The kinetics of vapour-phase cellulose fast pyrolysis reactions

Biomass fast pyrolysis reactions consist of primary activation and fragmentation reactions, followed by secondary vapour-phase cracking reactions. Kinetic data derived from in-house experiments and published literature have clearly indicated that under true fast pyrolysis conditions, the primary reaction rates exceed those of the secondary reactions by several orders of magnitude. Therefore, since the cracking reactions are rate-limiting, an estimation of the rate of conversion of biomass to secondary products is in fact an estimation of the secondary reaction rate. This paper focuses on the determination of the key kinetic parameters (rate constants, pre-exponential constant and activation energy) for the vapour-phase cracking reactions which occur during cellulose pyrolysis. The parameters were determined using a first-order kinetic model and a non-linear regression routine. The experimental work was conducted in the Ultrapyrolysis equipment at the University of Western Ontario in London, Canada.     

The influence of harvest and storage on the properties of and fast pyrolysis products from Miscanthus x giganteus

The research investigates the fuel property variations associated with the time of harvest and the duration of storage of Miscanthus x giganteus over a one year period. The crop has been harvested at three different times: early (September 2009), conventional (April 2010) and late (June 2010). Once harvested the crop was baled and stored. Biomass properties of samples taken from different storage zones were compared. The thermochemical properties have been investigated using a range of analytical equipment including thermogravimetric analysis (TGA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). In addition, bio-oil has been produced from the early, conventional and late harvest using a laboratory scale (300 g h⁻¹) fast pyrolysis unit. The potential organic liquid yield (on dry basis, also excluding the reaction water generated) based on the laboratory fast pyrolysis processing undertaken in this study, was found to vary between 2.82 and 3.18 dry t ha⁻¹ for the early and the late harvest respectively. The bio-oil organic yield was reduced by approximately 11% (0.36 t ha⁻¹) between the early and the late harvest. Char yield was also reduced by approximately 18% (0.61 t ha⁻¹). The highest gas yield (18.03%-1.60 t ha⁻¹) was observed for the conventional harvest. Gas chromatography-mass spectrometry (GC-MS) analysis of the bio-oil shows that levoglucosan, methylbenzaldehyde and 1,2-benzenediol all increase as a consequence of delayed harvest. It was also observed that by delaying the harvest time the O:C atomic ratio is reduced and a more carbonaceous feedstock is produced.     

Effect of zeolite structure on light aromatics formation during upgrading of cellulose fast pyrolysis vapor

Promising technology for the conversion of cellulose to aromatics by catalytic fast pyrolysis (CFP) was investigated using five zeolite catalysts, i.e., 5A, SAPO-34, HY, BETA and HZSM-5. The relationship between the porosity and acidity of different zeolites with product selectivity was studied. The results showed that both the acidity and pore size of the zeolite significantly affected the production of aromatics and coke, especially the bio-oil composition. The bio-oils obtained over 5A or SAPO-34 (small pore<5.5 nm) have relatively high oxygen content. The BTEXN (benzene, toluene, ethylbenzene, xylenes and naphthalene) carbon yields over weak acidic zeolites of HY and BETA are only 6.5% and 9.0%, respectively. Due to the appropriate pore size distribution and acid position, HZSM-5 gave the highest BTEXN carbon yield of 21.1%. Moreover, the coke deposited on the spent zeolites was analyzed by temperature programmed oxidation. Furthermore, three possible mechanisms that the acid sites catalyze vapor towards non-condensable gases, aromatics and coke were also studied. HZSM-5 achieved satisfactory deoxygenation and aromatic production simultaneously, made it a potential catalyst for producing light aromatics from reforming the biomass pyrolytic vapors.     

Effects of headspace fraction and aqueous alkalinity on subcritical hydrothermal gasification of cellulose

In order to better understand the pathways of hydrothermal gasification of cellulose, the effect of headspace fraction and alkalinity on the hydrothermal gasification of cellulose has been studied at 315 °C in the presence of Pt/Al₂O₃ as catalyst. It was found that regardless of alkalinity the headspace fraction had a large impact on gasification yield, with larger headspace fractions resulting in considerably more gas product. Without the addition of sodium carbonate, the effect of headspace fraction became more pronounced, with gas increasing by approximately a factor of forty from the lowest to highest headspace fraction. On the other hand, for the same residence time the addition of sodium carbonate co-catalyst dampened the magnitude of the effect, to a factor of 2.5 and 1.5, for 50 and 100 mM sodium carbonate solutions, respectively. These results indicated that the headspace fraction affected the phase behaviour, and that this altered the pathway of the cellulose decomposition. While furfural alcohol was the major product obtained with a 49% headspace fraction, it was effectively suppressed by using 78% or greater headspace fractions. Based on the effects of phase behaviour and previous literature, the reduced effect occurring upon the addition of sodium carbonate may relate to catalysis of the Lobry de-bruyn Van Eckenstein transform to produce lactic acid rather than intermediates proceeding through glycolaldehyde.     

Evaluating the effect of potassium on cellulose pyrolysis reaction kinetics

This paper proposes modifications to an existing cellulose pyrolysis mechanism in order to include the effect of potassium on product yields and composition. The changes in activation energies and pre-exponential factors due to potassium were evaluated based on the experimental data collected from pyrolysis of cellulose samples treated with different levels of potassium (0–1% mass fraction). The experiments were performed in a pyrolysis reactor coupled to a molecular beam mass spectrometer (MBMS). Principal component analysis (PCA) performed on the collected data revealed that cellulose pyrolysis products could be divided into two groups: anhydrosugars and other fragmentation products (hydroxyacetaldehyde, 5-hydroxymethylfurfural, acetyl compounds). Multivariate curve resolution (MCR) was used to extract the time resolved concentration score profiles of principal components. Kinetic tests revealed that potassium apparently inhibits the formation of anhydrosugars and catalyzes char formation. Therefore, the oil yield predicted at 500 ^°C decreased from 87.9% from cellulose to 54.0% from cellulose with 0.5% mass fraction potassium treatment. The decrease in oil yield was accompanied by increased yield of char and gases produced via a catalyzed dehydration reaction. The predicted char and gas yield from cellulose were 3.7% and 8.4%, respectively. Introducing 0.5% mass fraction potassium treatment resulted in an increase of char yield to 12.1% and gas yield to 33.9%. The validation of the cellulose pyrolysis mechanism with experimental data from a fluidized-bed reactor, after this correction for potassium, showed good agreement with our results, with differences in product yields of up to 5%.     

Influence of impregnated iron and nickel on the pyrolysis of cellulose

In this work, we prepared iron- or nickel-impregnated cellulose to examine the influence of the metal on the yield and composition of fast pyrolysis products. In order to identify the mechanisms promoted during the catalytic conversion, pyrolysis was investigated using an experimental set-up coupling TG (thermogravimetric) analysis and Micro-GC (Gas Chromatography). The results showed that with relatively low catalyst loading (mass fraction of 1.5% Fe or 1.7% Ni) impregnated metal can catalyze some rearrangement reactions such as dehydration and decarboxylation starting from 180 °C, promoting the char formation and thus inhibiting cellulose depolymerization. As a consequence metal impregnation led to a decrease of tar and CO yields balanced by an increase of char, H₂O and CO₂ yields. Depending on the applied metal, other primary reactions can be specifically catalyzed. In particular, in the presence of nickel TG analysis revealed an important mass loss at temperatures as low as 210 °C and an important increase of H₂ production in the temperature range 400–500 °C. These findings open promising perspectives to optimize the production of fuels and chemicals from biomass.     

TG-FTIR and Py-GC/MS study of the pyrolysis mechanism and composition of volatiles from flash pyrolysis of PVC

To facilitate the reuse and recycling of polyvinyl chloride (PVC) to achieve sustainable development and new industrialization, the composition and mechanism of formation of volatiles during the flash pyrolysis of PVC were studied by thermogravimetry-Fourier transform infrared (TG-FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TG and derivative thermogravimetry (DTG) analyses indicated two main degradation stages during flash pyrolysis of PVC, namely dehydrochlorination of PVC and decomposition of dechlorinated-PVC. Simultaneously, the FTIR results revealed that the main functional groups in the pyrolysis process were H–Cl, -C-Cl, C–H, CH, and aromatic groups. The relative content of main volatiles was determined by Py-GC/MS, and decreased in the following order: aromatics > alkenes > hydrogen chloride (HCl) > chlorinated hydrocarbons. Specifically, the relative content of aromatics was as high as 76.790–81.809%, while that of HCl was in the range of 3.016–3.096%. The carbon number distribution and the relative content of main products obtained from the flash pyrolysis of PVC at different final temperatures were also analysed. According to the experimental results, the mechanism of formation of the main volatiles based on free-radical reactions was deduced in detail. Therefore, this study provides further details for deepening the understanding of the PVC pyrolysis process.     

Mesocellular-foam-silica-supported Ni catalyst: Effect of pore size on H2 production from cellulose pyrolysis

Supported nickel metal can be used as a tar-cracking catalyst in the thermal processing of large organics to give H₂. Though porous supports offer the opportunity to disperse a relatively large amount of nickel, catalytic sites within small pores may be inaccessible to large tar molecules. To investigate this, we prepared nickel catalysts supported on γ-Al₂O₃ and on SBA-15- and mesocellular-foam-(MCF)-type silicas and studied their catalytic activities in the pyrolytic decomposition of cellulose (RT → 800 °C, ∂T/∂t = 40 °C/min). A thermogravimetric analyser-mass spectrometer (TG-MS) was used to study the influence of the Ni catalyst and support materials on the H₂ yield and selectivity. The silica-MCF-supported Ni catalyst decreased char residue and enhanced H₂ yield, producing 1.6 and 3.5× the H₂ yield obtained using SBA-15-supported Ni and γ-Al₂O₃-supported Ni, respectively. MCF, with ultra-large pores (d ∼ 15−50 nm), was thus identified as the most beneficial catalyst support for this application.     

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.     

Effect of cellulose and lignin content on pyrolysis and combustion characteristics for several types of biomass

Fundamental pyrolysis and combustion behaviors for several types of biomass are tested by a thermo-gravimetric analyzer. The main compositions of cellulose and lignin contents for several types of biomass are analyzed chemically. Based on the main composition results obtained, the experimental results for the actual biomass samples are compared with those for the simulated biomass, which is made of the mixture of the cellulose with lignin chemical. The morphological changes before and after the reactions are also observed by a scanning electron microscope. The main compositions in the biomass consisted of cellulose and lignin. The cellulose content was more than lignin for the biomass samples selected in this study. The reaction for the actual biomass samples proceeded with the two stages. The first and second stage corresponded to devolatilization and char combustion during combustion, respectively. The first stage showed rapid mass decrease caused by cellulose decomposition. At the second stage, lignin decomposed for pyrolysis and its char burned for combustion. For the biomass with higher cellulose content, the pyrolysis rate became faster. While, the biomass with higher lignin content gave slower pyrolysis rate. The cellulose and lignin content in the biomasses was one of the important parameters to evaluate the pyrolysis characteristics. The combustion characteristics for the actual biomass depends on the char morphology produced.     

Effects of Fe2O3 on pyrolysis characteristics of soybean protein and release of NOx precursors

The effects of ferric oxide (Fe₂O₃) on the pyrolysis characteristics of soybean protein and the release of precursors to nitrogen oxides (NOx) were studied using thermogravimetry and mass spectrometry. The results show that, as the content of Fe₂O₃ increases, there is no major difference between initial and peak temperatures of protein pyrolysis samples. Moreover, between the temperature range of 204 and 550°C where weight loss mainly occurs, total weight-loss rate decreases before increasing, with obvious weight loss occurring around the temperature of 650°C. Fe₂O₃ displays both inhibiting and promoting effects on the precipitation of nitrogen-containing gases such as ammonia (NH₃), hydrogen cyanide (HCN), isocyanic acid (HNCO), and acetonitrile (CH₃CN), with the inhibition effect prevailing over promotion effect on the whole.     

An investigation on the characteristics of cellulose nanocrystals from Pennisetum sinese

The aim of this study was to explore the utilization of Pennisetum sinese as cellulose source for the preparation of cellulose nanocrystals (CNC). The cellulose was extracted from P. sinese by chemical treatment and bleaching, and obtained cellulose nanocrystals by acid hydrolysis. Transmission electron microscopy (TEM) showed that CNC were rod-like with the diameter of 20–30 nm and the length of 200–300 nm. Fourier transform infrared (FTIR) showed that chemical treatment removed most of the lignin and hemicellulose from P. sinese, and CNC had similar structure to that of native cellulose. The crystallinity indexes calculated from X-ray diffraction (XRD) for P. sinese and CNC were 40.6% and 77.3%, respectively. The zeta-potential analysis showed that CNC had higher stability than P. sinese had. The thermal stability was investigated by thermogravimetric analysis (TGA), and the result showed that P. sinese had higher thermal stability than that of prepared CNC.     

Effects of ionic catalysis on hydrogen production by the steam gasification of cellulose

In this study, significant effects of ionic catalysis on the formation of H₂ and CO during the steam gasification process of cellulose are revealed. The energy of the C–H bonds of cellulose can be remarkably reduced by Na⁺ and OH⁻ ions produced by the dissociation of NaOH, enabling dehydrogenation of cellulose at low temperature. Dehydrogenation of cellulose is evidently affected by the concentration of Na⁺ and OH⁻ ions that cellulose can come into contact with. Higher concentrations of Na⁺ and OH⁻ ions can reduce the initial dehydrogenation temperature of cellulose to lower than 403 K. The production of CO increases after this remarkable dehydrogenation of cellulose, which indicates that the C–O bonds of cellulose are prone to forming CO by pyrolysis.     

Thermophilic hydrogen production from cellulose with rumen fluid enrichment cultures: Effects of different heat treatments

Elevated temperatures (52, 60 and 65 °C) were used to enrich hydrogen producers on cellulose from cow rumen fluid. Methanogens were inhibited with two different heat treatments. Hydrogen production was considerable at 60 °C with the highest H₂ yield of 0.44 mol-H₂ mol-hexose⁻¹ (1.93 mol-H₂ mol-hexose-degraded⁻¹) as obtained without heat treatment and with acetate and ethanol as the main fermentation products. H₂ production rates and yields were controlled by cellulose degradation that was at the highest 21%. The optimum temperature and pH for H₂ production of the rumen fluid enrichment culture were 62 °C and 7.3, respectively. The enrichments at 52 and 60 °C contained mainly bacteria from Clostridia family. At 52 °C, the bacterial diversity was larger and was not affected by heat treatments. Bacterial diversity at 60 °C remained similar between heat treatments, but decreased during enrichment. At 60 °C, the dominant microorganism was Clostridium stercorarium subsp. leptospartum.     

Bio-hydrogen production based on catalytic reforming of volatiles generated by cellulose pyrolysis: An integrated process for ZnO reduction and zinc nanostructures fabrication

The paper presents a process of cellulose thermal degradation with bio-hydrogen generation and zinc nanostructures synthesis. Production of zinc nanowires and zinc nanoflowers was performed by a novel processes based on cellulose pyrolysis, volatiles reforming and direct reduction of ZnO. The bio-hydrogen generated in situ promoted the ZnO reduction with Zn nanostructures formation by vapor-solid (VS) route. The cellulose and cellulose/ZnO samples were characterized by thermal analyses (TG/DTG/DTA) and the gases evolved were analyzed by FTIR spectroscopy (TG/FTIR). The hydrogen was detected by TPR (Temperature Programmed Reaction) tests. The results showed that in the presence of ZnO the cellulose thermal degradation produced larger amounts of H₂ when compared to pure cellulose. The process was also carried out in a tubular furnace with N₂ atmosphere, at temperatures up to 900 °C, and different heating rates. The nanostructures growth was catalyst-free, without pressure reduction, at temperatures lower than those required in the carbothermal reduction of ZnO with fossil carbon. The nanostructures were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The optical properties were investigated by photoluminescence (PL). One mechanism was presented in an attempt to explain the synthesis of zinc nanostructures that are crystalline, were obtained without significant re-oxidation and whose morphologies are dependent on the heating rates of the process. This route presents a potential use as an industrial process taking into account the simple operational conditions, the low costs of cellulose and the importance of bio-hydrogen and nanostructured zinc.     

CuO对木粉/PVC复合材料热解和燃烧过程中烟释放行为的影响

采用热重分析法、锥形量热仪测试及Py-GC-MS联机方式研究了CuO对木粉/PVC复合材料(WF-PVC)热解和燃烧过程烟释放行为的影响.实验结果表明,WF-PVC热解过程具有PVC热解的特性;与WF-PVC相比,用CuO处理WF-PVC能明显提高第1阶段质量损失,降低第2阶段的质量损失,提高成炭量;WF-PVC燃烧过程中烟释放速率和总烟量低于PVC,用CuO处理WF-PVC总烟量降低更显著;Py-GC-MS分析结果表明,与PVC相比,WF-PVC以及用CuO处理的WF-PVC,燃烧气相组分中芳香族化合物含量分别降低52.29%和49.34%;加入CuO,抑制了气相组分中多环化合物的生成.     

Chemical evaluation of chars produced by thermochemical conversion (gasification,pyrolysis and hydrothermal carbonization) of agro-industrial biomass on a commercial scale

Technologies for agro-industrial feedstock utilization such as pyrolysis, gasification and hydrothermal carbonization at industrial scale develop rapidly. The thermochemically converted biomasses of these production technologies have fundamentally different properties controlled by the production technology. This is reflected by general properties such as pH or elemental composition. The ¹³C NMR spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy and black carbon results confirmed these observations showing that hydrochars have lower proportions of aromatic compounds than biochars (less stable) but are rich in functional groups (higher cation exchange capacity) than biochars. Analyses of pollutants indicate that polycyclic aromatic hydrocarbons as well as dioxin contents of most samples were under the threshold values recommended by International Biochar Initiative and European Biochar Certificate. In conclusion, biochars and hydrochars are entirely different from each other and these materials will probably have a complementary reaction in a soil environment.     

聚三氟氯乙烯纯氧环境热解气体产物分析

使用针筒采样法采集聚三氟氯乙烯纯氧环境等温(400℃/450℃)热解气体产物,通过气相色谱-质谱联用技术和真空紫外光电离质谱技术,定性分析热解气体产物组成成分,为评估氧气系统在设计和使用过程中的安全性提供参考．结果表明：聚三氟氯乙烯纯氧热解气体产物中共检出13种气体成分,其中氟氯烷类4种,单烯类5种,小分子类4种．分析认为氟氯烷类和单烯类气体产物的生成是由于聚三氟氯乙烯在热解过程中发生碳链、碳氯键及碳氟键的无规则断裂和重新结合,而小分子类气体产物的生成是由于聚三氟氯乙烯在热解过程中发生氧化生成中间体(COF₂、COFCl),中间体进一步分解产生CO、CO₂、Cl₂和F₂.     

麦秆水热炭化水溶液循环对碳及水溶物分布的影响

以农业废弃物麦秆为原料,通过水溶液循环利用的水热炭化实验,对麦秆水热炭化过程中碳及水溶有机物主要组分浓度的分布进行了深入研究。结果表明:在220℃、120 min、液固比为30∶1的水热条件下,随水循环次数的增加,水溶产物产率及碳质量分数逐渐减少,水循环第6次以后,水溶产物产率和碳质量分数变化不大,分别约为15%和5%;水溶产物中还原糖、糠醛和5-羟甲基糠醛(5-HMF)的浓度均随循环次数的增加而减少,而乙酸浓度一直呈逐渐增加趋势,并催化了水热炭化反应,水循环第10次时,乙酸浓度达到18.32 g/L。     

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.