TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The liquid phase contains at least 300 mol.ppm, preferably at least 1500 mol.ppm of glyoxal, related to the amount of acrylic acid contained in the liquid phase. The liquid phase consists of up to at least 75 wt.%, preferably up to at least 97 wt.% of acrylic acid. The three carbon precursor compound is propylene, acrolein, propane and glycerin. A reaction starting mixture is used for the heterogeneously catalyzed partial gas phase oxidation of a three carbon precursor compound. The reaction starting mixture contains greater than or equal to 200 mol.ppm, preferably greater than or equal to 1500 mol.ppm of two carbon compounds, related to the molar amount of three carbon precursor compound contained in the mixture. The reaction starting mixture contains: 4-20 vol.% of three carbon precursor compound; greater than or equal to 1 wt.%, preferably greater than or equal to 7 wt.% of water vapor. The liquid phase contains 0.2-30 wt.% of water related to the acrylic acid contained in the liquid phase. The liquid phase of the glyoxal contains more than 50 mol.%, preferably more than 90 mol.% of glyoxal mono hydrates and/or monomer glyoxal dihydrates as monomer. The product mixture contains 200 mol.ppm, preferably 750 mol.ppm of glyoxal related to the molar amount of acrylic acid in the product mixture. Preferred Process: The liquid phase is produced from the product gas mixture of the heterogeneously catalyzed partial gaseous phase oxidation by the use of at least a non-crystallization thermal separation process. The non-crystallization thermal separation process comprises at least a separation process comprising absorption, partial condensation, fractionating condensation, rectification, stripping and desorption. During the crystallization, remaining mother liquor containing glyoxal is led back in at least one of the non thermal crystallization separation procedure. During the crystallization, remaining mother liquor containing glyoxal is led back in a fractioned condensation of the product gas mixture of the heterogeneously catalyzed gas phase oxidation. The crystallization separation is a suspension crystallization. During the suspension crystallization, formed suspension crystallisate and remaining mother liquor are separated from one another in a washing column. In the washing column, the suspension crystallisate is washed with melting acrylic acid crystals separated in the washing column. The method further comprises: (a) crystallization of acrylic acid from the liquid phase; (b) separating the acrylic acid crystallisate from mother liquor remaining during the crystallization; (c) at least partially melting the acrylic acid crystallisate separated in the step (b); (d) at least partially conducting back the melted acrylic acid crystallisate of step (c) to the step (b) and/or step (a). Acrylic acid and glyoxal containing in the product mixture are transformed in to an aqueous fluid phase for producing the liquid phase. At least a partial amount of water is separated from the liquid phase by azeotropic rectification. Acrylic acid contained in the product mixture is transformed in to the condensed phase, so residual gas is led back at least partially in the heterogeneously catalyzed partial gas phase oxidation of the three carbon precursor compound. In the method, acrylic acid crystallisate is melted and is incorporated in a polymer by radical polymerization. EXAMPLE - No suitable example given.