The invention provides a process for producing and/or purifying acrylic
acid or methacrylic acid or an ester of any of these, wherein mixtures of
high-boiling heavy ingredients (high-boiling matter mixtures) discharged
from individual step units are classified by the content therein of
(meth)acrylic acid and/or of the dimer thereof and handled. According to
the invention, even when high-boiling matters which have been discharged
from distillation columns, high-boiling-matter cracking reactors, and the
like in a plant for producing (meth)acrylic acid and/or an ester thereof
and are alike in liquid nature are mixed with each other in the same
tank, no polymer precipitation occurs. The handling and storage thereof
are hence easy. Consequently, tanks can be united into one, and the
process is extremely advantageous in reducing the construction cost and
the area necessary for equipment.