Feed Space Velocity Research Articles

ИССЛЕДОВАНИЕ АКТИВНОСТИ PT-СОДЕРЖАЩЕГО ЦЕОЛИТНОГО КАТАЛИЗАТОРА В ПРОЦЕССЕ ПРЕВРАЩЕНИЯ ПРОПАН-БУТАНОВОЙ СМЕСИ

Conversion of the propane-butane mixture at presence Pt-containing zeolite catalyst is researched at 300-500°C. It is shown that with increase in temperature of carrying out of process the yield of aromat­ic hydrocarbons, the maximum quality aromatics Ce-Ce increases reaches 40.0%wt at 500°C and a feed space velocity of raw materials 100 lr1. Conversion butanes thus reach is 94.0%.

Hydrogen-rich gas production from oxygen pressurized gasification of biomass using a Fe–Cr Water Gas Shift catalyst

In this paper the catalytic activity of a Fe–Cr WGS catalyst is evaluated in terms of CO conversion and H 2 production. The experimental study has been carried out under realistic conditions typical of oxygen pressurized gasification of biomass. The influence of temperature, excess steam, feed gas composition and space velocity on the activity and selectivity of the catalyst for the WGS reaction is investigated. The experimental work was carried out in a micro reactor testing unit using synthetic gas feed mixtures. Despite the high CO content in the feed gas (44–60% dry basis) the catalyst has shown very good performance at intermediate temperatures 350–450 °C, providing hydrogen content increases in the exit gas in the range of 10–17% (dry basis) and CO concentration at the reactor outlet lower than 3% v/v. Best performance operating conditions and the suitability of the catalyst to be incorporated in a palladium membrane reactor is discussed in this article.

Oxidative steam reforming of ethanol over Ru–Al 2O 3 catalyst in a dense Pd–Ag membrane reactor to produce hydrogen for PEM fuel cells

This study focuses on the influence of oxygen addition on ethanol steam reforming (ESR) reaction performed in a dense Pd–Ag membrane reactor (MR) for producing hydrogen directly available for feeding a polymer electrolyte membrane fuel cell (PEMFC). In particular, oxygen addition can prevent ethylene and ethane formation caused by dehydration of ethanol as well as carbon deposition. The MR is operated at 400 °C, H 2O:C 2H 5OH = 11:1 as feed molar ratio and space velocity (GHSV) ∼2000 h −1. A commercial Ru-based catalyst was packed into the MR and a nitrogen stream of 8.4 × 10 −2 mol/h as sweep gas was flowed into the permeate side of the reactor. Both oxidative ethanol steam reforming (OESR) and ESR performances of the Pd–Ag MR were analyzed in terms of ethanol conversion to gas, hydrogen yield, gas selectivity and CO-free hydrogen recovery by varying O 2:C 2H 5OH feed molar ratio and reaction pressure. Moreover, the experimental results of the OESR and ESR reactions carried out in the same Pd–Ag MR are compared in order to point out the benefits due to the oxygen addition. Experimentally, this work points out that, overcoming O 2:C 2H 5OH = 1.3:1, ethanol conversion is lowered with a consequent drops of both hydrogen yield and hydrogen recovery. Vice versa, a complete ethanol conversion is achieved at 2.5 bar and O 2:C 2H 5OH = 1.3:1, whereas the maximum CO-free hydrogen recovery (∼30%) is obtained at O 2:C 2H 5OH = 0.6:1.

Artificial Neural Network (ANN)-Aided Optimization of ZSM-5 Catalyst for the Dimethyl Ether to Olefin (DTO) Reaction from Neat Dimethyl Ether (DME)

A ZSM-5 catalyst for light olefin synthesis from dimethyl ether (the reaction of dimethyl ether (DME) to olefin, abbreviated as DTO) was developed. In comparison with the reaction of DTO from diluted dimethyl ether (abbreviated as Diluted-DTO), lower light olefin selectivity and shorter catalyst life are the drawbacks of the reaction of DTO from neat (90 vol %) DME (abbreviated as Neat-DTO). After the effects of Si/Al ratio of zeolite, DME concentration, gas hourly space velocity (GHSV) of gas feed, and Si/Al ratio on the activity of calcium-incorporated ZSM-5 were examined, additives were screened using the physicochemical properties of the additive elements and an artificial neural network. The addition of boron or phosphorus to ZSM-5 improved the catalyst life. The catalyst composition such as Si/Al, Si/Ca, Si/P, and Si/B was then optimized for longer catalyst life, using an L9 orthogonal array and an artificial neural network (ANN). Grid search was applied to find the maximum catalyst life. The catalyst life of H−Ca-ZSM-5 (Si/Al = 250, Si/Ca = 20, Si/P = 400, Si/B = 200) was 146 h when Neat-DTO was performed at 803 K and GHSV = 1000 h−1. The life is comparable to that of the catalyst supplied to Diluted-DTO.

Water–gas shift reaction in a Pd membrane reactor over Pt/Ce0.6Zr0.4O2 catalyst

A water–gas shift (WGS) Pt/Ce 0.6 Zr 0.4 O 2 catalyst has been prepared, which exhibits much faster kinetics than conventional high-temperature ferrochrome catalysts in the temperature range most suitable for operation of WGS Pd membrane reactors, i.e. above 623 K. The performance of the Pt catalyst was tested in a reactor furnished with a supported, 1.4 μm thick high-flux Pd membrane using feeds obtained by autothermal reforming of natural gas. CO conversion remained above thermodynamic equilibrium up to feed space velocities of 9100 l kg −1 h −1 at 623 K, P total = 1.2 MPa and steam-to-carbon ratio S/C = 3, but H 2 recovery decreased from 84.8% at GHSV = 4050 l kg −1 h −1 to 48.7% at the highest space velocity. This rapid decline of separation performance is attributed to slow H 2 diffusion through the catalyst bed, suggesting that external mass flow resistance has a significant impact on the H 2 permeation rate in such membrane reactors. This could be minimized by the development of WGS catalysts with even faster kinetics which would allow further reduction of the catalyst bed height.

Steam reforming of dimethyl ether over CuO–ZnO–Al2O3–ZrO2+ZSM-5: A kinetic study

Experiments were carried out to characterize the kinetics of dimethyl ether (DME) steam reforming (SR) in a fixed bed reactor catalyzed by a bifunctional catalyst comprising a physical mixture of 50:50 wt.% CuO–ZnO–Al 2 O 3 –ZrO 2 + ZSM-5 at 200–300 °C and atmospheric pressure. The influences of the feed composition (steam/DME ratio), temperature and space velocity on DME conversion, hydrogen yield and CO 2 selectivity were obtained. A kinetic model for combined DME SR based on the reaction mechanisms for methanol to DME from Park and Froment and methanol SR from Peppley et al. was used. The kinetic parameters were determined by regression using the DME conversion, hydrogen yield and CO 2 selectivity at a given steam/DME feed ratio (steam/DME molar ratio of 3.5).

Effects of Feed Composition and Space Velocity on Direct Synthesis of Dimethyl Ether from Syngas

Full factorial experimental design method was applied for investigation of the effects of different space velocity (SV) (500−1500 mLn/(g-cat.h)) and H2/CO molar feed ratio (1−2) on CO conversion and/or DME selectivity as the response variables over a physically prepared bifunctional catalyst (CuO/ZnO/Al2O3+ H-ZSM-5) for liquid phase direct DME synthesis from synthesis gas. The results showed that feed composition is the more effective factor on the response and the interaction of the SV and H2/CO only slightly influenced the response. The factor levels that can maximize the SDME are SV of 1500 mLn/(g-cat.h) and H2/CO of 1.5 at 240 °C and 35 bar.

The influence of phosphotungstic acid acidity on Al-MCM-41 in t-butylation of phenol with t-butyl alcohol

Al-MCM-41 (Si/Al = 20) molecular sieve was synthesized hydrothermally and phosphotungstic acid (PW) of 10, 20 and 40 wt% was supported on it. Their catalytic performance was examined in the vapour phase alkylation of phenol with tert-butyl alcohol (TBA) in the temperature range 190–275 °C. The major products were 2- tert-butyl phenol (2-TBP), 4- tert-butyl phenol (4-TBP), 2,4-di- tert-butyl phenol (2,4-DTBP) and small amounts of undesired products. 4-TBP was obtained as the major product with high selectivity. The results revealed that 20 wt% PW supported on Al-MCM-41 is found to be more active than other catalysts. The effects of molar feed ratio, space velocity and reaction temperature on conversion and products selectivity were studied and the results are discussed. The reaction parameters were optimized to obtain high selectivity of 4-TBP at high phenol conversion.

Adsorption Behaviour of Normal Paraffins in a Fixed Bed Adsorber Containing 5 Å Molecular Sieves

The adsorption process for separating normal paraffins from naphtha using 5 Å molecular sieves was studied with the purpose of optimizing the utilization of naphtha and providing a proper allocation of the feeds for the steam cracking and catalytic reforming processes. The separation efficiency of the normal paraffins was > 99.9% while their purity in the desorption oil could reach 98.2%. The effects of adsorption temperature and space velocity on the adsorption process were investigated. The adsorption capacity was large and the adsorption mass-transfer zone was short when the adsorption temperature was low in the range of 180–340°C and the feed space velocity was small in the range of 30–300 h−1. The adsorptivity of the normal paraffins improved with increasing carbon number. Long-chain normal paraffins had a notable displacement desorption relative to short-chain normal paraffins.

Synthesis, characterisation and catalytic performance of boron substituted SBA-15 molecular sieves

Boron substituted mesoporous SBA-15 molecular sieves with varying boron content were synthesised by hydrothermal method. The effects of incorporation of boron in the framework on the structure, crystal parameters, framework vibrations and textural properties of SBA-15 were discussed based on the results from XRD, FT-IR and nitrogen adsorption studies. The morphology changes due to boron incorporation were monitored by SEM analysis. The coordination environment of boron in the framework was revealed by 11B MAS NMR and MQMAS NMR techniques. The type of acid sites created by boron incorporation was analysed by DRIFT study of pyridine adsorbed catalysts. All the characterisation results indicate the successful incorporation of boron in the silica framework of SBA-15 in both tetra and tri coordination. Isopropylation of naphthalene with isopropyl alcohol was carried out to test the acidity of the synthesised materials. The effects of reaction temperature, feed ratio and feed space velocity on naphthalene conversion and products selectivity were discussed. The higher activity in naphthalene conversion and selectivity of di-isopropylated naphthalenes were accounted in terms of the increased acid sites due to boron incorporation in the framework.

Preparation of highly ordered mesoporous AlSBA-15 and its application to isopropylation of m-cresol

Aluminum incorporated SBA-15 mesoporous molecular sieves with different n Si/ n Al ratios have been hydrothermally synthesized by adjusting the synthesis gel pH below the isoelectric point of silica (pH ∼ 2) using nonionic surfactant as the structure directing agent. All the samples were characterized by X-ray diffraction, N 2 adsorption to determine specific pore volume, pore size and specific surface area, FT-IR, TGA-TPD to determine the acid sites and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). Vapor phase alkylation of m-cresol with isopropanol was carried out over large pore AlSBA-15 catalysts with different n Si/ n Al ratios. The influence of various reaction parameters such as reaction temperature, reactant feed ratio and space velocity affecting the activity and selectivity of AlSBA-15, were studied. 2-Isopropyl-5-methylphenol (2I-5MP) was obtained as a major product with high selectivity. AlSBA-15 (45) was found to be the most active catalyst in this study. It showed 73.5% m-cresol conversion and a selectivity of 45.68% for 2I-5MP under the optimized reaction conditions. Further, large pore AlSBA-15 (45) catalyst was not deactivated when the reaction was carried out for several hours of reaction time.

Oxidative conversion of ethane to ethylene over supported SrO-promoted Er2O3 catalyst

Oxidative conversion of ethane to ethylene over a SrO-promoted Er2O3 supported on low-surface area macroporous silica–alumina commercial catalyst carrier (SA5205, obtained from Norton Co., USA) in presence of steam (steam/C2H6 mole ratio = 1.0) and limited O2 (C2H6/O2 mole ratio ≥ 4.0) has been thoroughly investigated. Influence of different process parameters such as temperature (700–850 °C), C2H6/O2 feed ratio (4.0–8.0) and space velocity (50, 000–200, 000 cm3 g−1 h−1) on the conversion of ethane and product selectivity in the process has been studied. High selectivity (≥80%) of C2+ olefins at 50–70% conversion of ethane could be obtained at very low contact time without coke deposition on the catalyst at 800–850 °C.

Supercritical Solvent Effects on Hydrocarbon Product Distributions from Fischer−Tropsch Synthesis over an Alumina-Supported Cobalt Catalyst

This study is designed to examine the effects of supercritical fluid (SCF) solvents (pentane or hexane) on product distributions from Fischer−Tropsch synthesis (FTS) over an alumina-supported cobalt catalyst in a fixed-bed-reactor. The influence of reaction conditions (such as temperature, pressure, syngas feed ratio, contact time, and space velocity) on the FTS hydrocarbon product distributions in the supercritical solvents was studied. Changing the density-dependent bulk thermophysical properties of the supercritical pentane medium, by tuning either temperature (210−250 °C) or pressure (45−65 bar), resulted in notable effects on the (C6+) hydrocarbon product distributions and selectivity. One particular set of experiments was designed to directly compare hexane and pentane solvent effects at constant density (ca., ρ = 0.3 g/cm3) and temperature (240 °C) where significantly higher pressure was required in pentane to achieve this density. Interestingly, both pentane and hexane supercritical FTS performed almost identically at the common density, in terms of hydrocarbon product distribution; however, higher CO conversion was obtained for the pentane phase reaction, because of the pressure effects on the kinetics. Within the investigated range of conditions, the chain-growth probability (α-value) increases as the pressure increases and the temperature decreases; however, the influence of reaction temperature on the chain growth probability was determined to be more pronounced than that of the effect of pressure. Through comparison of hydrocarbon distributions in both SCF-phase and gas-phase FTS, we conclude that the enhanced α-value in SCF−FTS is due to the enhanced solubilities of heavy hydrocarbon products in the SCF medium, thereby improving vacant-site accessibility for the readsorption of olefins and subsequent chain growth, as well as the elimination of the adsorption layer.

Energy efficient simultaneous oxidative conversion and thermal cracking of ethane to ethylene using supported BaO/La 2O 3 catalyst in the presence of limited O 2

Abstract An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C2H6 mol ratio=1.0) and limited O2 (C2H6/O2 mol ratio ⩾ 4.0) over a BaO-promoted La2O3 supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C2H6/O2 feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm3 g−1 h−1) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity (⩾ 85%) for C2+ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (

Energy efficient simultaneous oxidative conversion and thermal cracking of ethane to ethylene using supported BaO/La 2O 3 catalyst in the presence of limited O 2

An energy efficient conversion of ethane to ethylene involving simultaneous oxidative conversion (which is exothermic) and thermal cracking (which is endothermic) reactions of ethane in the presence of steam (steam/C 2H 6 mol ratio=1.0) and limited O 2 (C 2H 6/O 2 mol ratio ⩾ 4.0) over a BaO-promoted La 2O 3 supported on low surface area macroporous silica-alumina commercial catalyst carrier has been thoroughly investigated. Influence of various process parameters such as temperature (700–850°C), C 2H 6/O 2 feed ratio (4.0–8.0) and space velocity (50,000–200,000 cm 3 g −1 h −1) on the conversion, product selectivity and net heat of reactions in the process has also been studied. At all the process conditions, there was no coke deposition on the catalyst. High selectivity (⩾ 85%) for C 2+ olefins (at 50–60% conversion) can be obtained in the process at a low contact time (<10 ms), particularly for the higher C 2H 6/O 2 ratios (⩾ 6.0) and temperatures (⩾ 800°C). The process exothermicity is decreased appreciably with increasing the temperature and/ or the C 2H 6/O 2 ratio. The net heat of reaction in the process can be controlled by manipulating the C 2H 6/O 2 ratio and reaction temperature. Also, because of simultaneously occurring endothermic and exothermic reactions, the process is highly energy efficient and non-hazardous.

Simulation of the Methane Steam Re-forming Process in a Catalytic Pd-Membrane Reactor

Methane steam re-forming is one of the most important chemical processes in hydrogen and syngas production. Simulation of reactors with parallel-flow and counterflow configuration has been performed to study the methane steam re-forming reaction in a packed-bed inert membrane reactor (PBIMR). In this kind of reactor complete methane conversion can be achieved by means of the total removal of hydrogen from the reaction products. In the model a dense Pd membrane was simulated, assuming an infinite permselectivity to hydrogen. Membrane reactor performance was compared to that of a conventional fixed-bed reactor. The effect on the degree of conversion was analyzed for different parameters such as temperature, reactor pressure, feed and sweep flow rate, feed molar ratio, membrane thickness, and space velocity. Comparison with experimental data of Shu et al. (1994) showed a good agreement. An analysis of the results indicated that the choice of operating conditions requires a complex process strategy.

Fine Details on the Selectivity and Kinetics of the Fischer−Tropsch Synthesis over Cobalt Catalysts by Combination of Quantitative Gas Chromatography and Modeling

A combination of quantitative gas chromatography (for the lighter products up to C10 and for the determination of the chain-growth probability) and calculations based on a modified Anderson−Schulz−Flory (ASF) model (for the heavy products) provided instantaneous product determinations for studying the influence of feed composition, pressure, space velocity, and temperature on the rate and chain-growth probability of the reaction in a plug flow reactor. Material balances were often less than 100%, due to underestimation of the heavy products by the model. Inert species were shown to impede both the rate and the chain growth. Small pressure increases in the near-atmospheric region resulted in significant increases of the rate and the chain growth. Increasing space velocity resulted in a higher rate, but the chain growth was hardly affected. Over a wide conversion range, the rate was found to be a linear function of the temperature. These and other results attest to a multiplicity of the chain-growth probabi...

The role of catalyst support on the activity of nickel for reforming methane with CO 2

Thermodynamic studies were conducted to determine the operating conditions needed to inhibit carbon deposition and nickel carbide formation as well as to study the possible solid-state reactions within the catalysts in reforming methane with CO 2. Five nickel commercial catalysts, manufactured for steam reforming, on supports containing alumina in different forms were studied and their catalytic activity, selectivity and stability were established using different feed ratios, space velocities and temperatures. Fused α-Al 2O 3 was the only stable catalyst support but such a system yielded relatively lower conversion. Although γ-alumina partly transformed to the α-form with a resultant exothermic effect and drastic decrease in surface area, a decrease in conversion was not detected. α-Al 2O 3 in the presence of mullite caused a rapid irreversible deactivation which is accompanied by an increase in volume of 21%. On the other hand the presence of α-Al 2O 3 in the presence of MgAl 2O 4 or calcium aluminate gave high conversions which increase with time due to the formation of phases more active than metallic nickel. In both cases the resultant solid-state reactions are endothermic and are accompanied by a decrease in surface area. In the presence of MgAl 2O 4 the residual alumina forms NiAl 2O 4 which is soluble in MgAl 2O 4.

Extrapolating conversions to zero external gradients in vapor phase catalytic recirculation reactors

A method is outlined for extrapolating conversions to zero external gradients and it is shown to be significantly superior to the method traditionally used. The objective is to develop a functional relationship based on theoretical considerations. External temperature gradients were found to be significant in an earlier study of cyclohexane deydrogenation kinetics at atmospheric pressure with the Berty reactor. Extrapolation to zero external gradients is commonly done by plotting conversion (X) vs. the reciprocal mass velocity (0) over the catalyst bed. As the mass velocity approaches infinity (0 ..-->.. 0), external gradients are essentially eliminated. Therefore, a polynomial fit for a plot of X vs. 0 would yield conversion at zero external gradients upon intersection with the ordinate. To test the proposed extrapolation scheme, conversions at different mass velocities were calculated for a recirculation reactor with a specified feed composition, temperature, pressure and space velocity.

Isolation of benzene from gas condensate using zeolites

1. The adsorbent which has the greatest activity for separating benzene from the 60–95‡ fraction of Shebelinsk gas condensate has been selected. The activity of CaX zeolite with respect to benzene at 20 ‡C and a benzene concentration in the starting raw material of 8.92% by wt. was 11.34% by wt. 2. It has been established that adsorption equilibrium in the system CaX zeolite-60–95‡ fraction sets in within 60 min. 3. The optimum space velocity of benzene-fraction feed from gas condensate into the percolator is a space velocity of 0.25 h−1, since the largest yield of percolate is obtained with a minimum benzene content thereby. 4. It has been established that an increase in the benzene content in the original raw-material up to 40% by wt., at the expense of complete recirculation of product 1, permits one to obtain benzene of 100% purity.