Catalytic microwave pyrolysis of waste engine oil using metallic pyrolysis char

Abstract

a b s t r a c tMicrowave pyrolysis was performed on waste engine oil pre-mixed with different amounts of metallicchar catalyst produced previously from a similar microwave pyrolysis process. The metallic-char catalyst was first prepared by pretreatment with calcination followed by analyses to determine its various properties. The heating characteristics of the mixture of waste oil and metallic-char during the pyrolysis were investigated, and the catalytic influence of the metallic-char on the yield and characteristics of the pyrolysis products are discussed with emphasis on the composition of oil and gaseous products. The metallic-char, detected to have a porous structure and high surface area (124 m 2 /g), showed high thermal stability in a N 2 atmosphere and it was also found to have phases of metals and metal oxides attached or adsorbed onto the char, representing a potentially suitable catalyst to be used in pyrolysis cracking process. The metallic-char initially acted as an adsorptive-support to adsorb metals, metal oxides and waste oil. Then, the char became a microwave absorbent that absorbed microwave energy and heated up to a high temperature in a short time and it was found to generate arcing and sparks during microwave pyrolysis of the waste oil, resulting in the formation of hot spots (high temperature sites with temperature up to 650 • C) within the reactor under the influence of microwave heating. The presence of this high temperature metallic-char, the amounts of which are likely to increase when increasing amounts of metallic-char were added to the waste oil (5, 10, and 20 wt% of the amount of waste oil added to the reactor), had provided a reducing chemical environment in which the metallic-char acted as an intermediate reductant to reduce the adsorbed metals or metal oxides into metallic states, which then functioned as a catalyst to provide more reaction sites that enhanced the cracking and heterogeneous reactions that occurred during the pyrolysis to convert the waste oil to produce higher yields of light hydrocarbons, H 2 and CO gases in the pyrolysis products, recording a yield of up to 74 wt% of light C 5 -C 10 hydrocarbons and 42 vol% of H 2 and CO gases. The catalytic microwave pyrolysis produced 65-85 wt% yield of pyrolysis-oil containing C 5 -C 20 hydrocarbons that can potentially be upgraded to produce transport-grade fuels. In addition, the recovered pyrolysis-gases (up to 33 wt%) were dominated by aliphatic hydrocarbons (up to 78 vol% of C 1 -C 6 hydrocarbons) and significant amounts of valuable syngas (up to 42 vol% of H 2 and CO in total) with low heating values (LHV) ranging from 4.7 to 5.5 MJ/m 3 , indicating that the pyrolysis-gases could also be used as a gaseous fuel or upgraded to produce more hydrogen as a second-generation fuel.The results indicate that the metallic-char shows advantages for use as a catalyst in microwave pyrolysis treatment of problematic waste oils.

Oil sludge recycling by ash-catalyzed pyrolysis-reforming processes

“…Significantly, the deactivated catalysts could be much easier renewed and regenerated. So far, many types of catalysts have been used for the catalytic pyrolysis of oily wastes [20][21][22][23][24]. Lam et al [21] also found that the metallic pyrolysis char could be used for waste engine oil upgrading by catalytic microwave pyrolysis.…”

Pyrolysis Recovery of Waste Shipping Oil Using Microwave Heating

“…The alkanes in the pyrolysis oil were found to decrease with the increase of the pyrolysis temperature. This could be accounted for by the increased occurrence of secondary reactions such as dehydration, aromatization and decarboxylation at higher temperatures during the pyrolysis process, converting the alkanes into alkenes or aromatic compounds [10,18]. …”

“…The volatiles are comprised of gaseous hydrocarbons, light hydrocarbons (<C 25 ) and permanent gases such as CO and H 2 . In the secondary pyrolysis stage, enhanced cracking and heterogeneous reactions could occur to produce lighter gaseous hydrocarbons (C 1 -C 4 ), liquid oil hydrocarbons (<C 18 ) and some other gas species [10]. In addition, various types of reactions such as deoxygenation, aromatization, dehydrogenation and reforming could occur and influence the product yield and compositions.…”

“…Microwave pyrolysis has been explored as a promising technique to convert waste materials to produce potentially useful pyrolysis products [5][6][7][8][9][10]. It is a thermochemical conversion method performed in an inert atmosphere from which oxygen is excluded to produce liquid oil, gases and char product.…”

Microwave pyrolysis using self-generated pyrolysis gas as activating agent: An innovative single-step approach to convert waste palm shell into activated carbon

“…Microwave radiation as a heat source provide rapid and targeted heating to the inside waste palm shell by dipole rotation and ionic conduction [10]. The study also examined the influence from varying the amount of waste palm shell as feedstock and the pyrolysis temperature on the process features, the yield and composition of the WPSAC obtained, and its adsorption of methylene blue.…”