Performance studies of various cracking catalysts in the conversion of canola oil to fuels and chemicals in a fluidized-bed reactor

Studies were conducted at atmospheric pressure at temperatures in the range of 400–500°C and fluidizing gas velocities in the range of 0.37–0.58 m/min (at standard temperature and pressure) to evaluate the performance of various cracking catalysts for canola oil conversion in a fluidized-bed reactor. Results show that canola oil conversions were high (in the range of 78–98 wt%) and increased with an increase in both temperature and catalyst acid site density and with a decrease in fluidizing gas velocity. The product distribution mostly consisted of hydrocarbon gases in the C₁–C₅ range, a mixture of aromatic and aliphatic hydrocarbons in the organic liquid product (OLP) and coke. The yields of C₄ hydrocarbons, aromatic hydrocarbons and C₂–C₄ olefins increased with both temperature and catalyst acid site density but decreased with an increase in fluidizing gas velocity. In contrast, the yields of aliphatic and C₅ hydrocarbons followed trends completely opposite to those of C₂–C₄ olefins and aromatic hydrocarbons. A comparison of performance of the catalysts in a fluidized-bed reactor with earlier work in a fixed-bed reactor showed that selectivities for formation of both C₅ and iso-C₄ hydrocarbons in a fluidized-bed reactor were extremely high (maximum of 68.7 and 18 wt% of the gas product) as compared to maximum selectivities of 18 and 16 wt% of the gas product, respectively, in the fixed-bed reactor. Also, selectivity for formation of gas products was higher for runs with the fluidized-bed reactor than for those with the fixed-bed reactor, whereas the selectivity for OLP was higher with the fixed-bed reactor. Furthermore, both temperature and catalyst determined whether the fractions of aromatic hydrocarbons in the OLP were higher in the fluidized-bed or fixed-bed reactor.     

Steam gasification of an australian bituminous coal in a fluidized bed

To produce low calorific value gas, Australian coal has been gasified with air and steam in a fluidized bed reactor (0.1 m-I.Dx1.6 m-high) at atmospheric pressure. The effects of fluidizing gas velocity (2–5 U_f/U_mf), reaction temperature (750–900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63–1.26) on gas composition, gas yield, gas calorific value of the product gas and carbon conversion have been determined. The calorific value and yield of the product gas, cold gas efficiency, and carbon conversion increase with increasing fluidization gas velocity and reaction temperature. With increasing air/coal ratio, carbon conversion, cold gas efficiency and yield of the product gas increase, but the calorific value of the product gas decreases. When steam/coal ratio is increased, cold gas efficiency, yield and calorific value of the product gas increase, but carbon conversion is little changed. Unburned carbon fraction of cyclone fine decreases with increasing fluidization gas velocity, reaction temperature and air/coal ratio, but is nearly constant with increasing steam/coal ratio. Overall carbon conversion decreases with increasing fluidization velocity and air/ coal ratio, but increases with increasing reaction temperature. The particle entrainment rate increases with increasing fluidization velocity, but decreases with increasing reaction temperature. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Experimental study of CO2 hydrate formation in porous media with different particle sizes

To investigate the effect of the particle size of porous media on CO₂ hydrate formation, the formation experiments of CO₂ hydrate in porous media with three particle sizes were performed. Three kinds of porous media with mean particle diameters of 2.30 μm (clay level), 5.54 μm (silty sand level), and 229.90 μm (fine sand level) were used in the experiments. In the experiments, the formation temperature range was 277.15–281.15 K and the initial formation pressure range was 3.4–4.8 MPa. The final gas consumption increases with the increase in the initial pressure and the decrease in the formation temperature. The hydrate formation at the initial formation pressure of 4.8 MPa in 229.90 μm porous media is much slower than that at the lower formation pressure and displays multistage. In the experiments with different formation temperatures, the gas consumption rate at the temperature of 279.15 K is the lowest. In 2.30 and 5.54 μm porous media, the hydrate formation rates are similar and faster than those in 229.90 μm porous media. The particle size of the porous media does not affect the final gas consumption. The gas consumption rate per mol of water and the final water conversion increase with the decrease in the water content. The induction time in 5.54 μm porous media is longer than that in 2.30 and 229.90 μm porous media, and the presence of NaCl significantly increases the induction time and decreases the final conversion of water to hydrate.     

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

This paper describes the influence of gas pressure on the conversion of O₂ to O₃ and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O₂ to O₃ is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.     

CFD study on partial oxidation of methane in fixed-bed reactor

Partial oxidation of methane (POM) is a preferred method for synthesis gas, which usually occurs in fixed bed reactors. In this paper, the discrete element method (DEM) is used to reconstruct the structure of a reactor bed via simulating the process of filling the reactor with catalyst. The particle resolved CFD physical model with the detailed micro-kinetcis of the POM reaction was established to study the interaction among reactant flow, heat and mass transfer, and reaction in the fixed bed. The gas composition and temperature distribution in the reactor were obtained based on the simulation results. The effects of the space velocity and the reaction temperature on the CH₄ conversion, catalyst selectivity, and catalyst surface coke formation were analyzed. The simulation results show that the temperature hot spots of the catalyst in the bed occur at the inlet and the temperature increases further near the wall. With the increase in space velocity, the conversion rate of CH₄ decreases gradually, and the selectivity does not change significantly. As the temperature increases, the conversion rate of CH₄ gradually increases and the selectivity decreases. The risk of coke formation on the catalyst surface rises axially and the C species concentration is relatively higher near the outlet. Appropriately increasing the gas velocity and increasing the temperature helps to reduce the surface coke accumulation of the catalyst.     

城市污泥流化床中低温空气气化及重金属迁移特性

利用自行搭建的流化床热态实验装置，系统研究了污泥的中低温气化及重金属迁移特性。研究表明，对冷煤气效率和碳转化率影响最大的是气化温度，其次是空气当量比，而一二次风配比和流化数影响较弱。污泥中低温气化的焦油产率较之高温气化明显增加。随着二次风占比和空气当量比的提高，焦油产率单调下降。气化温度由600℃升至850℃，冷煤气效率和碳转化率均呈升高趋势；空气当量比由0.2升至0.4，冷煤气效率呈先升高后下降的趋势，在0.3时达到最大值，而碳转化率则呈单调升高趋势。随着气化温度的升高，污泥中重金属转移至产气、焦油及飞灰的迁移率升高。随着空气当量比的升高，Ni、Cu的迁移率降低，Cr升高，Cd、Zn、As和Pb等其他重金属的迁移率几乎不变。     

Modeling of naphtha pyrolysis in swaged coils

Pyrolysis of naphtha in uniform diameter and swaged reactors has been modeled. Pyrolysis and coking models available for naphtha cracking were used to calculate the reactor profiles of pressure, process gas temperature, tube metal temperature, conversion and the product yields. For the swaged coil, not only was the inlet pressure and maximum tube wall temperature in the clean condition lower than for a uniform diameter reactor, but the increase in the inlet pressure and maximum tube wall temperature due to coke deposition was also less. Swaging the reactor can result in a significant increase in the run length between decokings.     

Effect of rank,temperatures and inherent minerals on nitrogen emissions during coal pyrolysis in a fixed bed reactor

Pyrolysis of 11 coals with carbon contents of 77–93 wt.% (daf) and corresponding demineralized samples has been studied in a fixed bed quartz reactor with a heating rate of 20 K/min to examine rank, demineralization, temperature and inherent mineral species dependences of nitrogen distribution. Nitrogen mass balances fall within 92.5–104.6%. The results indicate that the chars derived from the coals with higher rank show larger nitrogen retention. Demineralization suppresses volatile nitrogen emission during coal pyrolysis, especially for low rank coals. Coal-N conversion to tar-N reaches the asymptotic values at 600 °C. HCN yields are lower than NH₃ yields during coal pyrolysis. The trends in HCN and NH₃ emissions are very similar and the yields reach the asymptotic value at about 1200 °C. N₂ starts emitting at 600 °C, and as the temperature increases the conversion increases linearly with a corresponding reverse change of char-N. With the catalysts added, N₂ formation is prompted with the sequence of Fe>Ca>K>Ti≫Na≫Si≈Al, meanwhile, char-N decreases correspondingly. Fe, Ca, K, Na, Si and Al increase coal-N conversion to NH₃ with the sequence of Fe>Ca>K≈Na≫Si≈Al in the pyrolysis. Na addition prompts HCN formation; however, the presence of Ti and Ca decrease the HCN yields with small value. The other catalysts have no notable influence on HCN emission in the pyrolysis. Demineralization and Ti addition increase coal-N conversion to tar-N slightly whereas K, Ca, Mg, Na, Si and Al additions decrease tar-N yield weakly, other catalysts hardly influence tar nitrogen emission. N₂ emits mainly from char-N with slight contribution of volatile nitrogen. The mechanism of different N-containing species formation and catalysts influence in the pyrolysis is also discussed in the paper.     

Experiment and mathematical modeling of a bench-scale circulating fluidized bed gasifier

The gasification of two different coals and chars with CO₂ and CO₂/O₂ mixture in a 48-mm-i.d. circulating fluidized bed (CFB) gasifier is investigated. The effects of operation condition on gas composition, carbon conversion and gasification efficiency were studied. A simple CFB coal gasification district mathematical model has been set up. The effects of coal type and CFB operating conditions on CFB coal gasification are discussed based on the CFB gasification test and model simulation. The main operation parameters in CFB gasification system are coal type, gas superficial velocity, circulating rate of solids and reaction temperature. It is found that CO concentration and carbon conversion increase with increasing solids circulating rate and decreasing gas velocity due to the increase in gas residence time and solids holdup in the CFB. The carbon conversion increases with increasing temperature and O₂ concentration in the inlet gas. The experimental results prove that the CFB gasifier works well for high volatile, high reactivity coal.     

Production of H2 and medium Btu gas via pyrolysis of lignins in a fixed-bed reactor

Lignins are generally used as a low-grade fuel in the pulp and paper industry. In this work, pyrolysis of Alcell and Kraft lignins obtained from Alcell process and Westvaco, respectively, was carried out in a fixed-bed reactor to produce hydrogen and gas with medium heating value. The effects of carrier gas (helium) flow rate (13.4–33 ml/min/g of lignin), heating rate (5–15°C/min) and temperature (350–800°C) on the lignin conversion, product composition, and gas yield have been studied. The gaseous products mainly consisted of H₂, CO, CO₂, CH₄ and C₂₊. The carrier gas flow rate did not have any significant effect on the conversion. However, at 800°C and at a constant heating rate of 15°C/min with increase in carrier gas flow rate from 13.4 to 33 ml/min/g of lignin, the volume of product gas decreased from 820 to 736 ml/g for Kraft and from 820 to 762 ml/g for Alcell lignin and the production of hydrogen increased from 43 to 66 mol% for Kraft lignin and from 31 to 46 mol% for Alcell lignin. At a lower carrier gas flow rate of 13.4 ml/min/g of lignin, the gas had a maximum heating value of 437 Btu/scf. At this flow rate and at 800°C, with increase in heating rate from 5 to 15°C/min both lignin conversion and hydrogen production increased from 56 to 65 wt.% and 24 to 31 mol%, respectively, for Alcell lignin. With decrease in temperature from 800°C to 350°C, the conversion of Alcell and Kraft lignins were decreased from 65 to 28 wt.% and from 57 to 25 wt.%, respectively. Also, with decrease in temperature, production of hydrogen was decreased. Maximum heating value of gas (491 Btu/scf) was obtained at 450°C for Alcell lignin.     

Thermodynamic analysis of glycerol dry reforming for hydrogen and synthesis gas production

A thermodynamic analysis of glycerol dry reforming has been performed by the Gibbs free energy minimization method as a function of CO₂ to glycerol ratio, temperature, and pressure. Hydrogen and synthesis gas can be produced by the glycerol dry reforming. The carbon neutral glycerol reforming with greenhouse gas CO₂ could convert CO₂ into synthesis gas or high value-added inner carbon. Atmospheric pressure is preferable for this system and glycerol conversion keeps 100%. Various of H₂/CO ratios can be generated from a flexible operational range. Optimized conditions for hydrogen production are temperatures over 975 K and CO₂ to glycerol ratios of 0-1. With a temperature of 1000 K and CO₂ to glycerol ratio of 1, the production of synthesis gas reaches a maximum, e.g., 6.4 mol of synthesis gas (H₂/CO = 1:1) can be produced per mole of glycerol with CO₂ conversion of 33%.     

Decomposition of tetrafluorocarbon in dielectric barrier discharge reactor

The decomposition of CF₄ in dielectric barrier discharge at atmospheric pressure was examined. The effect of O₂ contents, N₂ contents, and total flow rate on CF4 conversion was experimentally investigated. The maximum conversion of CF₄ was about 87% at 5 kV, 15 kHz for the feed gas stream containing 5 sccm CF₄, 7.5 sccm O₂, and 187.5 sccm Ar. CO, CO₂, and COF₂ were the main products when O₂ was used as the additive gas. NO_x was produced when N2 was used as the additive gas. The conversion of CF₄ was increased while the applied voltage and the residence time were increased. When nitrogen was added to argon as the diluent gas, the conversion of CF₄ was decreased with the increase of the nitrogen content.     

Glycerol dehydroxylation in hydrogen on a Raney cobalt catalyst

Glycerol dehydroxylation on a Raney cobalt catalyst in hydrogen was studied. It was found that with an increase in temperature from 140 to 200°C at a hydrogen pressure of 30 MPa, glycerol conversion increases from 14 to 97%. The glycerol is completely converted in 20 h, and the yield of 1,2-propanediol is 40%. With an increase in H₂ pressure from 3 to 8 MPa, the glycerol conversion increases from 34 to 95%, and the yield of 1,2-propanediol increases from 18 to 38%. The maximum yield of 1,2-propanediol is 44% at 200°C and a hydrogen pressure of 3 MPa. The glycerol dehydroxylation in hydrogen on heterogeneous catalysts can be considered a promising method of glycerol conversion when glycerol is a byproduct of biodiesel manufacture from vegetable oil and animal fats.     

Experimental study on sawdust air gasification in an entrained-flow reactor

Experiments were performed in an entrained-flow reactor to better understand the processes involved in biomass air gasification. Effects of the reaction temperatures (700 °C, 800 °C, 900 °C and 1000 °C), residence time and the equivalence ratio in the range of 0.22-0.34 on the gasification process were investigated. The behavior of biomass gasification was discussed in terms of composition of produced gas. Four parameters, i.e. the low heating value, fuel gas production, carbon conversion and cold gas efficiency were used to evaluate the gasification. The results show that CO, CO₂ and H₂ are the main gasification products, while hydrocarbons (CH₄ and C₂H₄) are the minor ones. With the increase of the reaction temperature, the concentration of CO decreases, while the concentrations of CO₂ and H₂ increase. The concentrations of CH₄ and C₂H₄ reach their maximum value when the reaction temperature is 800 °C. The optimal reaction temperature is considered to be 800 °C and the optimal equivalence ratio is 0.28 in that the low heating value of the produced gas, carbon conversion and cold gas efficiency achieve their maximum values. The kinetic parameters of sawdust air gasification are calculated basing on the Arrhenius correlation.     

A kinetic study on the conversion of methane to higher hydrocarbons in a radio-frequency discharge

This study investigated methane conversion with direct current discharge at low pressure in a radio frequency. The main gaseous products of the reaction were ethane, ethylene, acetylene and propane. This study was concentrated on the influence of discharge conditions on the conversion of methane to higher hydrocarbons. Reaction temperature, electron density and mean residence time were calculated from experimental data and mathematical relations. The maximum conversion of the methane was about 45% with the pure methane as a reactant. Ethane was the main product when the reaction occurred in the glow discharge. Ethane selectivity decreased with the increase of the gas temperature. The kinetics of reactions was also analyzed from possible reaction equations and various rate constant data. Consequently, the dissociation constant and the density of radicals could be obtained at any experimental conditions.     

Reaction path of ethanol and acetic acid steam reforming over Ni–Zn–Al catalysts. Flow reactor studies

Ethanol steam reforming (ESR) experiments have been performed in dilute conditions over a NiZnAl catalyst. Experiments have been performed by varying catalyst surface area, reactants flow rate, contact time, reactants feed composition and temperature. Acetic acid steam reforming experiments have also been performed. The data suggest that adsorbed acetaldehyde and acetic acid play an important role as intermediates of ESR, while also acetone may have a role in the ESR reaction. The key step for high hydrogen yield during ESR is represented by the evolution of acetate species, either towards decomposition giving rise to methane + CO_x, or to steam reforming to CO₂ and H₂. At high temperature hydrogen production depends on approaching methane steam reforming and reverse water gas shift equilibria. Ethylene end dimethylether are parallel products found at low conversion. With excess water acetaldehyde is not found among the products, and hydrogen yields as high as 95% have been obtained at 853 K.     

Hydroisomerization and hydrocracking of long chain n-alkanes on Pt/amorphous SiO2–Al2O3 catalyst

The hydroisomerization and hydrocracking of n-hexadecane, n-octacosane and n-hexatriacontane on a 0.3% platinum/amorphous silica–alumina (MSA/E) catalyst was investigated in a stirred microautoclave at 345, 360 and 380°C and between 2 and 13.1 MPa hydrogen pressure. For each n-paraffin, the reaction pathway and the kinetic parameters were determined. The results were used to elucidate the effect of chain length and operating conditions on isomerization and cracking selectivity. The conversion of the n-paraffins lead to the formation of a mixture of the respective isomers, as the main product, together with cracking products. At every temperature, the iso-alkane/n-alkane ratio of cracking products increased considerably with increasing conversion degree. At the same conversion level, higher reaction temperatures lead to cracking products characterized by a lower iso-alkane/n-alkane ratio. The conversion rate constants showed a considerable increase between n-C₁₆ and n-C₂₈, whereas a slight decrease between n-C₂₈ and n-C₃₆ was observed. The hydroisomerization selectivities showed a decrease as a function of chain length and with increasing conversion levels. The increase in reaction temperature leads to a small decrease in the isomerization selectivities only at low-medium conversion degrees and at the highest temperature investigated, while the effect of this parameter on the maximum yields achievable in iso-C16, iso-C28 and iso-C36 was negligible. The results indicate that the conversion of the n-paraffins follows a first-order kinetic in hydrocarbon while the order in hydrogen pressure was −1.1 ± 0.21 for n-C₁₆ and −0.66 ± 0.15 for n-C₂₈. Furthermore, an increase in hydroisomerization selectivity at higher hydrogen pressure for n-C₂₈ conversion was observed.     

Liquid fuel production from syngas using bifunctional CuO-CoO-Cr2O3 catalyst mixed with MFI zeolite

CuO-CoO-Cr₂O₃ mixed with MFI Zeolite (Si/Al = 35) prepared by co-precipitation was used for synthesis gas conversion to long chain hydrocarbon fuel. CuO-CoO-Cr₂O₃ catalyst was prepared by co-precipitation method using citric acid as complexant with physicochemical characterization by BET, TPR, TGA, XRD, H₂-chemisorptions, SEM and TEM techniques. The conversion experiments were carried out in a fixed bed reactor, with different temperatures (225-325 °C), gas hourly space velocity (457 to 850 h⁻¹) and pressure (28-38 atm). The key products of the reaction were analyzed by gas chromatography mass spectroscopy (GC-MS). Significantly high yields of liquid aromatic hydrocarbon products were obtained over this catalyst. Higher temperature and pressure favored the CO conversion and formation of these liquid (C₅-C₁₅) hydrocarbons. Higher selectivity of C₅ + hydrocarbons observed at lower H₂/CO ratio and GHSV of the feed gas. On the other hand high yields of methane resulted, with a decrease in C₅+ to C₁₁+ fractions at lower GHSV. Addition of MFI Zeolite (Si/Al = 35) to catalyst CuO-CoO-Cr₂O₃ resulted a high conversion of CO-hydrogenation, which may be due to its large surface area and small particle size creating more active sites. The homogeneity of various components was also helpful to enhance the synergistic effect of Co promoters.     

Effects of Reaction Variables on Fischer–Tropsch Synthesis with Co-Precipitated K/FeCuAlO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Catalysts

Abstract  

The effects of reduction temperature and reaction temperature, pressure and space velocity on iron-based K/FeCuAlO _x Fischer–Tropsch catalysts prepared by co-precipitation were investigated. The catalyst reduced at 150 °C deactivated quickly due to an abundance of unreduced iron species. With increasing reduction temperature, the iron oxide’s phase transformed from hematite (α-Fe₂O₃) to magnetite (Fe₃O₄) and finally to metallic iron (α-Fe). The induction period to reach steady-state catalytic activity was reduced at increased reduction temperatures due to in situ reduction by syngas during reaction. CO conversion increased with increasing reaction temperature, and selectivity to C₅+ decreased with increasing reaction pressure and space velocity. At reaction temperatures up to of 300 °C, CO₂ formation by the water–gas shift reaction was linearly correlated with the extent of CO conversion, and CO₂ formation was slightly suppressed at ≥350 °C by a reverse water–gas shift reaction.     

水合物法分离低浓度煤层气中的甲烷

向模拟煤层气(13.11vol% CH4+86.89vol% N2)中添加5.8mol%四氢呋喃(THF)?0.03mol%十二烷基硫酸钠(SDS)促进剂溶液分离提纯煤层气,考察了压力、温度、反应时间对气体消耗量、反应速率、分解气中甲烷浓度、甲烷回收率和甲烷分离因子的影响,采用色谱分析法分别测定了CH4在剩余气相和分解气相中的浓度。结果表明,压力增加,CH4回收率增大,CH4分离因子增大,CH4分离效果越好;温度是影响甲烷分离因子的关键因素,温度降低,氮气和甲烷竞争进入水合物晶体中,导致水合物相中甲烷浓度降低;温度升高有利于提高水合物对甲烷的选择性。甲烷回收效率最高可达98.65%,分离因子最大为14.83。随反应时间增加,分解气中CH4浓度升高。