Characterization and Artificial Neural Networks Modelling of methylene blue adsorption of biochar derived from agricultural residues: Effect of biomass type,pyrolysis temperature,particle size

Biochar has been explored as a sorbent for contaminants, soil amendment and climate change mitigation tool through carbon sequestration. Through the optimization of the pyrolysis process, biochar can be designed with qualities to suit the intended uses. Biochar samples were prepared from four particle sizes (100–2000 µm) of three different feedstocks (oak acorn shells, jift and deseeded carob pods) at different pyrolysis temperatures (300–600 °C). The effect of these combinations on the properties of the produced biochar was studied. Biochar yield decreased with increasing pyrolysis temperature for all particle sizes of the three feedstocks. Ash content, fixed carbon, thermal stability, pH, electrical conductivity (EC), specific surface area (SSA) of biochar increased with increasing pyrolysis temperature. Volatile matter and pH value at the point of zero charge (pH_pzc) of biochar decreased with increasing pyrolysis temperature. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the surface of the biochar was rich with hydroxyl, phenolic, carbonyl and aliphatic groups. Methylene blue (MB) adsorption capacity was used as an indicator of the quality of the biochar. Artificial neural networks (ANN) model was developed to predict the quality of the biochar based on operational conditions of biochar production (parent biomass type, particle size, pyrolysis temperature). The model successfully predicted the MB adsorption capacity of the biochar. The model is a very useful tool to predict the performance of biochar for water treatment purposes or assessing the general quality of a design biochar for specific application.     

Preparation and Characterization of MgO-Modified Rice Straw Biochars

Rice straw is a common agricultural waste. In order to increase the added value of rice straw and improve the performance of rice straw biochar. MgO-modified biochar (MRBC) was prepared from rice straw at different temperatures, pyrolysis time and MgCl₂ concentrations. The microstructure, chemical and crystal structure were studied using X-ray diffraction (XRD), a Scanning Electron Microscope (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption desorption isotherms and Elementary Analysis (EA). The results showed that the pyrolysis temperature had significant influence on the structure and physicochemical property of MRBCs. MRBC-2 h has the richest microporous structure while MRBC-2 m has the richest mesoporous structure. The specific surface area (from 9.663 to 250.66 m²/g) and pore volume (from 0.042 to 0.158 cm³/g) of MRBCs increased as temperature rose from 300 to 600 °C. However, it was observed MgCl₂ concentrations and pyrolysis time had no significant influence on pore structure of MRBCs. As pyrolysis temperature increased, pH increased and more oxygen-containing functional groups and mineral salts were formed, while MgO-modified yield, volatile matter, total content of hydrogen, oxygen, nitrogen, porosity and average pore diameter decreased. In addition, MRBCs formed at high temperature showed high C content with a low O/C and H/C ratios.     

Revolutions in algal biochar for different applications: State-of-the-art techniques and future scenarios

Algae are potential feedstock for the production of bioenergy and valuable chemicals. After the extraction of specific value-added products, algal residues can be further converted into biogas, biofuel, and biochar through various thermochemical treatments such as conventional pyrolysis, microwave pyrolysis, hydrothermal conversion, and torrefaction. The compositions and physicochemical characteristics of algal biochar that determine the subsequent applications are comprehensively discussed. Algal biochar carbonized at high-temperature showed remarkable performance for use as supercapacitors, CO₂ adsorbents, and persulfate activation, due to its graphitic carbon structure, high electron transport, and specific surface area. The algal biochar produced by pyrolysis at moderate-temperature exhibits high performance for adsorption of pollutants due to combination of miscellaneous functional groups and porous structures, whereas coal fuel can be obtained from algae via torrefaction by pyrolysis at relatively low-temperature. The aim of this review is to study the production of algal biochar in a cost-effective and environmental-friendly method and to reduce the environmental pollution associated with bioenergy generation, achieving zero emission energy production.     

Pore structure of pyrolyzed scrap tires

Internal structure of carbon black produced by pyrolysis (CBp) of rubber samples from the top and bottom parts of sidewall and tread of a passenger car tire was investigated in nitrogen flow at different temperatures. The pore structure (specific surface area, pore size distribution, and porosity) of CBp and commercial CB, was compared. The development of pore structure and the increase of the specific surface area were most intensive during the thermal decomposition at temperatures ranging from 300°C to 500°C. This is caused by the intensive release of volatiles during the pyrolysis. After the pyrolysis was finished, at temperatures above 500°C, further decomposition of solid matter was associated with a slight increase of the specific surface area. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

炭化程度对核桃壳焦孔隙结构和燃烧特性的影响

利用傅里叶变换红外光谱仪(FT-IR)、扫描电子显微镜(SEM)和X射线衍射仪(XRD)研究了炭化程度对核桃壳焦孔隙及微晶结构的影响,并使用热重-差示扫描量热仪(TG-DSC)对核桃壳焦及其原料的燃烧特性进行了分析。结果表明,合适的炭化程度(焦炭挥发分含量为6%-15%)使焦炭内乱层石墨变得无序,碳质微晶结构中缺陷增多,导致焦炭内孔隙结构相对发达;热解温度为500℃时,核桃壳焦的比表面积最大,为374.60 m~2/g;热解温度为600℃时,核桃壳焦的燃烧特性最优,其燃烧特性指数为7.16×10~6;合适的炭化程度可使焦炭内的挥发分含量减少,从而使得核桃壳焦的高位热值升高,且由于相对发达的孔隙使焦炭在燃烧时与空气的接触面积增大,导致焦炭的燃烧速率加快。     

Effect of different temperatures on the properties of pyrolysis products of Parthenium hysterophorus

This research encompasses the use of noxious weed Parthenium hysterophorus as feedstock for pyrolysis carried out at varying temperatures of 300, 450 and 600°C. Temperature significantly affected the yield and properties of the pyrolysis products including char, syngas and bio-oil. Biochar yield decreased from 61% to 37% from 300 °C to 600 °C, whereas yield of gas and oil increased with increasing temperature. The pyrolysis products were physico-chemically characterized. In biochar, pH, conductivity, fixed carbon, ash content, bulk density and specific surface area of the biochar increased whereas cation exchange capacity, calorific value, volatile matter, hydrogen, nitrogen and oxygen content decreased with increasing temperature. Thermogravimetric analysis showed that the biochar prepared at higher temperature was more stable. Gas Chromatography-Mass Spectrometry analysis of biochar indicated the presence of alkanes, alkenes, nitriles, fatty acids, esters, amides and aromatic compounds. Number of compounds decreased with increasing temperature, but aromatic compounds increased with increasing temperature. Scanning electron micrographs of biochar prepared at different temperatures indicated micropore formation at lower temperature while increase in the size of pores and disorganization of vessels occurred at increasing temperature. The chemical composition was found to be richer at lower pyrolysis temperature. GC–MS analysis of the bio-oil indicated the presence of phenols, ketones, acids, alkanes, alkenes, nitrogenated compounds, heterocyclics and benzene derivatives.     

快速热处理石油焦与煤的微观结构变化及气化活性分析

为了研究在接近工业气化条件下石油焦和煤的结构和气化活性变化规律的差异,在滴管炉装置内,800~1 400℃对两种石油焦和一种烟煤进行快速热处理。用比表面积孔隙分析仪、XRD分析仪考察快速热处理对石油焦和煤的孔隙结构、碳微晶结构的影响,用热重分析仪考察不同温度快速热处理后石油焦和煤的CO₂气化活性。结果表明,石油焦与煤相比,孔隙结构主要由微孔组成,随快速热处理温度的升高,石油焦和煤微孔比表面积和孔容均先增大后逐渐减小;快速热处理降低了石油焦和煤的石墨化程度,石油焦碳微晶结构变化主要表现在堆垛高度的变化,而煤的碳微晶结构变化在衍射峰对应的2θ₀₀₂值、晶面间距和堆垛高度上均有体现;石油焦和煤的气化活性随快速热处理温度升高的变化趋势不同,但均与碳微晶结构参数(石墨化程度)的变化紧密相关。     

高温下热解温度对煤焦孔隙结构的影响

利用高温沉降炉在1500K～1800K制备京西无烟煤煤焦,使用化学吸附法测定不同热解温度下煤焦比表面积及孔容积与孔径的分布特征,并采用SEM观察煤焦颗粒表面的形态,分析了高温下热解温度对煤焦孔隙结构的影响规律。结果表明,煤焦的比表面积主要由孔径小于10nm的微孔和中孔构成,而其孔容积则主要由孔径为2nm~50nm的中孔构成。高温下煤焦比表面积和孔容积随热解温度的升高,呈现先增大后减小的非单调变化现象,转折温度约为1600K。出现这种变化的主要原因是煤焦在热解温度超过1600K后开始烧结,产生较为光滑致密的表面结构,部分孔隙封闭。     

负载碳酸钠煤焦催化气化反应特性研究

基于热重分析仪开展负载碳酸钠神府烟煤/遵义无烟煤煤焦气化实验,并借助扫描电子显微镜和孔结构及比表面积分析仪表征焦样孔结构及表观结构变化,考察了反应温度(650-800℃)、气化剂(水蒸气、二氧化碳)及碳酸钠负载量(钠离子负载量2.2%、4.4%、6.6%,质量分数)对神府烟煤/遵义无烟煤焦样气化反应活性的影响。结果表明,碳酸钠有利于促进神府/遵义煤热解过程孔隙结构的发展。在二氧化碳气氛下,适宜催化剂负载量使神府烟煤反应活性提高,过多负载催化剂堵塞煤焦内部孔隙结构,使得气化反应活性降低,遵义无烟煤反应活性随负载量增加而提高,两者反应活性均随温度升高而提高。在水蒸气气氛下,神府烟煤/遵义无烟煤在一定条件下反应活性随催化剂负载量增大、温度升高而提高。碳酸钠的添加能够在保证气化反应性的前提下降低气化反应温度和活化能。     

滴管炉内新疆后峡煤挥发分释放和形态变化

对新疆后峡煤和滴管炉内的快速热解焦的比表面积、平均孔径、粒径和表面结构进行了分析,研究快速热解过程中原煤的形态变化。将热解焦在热重分析仪上进行气化实验,研究形态变化对气化反应的影响。结果表明,随热解温度的升高,煤焦比表面积与平均孔径变化趋势不同;快速热解过程中煤颗粒除破碎外,还会发生膨胀及凝聚形态变化;不同热解碎片气化趋势不一样,1200℃热解温度下的热解焦气化稳定性最好。     

Thermogravimetric analysis of gasification reactivity of coal chars with steam and CO2 at moderate temperatures

Comparative study on the gasification reactivity of the three types of Chinese coal chars with steam and CO₂ at 850–1050 °C was conducted by isothermal thermogravimetric analysis. The effects of coal rank, pore structure, ash behavior, and gasification temperature on the gasification reactivity of coal chars were investigated. It is found that the gasification reactivity difference between different coal chars changes with reaction degree and gasification temperature, and has no immediate connection with coal rank and initial pore structure. Ash behavior plays an important role in the char reactivity, and changes with gasification temperature and reaction degree due to the variation in the compositions and relative amount. The influence of pore structure is more noticeable during a relatively moderate reaction process. The relative reactivity ratio of steam to CO₂ gasification generally decreases with the increasing temperature, and is related with the catalytic effect of inherent minerals. The characteristic parameters of the chars were analyzed, finding that the value of half reaction specific rate is approximate to the average specific rate under the same conditions. The nth-order distributed activation energy model is proposed to describe the coal char gasification process, and the results show that the activation energy increases with the increasing carbon conversion.     

Quality variations of poultry litter biochar generated at different pyrolysis temperatures

Producing biochar and biofuels from poultry litter (PL) through slow pyrolysis is a farm-based, value-added approach to recycle the organic waste. Experiments were conducted to examine the effect of pyrolysis temperature on the quality PL biochar and to identify the optimal pyrolysis temperature for converting PL to agricultural-use biochar. As peak pyrolysis temperature increased incrementally from 300 to 600 °C, biochar yield, total N content, organic carbon (OC) content, and cation exchange capacity (CEC) decreased while pH, ash content, OC stability, and BET surface area increased. The generated biochars showed yields 45.7–60.1% of feed mass, OC 325–380 g kg⁻¹, pH 9.5–11.5, BET surface area 2.0–3.2 m² g⁻¹, and CEC 21.6–36.3 cmol_c kg⁻¹. The maximal transformation of feed OC into biochar recalcitrant OC occurred at 500 °C, yet 81.2% of the feed N was lost in volatiles at this temperature. To produce agricultural-use PL biochar, 300 °C should be selected in pyrolysis; for carbon sequestration and other environmental applications, 500 °C is recommended.     

Combustion synthesis and properties of nanocrystalline zirconium oxide

Nanocrystalline tetragonal zirconia powders have been synthesized by aqueous combustion using glycine (Gly) as a fuel and zirconyl nitrate (ZN) as an oxidizer. The effect of the fuel-to-oxidant molar ratio on the structural and morphological properties of nanocrystalline zirconia powders was studied. Thermodynamic modeling of the combustion reaction showed that the increase in the Gly:ZN molar ratio leads to the increase in theoretical combustion temperature, heat of combustion and amount of produced gases. Powder properties were correlated with the nature of combustion and results of thermodynamic modelling. The increase in the Gly:ZN molar ratio produces more agglomerated powders characterized by a lower degree of uniformity, a lower specific surface area and a slightly bigger crystallite size. On the other hand, the presence of hard agglomerates suppresses the volume expansion, stabilizing tetragonal zirconia, as confirmed by Rietveld refinement. The absence of cubic zirconia was confirmed by FTIR and Raman Spectroscopy. The increase in the calcination temperature led to more agglomerated, compact and less uniform powders. The nanocrystalline nature of zirconia is the reason for the formation of bigger crystallites, the increase in the relative amount of monoclinic phase and sample sintering after calcination at high temperature. The highest measured specific surface area of zirconia was 45.8 m²·g⁻¹, obtained using a fuel-lean precursor.     

高硫石油焦高温热解过程及硫析出特性研究

为深入了解高硫石油焦在工业应用高温工况下的热解过程以及硫的析出特性,本研究采用高温固定床对青岛高硫石油焦进行了高温(900-1500℃)热解实验,考察了高温热解下热解气体释放规律,热解过程中焦的物理孔隙结构以及化学特性的演变,并对热解过程中硫的析出与演变特性进行了研究。结果表明,随着热解温度的升高,石油焦热解气中的H_2含量逐渐增加,CO含量变化不大,CH_4与CO_2含量则逐渐下降;热解焦的比表面积与平均孔隙均随热解温度的升高有所增加,颗粒的表面形态则受温度影响较小;热解温度的升高会降低石油焦中含有的非定型碳比例,提高其微晶结构的有序性以及石墨化程度;热解焦的气化活性随热解温度的升高先降低后升高,在1100℃附近有最小值; 1500℃高硫石油焦硫元素析出率达81.34%,仅少量硫醇类有机硫和噻吩环内的硫元素得以残存。     

Part I: NiMoO4 Nanostructures Synthesized by the Solution Combustion Method: A Parametric Study on the Influence of Synthesis Parameters on the Materials’ Physicochemical,Structural, and Morphological Properties

The impact of process conditions on the synthesis of NiMoO₄ nanostructures using a solution combustion synthesis (SCS) method, in which agar powder and Ni(NO₃)₂ were utilized as fuel and as the oxidant, respectively, was thoroughly studied. The results show that the calcination temperature had a significant implication on the specific surface area, phase composition, particle size, band gap, and crystallite size. The influence of calcination time on the resulting physicochemical/structural/morphological properties of NiMoO₄ nanostructures was found to be a major effect during the first 20 min, beyond which these properties varied to a lesser extent. The increase in the Ni/Mo atomic ratio in the oxide impacted the combustion dynamics of the system, which led to the formation of higher surface area materials, with the prevalence of the β-phase in Ni-rich samples. Likewise, the change in the pH of the precursor solution showed that the combustion reaction is more intense in the high-pH region, entailing major implications on the physicochemical properties and phase composition of the samples. The change in the fuel content showed that the presence of agar is important, as it endows the sample with a fluffy, porous texture and is also vital for the preponderance of the β-phase.     

煤快速热解焦的微观结构对其气化活性的影响

在滴管炉内对中国三种不同煤阶的典型煤种在800~1 400 ℃进行快速热解实验,利用XRD和氮气气体吸附法对所得煤焦进行微晶结构和孔隙特征分析,在热重分析仪上进行CO₂气化反应活性的测定,研究不同热解温度煤焦结构特性与气化活性之间的关系。结果表明,随着热解温度的升高,内蒙古褐煤焦和神府烟煤焦的比表面积在1 200 ℃达到极大值,但气化活性却相对较低;遵义无烟煤焦在800~1 200 ℃气化活性逐渐提高,但比表面积在900 ℃达到极大值,表明煤焦比表面积与气化活性不存在严格关联。煤焦碳微晶结构变化所反映出煤焦石墨化进程与煤焦气化活性随热解温度的变化具有一致的变化趋势,表明快速热解煤焦的碳微晶结构变化对煤焦气化活性的影响更大。     

生物质焦制备条件对其燃烧反应特性的影响

在热重分析仪上,研究了生物质焦的制备条件对其燃烧反应特性的影响。生物质焦由闪速裂解技术制得,裂解温度为 748 K、773 K和823 K;原料含水质量分数为0、7.0%和11.3%。研究发现,生物质焦中挥发性物质的质量分数和H/C质量比随裂解温度的增加而降低,其燃烧反应性随裂解温度的增加而降低;与高裂解温度条件下制得的生物质焦相比,低裂解温度条件下制得的生物质焦具有较高的反应活化能和对燃烧温度更敏感。原料含水量对生物质焦的燃烧反应特性影响很小;但对高裂解温度条件下制得的生物质焦中的挥发性组分含量有较大的影响。简化的生物质焦本征燃烧反应幂函数动力学模型可以很好地描述其燃烧行为。     

Evaluation of the porous structure development of chars from pyrolysis of rice straw: Effects of pyrolysis temperature and heating rate

The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N₂ physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 °C. The carbon structure shrinkage and pore narrowing occurred above 600 °C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 °C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 °C. The total surface area (S_total) and micropore surface area (S_micro) reached maximum values of 30.94 and 21.81 m²/g at 900 °C and decreased slightly at higher temperatures. The influence of heating rate on S_total and S_micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship.     

Effect of carbon pore structure on the CH4/N2 separation

The separation between CH₄ and N₂ bears importance in coalbed methane enrichment, and activated carbon is a major adsorbent for industrial PSA (pressure swing adsorption) separation. However, the adsorption of both gases shows supercritical features, and the physicochemical properties are also similar, which results in similar adsorption behavior and renders the separation difficult. To maximize the separation coefficient, the effect of carbon pore structure on the separation was studied and a series of carbons was prepared at different extent of activation. The effect of specific surface area, pore size and pore volume on the separation coefficient was observed and a linear correlation between the separation coefficient and the small pore (0.7–1.3?nm) volume reduced to unit surface area was shown.     

甲醇处理煤的微孔性质及反应性研究

在低于临界温度下,用甲醇处理了三种不同变质程度的煤,以研究其比表面积及微孔容积等表面特性的变化。结果表明,用甲醇处理后煤的微孔性质发生了较大变化,其变化的大小顺序是:沈北褐煤>大同烟煤>晋城无烟煤。随甲醇处理温度或干馏温度升高,煤及半焦的孔径均向小的方向偏移。煤的平均孔径为8.2—8.6A;半焦的平均孔径为6.3—7.5A。煤经甲醇处理后其半焦的反应性均比未处理的高。