Pyrolysis Of Rice Straw Research Articles

Effects of biochar on N2O emission in denitrification pathway from paddy soil: A drying incubation study

N2O emission from paddy soil is a potential environmental risk, especially when the soil moisture content of paddy soil changes and excessive nitrogen retention occurs. Biochar is known to have a positive effect on reducing N2O emissions. However, the influence of different types of biochar on N2O emission with varying soil moisture contents is unclear. The objective of this study was to investigate the effects of biochar made from different feedstocks and at different pyrolysis temperatures on the release of N2O during drying process of paddy soil. An incubation experiment with four kinds of biochar (rice straw and rice husk biochar pyrolyzed at 400 °C and 700 °C, respectively) applied at 1% (w/w) was conducted on paddy soil with the same initial moisture content (105% water-filled pore space). The emission rate of N2O, concentrations of ammonium and nitrate, and the abundance of N2O related microbial functional genes (narG and nosZ) were monitored throughout the incubation period. Biochar amendments reduced cumulative N2O emissions by 56.8–90.1% compared to the control. Low-temperature rice straw biochar decreased nosZ gene abundance, downregulated the denitrification pathway, and reduced nitrogen loss and N2O emission. The low-temperature pyrolysis rice husk biochar and the control showed similar trends in narG and nosZ gene abundance and N2O emission. The high-temperature pyrolysis of rice straw and rice husk biochar showed opposite trends in narG gene abundance, but both increased nosZ gene abundance at the later incubation period. Different feedback on denitrification-derived N2O emission in biochar application was revealed in this study by establishing a link between biotic and abiotic factors, showing that caution should be exercised when considering the use of biochar to mitigate N2O emission under drying soil conditions.

Synergistic effect of mixed fungal pretreatment on thermogravimetric characteristics of rice straw

The thermogravimetric properties and chemical characterization of rice straw (RS) pretreated by mixed culture of white-rot fungi Phanerochaete chrysosporium (P. chrysosporium) and brown-rot fungi Gloeophyllum trabeum (G. trabeum) were investigated. The mixed fungal pretreatment showed a synergistic effect, which resulted in an energy-efficient pyrolysis of pretreated rice straw. The differences in thermochemical conversion of rice straw before and after fungal pretreatment were investigated using thermogravimetric analysis and the Flynn–Wall–Ozawa (FWO) method. Furthermore, the pretreated samples were also analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to illuminate the changes in chemical composition and pyrolysis behavior. Compared to single fungal pretreatment, the mixed fungal pretreatment worked better and exhibited great potential in biomass pyrolysis.

Silicic acid increases dispersibility of micro-sized biochars

Fine-sized biochars have been cautioned as an emerging environmental concern because of their dispersibility, hence agrochemicals-facilitated cotransport. While inspecting factors that are responsible for the dispersibility of biochars, we likely overlook the effect of silicic acid, a common compound in nature. This work aims to address the gaps in knowledge concerning the potential influence of silicic acid on surface charge and dispersibility of biochar. The pyrolysis of rice straw at 300 and 900 °C correspondingly produced so-called ‘C-rich biochar’ and ‘Si-rich biochar’, while the ‘hybrid biochar’ was obtained from the pyrolysis at 600 °C. Having low density (i.e., 1.15 to 1.46 g cm−3) might be an initial reason for the more dispersibility and transportability of biochars. Particle size could be another initial factor, causing biochars more vulnerable to be transported. The coarser C-rich biochar showed the fastest aggregation while the finer biochars (i.e., Si-rich and hybrid biochars) presented a slower aggregation. In addition to the effect of particle size, the presence of silicic acid was also involved in regulating the colloidal dynamics of the biochars. The test-tube method used to evaluate the colloidal dynamics of the biochars revealed that adsorption of silicic acid increased negative surface charge, by which dispersion state of biochar particles was favoured. The hybrid and Si-biochars showed their higher dispersibility while the C-rich biochar represented the lowest dispersibility and highest resistance to silicic acid. Pyrolysis is, therefore, the initial factor that shapes the nature and hence the dispersibility of the biochars, while silicic acid played an additional role in enhancing the dispersibility. As biochars obtained from higher pyrolysis temperatures are more dispersive, their application to agricultural lands needs to be carefully considered.

Study on co-hydrothermal treatment combined with pyrolysis of rice straw/sewage sludge: Biochar properties and heavy metals behavior

Reasonable disposal of sewage sludge (SS) as a resource to avid secondary pollution is the major objective. In this study, co-hydrothermal treatment combined with pyrolysis (co-HTP) of rice straw (RS) and sewage sludge for production of biochar was evaluated. The biochar yield was evaluated, and the basic characteristics of biochar including fuel characteristics, porosity characteristics and crystalline characteristics, as well as the heavy metals behaviors were examined. The results indicated that biochar yield exhibited a decreasing trend with the increase of RS blending ratio, and there was a synergy between RS and SS during co-HTP process for the slightly higher biochar yield than that of the predicted values. The co-HTP process promoted the increase of aromaticity and stability of biochar, along with an obvious increase of specific surface area of 116.81 m2/g for H-7RS/3SS-Char. The results also indicated that co-HTP process decreased the total concentrations of heavy metals in biochar and had the promoting effect on heavy metals immobilization for reducing environmental risks due to the reduced percentage of heavy metals in bioavailable fractions.

Insights into kinetics, reaction mechanism, and thermodynamic analysis of pyrolysis of rice straw from rice bowl of India

In the present work, various aspects of pyrolysis of rice straw (RS) from rice bowl of India including thermal degradation, kinetics, reaction mechanism, and thermodynamic parameters have been deliberated based on thermogravimetric experiments conducted at different heating rates, such as, 5, 10, 15, and 20 °C/min in N2 environment. Maximum devolatilization (about 47–53%) was observed in the temperature range of 214–394 °C. Average activation energy obtained from KAS, FWO, Starink, and Tang methods were estimated to be 174.91, 174.77, 172.79, and 174.88 kJ/mol, respectively. Master and Coats-Redfern plots showed that R1 (one dimension) and D1 (one-way transport) models were best fitted for pyrolysis of rice straw. Enthalpy values suggested that about 2 kJ/mol extra energy is required in addition to activation energy to form activated complex. Low values of entropy indicated the closeness of the system with thermodynamic equilibrium.

(3-Aminopropyl)triethoxysilane and iron rice straw biochar composites for the sorption of Cr (VI) and Zn (II) using the extract of heavy metals contaminated soil

Heavy metals like Cr (VI), when released into the environment, pose a serious threat to animal and human health. In this study, iron and (3-Aminopropyl)triethoxysilane (APTES) biochar composites were prepared from the biochar, which was produced through the pyrolysis of rice straw at 400 and 600 °C, using the chemical processes with an aim that the doping of pristine biochar structure with the Fe and NH2 radicals would enhance the removal of Cr (VI) and Zn (II) adsorption in both aqueous solution and soil. Both biochar composites were mixed at a rate of 3% (w/w) with the mine soil for the soil incubation test, and after completion of the test, a soil fertility index (SFI) was calculated. Results showed that both iron and APTES biochar composites followed the Langmuir-Freundlich isotherm showing the maximum removal capacity of 100.59 mg/g for Cr (VI) by APTES/SiBC 600 and maximum adsorption capacity of 83.92 mg/g for Zn2+ by Fe/BC 400. The SFI of the mine-soil amended with both Fe and APTES biochar composites were 16.67 and 13.04%, respectively higher than the controlled study. The mitotic index of the A. cepa cells that grew up in the soil amended with Fe/BC and APTES/SiBC were 40.47 and 44.45%, respectively, higher than the controlled study. The results indicated that the incorporation of the Fe and APTES biochar composites in the soil effectively reduced the metal toxicity and improved the soil physicochemical properties. This study opens up the prospects of using biochar composites in contaminated soil and water treatments.

Rapid formation of pyrogenic char (biochar) with high and low sorption capacity towards organic chemicals.

Pyrogenic char (biochar) with a high sorption capacity (B-HSC) can sequester hazardous chemicals (e.g., phenanthrene). However, when sorption inhibits bioavailability of some functional chemicals (e.g., the herbicidal efficacy of diuron in soil), biochar with a low sorption capacity (B-LSC) is required to prevent sorption effects. The pyrolytic B-HSC generation has been reported, but information on B-LSC formation is scarce. How fast B-HSC and B-LSC could be generated is unknown until now. Here, biochars were rapidly prepared (the shortest heating time reached 5min and the cooling time reached<30min) by a direct-pyrolysis method by directly exposing packaged rice straw and pine wood to 350°C, 500°C and 700°C and out-of-furnace cooling at room temperature. The sorption of diuron, phenanthrene, and twelve other chemicals was investigated. B-HSCs were obtained within 30min of rice straw pyrolysis, and the biochar Kd values quickly increased to 7-730-fold that of the raw biomass as -OH and C-O-C in (hemi)cellulose of rice straw rapidly degraded, increasing hydrophobic interactions between the char and chemicals (solubility≤82.8g/L). In contrast, B-LSCs were generated within 30min of PW pyrolysis, and the Kd values of the biochars were 0.2-3.0-fold that of the raw biomass, as the surface area development and hydrophobicity-driven sorption were probably delayed by the late degradation of lignin aromatic C-O and phenolic -OH. Biochar amendment revealed an enhancement effect of B-HSC but not of B-LSC on soil sorption. The fast formation of B-LSC and B-HSC provides a guide to develop time- and cost-effective technique in pyrolytically producing weakly or strongly sorbing biochars for organic chemical management.

Fast pyrolysis kinetics of lignocellulosic biomass of varying compositions

This study is focused on evaluating the apparent kinetics of fast pyrolysis of different lignocellulosic biomass viz, rice straw, pine wood and empty fruit bunch. The goal of the study is to investigate the effect of biomass composition on kinetics, time evolution of pyrolysis vapors and the production of major bio-oil components during the fast pyrolysis of biomass. The isothermal mass loss data were generated at different pyrolysis times between two and sixty seconds in the temperature range of 400–700 °C. The data generated were then analyzed using various reaction models, viz., first-order model, diffusion models, contracting cylinder model and Avrami-Erofeev model to determine the rate constants and the rate parameters. Kinetic compensation effect was established using a large number of kinetic data reported in the literature to validate the results. The time evolution of major functional groups in the pyrolysates was analyzed using in-situ analytical pyrolyzer coupled with Fourier transform infrared spectrometer (Py-FTIR), and evolution of the volatiles was observed in time range of 5–60 s. Increase in pyrolysis temperature led to faster evolution of volatiles as evidenced by the shifting of maximum rate of vapor evolution to shorter time periods.

CO2 can decrease the dissolution rate of ashed phytoliths

Phytoliths are silica structures formed in various silicon (Si)-rich plant species. These structures are a fast-reacting source of available Si for soils and crops and act as a platform for the sequestration of organic matter and CO2. The solubility of phytoliths has been intensively studied. However, little is known about the effect of gases, e.g., CO2, which are commonly emitted from soils. It is hypothesized that CO2 can interact and alter the dissolution rate of phytoliths. In this study, we conducted batch experiments for ashed phytoliths obtained from the controlled pyrolysis of rice straw at 300, 500, 700 and 900 °C and evaluated the Si release along with changes in surface charge (zeta potential) under the influence of CO2 flow. It was found that the ashed phytoliths possessed negative surface charges and released soluble alkaline ions, which enabled sequestration of CO2 by shifting the equilibrium of H2CO3, HCO3− and CO32− more towards HCO3− and CO32−. Conversely, the intensifying presence of CO2 acidified the suspensions containing the phytoliths, stimulated the protonation of the phytolith surface, and decreased nucleophilic attacks from OH− and other anions, thereby preserving the phytolith from dissolution. CO2 showed a higher prohibition efficacy for the phytoliths obtained from 300 and 500 °C than those obtained from 700 and 900 °C. It can be highlighted that CO2 acts to protect phytoliths by altering the solution pH; managing CO2 flux is therefore a potentially effective practice to govern the soil phytolith pool.

Study on the mechanism of co-catalyzed pyrolysis of biomass by potassium and calcium

The effects of K and Ca on the pyrolysis of rice straw were studied. The results showed that impregnating a certain amount of Ca is beneficial to the uniform distribution of K, and mixing a certain amount of K is also beneficial to the uniform distribution of Ca. Ca and K would combine with the silicon-aluminum compound in the sample during the pyrolysis and become invalid. Ca can effectively reduce the invalid K, but cannot completely protect K from combining with the silicon-aluminum compound. The binary metal carbonates K2Ca(CO3)2 and K2Ca2(CO3)3 were produced during the pyrolysis of the samples, which have a limited effect for the uniform distribution of the catalysts. In addition, acid-leaching removed most of the inorganic components in rice straw, which made it difficult for the catalyst to be evenly distributed, indicating that the inorganic components play an important role in evenly distributing the catalyst.

Sustainable utilization of rice straw to mitigate climate change: A bioenergy approach

With the growing population, agriculture productivity is increasing due to the high demand for food, which in turn produces a large amount of agricultural waste. Pyrolysis of crop residues is one of the suitable options to produce biochar and can be utilized as a fuel. In the present study, the slow pyrolysis of rice straw was carried out at four temperatures, 300 °C, 400 °C, 500 °C, and 600 °C. It was observed that biochar yield decreases (57.87–35.63%) with an increase in the process temperature. The physiochemical properties such as fixed carbon (43.91–57.63%), heating value (16.59–19.69 MJ/kg), carbon (63.77–85.13%) in biochar increases with temperature. Burning of rice straw (3Mt/year) emits the greenhouse gas (GHG) emission of about 10,953 (CO2e) Gg/year, while the combustion of biochar produced from rice straw at different temperatures emits the emission in the range of 2131–3239 (CO2e) Gg/year. The electricity generation potential analysis for produced biochars was carried out with two different power plant efficiency 25 and 30%. The electricity potential for power plant efficiency 25% and 30% was observed in the range of 1.2–1.82 TWh and 1.44–2.18 TWh, respectively.

CO2-Mediated catalytic pyrolysis of rice straw for syngas production and power generation

As emissions of anthropogenic CO2 from the use of fossil fuels become more severe, the renewable energy production has received considerable interests. In this study, CO2 was used as a raw material to produce energy as a form of syngas (H2/CO) as a precautious measure for mitigating the atmospheric CO2 levels. Rice straw pyrolysis was conducted under various N2/CO2 purge gas environments. The present study experimentally proved that CO2 expedited gas phase homogeneous reactions between volatile organic compounds (VOCs), evolved from rice straw pyrolysis. These CO2 functionalities led to the conversion CO2/rice straw into CO at ≥ 480°C. To accelerate reaction kinetics of syngas formation, additional thermal energy (500 or 700°C) was applied through multi-stage pyrolysis setups. In addition, SiO2 supported Co (Co/SiO2) catalyst was further accelerate reaction kinetics of CO (3 times) and H2 (6 times) in reference to non-catalytic pyrolysis at 500°C. The synergistic effects of Co/SiO2 catalyst and CO2 feedstock resulted in substantial formations of H2 and CO at ≤ 480°C. To analyze the potential capability of rice straw fuels, their power generation performances were evaluated through a simple gas turbine cycle. When the constant amount of air was assumed to be supplied to a combustion chamber, different amounts of fuel feedstocks were required for their complete combustions. In this condition, the resulting power generations of rice straw fuels (maximum 138 MJ s−1 from catalytic pyrolysis under 100% CO2) were up to 1.9 times higher than the power generations from natural gas references (74 and 82 MJ s−1). These results suggest that a renewable power generation platform could be constructed with a valorization of greenhouse gas (CO2) and biomass waste (rice straw) through pyrolysis process at mild temperature.

Electrochemically assisted pyrolysis of rice straw in molten carbonates

Abstract The pyrolysis of rice straw as a feedstock in molten carbonates pyrolysis (MCP) and electrochemically assisted molten carbonates pyrolysis (EMCP) systems was investigated in this study. Molten carbonates (MC) were utilized as both the heat transfer medium and the electrolyte in EMCP. The results suggested that EMCP helped to reduce the formation of tar and water, while promoting the formation of gases, especially CO2. The optimum reaction conditions were 600 mA/cm2 of current density in a particle size of 3 mm at 550 °C, with the maximum H2 and CH4 yields of 0.26 mol/100 g and 0.17 mol/100 g, and the yield of hydrocarbons peaked at 5.0%. EMCP system reinforced the reaction by accelerating the reaction rate rather than reducing the activation energy. The electrochemical process facilitated the conversion of the hydroxyl groups and a fraction of the carbonyl groups in the biomass to carboxyl groups, which then underwent decarboxylation to release CO2 in the MC medium. Because oxygen atoms were removed from the system as CO2, the water formation decreased. The EMCP system showed benefits in the synthesis of hydrogen and hydrocarbons, and opened a novel pathway for the deoxygenation of biomass in pyrolysis.

Catalytic pyrolysis of rice straw: Screening of various metal salts, metal basic oxide, acidic metal oxide and zeolite catalyst on products yield and characterization

Lignocellulosic biomass is a promising renewable feedstock for the production of chemicals and fuels in light of the extensive use of fossil fuels associated with increasingly serious environmental problems. In this study, pyrolysis of rice straw with different types of catalyst such as metal salts (FeCl3, CuCl2, MgCl2 and MnCl2), metal basic oxides (MgO, CaO, MgCO3 and CaCO3), acidic metals (ZnO, ZrO2, CeO2 and TiO2), zeolites catalysts (ZSM-5, Y-Zeolite, Mordenite and SBA-15), catalyst amount (5, 10, 15 and 20 wt%) and reaction temperatures (350, 400, 450 and 500 °C) were examined on product yield and products characterization. The maximum bio-oil (38.5 wt%) was obtained for non-catalytic reaction at 450 °C. However for catalytic reaction highest bio-oil yield were observed 55.2, 52.1, 48.7 and 48.4 wt% with Y-zeolite, MgO, ZrO2 and MgCl2 catalyst at 450 °C respectively. GC-MS, FT-IR, NMR, GPC, TGA, and CHNS were used for bio-oil characterization. Y-zeolite effectively produced phenolics monomers as compare to basic (MgO), acidic (CeO2) and metal salt (MgCl2) catalyst. The use of catalysts was increased the boiling point range and the higher boiling point range was observed in case of Y-zeolite and MgO catalytic bio-oil. The highest higher heating value (HHV) 36.7 MJ/kg and highest carbon 75.2% was observed for zeolite catalytic bio-oil. Moreover lower molecular weight in the catalytic bio-oil was observed as compare to non-catalytic bio-oil.

Preparation of biochar as a coating material for biochar-coated urea

Biochar was used as a coating material for slow release urea. However, influence of biochar performance on preparing biochar-coated urea (BCU) and nitrogen release characteristics is rarely reported. In this study, total of 24 biochars were prepared and characterized from six biomass residues (rice straw, chicken manure, vinasse, Phyllostachys pubescens, Arundo donax and sugarcane bagasse) at four pyrolysis temperatures (400–700 °C). Grey correlation analysis (GCA) was used to select biochar as a coating material for BCU based on biochar performance indicators. The feasibility (BCU formability) for preparing BCU and characteristics of nitrogen release in BCU based on hydrostatic dissolution test and soil column leaching experiment were evaluated. Biochar prepared at low pyrolysis temperature was not suitable as a coating material for BCU due to low specific surface area. Biochars derived from pyrolysis of Phyllostachys pubescens (BP6), vinasse (BV6) and rice straw (BR6) at 600 °C were selected as coating materials for BCU based on grey correlation analysis (GCA). The adhesion of biochar to urea surface was related to biomass type that preparing biochar. BV6 was recommended for use as coating material for BCU because the feasibility of the biochars followed the order BR6 > BV6 > BP6, and the practicality of the biochars followed the order BP6 > BV6 > BR6. The findings suggest that biochar with a high specific surface area, hydrophilic oxygen-containing functional groups and low pH is a suitable material for BCU.

Raman spectroscopy of biochar from the pyrolysis of three typical Chinese biomasses: A novel method for rapidly evaluating the biochar property

Biochar from the pyrolysis of rice husk, pine wood and rice straw under the temperature from 250 °C to 800 °C were obtained and characterized by Raman spectroscopy. The biochar properties and chemical structure evolution were investigated, and correlations between biochar properties and Raman spectral parameters were set up. The results indicate that pyrolysis temperature has a more significant influence on biochar yield than feedstock. The volatile content in raw biomass linearly decreases with the decrease of biochar yield, and the atom H/C ratio of biochar linearly decreases with the decrease of Vdaf (volatile content in dry ash free basis). The change characteristics of Raman bands position and bandwidth indicate that carbon order degree of biochar progressively increases with the increase of pyrolysis temperature, and detailed chemical structure of biochar from different raw biomass can significantly differ from each other. Reasonable correlations between biochar properties including yield, Vdaf, the atom H/C ratio and the fluorescence interference degree in Raman spectrum (defined as α) of biochar have been found. A series of functions were proposed for rapid evaluation of biochar properties. Specially, the correlation that H/C = 0.3652 + 2.2887∗α-2.4035∗α^2 + 0.8221∗α^3 can be universal for carbon-based fuels including biochar, coals, coal chars and bio-oil chars.

Characterization of non-oxygenates hydrocarbon product from the catalytic pyrolysis of rice straw

The usage of fossil fuel as petrochemical feedstock becomes problems due to the depletion of its supply coupled with the issue of global warming and air pollution, thus a new alternative is needed. Lignocellulose biomass can be converted into hydrocarbons for the petrochemical industry’s feedstock through pyrolysis process, which is a thermal decomposition of biomass in an oxygen-free condition. The materials used in this experimental study consist of rice straw as the main feedstock, ZSM-5 as the catalyst. Rice straw is lignocellulose biomass that has the potential in Indonesia because of its abundant supply in many locations. Biomass catalytic pyrolysis was carried out using a fixed bed reactor with the varied ratios of ZSM-5 and biomass mixture and the products in the form of gaseous phase come out from the bottom of the reactor by flowing it into a glass test tube with a diameter of 2.5 cm. Pyrolysis process was carried out at temperature variations of 450°C, 500°C, and 550°C in a nitrogen gas flowing condition of 10-20 ml/minute. To detect the non-oxygenate hydrocarbon products, the sampling of the gas product was done by taken it using the glass syringe in the reactor bottom. The gas analysis was performed using Gas Chromatography-Mass Spectroscopy (GC-MS) and the calibration curve was then prepared to quantify the results by GC-MS analysis for various pyrolysis vapor compounds with their respective peak areas. With the variation of pyrolysis temperature, this study shows that the olefin group produced in catalytic pyrolysis neither does the conventional pyrolysis. But the pyrolysis produced the paraffin group in any type of pyrolysis condition process. This study also found that olefin group production was decreased in the longer time of stream reaction, while the aromatic group was increased. Generally, the amount of aromatic compound formation depends on catalyst ratio.

Biochar as a catalytic material for the production of 1,4-butanediol and tetrahydrofuran from furan

Biomass valorization is emerging as a new trend for the synthesis of materials for various environmental applications. In this connection, a biochar resulting from pyrolysis of rice straw was employed as a catalytic material for the conversion of hemicellulose-derived furan into value-added platform chemicals such as 1,4-butanediol (1,4-BD) and tetrahydrofuran (THF). The biochar was used as catalyst support of bifunctional Ru–Re catalyst. Two different catalysts were prepared: a conventional activated carbon (AC)-supported Ru–Re catalyst (Ru–Re/AC) and a biochar-supported Ru–Re catalyst (Ru–Re/biochar). The Ru–Re/biochar had a different form of Re species from the Ru–Re/AC, resulting in different reducibility. The difference of reducibility between the two was attributed to alkali metal present in the biochar such as potassium. The Ru–Re/biochar had a 17 times lower metal dispersion on the surface than the Ru–Re/AC, ascribed to a lower surface area of the biochar than the AC. Catalytic activities of the catalysts with regard to reaction rate per available surface active site for transforming furan to 1,4-BD and THF were measured. The Ru–Re/AC was 3 times less active than the Ru–Re/biochar. This study not only provides a way to efficiently use biomass both for environmental catalysts and for feedstock of producing value-added platform chemicals, but also shows potential of biochar for the replacement of typical catalysts employed in biorefinery.

Study of the Relationship Between a Nutrient Element and Two Energy Elements During the Biochar Preparation Process

To investigate the relationship between the retention of the nutrient element nitrogen (N) and the release of the energy elements carbon and hydrogen (C and H) during rice straw pyrolysis, biochar samples were produced at a temperature of 800 °C under different atmospheres (N2 or CO2). Thermogravimetric/mass spectrometry monitoring was used to measure the gases released during pyrolysis. The straw samples were also pre-treated with alkaline solutions to improve the retention rate of the nutrient element N in the biochar, making it suitable to be used for soil amendment. These studies yielded some important results: (1) When the evolution of gases containing the nutrient element N was high, the release of gases containing energy elements also increased; i.e., the N and C/H release showed a consistent positive correlation. (2) Pre-treatment with an alkaline solution inhibits N loss during straw pyrolysis, and higher-concentration alkaline solutions more effectively reduce the release of N. The amounts of N-containing gases released during the pyrolysis of straw samples subjected to the different pre-treatment procedures followed the order raw straw ≈ 0.15% KOH > 0.15% Ca(OH)2 > 0.15% NaOH. (3) Raw rice straw is mainly composed of cellulose (32.1%), hemicellulose (35.7%), and lignin (22.3%). Soaking the straw in an alkaline solution increases the relative contents of cellulose and hemicellulose. Because cellulose has an ordered crystalline structure with high thermal stability, the energy and nutrient elements were not easily released from cellulose as gases during pyrolysis.

Syngas production by catalytic pyrolysis of rice straw over modified Ni-based catalyst

Ni-xLa/Al2O3-MgO-sawdust char catalysts were prepared by modifying the Ni/Al2O3 catalyst from two aspects of support and active components. The effect of Al2O3, MgO, sawdust char molar ratio, and La content of catalysts on syngas (H2 + CO) production in the catalytic pyrolysis of rice straw was investigated in a horizontal fixed-bed quartz tube reactor. Furthermore, the stability of catalysts with the optimum catalytic performance was tested and compared with that of the Ni/Al2O3 catalysts. X-ray diffraction, X-ray fluorescence, field emission scanning electron microscopy, energy disperse X-ray, and Brunauer-Emmett-Teller analyses were applied to understand the physiochemical properties of the supports and catalysts. The study revealed that the supports were composed of many irregular flaky particles and thus formed many pores. Moreover, the addition of La decreased the particle size of NiAl2O4 and increased the active metal surface of the Ni/Al2O3-MgO-sawdust catalysts. When the molar ratio of Al2O3, MgO, and sawdust char was 1:1:1 and the La content was 10 wt% (dry weight basis), the catalysts presented the highest syngas concentration of 78.9 vol% and the most stable performance during the catalytic pyrolysis process.