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A stable high-temperature reaction site and the rapid and uniform heating of the feedstocks are particularly important in pyrolysis. A novel device consisting of microwave-assisted heating (MAH) coupled with atomization feeding was used for continuous pyrolysis of methyl ricinoleate (MR) using silicon carbide (SiC) as the microwave absorbent bed. The heat transfer in microwave heating and MR pyrolysis in MAH device was studied by three-dimensional simulation. The effects of number of ports and heating power in microwave heating process, flow rate, feed mode and average droplet diameter of MR in pyrolysis process were investigated. Uniform temperature distribution of SiC bed surface was obtained with different numbers of ports. Higher energy efficiency was obtained at higher microwave power, with the highest value reaching 81% at 1000 W. The maximum flow rate of MR could reach 40 mL/min at a stable high-temperature bed surface. The atomization feed mode was beneficial to the temperature uniformity of SiC bed. The heating rate of atomized MR droplets was about 50000 °C/s, significantly higher than that of dropped MR droplets. The simulated results agreed well with the experimental results. It indicated the MAH coupled with atomization feeding could provide a stable high-temperature reaction site and increase the rapid and uniform heating of the feedstocks.

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.

Undecylenic acid methyl ester (UAME) and heptanal (HEP) are important chemical intermediates, which can be produced from pyrolysis of methyl ricinoleate (MR). The temperature gradient existing in conventional tubular reactor for MR pyrolysis would cause the reduction of UAME and HEP yields. An inductively heated reactor coupled with atomization feeding was developed in this study and used for MR pyrolysis. Numerical simulation was first adopted to examine the effect of nozzle number on temperature distribution of the reactor. Results showed that uniform temperature distribution was achieved when three nozzles were used. The average temperature and the standard deviation of the reaction area were 496.54 °C and 6.34 °C respectively at the set temperature of 500 °C. Experimental tests of MR pyrolysis on the reactor were then performed using three nozzles. Results showed that MR conversion increased with the increasing temperature from 440 to 560 °C. The highest UAME and HEP yields of 56.1 wt% and 60.2 wt% respectively were achieved at 520 °C. The product yields were obviously higher than those obtained using conventional tubular reactor. It was mainly due to the uniform temperature distribution of reactor and rapid heating of feedstock by using the inductively heated reactor coupled with atomization feeding.

The density and viscosity of methyl ricinoleate were measured in the temperature range from (293.16 to 383.23) K and (298.23 to 358.15) K, respectively. The vapor pressure of methyl ricinoleate was determined using a static method in the temperature range of (451.58 to 476.80) K at the pressure between (232 and 868) Pa, and methyl palmitate was employed to examine the reliability of the experimental apparatus. The experimental data were compared with the open data for methyl ricinoleate and other fatty acid methyl esters with similar molecular weight. Temperature-dependence correlation equations for the density, viscosity, and vapor pressure were proposed.

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.