneous catalyst and a co-feed gas comprising at least one of the components selected from the group consisting of hydrogen, oxygen, and water,
• b) reacting the acrolein of process step a) with hydrogen to produce propanal,
• c) reacting the propanal of process step b) with formaldehyde to produce methacrolein, and
• d) oxidizing the methacrolein in the presence of an oxygen containing gas to the methacrylic acid or in the presence of an alcohol to the methacrylic acid ester,
• wherein process step d) is carried out in a liquid phase at a pressure of from 1 to 100 bar, and in the presence of a heterogeneous noble-metal-comprising catalyst comprising a metal and/or a metal oxide, and
• wherein the propanal produced in process step b) before being condensed in the presence of formaldehyde in process step c), is purified from hydroxyl acetone.