Hydrogen production via catalytic pyrolysis of biomass in a two-stage fixed bed reactor system

This study introduces an innovative process of generating hydrogen-rich gas from biomass through the catalytic pyrolysis of biomass in a two-stage fixed bed reactor system. Water hyacinth was used as the biomass feedstock. The effects of various factors such as pyrolysis temperature, catalytic bed temperature, residence time, catalyst, and the nickel content of the catalyst on the pyrolysis productivity were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. Results showed that the high productivity of hydrogen can be obtained particularly by increasing the catalytic bed temperature, residence time, and catalysts. The favorable reaction conditions are as follows: a first-stage pyrolysis temperature of 650 °C–700 °C, a second-stage catalytic bed temperature of 800 °C, a catalytic pyrolysis reaction time of 17 min, and a nickel content of 9% (wt %).     

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.     

Thermogravimetric study on the pyrolysis kinetics of apple pomace as waste biomass

Biomass waste-to-energy is an attractive alternative to fossil feedstocks because of essentially zero net CO₂ impact. A viable option consists in an integrated process, in which biomass is partly used to produce valuable chemicals with residual fractions employed for hydrogen production. One example of a biomass waste is the apple pomace, which is the residue generated in the process of extraction of apple juice. In this research, a kinetic study of the pyrolysis of apple pomace biomass (APB) was performed by TGA aiming its liquid and gaseous products be utilized for the production of valuable chemicals and hydrogen. Characterization of APB consisted in calorific value, compositional, proximal and elemental analyzes. Kinetics were evaluated using three iso-conversional TGA models at 5, 10, 15 and 20 °C/min. Activation energy values of 213.0 and 201.7 kJ/mol were within the range for hemicellulose and cellulose, respectively, which are the main components of biomass.     

Integrated production of aromatic amines,aromatic hydrocarbon and N-heterocyclic bio-char from catalytic pyrolysis of biomass impregnated with ammonia sources over Zn/HZSM-5 catalyst

By introducing exogenous nitrogen during biomass pyrolysis under nitrogen-rich conditions, high-value nitrogen-containing products, i.e., nitrogen-rich char and oil may be produced. Based on the cogeneration of high-value nitrogen products from biomass, biomass nitrogen-enriched pyrolysis was performed in a fixed bed with different sources and contents of ammonia. The yields, composition and characteristics of the products were investigated. Moreover, the formation mechanism of N-containing species was explored in depth for the pyrolysis and catalytic pyrolysis with HZSM-5 and Zn/HZSM-5 catalysts via elemental analysis, XPS, FTIR and BET. The results showed that ammonia impregnation could promote a Maillard reaction, reduce the content of small aldehydes and ketones, and produce a nitrogen-enriched bio-oil. The contents of N-containing species and phenolic substances in the pyrolysis oil of biomass impregnated with 10% urea reached 15.66% and 56.69%, respectively. Moreover, the nitrogen on the coke surface after pretreatment was mainly composed of CN, CN and NCOO functional groups. The bio-char generated abundant pyridinic-N, pyrrolic-N, quaternary-N, and pyridone-N oxides. The presence of urea introduced many alkaline N-containing functional groups on the surface of the bio-char and promoted the transformation of nitrogen from amides and imides to heterocyclic nitrogen with higher thermal stability. Furthermore, Zn was an excellent catalyst for the Maillard reaction, and the Zn/HZSM-5 catalyst had a higher selectivity for aromatic hydrocarbons (96.98% for biomass and 86.48% for urea/biomass) and N-containing heterocyclic compounds, such as indoles (6.16% for biomass and 13.51% for urea/biomass). Additionally, the coke content decreased, and the catalyst deactivation decreased.     

Understanding the pyrolysis behavior of agriculture,forest and aquatic biomass: Products distribution and characterization

Pyrolysis studies on agricultural (rice straw), forest (pine) and aquatic (Ulva lactuca) biomass were carried out in a fixed bed reactor at different temperature range of 300–550 °C. The product distributions and their characterization of products were compared among these biomasses. The maximum liquid product yield 29.4, 57.5 and 25.6 wt% obtained at 400, 500 and 400 °C respectively from rice straw (RS), pine (PN) and Ulva lactuca (UL) biomass. However, the higher conversion was observed in the case of pine wood biomass 77.0% at 550 °C. From the GC-MS analysis, it is observed that RS and PN bio-oil mostly composed of derivatives of phenolic compounds, while UL bio-oil composed of cyclopentenone derivatives compounds. The highest higher heating value (HHV) was found in pine bio-oil 34.8 MJ/kg. Also PN pyrolytic bio-oil had higher boiling point differences compounds. The bio-char analysis showed that the PN bio-char is a carbon rich and porous in nature as compared to the RS and UL bio-char.     

Insights into pyrolysis and catalytic co-pyrolysis upgrading of biomass and waste rubber seed oil to promote the formation of aromatics hydrocarbon

To solve the problem of low aromatic hydrocarbon yield and selectivity in biomass catalytic pyrolysis, we used added oxygen-containing hydrogen supplier of rubber seed oil (RSO) with a higher hydrogen-to-carbon ratio to investigate the thermal decomposition behaviors, kinetic and production distribution of biomass, cellulose and RSO with the weight ratio of 1:2 using thermogravimetric analyzer (TGA) for kinetic analysis and fixed bed reactor with the feed composition of 1.2 g: 0.4 mL/min (Biomass to RSO) for product distribution in non-catalytic and catalytic co-pyrolysis over a HZSM-5 catalyst. The results show that there was a positive synergistic interaction between biomass and RSO according to the difference in weight loss, which could decrease the formation of solid coke at the end of experiment. The addition of the HZSM-5 catalyst can markedly increase the reaction activity, accelerate the reaction rate, and the reaction Ea, leading to a substantial increase in the conversion rate; furthermore, the residual carbon content will decrease, and the activations of Cellulose + RSO + Catalyst and Biomass + RSO + Catalyst are only 50.80 kJ/mol and 62.36 kJ/mol, respectively. The kinetic analysis showed that adding a catalyst did not change the decomposition mechanism. Co-pyrolysis of biomass and RSO could effectively improve the yield and selectivity of aromatics, when the pyrolysis temperature and catalytic temperature were 550 °C and 500 °C, respectively, the mass space velocity of RSO was 0.4 mL/min, the reaction time was 30min, the yields of benzene, toluene, xylene and ethyl benzene (BTXE) were up to 78.77%, and the selectivity of benzene, toluene and xylene was much better. Finally, the coke yield was substantially lower.     

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.     

Detailed kinetic study of anisole pyrolysis and oxidation to understand tar formation during biomass combustion and gasification

Anisole was chosen as the simplest surrogate for primary tar from lignin pyrolysis to study the gas-phase chemistry of methoxyphenol conversion. Methoxyphenols are one of the main precursors of PAH and soot in biomass combustion and gasification. These reactions are of paramount importance for the atmospheric environment, to mitigate emissions from wood combustion, and for reducing tar formation during gasification. Anisole pyrolysis and stoichiometric oxidation were studied in a jet-stirred reactor (673–1173 K, residence time 2 s, 800 Torr (106.7 kPa), under dilute conditions) coupled with gas chromatography–flame ionization detector and mass spectrometry. Decomposition of anisole starts at 750 K and a conversion degree of 50% is obtained at about 850 K under both studied conditions. The main products of reaction vary with temperature and are phenol, methane, carbon monoxide, benzene, and hydrogen. A detailed kinetic model (303 species, 1922 reactions) based on a combustion model for light aromatic compounds has been extended to anisole. The model predicts the conversion of anisole and the formation of the main products well. The reaction flux analyses show that anisole decomposes mainly to phenoxy and methyl radicals in both pyrolysis and oxidation conditions. The decomposition of phenoxy radicals is the main source of cyclopentadienyl radicals, which are the main precursor of naphthalene and heavier PAH in these conditions.     

Kinetic study of the catalytic reforming of biomass pyrolysis volatiles over a commercial Ni/Al2O3 catalyst

An original kinetic model has been proposed for the reforming of the volatiles derived from biomass fast pyrolysis over a commercial Ni/Al₂O₃ catalyst. The pyrolysis-reforming strategy consists of two in-line steps. The pyrolysis step is performed in a conical spouted bed reactor (CSBR) at 500 °C, and the catalytic steam reforming of the volatiles has been carried out in-line in a fluidized bed reactor. The reforming conditions are as follows: 600, 650 and 700 °C; catalyst mass, 0, 1.6, 3.1, 6.3, 9.4 and 12.5 g; steam/biomass ratio, 4, and; time on stream, up to 120 min. The integration of the kinetic equations has been carried out using a code developed in Matlab. The reaction scheme takes into account the individual steps of steam reforming of bio-oil oxygenated compounds, CH₄ and C₂-C₄ hydrocarbons, and the WGS reaction. Moreover, a kinetic equation for deactivation has been derived, in which the bio-oil oxygenated compounds have been considered as the main coke precursors. The kinetic model allows quantifying the effect reforming conditions (temperature, catalyst mass and time on stream) have on product distribution.     

Pyrolysis of North-American grass species: Effect of feedstock composition and taxonomy on pyrolysis products

In the Midwest of the U.S., several members of the Poaceae family can be grown as bioenergy crops. Besides Miscanthus and switchgrass, which have been extensively studied, native Midwestern grasses such as big bluestem, coastal panicgrass, deertongue, indiangrass, sandreed and sideoats grama can be grown in monoculture or polyculture plantations. In addition to climate, soil fertility and water availability, the selection of bioenergy crops depends on the choice of conversion technology. One such technology, fast pyrolysis, is a thermochemical approach for converting biomass into a liquid product known as bio-oil, a hydrocarbon fuel intermediate. In this research, the eight aforementioned grass varieties were characterized by fiber and metal analyses as well as calorimetry and thermal gravimetry. Conversion by analytical pyrolysis showed that although variability exists, all eight grasses produced a similar spectrum of chemical compounds. Principal component analysis of pyrolysis-GC/MS data detected statistically significant differences amongst the grass varieties on the basis of six key chemical markers: glycolaldehyde, acetic acid, acetol, methyl glyoxal, 4-vinylphenol and levoglucosan. Though taxonomic classification was not found to affect product composition, correlation analysis verified that biomass composition and thermal properties might be responsible for the differences in pyrolysis products.     

Experimental study of pyrolysis for potential energy,hydrogen and carbon material production from lignocellulosic biomass

Experimental results of slow, fast and catalytic pyrolysis of five lignocellulosic residues (corncobs and corn stalks, sunflower residues, olive kernels and olive tree prunings) are reported in this paper. Pyrolysis took place in two different reactor configurations: a captive sample wire mesh reactor for fast pyrolysis and a fixed bed reactor for non-catalytic and catalytic pyrolysis. Comparison of the experimental results showed that pyrolysis in the captive sample reactor produced more H₂-rich gas than in the fixed bed reactor, while the fixed bed reactor configuration seemed to favor the production of liquid products. Analysis of gaseous, liquid and solid products was performed by GC and GC/MS. Pyrolysis results were assessed, and recommendations for the further use of their products were made.     

Formation of HNCO, HCN, and NH3 from the pyrolysis of bark and nitrogen-containing model compounds

Bark pellets have been pyrolyzed in a fluidized bed reactor at temperatures between 700 and 1000 °C. Identified nitrogen-containing species were hydrogen cyanide (HCN), ammonia (NH₃), and isocyanic acid (HNCO). Quantification of HCN and to some extent of NH₃ was unreliable at 700 and 800 °C due to low concentrations. HNCO could not be quantified with any accuracy at any temperature for bark, due to the low concentrations found. Since most of the nitrogen in biomass is bound in proteins, various protein-rich model compounds were pyrolyzed with the aim of finding features that are protein-specific, making conclusions regarding the model compounds applicable for biomass fuels in general. The model compounds used were a whey protein isolate, soya beans, yellow peas, and shea nut meal. The split between HCN and NH₃ depends on the compound and temperature. It was found that the HCN/NH₃ ratio is very sensitive to temperature and increases with increasing temperature for all compounds, including bark. Comparing the ratio for the different compounds at a fixed temperature, the ratio was found to decrease with decreasing release of volatile nitrogen. The temperature dependence implies that heating rate and thereby particle size affect the split between HCN and NH₃. For whey, soya beans, and yellow peas, HNCO was also quantified. It is suggested that most HCN and HNCO are produced from cracking of cyclic amides formed as primary pyrolysis products. The dependence of the HNCO/HCN ratio on the compound is fairly small, but the temperature dependence of the ratio is substantial, decreasing with increasing temperature. The release of nitrogen-containing species does not seem to be greatly affected by the other constituents of the fuel, and proteins appear to be suitable model compounds for the nitrogen in biomass.     

镍基镁渣催化剂对生物质焦油模化物催化重整特性实验研究

采用湿浸渍法制备Ni/γ-Al₂O₃和Ni/MS(magnesium slag)催化剂,选择糠醛、甲苯、萘、芘作为生物质焦油的模化物,研究不同镍基催化剂对四类焦油模化物在固定床反应器内进行催化重整的重整特性。结果表明,Ni/MS催化剂在催化所有模化物的重整反应时,气相碳转化率和气体产率均明显高于Ni/γ-Al₂O₃催化剂。当水分子物质的量与碳原子物质的量之比为1.5时,糠醛的气相碳转化率达到最高值86.54%。X 射线衍射 (XRD)结果表明,Ni/MS催化剂上存在的多种固溶体（NiO-Fe₂O₃、NiO-MgO）形成了多种活性位点。     

A study on torrefaction of various biomass materials and its impact on lignocellulosic structure simulated by a thermogravimetry

Torrefaction processes of four kinds of biomass materials, including bamboo, willow, coconut shell and wood (Ficus benjamina L.), were investigated using the thermogravimetric analysis (TGA). Particular emphasis is placed on the impact of torrefaction on hemicellulose, cellulose and lignin contained in the biomass. Two different torrefaction processes, consisting of a light torrefaction process at 240 °C and a severe torrefaction process at 275 °C, were considered. From the torrefaction processes, the biomass could be divided into two groups; one was the relatively active biomass such as bamboo and willow, and the other was the relatively inactive biomass composed of coconut shell and wood. When the light torrefaction was performed, the results indicated that the hemicellulose contained in the biomass was destroyed in a significant way, whereas cellulose and lignin were affected only slightly. Once the severe torrefaction was carried out, it further had a noticeable effect on cellulose, especially in the bamboo and willow. The light torrefaction and severe torrefaction were followed by a chemically frozen zone, regardless of what the biomass was. From the viewpoint of torrefaction application, the investigated biomass torrefied in less than 1 h with light torrefaction is an appropriate operation for producing fuels with higher energy density.     

Comparative study on pyrolysis characteristics and kinetics of oleaginous yeast and algae

The pyrolysis processes of oleaginous yeast and algae were studied and compared using a non-isothermal thermogravimetric analyzer at heating rates of 10–50 °C/min, and the most probable mechanism function and kinetic analyses of the main stage of pyrolysis were carried out by the Popuse method, Starink method, and Fridemen method. The main pyrolysis stage of the samples could be described by the Jander equation and Z–L–T equation and the activation energy of the three biomass was 108–117, 107–121 and 93–108 kJ/mol, respectively. For the three kinds of biomass, the DTG curves were divided based on the four pseudo-components by performing Gaussian fitting which are carbohydrates, proteins, lipids, others, and the weight coefficients of them could be identified. The activation energy of each pseudo-component was obtained in the range of 58.36–140.44 kJ/mol by the Kissinger method. The four-pseudo-component model based on Gaussian fitting provides effective data for the design of oleaginous yeast and algae thermal decomposition systems and the kinetic analysis of the pyrolysis process.     

Comparative study on combustion and oxy-fuel combustion environments using mixtures of coal with sugarcane bagasse and biomass sorghum bagasse by the thermogravimetric analysis

Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O₂/N₂) and oxy-fuel combustion (O₂/CO₂) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N₂ is replaced with CO₂, it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.     

Comparative studies on the pyrolysis of cellulose,hemicellulose, and lignin based on combined kinetics

The thermal degradation behavior and pyrolytic mechanism of cellulose, hemicellulose, and lignin are investigated at different heating rates from 10 Kmin^?1 to 100 Kmin^?1 with a step-size of 10 Kmin^?1 using thermogravimetric analysis (TGA) equipment. It is observed that there are one, two, and three stages of pyrolytic reactions takes place in cellulose, hemicellulose, and lignin respectively. Isoconversional method is not suitable to analyse pyrolysis of hemicellulose and lignin as it involves multi-step reactions. The activation energies of the main decomposition stage for cellulose, hemicellulose, and lignin are 199.66, 95.39, and 174.40 kJ mol^?1 respectively. It is deduced that the pyrolysis reaction of cellulose corresponds to random scission mechanism while the pyrolysis reaction of hemicellulose and lignin follows the order based reaction mechanisms.     

Fast and catalytic pyrolysis of xylan: Effects of temperature and M/HZSM-5 (M= Fe,Zn) catalysts on pyrolytic products

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of xylan and on-line analysis of pyrolysis vapors. Tests were conducted to investigate the effects of temperature on pyrolytic products, and to reveal the effect of HZSM-5 and M/HZSM-5 (M= Fe, Zn) zeolites on pyrolysis vapors. The results showed that the total yield of pyrolytic products first increased and then decreased with the increase of temperature from 350°C to 900°C. The pyrolytic products were complex, and the most abundant products included hydroxyacetaldehyde, acetic acid, 1-hydroxy-2-propanone, 1-hydroxy-2-butanone and furfural. Catalytic cracking of pyrolysis vapors with HZSM-5 and M/HZSM-5 (M= Fe, Zn) catalysts significantly altered the product distribution. Oxygen-containing compounds were reduced considerably, and meanwhile, a lot of hydrocarbons, mainly toluene and xylenes, were formed. M/HZSM-5 catalysts were more effective than HZSM-5 in reducing the oxygen-containing compounds, and therefore, they helped to produce higher contents of hydrocarbons than HZSM-5.     

Slow and fast pyrolysis of Douglas-fir lignin: Importance of liquid-intermediate formation on the distribution of products

The formation of liquid intermediates and the distribution of products were studied under slow and fast pyrolysis conditions. Results indicate that monomers are formed from lignin oligomeric products during secondary reactions, rather than directly from the native lignin. Lignin from Douglas-fir (Pseudotsuga menziesii) wood was extracted using the milled wood enzyme lignin isolation method. Slow pyrolysis using a microscope with hot-stage captured the liquid formation (>150 °C), shrinking, swelling (foaming), and evaporation behavior of lignin intermediates. The activation energy (E_a) for 5–80% conversions was 213 kJ mol⁻¹, and the pre-exponential factor (log A) was 24.34. Fast pyrolysis tests in a wire mesh reactor were conducted (300–650 °C). The formation of the liquid intermediate was visualized with a fast speed camera (250 Hz), showing the existence of three well defined steps: formation of lignin liquid intermediates, foaming and liquid intermediate swelling, and evaporation and droplet shrinking. GC/MS and UV-Fluorescence of the mesh reactor condensate revealed lignin oligomer formation but no mono-phenols were seen. An increase in pyrolytic lignin yield was observed as temperature increased. The molar mass determined by ESI-MS was not affected by pyrolysis temperature. SEM of the char showed a smooth surface with holes, evidence of a liquid intermediate with foaming; bursting from these foams could be responsible for the removal of lignin oligomers. Py-GC/MS studies showed the highest yield of guaiacol compounds at 450–550 °C.     

Isothermal torrefaction kinetics of hemicellulose, cellulose, lignin and xylan using thermogravimetric analysis

In recent years, torrefaction, a mild pyrolysis process carried out at the temperature range of 200-300 °C, has been considered as an effective route for improving the properties of biomass. Hemicellulose, cellulose, lignin and xylan are the basic constituents in biomass and their thermal behavior is highly related to biomass degradation in a high-temperature environment. In order to provide a useful insight into biomass torrefaction, this study develops the isothermal kinetics to predict the thermal decompositions of hemicellulose, cellulose, lignin and xylan. A thermogravimetry is used to perform torrefaction and five torrefaction temperatures of 200, 225, 250, 275 and 300 °C with 1 h heating duration are taken into account. From the analyses, the recommended values of the order of reaction of hemicellulose, cellulose, lignin and xylan are 3, 1, 1 and 9, respectively, whereas their activation energies are 187.06, 124.42, 37.58 and 67.83 kJ mol⁻¹, respectively. A comparison between the predictions and the experiments suggests that the developed model can provide a good evaluation on the thermal degradations of the constituents, expect for cellulose at 300 °C and hemicellulose at 275 °C. Eventually, co-torrefaction of hemicellulose, cellulose and lignin based on the model is predicted and compared to the thermogravimetric analysis.