Abstract: The present invention provides a polyvinyl alcohol powder which comprises a pore having an average diameter of 0.1 to 10 .mu.m in the range of 0.05 to 0.4 cc/g.Since the PVA powder of the present invention has an excellent solubility in water, an aqueous solution thereof can easily be prepared industrially.Since the PVA powder of the present invention has a low content of an organic volatile component and a low content of a nonvolatile component such as a carboxylic acid salt or the like which is derived from a basic catalyst, it has an excellent industrial handleability.

Abstract: A process for producing terephthalic acid suitable for use in direct polymerization, which comprises oxidizing p-xylene with molecular oxygen in an acetic acid solvent in the presence of a heavy metal compound and a bromine compound, wherein after a main reaction step of oxidizing at least 90 mole % of p-xylene fed has been performed,(1) a first purifying step of feeding a gas containing molecular oxygen to the oxidation reaction mixture obtained from the main reaction step in such a proportion that the concentration of oxygen in the off-gas becomes at least 0.5% by volume and smashing the oxidation reaction mixture at a temperature of 140.degree. to 230.degree. C. to decrease the average particle diameter of terephthalic acid by at least 20% from its average particle diameter before smashing, and(2) a second purifying step of feeding a gas containing molecular oxygen to the slurry from the first purifying step in such a proportion that the concentration of oxygen in the off-gas becomes 0.