Microwave Pyrolysis Of Biomass Research Articles

A critical review on the influence of operating parameters and feedstock characteristics on microwave pyrolysis of biomass.

Biomass pyrolysis is the most effective process to convert abundant organic matter into value-added products that could be an alternative to depleting fossil fuels. A comprehensive understanding of the biomass pyrolysis is essential in designing the experiments. However, pyrolysis is a complex process dependent on multiple feedstock characteristics, such as biomass consisting of volatile matter, moisture content, fixed carbon, and ash content, all of which can influence yield formation. On top of that, product composition can also be affected by the particle size, shape, susceptors used, and pre-treatment conditions of the feedstock. Compared to conventional pyrolysis, microwave-assisted pyrolysis (MAP) is a novel thermochemical process that improves internal heat transfer. MAP experiments complicate the operation due to additional governing factors (i.e. operating parameters) such as heating rate, temperature, and microwave power. In most instances, a single parameter or the interaction of parameters, i.e. the influence of other parameter integration, plays a crucial role in pyrolysis. Although various studies on a few operating parameters or feedstock characteristics have been discussed in the literature, a comprehensive review still needs to be provided. Consequently, this review paper deconstructed biomass and its sources, including microwave-assisted pyrolysis, and discussed the impact of operating parameters and biomass properties on pyrolysis products. This paper addresses the challenge of handling multivariate problems in MAP and delivers solutions by application of the machine learning technique to minimise experimental effort. Techno-economic analysis of the biomass pyrolysis process and suggestions for future research are also discussed.

Water-washing treatment can change biochar microstructure: microwave pyrolysis of biomass

ABSTRACT In this study, biochar was produced in a microwave pyrolysis reactor and three microwave reaction conditions were introduced. They were pyrolysis temperatures (500, 600, 700, 800, and 900°C), microwave powers (600, 650, 700, 750, and 800 W), and pyrolysis times (30, 40, 50, 60, and 70 min), respectively. The produced biochar was mixed with deionized water and then treated with water washing in a shaker. The yields and microstructure of biochar obtained from the microwave reactor were detailed and the pore structure of washed biochar was also studied. Results showed that the corn stover biochar yield ranged between 44.71 wt.% and 59.92 wt.% depending on the conditions used. The pores in biochar were dominated by macropores and mesopores. As the three reaction conditions were elevated, nanoscale pores appeared, pores were clogged, the pore structure became more obvious and the biochar structure got fragile. Water-washing treatment enlarged the pore sizes, cleaned the clogged pores, and removed water-soluble salts. At longer pyrolysis times, the action of water flow can cause biochar to collapse This study can provide guidance for future microstructure regulation of biochar.

Synthesis of multifunctional porous carbon-silicon composites from coal gasification fine slag: Adsorption of methylene blue and microwave-induced biomass catalytic pyrolysis

Coal gasification fine slag (CGFS) is an important byproduct in the coal gasification process with a huge annual output in China and its efficient and green conversion is one of the key issues in the development of coal chemical technology. In this study, using CGFS as the raw material, a facile method was designed for the preparation of multifunctional porous carbon-silicon composites through one-step alkali fusion based on its carbon, silicon and metal elements composition. It was found that the reaction proceeded more adequately using KOH as the activator and the obtained material (T-K1) was mainly composed of micropores and mesopores. A great number of prismatic nepheline crystals were formed and embedded in the honeycomb porous carbon. The specific surface area of T-K1 reached 424.33 m2/g with a variety of active functional groups on the surface. The porous composite exhibited great potential as a multifunctional adsorbent and catalyst. Using T-K1 as an adsorbent, its equilibrium adsorption capacity on methylene blue (MB) reached 208.44 mg/g at 298 K. The adsorption process was consistent with the situation described by the pseudo-second-order kinetic and the Langmuir model, and the adsorption mechanism mainly originated from cation exchange, van der Waals forces, π-π interaction, hydrogen bond and electrostatic attraction. In addition, T-K1 can act as both a catalyst and a microwave absorber in the microwave pyrolysis of biomass. Taking pine sawdust as an example, H2 and CO in the gas product were enriched with high yields of 126.4 and 178.9 ml/g at 550 °C respectively, and the relative content of the phenolic in bio-oil increased to 53.6%. It is believed that this process can provide a useful alternative for the high-value-added transformation of solid waste containing carbon and silicon.

Comparative microwave catalytic pyrolysis of cellulose and lignin in nitrogen and carbon dioxide atmospheres

In this paper, a cleaner pyrolysis strategy combining microwave heating, catalyst and carbon dioxide was explored for converting biomass components into higher quality products. Catalytic pyrolysis was more favorable for the decomposition and conversion of complex biomass structures. For furfural residue pyrolysis, potassium sulfate contained in sample served as the main catalytic component. Potassium sulfate promoted the increase of phenols in bio-oil. Notably, carbon dioxide atmosphere promoted the decomposition of substances and exerted a significant effect on biomass pyrolysis, which increased bio-oil yield and declined gas yield. When the pyrolysis atmosphere was changed from nitrogen to carbon dioxide, the ID/IG ratio decreased from 1.07 to 0.74, indicating that carbon dioxide decreased defect structure in biochar. Carbon dioxide enriched the porous structure and surface roughness of biochar. Also, carbon dioxide as a carrier gas was found to be more effective than nitrogen in improving the heating values of biochar and the acidity of bio-oil under carbon dioxide was lower than that under nitrogen, which was conducive to the subsequent utilization of biochar and bio-oil. Carbon dioxide promoted the production of alcohols, alkenes, and alkanes in bio-oil. Beneficially, the interaction of cellulose and lignin inhibited the release of hydrogen chloride. At last, this study also provides insights into the mechanism of catalyst and CO2 on biomass microwave pyrolysis.

Microwave pyrolysis of agricultural waste: Influence of catalysts, absorbers, particle size and blending components

The paper presents the results of experimental study of thermochemical conversion, phase transformations and chemical reactions during microwave pyrolysis of biomass (sawdust, straw, nutshells, rice husk, etc.). For the first time, the characteristics of the microwave co-pyrolysis of agricultural waste have been analyzed. The experiments aimed to register the yield of the main pyrolysis products (gas, char and bio-oil) by varying the following factors: type of biomass, particle size, type of absorber/catalyst, and composition of mixtures. The biomass particle size of 800 µm was optimal in terms of pyrolysis gas yield and quality. Pyrolysis of sawdust and straw had the maximum yield of combustible gas components in relation to CO2. The volumetric concentrations of CO, CH4, and H2 for these types of biomass were 20–70% higher than those for wheat bran, rice husk, and nut shell. Among the low-grade catalysts studied, carbon residue and charcoal were the most efficient in terms of maximizing combustible gas yield and reducing CO2. These catalysts reduced the bio-oil yield by a factor of 1.2 and increased the yield of combustible gases by a factor of 1.3. Pyrolysis of mixtures showed significant synergy, both positive and negative. The minimum yield of gas with the worst quality was typical for the mixture “rice husk 50%, sawdust 50%”. The maximum positive synergistic effects were recorded for the composition “rice husk 33%, sawdust 33%, and bran 33%”. The combination of these components increased the yield of CO, CH4 and H2 by 5–24%, 8–53% and 2–45%, respectively, compared to other mixtures. Thus, microwave co-pyrolysis creates great scope for the conversion of those components that do not provide the required gas characteristics during individual pyrolysis. Pyrolysis of mixtures contributes to the utilization of a large amount of plant waste while maintaining the quality of the end products.

Biomass microwave pyrolysis characterization by machine learning for sustainable rural biorefineries

Microwave heating is a promising solution to overcome the shortcomings of conventional heating in biomass pyrolysis. Nevertheless, biomass microwave pyrolysis is a complex thermochemical process governed by several endogenous and exogenous parameters. Modeling such a complicated process is challenging due to the need for many experimental measurements. Machine learning can effectively cope with the time and cost constraints of experiments. Hence, this study uses machine learning to model the quantity and quality of products (biochar, bio-oil, and syngas) that evolve in biomass microwave pyrolysis. An inclusive dataset encompassing different biomass types, microwave absorbers, and reaction conditions is selected from the literature and subjected to data mining. Three machine learning models (support vector regressor, random forest regressor, and gradient boost regressor) are used to model the process based on 14 descriptors. The gradient boost regressor model provides better prediction performance (R2 > 0.822, RMSE <12.38, and RRMSE <0.765) than the other models. SHAP analysis generally reveals the significance of operating temperature, microwave power, and reaction time in predicting the output responses. Overall, the developed machine learning model can effectively save cost and time during biomass microwave pyrolysis while serving as a valuable tool for guiding experiments and facilitating optimization.

Microwave Pyrolysis of Biomass in Steam

Microwave Pyrolysis of Biomass in Steam

Microwave directional pyrolysis and heat transfer mechanisms based on multiphysics field stimulation: Design porous biochar structure via controlling hotspots formation

The microwave pyrolysis of biomass and the directional design of biochar structure are examined in this study by exploring the internal connection between energy conversion and biochar structure evolution. Through the optimization of process parameters (microwave power and sample volume), the average utilization efficiency of microwave energy increased from 11.96% to 32.84%, and the specific surface area of the biochar increased from 453.89 m2/g to 638.82 m2/g. According to the simulation results of the COMSOL Multiphysics software, the distribution of the temperature field was closely related to the evolution of the microwave electric field intensity. The local high temperature areas (hotspots) were primarily located in the center of the biochar, and the temperature distribution gradually decreased from the inside to the outside. The hotspots contributed to the promotion of the conversion of amorphous carbon to graphite carbon. Meanwhile, the graphite carbon with a stronger microwave absorption capacity formed a local hotspot and promoted the growth of the pore structure. The rich pore structure of the biochar facilitated the multiple reflection of microwave energy and prolonged the microwave residence time. Graphite carbon can absorb microwave energy and convert it into heat energy to improve the utilization efficiency of microwave energy. This paper combined the experimental and simulation results to reveal the heat transfer mechanism in the microwave pyrolysis process, which provided a new perspective for the directional reduction of microwave pyrolysis energy consumption and the optimization of the microstructure of biochar.

Microwave-assisted pyrolysis of formic acid pretreated bamboo sawdust for bio-oil production

The integrated process of formic acid pretreatment and pyrolysis of bamboo sawdust (BS) under microwave irradiation is developed to produce high-quality bio-oil in this study. Experimental results indicated that microwave-assisted formic acid (MFA) pretreatment was able to reduce the contents of hydrogen, ash, and volatile in biomass. In the meanwhile, a distinct increase in the higher heating value of pretreated BS was observed. Although a higher pretreatment temperature led to lower mass yield, the corresponding energy yield of solid product was remarkably higher. X-ray diffraction and Fourier transfer infrared spectrometry analyses of pretreated BS suggested that MFA pretreatment could destruct the pristine structure of BS. Therefore, thermal properties of pretreated BS were significantly altered in terms of thermal stability and decomposition temperature according to thermogravimetric analysis. Microwave-assisted pyrolysis of pretreated samples could produce less acids, phenols, and ketones but more sugars, especially gluopyranose. Furthermore, the relevant mechanism of microwave-assisted pyrolysis of pretreated BS was interpreted. In sum, MFA was a feasible and promising technology to improve the quality of bio-oil from microwave pyrolysis of biomass.

Mechanistic study on direct synthesis of carbon nanotubes from cellulose by means of microwave pyrolysis

Abstract This paper investigates the impact of biomass components (i.e. cellulose and lignin) on direct production of carbon nanotubes (CNTs) from renewable biomass by means of microwave pyrolysis at low temperature. Palm Kernel Shell (PKS) was treated using two methods to isolate its bio-components, i.e. cellulose and lignin. The treated PKS samples were then pyrolyzed under microwave at 600 °C. Scanning electron microscopy (SEM) analysis revealed the formation of a large number of CNTs on the surface of cellulose bio-chars, while no CNTs were formed from lignin under the same pyrolysis conditions. It was inferred that cellulose was the component responsible for the formation of CNTs during microwave pyrolysis of biomass. High-resolution transmission electron microscope (HRTEM) analysis revealed that CNTs formed under such conditions had a multiwall structure. Raman spectroscopy analysis showed that the carbon order of CNTs increased when cellulose was used instead of the raw biomass for the synthesis of CNTs. Further analysis of the volatiles showed that unlike lignin, the volatile matter derived from cellulose were rich in monosaccharides such as D-Glucopyranose and glucopyranose which were postulated to have acted as an effective carbon source for the formation of CNTs. Self-extrusion of volatiles rich in monosaccharides and hydrocarbons during pyrolysis of cellulose, followed by the condensation and re-solidification of volatiles on the softened cellulose particles at elevated temperatures was proposed as the mechanism of formation of CNTs. The findings of this study may pave the way for the development of an effective, sustainable, and low-cost method for large scale production of CNTs from renewable biomass.

An overview of microwave hydrothermal carbonization and microwave pyrolysis of biomass

Biomass utilization has received much attention for production of high density solid fuels. Utilization of cheap and naturally available precursors through environmentally friendly and effective processes is an attractive and emerging research area. Pyrolysis and hydrothermal carbonization (HTC) are well-known technologies available for production of solid biofuel using conventional or microwave heating. Microwave heating is a simpler and more efficient heating method than conventional heating. This study presents a critical review on microwave pyrolysis and microwave HTC for solid fuel production in terms of yield and quality of products. Moreover, a brief summary of parameters of microwave pyrolysis and microwave HTC are discussed. The fuel, chemical, structural and thermal weight loss characteristics of solid fuels produced from different biomass are discussed and compared.

Microwave pyrolysis of biomass within a liquid medium

A new approach to pyrolysis is demonstrated that uses microwave heating combined with an external liquid media at atmospheric pressure. The liquid acts as the inerting medium instead of the traditional inert gas, and also acts as a heat-sink to maintain the external temperature at the normal boiling point of the liquid. The ability to regulate the external temperature using a liquid offers significant advantages over established pyrolysis technologies and is only possible due to the selective and volumetric heating that occurs with microwaves. The new concept overcomes many of the challenges encountered in traditional and gas-based microwave pyrolysis processes, producing a bio-oil that naturally partitions into a sugar-rich aqueous phase and a phenol-rich organic phase. Energy requirements are as low as 2 kJ/g for 50% volatilisation, comparable to microwave pyrolysis using inert gases. It is shown that the new concept works effectively with both microwave-transparent and microwave-absorbent solvents. The liquid media also acts to eliminate arcing and prevent carbonaceous residues from forming, phenomena which have so far proved challenging for the scale-up of microwave pyrolysis processes.

New insights into microwave pyrolysis of biomass: Preparation of carbon-based products from pecan nutshells and their application in wastewater treatment

Microwave pyrolysis of pecan nutshell (Carya illinoinensis) biomass was used to produce carbon-based solid products with potential application in contaminated water treatment.A range of analytical techniques were applied to characterize the intermediate products of microwave pyrolysis in order to monitor the physico-chemical effects of the interacting energy on the biomass.The performance of the carbon-based products was tested through evaluation of lead ion removal capacity from solution. Further analyses demonstrated that ion-exchange by calcium ions on the material surface was the main mechanism involved in lead removal. Calcium compound development was directly correlated to the interaction of the electromagnetic waves with the biomass.Through monitoring the physico-chemical effects of biomass–microwave interactions during microwave pyrolysis, we have shown for the first time that the intermediate products differ from those of conventional pyrolysis. We hypothesize that selective heating leads to the (hemi)cellulosic and lignin degradation processes occurring simultaneously, whereas they are largely sequential in conventional pyrolysis.This work provides optimization parameters essential for the large scale design of microwave processes for this application as well as an understanding of how the operating parameters impact on functionality of the resulting carbon-based materials.

Microwave-assisted catalytic pyrolysis of lignocellulosic biomass for production of phenolic-rich bio-oil

Catalytic microwave pyrolysis of peanut shell (PT) and pine sawdust (PS) using activated carbon (AC) and lignite char (LC) for production of phenolic-rich bio-oil and nanotubes was investigated in this study. The effects of process parameters such as pyrolysis temperature and biomass/catalyst ratio on the yields and composition of pyrolysis products were investigated. Fast heating rates were achieved under microwave irradiation conditions. Gas chromatography–mass spectrometry (GC–MS) analysis of bio-oil showed that activated carbon significantly enhanced the selectivity of phenolic compounds in bio-oil. The highest phenolics content in the bio-oil (61.19 %(area)) was achieved at 300°C. The selectivity of phenolics in bio-oil was higher for PT sample compared to that of PS. The formation of nanotubes in PT biomass particles was observed for the first time in biomass microwave pyrolysis.

Preparation and characterization of bio-oil by microwave pyrolysis of biomass

ABSTRACTA low temperature method was used to produce bio-oil from fir sawdust by means of microwave pyrolysis. Effects of reaction temperature, ratios of the microwave absorption medium to sawdust, and reaction time on the yield of bio-oil were investigated. The results show that an optimized yield of 21.22% is achieved. Bio-oil obtained was analyzed by gas chromatography-mass spectrometry and Fourier transform infrared, and the result reveals that the product mainly consists of phenolic compounds with esteric compounds as the minor components. Thermal weight loss curves of bio-oil were determined by thermogravimetry-differential thermal analysis in the oxygen atmosphere at different super-heating rates, and combustion kinetic parameters were calculated.

Microwave-induced cracking and CO2 reforming of toluene on biomass derived char

The objective of this work was to investigate the ability of char from biomass microwave pyrolysis at 800°C for tar removal, using toluene as the model compound. The experiments were conducted in a fixed bed with microwave heating and electrical heating, respectively. Carbon weight in biomass char was calculated after the experiments, and the chars were characterized by Brunauer–Emmett–Teller (BET) analysis and Scanning Electron Microscope (SEM) measurement. The results indicated that microwave heating had a promoting effect on toluene conversion. With the temperature increasing to 750°C, cracking conversion and hydrogen selectivity rose respectively to 92.77% and 91.74%. CO2 reforming of toluene was effective to produce more syngas. An optimum CO2 flow rate, i.e., 80mLmin−1, was existed under microwave heating. In this case, toluene conversion reached a maximum of 92.03%, and the syngas yield also increased to 91.03%. The ratios of H2/CO exhibited a substantial reduction with increasing CO2 flow rate. At CO2 flow rate of 100mLmin−1, the ratio approached stoichiometric ratio in reforming reaction, and the ratio further reduced to 0.22 at CO2 flow rate of 120mLmin−1. Toluene reforming displayed a relative stable performance for the conversion of toluene, since the existence of CO2 efficiently relieved biomass char deactivation. Toluene reforming conversion retained at about 86% in a time range of 20–140min. Carbon gasification during the reforming reaction possessed a resistance to carbon deposition, but it simultaneously caused carbon loss in biomass char. The most serious weight-loss ratio was 5.42% in this work, obtained at CO2 flow rate of 120mLmin−1. The consumed carbons were gasified into part of syngas production and provided the biggest contribution of 15.4% to final syngas production.

Microwave Pyrolysis of Biomass: Control of Process Parameters for High Pyrolysis Oil Yields and Enhanced Oil Quality

The oil yield and quality of pyrolysis oil from microwave heating of biomass was established by studying the behavior of Larch in microwave processing. This is the first study in biomass pyrolysis to use a microwave processing technique and methodology that is fundamentally scalable, from which the basis of design for a continuous processing system can be derived to maximize oil yield and quality. It is shown systematically that sample size is a vital parameter that has been overlooked by previous work in this field. When sample size is controlled, the liquid product yield is comparable to conventional pyrolysis and can be achieved at an energy input of around 600 kWh/t. The quality of the liquid product is significantly improved compared to conventional pyrolysis processes, which results from the very rapid heating and quenching that can be achieved with microwave processing. The yields of levoglucosan and phenolic compounds were found to be an order of magnitude higher in microwave pyrolysis when compared with conventional fast pyrolysis. Geometry is a key consideration for the development of a process at scale, and the opportunities and challenges for scale-up are discussed within this paper.

Renewable phenols production by catalytic microwave pyrolysis of Douglas fir sawdust pellets with activated carbon catalysts

The effects of different activated carbon (AC) catalysts based on various carbon sources on products yield and chemical compositions of upgraded pyrolysis oils were investigated using microwave pyrolysis of Douglas fir sawdust pellets. Results showed that high amounts of phenols were obtained (74.61% and 74.77% in the upgraded bio-oils by DARCO MRX (wood based) and DARCO 830 (lignite coal based) activated carbons, respectively). The catalysts recycling test of the selected catalysts indicated that the carbon catalysts can be reused for at least 3-4 times and produced high concentrations of phenol and phenolic compounds. The chemical reaction mechanism for phenolics production during microwave pyrolysis of biomass was analyzed.

The microwave pyrolysis of biomass

Microwave pyrolysis of various biomass types has been reviewed. A range of biomass types has been subjected to microwave pyrolysis under various conditions, with char, bio‐oil, and a range of gases (predominantly CO2, CO, CH4 and H2) being produced. Studies aimed at individual biomass components, such as cellulose and hemicellulose, are included to develop a mechanistic understanding of the processes involved.

The Performances of Fixed and Stirred Bed in Microwave Pyrolysis of Biomass

This paper presents for the first time the comparative study between fixed bed (FB) and stirred bed (SB) pyrolysis of biomass in a 1kW and 2.45GHz microwave (MW) system. Generally biomass is poor absorber of MW and pyrolysis reaction cannot takes place unless induced with absorber. However, MW absorber not only the affects the temperature profile but also it initiates the pyrolysis reaction. Interestingly, in SB, approach of varying MW absorber quantity can be a used to control the pyrolysis temperature which otherwise is difficult in domestic MW system. Bio-oil was subjected to FT-IR analysis in order to determine possible chemical functional groups. Overall, SB produced much better results in terms of complete pyrolysis which could save energy, time and cost of the MW pyrolysis process.