Abstract: A method for purifying a crude chlorosilane containing a boron compound, which is characterized by comprising a step wherein a chlorosilane containing a boron compound is brought into contact with an ion-exchange resin, and a step wherein the chlorosilane containing a boron compound is brought into contact with a silica adsorbent. It is preferable that the crude chlorosilane is brought into contact with the ion-exchange resin first, and then brought into contact with the silica adsorbent. In this connection, a silica gel is preferable as the silica absorbent, and a resin having a functional group represented by the following general formula: —CH2NR1R2 (wherein R1 and the like are as defined in the description) is preferable as the ion-exchange resin.

Abstract: A polyvinylacetal resin powder with a low metal content, being excellent in transparency, moisture resistance and electrical insulating properties and having a large specific surface area, and a process for its production, are presented. A polyvinylacetal resin powder obtained by reacting polyvinyl alcohol and an aldehyde in the presence of an acid catalyst, which has an acetalization degree of at least 60 mol %, a specific surface area of from 1.50 to 3.50 m2/g, a bulk density of from 0.12 to 0.19 g/cm3, an average particle diameter of from 0.5 to 2, 5 ?m and a metal content of at most 80 ppm.

Abstract: A polyvinylacetal resin powder with a low metal content, being excellent in transparency, moisture resistance and electrical insulating properties and having a large specific surface area, and a process for its production, are presented. A polyvinylacetal resin powder obtained by reacting polyvinyl alcohol and an aldehyde in the presence of an acid catalyst, which has an acetalization degree of at least 60 mol %, a specific surface area of from 1.50 to 3.50 m2/g, a bulk density of from 0.12 to 0.19 g/cm3, an average particle diameter of from 0.5 to 2, 5 ?m and a metal content of at most 80 ppm.