Tertiary Recycling of Polyethylene to Hydrocarbon Fuel by Catalytic Cracking over Aluminum Pillared Clays

Abstract

The catalytic cracking of polyethylene over an Al pillared saponite, an Al pillared montmorillonite, and their regenerated samples was studied in a semi-batch reactor. Pillared clays were able to convert completely polyethylene in gaseous and liquid hydrocarbons, showing low coking levels. The selectivity and yield to liquid hydrocarbons were high, as the mild acidity of pillared clays avoided excessive cracking to small molecules. Regenerated catalyst samples showed practically identical levels of conversion and selectivity with fresh pillared clay samples. Furthermore, they produced hydrocarbons with practically the same distribution as the fresh samples, confirming that pillared clays can be completely regenerated. Both facts of high yield to liquid products and regenerability make pillared clays potential catalysts for an industrial process of catalytic cracking of plastic waste. The effect of the heating program on the liquid product quality and distribution is also investigated, using two different temperature programs with the same levels of temperature steps, but different duration. The boiling point distribution of the liquid products formed during the second interval of the shorter program was intermediate between this of the lighter liquid produced in the first 10 min of the longer program and the heavier liquid produced between 10 and 20 min. This result clearly shows the importance of the polymer state during each temperature stage.

Catalytic Upgrading of Plastic Wastes

“…Both natural clays and their aluminium oxide pillared analogues have also been tested for the catalytic cracking of polyethylene [49][50][51]. The clays investigated include montmorillonite and saponite.…”

Mechanisms of Catalytic Activity in Heavily Coated Hydrocracking Catalysts

“…Pillared clays have been tested in several applications: as catalysts for heavy oil upgrading [9][10][11], polyethylene catalytic cracking [12], denox processes [13], clean up of aqueous environments [14,15] and sorption of humic substances [16].…”

Catalytic Degradation of Plastic Waste to Fuel over Microporous Materials

“…The first catalyst systems used in those works were well-established industrial acidic catalysts such as silica-alumina and zeolites, mainly Y-type. In the 1990s numerous studies have been carried out using as catalysts silica-alumina [5][6][7], zeolites [6][7][8][9][10][11], zeolite-based commercial cracking catalysts [12][13][14], MCM mesoporous materials [15] or clays and pillared clays [16,17] Besides the direct catalytic conversion of plastic, the subsequent in situ catalytic conversion of products of noncatalytic thermal degradation was also researched [18,19]. These studies have confirmed the superior quality of the hydrocarbon mixtures produced and highlighted the potential of catalytic degradation.…”

“…Generally over clays and pillared clays higher liquid yield values are reached than over zeolites [13,16,17]. Over US-Y zeolite values around 45% are achieved compared with values around 70% over clay-based catalysts.…”

“…The suitability of commercial cracking catalysts to degrade polymer waste is vital as one of the options of commercializing this polymer recycling method is to co-feed polymer waste to existing refinery crackers [13]. Furthermore, in the search for cheaper catalysts, clays and their pillared analogues are also introduced in the polymer catalytic degradation [16,17].…”