Methanol Synthesis Reaction Research Articles

03/01705 Optimal temperature profile in methanol synthesis reactor: Jahanmiri, A. and Eslamloueyan, R. Chemical Engineering Communications, 2002, 189, (6), 713–741

03/01705 Optimal temperature profile in methanol synthesis reactor: Jahanmiri, A. and Eslamloueyan, R. Chemical Engineering Communications, 2002, 189, (6), 713–741

Theoretical Investigation of a Pd‐membrane Reactor for Methanol Synthesis

AbstractA numerical study is performed in order to evaluate the performance and optimal operating conditions of a palladium membrane reactor for methanol synthesis. A novel reactor configuration with a Pd wall, which is perm‐selective to hydrogen, has been proposed. In this configuration the reactants are added to the tube side while pure hydrogen is added to the shell side, as a result, the hydrogen diffuses across the membrane from the shell side to the tube side. In this membrane reactor, hydrogen penetrates to the reaction side in order to maintain a suitable hydrogen level in the whole length of the reactor and shift the equilibrium reaction. The effects of different parameters on the methanol output mole fraction were investigated in the co‐current mode. These parameters were membrane thickness, reaction side flow rate, reaction side pressure, shell side pressure and H2/CO2 ratio in the feed.

QUASI: A general purpose implementation of the QM/MM approach and its application to problems in catalysis

We describe the work of the European project QUASI (Quantum Simulation in Industry, project EP25047) which has sought to develop a flexible QM/MM scheme and to apply it to a range of industrial problems. A number of QM/MM approaches were implemented within the computational chemistry scripting system, ChemShell, which provides the framework for deploying a variety of independent program packages. This software was applied in several large-scale QM/MM studies which addressed the catalytic decomposition of N 2O by Cu-containing zeolites, the methanol synthesis reaction catalysed by Cu clusters supported on ZnO surfaces, and the modelling of enzyme structure and reactivity.

Development of a new methanol synthesis reactor : Kobayashi, K. and Morita, K. Kagaku Kogaku, 2002, 66, (6), 373. (In Japanese)

Development of a new methanol synthesis reactor : Kobayashi, K. and Morita, K. Kagaku Kogaku, 2002, 66, (6), 373. (In Japanese)

Fundamentals of Methanol Synthesis and Decomposition

Fundamental studies of methanol synthesis and decomposition (mainly over Cu-based catalysts) have been carried out. Various kinetic approaches, i.e. TPD study after various chemical treatments of catalyst, non-steady-state transformation of strongly adsorbed species, tracer technique, and steady-state kinetics, have been used. The macroscopic mechanism and detailed reaction scheme of methanol synthesis, as well as the kinetic description of the process have been established and proven. Methanol synthesis over Cu-based catalysts was found to occur by CO2 hydrogenation only, which was coupled with the water-gas shift reaction. Methanol decomposition and steam reforming over Cu-based catalysts have been studied. It was shown that methanol decomposed into a mixture of CO and H2 via methyl formate as an intermediate. Methanol transformation into the mixture of CO2 and H2 occurred by interaction of methanol and water. The reaction proceeded as the reverse methanol synthesis reaction, accompanied by the reverse water-gas shift reaction.

Optimal temperature profile in methanol synthesis reactor

An optimal temperature profile is determined for a methanol synthesis reactor of LURGI type. The temperature profile is estimated so that methanol production rate in the reactor outlet will be maximized. First, the reactor is simulated based on heterogeneous one- and two-dimensional models. The comparison of the simulation results and plant data shows that the heterogeneous one-dimensional model can reliably be used for determining optimal temperature profile. Since optimal temperature profile for reversible exothermic reaction in tubular reactors is a decreasing function of reactor length, the technique of control variable parameterization is used for determining optimal temperature profile in a methanol reactor. In this way, a third order polynomial is considered for the temperature profile and the polynomial coefficients are as decision variables. The optimization is based on a Quasi-Newton's method (BFS technique), and the objective function is methanol flow rate at the reactor outlet. The results of optimization indicate that if optimal temperature profile is implemented in the reactor, methanol production will significantly be increased.

Synthesis of Methyl Acetate from Dimethyl Ether Using Group VIII Metal Salts of Phosphotungstic Acid

Dimethyl ether (DME) can be produced much more efficiently in a single-stage, liquid-phase process from natural gas-based syngas as compared to the conventional process via dehydration of methanol. This process, based on dual catalysts slurried in inert oil, alleviates the chemical equilibrium limitation governing the methanol synthesis reaction and concurrently improves per-pass syngas conversion and reactor productivity. The potential, therefore, for production of methyl acetate via dimethyl ether carbonylation is of industrial importance. In the present study, conversion of dimethyl ether and carbon monoxide to methyl acetate is investigated over a variety of group VIII metal-substituted phosphotungstic acid salts. Experimental results of this catalytic reaction using rhodium, iridium, ruthenium, and palladium catalysts are evaluated and compared in terms of selectivity toward methyl acetate. The effects of active metal, support types, multiple metal loading, and feed conditions on carbonylation activity of DME are examined. Iridium metal substituted phosphotungstic acid supported on Davisil type 643 (pore size 150 A, surface area 279 m 2 /g, mesh size 230-425) silica gel shows the highest activity for DME carbonylation.

A New Low-Temperature Synthesis Route of Methanol: Catalytic Effect of the Alcoholic Solvent

The effects of different alcohols as reaction solvent on the synthesis of methanol from CO/CO2/H2 on solid Cu/ZnO catalyst were investigated. In the presence of some alcohol, especially 2-alcohol, as reaction medium, the reaction of methanol synthesis proceeded with high activity at temperatures as low as 423−443 K, much lower than the temperature in the present industrial methanol production process. This method is very promising to become a new technology for low-temperature synthesis of methanol where complete purification of syngas is not necessary.

Dynamics of a mixed slurry reactor for the three-phase methanol synthesis

A dynamic model for the liquid-phase methanol synthesis with the Langmuir–Hinshelwood kinetic formulation is presented for a well-mixed slurry reactor. Responses to a step-change in the reactor feed composition were studied in a temperature range of 200–240°C and total pressures between 34 and 41 bar . A commercial Cu/ZnO/Al 2O 3 and squalane were used as a catalyst and inert liquid phase, respectively. All transport, kinetic, and adsorption parameters, excepting the equilibrium adsorption constants for water and methanol, were evaluated in separate experiments. The two parameters were obtained by fitting the model predictions to the experimental responses and were found to obey the van't Hoff relation. A good agreement between experimental and predicted results found in a rather wide range of operating conditions validates the Langmuir–Hinshelwood kinetic formulation as an appropriate tool for describing the processes on catalyst surface.

STUDY ON THE BEHAVIOR OF AN INTEGRATED TWO-STAGE REACTOR FOR TWO-STEP METHANOL SYNTHESIS

The behavior of an integrated two-stage reactor for two-step methanol synthesis was investigated. The results show that the effect of mass transfer on the overall process is important in the system. Under the conditions used in this study, the carbonylation stage (the first stage) controls the overall process. The mass transfer of CO from the gas phase to the liquid phase is the rate-limiting step in the transient period, and the evaporation of the intermediate, methyl formate, from the liquid phase to the gas phase is the rate-limiting step at the steady state. Pressure, space velocity and temperature show significant influence on the rate of CO reaction at the steady state, while catalyst loading, inert packing and promoters in the first stage show little effects on the rate of CO reaction at the steady state.

Methanol synthesis in a fluidized-bed reactor coupled with an external heat exchanger: The effect of feedback deformation

Quantitative analysis of the steady states multiplicity, linear stability and the yield of a fluidized-bed reactor for the low pressure methanol synthesis has been performed. The reactor coupled with an external heat exchanger has been considered. Particular attention has been focused on the analysis of the effect of external feedback deformation on the stationary properties of this configuration. The obtained results show a significant influence of operational parameters on the yield of the reactor. The existence of maxima of the yield has been proven.

Methanol synthesis reactions over a CuZr based catalyst investigated using periodic variations of reactant concentrations

The application of the modulation concept to study the reaction pathway and the reaction rate constants of the methanol synthesis starting from CO and CO 2 over a CuZr based catalyst is described. Kinetic data of different reaction steps can be calculated by performing modulation experiments using different feed gas compositions. The dynamic variations in the concentrations of products, intermediates and reactants are monitored in situ in a DRIFT cell. The observed retardation (phase shift Δ ϕ) is examined depending on the modulation frequency ω. This method is used to derive equilibrium and overall rate constants characterising the investigated reaction steps. By repeating the experiments at different reaction temperatures, constants such as Arrhenius activation energies can be assessed.

An ab Initio Study of Hydrogen Adsorption on ZnO(101̄0)

The interaction of hydrogen with the stoichiometric ZnO(101̄0) surface has been studied using ab initio, all-electron total energy calculations. A highly accurate hybrid density functional (B3LYP) implemented within a local Gaussian basis set has been employed. Details of the geometric and electronic structure of the surface have been determined. The results are discussed in terms of the role of this surface as a model system for both catalytic reactions and gas sensing applications. The Zn−O dimers on the (101̄0) surface provide a model system for the type I adsorption sites known to be important in surface mediated methanol synthesis reactions. The interaction of hydrogen with the surface does not result in surface metallisation, and hence, the (101̄0) surface is unlikely to be an active gas sensing material.

A New Method of Low-Temperature Methanol Synthesis

A novel reaction system has been developed to synthesize methanol from carbon monoxide and hydrogen containing carbon dioxide as well as water by copper-based catalysts at low temperature and low pressure, compared to the present industrial process. This may be a new method for commercial methanol production. Carbon dioxide and water, which usually act as poisons to alkali metal methoxide catalyst in the low-temperature methanol synthesis reaction, play a promotional role in this new route. Accompanying alcohol, as a “catalytic liquid medium,” with the aid of copper-based solid catalyst, altered the reaction path to a low-temperature direction.

Global Kinetics Study of LPDME Process from Syngas

Global kinetic models are firstly developed for liquid phase dimethyl ether synthesis from syngas (LPDME), which is successfully based on reasonable assumptions and simplifications. The activation energies of methanol synthesis reaction and methanol dehydration reaction are 14.06 kJ/mol and 23.53 kJ/mol, respectively. CO and CO2 are strongly adsorbed on methanol catalyst of C301, and methanol and water are on gamma-alumina. The relative errors of experimental data and the calculated ones for methanol equivalent productivity and DME productivity are mostly within 10% and 20%. The model also gives a satisfactory explanation for experimental phenomena.

Mathematical modeling of internal mass transport limitations in methanol synthesis

Several simplifications on the dusty gas model were analyzed with respect to the accuracy of the resulting mathematical models in describing the effects of internal mass transport limitations in methanol synthesis. It turned out that all the models, including the simplest one, viz. Thiele modulus concept using pseudo-first-order kinetics, are capable to predict the methanol and water effectiveness factors with a sufficient accuracy. Therefore, application of the simplest Thiele modulus concept is advised, since this model is easily incorporated in complex methanol synthesis reactor models. Moreover, we expect that the Thiele modulus approach can be applied for other complex reaction/diffusion systems, provided that proper linearization of the kinetic model is possible. The experimental data of Seyfert and Luft (1985) on the rate of methanol production for different catalyst sizes can be described with the kinetic expressions of Graaf et al. (1988,1990), using the mathematical mass transport models presented in this paper.

Modification of Cu/ZnO/SiO 2 catalysts by high temperature reduction

In this overview results obtained in three laboratories on Cu/ZnO/SiO 2 catalysts prepared by homogeneous deposition–precipitation are summarised. It is concluded that the system adopts a layered ‘zincsilite’ structure. In this copper–zinc hydrosilicate the Cu and/or Zn cations are located in octahedral sites and in the interlayer. When copper or zinc is present in excess of the zincsilite ratio (Cu y + Zn 1− y : Si = 0.75) or at relatively high copper content ( y ≥ 0.40), copper–zinc and copper hydroxocompounds are formed, the latter yielding CuO after calcination. Cu/ZnO/SiO 2 shows increased activity in ester hydrogenolysis and methanol synthesis reactions as a function of reduction temperature, in contrast to the unpromoted catalyst. Inert treatment at 700 K significantly decreases activity, whereas subsequent reductive treatment restores the high activity mode. The copper metal surface area of the promoted catalyst increases modestly with reduction temperature when the catalyst is carefully evacuated preceding a N 2O chemisorption measurement. Significantly lower surface areas result after prolonged evacuation at higher temperatures. It was shown using infrared spectroscopy that upon high temperature (700 K) reduction cationic copper sites are created. Investigation of 63Cu/ 68ZnO/SiO 2 by low energy ion scattering demonstrates that the surface of the catalyst reduced at 700 K is enriched in zinc. In the 600 K reduced catalyst the zinc enrichment was less prominent. It is proposed that the Cu–ZnO interface plays a crucial role in catalysing the reactions studied. It is not yet possible to decide between two models arriving at a situation where this interface is enlarged: (1) Reversible formation of flat epitaxial particles upon high temperature reduction from the fraction of the copper dissolved in the mixed oxide catalyst precursor phase. (2) Migration of partly reduced ZnO on top of copper.

Development of skeletal copper–chromia catalysts: I. Structure and activity promotion of chromia on skeletal copper catalysts for methanol synthesis

Studies of promotional effects of chromia on structure and properties of skeletal copper catalysts for methanol synthesis have been carried out. Catalysts were prepared by selective dissolution of aluminum from CuAl 2 alloy and, at the same time, precipitation of chromia on the surface of residual skeletal copper using a caustic solution containing sodium chromate. Deposition of chromia on the skeletal copper catalysts was found to greatly influence the pore structure and specific surface area, resulting in a relative decrease of pore diameter and remarkable enhancement of specific surface area, while the total pore volume was maintained constant. Significant improvements to methanol synthesis activity and selectivity were achieved by adding small amounts of chromia (about 3.5 wt.%) to the skeletal copper. However, higher chromia loadings were found to be unfavorable for methanol synthesis reactions. The results obtained in this study suggest that chromia acts as a structural promoter and provides high specific copper surface area for methanol synthesis. The chromia-promoted catalysts produced by this method are likely to have applications in organic hydrogenation reactions and for the water gas shift reaction.

Carbon Dioxide Hydrogenation To Form Methanol via a Reverse-Water-Gas-Shift Reaction (the CAMERE Process)

The CAMERE process (carbon dioxide hydrogenation to form methanol via a reverse-water-gas-shift reaction) was developed and evaluated. The reverse-water-gas-shift reactor and the methanol synthesis reactor were serially aligned to form methanol from CO2 hydrogenation. Carbon dioxide was converted to CO and water by the reverse-water-gas-shift reaction (RWReaction) to remove water before methanol was synthesized. With the elimination of water by RWReaction, the purge gas volume was minimized as the recycle gas volume decreased. Because of the minimum purge gas loss by the pretreatment of RWReactor, the overall methanol yield increased up to 89% from 69%. An active and stable catalyst with the composition of Cu/ZnO/ZrO2/Ga2O3 (5:3:1:1) was developed. The system was optimized and compared with the commercial methanol synthesis processes from natural gas and coal.

Structural and catalytic promotion of skeletal copper catalysts by zinc and chromium oxides

ZnO and Cr2O3 promoted skeletal copper catalysts have been prepared by leaching CuAl2 alloy particles in aqueous sodium hydroxide containing various concentrations of sodium zincate (Na2Zn(OH)4) (0–0.62 M), of sodium chromite (NaCrO2) (0–0.1 M) or of a mixture of sodium zincate (0.005 M) and sodium chromite (0.02 M). Both sodium zincate and sodium chromite in the caustic solution were found to affect the leaching process. The presence of sodium zincate retarded the leaching rate and enhanced the specific surface area of the catalyst but did not protect copper rearrangement on extended leaching. On the other hand, sodium chromite in the leachant did not influence the leaching rate but the leached catalyst was more stable with the structure and surface area of the skeletal copper being maintained. The activities of ZnO and Cr2O3 promoted skeletal copper catalysts for the reactions of methanol synthesis, water gas shift and methanol steam reforming were determined separately. The results indicated that deposition of both ZnO and Cr2O3 on skeletal copper catalysts significantly improved the activities for these reactions. Chromia is found to act mainly as a structural promoter.