FIELD: chemistry.
SUBSTANCE: invention relates to an improved method for heterogeneously catalysed partial gas-phase oxidation of propylene to acrylic acid, according to which in the first reaction zone an initial gaseous reaction mixture 1, containing propylene and molecular oxygen as reactants and at least propane as an inert diluent gas, with molar ratio O2: C3H6 ≥ 1, at a first reaction step at high temperature, is passed through at least one first catalyst layer whose active mass contains at least one polymetallic oxide based on molybdenum, iron and bismuth, wherein conversion of propylene during single passage through the first catalyst layer is ≥90 mol %, while total selectivity (SAC) of formation acrolein and acrylic aicd as a by-product is ≥80 mol %; if necessary, temperature of the gaseous mixture of reaction products obtained at the first reaction step is lowered by direct cooling, indirect cooling or direct and indirect cooling; if necessary, a secondary gas is added to said mixture in form of molecular oxygen or inert gas or molecular oxygen and inert gas, and in form of an initial gaseous reaction mixture 2, containing acrolein and molecular oxygen as reactants and at least propane as an inert diluent gas, with molar ratio molecular oxygen O2: C3H4O≥0.5, at a second reaction step at high temperature and with formation of a gaseous mixture of reaction products 2, is passed through at least one second catalyst layer whose active mass contains at least one polymetallic oxide based on molybdenum and vanadium, wherein conversion of acrolein during single passage through the second catalyst layer is ≥95 mol %, and where total selectivity (SAA) of formation of acrylic acid at both reaction steps in terms of converted propylene is ≥70 mol %, and where the initial gaseous reaction mixture 1 contains ≤3 mol % cyclopropane in terms of the molar amount of propane contained therein, and which was obtained using crude propylene consisting of at least 90 wt % propylene from at least 97 wt % propane and propylene.
EFFECT: product obtained using the disclosed method has very low content of propionic acid.
28 cl, 2 ex
