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Oily sludge, as a critical hazardous waste, requires appropriate treatment for resource recovery and harmfulness reduction. Here, fast microwave-assisted pyrolysis (MAP) of oily sludge was conducted for oil removal and fuel production. The results indicated the priority of the fast MAP compared with the MAP under premixing mode, with the oil content in solid residues after pyrolysis reaching below 0.2%. The effects of pyrolysis temperature and time on product distribution and compositions were examined. In addition, pyrolysis kinetics can be well described using the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods, with the activation energy being 169.7–319.1 kJ/mol in the feedstock conversional fraction range of 0.2–0.7. Subsequently, the pyrolysis residues were further treated by thermal plasma vitrification to immobilize the existing heavy metals. The amorphous phase and the glassy matrix were formed in the molten slags, resulting in bonding and, hence, immobilization of heavy metals. Operating parameters, including working current and melting time, were optimized to reduce the leaching concentrations of heavy metals, as well as to decrease their volatilization during vitrification. [ABSTRACT FROM AUTHOR]

Highlights • The effects of feed mode, reaction and preheating temperatures were studied. • Maximum selectivities of heptanal and undecylenic acid methyl ester were 91.4% and 76.6%. • The gas, liquid and solid products were analyzed. • The material balance was calculated to design the amplifying device. • Theoretical and actual heat was 1461 kJ/kg and 2629 kJ/kg at 500 °C, respectively. Abstract A stable high-temperature reaction site and the uniformity and speed of heating the feedstocks play a key role in pyrolysis processes. In this study, microwave-assisted heating coupled with atomization feeding was used to pyrolyze methyl ricinoleate (MR) for the efficient, continuous production of undecylenic acid methyl ester (UAME) and heptanal (HEP). The effects of feed mode, reaction temperature and preheating temperature on microwave-assisted pyrolysis (MAP) were examined. The maximum selectivities of HEP and UAME could reach 91.4 wt.% and 76.6 wt.%, respectively, at the reaction and preheating temperatures of 500 °C and 150 °C, respectively, using atomization feeding. The gas, liquid and solid products were determined by gas chromatography (GC), GC-mass spectrometry (MS) and Fourier transform infrared (FT-IR), and the gas, liquid and solid yield reached 7.0 wt.%, 89.0 wt.% and 0.1% wt.%, respectively, with an error of 3.9 wt.% at 500 °C. The pyrolysis of MR via microwave-assisted heating coupled with atomization feeding was found to be more efficient than the conventional pyrolysis process. In addition, the theoretical and actual heat for MAP of MR was 1461 kJ/kg and 2629 kJ/kg at 500 °C, respectively. The material balance and heat analysis results can be used to guide the design of an amplifying device. [ABSTRACT FROM AUTHOR]

A stable temperature site and the speed of heating the feedstocks play a key role in pyrolysis processes. In this study, the product distribution arising from pyrolysis of methyl ricinoleate (MR) at 550 °C with low and high heating rates was first studied by pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The results show that fast pyrolysis of MR favored the production of undecylenic acid methyl ester (UAME) and heptanal (HEP). Density functional theory (DFT) calculations were employed to reveal the UAME and HEP formation process from pyrolysis of MR. The bond dissociation energies (BDEs) of C–C bonds in MR showed that the C11–C12 bond is the weakest. This suggests that UAME and HEP are two major products. The process of slow and fast MR pyrolysis was the dehydration-first and the pyrolysis-first trend, respectively. The calculated activation energies of MR pyrolysis to UAME and HEP and MR dehydration to 9,12-octadecadienoic acid methyl ester were 287.72 and 238.29 kJ/mol, respectively. The much higher product yields obtained in the fast pyrolysis reactors than those from conventional tubular reactors confirmed the proposed process. [ABSTRACT FROM AUTHOR]

• Scaled-up of microwave-assisted pyrolysis methyl ricinoleate was carried out. • SiC bed surface temperature distribution in microwave heating was measured. • Feeding load of the scaled-up device was estimated. • The results of scale-up test exceeded those of lab-scale test by comparison. The microwave-assisted pyrolysis reactor with microwave absorbent bed can work continuously and efficiently to pyrolysis reactions, which makes it potential for reactor scale-up. In this paper, the scale-up of microwave-assisted pyrolysis reactor using silicon carbide (SiC) as microwave absorbent bed that was used for methyl ricinoleate (MR) pyrolysis was studied. The microwave power, SiC bed diameter and MR feed rate were enlarged from 1 kW, 126 mm and 0.9 kg/h for the lab-scale reactor to 7 kW, 580 mm and 7.0 kg/h for our self-designed scale-up reactor, respectively. The results show that temperature distribution of the scaled up SiC bed surface before feeding of MR was uniform and stable, which provides favorable conditions for efficient pyrolysis reaction on the bed surface. The selectivity and yield of the target product undecenoic acid methyl ester were 75.55% and 63.08%, respectively that reached the lab-scale test results. It needs to be emphasized that the scale-up process of microwave-assisted pyrolysis of MR has no obvious scale-up effect by using the microwave intensification heating and the microdroplet rapid heating technology. This study will provide guidance for the large-scale application of the microwave-assisted pyrolysis reactor in chemical industry. [ABSTRACT FROM AUTHOR]

Undecylenic acid methyl ester (UAME) was continuously produced from methyl ricinoleate using a microwave-assisted pyrolysis system with atomization feeding. The UAME yield of 77 wt.% was obtained at 500 °C using SiC as the microwave absorbent and heating medium. The methyl ricinoleate conversion and UAME yield from microwave-assisted pyrolysis process were higher than those from conventional pyrolysis. The effect of temperature on the pyrolysis process was also investigated. The methyl ricinoleate conversion increased but the cracking liquid yield decreased when the temperature increased from 460 °C to 560 °C. The maximum UAME yield was obtained at the temperature of 500 °C. [ABSTRACT FROM AUTHOR]