Fuels by Waste Plastics Using Activated Carbon, MCM-41, HZSM-5 and Their Mixture

Abstract

Abstract. Waste material was pyrolyzed in a horizontal tubular reactor at 530-540°C using different catalysts, such as activated carbon, MCM-41, HZSM-5 and their mixtures. Products were investigated by gas-chromatography, EDXRFS and standardized methods. Catalysts significantly affected the yields of volatiles; e.g. HZSM-5 catalyst increased especially the yield of gaseous hydrocarbons, while MCM-41 catalyst was responsible for increasing the pyrolysis oil yield. Synergistic effects were found using mixtures of different catalysts. Furthermore the catalysts modified the main carbon frame of the products. Pyrolysis oil obtained over HZSM-5 catalyst contained large amounts of aromatics, while MCM-41 catalyst mainly isomerized the carbon frame. Regarding contaminants it was concluded, that the sulphur content could be significantly decreased by activated carbon, however it had only a slight effect to the other properties of the products.

The Use of Heterogeneous Catalysis in the Chemical Valorization of Plastic Waste

“…The large surface area and uniform mesoporous structure has bridging oxygen atoms lining the channels that can interact with hydrogen atoms of the plastics to induce cracking [103] . Because of this, MCM‐41 catalysts increase the yield of liquid products at the expense of the heavy oil and wax fractions and induce PSW degradation at lower operation temperatures than thermal cracking [103,126,147,148] . The catalyst will also enhance alkene and monoaromatic production and reduce selectivity towards dienes and multi‐ring aromatic products within the gaseous and liquid fractions, as compared to thermal degradation [126,147,148] .…”

“…Because of this, MCM‐41 catalysts increase the yield of liquid products at the expense of the heavy oil and wax fractions and induce PSW degradation at lower operation temperatures than thermal cracking [103,126,147,148] . The catalyst will also enhance alkene and monoaromatic production and reduce selectivity towards dienes and multi‐ring aromatic products within the gaseous and liquid fractions, as compared to thermal degradation [126,147,148] . Alumina can be incorporated into the MCM‐41 structure to create more acidic mesoporous catalysts such as Al‐MCM‐41.…”

“…These zeolites are MFI (silicalite‐1) structured porous aluminosilicate zeolites that have been reported to have increased cracking activity for polyolefins – in particular PE – resulting in a decrease in the heavy oil fraction, reduction in wax production, minimization in char production, and an increase in light hydrocarbon content in the liquid and gas produced [76,80,105,108,111,147,152,165–167] . These desirable results are attributed to the smaller pores in combination with strongly acidic sites which allow for initially cracked fragments to diffuse through the channels and further react within the cavities to produce higher value products [95,99,103,105,126,147,152,165,168,169] . ZSM‐5 catalysts generally produce higher yields of light alkene and aromatic compounds.…”

“…In addition to FCC, other types of multi‐catalyst systems have been investigated for the degradation of plastic waste. In particular, studies have focused on the combination of zeolite and silica‐alumina catalysts, similar to FCC catalysts but without binders, such as ZSM‐35/MCM‐41 and HZSM‐5/MCM‐41 [118,119,126,208] . Often, these materials are formed by mechanical synthesis via mortar and pestle mixing of the two separate catalysts with varying mass portions [118] .…”

“…Furthermore, these properties can be tuned through various physical and chemical activation processes. Activated carbons have been found to only minimally shift the gas, liquid, residue product selectivity, as compared to MCM‐41 and HZSM‐5,due to larger heat transmission area as a result of the high specific surface area of carbon [126] . However, it has been determined that activated carbons – regardless of physical and chemical activation processes used in generation – exhibited superior catalytic performance in shifting the liquid fraction produced from LDPE and waste plastic mixtures into jet fuel range compounds and H 2 ‐enriched gases [127,128] .…”