Production and investigation of porous structure of mineral-carbon adsorbents based on silica-gel and polymer wastes

Abstract

     The work is devoted to investigation of porous structure of adsorbents, obtained from silica gels KSM and KSK and waste polyethylene, polypropylene and polyurethane by the method of chemical vapor deposition. This direction of treatment provides production of composite porous materials from thermoplastic polymers, completely decomposing during pyrolysis. Electron microscopy of the adsorbents reveals uneven
deposition of pyrolysis carbon on the surface of silica gel in form of globules. The pore parameters of carbonized silica gels and were measured by low-temperature adsorption-desorption of nitrogen using the theories of BET, BJH, Dubinin-Astakhov and estimated by the method of molecular probes (water, benzene, tetrachlormethane). The obtained mineral-carbon adsorbents based on wide-porous silica gel refer to mesoporous materials, adsorbents based on narrow-porous silica gel are mostly microporous (the total pore volume up to 0.97 and 0.52 cm3/g, respectively). Pore shrinkage of silica gels due to coating with a layer of carbon during the pyrolysis of polymers is found: for wide-porous silica gel it changes their porous structure insignificantly (specific surface 333-321 m2/g), for narrow-porous - to partial blocking of micropores and to decreasing of their parameters (fall of specific surface from 712to 378 m2/g). The similarity of adsorption-desorption isotherms and pore distribution curves of the samples indicate a weak effect of the type of pyrolyzed polymer, pyrolysis regime for wide-porous silica gel, and the ratio of polymer to narrow-porous silica gel on the adsorbent parameters (average pore size 11.4-11.6 nm and 2.74-2.95 nm, respectively).Wide-porous silica gel KSK as a more heat-resistant and porous material is the best matrix for production of mineral-carbon adsorbents. The obtained granulated adsorbents qualitatively exceed the industrial activated carbons, and the described method of their synthesis contributes to utilization of the widespread polymer waste.