Behaviour of dolomite, olivine and alumina as primary catalysts in air-steam gasification of sewage sludge

Sewage sludge gasification assays were performed in an atmospheric fluidised bed reactor using air and air-steam mixtures as the gasifying agents. Dolomite, olivine and alumina are three well known tar removal catalysts used in biomass gasification processing. However, little information is available regarding their performance in sewage sludge gasification. The aim of the current study was to learn about the influence of these three catalysts in the product distribution and tar production during sewage sludge gasification. To this end, a set of assays was performed in which the temperature (750-850 °C), the in-bed catalyst content (0, 10 and 15 wt.%) and the steam-biomass ratio (SB) in the range of 0-1 were varied with a constant equivalence ratio (ER) of 0.3. The results were compared to the results from gasification without a catalyst. We show that dolomite has the highest activity in tar elimination, followed by alumina and olivine. In addition to improving tar removal, the presence of water vapour and the catalysts increased the content of H₂ in the gases by nearly 60%.     

Steam gasification of coal char using alkali and alkaline-earth metal catalysts

The catalytic effect of alkali and alkaline-earth metal salts or oxides on the gasification of Chinese Linnancang coal char was investigated at atmospheric pressure and a temperature of 800 °C. The order of catalytic activity is K₂SO₄ or K₂CO₃ Na₂CO₃ KCl NaCl CaCl₂ or CaO. The effect of amount of catalysts added on catalytic activity was studied. The distribution of K₂CO₃ or CaO catalysts on the coal char surface for different methods of catalyst loading was examined by an electron microprobe analyser. The relation between the catalytic activity and distribution of catalysts were illustrated. The loading method of K₂CO₃ has little effect on its catalytic activity but that of CaO influences the activity significantly.     

Steam reforming of tar from a biomass gasification process over Ni/olivine catalyst using toluene as a model compound

A Ni/olivine catalyst, previously developed for biomass gasification and tar removal during fluidized bed steam gasification of biomass, was tested in a fixed bed reactor in toluene steam reforming as a tar destruction model reaction. The influence of the catalyst preparation parameters (nickel precursor, calcination temperature and nickel content) and operating parameters (reaction temperature, steam to carbon S/C ratio and space-time) on activity and selectivity was examined showing a high toluene conversion and a low carbon formation compared to olivine alone. The steam reforming of toluene was found to be of zero order for water and first order for toluene. Activation energy required for Ni/olivine was determined to be about 196 kJ mol⁻¹ in accordance with literature. Catalyst activity and stability and its resistance against carbon formation were discussed on the basis of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature programmed oxidation (TPO) results. Characterization before test (XRD, temperature programmed reduction (TPR), Mössbauer spectroscopy) have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support, which explains the efficiency of the catalyst calcined at 1100 °C. After test, Ni–Fe alloys were observed (TEM, Mössbauer spectroscopy). It was suggested that magnesium oxide enhanced steam adsorption, facilitating the gasification of surface carbon and that Ni–Fe alloys prevented carbon deposition by dilution effect.     

Catalytic steam gasification of Miscanthus X giganteus in fluidised bed reactor on olivine based catalysts

The Miscanthus X giganteus (MXG) presents many advantages (high yield, perennial crop, easy harvesting…) so it can be considered as a good candidate in terms of renewable energy sources. Several works have been carried out and were devoted to the MXG, especially in the agricultural field, but this study is the first which deals with gasification in order to produce syngas. The catalytic steam gasification of MXG in a fluidised bed reactor into presence of olivine based catalysts was investigated. Three parameters were studied, the temperature (800 °C and 900 °C), the pellets size (6 mm and 8 mm) and the nature of catalyst (olivine and Ni/olivine). Noteworthy is the efficiency shown by the Ni/olivine at 800 °C, which leads to the production of 1.7 m³ kg^− 1 daf of gas, containing 50% of H₂. Ni/olivine catalyst was characterised by XRD, TPR and SEM-EDX in order to monitor its structural changes during the process. Moreover, a solvent system of tar recovery was tested, which allows to obtain a more representative set of the whole tars. Then, the tars composition was determined by GC/MS. The identification of different compounds shows the presence of different PAHs, in majority naphthalene.     

Staged carbon gasification with nickel catalysts

The deactivation of a model coal char during nickel catalyzed steam gasification is mathematically modeled. A previously demonstrated mechanism of deactivation wherein the catalyst particles are encapsulated by a graphitic carbon overlayer is used in the model. It is shown that when the gasification process is conducted in two isothermal stages the amount of carbon converted is greater than when a single isothermal reaction is used.     

Steam gasification of German hard coal using alkaline catalysts: Effects of carbon burn-off and ash content

Laboratory-scale experiments were performed on chars from German hard coals with potassium carbonate addition. The steam gasification rate at 4 MPa and 700 °C as a function of the amount of catalyst added is described for a low-and high-ash char. From the burn-off behaviour the reaction order relative to carbon was determined. For the low-ash char a uniform reaction order was found but the high-ash char indicated a complex interaction of catalytic gasification, catalyst deactivation, and the development of the reacting surface.     

生物质气化焦油裂解用颗粒催化剂的再生性能

为开发适用于生物质气化焦油裂解的多孔白云石颗粒催化剂,以乙酸为生物质气化焦油的模型化合物,讨论了积炭对多孔白云石颗粒催化能力以及再生性能的影响。结果表明,在积炭率0～4.4%时,多孔白云石颗粒的催化能力随积炭率呈线性下降。当积炭率从0增加到4.4%时,颗粒的孔隙率从0.74 cm³·g^-1减小到0.48 cm³·g^-1,乙酸裂解率从99.3%降至32.3%。采用900 ℃和2 h焙烧法对积炭多孔白云石颗粒进行再生处理后,多孔白云石颗粒的强度基本不变,孔隙率增至0.55 cm³·g^-1。在再生多孔白云石颗粒上,乙酸裂解率达到99.5%。多孔白云石颗粒催化剂具有良好的再生性。     

Reaction of catalysts with mineral matter during coal gasification

After a review of mineral matter of German hard coal, its reactions with catalysts during gasification with steam to form new crystalline phases are dealt with. Products of commercial plants and laboratory experiments were investigated by means of microscopy, XRD, XRF and microprobe analysis.     

Adsorption kinetics of methylene blue using alkali and microwave-modified apricot stones

In this study, adsorption of the methylene blue dye was investigated by using apricot stones, applied chemical and microwave modification. Adsorption is suitable for pseudo-second-order kinetic model and chemisorption was determined as rate controlling step. It was determined that the pore diffusion is not sole rate-limiting step and other mechanisms also play a role on the adsorption. A significant increase was observed in the adsorption capacity as the pH value increased. Adsorption was best described with Langmuir isotherm. As the temperature increased, adsorption capacity showed an increase, which revealed endothermic nature of the adsorption.     

Preparation,modification, and characterization of pitches from apricot stones

Apricot stones steam pyrolysis tar and mixtures with petroleum pitch were modified by sulfuric acid and heat treatment at various temperatures for the purpose of obtaining a raw material for the production of carbon-related materials. The products obtained were characterized by elemental analysis, total carbon contents, FTIR spectroscopic analysis, ¹H and ¹³C NMR spectroscopic analyses, softening point measurement, and oxygen functional group content. During the acid and heat treatment, the reactions of polycondensation and polymerization occur. The heat-treatment modification of the pitches decreases the oxygen-containing groups and sulfur content and increases the content of aromatic structures. Chemical transformations and the removal of light components increase the softening point of the pitches. The results show that apricot stones tar with some additional modifications can be used as a raw material for the production of advanced carbon materials.     

Effectiveness of K2CO3 and Ni as catalysts in steam gasification

The catalytic steam gasification of 34 coals ranging from anthracite to peat was conducted in a thermobalance at 1023 K. When the difference in the reactivities of coals with and without catalyst is taken as a measure of the catalyst efficacy, that of K₂CO₃ was found to be extremely large and almost independent of coal rank. The effectiveness of Ni depends on the coal type to a great extent and it was very large for several low rank coals. SEM observation and EDAX analysis showed that the K₂CO₃ catalyst was finely dispersed over the char and such a good dispersion was common for all the coals examined. The dispersion state of Ni catalysts depends on the coal type, Ni catalysts were well dispersed over low rank coal chars which showed high reactivity in the Ni-catalysed gasification.     

松木成型燃料水蒸气气化反应特性

采用自制蒸气气化炉试验系统,以废弃松木屑为原料制作成型颗粒燃料,采用高温水蒸气气化,考察不同气化温度及气料比（S/B）对生物质水蒸气气化反应的影响,利用XRD射线衍射和傅里叶红外图谱分别分析生物质反应残留物及气化焦油,反应残留物的比表面积及空隙特性由BET多点法和BJH法测得。结果表明,蒸汽流量和反应温度有利于促进蒸汽重整、碳还原、CO的变换反应,当S/B由0.5增加到1.5时,温度为900℃,H₂体积分数由52.32%增长到67.3%;随温度升高（750~950℃,S/B=1）,松木颗粒的失重率由82.91%升高到91.27%,其微孔结构充分发展,平均孔直径由20.96 nm降低到3.76 nm,焦油中脂肪烃含量增加,芳香烃因发生开环反应使其含量降低,有益于降低气化气中焦油含量。     

生物质炭水蒸气气化制取富氢合成气

以生物质炭为原料在上吸式固定床气化炉中进行水蒸气气化制备富氢合成气,考察了不同原料、粒径和催化剂对生物质炭水蒸气气化影响。结果表明,不同类型炭气化结果存在较大差异,其中木片炭气化结果最优,其次是玉米芯炭和稻壳炭,秸秆炭气化结果最差,木片炭产氢率最大为222.8g/kg。粒径的改变主要影响炭转化率,炭转化率随着粒径的增加呈增加趋势。通过炭吸收方式负载催化剂为有效的方法,其中在相同钾盐质量分数下,KOH催化能力较优于K₂CO₃,且气化速率为未加催化剂条件下的两倍。炭转化率随着碱液浓度的增加而增加,但浓度过高会增加灰分含量从而不利于产氢率,玉米芯炭催化气化最高产氢率为197.8g/kg,在碱质量分数为6%下获得。     

Effects of promoters on biomass gasification using nickel/dolomite catalyst

Metallic nickel has been selected as a catalyst for biomass gasification because of its activity in biomass steam gasification and tar reduction. The effects of types of promoters such as platinum, cobalt, and iron on biomass gasification were evaluated. The area of interest was the effects of preparation methods, which were impregnation and coprecipitation. Catalyst preparation by the impregnation method showed superior performance. The conclusion can be drawn from the experiments that the platinum promoter enhanced the reforming reaction, iron promoted a water-gas shift reaction, and the cobalt promoter favored a methanation reaction. Moreover, the addition of noble metal reduced carbon deposition on Ni/dolomite.     

Hydrogen production by steam gasification of polypropylene with various nickel catalysts

Several nickel-based catalysts (Ni/Al₂O₃, Ni/MgO, Ni/CeO₂, Ni/ZSM-5, Ni-Al, Ni-Mg-Al and Ni/CeO₂/Al₂O₃) have been prepared and investigated for their suitability for the production of hydrogen from the two-stage pyrolysis–gasification of polypropylene. Experiments were conducted at a pyrolysis temperature of 500 °C and gasification temperature was kept constant at 800 °C with a catalyst/polypropylene ratio of 0.5. Fresh and reacted catalysts were characterized using a variety of methods, including, thermogravimetric analysis, scanning electron microscopy with energy dispersive X-ray spectrometry and transmission electron microscopy. The results showed that Ni/Al₂O₃ was deactivated by two types of carbons (monoatomic carbons and filamentous carbons) with a total coke deposition of 11.2 wt.% after reaction, although it showed to be an effective catalyst for the production of hydrogen with a production of 26.7 wt.% of the theoretical yield of hydrogen from that available in the polypropylene. The Ni/MgO catalyst showed low catalytic activity for H₂ production, which might be due to the formation of monoatomic carbons on the surface of the catalyst, blocking the access of gaseous products to the catalyst. Ni-Al (1:2) and Ni-Mg-Al (1:1:2) catalysts prepared by co-precipitation showed good catalytic abilities in terms of both H₂ production and prevention of coke formation. The ZSM-5 zeolite with higher surface area was also shown to be a good support for the nickel-based catalyst, since, the Ni/ZSM-5 catalyst showed a high rate of hydrogen production (44.3 wt.% of theoretical) from the pyrolysis–gasification of polypropylene.     

Highly efficient sulfur and coking resistance catalysts for tar gasification with steam

Ni-on-dolomite catalysts were found to be effective catalysts for coking resistance and promising sulfur tolerance for steam reforming of tar. Experiments were carried out in a fixed bed reactor at 730–850 °C with a short contact time (W/F: 0.55 g h/mol) and under atmospheric pressure. Toluene and naphthalene were selected as the model component of tar. The process variables such as calcination temperature, reaction temperature and the content of nickel had substantial influence on promising sulfur tolerance in catalytic tar removal by Ni/Dolomite catalysts. Results were compared with the Ni/Al₂O₃, Ni/SiO₂ as a representative of commercial catalysts. The novel 15%Ni/Dolomite almost gasified tar component even at 770 °C and the presence of 100 ppm H₂S in the feed. The poisoning effect of H₂S was discovered to be reversible. The suppression of the catalytic activity by adding H₂S was much lower for Ni/Dolomite than Ni/Al₂O₃. The TGA–DTA analysis of used catalysts revealed that Ni/Dolomite exhibited high resistance to coke deposition over those of the Ni/Al₂O₃, Ni/SiO₂.     

蒙古国典型煤种水蒸气气化性能及其动力学特性

利用固定床装置对来自蒙古国的巴嘎诺尔煤(BN)、纳赖呼煤(NL)、阿拉格陶盖煤(AT)和塔本陶勒盖煤(TT)进行程序升温水蒸气气化实验,考察了4种煤样气化合成气主要组分H_2,CO和CO_2的生成规律,着重研究了煤样气化反应动力学和合成气各组分生成动力学特性,并对2种动力学特性进行分析。研究发现,BN,NL和AT3种煤样气化合成气中H_2和CO_2主要在较低温区(900—1 050 K)生成,CO则在较高温区(>1 000 K)生成,而TT煤气化反应H_2,CO和CO_2均需要在较高温区(>1 000 K)生成。AT和TT煤水蒸气气化反应动力学所选取的模型与其气化合成气各组分生成动力学所选取的模型一致,分别为均相模型和缩核模型。BN和NL煤气化生成H_2,CO_2的生成动力学适宜采用均相模型,而CO的生成动力学适宜采用缩核模型,但这2种煤样的水蒸气气化反应动力学均可采用均相模型。     

Synthesis and properties of manganese oxide catalysts deposited on dolomite substrate

Physicochemical properties of Mn oxide catalysts deposited on a dolomite substrate have been studied using the techniques of scanning electron microscopy, atomic-emission, and X-ray phase analysis, as well as low-temperature physical adsorption-desorption of nitrogen. The catalytic activity and retarding ability of the obtained materials in the process of water purification from the dissolved iron compounds are estimated by the values of the degree of transferring Fe(II) into Fe(III) and the degree of retarding Fe(III). It is shown that the highest catalytic activity have the samples produced by the impregnation of the dolomite baked at 800°C with the solution of 0.4–1.0 M manganese(II) chloride.     

Oxidation of the sulphurised dolomite produced in the desulphurisation of the gasification gases

Dolomite reacts with H₂S to produce calcium sulphide and has been broadly investigated as a desulphurisation agent due to its low-cost and favourable properties.Because CaS reacts with water or water vapour in the environment to regenerate hydrogen sulphide and, therefore, disposal is problematic and the chemical cannot be uses as a landfill material. One of the methods used to make this material inert is oxidation to convert calcium sulphide into calcium sulphate or calcium oxide.In our study, tests were carried out using dolomite from Granada, Spain, that was previously calcined and sulphurised at high temperature with a gas similar to that produced in gasification facilities. To approximate real-scale results, a relatively large amount of substance was used for each sample (100–150 g) and the samples were used in a fixed-bed position.The influence of different conditions, such as grain size, composition of the oxidation gas, gas velocity, bed length and temperature, was them investigated. The final solid products were characterised by X-ray diffraction and chemical analysis and the CO₂, SO₂, H₂S and COS concentrations in the gases produced during oxidation were analysed by gas chromatography.The results showed that the most influential factor was grain size and that the best oxidant was O₂ mixed with nitrogen.The presence of water vapour increases the residual concentration of CaS in the end product, but increased the CaO contentThe higher the oxygen concentration and the higher the gas velocity, the lower the residual content of CaS. CO₂ used alone oxidises CaS to produce SO₂ and COS, but at very low rates. It also produces some CS₂. Water vapour used alone can also oxidise the CaS to produce H₂S and SO₂ but also at very low velocity.At higher oxidation temperature, between 700°C and 850 °C, lesser residual CaS is obtained in the oxidised product.