Patent ID: 7473338

Claim:
A method of purifying of a readily polymerizable compound by subjecting a crude readily polymerizable compound to distillation under vacuum conditions to purify it, comprising: using a distillation apparatus having a distillation column and a vacuum generator and an exhaust gas conduit of the vacuum generator connected to a connecting conduit therebetween through a pressure control valve; controlling the action of the pressure control valve based on a pressure of the distillation column, thereby controlling the amount of exhaust gas to be introduced to control the pressure of the distillation column; and purifying (meth)acrylic acid using the distillation column, wherein at least a part of trays is a weir-free perforated tray, wherein openings of the weir-free perforated tray are positioned on respective intersections of an oblique lattice comprising a first group of lines aligned in parallel and at even intervals and a second group of lines oblique to the first group of lines and aligned in parallel and at even intervals; with respect to a local opening rate (B/A) that is a ratio of a sum B of areas of openings of a region comprising of a parallelogram surrounded by the oblique lattice to an area A of the region and a ratio u/S of a total area u of all of the openings to a column sectional area S, a value of (u/S)/(B/A) ratio is 0.67 or more; the flow rate dropping along an edge of the opening is 0.035 m 3 /m·h or more; the distillation column has a column diameter of 1.2 m or more; and an oxygen concentration in a gas within the column is from 0.008 to 0.1% by mole.