Fixed-bed Reactor System Research Articles

Transformation of Isobutyl Alcohol to Aromatics over Zeolite-Based Catalysts

One-step transformation of isobutyl alcohol to aromatics (benzene, toluene, and xylene) has been studied in a gas phase, fixed-bed reactor system over several purely acidic zeolites and zeolite-supported metal catalysts. ZSM-5 zeolites give higher aromatics yields (∼42 wt %) among the evaluated zeolites, and the Si/Al ratios (Si/Al = 13–43) of ZSM-5 slightly influence their catalytic performances. During the transformation of isobutyl alcohol, large amounts of short alkanes (mainly propane and butane isomers) are also generated on the acidic ZSM-5. To improve the conversion to aromatics, several metal species (Zn, Ga, Mo, La, Ni, Ag, and Pt) are supported on the ZSM-5. The enhancements in aromatics yields (∼60 wt %) are observed only on the Zn/ZSM-5 catalysts. The incorporation of Zn species preferentially decreases the strong-strength Bronsted acidity and, thus, suppresses the cracking to C3 fragments. Moreover, mainly the Zn species at the exchange sites facilitate the recombinative desorption of H2 and...

Comparison of Gas–Liquid–Liquid–Solid Four-Phase Trickle-Bed Reactor with Upflow Reactor under High Liquid Flow Rate

The hydrogenation of carbobenzoxy phenylalanine was investigated in order to better understand the influence of mass transfer effects in four-phase fixed-bed reactor systems. In this reaction, the carbobenzoxy phenylalanine is dissolved in an organic solvent and is reacted with a gas in the presence of a hydrophilic catalyst (Pd/Al2O3). An aqueous phase is also required to dissolve the reaction product, leading to a four-phase gas–liquid–liquid–solid system. Results indicate that higher liquid flow rates lead to faster rates of reaction due to improved contact efficiency between the organic phase and catalyst. Similar performance was observed through experiment and modeling in two fixed-bed reactor configurations (trickle-bed reactor and gas–liquid cocurrent upflow reactor) at higher liquid flow rates.

A CuZnAl-Based Hybrid Material for the Direct Synthesis of Dimethyl Ether from Syngas

A CuZnAl-based hybrid material was prepared by co-precipitation impregnation method using the active components of methanol synthesis material and pseudo-boehmite as the precursors. The as-prepared material was evaluated for the direct synthesis of dimethyl ether (DME) from syngas in a pressurized continuous flow fixed-bed reactor system. It was revealed that the hybrid material showed high activity and selectivity after an induced period, i.e. the CO conversion and DME selectivity reached as high as 81% and 67%, respectively. Moreover, it was observed that there was only slight carbon which could be eliminated rather than graphite carbon deposited on the material after run for 150 h, indicating its good stability for the direct synthesis process .

A CuZnAl-Based Hybrid Material for the Direct Synthesis of Dimethyl Ether from Syngas

A CuZnAl-based hybrid material was prepared by co-precipitation impregnation method using the active components of methanol synthesis material and pseudo-boehmite as the precursors. The as-prepared material was evaluated for the direct synthesis of dimethyl ether (DME) from syngas in a pressurized continuous flow fixed-bed reactor system. It was revealed that the hybrid material showed high activity and selectivity after an induced period, i.e. the CO conversion and DME selectivity reached as high as 81% and 67%, respectively. Moreover, it was observed that there was only slight carbon which could be eliminated rather than graphite carbon deposited on the material after run for 150 h, indicating its good stability for the direct synthesis process .

Enhancement mechanism of SO2 removal with calcium hydroxide in the presence of NO2

The enhancement mechanism of SO2 removal by the presence of NO2 under low temperature and humid conditions was studied in a fixed bed reactor system. The presence of NO2 in the flue gas can enhance SO2 removal. The interaction between SO2 and NO2 in gas phase could not explain the effect of NO2 on SO2 removal under low-temperature and humid conditions. When Ca(NO3)2 and Ca(NO2)2 as additive were added on the surface of sorbent, the desulfurization activity of sorbent decreased. However, the sorbent pretreated by NO2 for a moment has higher SO2 removal. The oxidization of SO32− to SO42− and the evolution of sorbent surface structure in the presence of NO2 can explain the enhancement of SO2 removal by the presence of NO2. HSO3− and SO3− reacted with NO2 to form sulfate, which can accelerate the hydrolysis of SO2. The reaction between NO2 and Ca(OH)2 can make the unreacted sorbet under the SO2 removal product exposed to the reactant gas.

Hydrogen production from methane and natural gas steam reforming in conventional and microreactor reaction systems

Ni-based (over MgO and Al2O3) and noble metal-based (Pd and Pt over Al2O3) catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors. The catalytic activity was measured at several temperatures, atmospheric pressure and different steam to carbon, S/C, ratios. These conditions were the same for conventional, fixed bed reactor system, and microreactors. Weight hourly space velocity, WHSV, was maintained equal in order to compare the activity results from both reaction systems. For microreactor systems, similar activities of Ni-based catalyst were measured in the steam methane reforming (SMR) activity tests, but not in the case of natural gas steam reforming tests. When noble metal-based catalysts were used in the conventional reaction system no significant activity was measured but all catalysts showed some activity when they were tested in the microreactor systems. The analysis by SEM and TEM revealed a carbon-free surface for Ni-based catalyst as well as carbon filaments growth in case of noble metal-based catalysts.

Thermal durability of Cu-CHA NH3-SCR catalysts for diesel NOx reduction

Multiple catalytic functions (NOx conversion, NO and NH3 oxidation, NH3 storage) of a commercial Cu-chabazite (CHA) urea/NH3-SCR catalyst were assessed in a laboratory fixed-bed flow reactor system after differing degrees of hydrothermal aging. Catalysts were characterized by using X-ray diffraction (XRD), 27Al solid state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM)/energy dispersive X-ray (EDX) spectroscopy to develop an understanding of degradation mechanisms during catalyst aging. The catalytic reaction measurements of laboratory-aged catalysts were performed, which allows us to obtain a universal curve for predicting the degree of catalyst performance deterioration as a function of time at each aging temperature. Results show that as the aging temperature becomes higher, the zeolite structure collapses in a shorter period of time after an induction period. The decrease in SCR performance was explained by zeolite structure destruction and/or Cu agglomeration, as detected by XRD/27Al NMR and by TEM/EDX, respectively. Destruction of the zeolite structure and agglomeration of the active phase also results in a decrease in NO/NH3 oxidation activity and NH3 storage capacity of the catalyst. Laboratory aging conditions (16h at 800°C) compare well with a 135,000mile vehicle-aged catalyst, except for the chemically poisoned inlet section of the vehicle-aged catalyst.

Effect of process conditions on the steam reforming of ethanol with a nano-Ni/SiO2 catalyst

In this paper, a nano-Ni/SiO2 catalyst was prepared by a sol-gel method and tested for hydrogen production from ethanol steam reforming using a two-stage fixed-bed reaction system. The reaction conditions, such as reaction temperature, water/ethanol ratio and sample feeding rate, were investigated with the prepared nano-Ni/SiO2 catalyst. Brunauer–Emmett–Teller surface area and porosity, temperature-programmed oxidation, X-ray diffraction and focused ion beam (FIB)/scanning electron microscopy were used in this work to analysis the fresh and/or reacted catalysts. An extended catalyst stability test for ethanol steam reforming with the Ni/SiO2 catalyst was carried out at a reaction temperature of 600 °C, when the water/ethanol ratio was kept at 3.5 and sample feeding rate was 4.74 g h−1. The results showed that a stabilized gas and hydrogen production was obtained with a potential H2 production of about 40 wt.%. Increasing the reaction temperature during ethanol steam reforming with the Ni/SiO2 catalyst resulted in an increase of gas and hydrogen production. The gas yield was slightly reduced when the water/ethanol ratio was increased from 2.0 to 3.5. However, the potential H2 production was increased. The investigation of the sample feeding rate showed that the gas production per hour was increased due to the higher sample feeding rate, but the potential H2 production was reduced.

Experiment Investigation Absorption of Mercury by Modified Fly Ash Dust Layer Attaching on Filter

As to figure out the effect that modified fly ash, which is prepared by fly ash –CaO, and modified fly ash dust layer attached on the surface of the filter material adsorbed elemental mercury, experimental studies are administrated in a laboratory-scale fixed bed reactor system with gaseous elemental mercury produced by a mercury vapor generator and simulated flue gas composition. The experimental results indicated that the adsorption performance of fly ash and CaO relatively poor. The proportion of CaO in the modified fly ash will affected the mercury removal efficiency of the absorbent which prepared by fly ash and CaO. It will be an optimal effect when the blend ratio of the flying ash and CaO is 2 to 1, and the maximum removal efficiency is up to 34%.As the adsorption temperature increases the removal efficiency of the modified fly ash deteriorates. The efficiency of dust layer attaching on the surface of the filter material is getting higher with the larger porosity of dust layer and smaller particle material size.

Dynamic measurement of mercury adsorption and oxidation on activated carbon in simulated cement kiln flue gas

Mercury emissions from cement plants are being regulated by environmental agencies in most countries. Both dynamic mercury emissions in cement kiln systems and removal of mercury by sorbent injection require continuous mercury emission monitoring. Dry converters for total mercury measurements are still under development and are investigated in this work. A commercial red brass converter was tested at 180°C and it was found that the red brass chips work in nitrogen atmosphere only, but do not work properly under simulated cement kiln flue gas conditions. Test of the red brass converter using only elemental mercury shows that when HCl is present with either SO2 or NOx the mercury measurement after the converter is unstable and lower than the elemental mercury inlet level. The conclusion is that red brass chips cannot fully reduce oxidized mercury to elemental mercury when simulated cement kiln gas is applied. A sodium sulfite-based converter material was prepared by dry impregnation of sodium sulfite and calcium sulfate powders on zeolite pellets using water glass as binder. The sulfite converter works well at 500°C with less than 10ppmv HCl in the simulated cement kiln flue gas. The 95% response time of the sulfite converter is short and typically within 2min. Dynamic mercury adsorption and oxidation tests on commercial activated carbons Darco Hg and HOK standard were performed at 150°C using simulated cement kiln gas and a fixed bed reactor system. It is shown that the converter and analyzer system is capable of following the transient mercury outlet concentration in a satisfactory way. Suggestions for practical applications of the sulfite converter in both lab and cement plants are presented.

The First Case of Competitive Heterogeneously Catalyzed Hydrogenation using Continuous-Flow Fixed-Bed Reactor System: Hydrogenation of Binary Mixtures of Activated Ketones on Pt-Alumina and on Pt-Alumina-Cinchonidine Catalysts

Under the experimental conditions of the Orito reaction the competitive hydrogenations of four binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), pyruvic aldehyde dimethyl acetal (PA) and 2,2-diethoxyacetophenone (DAP) on unmodified Pt/Al2O3 (racemic hydrogenation) and catalyst modified by cinchonidine (chiral hydrogenation) were studied using continuous-flow fixed-bed reactor system (CFBR). Conversions of chiral and racemic hydrogenations were determined under 4 MPa H2 pressure, at 293 K using toluene/acetic acid 9/1 as solvent. In the competitive chiral hydrogenation of MBF + EP and DAP + PA binary mixtures (S1 + S2) a new phenomenon was observed: namely the EP and PA are hydrogenated faster than MBF and DAP, whereas in racemic one the MBF and DAP are hydrogenated faster than the former ketones. The phenomenon verified for the first time in CFBR is dependent on the adsorption mode of the surface complexes of various compositions (S1–Pt, S2–Pt, S1–CD–Pt, S2–CD–Pt, CD = cinchonidine). In the chiral hydrogenation of DAP a rate decrease, i.e., “ligand deceleration” was observed instead of rate enhancement.

Hydrotreatment of Vegetable Oils to Produce Bio-Hydrogenated Diesel and Liquefied Petroleum Gas Fuel over Catalysts Containing Sulfided Ni–Mo and Solid Acids

Biohydrogenated diesel (BHD) and liquefied petroleum gas (LPG) fuel were produced by the hydrotreatment of vegetable oils over Ni–Mo-based catalysts in a high-pressure fixed-bed flow reaction system at 350 °C under 4 MPa of hydrogen. Because triglycerides and free fatty acids underwent the hydrogenation and deoxidization at the same time during the reaction, various vegetable oils (jatropha oil, palm oil, and canola oil) were converted to mixed paraffins by the one-step hydrotreatment process although they contained quite different amounts of free fatty acids. Ni-Mo/SiO2 formed n-C18H38, n-C17H36, n-C16H34, and n-C15H32 as predominant products in the hydrotreatment of jatropha oil. These long normal hydrocarbons had high melting points and thus gave the liquid hydrocarbon product over Ni-Mo/SiO2 a high pour point of 20 °C. Either Ni-Mo/H-Y or Ni-Mo/H-ZSM-5 was not suitable for producing BHD from jatropha oil because a large amount of gasoline-ranged hydrocarbons was formed on the strong acid sites of zeol...

Hydrogen production from biomass gasification with Ni/MCM-41 catalysts: Influence of Ni content

The steam pyrolysis-gasification of biomass, wood sawdust, was carried out with a Ni/MCM-41 catalyst for hydrogen production in a two-stage fixed bed reaction system. The wood sawdust was pyrolysed in the first reactor and the derived products were gasified in the second reactor. The synthesised MCM-41 mesoporous catalyst supports were impregnated with different Ni loadings (5, 10, 20 and 40wt.%), which were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). NiO particles were homogeneously dispersed inside the pores of 5, 10, and 20wt.% Ni/MCM-41 catalysts; however, more bulkly NiO particles (up to 200nm particle size) were detected outside the pores with an increase of the Ni loading up to 40wt.%. Gas production was increased from 40.7 to 62.8wt.%, hydrogen production was increased from 30.1 to 50.6vol.% of total gas composition when the Ni loading was increased from 5 to 40wt.% during the pyrolysis-gasification of wood sawdust. This work showed low coke deposition (from 0.5 to 4.0wt.%) with valuable bio-oil by-products using the Ni/MCM-41 catalyst. The highly efficient conversion of renewable biomass resource to hydrogen and bio-oil with very low coke deposition indicates that biomass gasification on Ni/MCM-41 catalysts via two-stage reaction is a promising method for the development of the biorefinery concept.

Hydrogen production by methane cracking over different coal chars

Hydrogen production by methane cracking over a bed of different coal chars has been studied using a fixed bed reactor system operating at atmospheric pressure and 1123K. The chars were prepared by pyrolysing four parent coals of different ranks, namely, Jincheng anthracite, Binxian bituminous coal, Xiaolongtan lignite and Shengli lignite, in nitrogen in the same fixed bed reactor operating at different pyrolysis temperatures and times. Hydrogen was the only gas-phase product detected with a GC during methane cracking. Both methane conversion and hydrogen yield decreased with increasing time on stream and pyrolysis temperature. The lower the coal rank, the greater the catalytic effect of the char. While the Shengli lignite char achieved the highest methane conversion and hydrogen yield in methane cracking amongst all chars prepared at pyrolysis temperature of 1173K for 30min, a higher catalytic activity was observed for the Xiaolongtan lignite char prepared at 973K, indicating the importance of the nature of char surfaces. The catalytic activity of the coal chars were reduced by the carbon deposition. The coal chars had legible faces and sharp apertures before being subjected to methane cracking. The surfaces and pores of coal chars were covered with carbon deposits produced by methane cracking as evident in the SEM images. The results of BET surfaces areas of the coal chars revealed that the presence of micropores in the chars was not an exclusive reason for the catalytic effect of the chars in methane cracking.

Reactivity and in situ X-ray absorption spectroscopy of Rb-promoted Mo 2C/MgO catalysts for higher alcohol synthesis

The influences of MgO support and Rb 2CO 3 promoter on the activity and selectivity of Mo 2C-based catalysts for higher alcohol synthesis from syngas were explored. The reaction was performed in a fixed-bed reactor system operating at 573 K, 30 bar, gas flow rate of 24,000 cm 3 g Mo - 1 h −1, and H 2:CO ratio of 1:1. When promoted by Rb 2CO 3, the selectivity of alcohols over 5 wt.% Mo 2C/MgO can reach 61 C% on a CO 2-free basis, with C1–C4 hydrocarbons being the main side products. Production of higher alcohols was enhanced at high promoter loading and low conversion. Characterization by X-ray absorption spectroscopy (XAS) indicated that passivated Mo 2C/MgO was more oxidized than bulk Mo 2C, but exposure to reaction conditions for 4 h partially reduced the passivated sample. Electron microscopy and XAS confirmed that Mo 2C was highly dispersed on MgO. The Rb K edge structure suggested that the Rb 2CO 3 promoter was structurally modified in the reaction.

Steam Reforming of Bio-oil Fractions: Effect of Composition and Stability

The efficacy of steam reforming of the aqueous species in bio-oils produced from the fast pyrolysis of biomass is examined. A fractionating condenser system was used to collect a set of fractions of fast pyrolysis liquids with different chemical characteristics. The water-soluble components from the different fractions were steam-reformed using a nickel-based commercial catalyst in a fixed-bed reactor system. When reforming at 500 °C, an overall positive effect in hydrogen yields was observed for the fractions with higher concentrations of lower molecular-weight oxygenates, such as acetic acid and acetol, while the heavier compounds, such as the carbohydrates, showed an opposite effect. In general, higher selectivity toward hydrogen correlated to a lower tendency toward carbon deposits. Overall, the bio-oil fraction corresponding to the light end performed the best with the highest activity toward hydrogen. A range of steam/carbon ratios was examined. Carbon accumulation in the reactor was clearly a main issue during steam reforming of all of the bio-oil fractions studied. Chemical changes caused by aging of aqueous bio-oil were found to have a detrimental effect on hydrogen production.

Feasibility study for thermal treatment of solid tire wastes in Bangladesh by using pyrolysis technology

In this study on the basis of lab data and available resources in Bangladesh, feasibility study has been carried out for pyrolysis process converting solid tire wastes into pyrolysis oils, solid char and gases. The process considered for detailed analysis was fixed-bed fire-tube heating pyrolysis reactor system. The comparative techno-economic assessment was carried out in US$ for three different sizes plants: medium commercial scale (144 tons/day), small commercial scale (36 tons/day), pilot scale (3.6 tons/day). The assessment showed that medium commercial scale plant was economically feasible, with the lowest unit production cost than small commercial and pilot scale plants for the production of crude pyrolysis oil that could be used as boiler fuel oil and for the production of upgraded liquid-products.

Studies on the steam and CO 2 reforming of methane for GTL-FPSO applications

Steam CO 2 reforming (SCR) of methane for the production of syngas was simulated using PRO-II and investigated over Ni-based catalysts for GTL-FPSO applications. The Ni-based catalysts were prepared by an impregnation method. The catalysts before and after the reaction were characterized by N 2 physisorption, XRD and TEM techniques. The conversion of CH 4 was increased by increasing the concentration of H 2O and CO 2 in the feed. For the application in Co-based Fischer–Tropsch synthesis, the synthesis gas ratio of H 2/CO = 1.85–2.0 in the SCR was designed by the modeling of PRO-II simulator, and identified in a fixed bed reactor system by controlling the feed molar ratios of CH 4:H 2O:CO 2. It was found that Ni/MgO catalyst is more desirable catalyst for the production of synthesis gas than Ni/γ-Al 2O 3 and Ru/TiO 2 catalysts on the point of the low carbon formation and suitable H 2/CO ratio for the GTL-FPSO applications with Co-based FT process.

Hydrogen production from the pyrolysis–gasification of waste tyres with a nickel/cerium catalyst

Hydrogen production from the pyrolysis–gasification of waste tyres has been investigated with a Ni/CeO 2/Al 2O 3 catalyst using a two-stage fixed bed reaction system. The conditions of catalyst preparation such as Ni and CeO 2 content and calcination temperature were investigated in relation to product yield and composition. The fresh and reacted catalysts were analysed using thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results showed that there were small changes in the gas and hydrogen yield by adding 5 wt.% of CeO 2 into the Ni/CeO 2/Al 2O 3 catalyst. The gas yield related to the mass of waste tyre and the amount of reacted water were increased with the increase of CeO 2 content from 5 to 15 wt.%. However, with the further increase of CeO 2 content to 30 wt.%, the gas yield related to the mass of tyre and the amount of reacted water was reduced. Increasing the Ni content of the catalyst showed a positive influence on the gas yield and hydrogen production. The investigation of the calcination temperature of the Ni/CeO 2/Al 2O 3 catalyst showed that the oil yield related to the mass of tyre and reacted water decreased from 28.4 to 23.4 wt.% for the catalyst calcined at 500 °C, and decreased from 24.2 to 17.7 wt.% for the catalyst calcined at 750 °C. When the Ni content of the catalyst was increased from 5 to 20 wt.%. there were only small changes in total gas and hydrogen production from the pyrolysis–gasification of waste tyre. Lower coke deposition on the reacted catalyst was obtained for the Ni/CeO 2/Al 2O 3 catalyst prepared at the calcination temperature of 750 °C compared with the 500 °C calcination temperature.

Selective hydrogenation of levulinic acid to γ-valerolactone over carbon-supported noble metal catalysts

Selective hydrogenation of biomass derived levulinic acid (LA) to γ-valerolactone (GVL) has been efficiently catalyzed by Ru, Pt and Pd noble metal supported on carbon under vapor phase in a continuous down flow fixed-bed reactor system. Among the catalysts, 5 wt.% Ru/C gave GVL with 100% selectivity at 100% LA conversion up to 240 h (10 days) without loss in its activity. The higher catalytic activity and product selectivity of 5 wt.% Ru/C catalyst has been attributed to the higher dispersion of metallic Ru over carbon in nano-sizes compared to Pt and Pd catalysts.