Deriving crude diesel from waste tyres by fast pyrolysis using calcium bentonite clay as a catalyst.

Abstract

The aim of this research project was to explore the possibility of increasing yield of crude diesel from catalytic pyrolysis of waste tyres over a cheap clay-based catalyst – calcium bentonite in order to provide an alternative fuel source. The tyres were cut into small pieces using a cutter and weighed using a mass balance to prepare them for pyrolysis. The smaller the size the greater the surface area to volume ratio and the better the heat contacts the tyres during pyrolysis. The calcium bentonite clay (Fuller’s activated clay) powder required was weighed and prepared into pellets using distilled water. To 50 g of calcium bentonite clay, 30 cubic centimeters of distilled water were added and the mixture was stirred to form a thick paste. The paste was moulded into small pellets that were oven dried for 15 minutes at 160 ˚C.The crude oil obtained separated into two layers as shown in fig 8. This is because of the different alkane compounds of different densities in the crude oil obtained. The results showed that the yield of the crude oil increased slightly with the use of calcium bentonite clay catalyst from 41.3% to 44.7%. The density and kinematic viscosity of the crude oil obtained using calcium bentonite clay catalyst i.e. 0.878 kg/l and 1.72 cSt respectively are within the acceptable limits of crude diesel. However, the suplhur content of the crude diesel obtained from the copper strip tests is on the upper limit of the range and therefore the oil requires further treatment to enhance its properties and reduce corrosiveness. This further treatment can be done by fractional distillation of the oil to remove the sulphur compounds and increase the concentration of the lower alkanes. Desulphrurisation techniques can also be employed to further remove sulphur. The catalyst reduced the residence time of the gases in the condenser and therefore pyrolysis was faster with the catalyst. This helped reduce the time required for pyrolysis hence making the process more energy efficient.