Method of preparation of porous membranes and adsorbents

An article of manufacture in the form of a porous membrane or an adsorbent, comprising a silicic acid heteropolycondensate made by:

• (i) forming a reaction mixture comprising:
• (a) at least one hydrolysable silicic acid derivative of the general formula I:
• SiR.sub.4 (I)
• wherein each R is selected from the group consisting of hydrogen, halogen, alkoxy and --NR'.sub.2, wherein each R' is a hydrogen atom or an alkyl group, with the proviso that not all the R radicals are hydrogen atoms, and
• (b) at least one substituted silane of the general formula II:
• SiR.sub.n R".sub.(4-n) (II)
• wherein R is as defined above, each R" is selected from the group consisting of alkyl, alkenyl, aryl and aralkyl and n is an integer from 1 to 3, and
• (c) optionally at least one functional silane of the general formula III:
• SiR.sub.n (R'"Y).sub.(4-n) (III)
• wherein R and n have the meanings defined above, each R'" is selected from the group consisting of alkylene, phenylene, alkylphenylene and alkylenephenylene and Y is selected from the group consisting of halogen, amino, anilino, aldehyde, keto, carboxy, hydroxy, mercapto, cyano, hydroxyphenyl, diazo, carboxylic alkyl ester, sulphonic acid (--SO.sub.3 H) and phosphoric acid (--PO.sub.3 H.sub.2), and/or
• (d) optionally at least one oxide component selected from the group consisting of non-volatile oxides soluble in the reaction medium and compounds capable of forming non-volatile oxides soluble in the reaction medium, the oxide component being an oxide of an element selected from Groups Ia to Va, Group IVb and Group Vb of the Periodic System,
• (ii) subjecting the reaction mixture to hydrolysis and condensation in the presence of 10% to 75% by weight, based on the weight of the reaction mixture, of a condensation catalyst, with the proviso that when water is the condensation catalyst at least the amount of water stoichiometrically required for hydrolysis is used, optionally in the presence of a solvent,
• wherein the amounts of the components (a) to (d) are selected so that the resultant silicic acid heteropolycondensate, calculated as oxide units, contains, by weight, 35% to 90% of component (a), 10% to 50% of component (b), 0% to 15% of component (c) and 0% to 40% of component (d) and
• (iii) removing said water or solvent and drying the obtained polycondensate thereby obtaining a porous adsorbent having two definite different pore sizes including a smaller pore size in the nanometer range and a larger pore size in the micrometer range.

A porous silicic acid heteropolycondensate porous adsorbent having two definite different pore sizes including a smaller pore size in the nanometer range and a larger pore size in the micrometer range, comprising:

• a three-dimensional structure including channels having an average diameter of approximately 0.1 to 10 micrometers and spherical primary particles which contain smaller pores having an average diameter of 0.5 to 10 nanometers, said heteropolycondensate porous adsorbent being produced by a process comprising the steps of:
• (i) forming a reaction mixture comprising:
• (a) at least one hydrolysable silicic acid derivative of the general formula I:
• SiR.sub.4 (I)
• wherein each R is selected from the group consisting of hydrogen, halogen, alkoxy and --NR'.sub.2, wherein each R' is a hydrogen atom or an alkyl group, with the proviso that not all the R radicals are hydrogen atoms, and
• (b) at least one substituted silane of the general formula II:
• SiR.sub.n R".sub.(4-n) (II)
• wherein R is as defined above, each R" is selected from the group consisting of alkyl, alkenyl, aryl and aralkyl and n is an integer from 1 to 3, and
• (ii) subjecting the reaction mixture to hydrolysis and condensation in the presence of 10% to 75% by weight, based on the weight of the reaction mixture, of a condensation catalyst, with the proviso that when water is the condensation catalyst at least the amount of water stoichiometrically required for hydrolysis is used, optionally in the presence of a solvent,
• wherein the amounts of components (a) and (b) are selected so that the resultant silicic acid heteropolycondensate, calculated as oxide units, contains, by weight, 35% to 90% of component (a) and 10% to 50% of component (b) and
• (iii) removing the water or solvent from the obtained polycondensate to obtain a porous adsorbent.