Study of the potential valorisation of heavy metal contaminated biomass via phytoremediation by fast pyrolysis: Part II: Characterisation of the liquid and gaseous fraction as a function of the temperature

Fast pyrolysis of heavy metal contaminated birch (CMB), resulting from phytoremediation, is investigated. The effect of the pyrolysis temperature (673, 773, 873 K) on the composition and evolution of the bio-oil/tar fraction and the gas fraction has been studied. The knowledge of the composition of the gaseous and liquid pyrolysis fractions, as a function of the pyrolysis temperature, affects directly future applications and valorisation of the pyrolysis products and are indispensable for making and selecting the proper thermal conditions for their optimal use. In view of the future valorisation of this heavy metal contaminated biomass, the pyrolysis temperature is imperative, because some of the heavy metals can volatilize at temperatures generally used for the co-combustion or fast pyrolysis of biomass.     

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.     

Rationale of lead immobilization by ball milling in synthetic soils and remediation of heavy metals contaminated tailings

In this work, the use of mechanical milling for the remediation of heavy metals in synthetic soils and tailings sampled from the mining area of “Barraxiutta”, SW of Sardinia, Italy is investigated. Specifically, Pb(II) contaminated synthetic soils of sandy, bentonitic and kaolinitic type are taken into account following the results obtained in previous works. Suitable sequential extraction procedures have been performed on both untreated and treated synthetic soils. It is found that mechanical loads which occur during collisions among milling media and soils are able to modify the distribution of Pb(II) onto the different solid fractions of contaminated synthetic soils. Specifically, for sandy soils the milling treatment induces a significant increase in Pb(II) content in the Fe–Mn oxides fraction. On the other hand, for bentonitic and kaolinitic soils, Pb(II) content in both carbonate and Fe–Mn oxide fractions is augmented after treatment. Such phenomena may contribute to Pb(II) immobilization efficiency since the heavy metal trans-speciation occurs in favor of fractions characterized by stronger bonds and lower solubility.As for the heavy metals contaminated tailings, their immobilization is obtained using both ball and attrition milling devices under specific ball to powder ratio values. The degree of metals immobilization is evaluated by analyzing the corresponding leachable fraction obtained through the Synthetic Precipitation Leaching Procedure (SPLP) proposed by EPA. X-ray diffraction and granulometric analyses revealed no significant alterations of the intrinsic character of the tailings after milling except for a relatively small increase in particles size.The increase in immobilization efficiency when tailings are mechanically treated may be due to specific phenomena induced during milling such as entrapment of heavy metals into aggregates, solid diffusion of metals into the crystalline reticulum of soil particles, the formation of new fresh surfaces onto which heavy metals may be irreversibly adsorbed as well as metal trans-speciation onto tailings fractions characterized by stronger bonds and lower solubility.     

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。     

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.     

Is it possible to predict gas yields of any biomass after rapid pyrolysis at high temperature from its composition in cellulose, hemicellulose and lignin?

Ligno-cellulosic biomass from different sources presents very variable compositions. Consequently, there is a wide variation in the nature and quantities of gaseous products obtained after thermal treatment of biomasses.The objective of this work is to establish a link between the composition of a biomass and its pyrolysis gas yields and composition. Experimental flash pyrolysis of several biomasses at a temperature of 950 °C and a gas residence time of about 2 s was carried out. An attempt was then made to predict gas yields of any biomass according to its composition. We show that an additivity law does not allow the gas yields of a biomass to be correlated with its fractions of cellulose, hemicellulose and lignin. Several potential explanations are then offered and quantitatively demonstrated: it is shown that interactions occur between compounds and that mineral matter influences the pyrolysis process.     

Effect of water vapour and biomass nature on the yield and quality of the pyrolysis products from biomass

Slow pyrolysis/activation of biomass in a flow of steam is studied in laboratory equipment supplied with a fixed bed reactor. Forestry and agricultural residues of different origin are selected as raw materials (birch wood, olive stones, bagasse, pelletised straw and miscanthus). The final pyrolysis temperature is varied in the range 700–800°C and the duration of the activation is 1 or 2 h. The effect of both the nature of the investigated biomass samples and the presence of water vapour on the quality of the pyrolysis products is in the focus of interest of this work. Column chromatography is used to characterize the liquid products. The surface area and the acid–base neutralization capacity of the solid products are determined by the adsorption capacity towards iodine and reactions with EtONa and HCl. The results are compared with those obtained in pyrolysis in inert atmosphere of nitrogen. It is shown that the presence of steam has strong effect on the yield and properties of the products. Significant part of the liquid product is found dissolved in the water phase obtained after condensation of the volatiles. The solid products obtained in the presence of steam have the properties of activated carbons.     

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。     

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.     

污泥热解残渣中重金属形态分布的研究进展

目前,我国城市及工业污水产生量已达7.34×10¹⁰ t/a,对其处理产生的污泥量达7.29×10⁷ t/a。污泥的主要去向为土地利用、焚烧发电和建材利用等。在这些再利用过程中,重金属特别是Cr、Cu、Zn、Ni等对其再利用影响较大。污泥处理多采用热解处理,重金属在处理过程中会富集在热解残渣中。阐释重金属在热解残渣中的形态分布,对于其再利用过程意义重大。本文以改进的欧共体物质标准局(BCR)连续提取法为基础,总结了污泥热解残渣中重金属的形态分布,阐述了热解工况(热解温度、停留时间、催化剂)、共热解及预处理对热解残渣中重金属形态分布的影响,探讨了污泥热解残渣中重金属未来的研究趋势。     

Simultaneous catalytic esterification of carboxylic acids and acetalisation of aldehydes in a fast pyrolysis bio-oil from mallee biomass

This paper reports the simultaneous catalytic esterification and acetalisation of a bio-oil with methanol using a commercial Amberlyst-70 catalyst at temperatures between 70 and 170 °C. The bio-oil was prepared from the pyrolysis of mallee woody biomass in a fluidised-bed pyrolysis reactor under the fast heating rate conditions. Our results show that the conversion of light organic acids and aldehydes to esters and acetals rises significantly with increasing temperature, reaction time and catalysts loading. However, some acetals (e.g. dimethoxymethane) could decompose at higher operating temperatures (>110 °C) and catalyst loadings (>6 wt.%). The medium and heavy fractions of bio-oil also reacted with methanol to result in increases in their volatility (or decreases in boiling points) when their reactive O-containing functional groups were stabilised. The acid-catalysed reactions between bio-oil and methanol also decreased the coking propensity of the bio-oil reaction products.     

葵花杆的热解特性及热解产物分析

为充分利用生物质葵花杆,采用同步热分析仪以升温速率为影响因素对葵花杆的热解特性进行研究,利用Coats-Redfern积分法计算主要阶段热解动力学参数,并采用气相色谱/质谱联用仪对热解产物进行了定量分析.研究结果表明:葵花杆的热解过程可分为预热干燥、主要热解及炭化3个阶段;随着升温速率的增大,葵花杆热解的TG曲线向高温...     

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.     

Influence of particle size on the analytical and chemical properties of two energy crops

Two energy crops (switchgrass and reed canary grass) have been processed using ball mills and divided into two size fractions (<90 μm and 90–600 μm) and analysed using an array of analytical techniques including proximate and ultimate analysis, metal analysis, calorific value determination, and plant component analysis (cellulose, lignin and hemicellulose contents). The results indicate that smaller particles of the two grasses have a significantly higher concentration of inorganic matter and moisture content than larger particles. In contrast the larger size fractions had a higher carbon content, and lower nitrogen content, with a resulting higher calorific value. The volatile content was also higher in the larger size fraction. The composition of the organic content varied between the two size fractions, most noticeable was the difference in cellulose concentration which was approximately 50% higher in the >90 μm sample. Two laboratory scale techniques, thermogravimetric analysis (TGA) and pyrolysis–GC–MS (py–GC–MS), were used to study the significance of these differences in thermal conversion. In py–GC–MS of reed canary grass, and switchgrass to a lesser extent, the amounts of cellulose and lignin decomposition products were higher for the larger particle size fraction. The differences in cellulose contents were also apparent from the TGA studies, where different mass losses were seen in the cellulose decomposition region of the two size fractions. From the results of these two techniques it was concluded that the differences in ash, and therefore catalytic metal contents, between the two size fractions, resulted in lower pyrolysis temperatures, lower char combustion temperatures, and higher yields of catalytic pyrolysis decomposition products for the smaller size fractions. The implications of the results are discussed in terms of the bio-oil quality in fast pyrolysis and the predicted behaviour of the ash in combustion. It is suggested that pre-treatment by milling is one route that might be used routinely as a feedstock quality improvement strategy in integrated biomass conversion processes.     

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.     

Effects of organic and inorganic metal salts on thermogravimetric pyrolysis of biomass components

Thermogravimetric analyzer (TGA) was employed to elucidate the catalytic effects of organic and inorganic metal salts (K₂CO₃, KAc, Na₂CO₃ and NaAc) on the pyrolysis of three biomass components (cellulose, hemicellulose and lignin). In case of cellulose, TG analysis results showed that all the four metal salts increased the yield of char products and decreased the weight loss rates of cellulose pyrolysis, which followed the order of Na₂CO₃>K₂CO₃>NaAc>KAc. In contrast to cellulose, the four organic and inorganic salts employed had no significant effects on the remaining two biomass components:, hemicellulose and lignin. However, the four metal salts led to the devolatilization reaction of hemicellulose to occur at lower temperature region, and the dehydration reaction of lignin was promoted more or less. An increase in the heating rate might augment the maximum degradation rate. Different mixing ratios had little influence on the progress of catalytic pyrolysis. Based on the observations, the potential mechanism of the catalytic pyrolysis of biomass components with metal salts was discussed.     

生物质热解利用中主要催化剂的研究进展

催化热解目前逐渐成为生物质转化利用技术的主要研究方向,相比常规热解,催化热解可以对生物油进行有效提质并且定向产生高值化产品。本文通过对近年来新兴的催化剂进行综述,包括分子筛类催化剂（ZSM-5、HZSM-5、USY等）、炭基催化剂、金属氧化物、白云石、整体式催化剂等,了解了目前生物质热解利用中催化剂领域内的最新研究进展。文中指出,良好的催化剂是保证反应顺利进行的关键,不同催化剂定向产生的高值化产品也有所不同,因此催化剂的正确选择对于生物油的提质起着重大作用。根据目前领域内所研究内容,本文还对各类催化剂的优缺点、产物特性进行了详细比较,并针对该技术现有问题提出了部分建议并进行展望,为以后生物质热解领域催化剂的研究提供了重要的理论依据。     

A review of methods for the demetallization of residual fuel oils

Crude oils typically contain trace amounts of metals with vanadium and nickel being the most common. Usually they are in an oil-soluble form and in conventional refining processes they become concentrated in the residual fuel oil fractions. The deleterious effects of metals in petroleum have been known for some time. The metals not only contaminate the products, the metal chelates also cause poisoning and fouling of catalyst and corrode equipments. The metals also tend to form particulate emissions in the sub-micron range. This review presents discussion of methods for the removal of metals from the heavy oils and residuum fractions. These methods include physical, chemical and catalytic treatment processes.     

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.     

钙钛矿催化剂在生物质热化学利用领域的研究进展

钙钛矿催化剂优异的氧化还原性能、离子迁移率、热稳定性和较低的生产成本,使得其在生物质热化学利用领域具有广阔的应用前景。基于生物质热解/气化、生物质重整制氢和生物质下游产物化学合成等应用场景,重点阐述并总结了钙钛矿催化剂的催化性能和机制。聚焦于金属阳离子的催化作用和晶格氧的氧化还原作用,从A/B位离子取代、空间结构改变等方面总结了钙钛矿催化剂的优化设计方法。为钙钛矿催化剂在生物质热化学利用领域的应用与优化指明了方向。