Study of the potential valorisation of heavy metal contaminated biomass via phytoremediation by fast pyrolysis: Part I. Influence of temperature, biomass species and solid heat carrier on the behaviour of heavy metals

Presently, little or no information of implementing fast pyrolysis for looking into the potential valorisation of heavy metal contaminated biomass is available. Fast pyrolysis of heavy metal contaminated biomass (birch and sunflower), containing high amounts of Cd, Cu, Pb and Zn, resulting from phytoremediation, is investigated. The effect of the pyrolysis temperature (623, 673, 773 and 873 K) and the type of solid heat carrier (sand and fumed silica) on the distribution of the heavy metals in birch and sunflower pyrolysis fractions are studied. The goal of the set-up is “concentrating” heavy metals in the ash/char fraction after thermal treatment, preventing them to be released in the condensable and/or volatile fractions. The knowledge of the behaviour of heavy metals affects directly future applications and valorisation of the pyrolysis products and thus contaminated biomass. They are indispensable for making and selecting the proper thermal conditions for their maximum recovery. In view of the future valorisation of these biomasses, the amounts of the pyrolysis fractions and the calorific values of the obtained liquid pyrolysis products, as a function of the pyrolysis temperature, are determined.     

生物质炭在重金属污染土壤修复中的应用研究现状

为充分发挥生物质炭多孔性、表面活性、选择性吸附和高碱性等性能在有效控制重金属生物迁移中的作用,以期为重金属污染土壤修复技术提供参考。介绍了我国重金属污染土壤的概况,综述了生物质炭在重金属污染土壤修复中的应用,重点介绍了植物修复、化学淋洗、土壤性能改良、固化/稳定化、热解吸修复和电动力学修复等技术的应用情况,简要概述了原料种类、热解温度和表面官能团对生物质炭性质及生物质炭对土壤环境的影响,并展望了生物质炭在重金属污染土壤修复中的发展前景。     

Fast pyrolysis of heavy metal contaminated willow: Influence of the plant part

Fast pyrolysis of heavy metal contaminated willow, with high concentrations of Cd, Cu, Pb and Zn, resulting from phytoremediation, is investigated. The distribution of the heavy metals depends on the plant part (leaves and branches). Nevertheless, their individual pyrolysis fractions (at an operational temperature of 623 K), i.e., bio-oil/tar and gas, are both heavy metal free. Some small differences in the kind and amounts of the organic compounds are found in the bio-oil and gaseous fraction. In view of practical considerations leaves and branches should nevertheless be pyrolysed simultaneously. The use of hyphenated thermal analytical techniques allows obtaining more detailed information on the compositional features of the pyrolysis fraction.     

Energy production from biomass pyrolysis: a new coefficient of pyrolytic valorisation

The use of renewable energy sources is becoming increasingly necessary to diminish the greenhouse effect gases production. Biomass is the most common form of renewable energy, widely used in the third world. Pyrolysis, which corresponds to the thermal decomposition of biomass under the action of heat and without any oxidant, is particularly well-adapted to the valorisation of lignocellulosic products such as wood or straw. The BIOCARB programme of the Commissariat à l'Energie Atomique (CEA), to which the Groupe de Recherche sur l'Environnement et la Chimie Atmosphérique (GRECA) contributes, aims to produce carburant from the gasification of biomass. This fuel can be either pure hydrogen, or gasoil produced by the Fischer-Tropsch process after the pyrolysis and syngas production. It is absolutely necessary to control the different parameters of the pyrolysis (gas composition, formation of tars) to maximise the production of hydrogen or syngas. The new coefficient of pyrolytic valorisation presented here helps to meet this requirement. This work presents also experiments on the pyrolysis of straw and fescue in a 550-650 °C temperature range with different residence times, on which was based our investigation.     

热解温度及AAEM元素对生物质快速热解焦油的影响

生物质热解受热解温度、热解速率和碱金属及碱土金属(AAEM)元素影响显著。利用热裂解气相色谱质谱联用法(Py-GC/MS)针对热解温度及AAEM元素对生物质快速热解焦油的影响展开深入研究,通过样品热解前后的失重情况分析了热解温度及AAEM元素对生物质(稻壳和木屑、酸洗稻壳和酸洗木屑)热解特性的影响规律,利用气相色谱质谱仪(GC/MS)对热解焦油组分及含量进行了在线半定量分析,并对热解焦油组分分子量分布情况展开了讨论。结果表明生物质Py-GC/MS快速热解实验,酸洗脱除AAEM元素致使热解失重率减小。500~900℃范围内随温度的升高,大分子焦油成分逐渐减少,逐渐转化为轻质组分。AAEM元素限制了焦油前体的聚合,进一步抑制了含氧杂环类碳环(糠醛等)的生成。稻壳的热解焦油的相对分子质量主要分布在110~129。木屑快速热解焦油产率明显高于稻壳,且热解焦油中分子量分布广泛,含有更多较大分子量(150~209)的化合物成分。     

生物质微波热解制备液体燃料和化学品的研究进展

微波热解是一种高效的生物质转化利用技术,具有独特的热效应和非热效应,可将生物质转化为液体燃料和化学品,能有效缓解能源压力,减少环境污染。本文着重探讨了生物质原料特性、微波吸收剂、催化剂对生物质微波热解制备高品质液体燃料和化学品的影响。原料特性的影响主要从生物质的水分含量、灰分含量和有效氢碳比三方面展开论述,催化剂包括金属盐、金属氧化物、ZSM-5、微波驱动型催化剂以及其他一些催化剂,如HY、MCM-41和碳基催化剂等。简述了生物质的微波热解特性、液体燃料的组成以及转化机理,并对现存的热解机理复杂、产物复杂不稳定、目标产物选择性差、催化剂易结焦失活、重复性差等问题进行了分析,展望了未来的发展方向,以期为生物质的高效转化利用提供依据。     

重质有机质热解过程中挥发物的产出与逸出气体分析研究进展

煤、重质油、生物质等重质有机质富含碳氢共价结构,其轻质化和定向化学品转化是加工利用的主要目标。热解是重质有机质加工过程中最直接、最基础的反应过程,挥发物作为重要的热解产物,其组成分布及在热解过程的演变规律解析是研究的关键和热点问题。本文综述了重质有机质热解过程中挥发物的生成过程,总结了反应类型及产物组成随温度升高的阶段性变化,并以煤、油砂、油页岩、生物质、含油污泥、市政污泥以及废橡胶为例,对比了不同种类的重质有机质热解挥发物产出的异同。针对重质有机质挥发物逸出特性分析方法,本文重点介绍了质谱、傅里叶变换红外光谱逸出气体分析技术,举例说明了各方法在重质有机质有机结构解析、热解工艺条件优化、污染物控制、催化剂设计等研究上的应用,并且就现阶段热解过程逸出气体的定量分析方法和应用进行了概述。最后,本文还就重质有机质热解逸出气体分析技术提出了建议和展望,以期为重质有机质的热解研究提供参考和借鉴。     

Evaluation of various types of Al-MCM-41 materials as catalysts in biomass pyrolysis for the production of bio-fuels and chemicals

MCM-41, is one of the latest members of the mesoporous family of materials. They possess a hexagonal array of uniform mesopores (1.4–10 nm), high surface areas (>1000 m²/g) and moderate acidity. Due to these properties the MCM-41 materials are currently under study in a variety of processes as catalysts or catalyst supports. The objective of this study was to evaluate different types of MCM-41 materials as potential catalysts in the catalytic biomass pyrolysis process. We expected that the very high pore size and the mild acidity of these materials could be beneficial to reformulate the high molecular weight primary molecules from biomass pyrolysis producing useful chemical (and especially phenolic compounds) and lighter bio-oil with less heavy molecules. Three different samples of Al-MCM-41 materials (with different Si/Al ratio) and three metal containing mesoporous samples (Cu–Al-MCM-41, Fe–Al-MCM-41 and Zn–Al-MCM-41) have been synthesised, characterized and tested as catalysts in the biomass catalytic pyrolysis process using a fixed bed pyrolysis combined with a fixed catalytic reactor and two different types of biomass feeds. Compared to conventional (non-catalytic) pyrolysis, it was found that the presence of the MCM-41 material alters significantly the quality of the pyrolysis products. All catalysts were found to increase the amount of phenolic compounds, which are very important in the chemical (adhesives) industry. A low Si/Al ratio was found to have a positive effect on product yields and composition. Fe–Al-MCM-41 and Cu–Al-MCM-41 are the best metal-containing catalysts in terms of phenols production. The presence of the Al-MCM-41 material was also found to decrease the fraction of undesirable oxygenated compounds in the bio-oil produced, which is an indication that the bio-oil produced is more stable.     

Demetallization of heavy oil through pyrolysis: A reaction kinetics analysis

By tracking the transfer of vanadium and nickel in pyrolysis products, a seven-lump reaction kinetic model for pyrolysis-based demetallization of heavy oil was established. During pyrolysis, the demetallization of heavy oil is achieved by condensing metal-rich resins and asphaltenes to coke. The condensation of oil components originally contained in heavy oil differs greatly in reaction behavior, having the activation energy between 167 and 361 kJ/mol. As the pyrolysis progresses, the newly formed heavy components show a condensation behavior close to that of the light components. Limited by high activation energy and low initial fraction, the condensation of asphaltenes to coke and the resulting removal of metals contained in asphaltenes are hindered. Meanwhile, the condensation of light components has a major contribution to coke formation. An increase in reaction temperature accelerates the demetallization, but hardly changes the yield and component distribution of liquid products at the same metal removal rate.     

不同金属氧化物对重质生物油再裂解的比较性研究

通过TG-FTIR、GC/MS和XRD等分析手段,研究了Fe₂O₃、Al₂O₃、CaO和TiO₂四种金属氧化物催化下重质生物油的热解特性及产物差异。结果表明：应用上述四种催化剂的再裂解实验均促进了重质生物油的脱氧,其中CaO催化下脱氧效果最好,Al₂O₃能够有效降低反应温度,Fe₂O₃有效促进了重质生物油成炭前的解聚、固相产物质量降幅达21.23%,TiO₂对CO₂的生成有最明显的抑制效果、同时可以降低反应结束温度;在低温下,除CaO外的三种催化剂均对有效产物的生成有促进作用,但对不同种类的物质各有侧重,而CaO则会使反应所需温度升高且对愈创木酚的富集有很强的选择性;在中温下,CaO和TiO₂表现出较好的催化效果。上述催化热解过程有效促进了酚类的富集,效果最好的是Al₂O₃,酚类相对含量增幅达31.10%。除Fe₂O₃外的三种金属氧化物均降低了生物炭的有序度,添加CaO制备的生物炭具有最无序的炭结构和最高的固相产率。     

Co-pyrolysis of pine cone with synthetic polymers

Biomass from pine cone (Pinus pinea L.) was co-pyrolyzed with synthetic polymers (PE, PP and PS) in order to investigate the effect of biomass and plastic nature on the product yields and quality of pyrolysis oils and chars. The pyrolysis temperature was of 500 °C and it was selected based on results from thermogravimetric analysis of the studied samples. Co-pyrolysis products namely gases, aqueous and tar fraction coming from biomass, oils from synthetic polymers and residual char were collected and analyzed. Due to the synergistic effect in the pyrolysis of the biomass/polymer mixtures, higher amounts of liquid products were obtained compared to theoretical ones. To investigate the effect of biomass content on the co-pyrolysis, the co-pyrolysis of pure cellulose as model natural polymer for biomass with polymer mixture was also carried out. In the presence of cellulose, degradation reaction leading to more gas formation and less char yield was more advanced than in the case of co-pyrolysis with pine cone. Co-pyrolysis gave polar oxygenated compounds distributed between tar and aqueous phase and hydrocarbon oils with composition depending on the type of synthetic polyolefin. Co-pyrolysis chars had higher calorific values compared to pyrolysis of biomass alone.     

葡萄糖催化热解制备左旋葡萄糖酮特性研究

催化热解制备左旋葡萄糖酮（LGO）是生物质制备高值化学品的重要方法。开发了一种新型的金属磺化炭催化剂用于高效制备LGO,并研究了热解温度、催化剂与生物质的比例以及金属盐类型对左旋葡萄糖酮生成的影响,研究表明：金属磺化炭明显促进了LGO的选择性,在Ce-SC催化剂作用下,催化热解温度为300℃、原料/催化剂比例为1∶1时,LGO的含量达到了82%;在Co-SC催化剂作用下,催化热解温度为400℃、原料/催化剂比例为1∶1时,LGO的含量达到了64%。     

碱土金属氧化物基催化剂催化热解生物质研究进展

快速热解是生物质高效转化利用的重要方法之一,然而其目标产物生物油因含氧量高、组分复杂等不足而难以直接利用。通过在热解体系中引入碱土金属氧化物基催化剂,可以将热解产物中的氧元素以CO₂和H₂O等方式脱除,从而实现生物油品质的提升。总结了典型碱土金属氧化物基催化剂对生物质催化热解过程中发生的酮基化、羟醛缩合、开环和侧链断裂反应及机理,讨论了催化剂类型（CaO、MgO、基于碱土金属氧化物的分子筛和活性炭等）、生物质原料、温度、催化剂用量、停留时间、催化方式、催化剂失活等因素对生物油产率与品质的影响,并对生物质催化热解制备高品质生物油及其应用进行了展望。     

Properties of bio-oils produced by biomass fast pyrolysis in a cyclone reactor

The present paper reports the experimental results of the fast pyrolysis of biomass performed in a cyclone reactor heated at its walls. The conditions of pyroliquefaction are chosen (walls temperature between 900 and 983 K) in order to enhance bio-oils production. Their yields reach 74% while those of char and gases are respectively 10% and 16%. The bio-oils are condensed and trapped at different temperatures. Three main fractions are recovered: heavy oils, light oils and aerosols. Their physicochemical properties (water and particles content, viscosity, density, pH, fraction of pyrolytic lignin and elementary molar composition) as well as stability during storage are measured and compared with literature. The results show very different behaviours according to the types of oils fractions.     

生物质燃烧和热解中钾的释放规律研究进展

生物质中碱金属钾的含量较高,钾在燃烧和热解过程中释放到炉内,会造成积灰、结渣、腐蚀等问题,影响锅炉安全、经济运行。本文通过对文献进行比较和分析,介绍了生物质中钾的含量和赋存形式,碱金属的定量检测方法,生物质中钾在不同条件下热解和燃烧过程中的释放规律,以及燃料成分和粒径、反应温度和升温速率、反应器类型等因素对钾释放规律的影响。结果表明,生物质燃料中钾的赋存形式包括有机钾、无机钾和含钾矿物质等;有机钾分解所释放出的一次产物,最终会经过不同路径的二次反应以其他形式释放或留在灰中;钾的最终释放形式与释放过程中发生的二次反应密切相关,主要包括KCl、K₂SO₄、KOH和含钾矿物质。     

Chemical Modification and XPS Study for Lead(II) Binding by Wheat Stems Biomass

Abstract

Increasing concern over heavy metal contamination of the aquatic environment is urging the more effective and environmentally friendly methods of remediating heavy metals from contaminated waters. The use of plant materials as metal adsorbents may be a possible solution. In this study, wheat stems biomass has been utilized as bioadsorbent to bind lead(II) from aqueous solution. Selected binding conditions such as reaction time and solution pH were optimized. The effect of chemical modification on lead(II) binding capacity of the biomass was investigated. Results showed that the lead(II) binding process by wheat stems biomass is fast and the process is strongly affected by the solution pH. After esterification of the biomass, the lead(II) binding capacity decreased dramaticly, while the lead(II) binding capacity increased greatly after base hydrolyzation of wheat stems. FTIR spectra showed that hydroxyl groups and carbonyl groups in wheat stems biomass may play an important role in the binding of lead(II). In addition, XPS analysis also supports this explanation. These studies are useful for determining ligands that may involve in lead(II) ions binding by wheat stems, thus aiding in our understanding of the mechanisms involved in the removal of metal ions from contaminated waters through biosorption.     

Effects of particle size on the fast pyrolysis of oil mallee woody biomass

This study aims to investigate the effects of biomass particle size (0.18-5.6 mm) on the yield and composition of bio-oil from the pyrolysis of Australian oil mallee woody biomass in a fluidised-bed reactor at 500 °C. The yield of bio-oil decreased as the average biomass particle size was increased from 0.3 to about 1.5 mm. Further increases in biomass particle size did not result in any further decreases in the bio-oil yield. These results are mainly due to the impact of particle size in the production of lignin-derived compounds. Possible inter-particle interactions between bio-oil vapour and char particles or homogeneous reactions in vapour phases were not responsible for the decreases in the bio-oil yield. The bio-oil samples were characterised with thermogravimetric analysis, UV-fluorescence spectroscopy, Karl-Fischer titration as well as precipitation in cold water. It was found that the yields of light bio-oil fractions increased and those of heavy bio-oil fractions decreased with increasing biomass particle size. The formation of pyrolytic water at low temperatures (<500 °C) is not greatly affected by temperature or particle size. It is believed that decreased heating rates experienced by large particles are a major factor responsible for the lower bio-oil yields from large particles and for the changes in the overall composition of resulting oils. Changes in biomass cell structure during grinding may also influence the yield and composition of bio-oil.     

间热径向流反应器料层厚度对煤热解特性的影响

考察了方形径向流固定床煤热解反应器中变化煤层厚度对料层升温速度及煤热解产物分布特性的影响。随着料层厚度增加,导致煤热解反应要求的时间增长,热解水和气的产率相应增加,焦油和半焦收率逐渐降低,但焦油中轻质组分(沸点低于360℃组分)含量呈升高趋势,半焦和煤气热值稍许降低。如,加热壁温度900℃、从45 mm至105 mm增加煤料层厚度时,焦油产率从7.17%(质量,下同)下降到6.26% (相对干基煤),但焦油中的轻焦油组分含量则从67%升至72.7%,半焦产率由80.0%降至77.0%,热解水和煤气产率分别由6.96%和5.91%增至8.85%和7.90%,煤气热值则由24348.5 kJ·m^-3下降至20649.2 kJ·m^-3。所得半焦的热值径向上由高温侧向低温侧逐渐降低,煤料层越厚、热值降幅越大,而相同煤料层厚度处与加热壁平行的同一轴向平面上的半焦热值基本相同。针对研究的反应器,气相热解产物在反应器内沿径向(横向)由高温料层区向低温料层区流动。在该过程中伴随着热解产物对远离加热壁的低温煤料的传热、热解生成重质组分的冷凝和在煤/半焦颗粒表面的吸附截留,进而在低温料层进一步升高温度时发生二次裂解等物理化学过程。反应器内煤层厚度越大,上述各种伴随的物化作用越显著,从而明显影响煤料层的升温及热解特性。     

生物质热解技术研究进展

生物质能源是一种可再生的能源,占世界能源的 14% 以上,可以有效地替代日渐枯竭的化石能源。生物质热解转化为高能量密度的燃料,不仅可以缓解能源的短缺,还可以减少大气污染,改善生态环境。本文介绍了生物质的分类及其结构组成,并从热解反应起始温度和终止温度以及热解产物组成和分布等方面,阐述了生物质类别、催化剂、热解温度、热解压力、升温速率以及气相滞留期等因素对热解过程的影响。     

Non-isothermal programmed pyrolysis studies of oil sand bitumens and bitumen fractions: 1. Athabasca asphaltene

Characteristic pyrolysis thermograms for 12 gases have been obtained for Athabasca asphaltene, using a combination of non-isothermal, programmed pyrolysis (ambient to 1200 K at 3 K min^?1) and gas chromatography. Such thermograms provide information for the characterization of asphaltenes in the form of gas yields, specific rates and Arrhenius kinetic parameters. All thermograms comprised more than one peak. These peaks lie in distinct temperature zones and are associated with primary and secondary cracking and coking reactions. Useful insights into the structure of Athabasca asphaltene and, indirectly, the composition of its pyrolytic cokes have been obtained. The present results provide a body of useful reference material which may be useful for monitoring processes, which may chemically modify the asphaltene fraction of bitumens and heavy oils, and for comparative studies of asphaltenes from a variety of sources.