Catalytic pyrolysis of a coal tar in a fixed-bed reactor

Abstract

The product yields from cracking a bituminous coal tar In a fixed-bed reactor were determined at various temperatures in the presence and absence of some packing materials. Synthetic zeolttes, Linde LZ-Y82, Norton Zeokn 900-H, and Davison 13-X, as well as a natural zeolite, chabarite, showed strong catalytic activity. I n contrast, molecular sieves 5-A and natural erionite having smaller pore diameters were found to be much less active. Clay minerals such as kaolinite, montmoriibnlte, and Kieselguhr exhibited catalytlc actMtles whlch were similar to those of the zeolites with small pore slzes, but they were still far more effective than quartz particles. I t was found that the zeolite LZ-Y82 was remarkably effective in converting tar to chars and gases in the temperature range of 400 to 500 OC. Among the factors involved for catalytic effectiveness are (I) an effective pore size greater than about 0.7 nm, (ii) a large internal surface area accessible to the tar vapor, and (ill) a large number of strongly acMic sites.

The effect of added minerals on the pyrolysis products derived from a vitrinite-rich demineralised South African coal

“…The importance of this equation with regard to product yields and composition with the addition of dolomite or calcite was previously confirmed [43,56]. If the yields are taken into account in the current study it seems probable that the left hand side of the equation is favoured by the presence of minerals within the coal matrix.…”

“…In previous studies, this was attributed to assist the decrease in tar yield [5,6]. The effect of kaolinite in tar reduction is attributed to the acidity of the mineral, thus providing protonates for increased pyrolysis conversion [5,6,43]. Kaolinite is however less active than dolomite and calcite in tar reduction [6,44].…”

“…Kaolinite is however less active than dolomite and calcite in tar reduction [6,44]. This was attributed to the loss of pore structure at increased temperatures and a small surface area of 15-20 m 2 /g [43,44].…”

“…Howard [47] accepted this explanation in their tar pyrolysis studies. Wen and Cain [43] went further, stating that the surface-assisted reactions due to solid mineral additions, transform part of the large hydrocarbons into free radicals and/or carbenium ions. Polymerization occurs when the immobilized species react with the colliding hydrocarbons to form char, releasing hydrogen and other gases such as CH4, C2H4, etc.…”

The Zeolite-catalyzed Hydroconversion of Demineralized Shengli Coal Liquefaction Residue Under Microwave Irradiation

“…It is generally accepted that the strong sites of acidity in the zeolites are the key factor in cracking activity, and the pore size of the zeolites influence the cracking activity too. Wen and Cain (1984) found that a zeolite with a pore size of >0.7 nm is effective for converting coal tar to light products. Their explanation was as follows: although many molecules in coal tar are too large to enter into the pores with diameters of about 0.8 nm, a side group or a part of the large molecule can be partially trapped on the surface of a zeolite and cracked to smaller molecules.…”