Formation Of Dimethyl Ether Research Articles

Confinement Effect and Synergistic Function of H-ZSM-5/Cu-ZnO-Al2O3 Capsule Catalyst for One-Step Controlled Synthesis

Dimethyl ether (DME) is an industrially important intermediate, as well as a promising clean fuel, but the effective production through traditionally consecutive steps from syngas to methanol and then to DME has been hindered by the poorly organized structure of the conventional physical mixture catalyst. Here, a novel zeolite capsule catalyst possessing a core-shell structure (millimeter-sized core catalyst and micrometer-sized acidic zeolite shell) was proposed initially through a well-designed aluminum migration method using the core catalyst as the aluminum resource and for the first time was applied to accomplish the DME direct synthesis from syngas. The selectivity of the expected DME on this zeolite capsule catalyst strikingly exceeded that of the hybrid catalyst prepared by the traditional mixing method, while maintaining the near-zero formation of the unexpected alkanes byproduct. The preliminary methanol synthesis reaction on the core catalyst and the following DME formation from methanol inside the zeolite shell cooperated concertedly and promoted mutually. This zeolite capsule catalyst with a synergetic confinement core-shell structure can be used to efficiently realize the combination of two and more sequential reactions with many synergistic effects.

Dehydration of methanol on zeolite-containing catalysts

Conversion of methanol on unmodified industrial cracking catalysts (ICC) containing zeolite Y (KM, Zeocar-2 and KM-R) and NZHS (KM-1 and KM-1R), unmodified and modified with phosphoric acid, was investigated. It was shown that conversion from selective formation of hydrocarbon products whose composition is a function of the temperature to selective formation of dimethyl ether (DME) is observed on KM-1 catalyst as a function of the duration of the experiment. The catalyzates formed on the KM and Zeocar-2 catalysts and hydrocarbons and DME (∼50%) differ from the catalyzates formed on the KM-1 catalyst, with a stable composition for the duration of the experiments. Modified catalysts KM-1R and KM-R provide a stable, highly selective yield of hydrocarbons and DME, respectively. The results obtained demonstrate the promise of using ICC for dehydration of methanol into DME.

Effect of zeolite framework type and Si/Al ratio on dimethoxymethane carbonylation

This work reports on the effects of zeolite framework type and Si/Al ratio on the carbonylation of dimethoxymethane (DMM) to produce methyl methoxyacetate (MMAc). Faujasite (FAU), ZSM-5 (MFI), Mordenite (MOR) and Beta (BEA) showed very similar activity for DMM carbonylation. However, FAU had a very high selectivity to MMAc compared to MFI, MOR and BEA because of very low rates of dimethyl ether (DME) and methyl formate (MF) formation, by-products of the disproportionation of DMM. The high rate of DMM disproportionation observed for MFI, MOR and BEA is ascribed to the small pores of these zeolites, which facilitate a critical initial step in the formation of DME and MF. FER showed very low activity for both carbonylation and disproportionation. Increasing the Si/Al ratio for both FAU and MFI led to an increase in the turnover frequency for DMM carbonylation. It is proposed that the low rate of MMAc formation found at low Si/Al ratios is due to repulsive interactions occurring between adsorbed species located within the same supercage (FAU) or channel intersection (MFI).

A First-Principle Study of Oxonium Ylide Mechanism over HSAPO-34 Zeolite

Abstract Based on density functional theory calculation with periodic boundary conditions, the possibility of the direct coupling of methanol into ethene by oxonium ylide mechanism was investigated. The calculated results indicate that the energy barriers for the formation of dimethyl ether and trimethyl oxonium ion inside HSAPO-34 zeolite are 1.68 and 0.93 eV, respectively. The suggested intermediate oxonium ylide is very unstable and the energy barriers for the formation of C-C bond are over 3.0 eV by concerted pathway. It is thus concluded that the methanol to olefin reaction cannot follow the oxonium ylide mechanism.

Poly(4-vinylpyridine) catalyzed selective methanolysis of methyl and methylene bromides

The effect of poly(4-vinylpyridine) (PVP) on the methanolysis of methyl bromide and methylene bromide was studied at temperatures between 75 °C and 125 °C. PVP acts as an efficient HBr scavenger promoting the formation of dimethyl ether (DME) and dimethoxymethane (DMM) from the corresponding bromomethanes and methanol in moderate yields with high selectivity. No reaction was observed in the absence of PVP under the conditions adopted. The activity of the catalyst remained unchanged even after five cycles showing the efficacy and application of the polymer as an environmentally green reagent as well as catalyst in this methanolysis reaction.

Catalytic conversion of chloromethane to methanol and dimethyl ether over metal-exchanged zeolite Y

The catalytic hydrolysis of chloromethane to methanol and dimethyl ether was studied over metal-exchanged zeolite Y (NaY, KY, CsY, MgY, CuY and FeY). All catalysts showed higher conversions than the blank reaction in the temperature range between 453 and 673 K. Methanol was the major product on all catalysts, with selectivity ranging from 76 to 95%. Dimethyl ether (DME) was the other major product formed with selectivity of 5–7% over alkaline cation-exchanged zeolite Y and 10–24% over the zeolites exchanged with polyvalent cations. The higher selectivity to DME over MgY, CuY and FeY is associated with the presence of stronger acid sites with respect to NaY. Theoretical calculations indicated that a mechanistic pathway involving methanolysis of an adsorbed methoxy group may account for the formation of dimethyl ether on alkaline cation-exchanged zeolites.

A comparative study of methanol carbonation on unsupported SnO 2 and ZrO 2

The aim of this work was to explore the catalytic properties of SnO 2 in the coupling of methanol with carbon dioxide to afford dimethyl carbonate. SnO 2 nanopowders were produced by hydrolysis of tin tetra- tert-butoxide dissolved in n-butanol. The samples were much more active than a commercial one due to their higher surface areas. In addition, they exhibited excellent recyclability. However, comparison with ZrO 2, prepared and tested under the same experimental conditions, showed that zirconia-based catalysts were more selective and are, among the heterogeneous catalysts already reported, still the more selective. SnO 2 also catalyzed the formation of dimethyl ether likely due to lower rates in the formation of the key intermediate CH 3OC(O)O–Sn and its subsequent alkylation by activated methanol. This lack of selectivity contrasts with that of soluble organotin(IV) which are totally selective to DMC formation. Structural characterization of SnO 2 was performed by X-ray powder diffraction, laser Raman spectroscopy, transmission electron microscopy, and nitrogen isotherm. As found from X-ray diffraction line broadening, the crystallite size of all powders was in the nanometric range (cassiterite structure) which was confirmed by transmission electron microscopy. Moreover, the low-frequency Raman scattering allowed to determine an average particle size diameter of 4 nm.

A one-step route to SAPO-46 using H 3PO 3-containing gel and its application as the catalyst for methanol dehydration

SAPO-46 molecular sieve has been synthesized on a new one-step route by using phosphorous acid (H 3PO 3) or the mixture of H 3PO 3 and phosphoric acid (H 3PO 4) as the phosphorus source. It has been found that the pure phase of SAPO-46 could be obtained more conveniently from the H 3PO 3-containing gels at 200 °C. Meanwhile, SAPO-46 with higher crystallinity can be synthesized in a wide range of gel compositions, containing higher silica in the product. As the catalyst for the dehydration of methanol to dimethyl ether (DME), it has exhibited high selectivity for the formation of DME as well as the activity of methanol conversion. Raman and IR have been employed to characterize the initial gel and as-synthesized sample to investigate the formation of SAPO-46 and the one-template-multiple-structures phenomena in the new one-step route, where SAPO-41 or SAPO-46 can be formed according to silica concentration. The transformation of P(III) species in the initial gels to P(V) species during crystallization have been found. It may be the key role for the formation of SAPO-46 on the new route. Besides, the correlation between silica content and the structure type of crystalline products with di-n-propylamine as the template has also been obtained.

Influence of Catalytic Functionalities of Zeolites on Product Selectivities in Methanol Conversion

In an attempt to understand the textural and acidic properties of zeolites on the methanol conversion and product selectivities, three zeolites, ferrierite, clinoptilolite, and SAPO-34, are studied. Temperature-programmed desorption of ammonia (NH3−TPD) indicated the presence of more weak acidity on ferrierite and clinoptilolite compared to the considerable strong acidity on SAPO-34. At 250 °C, all three samples exhibited comparable methanol conversions, but relatively lower dimethyl ether (DME) and higher light olefins are observed on SAPO-34. Ferrierite and clinoptilolite samples exhibited high selectivity for the formation of DME even at higher reaction temperatures (400 °C), while the product shifted from DME to light olefins with an increasing reaction temperature on SAPO-34. Especially, ferrierite, owing to its mild acidity and small pore size, is found to be a good catalyst for the methanol conversion to DME at 250 °C without significant deactivation for 100 h time on stream.

Properties of surface compounds in methanol conversion on γ-Al2O3: Data of in situ IR spectroscopy

In situ IR spectroscopic studies show that a formate, an aldehyde-like complex, and bridging and linear methoxy groups exist on the alumina surface involved in methanol conversion. In the absence of methanol in the gas phase, the interaction between two bridging methoxy groups yields dimethyl ether in the gas phase. When methanol is present in the gas phase, it interacts with methoxy groups on the surface. This reaction makes the main contribution to the formation of dimethyl ether. The linear methoxy group undergoes conversion via several routes. The main route is desorption with methanol formation in the gas phase, and no more than 10% of the linear methoxy groups are converted into formate and aldehyde, which are CO2 sources in the gas phase. In the absence of methanol in the gas phase, the conversion rate of the methoxy groups is independent of the presence of water and oxygen. A scheme of the surface reactions is suggested to explain the conversion of the methoxy groups.

Oxidation of Lignin Using Aqueous Polyoxometalates in the Presence of Alcohols

A novel approach has been developed in order to use Kraft lignin as a renewable resource for the production of chemicals. The concept is based on the use of polyoxometalates as reversible oxidants and on the use of radical scavengers, which prevent lignin fragments from repolymerizing. The oxidation of Kraft lignin, which is a potential source of functionalized phenols, by H3PMo12O40 in water yields a relatively small amount of monomeric species detected by GC-MS. The addition of methanol to the reaction resulted in an increase in the yield of monomeric products by a factor of up to 15. Vanillin and methyl vanillate are the main products obtained, in a maximum yield of 5 wt % based on dry Kraft lignin. Methanol plays a decisive role in the prevention of repolymerization by reducing lignin-lignin condensation reactions. Furthermore, it is proposed that methanol generates small amounts of .CH3 and CH3O. radicals through the acid-catalyzed formation of dimethyl ether which couple with lignin fragments.

Surface nature of nanoparticle zinc-titanium oxide aerogel catalysts

Nanoparticle zinc-titanium oxide materials were prepared by the aerogel approach. Their structure, surface state and reactivity were investigated. Zinc titanate powders formed at higher zinc loadings possessed a higher surface area and smaller particle size. X-ray photoelectron spectroscopy (XPS) revealed a stronger electronic interaction between Zn and Ti atoms in the mixed oxide structure and showed the formation of oxygen vacancy due to zinc doping into titania or zinc titanate matrices. The 8–45 nm aerogel particles were evaluated as catalysts for methanol oxidation in an ambient flow reactor. Carbon dioxide was favorably produced on the oxides with anion defects. Titanium based oxides exhibited a high selectivity to dimethyl ether, so that a strong Lewis acidic character suggested for the catalysts was associated primarily with the Ti 4+ center. Both methanol conversion and dimethyl ether formation rates increased with increasing the zinc content added to the oxide support. Results demonstrate that cubic zinc titanate phases produce new Lewis acid sites having also a higher reactivity and that the nature of the catalytic surface transforms from Lewis acidic to basic characters due to the presence of reactive oxygen vacancies.

Transformations of Gaseous Methanol over Supported and Unsupported Ruthenium Containing Polyoxomolybdate Catalysts

Catalytic features of supported and unsupported ruthenium containing polyoxomolybdate anion (Ru2Mo14) were evaluated using the methanol transformation reaction. Decomposition of methanol into hydrogen (H2) and carbon monoxide (CO) predominantly occurred over unsupported Ru2Mo14 whereas no acid-catalyzed reaction (formation of dimethyl ether, DME) occurred indicating that Ru2Mo14 had a weak acidity or had no acidity. Ru2Mo14 was homogeneously loaded up to ca. 40 wt% on silica and titania that had been chemically modified with N -(2-aminoethyl-3-aminopropyltrimethoxysilane. Ru2Mo14 catalysts supported on these modified supports exhibited higher conversion of methanol than Ru2Mo14 catalysts either unsupported or supported on unmodified supports, indicating that Ru2Mo14 was highly dispersed on the modified supports. Even in the presence of water vapor, no steam reforming of methanol or shift reaction of CO occurred over the supported Ru2Mo14 catalysts. Ru2Mo14 catalyst supported on modified alumina support converted methanol to DME by acid-catalyzed reaction together with the decomposition products, CO and H2, indicating that the Ru2Mo14 catalyst supported on modified alumina possessed strong acidity. FT-IR measurement of the methanol species adsorbed on Ru2Mo14 catalyst supported on modified alumina and the contact time dependency of this reaction suggested that methanol decomposition proceeded via formation of formaldehyde and subsequent decomposition into CO and H2.

Improved atom efficiency via an appreciation of the surface activity of alumina catalysts: Methyl chloride synthesis

The hydrochlorination of methanol over a commercial grade η-alumina catalyst has been investigated via temperature-programmed reaction (TPR). Experiments were conducted over a temperature range of 295–1000K using: (i) a methanol-only feed stream and (ii) a methanol/HCl mixed feed stream in a 1:1 mole ratio. Methanol-only studies showed activity for the formation of dimethyl ether (DME) above 450K, consistent with temperature-programmed desorption studies. A rapid decline in DME activity and consumption of methanol at higher temperatures were observed and are attributed to a deactivation pathway, involving the conversion of methoxy species to surface formate species. At elevated temperatures these processes lead to the deposition of carbon on the substrate. The introduction of HCl to the reaction stream resulted in the formation of methyl chloride (MC) over a temperature range of 400–750K. Relatively small quantities of DME by-product were also observed over a similar temperature range. The coincidence of the reaction profiles of both MC and DME imply that the same reactive methoxy species are involved in both processes. The rate of reaction for the formation of both products declines rapidly above 700K. This is attributed to the methoxy decomposition pathway to formate and, ultimately, to carbon retention by the catalyst.The effect of carbon deposition was also investigated via a subsequent cooling process carried out immediately after TPR experiments. Reaction profiles showed comparable activity for the formation of both products with respect to initial TPR experiments. Taken together, these results indicate an optimum reaction temperature for the formation of methyl chloride from the hydrochlorination of methanol. At such temperatures, carbon deposition is minimized and high conversion is maintained.

The mechanism of phenol methylation on acid and basic zeolite catalysts

The alkylation of phenol with methanol on HY and CsY/CsOH catalysts was studied in situ under static conditions by 13C NMR spectroscopy. Attention was largely given to the identification of intermediate compounds and mechanisms of anisole, cresol, and xylenol formation. The mechanisms of phenol methylation were found to be different on acid and basic catalysts. The primary process on acid catalysts was the dehydration of methanol to dimethyl ether and methoxy groups. This resulted in the formation of anisole and dimethyl ether, the ratio between which depended on the reagent ratio, which was evidence of similar mechanisms of their formation. Subsequent reactions with phenol gave cresols and anisoles. Cresols formed at higher temperatures both in the direct alkylation of phenol and in the rearrangement of anisole. The main alkylation product on basic catalysts was anisole formed in the interaction of phenolate anions with methanol; no cresol formation was observed. The deactivation of acid catalysts was caused by the formation of condensed aromatic hydrocarbons that blocked zeolite pores. The deactivation of basic catalysts resulted from the condensation of phenol and formaldehyde with the formation of phenol-formaldehyde resins.

Kinetics of the partial oxidation of methanol over a Fe-Mo catalyst

The intrinsic steady-state kinetics of the partial oxidation of methanol to formaldehyde over a commercial Fe-Mo catalyst has been studied experimentally in a differentially operated reactor at temperatures of 230–260 °C, over a wide range of methanol and oxygen concentrations. The principal products found were formaldehyde, water, dimethyl ether (DME) and dimethoxymethane (DMM). The kinetics of the formaldehyde formation from methanol could be well described with Langmuir–Hinshelwood kinetics, assuming two different metal oxide sites, one containing adsorbed oxygenates and the other one containing lattice oxygen. The presence of water vapor lowered the formaldehyde formation rate significantly, especially at lower water partial pressures. These results could be well explained in terms of competitive adsorption of water with methanol on the free active catalyst sites. For the most important side reactions, i.e. dimethyl ether formation as well as dimethoxymethane formation the forward reaction rates were determined from the selectivity data. The conversion rate of dimethyl ether to formaldehyde was also measured with separate experiments in the differential reactor. Carbon monoxide was not formed during the differential kinetic measurements of formaldehyde formation from methanol. Therefore, the rate of formaldehyde oxidation to CO was studied separately in a dual bed catalyst, where formaldehyde was formed in the first integral reactor at low temperatures and subsequently converted to CO in a differential reactor. The rate of CO formation was first order in formaldehyde and the oxygen dependency was the same as that for the formaldehyde formation from methanol. Rate expressions for all reactions were formulated based on the above assumptions and a multivariate Levenberg–Marquardt method was used to fit all the model constants to all the experiments for all reaction rates simultaneously, while additionally accounting for axial concentration profiles in the reactor. The observed influences of composition and temperature on the reaction rates could be well described.

Nanocluster iron oxide-silica aerogel catalysts for methanol partial oxidation

Nanostructured pure and silica-supported iron oxide materials have been prepared by the aerogel approach. Pure iron oxide powder derived from sol-gel ferric acetylacetonate formed agglomerates of 5–30 nm small crystallites of hematite and maghemite according to TEM identification of crystal faces. Depositing ferric species to mesoporous silica aerogels generated 1–5 nm particles in the amorphous matrix. They were evaluated for methanol oxidation in an ambient fixed-bed flow reactor from 225 to 300 °C. Product selectivity and oxidation activity were dependent upon iron dispersion and reactor operation. The formation of dimethyl ether was mainly related to the bulk phase and Lewis acidity of iron oxide. Active catalysts that were selective to formaldehyde and methyl formate required appropriate iron dispersion on the silica surface, including a strong electronic interaction. Methoxy transformation to formaldehyde and formate species was found to be a function of surface temperature based on a Fourier transform infrared (FT-IR) analysis. Low to moderate reactor temperature and short catalyst contact time favored methanol conversion to formaldehyde. The formation of methyl formate was found to compete with that of formaldehyde. The dependence of response time on oxygen feed attenuation suggests that mobile lattice oxide ions participate in the surface reaction and that oxygen molecules help to maintain surface iron sites highly oxidized for Lewis chemisorption and redox electron transfer. A good correlation between microstructures and reaction characteristics is proposed.

Conversion of Biomass Syngas to DME Using a Microchannel Reactor

The capability of a microchannel reactor for direct synthesis of dimethyl ether (DME) from biomass syngas was explored. The reactor was operated in conjunction with a hybrid catalyst system consisting of methanol synthesis and dehydration catalysts, and the influence of reaction parameters on syngas conversion was investigated. The activities of different dehydration catalysts were compared under DME synthesis conditions. Reaction temperature and pressure exhibited similar positive effects on DME formation. A catalytic stability test of the hybrid catalyst system was performed for 880 h, during which CO conversion only decreased from 88% to 81%. In the microchannel reactor, the catalyst deactivation rate appeared to be much slower than in a tubular fixed-bed reactor tested for comparison. Test results also indicated that the dehydration reaction rate and the water depletion rate via a water-gas-shift reaction should be compatible to achieve high selectivity to DME. Using the microchannel reactor, it was p...

Role of substitution in catalytic activity of La–Th–V–O mixed oxides for the reaction of methanol

Abstract A series of composite metal oxide catalysts of nominal composition La x Th 1− x V 2 O 7−δ ( x = 0.0–0.5) were synthesized by ceramic route and characterized using XRD, IR and temperature programmed reduction (TPR) measurements. The partial substitution at A-sites had profound effect on the catalytic behavior of thorium pyrovanadate for the dehydration of methanol, the extent of which depended upon the value of x . The following was the trend of catalytic activity of different samples as a function of the value of x : x up to 0.2 > 0.3 > 0.5 > 0 > ThO 2 . In addition, the substituted samples exhibited higher selectivity for the formation of dimethyl ether and also a better compositional stability towards the successive cycles of reduction/reoxidation. These characteristics of substituted samples are found to be related to existence of a phase, viz. La x Th 1− x V 2 O 7−δ , where a part of lattice Th sites are substituted by La. On the other hand, the other secondary phases, viz. LaTh(VO 4 ) 3−δ and Th(VO 3 ) 4 that were produced simultaneously during the sample preparation, play no important role. It is suggested that the nonstoichiometry generated in the pyrovanadate phase is responsible to the improvement in the catalytic activity and the stability of the substituted samples.

Surface Properties and Catalytic Activity of TiO2–ZrO2Mixed Oxides in Dehydration of Methanol to Dimethyl Ether

A series of TiO2–ZrO2 mixed oxides with varying molar ratio of TiO2 to ZrO2 were prepared by the co-precipitation method. The crystalline phases of the oxides were characterized by XRD and their acid–base properties by TPD of NH3 and CO2 and IR of adsorbed pyridine. The catalytic activities were investigated for the vapor phase dehydration of methanol to dimethyl ether (DME) in a fixed-bed reactor under atmospheric pressure. The mixed oxides are highly amorphous in nature. The acid–base properties and CH3OH conversion activity are increasing with TiO2 content and an optimum value is achieved for a molar ratio of Ti/Zr in the vicinity of 1/1. At lower reaction temperature (<300 °C), the selectivity for DME is nearly 100%. A good correlation is observed between dehydration activity and the acid–base properties of the TiO2–ZrO2 catalysts. It is significant to note that TiO2–ZrO2 catalysts show high stability against water during dehydration reaction. Based on our results, a surface mechanism involving both acid–base sites has been proposed for DME formation.