Process for inhibiting the undesired free-radical polymerization of acrylic acid present in a liquid phase P, wherein the acrylic acid content of P is at least 10% by weight, the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal based on the weight of the acrylic acid present in P and the liquid phase P is admixed with furfural in an amount that results in a furfural content in the range from 25 to 1000 ppmw based on the weight of the acrylic acid present in P. Liquid phase P, wherein the acrylic acid content of P is at least 10% by weight and the liquid phase P comprises in the range from 25 to 1000 ppmw of glyoxal and in the range from 25 to 1000 ppmw of furfural in each case based on the weight of the acrylic acid present in P.

Described are compositions and methods for inhibiting polymerization of a monomer (e.g., styrene) composition, which use an N—O polymerization inhibitor, a quinone methide polymerization retarder, and an amine stabilizer having a primary and/or secondary amine group. In a mixture, the amine-based stabilizer can prevent antagonistic effects and can provide greater antipolymerant activity. In turn, the mixture inhibits apparatus fouling and improves the purity of monomer streams.

Described are compositions and methods for inhibiting polymerization of a monomer (e.g., styrene) composition, which use an N—O polymerization inhibitor, a quinone methide polymerization retarder, and an amine stabilizer having a primary and/or secondary amine group. In a mixture, the amine-based stabilizer can prevent antagonistic effects and can provide greater antipolymerant activity. In turn, the mixture inhibits apparatus fouling and improves the purity of monomer streams.

The present invention relates to a method for preparing 4,4′-dihydroxy-[1,1′-biphenyl-3,3′-dicarboxylic acid], the method comprising a step for preparing a compound represented by chemical formula 1 by reacting a compound represented by chemical formula 2 with a base according to reaction formula 1. [reaction formula 1] [chemical formula 1] [chemical formula 2] According to the present invention, because use of additional carbon dioxide is unnecessary during the reaction, internal pressure is lowered during same, the reaction can be carried out at a lower temperature, the yield from the synthesis is notably improved as hardening of the resulting substance is absent, and H.sub.4dobpdc can be synthesized in large amounts as an additional process for obtaining pure ligands is unnecessary.

The present invention relates to a method for preparing 4,4′-dihydroxy-[1,1′-biphenyl-3,3′-dicarboxylic acid], the method comprising a step for preparing a compound represented by chemical formula 1 by reacting a compound represented by chemical formula 2 with a base according to reaction formula 1. [reaction formula 1] [chemical formula 1] [chemical formula 2] According to the present invention, because use of additional carbon dioxide is unnecessary during the reaction, internal pressure is lowered during same, the reaction can be carried out at a lower temperature, the yield from the synthesis is notably improved as hardening of the resulting substance is absent, and H.sub.4dobpdc can be synthesized in large amounts as an additional process for obtaining pure ligands is unnecessary.

The present invention relates to a continuous recovery method of (meth)acrylic acid and an apparatus for use in the recovery method. A continuous recovery method of (meth)acrylic acid according to the present invention can ensure a high recovery rate of (meth)acrylic acid through a solvent recovering process in addition to enabling the stable recovery of (meth)acrylic acid and the operation of continuous processes.

The present invention relates to a continuous recovery method of (meth)acrylic acid and an apparatus for use in the recovery method. A continuous recovery method of (meth)acrylic acid according to the present invention can ensure a high recovery rate of (meth)acrylic acid through a solvent recovering process in addition to enabling the stable recovery of (meth)acrylic acid and the operation of continuous processes.

The present invention relates to a continuous recovery method of (meth)acrylic acid and an apparatus for use in the recovery method. A continuous recovery method of (meth)acrylic acid according to the present invention can ensure a high recovery rate of (meth)acrylic acid through an acetic acid separation process in addition to enabling the stable recovery of (meth)acrylic acid and the operation of continuous processes.

The present invention relates to a continuous recovery method of (meth)acrylic acid and an apparatus for use in the recovery method. A continuous recovery method of (meth)acrylic acid according to the present invention can ensure a high recovery rate of (meth)acrylic acid through an acetic acid separation process in addition to enabling the stable recovery of (meth)acrylic acid and the operation of continuous processes.

A synergistic polymerization inhibitor composition, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt. A method for inhibiting polymerization of unsaturated polymerizable monomers, the method providing adding a synergistic polymerization inhibitor composition to an methacrylic acid manufacturing system or component thereof, the composition having a copper salt, and a manganese salt; a copper salt or a manganese salt, and a cationic polymer; or a phenothiazine and a manganese salt.