Synthesis, Structure, and Thermal Stability of a Sulfonic Cation Exchanger Grafted to Carbonized Fiber

Abstract

A new kind of sulfonic cation exchanger based on carbonized fiber modified with poly(styrene3 divinylbenzene) was prepared by radiation grafting. The structural features and thermal stability of the cation exchangers prepared were studied.The reduction of toxicity of the automobile exhaust is a topical environmental problem. The solution of this problem includes the exclusion of tetraethyllead as an antiknock additive to gasoline. With this aim, benzine from catalytic craking and reforming is modified by adding high-octane oxygen-containing compounds: methyl tret-butyl ether (MTBE) and methyl tret-amyl ether (MTAE). In industrial production of these additives, granulated sulfonic cation exchangers Amberlyst 15, Dowex msm 31, KU-23, etc. are used as catalysts [133].It has been reported [4, 5] that FIBAN K-1 gel-like sulfonic cation exchanger based on polypropylene fiber [6] more effectively catalyzes MTBE and MTAE formation than KU-2 0 8 granulated gel-like and Dowex msm 31 macroporous sulfonic cation exchangers.In this context, it was of interest to develop a catalyst for preparing MTBE and MTAE based on carbonized fiber. Owing to several features (high porosity, small thickness, non swelling in polar solvents), carbonized fibers are more favorable for preparing grafted cation exchangers. In addition, these fibers exhibit a high electrical conductivity. Therefore, we can expect that sulfonic cation exchangers grafted to carbonized fiber will exhibit electrical conductivity irrespective of the moisture content. No data have been reported on sulfonic cation exchangers grafted to carbonized fibers. EXPERIMENTALIn our experiments, a nonwoven carbonized fabric Carbopon prepared by carbonization of viscose fiber was used as a fibrous base for a sulfonic cation exchanger.The main characteristics of Carbopon were as follows: fiber diameter 5310 mm, capillary moisture capacity 0.64 ml g !1 , average pore diameter d av 23 A, average surface area determined from low-temperature sorption of nitrogen 780 m 2 g !1 .In preparing sulfonic cation exchanger grafted to Carbopon, the following procedures were used. A weighed sample of air-dried Carbopon (5 g) was placed on the bottom of a 50-ml test tube and kept under vacuum (1 mm Hg) for 2 h at 90oC. Two identical Carbopon samples were used in parallel experiments. The test tubes containing Carbopon were cooled to room temperature, and a mixture of monomeric styrene and divinylbenzene (10 ml) in methanol (25 ml) was added. The styrene to divinylbenzene molar ratios in the reaction mixtures were 98 : 2 and 75 : 25, which corresponded to their relative content in gel-like (sample no. I) and maroporous (sample no. II) cation exchangers, respectively. The test tubes containing Carbopon and monomer mixture were closed, kept for 4h at 20oC and then placed in a channel of a RKhMgamma-20 cobalt (Co 60 ) unit for radiation grafting of styrene and divinylbenzene to Carbopon and their simultaneous copolymerization. In these experiments, the exposure time was 15 h, and the irradiation dose up...