Effect of catalysts in the quality of syngas and by-products obtained by co-gasification of coal and wastes. 2: Heavy metals, sulphur and halogen compounds abatement

This paper analyses the formation of sulphur and halogens compounds during co-gasification of low grade coals with different types of wastes that include: pine, petcoke and polyethylene (PE) with the aim of taking profit of waste energy value with the smallest possible impact on the environment. The influence of different types of catalysts or sorbents was studied: calcined dolomite, dolomite enriched with nickel, olivine, nickel and magnesium oxides, zinc oxide and cobalt and molybdenum oxides. The presence of dolomite led to the lowest HCl, HF and H₂S concentrations in the syngas produced. ZnO also gave rise to significant decrease in H₂S concentration, though higher concentrations were obtained than those with dolomite. It was found that when catalysts or sorbents were used, a significant fraction of sulphur, halogens and heavy metals were trapped in the solid residue left behind in the bed and cyclone. Higher temperatures increased the volatility of some metals and sulphur. Leachability assays of solids showed that small quantities of and Cl⁻ could be released and most metals were not leachable, although the use of dolomite slightly increased metals leachability, because of the higher alkaline nature of residual solids produced.     

Experimental comparison of biomass chars with other catalysts for tar reduction

In this paper the potential of using biomass char as a catalyst for tar reduction is discussed. Biomass char is compared with other known catalysts used for tar conversion. Model tar compounds, phenol and naphthalene, were used to test char and other catalysts. Tests were carried out in a fixed bed tubular reactor at a temperature range of 700–900 °C under atmospheric pressure and a gas residence time in the empty catalyst bed of 0.3 s. Biomass chars are compared with calcined dolomite, olivine, used fluid catalytic cracking (FCC) catalyst, biomass ash and commercial nickel catalyst. The conversion of naphthalene and phenol over these catalysts was carried out in the atmosphere of CO₂ and steam. At 900 °C, the conversion of phenol was dominated by thermal cracking whereas naphthalene conversion was dominated by catalytic conversion. Biomass chars gave the highest naphthalene conversion among the low cost catalysts used for tar removal. Further, biomass char is produced continuously during the gasification process, while the other catalysts undergo deactivation. A simple first order kinetic model is used to describe the naphthalene conversion with biomass char.     

Isoparaffin production by aqueous phase processing of sorbitol over the Ni/HZSM-5 catalysts: Effect of the calcination temperature of the catalyst

Ni/HZSM-5 catalysts calcined at different temperatures were used in the isoparaffin production by aqueous phase processing of sorbitol and characterized by N₂ physical adsorption, temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD) and Raman techniques. The effect of calcination temperature of the catalysts on the catalytic performance for the reaction was investigated. The activity test results indicated that the maximal i-C₆H₁₄ selectivity of 45.4% and the total i-C₆H₁₄ and i-C₅H₁₂ yield of 32.3% were obtained over the catalyst calcined at 500 °C, which exhibited the optimum surface area and pore structure with 100% of the reducibility of Ni species on the surface of HZSM-5. In addition, the amount and the strength distribution of acidic surface sites of the catalyst decreased with the increase of calcination temperature at 500 °C above. All these factors result in an increase in the formation of isoparaffin.     

Effect of calcination atmosphere and temperature on γ-Al2O3 supported cobalt Fischer-Tropsch catalysts

The effect of calcination temperature and atmosphere on the properties of γ-Al₂O₃ supported cobalt Fischer-Tropsch catalysts has been investigated. One common precursor for all the catalysts was prepared by incipient wetness impregnation of γ-Al₂O₃ with an aqueous solution of cobalt nitrate hexahydrate. It was subjected to four different calcination atmospheres (air/50% steam: 30 mL/min, air: 30 mL/min, air: 50 mL/min, N₂: 30 mL/min) and eight different calcination temperatures (range: 473–723 K), making the total number of samples 32. Both the post calcination nitrogen content and the cobalt dispersion were measured. The results demonstrated that in order to maximise the cobalt dispersion, it is necessary to use low calcination temperatures and remove the precursor decomposition products (NO, NO₂, H₂O) efficiently. The Fischer-Tropsch synthesis performance of two catalysts calcined at the same temperature, but at different air flow rates was evaluated. No significant effect of the air flow rate was found on the turnover frequency or C₅₊ selectivity, but a high flow rate resulted in 30% higher activity per gram catalyst.     

白云石对稻草水蒸气气化特性的影响

以稻草为生物质原料,水蒸气为介质,白云石为催化剂,在固定床气化炉中进行生物质水蒸气气化等反应,考察了白云石粒径(5~20mm)、白云石床高(550~1 000mm)和煅烧白云石等对生物质水蒸气气化特性的影响。结果表明,在气化炉中装入白云石,有助于生物质水蒸气气化、催化裂解、二氧化碳重整和水蒸气重整等反应进行。白云石粒径减小、白云石床高和煅烧白云石含量增加,有利于产气中氢体积分数的增加。当白云石粒径为5~10mm、白云石床高为1 000mm和煅烧白云石为100%时,产气中氢体积分数最大为53.18%,产氢率最大为0.92m³/kg,产气率最大为1.72m³/kg,气化效率最大为99.93%,水蒸气近似分解率最大为51.28%。     

焙烧温度对橄榄石催化甲苯裂解性能的影响

以橄榄石为催化剂,通过N2物理吸附、XRD、H₂-TPR和TEM等手段研究了焙烧温度对催化剂的结构、物相、还原性能以及甲苯裂解反应活性的影响。结果表明,焙烧温度对催化剂结构和活性影响显著,低温焙烧时主要存在Mg₂SiO₄和Fe₂O₃的晶相衍射峰,随着焙烧温度的升高,Fe₂O₃的晶相衍射峰逐渐消失,随之出现了非常明显的 (Fe, Mg)SiO₃的衍射峰。选择适中的焙烧温度可以增加表面上可还原Fe₂O₃的量,从而拥有较高的甲苯裂解活性位。在实验考察范围内,900℃焙烧的橄榄石表现了最高的甲苯裂解活性。TG结果表明,该温度焙烧的橄榄石具有较好的抗积炭性能。     

The effect of the calcination temperature of LaFeO3 precursors on the properties and catalytic activity of perovskite in methane oxidation

In the synthesis of perovskite-type LaFeO₃ oxides iron and lanthanum nitrates were used as a precursors. The nitrates were dissolved in water, evaporated, crushed and calcined in temperature range of 650–850?°C. The obtained perovskites were applied as an active layer on monolithic catalysts for the oxidation of methane. The increase in the calcination temperature of the perovskite precursors from 650° to 850°C results in a reduction in the surface area of the powders from 10.1 to 4.2?m²/g. XRD studies revealed that calcination at 800–850?°C caused the formation of an almost homogeneous LaFeO₃ perovskite phase. A decrease in the La/Fe surface ratio from 12 to 5.2 with the rise in calcination temperature from 650° to 800°C was detected by XPS. EDX results confirmed that at 750–850?°C, the La/Fe ratio in the perovskite layer is close to the stoichiometric and amount to 1.01–1.03. The highest activity in methane oxidation was achieved when the LaFeO₃ perovskite was calcined at 700?°C. A further slight increase in the activity was noticed after H₂ treatment. As the calcination temperature of the perovskites is increased, the catalyst activity decreases due to a reduction in the specific surface area, despite the more complete LaFeO₃ perovskite phase formation.     

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.     

Biomass to hydrogen via catalytic steam reforming of bio-oil over Ni-supported alumina catalysts

Production of hydrogen (H₂) from catalytic steam reforming of bio-oil was investigated in a fixed bed tubular flow reactor over nickel/alumina (Ni/Al₂O₃) supported catalysts at different conditions. The features of the steam reforming of bio-oil, including the effects of metal content, reaction temperature, W_bHSV (defined as the mass flow rate of bio-oil per mass of catalyst) and S/C ratio (the molar ratio of steam to carbon fed) on the hydrogen yield were investigated. Carbon conversion (moles of carbon in the outlet gases to moles of the carbon feed) was also studied, and the outlet gas distributions were obtained. It was revealed that the Al₂O₃ with 14.1% Ni content gave the highest yield of hydrogen (73%) among the catalysts tested, and the best carbon conversion was 79% under the steam reforming conditions of S/C = 5, W_bHSV = 13 1/h and temperature = 950 °C. The H₂ yield increased with increasing temperature and decreasing W_bHSV; whereas the effect of the S/C ratio was less pronounced. In the S/C ratio range of 1 to 2, the hydrogen yield was slightly increased, but when the S/C ratio was increased further, it did not have an effect on the H₂ production yield.     

Pyrolysis of palm oil wastes for enhanced production of hydrogen rich gases

A study on pyrolysis of palm oil wastes in a countercurrent fixed bed was carried out, aiming to characterize the hydrogen rich gas products in view of enhanced energy recycling. The effects of temperature, residence time and catalyst adding on the yields and distribution of hydrogen rich gas products were investigated. The main gas species generated, as identified by Micro-GC, were H₂, CO, CO₂, CH₄ and trace amounts of C₂H₄ and C₂H₆. With temperature increasing from 500 °C to 900 °C, the total gas yield was enhanced greatly and reached the maximum value (∼ 70 wt.%, on the raw biomass sample basis) at 900 °C with big portions of H₂ (33.49 vol.%) and CO (41.33 vol.%). Residence time showed a significant influence on the upgrading of H₂ and CO₂ yields. The optimum residence time (9 s) was found to get a higher H₂ yield (10.40 g/kg (daf)). The effect of adding chemicals (Ni, γ-Al₂O₃, Fe₂O₃ and La/Al₂O₃, etc.) on gas product yield was investigated and adding Ni showed the greatest catalytic effect with the maximum H₂ yield achieved at 29.78 g/kg (daf).     

Promoting effect of Ru on Ni/Mg(Al)O catalysts in DSS-like operation of CH4 steam reforming

Effects of Ru addition on the activity and the sustainability of Ni/Mg(Al)O catalysts were investigated in the daily start-up and shut-down (DSS) operation of the steam reforming of CH₄. Mg_2.5(Ni_0.5)–Al hydrotalcite was prepared by coprecipitation and calcined to form Mg_2.5(Al,Ni_0.5)O periclase. When the powders of the periclase were dipped in an aqueous solution of Ru(III) nitrate, the hydrotalcite was reconstituted on the surface of Mg_2.5(Al,Ni_0.5)O particles, resulting in the formation of highly dispersed Ru/Ni bimetal supported catalysts after the calcination, followed by the reduction. The addition of Ru on Ni caused a decrease in the reduction temperature of Ni and an increase in the amount of H₂ uptake on the Ni over the catalyst. Formation of Ru–Ni alloy or strong interaction between Ru and Ni was also suggested. When Ru–Ni_0.5/Mg_2.5(Al)O catalysts were tested in the DSS-like operation under steam purging, the deactivation due to the oxidation of Ni metal by steam was effectively suppressed by hydrogen spillover. Moreover, only 0.05 wt% of Ru loading was enough to effectively suppress the deactivation during the DSS-like operation.     

Visible light-irradiated degradation of alachlor on Fe-TiO<Subscript>2</Subscript> with assistance of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

0.1 Fe/Ti mole ratio of Fe-TiO₂ catalysts were synthesized via solvothermal method and calcined at various temperatures: 300, 400, and 500 °C. The calcined catalysts were characterized by XRD, N₂-adsorption-desorption, UV-DRS, XRF, and Zeta potential and tested for photocatalytic degradation of alachlor under visible light. The calcined catalysts consisted only of anatase phase. The BET specific surface area decreased with the calcination temperatures. The doping Fe ion induced a red shift of absorption capacity from UV to the visible region. The Fe-TiO₂ calcined at 400 °C showed the highest photocatalytic activity on degradation of alachlor with assistance of 30 mM H₂O₂ at pH 3 under visible light irradiation. The degradation fitted well with Langmuir-Hinshelwood model that gave adsorption coefficient and the reaction rate constant of 0.683 L mg⁻¹ and 0.136 mg/L·min, respectively.     

Effect of calcination atmospheres on the catalytic performance of nano-CeO<Subscript>2</Subscript> in direct synthesis of DMC from methanol and CO<Subscript>2</Subscript>

Nano-CeO₂ was prepared through the calcination of Ce(OH)₃ precursor in different atmospheres (H₂, Ar, air, O₂), which was prepared by a hydrothermal method, and then used as catalysts in the direct synthesis of dimethyl carbonate (DMC) from methanol and CO₂. The results indicated that the catalyst calcined in O₂ (CeO₂-O₂) showed an optimum catalytic performance, and the yield of DMC reached to 1.304 mmol/mmol_cat. In addition, reaction temperature and weight of catalyst were optimized. Based on characterizations of the catalysts, the ratio of Ce(IV)/Ce(III) and Lewis acid-base property of nano-CeO₂ catalyst could be adjusted through different calcination atmosphere treatment. It was determined that the higher activity of CeO₂-O₂ catalyst is mainly attributed to its higher ratio of Ce(IV)/Ce(III) as well as abundant and moderate intensity Lewis acid base sites.     

A novel Ni-Mg-Al-CaO catalyst with the dual functions of catalysis and CO2 sorption for H2 production from the pyrolysis-gasification of polypropylene

A novel Ni-Mg-Al-CaO catalyst/sorbent has been prepared by integration of the catalytic and CO₂ absorbing properties of the material to maximise the production of hydrogen. The prepared catalyst was tested for hydrogen production from the pyrolysis-gasification of polypropylene by using a two-stage fixed-bed reaction system. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDXS) were used to characterize the prepared Ni-Mg-Al-CaO catalyst/sorbent. Ni-Mg-Al-CaO and calcined dolomite showed a stable carbonation conversion after several cycles of carbonation/calcination, while CaO showed a certain degree of decay. The calcined dolomite showed low efficiency for hydrogen production from pyrolysis-gasification of polypropylene. Increasing the gasification temperature resulted in a decrease of H₂/CO ratio for the Ni-Mg-Al catalyst mixed with sand; however, a stable H₂/CO ratio (around 3.0) was obtained for the Ni-Mg-Al-CaO catalyst. An increased Ni-Mg-Al-CaO catalyst/polypropylene ratio promoted the production of hydrogen from the pyrolysis-gasification of polypropylene. Approximately 70 wt.% of the potential H₂ production was obtained, when the Ni-Mg-Al-CaO catalyst/polypropylene ratio and gasification temperature were 5 and 800 °C, respectively.     

CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts prepared via a route of solid-state reaction

Cu/ZnO/ZrO₂ catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO₂ hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N₂ adsorption, XRD, TEM, N₂O titration and H₂-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO₂ catalysts.     

Recent advances in catalysts for hot-gas removal of tar and NH3 from biomass gasification

Biomass gasification produces a low to medium-BTU product gas (or syngas) containing primarily CO₂, H₂, CO, CH₄ and (C₂ + C₃), as well as some contaminants such as tars, NH₃, H₂S and SO₂. In order to achieve better efficiencies of the syngas applications, these contaminants must be removed before the syngas is used for internal combustion, gas engines, and in particular for fuel cells and methanol synthesis. Compared with the wet scrubbing technology, hot-gas cleanup technology to remove tar, ammonia and other contaminants at the “hot” state is more advantageous with respect to energy efficiencies. This paper provides an overview on recent advances in catalysts for hot-gas removal of tar and ammonia from biomass gasification. The review focuses on the recent development and applications of dolomite catalysts, iron-based catalysts, nickel and other metal supported catalysts, and the novel carbon-supported catalysts for hot-gas tar removal and ammonia decomposition. The barriers in applications of hot-gas cleanup processes and catalysts for full-scale biomass gasification, and areas for future research, are also discussed.     

Cyclic calcination/carbonation looping of dolomite modified with acetic acid for CO2 capture

The dolomite modified with acetic acid solution was proposed as a CO₂ sorbent for calcination/carbonation cycles. The carbonation conversions for modified and original dolomites in a twin fixed-bed reactor system with increasing the numbers of cycles were investigated. The carbonation temperature in the range of 630 °C–700 °C is beneficial to the carbonation reaction of modified dolomite. The carbonation conversion for modified dolomite is significantly higher than that for original sorbent at the same reaction conditions with increasing numbers of reaction cycles. The modified dolomite exhibits a carbonation conversion of 0.6 after 20 cycles, while the unmodified sorbent shows a conversion of 0.26 at the same reaction conditions, which is calcined at 920 °C and carbonated at 650 °C. At the high calcination temperature over 920 °C modified dolomite can maintain much higher conversion than unmodified sorbent. The mean grain size of CaO derived from modified dolomite is smaller than that from original sorbent with increasing numbers of reaction cycles. The calcined modified dolomite possesses greater surface area and pore volume than calcined original sorbent during the multiple cycles. The pore volume and pore area distributions for calcined modified dolomite are also superior to those for calcined unmodified sorbent during the looping cycle. The modified dolomite is proved as a new and promising type of regenerable CO₂ sorbent for industrial applications.     

Hydrogenation of Levulinic Acid Using Formic Acid as a Hydrogen Source over Ni/SiO2 Catalysts

Several Ni/SiO₂ catalysts were developed for the hydrogenation of levulinic acid using formic acid as the hydrogen source. The catalysts were prepared by a variety of methods including impregnation, co‐precipitation, deposition‐precipitation, and citric acid assisted impregnation combustion. The morphological properties were investigated by XRD, N₂ sorption, HRTEM, and H₂ pulse chemisorption measurements. XRD patterns of the calcined material revealed the presence of NiO particles, while calcination in an inert atmosphere produced Ni particles through in situ reduction of NiO. The reaction proceeded without external H₂ flow using formic acid as hydrogen source. The Ni/SiO₂ catalyst prepared by the citric acid assisted method and calcined in inert gas flow was the most efficient for the hydrogenation of levulinic acid without external H₂ flow. The high catalytic performance was attributed to the high dispersion of cheap and earth‐abundant Ni nanoparticles and optimal porosity.     

Catalytic Synthesis of Thiophene from the Reaction of Furan and Hydrogen Sulfide

The catalysts were prepared from pseudo-boehmite mixed with dilute nitric acid and calcined at different temperatures. The vapour-phase reaction of furan and hydrogen sulfide was performed in a fixed-bed flow in the presence of catalyst. The catalysts were characterized by XRD, N₂ adsorption, FT-IR techniques. The Al₂O₃ calcined at 550 °C has large surface areas which resulted in high yield of thiophene under the conditions: at atmosphere, reaction temperature 500 °C, the ratio of H₂S to Furan about 10 (mol) and LHSV 0.2 h⁻¹. The reaction mechanism was proposed for the synthesis of thiophene from furan and hydrogen sulfide over Al₂O₃.     

Effect of calcination treatment of zirconia on W/ZrO2 catalysts for transesterification

In this present study, the nanocrystalline ZrO₂ particles synthesized by the solvothermal method were calcined in reductive (H₂), inert (N₂) and oxidative (O₂ and air) atmospheres prior to impregnation with tungsten (W) in order to produce the W/ZrO₂ (WZ) catalysts. Based on the ESR measurement, it revealed that only the ZrO₂ samples calcined in H₂ and N₂ exhibited the F-center (single charged oxygen vacancy) at g = 2.003. None of Zr³⁺ defect was detected for all calcined ZrO₂ samples. After impregnation with tungsten, the WZ catalysts were also characterized. It was present as the polycrystal, which can be seen by the selected area electron distribution (SAED). However, the presence of Zr³⁺ defect was evident in all WZ catalysts, while the F-center was absent. The highest Zr³⁺ intensity detected in the WZ catalyst using ZrO₂ under H₂ calcination atmosphere can be attributed to the transformation of F-center to Zr³⁺ defect. It revealed that the WZ-H₂ catalyst exhibited the highest conversion under transesterification of triacetin and methanol among other WZ catalysts. This can be attributed to the high surface acidity, which was probably induced by large amounts of Zr³⁺ defect.