Biochar from microwave pyrolysis of biomass: A review

Microwave based technology is an alternative heating method and has already been successfully used in biomass pyrolysis for biochar and biofuel production thanks to its fast, volumetric, selective and efficient heating. Previous review mainly focused on production and analysis of bio-oil and gas instead of biochar. The current paper provides a review of microwave-assisted pyrolysis (MWP) of biomass and its biochar characteristics, including product distribution and biochar yield, biochar properties, microwave absorbers (MWAs) and catalysts commonly used in MWP, as well as comparison of biochar derived from MWP and conventional pyrolysis (CP). MWAs not only absorb microwave energy, they also act as catalysts to interact with gas, vapor and solids in the reactor, adjusting the product distribution and quality of products. It was reported for MWP that the highest biochar yield was >60 wt% and the maximum BET surface area was about 450–800 m²/g. Technology status and economics of MWP of biomass in China were briefly introduced. The Optimization of yield and quality of biochar strongly depends on feedstock properties, reactor types, operating parameters, MWAs and catalysts added to the system.     

农林生物质热裂解制取合成气的研究

以树叶为原料，利用热裂解装置进行了试验。并对裂解产物的组成进行了分析。结果表明：树叶热裂解产物为生物油、合成气和炭，其合成气成分主要由CO、CH4、H2和水蒸气组成。     

Slow catalytic pyrolysis of rapeseed cake: Product yield and characterization of the pyrolysis liquid

The performance of three catalysts during slow catalytic pyrolysis of rapeseed cake from 150 to 550 °C over a time period of 20 min followed by an isothermal period of 30 min at 550 °C was investigated. Na₂CO₃ was premixed with the rapeseed cake, while γ-Al₂O₃ and HZSM-5 were tested without direct biomass contact. Catalytic experiments resulted in lower liquid and higher gas yields. The total amount of organic compounds in the pyrolysis liquid was considerably reduced by the use of a catalyst and decreased in the following order: non-catalytic test (34.06 wt%) > Na₂CO₃ (27.10 wt%) > HZSM-5 (26.43 wt%) > γ-Al₂O₃ (21.64 wt%). In contrast, the total amount of water was found to increase for the catalytic experiments, indicating that dehydration reactions became more pronounced in presence of a catalyst. All pyrolysis liquids spontaneously separated into two fractions: an oil fraction and aqueous fraction. Catalysts strongly affected the composition and physical properties of the oil fraction of the pyrolysis liquid, making it promising as renewable fuel or fuel additive. Fatty acids, produced by thermal decomposition of the biomass triglycerides, were converted into compounds of several chemical classes (such as nitriles, aromatics and aliphatic hydrocarbons), depending on the type of catalyst. The oil fraction of the pyrolysis liquid with the highest calorific value (36.8 MJ/kg) was obtained for Na₂CO₃, while the highest degree of deoxygenation (14.0 wt%) was found for HZSM-5. The aqueous fraction of the pyrolysis liquid had opportunities as source of added-value chemicals.     

Bio‐oil production from rapid pyrolysis of cottonseed cake: product yields and compositions

Fixed‐bed fast pyrolysis experiments have been conducted on a sample of cottonseed cake to determine the effects of pyrolysis temperature, heating rate and sweep gas flow rate on pyrolysis yields and chemical compositions of the product oil. The liquid products and the subfractions of pentane soluble part were characterized by elemental analysis, FT‐IR spectroscopy, ¹H‐NMR spectroscopy and pentane subfraction was analysed by gas chromatography. The maximum oil yield of 34.8% was obtained at final temperature of 550°C with a heating rate of 700°C min^?1 and nitrogen flow rate of 100 cm³ min^?1. Chromatographic and spectroscopic studies on bio‐oil have shown that the oils obtained from cottonseed cake can be used as a renewable fuel and chemical feedstock. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydrogen production from biomass combining pyrolysis and the secondary decomposition

An efficient method of hydrogen production from biomass was studied in this paper. The pyrolysis of biomass was combined with the secondary decomposition of gaseous intermediate for hydrogen-rich gas production, with the avoidance of N₂ and CO₂ dilution to the energy density of gaseous effluents. In order to acquire the optimum conditions for hydrogen generation, effects of operating parameters on this two-step decomposition of biomass were analyzed through simulation of thermodynamic equilibrium and experiments using Ni/cordierite catalyst. The results indicate that the operating parameters, including pyrolysis temperature 923 K, 18 min of residence time, the secondary decomposition temperature 1123 K and molar steam to carbon ratio 2, satisfy all the criteria for high hydrogen content and energy efficiency. Hydrogen content of above 60% and hydrogen yield of around 65 g/kg biomass were achieved with optimized conditions. The hydrogen-rich gas is preferred for potential utilization in downstream fuel cells for the implementation of distributed energy supply, and is also practical for pure hydrogen production.     

Production and characterization of bio-oil and biochar from rapeseed cake

New and renewable fuels are the major alternatives to conventional fossil fuels. Biomass in the form of agricultural residues is becoming popular among new renewable energy sources, especially given its wide potential and abundant usage. Pyrolysis is the most important process among the thermal conversion processes of biomass. In this study, the production of bio-oil and biochar from rapeseed cake obtained by cold extraction pressing was investigated and the various characteristics of biochar and bio-oil acquired under static atmospheric conditions were identified. The biochar obtained are carbon rich, with high heating value and relatively pollution-free potential solid biofuel. The bio-oil product was presented as an environmentally friendly green biofuel candidate.     

Flash pyrolysis of jatropha oil cake in electrically heated fluidized bed reactor

Fluidized bed flash pyrolysis experiments have been conducted on a sample of jatropha oil cake to determine particularly the effects of particle size, pyrolysis temperature and nitrogen gas flow rate on the pyrolysis yields. The particle size, nitrogen gas flow rate and temperature of jatropha oil cake were varied from 0.3 to 1.18 mm, 1.25 to 2.4 m³/h and 350 to 550 °C. The maximum oil yield of 64.25 wt% was obtained at a nitrogen gas flow rate of 1.75 m³/h, particle size of 0.7–1.0 mm and pyrolysis temperature of 500 °C. The calorific value of pyrolysis oil was found to be 19.66 MJ/kg. The pyrolysis gas can be used as a gaseous fuel.     

Manufacturing gaseous products by pyrolysis of microalgal biomass

Algal biomass is considered as an alternative raw material for biofuel production. The search for new types of raw materials including high-energy types of microalgae remains relevant, since the share of motor fuels in the world energy balance remains consistently high (about 35%) with the oil price characterized by high volatility. The authors have considered the advantages of microalgae as raw materials for fuel production. Biochemical and thermochemical conversion are proposed as technologies for their processing. The paper presents the results of the study on the pyrolysis of the biomass of the blue-green microalgae/cyanobacterium Arthrospira platensis rsemsu 1/02-P clonal culture from the collection of the Research Laboratory of Renewable Energy Sources of the Lomonosov Moscow State University. The experimental investigation on the pyrolysis process of microalgal biomass has been carried out with the experimental setup made at the Institute of High Temperatures RAS in pure nitrogen 6.0 to create an oxygen-free medium with a linear heating rate of 10°С/min from room temperature to 1,000°С. The entire pyrolysis process has proceeded in the endothermic region. The specific values for solid residue, pyrolysis liquid and gaseous products have been experimentally determined. The following products have been manufactured by pyrolysis of microalgal biomass weighing 15 g: 1) char with a solid residue mass of 2.68 g, or 17.7% of MAB initial mass (while 9.3% of MAB initial mass has remained in the reactor); 2) pyrolysis liquid with a mass of 3.3 g, or 21.9% of initial mass; 3) noncondensable pyrolysis gases, 1.15 L. The specific volumetric gas yield (amount of gas released from 1 kg of RM) has amounted to 0.076 nm³/kg.In the paper, the analysis of the composition and specific volumetric yield of non-condensable pyrolysis gases produced in the pyrolysis process depending on temperature has been carried out. It is shown that the proportion of high-calorific components of the gas mixture (hydrogen, methane and carbon monoxide) increases with the temperature increase. The heating value assessment for the mixture of these gases has been performed as well.     

Pyrolysis of black cumin seed cake in a fixed-bed reactor

The black cumin seed cake (BCSC) is a by-product obtained from the black cumin seeds with cold pressing. This by-product can be utilized as a biomass feedstock for conversion to bio-oil with pyrolysis process. The BCSC samples were initially pyrolyzed on a lab-scale pyrolysis system at different values in the ranges of 300-800 °C and 0.050-0.300 L min⁻¹ to determine the effects of operation temperature and N₂ flow rate on the yields on products, respectively. Then, the bio-oil in the highest yield (wB = 44.37%) which was obtained at pyrolysis final temperature (450 °C) temperature, heating rate (35 °C min⁻¹), particle size (dp > 850 ??m), and sweeping flow rate of 0.200 L min⁻¹ was characterized by Fourier Transform infra-red (FT-IR) spectroscopy, gas chromatography/mass spectrometry (GC-MS) and column chromatography. Consequently, it was shown that the operating temperature and N₂ gas flow rate parameters were effective on the product yields. Also, the important some physico-chemical properties of the pyrolytic oil obtained in high yield were determined as the calorific value of 38.48 MJ kg⁻¹, the empirical formula of CH_1.651O_0.105N_0.042S_0.001, the rich chemical content containing many different chemical groups, and the density of 970.25 kg m⁻³, and the viscosity of 63.42 mm² s⁻¹. Based on the determined properties of the pyrolytic oil, it was decided that the use of pyrolytic oil derived from the BCSC may possible be for the production of the alternative liquid fuels and finely chemicals after the necessary improvements.     

Synergistic effect of curcumin and activated carbon catalyst enhancing hydrogen production from biomass pyrolysis

This study observes the synergistic effect of low cost and environmentally friendly catalysts, Activated Carbon and curcumin on the production of hydrogen gas in the biomass pyrolysis process. The Study used turmeric containing curcumin as an anti-oxidant agent added to the activated carbon (AC) catalyst. Biomass from coconut wood was pyrolyzed up to 550 °C using a fixed bed reactor. Both AC and curcumin were combined with a ratio of 1:0, 1:1, 1: 3, 0:1, and 3:1. The addition of AC and curcumin was able to increase the production of hydrogen and methane gas. The combination of AC and curcumin with 1:1 ratio was able to increase hydrogen gas by 25.6%. In addition, this combination was also increase methane gas by 71.8%.Curcumin as an anti-oxidant is able to prevents recombination reactions between radical molecules. Activated carbon surface is more protected from free radicals attacking and sticking to the surface. The phi-phi interaction between the two aromatic rings and the surface of activated carbon produces electrostatic forces on the surface of activated carbon to become stronger therefore it is more reactive in cracking hydrocarbon molecules and producing hydrogen gas. Software simulation, SEM, XRD, and FTIR tests were performed to support the analysis of experimental results.     

Predictions of concentration in the pyrolysis of biomass materials—I

The present work involves the prediction of the concentration profiles in the case of pyrolysis of different lignocellulosic materials in isothermal and non-isothermal conditions. The operative temperature range is from 573 to 973 K for isothermal conditions, and for non-isothermal conditions, the heating rate ranges from 5 to 80 K/min (5, 20, 40, 60 and 80 K/min).

The concentration for the above mentioned conditions is predicted for various biomass components, viz. cellulose, hemicellulose and lignin. Based on the concentration profiles of different biomass materials, it is possible to predict the pyrolysis behavior over a wide range of temperatures under isothermal and non-isothermal conditions for a large number of biomass materials, provided the activation energy and the frequency factor for the various reaction steps are known. It is also possible to ascertain the degree of combustibility of different biomass materials.

The simulation model utilizes a 4th order Runge-Kutta Predictor-Corrector method to solve the coupled ordinary differential equations. Based on thermogravimetric analysis done elsewhere, it is considered that temperature and time have a linear relationship. The above technique enables us to predict concentration profiles of different biomass materials for the entire range of pyrolysis. The concentration vs time data is plotted graphically for both isothermal and non-isothermal conditions utilizing the Harvard Graphics package on a PC-A/T personal computer.     

Characterization and prediction of biomass pyrolysis products

In this study some literature data on the pyrolysis characteristics of biomass under inert atmosphere were structured and analyzed, constituting a guide to the conversion behavior of a fuel particle within the temperature range of 200-1000 °C. Data is presented for both pyrolytic product distribution (yields of char, total liquids, water, total gas and individual gas species) and properties (elemental composition and heating value) showing clear dependencies on peak temperature. Empirical relationships are derived from the collected data, over a wide range of pyrolysis conditions and considering a variety of fuels, including relations between the yields of gas-phase volatiles and thermochemical properties of char, tar and gas. An empirical model for the stoichiometry of biomass pyrolysis is presented, where empirical parameters are introduced to close the conservation equations describing the process. The composition of pyrolytic volatiles is described by means of a relevant number of species: H₂O, tar, CO₂, CO, H₂, CH₄ and other light hydrocarbons. The model is here primarily used as a tool in the analysis of the general trends of biomass pyrolysis, enabling also to verify the consistency of the collected data. Comparison of model results with the literature data shows that the information on product properties is well correlated with the one on product distribution. The prediction capability of the model is briefly addressed, with the results showing that the yields of volatiles released from a specific biomass are predicted with a reasonable accuracy. Particle models of the type presented in this study can be useful as a submodel in comprehensive reactor models simulating pyrolysis, gasification or combustion processes.     

Modeling chemical and physical processes of wood and biomass pyrolysis

This review reports the state of the art in modeling chemical and physical processes of wood and biomass pyrolysis. Chemical kinetics are critically discussed in relation to primary reactions, described by one- and multi-component (or one- and multi-stage) mechanisms, and secondary reactions of tar cracking and polymerization. A mention is also made of distributed activation energy models and detailed mechanisms which try to take into account the formation of single gaseous or liquid (tar) species. Different approaches used in the transport models are presented at both the level of single particle and reactor, together with the main achievements of numerical simulations. Finally, critical issues which require further investigation are indicated.     

The Evritania (Greece) demonstration plant of biomass pyrolysis

This paper is focused on describing the Evritania demonstration plant for pyrolysis of forestry biomass. This plant was constructed in the village of Voulpi, district of Evritania, in Central Greece, in 1995, with a threefold purpose; development of know-how, forest fire prevention and rural development. The products are charcoal and bio-oil. The plant capacity is 1200–1450 kg/h of wet biomass and the pyrolysis temperature is approx. 400°C. The raw material used is Arbutus unedo, which is an evergreen broad-leaf tree which covers the area. Other agricultural waste could also be used, such as olive pits and cuttings, almond shells and cotton kernels. The paper includes the conceptual process flow sheet, the changes and improvements made during the trial phase, data from the start-up phase, and product characteristics. Comparison of the process with the Alten process is presented. Additionally, comparisons are made of product characteristics with those from other pyrolysis processes. In general, the results obtained are encouraging even though several improvements of the pilot plant are required.     

Development of an experimental technique for oil recovery during biomass pyrolysis

A new system to collect and analyse some of the condensable products of biomass pyrolysis is developed and tested. Pyrolysis of olive stone, oak pellet, pine pellet and major components of biomass (cellulose, hemicellulose and lignin) is performed by means of a thermogravimetric analysis (TGA). Some of the pyrolysis oil generated during the pyrolysis process condenses on an aluminium ring located in the gas exhaust of the device. The validity and repeatability of the method were shown when a similar oil mass was collected when the test conditions were repeated with the same material. In the biomass experiments, a larger amount of oil was collected from pellet samples, which have the highest cellulose content. This is consistent with the pure component experiments, as avicel cellulose shows the highest depositions. The depositions of the pure components show greater percentage of oil deposited than those of the biomass samples. The results reveal the important influence that the compositions of the biomass and the interactions among its major components have on the composition and quantity in the final deposit. Finally, the differences between deposits from biomass and deposits from mixed components were revealed by an FTIR analysis of the liquid products.     

Hydrogen-rich gas production from a biomass pyrolysis gas by using a plasmatron

Pyrolysis and gasification is an energy conversion technology process that produces industrially useful syngas from various biomasses. However, due to the tars in the product gases generated from the pyrolysis/gasification of biomass, this process damages and causes operation problems with equipment that use product gases such as gas turbines and internal engines.     

Fundamentals, kinetics and endothermicity of the biomass pyrolysis reaction

The paper reviews the pyrolysis of biomass constituents and possible secondary reactions. Biomass pyrolysis yields mostly liquid and solid fuel, easy to store and transport.Relevant working conditions for experiments and large-scale operation are: (i) biomass particles < 200 μm, (ii) a particle heating rate of at least about 80 K min⁻¹ and (iii) a reactor environment where the internal resistance to heat penetration is smaller than the external resistance to heat transfer (Biot-number, Bi < 1).The circumstances of TGA and DSC experiments meet these requirements and fully determine the reaction kinetics and endothermicity of the pyrolysis reaction. The reaction rate constant and the heat of reaction are essential parameters in the design of a pyrolysis reactor. For most of the biomass species tested, the first order reaction rate constant is large and >0.5 s⁻¹. The heat of reaction ranges from 207 to 434 kJ kg⁻¹. All results tie in with literature data, although the reader is cautioned in using literature data since experiments were not always performed under relevant testing conditions.     

Synthesis gas production by biomass pyrolysis: Effect of reactor temperature on product distribution

This paper describes mass, C, H, and O balances for wood chips pyrolysis experiments performed in a tubular reactor under conditions of rich H₂ gas production (700–1000 °C) and for determined solid heating rates (20–40 °C s⁻¹). Permanent gases (H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆), water, aromatic tar (10 compounds from benzene to phenanthrene and phenols), and char were considered in the balance calculations. Hydrogen (H) from dry wood is mainly converted into CH₄ (more than 30% mol. of H at 900 °C), H₂ (from 9% to 36% mol. from 700 to 1000 °C), H₂O, and C₂H₄. The molar balances showed that the important yield increase of H₂ from 800 to 1000 °C (0.10 Nm³ kg⁻¹ to 0.24 Nm³ kg⁻¹ d.a.f. wood) cannot be solely explained by the analyzed hydrocarbon compounds conversion (CH₄, C₂, aromatic tar). Possible mechanisms of H₂ production from wood pyrolysis are discussed.     

Pyrolysis as a technique for separating heavy metals from hyperaccumulators. Part II: Lab-scale pyrolysis of synthetic hyperaccumulator biomass

Synthetic hyperaccumulator biomass (SHB) impregnated with Ni, Zn, Cu, Co or Cr was used to conduct 11 experiments in a lab-scale fluidized bed reactor. Two runs with blank corn stover, with no metal added, were also conducted. The reactor was operated in an entrained mode in a oxygen-free (N₂) environment at 873 K and 1 atm. The apparent gas residence time through the lab-scale reactor was 0.6 s at 873 K.

The material balance for the lab-scale experiments on N₂-free basis varied between 81% and 98%. The presence of a heavy metal in the SHB decreased the char yield and increased the tar yield, compared to the blank. The char and gas yields appeared to depend on the form of the metal salt used to prepare the SHB. However, the metal distribution in the product streams did not seem to be influenced by the chemical form of the metal salt used to prepare the SHB. Greater than 98.5% of the metal in the product stream was concentrated in the char formed by pyrolyzing and gasifying the SHB in the reactor. The metal concentration in the char varied between 0.7 and 15.3% depending on the type of metal in the SHB. However, the metal concentration was increased 4 to 6 times in the char compared to the feed.     

Castor bean cake residues upgrading towards high added value products via fast catalytic pyrolysis

Castor oil is a vegetable oil obtained by pressing the seeds of the castor oil plant (Ricinus communis). Its production leads to high volumes of solid residues, the castor bean cakes. The main objective of this study was to investigate the potential of these castor bean cakes as a valuable source for production of high added value products such as bio-fuels and renewable chemicals. The upgrading of the castor bean cakes was attempted via thermochemical processes; specifically fast thermal and catalytic pyrolysis. Initially thermal pyrolysis of two different castor cakes and one type of castor stalks took place in a fixed bed fast pyrolysis reactor. The best feed was chosen for catalytic pyrolysis testing where industrially available microporous and one mesoporous catalyst were studied. Mass balances and products characterization via elemental analysis and two dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS) in the case of the liquid products allowed for the estimation of the catalytic effect in each case.