Abstract: A process for purifying crude acrylic acid characterized in that high-purity purified acrylic acid containing little or no low boiling aldehydes is obtained by rectifying a crude acrylic acid consisting essentially of acrylic acid and containing low boiling substances such as acetaldehyde, acrolein, water and acetic acid and/or high boiling substances such as maleic acid, phenol, benzaldehyde and acrylic acid dimer, thereby removing said low boiling substances and then high boiling ones, and then stripping trace amounts of remaining low boiling aldehydes with an inert gas such as nitrogen or air at a liquid to gas molar ratio of 2 to 20.

Abstract: A method for removing efficiently and economically harmful materials from a waste gas exhausted in a process for producing acrylonitrile by ammoxidation of propylene, which comprises dividing the waste gas exhausted after the absorption of acrylonitrile into two flows, mixing the first flow gas with air in an amount necessary for combustion of the combustible gas contained in the whole waste gas, subjecting the main flow gas of the mixed gas thus obtained to heat-exchange with the gas of the outlet of the first catalyst layer, combining the main flow gas with the remainder of the mixed gas, preheating thereby the mixed gas at a temperature of 200.degree. to 450.degree. C, passing the preheated mixed gas through the first catalyst layer wherein at least one noble metal is dispersed on an alumina carrier, and therein burning the gas at a temperature of 650.degree. to 750.degree.

Abstract: A method for extraction of acrylic acid and/or methacrylic acid from a solution containing the same by treating the said solution with an organic solvent, which is characterized by using a mixture of methylethylketone and a xylene as the organic solvent. By such method, the extraction of acrylic acid and/or methacrylic acid is accomplished efficiently and economically.