Pyrolysis Process of Plant Fibers北大核心CSCD

The natural plant fiber has a large molecular weight and complex structure and composition,and its thermal cracking products and the composition distribution are also more complex. The fast pyrolysiscomprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry（Py-GC×GC-TOF/MS）,thermogravimetry-Fourier transform infrared spectroscopy（TG-FT-IR）,and in situ Fourier transform infrared spectroscopy（in situ FT-IR）methods were used to study the thermal pyrolysis process of six different natural fibers. The distribution of thermal pyrolysis products of different fibers under different pyrolysis temperatures was investigated and the product form was fully discussed. The research results show that the products of fiber pyrolysis mainly include alcohols,aldehydes,ketones,acids,esters,hydrocarbons, dehydrated sugars and CO2,etc. The types of pyrolysis products of different natural plant fibers are obviously different,and the main product types obtained are all different. At the same time,the results of in situ infrared spectroscopy and mass spectrometry show that pyrolysis products are closely related to the pyrolysis temperature. The results of in situ infrared experiments show that when the pyrolysis temperature is lower than 100 °C,the adsorbed water on the surface of the fiber structure is desorbed,but the fiber structure does not change significantly. When the pyrolysis temperature range is 100~200 °C,the temperature has little effect toward the pyrolysis process. When the temperature exceeds 300 °C,the fiber pyrolysis reaction intensifies and the surface structure changes significantly,and the main products are aldehydes and ketones. © 2022, Science Press (China). All rights reserved.     

硫酸盐法制浆黑液中主要有机组分的热解特性研究

采用管式炉对硫酸盐法竹子、阔叶木混合制浆黑液固形物(BLS)及其三种主要组分碱木素(AL)、多糖(PLS)和木素-碳水化合物复合体(LCC),在400~800℃进行热解,全面分析了各相热解产物组成与分布规律。结果表明,BLS及其三种主要组分的热解产物组成与分布规律存在明显差异。AL、PLS和LCC对BLS热解产生H₂和CO的产率影响不大,PLS热解生成CO₂的能力明显高于BLS、AL和LCC。BLS热解液相产物中的酚类和醚类主要是来自AL和LCC;酮类和酸类是由AL、PLS和LCC共同贡献的。BLS、AL、PLS和LCC热解半焦表面形貌存在明显差异。在BLS热解过程中,AL、PLS和LCC会相互影响、相互制约,共同决定着BLS的热解特性。     

生物质热解过程中NO、NH3和HCN的释放特性

在氩气气氛下,利用固定床反应器对稻草（DC）、麦杆（MG）和锯末（JM）三种生物质进行热解实验,采用傅里叶变换红外光谱仪（FT-IR）在线检测热解气体产物中的含氮组分,分析各种气相含氮组分的释放规律。实验结果表明,由于锯末中木质素含量较高,锯末热解开始快速释放NO、NH₃和HCN的温度明显高于稻草和麦杆。稻草热解过程中生成的NH₃、HCN和NO量最大。低温下NH₃的生成至少部分与生物质中氨基结构的分解有关,HCN的生成温度较高。不同生物质热解过程中NO、NH₃和HCN释放特性的差异,是由生物质大分子结构不同、灰分含量及成分不同、N含量不同等决定的,以及氮在生物焦、焦油和气相间的分配差异造成的。     

木质素二聚体模型化合物热解机理的量子化学研究

β-O-4连接是木质素主体结构单元之间的主要联结方式。采用密度泛函理论方法B3LYP,在6-31G (d, p)基组水平上,对β-O-4型木质素二聚体模型化合物(1-愈创木基-2-(2-甲氧基苯氧基)-1,3丙二醇)的热解反应机理进行了研究。提出了三种热解反应途径:C_β-O键均裂的后续反应、C_α-C_β键均裂的后续反应以及协同反应。对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化,计算了各热解反应途径的标准动力学参数。分析了各种主要热解产物的形成演化机理以及热解过程中温度对热解机理的影响。计算结果表明,C_β-O键的均裂反应和协同反应路径(1)和(3)是木质素二聚体热解过程中主要的反应路径,而C_α-C_β键的均裂反应和协同反应路径(2)和(5)是主要的竞争反应路径;热解的主要产物是酚类化合物如愈创木酚、1-愈创木基-3-羟基丙酮、3-愈创木基-3-羟基丙醛、愈创木基甲醛和乙烯等。在热解低温阶段协同反应是热解过程中的主要反应形式,而在高温阶段自由基均裂反应是热解过程的主要反应形式。     

秸秆含氮模型化合物热解氮转化规律的实验研究

采用TG-FTIR联用实验系统,在氩气氛围下研究了含氮模型化合物甘氨酸酐热解失重特性以及NO_x前驱物的释放特性;研究了K、Ca、Fe金属盐对甘氨酸酐热解氮转化的影响。结果表明,在20、40、60℃/min升温速率下,NH₃、HCN、HNCO为甘氨酸酐热解的主要气相含氮产物,其中,NH₃产率最大,HCN次之,HNCO生成量最小;随升温速率增加,TG失重曲线右移,热解剩余物减少;且HCN和HNCO的产率增加,NH₃产率降低;K、Ca、Fe盐均对甘氨酸酐热解氮转化具有催化作用,其中,K、Ca有利于促进NH₃、HCN的生成,Fe对HCN的生成具有促进作用,但对NH₃的生成起到抑制作用。     

Direct mass-spectrometric studies of the pyrolysis of carbonaceous fuels: III. Primary pyrolysis of lignin

The primary pyrolysis of lignins derived from different types of biomass and by the major separation methods has been investigated by molecular-beam sampling mass spectrometry. The lignins separated by the steam-explosion and kraft processes have altered pyrolysis characteristics while ball-milled lignins yield nearly the same product slate as observed in native biomass samples. The predominant and first-formed products, as determined by mass spectrometry, appear to be the precursor monomers, coniferyl and sinapyl alcohol. There is a distinct lack of higher-molecular-weight oligomers as is commonly observed in the pyrolysis of other types of natural and synthetic polymers. A group of peaks, with the most predominant being m/z 272, appear at masses greater than the monomer masses, but are significantly below the dimer mass range. A third group of predominant peaks are present at masses lighter than the monomers and consist of methoxyphenols that have double bonds and carbonyl groups in the alkyl side chains that are in conjugation with the aromatic ring, enhancing thermal stability. The results indicate that the thermolysis of the alkyl-aryl ether linkage, which is the major bonding unit in lignin, and the limited availability of transferable hydrogen, are the major factors that lead to the predominance of these products. The observed product distributions are indicative of specific, sterically favored rearrangement reactions, which allow devolatilization from the hydrogen deficient, solid matrix and favor double bond formation in the alkyl side chain of the products. A discussion of possible mechanisms of formation is given based on these results and the results of other workers in lignin pyrolysis.     

棕榈壳酶解-温和酸解木质素的结构及热解特性研究

采用酶解/温和酸解法提取了棕榈壳和麦秆的木质素(EMALs),利用傅里叶红外光谱(FT-IR)、裂解器-气相色谱质谱联用(Py-GC/MS)和热重-红外联用(TG-FTIR)技术,对两种EMALs的化学结构和热解特性进行了对比研究,并采用Ozaw a-Flynn-Wall方法计算了其热解反应的活化能。结果表明,棕榈壳EM AL和麦秆EM AL均为HGS型木质素。500℃下,两种EMALs的热解产物主要包括酚类、酸类和少量的醇类、醛酮类等化合物;棕榈壳EMAL热解酚类产物中H、G、S型单体酚类的比例分别为47.61%、25.64%和17.18%,而麦秆EMAL分别为23.66%、51.90%和15.50%。在热解反应主失重区(200-380℃),棕榈壳EM AL的主失重速率(50.80%/min)低于麦秆EM AL(78.63%/min);但棕榈壳EM AL热解同时存在肩状失重峰(265℃,27.40%/min),这与其较多H结构产物的释放相关。H型结构产物释放的放热效应降低了棕榈壳EMAL热解初期的活化能(20%,127.92 k J/mol),同时使其热解过程(20%-80%)的平均活化能(152.32 k J/mol)低于麦秆EMAL(161.75 k J/mol)。     

UF4/KBr在空气中的室温水解及其热转化行为在线FT-IR研究

采用原位透射式傅里叶变换红外(FT-IR)光谱仪在线研究了UF₄/KBr在空气中室温条件下的水解反应及其热转化行为,获取反应前后不同铀化合物的红外光谱变化图.结果表明, UF₄/KBr在空气中的水解反应,首先主要生成的是UO₂F₂及其水合物形式;随着时间增长,还伴生有U₃O₈, UO₂, UO₃等多种铀化合物;加热过程中, UF₄/KBr的水解产物发生相互转化反应,其中形成的铀酰化合物最后全部转变为铀的氧化物形式.     

钾元素对生物质主要组分热解特性的影响

采用热重-红外联用仪对松木及生物质主要化学组分半纤维素、纤维素、木质素的热解特性及钾元素对其热解特性的影响进行了研究.结果表明,半纤维素、纤维素、木质素发生热解的主要温度分别为200~350 ℃、300~365 ℃和200~600 ℃;半纤维热解产物中CO、CO₂较多;纤维素热解产物中LG和醛酮类化合物最多;木质素热解主要形成固体产物,气体中CH₄相对含量较高.三种组分共热解过程中发生相互作用使热解温度提高、固体产物增加,气体中CO增加而CH₄减少.添加K₂CO₃后半纤维素和纤维素热解温度区间向低温方向移动,固体产率提高.K对纤维素作用最明显,CO、CO₂气体与固体产物产率明显增加,醛酮类和酸类物质的产率降低;木质素受K影响相对较小,热解固体产物略有增加,挥发分中H₂O和羰基物质增加;三组分共热解减弱了钾元素的催化作用.     

基于密度泛函理论研究木质素二聚体C_α-OH基团的修饰对其热解均裂历程的影响

采用密度泛函理论方法,对四种β-O-4型二聚体木质素模型化合物2-(2-甲氧基苯氧基)-1-苯基乙烷-1-醇、2-(2-甲氧基苯氧基)-1-苯基乙烷-1-酮、1-甲氧基-2-(2-甲氧基-2-苯基乙氧基)苯、2-(2-甲氧基苯氧基)-1-苯乙基乙酸酯的C_(aromatic)-O、C_(aromatic)-C_α、C_α-C_β、C_β-O键均裂解离能进行了理论计算,并对所述二聚体的热解均裂历程进行了理论计算研究,分析了不同二聚体的热解产物形成途径。结果表明,C_β-O键均裂是二聚体初次热解的主要反应,C_α-C_β键均裂是竞争反应。C_α-OH官能团被氧化、乙酰化修饰后,C_β-O键均裂解离能降低,而C_α-C_β键的键解离能升高,C_β-O键裂解概率增大,C_α-C_β键均裂竞争性降低。基于上述四种模型化合物热解的主要芳香族产物有苯甲醇、甲苯、苯甲醛和愈创木酚等,C_α-OH官能团的选择性修饰可调控热解产物种类,其中,氧化修饰后的二聚体的热解产物种类变少,产物选择性增强;甲基化、乙酰化修饰后的二聚体热解可产生苯乙烷和甲苯。     

On-line product analysis of pine wood pyrolysis using synchrotron vacuum ultraviolet photoionization mass spectrometry

The pyrolysis process of pine wood, a promising biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. The mass spectra at different photon energies and temperatures as well as time-dependent profiles of several selected species during pine wood pyrolysis process were measured. Based on the relative contents of three lignin subunits, the data indicate that pine wood is typical of softwood. As pyrolysis temperature increased from 300 to 700 °C, some more details of pyrolysis chemistry were observed, including the decrease of oxygen content in high molecular weight species, the observation of high molecular weight products from cellulose chain and lignin polymer, and potential pyrolysis mechanisms for some key species. The formation of polycyclic aromatic hydrocarbons (PAHs) was also observed, as well as three series of pyrolysis products derived from PAHs with mass difference of 14 amu. The time-dependent profiles show that the earliest products are formed from lignin, followed by hemicellulose products, and then species from cellulose.

神府烟煤快速热解特性研究

利用高频电炉对神府煤进行快速热解,研究了不同热解温度和停留时间下,固相和气相产物的性质。结果表明,煤焦的失重率及真密度随温度升高和时间的延长而增长。红外光谱结果表明,热解过程中,煤中含氢/含氧官能团分解,生成H₂、CO、CO₂、CH₄等气体,并且其分解程度随温度的升高和时间的延长而加深。气相产物中H₂和CO的释放量随温度的升高和时间的延长而增加,而CO₂和CH₄存在释放量的峰值。气相产物随温度的升高和时间的延长而增多,导致高温煤焦出现大量的孔隙和裂缝。     

Pd-Cu/羟磷灰石的制备及常温常湿CO催化氧化性能

通过溶胶-凝胶法(SG)和水热法(HT)合成了羟磷灰石载体(HAP-SG, HAP-HT), 以浸渍法制备负载型Pd-Cu/HAP催化剂(PC-SG, PC-HT), 并考察其常温常湿条件下CO催化氧化反应性能. 采用电感耦合等离子体发射光谱(ICP-OES)、 N₂物理吸附-脱附、 X射线衍射(XRD)、 傅里叶变换红外光谱(FTIR)、 H₂程序升温还原(H₂-TPR)、 CO₂程序升温脱附(CO₂-TPD)、 X射线光电子能谱(XPS)和CO原位漫反射傅里叶变换红外光谱(in-situ DRIFTS)等手段对Pd-Cu/HAP催化剂进行了表征. 结果表明, 相比于PC-SG, PC-HT具有较大比表面积和孔容, 含有较多的Cu₂Cl(OH)₃物种且与Pd物种和载体直接产生了较强的相互作用; 而且PC-HT表面含有较强CO活化能力的Pd⁺物种和更多具有较强氧化还原性质的Cu⁺物种, 以及较少数量和较低强度的碱性位点, 因而表现出更加优异的常温常湿条件下CO催化氧化性能.     

Flow analysis-vapor phase generation-Fourier transform infrared (FA-VPG-FTIR) spectrometric determination of nitrite

In this work, the coupling between flow analysis (FA)–vapor phase generation (VPG) and Fourier transform infrared spectrometry (FTIR) has been proposed as a novel and alternative strategy for the determination of nitrite. The analyte was transformed into the gaseous nitric oxide (NO) by on-line reaction with potassium iodide (KI) or ascorbic acid in acidic medium. The gaseous NO generated was transported by means of a N₂ gas carrier stream inside the IR gas cell and the corresponding FTIR spectrum was acquired in a continuous mode. The absorbance at 1876 cm⁻¹, corrected by a baseline established between 1879 and 1872 cm⁻¹ at a nominal resolution of 2 cm⁻¹, was selected as a measurement criterion. The effect of different spectroscopic and flow analysis experimental parameters, such as nominal resolution, number of scans, reducing agent and its concentration, acidic medium, reagents and sample flow rates, and the carrier gas flow rate on the analytical signal, and then in the figures of merit were initially evaluated by using a standard short path length (10 cm) IR gas cell. The optimization of the system was carried out by the univariate method. The main aims of this study were: (i) to investigate the on-line generation of gaseous nitric oxide in a continuous flow system, and (ii) the use of Fourier transform infrared spectrometry as an alternative and selective detector for the determination of nitrite. The proposed method was initially tested and applied for the determination of nitrite in samples with very high concentration of nitrite, such as frankfurters.     

Palladium-Nafion SAC-13 catalysed depolymerisation of lignin to phenols in formic acid and water

Guaiacol, pyrocatechol and resorcinol, were isolated and quantified as the major products from catalytic pyrolysis of lignin of various origin. The novel procedure utilises formic acid as the hydrogen source in combination with a palladium catalyst and Nafion^® SAC-13 as a solid acid catalyst with water as reaction medium. The reaction is conducted at moderate pyrolysis temperature and short reaction time. Several palladium based catalysts and different types of lignin were investigated. The lignins and the model compounds demonstrated various chemical behaviour, under identical reaction conditions; various phenols were formed from the lignins, while the model compounds were hydrodeoxygenated, demethylated and demethoxylated.     

Structural features and thermal degradation properties of various lignin macromolecules obtained from poplar wood (Populus albaglandulosa)

Four different lignins obtained from poplar wood (milled wood lignin: ML, organosolv lignin: OL, ionic liquid lignin: IL and Klason lignin: KL) were subjected to several types of chemical/thermal analyses to compare their structural features and thermal decomposition properties. The ML, OL, IL and KL yield from poplar wood was 5.5, 3.9, 5.8, 19.5 wt%, respectively. Functional group analysis revealed that during the OL and KL extraction processes, the condensation reaction involved with phenolic hydroxyl groups of lignins significantly prevailed, which led to a highly condensed OL and KL structure. Thermogravimetric analysis (TGA) results showed that OL and KL thermal stability was much higher than that of ML and IL. The derivatization followed by reductive cleavage (DFRC) data showed that the thermal stability was highly associated with the frequency of arylglycerol-β-aryl ether (β-O-4) linkages in the lignin polymers. Pyrolysis-GC/MS (Py-GC/MS) analysis confirmed that acetic acid and several types of phenolic compounds were the main lignin pyrolysis products. The maximum sum of ML (13.8 wt%), OL (9.9 wt%) and IL (11.8 wt%) pyrolysis products was obtained at the pyrolysis temperature of 600 °C, whereas KL (1.6 wt%) was significantly lower due to its high thermal stability and condensation degree. The S- and G-type pyrolysis products (S/G) ratio varied from 1.61 to 1.93 for ML, 2.28 to 5.28 for OL, 2.06 to 2.86 for IL and 1.40 to 2.20 for KL, depending on the pyrolysis temperature, which ranged between 400 °C and 700 °C.     

Flash pyrolysis of Silopi asphaltite in a free-fall reactor under vacuum

Flash pyrolysis experiments on asphaltite samples were performed in a free-fall reactor under vacuum to determine the effects of pyrolysis temperature, feed rate and particle size. Maximum liquid yield of 13 wt.% was obtained in free-fall reactor under vacuum when the pyrolysis temperature was 700 °C, feed rate was 0.4 g min⁻¹ and particle sizes were between 0.075 and 0.250 mm. The liquid products obtained at various pyrolysis conditions were analyzed by gas chromatography/mass spectrometer (GC/MS) and liquid products were classified as following: C5–C10, C11–C15, C16–C20 and C20+. The amount of saturated hydrocarbons decreased while the amount of unsaturated hydrocarbons increased with increase of temperature. While percent of C5–C10 unsaturated hydrocarbons continuously increased with increase of temperature, the percent of C11–C15 unsaturated hydrocarbons increased up to 750 °C and then started to diminish. Functional group analysis of solid residue was carried out using Fourier transform infrared spectrometry (FT-IR). The proximate analysis of solid residue indicated that percent of fixed carbon and ash increased with temperature.     

木质素模化物紫丁香酚热解机理的量子化学研究

采用密度泛函理论方法B3LYP/6-31G++(d,p),对木质素模化物紫丁香酚的热解反应机理进行了量子化学理论研究。提出了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化。计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理。键离解能计算结果表明,紫丁香酚中CH₃-O键的键离解能最小,各种键离解能的大小顺序为CH₃-O < O-H < CH₃O-C_aromatic < CH₂-H < HO-C_aromatic < C_aromatic-H。在反应路径(1)中,主要热解产物是3-甲氧基邻苯二酚,其形成反应的总能垒为366.6 kJ/mol;在反应路径(2)中主要热解产物是2-甲氧基-6-甲基苯酚,其形成反应的总能垒为474.8 kJ/mol;在反应路径(3)中形成邻甲氧基苯酚的总能垒很低,为21.4 kJ/mol,这表明,在连接甲氧基的碳原子上加氢后能够有效地降低木质素芳环模化物紫丁香酚去甲氧基反应的反应能垒。     

压力对塔里木原油四组分热解性能的影响

压力对深层油藏原油热化学过程的影响尚存在较大争议,为研究其在油藏原油热解成气过程中的作用机理,我们在450℃、5~40 MPa压力下对塔里木原油四组分(饱和分、芳香分、胶质和沥青质)进行了封闭体系的热解实验,通过气相色谱(GC)和气相色谱/质谱(GC/MS)分别对原油四组分热解反应的气体产物及饱和分热解过程的液态产物进行了分析。结果表明,在450℃、24 h及不同压力下,沥青质热解产气率高于胶质、芳香分和饱和分;四组分的气相热解产物中,C1的产率明显高于C2~C5组分。增大压力抑制沥青质、胶质及芳香分的热解产气过程而促进饱和分的热解产气过程。随压力的增大,饱和分热解的液态产物的主峰组分碳数先减小,再增大。压力低于20 MPa时,饱和分热解过程中以裂解反应为主;高于30 MPa时,增大压力有利于缩合反应。研究结果可为认识深层油藏原油的稳定程度及天然气的成因提供一定的理论参考。     

The application of pyrolysis gas chromatography mass spectrometry for the identification of degraded early plastics in a sculpture by Naum Gabo

A study was carried out to characterise the materials of a highly degraded plastic sculpture by Naum Gabo in the collection of the Philadelphia Museum of Art. Samples from the sculpture were analysed using pyrolysis gas chromatography mass spectrometry (Py-GCMS) in conjunction with Fourier transform infrared microspectroscopy (MFTIR) and other techniques. Py-GCMS confirmed that Gabo had used cellulose acetate and cellulose nitrate plastics; the identification of the former was based on the detection of trace levels of 5-acetoxymethylfurfural and other characteristic carbohydrate-derived pyrolysis products bearing an acetyl group. Because of the unusually severe state of degradation of certain parts of the sculpture, the pyrolysis data were critical for identification of the cellulose acetate polymer, which could not be achieved using MFTIR. The original polymer has undergone almost complete reversion to a cellulose-like structure through hydrolysis and deacetylation.