Method for inhibiting polymerization of (METH) acrylic acid and its esters using an inhibitor and a process for making a compound useful as such an inhibitor

#The present invention relates to a method for inhibiting polymerization of (meth)acrylic acid and its esters, for example during separation and purification processes, using a polymerization inhibitor. The present invention also relates to an ion exchange resin process for making reduced halide-content azine dye-based compounds which are suitable for use as a polymerization inhibitor.

#When (meth)acrylic acid and its esters are prepared by conventional reaction processes, these products are generally present in a mixed product gas exiting the reactors of such processes. Typically, mixed product gases containing (meth)acrylic acid are cooled and contacted with an aqueous stream in an absorption tower, thereby providing a crude product stream which is then purified, often by dehydration in a distillation step, to provide a more concentrated and pure product solution. Mixed product gases containing esters of (meth)acrylic acid are generally non-aqueous streams, often with alcohols as the solvent-carrier, which are also subjected to purification by distillation, which also results in formation of a more concentrated and pure product solution.

#Unfortunately, under the high temperature conditions typical of purification by distillation, (meth)acrylic acid and its esters have a strong tendency to polymerize, creating unwanted polymer solids in the process equipment. It is important to prevent such unwanted polymerization of (meth)acrylic acid and its esters because process equipment may become blocked and clogged with the polymer solids which tends to interfere, sometimes dangerously, with ongoing operation of the purification process. In addition, loss of product yield often results from the polymerization of a portion of the product.

#For a better understanding of the present invention, reference is made to the following detailed description, considered in conjunction with the accompanying drawing, in which:

#FIG. 1 is a schematic representation of a separation and purification process which employs the method of the present invention.

#Throughout this specification and claims, unless otherwise indicated, references to percentages are by weight percent and all temperatures are in degrees centigrade (° C.).

#It is also to be understood that for purposes of this specification and claims that the range and ratio limits, recited herein, are combinable. For example, if ranges of 1-20 and 5-15 are recited for a particular parameter, it is understood that ranges of 1-15 or 5-20 are also contemplated.

#The term azine dye-based compounds (as distinguished from azine compounds in general), as used herein, means molecules having the following general molecular structure: