High Methanol Conversion Research Articles

Performance comparison of two low-CO 2 emission solar/methanol hybrid combined cycle power systems

Abstract Two novel hybrid combined cycle power systems that use solar heat and methanol, and integrate CO2 capture, are proposed and analyzed, one based on solar-driven methanol decomposition and the other on solar-driven methanol reforming. The high methanol conversion rates at relatively low temperatures offer the advantage of using the solar heat at only 200–300 °C to drive the syngas production by endothermic methanol conversions and its conversion to chemical energy. Pre-combustion decarbonization is employed to produce CO2-free fuel from the fully converted syngas, which is then burned to produce heat at the high temperature for power generation in the proposed advanced combined cycle systems. To improve efficiency, the systems’ configurations were based on the principle of cascade use of multiple heat sources of different temperatures. The thermodynamic performance of the hybrid power systems at its design point is simulated and evaluated. The results show that the hybrid systems can attain an exergy efficiency of about 55%, and specific CO2 emissions as low as 34 g/kW h. Compared to a gas/steam combined cycle with flue gas CO2 capture, the proposed solar-assisted system CO2 emissions are 36.8% lower, and a fossil fuel saving ratio of ∼30% is achievable with a solar thermal share of ∼20%. The system integration predicts high efficiency conversion of solar heat and low-energy-penalty CO2 capture, with the additional advantage that solar heat is at relatively low temperature where its collection is cheaper and simpler. The systems’ components are robust and in common use, and the proposed hybridization approach can be also used with similar benefits by replacing the solar heat input with other low heat sources, and the system integration achieves the dual-purpose of clean use of fossil fuel and high-efficiency conversion of solar heat at the same time.

Simultaneous production of dimethyl ether (DME), methyl formate (MF) and hydrogen from methanol in an integrated thermally coupled membrane reactor

The present study aims to presents two new configurations to improve dimethyl ether (DME) production rate besides producing methyl formate (MF) and hydrogen. In this regard, a thermally coupled reactor (TCR) and an integrated thermally coupled membrane reactor (TCMR) with feature of simultaneous production of DME, MF and hydrogen from methanol is proposed. A palladium–silver membrane with high hydrogen permeation rate is utilized to boost hydrogen recovery and MF production rate in TCMR. A one-dimensional plug flow model is considered to evaluate molar and thermal performance of the proposed configurations. Effect of various operating conditions such as inlet flow rates and permeation side configurations on the temperature profiles, methanol conversion, and DME and hydrogen production rate is studied numerically. Utilizing TCR and TCMR configurations promotes methanol conversion to DME to %85 and %87, respectively. Besides, a %22 increase in methanol conversion in the endothermic side was observed applying the hydrogen perm-selective membrane. Generally, higher methanol conversion in both endothermic and exothermic sides and hydrogen production rate in the permeation side was observed using a sweep gas with higher flow rates and lower temperature.

Increasing para-Xylene Selectivity in Making Aromatics from Methanol with a Surface-Modified Zn/P/ZSM-5 Catalyst

We report a ZSM-5 based catalyst with surface modification of SiO2 to increase the selectivity of para-xylene (PX) in xylene (X) in the methanol-to-aromatics process. The effect of acid strength and acid amount in HZSM-5, Zn/P/ZSM-5, and Zn/P/Si/ZSM-5 on the catalytic performance, including methanol conversion, aromatic yield, and PX selectivity, were studied. The total acid strength and acid amount of the catalyst were crucial for high methanol conversion (around 100%) and high yield of aromatics (>60%), whereas weak external acid sites present in a small amount played an important role in increasing the PX selectivity (in the X isomers) from the usual 23–24% to 89.6%. The results validated the use of a catalyst having a core with strong acid sites in a large amount and an external shell with weak acid sites in a small amount. The contribution of the external surface reaction, including alkylation, isomerization, and dealkylation, to the PX selectivity was evaluated by using PX or ortho-X separately as feedstock. A Zn/P/Si/ZSM-5 catalyst worked well in continuous reaction/catalyst-regeneration cycles, and it also converted recycled toluene into PX by an alkylation route.

Catalytic Performance of SAPO-34 Catalysts of Different Crystal Sizes in Methanol-to-Olefins Reactions: Effects of Synthetic Parameters

The catalytic performance of SAPO-34 catalysts which were synthesised hydrothermally under different conditions was investigated in methanol-to-olefins reactions. The significance of template, silicon sources and crystallisation time on catalytic performance, and deactivation of SAPO-34 catalysts, were studied. High methanol conversion and yield of light olefins were obtained over the nano-sized catalyst synthesised with tetraethylammonium hydroxide as template source and tetraethyl orthosilicate as silica source with a crystallisation time of 24 h, owing to its higher crystallinity and smaller crystal size. The SAPO-34 catalysts with larger sizes of crystals deactivate rapidly, while smaller crystals retain their activity for a longer time.

Co-conversion of methanol and light alkenes over acidic zeolite catalyst H-ZSM-22: Simulated recycle of non-gasoline range products

The zeolite-catalyzed methanol to gasoline process is one way of making synthetic transportation fuel from readily available carbon sources. In addition to the targeted chemicals, this process produces notable amounts of byproduct hydrocarbons (C2–C4). Here, we investigate the co-conversion of methanol and light alkenes (C2–C4) with aim of elucidating the effects of byproduct recycle over the ZSM-22 catalyst. ZSM-22 is a unidirectional 10-ring zeolite, which yields a C5+ product with virtually no aromatics. The addition of alkenes as co-reactants significantly improves the lifetime of ZSM-22 catalyst, and net conversion of the co-added alkenes is observed. At high methanol conversion or low partial pressure of co-reactant alkene, the product distribution is virtually unaffected compared to that found for the neat MTH reaction. However, ethene accumulation might require attention during actual process design. Using isotope-labeling experiments involving 12C-alkene and 13C-methanol, a clear tendency for methylation of the co-reactant alkene with methanol is observed with progressive deactivation of the catalyst. This investigation presents byproduct recycle as a potential route for utilization of light hydrocarbons during the MTH process over ZSM-22.

The one-step oxidation of methanol to dimethoxymethane over sulfated vanadia–titania catalysts: influence of calcination temperature

The highest methanol conversion was obtained on catalysts calcined at 723 and 773 K.

Study of different designs of methanol steam reformers: Experiment and modeling

Three reformers with different designs (multi-channel, radial and tubular) were developed for thermal integration with a high temperature polymeric electrolyte membrane fuel cell (HT-PEMFC). They were characterized experimentally at temperatures between 443 K and 473 K, using the commercial catalyst G66 MR from Süd-Chemie (CuO/ZnO/Al2O3). The reactors were modeled and simulated using a computational fluid dynamics (CFD) analysis. The models were validated using experimental data.The results showed that the multi-channel design is the best solution for thermal integration with a HT-PEMFC, presenting high methanol conversion and low pressure drop. Regarding the heat transfer ability, the multi-channel showed also the best performance, presenting the lowest temperature sink among the studied reformers. The low flow velocities and the absence of metallic surfaces in the radial reformer had detrimental effect on the heat transfer. Concerning the flow distribution a coefficient of variation of 0.6% was observed in the multichannel reformer. A quasi plug flow behavior was found in the tubular and a multichannel (channels region only) reformer, while in the radial a not fully developed laminar flow was found.At temperatures lower than 473 K was found that the reformate stream did not require further purification to be fed to a HT-PEMFC due to the low CO concentration (<1600 ppm).The advantages and limitations of each design is discussed based on experimental data and CFD modeling.

Cerium oxide-based catalysts made by template-precipitation for the dimethyl carbonate synthesis from Carbon dioxide and methanol

This paper mainly describes a novel synthesis of three different ceria catalysts CeO2, CeO2–SiO2 and CeO2-4A via template-precipitation method. The prepared catalysts were fully characterized by means of temperature-programmed desorption (TPD), X-ray powder diffraction (XRD), BET surface area test, SEM and FTIR. The catalytic performance over these ceria catalysts were examined for the dimethyl carbonate (DMC) synthesis from CO2 and methanol. The results indicate that CeO2-4A exhibits the highest DMC yield, followed by CeO2–SiO2 and CeO2 catalysts. Under the reaction conditions at 0.6 MPa and 120 °C with space velocity of 300 h−1, the highest methanol conversion is 3.97% with DMC selectivity of 81.4%.

Fuel cell grade hydrogen production via methanol steam reforming over CuO/ZnO/Al2O3 nanocatalyst with various oxide ratios synthesized via urea-nitrates combustion method

Hydrogen production via steam reforming of methanol has been studied over a series of CuO/ZnO/Al2O3 catalysts synthesized by the combustion method using urea as fuel. Furthermore, the effect of alumina loading on the properties of the catalyst has been investigated. XRD analysis illustrated the crystallinity of the Cu and Zn oxides decreases by enhancing alumina loading. BET showed the surface area improvement and FESEM images revealed lower size distribution by increasing the amount of alumina. EDX results gave approximately the same metal oxide compositions of primary gel for the surface of the nanocatalysts. Catalytic performance tests showed the well practicability of catalysts synthesized by the combustion method for steam reforming of methanol process. Alumina addition to the CuO/ZnO catalyst caused the higher methanol conversion and the lower CO generation. Among different compositions the sample with molar component of CuO/ZnO/Al2O3 = 4/4/2.5 showed the best performance which without CO generation at 240 °C its methanol conversion decreased from 90 to 60% after 90 h.

Dimethyl Ether Synthesis via Methanol Dehydration over BEA Zeolite from Bagasse Fly Ash with Zircronium- and Nickel-Ion Exchange

The synthesis of dimethyl ether via methanol dehydration has been carried out over Beta zeolite (BEA) and ion-exchanged Beta zeolite from bagasse fly ash using hydrothermal method. The reactions were taken place in a fixed-bed reactor. The effects of nickel and zirconium ion-exchanged of BEA were investigated. Ni-BEA zeolite exhibited high methanol conversion rate and DME-resultant upon the reaction temperature from 200 to 225°C with equilibrium-limiting condition over 225°C; Furthermore, the Ni-BEA zeolite presented the best stable activity at 225°C over 1,200 minute. The Ni-BEA zeolite has also been interesting as a zeolite which suited to be one role importance to improve the properties for methanol dehydration to dimethyl ether.

Dimethyl Ether Synthesis via Methanol Dehydration over Diatomite Catalyst Modified Using Hydrochloric Acid

The synthesis of dimethyl ether via methanol dehydration has been carried out over untreated-diatomite catalyst (DM) and hydrochloric acid modified treatment on diatomite catalyst (DMHC). The reactions were carried out in a fixed-bed reactor. The effects of hydrochloric acid modifications of diatomite on its catalytic performance were studied. The characterization such as XRD, SEM, FT-IR and FT-Raman had no deformation after HCl-modified treatment on catalysts. DMHC catalyst apparently gave the higher methanol conversion rate than DM due to the acidity while the selectivity of dimethyl ether from 250 to 350°C was slightly changed. The acidity was depended upon Al(IV) ions; nevertheless, both Al(V) and Al(VI) were affected and hence increasing the basic active sites. Not only was the competitively catalytic methanol dehydrogenation preferred with basic condition but also methanol-blocking water molecule interaction was the unwanted reaction. In this investigation, the chemical-bond arrangements of silicon and aluminium ions were proposed with solid MAS/NMR. The DMHC catalyst exhibited better DME yield than the DM catalyst, and it could be used as a selective catalyst for DME synthesis from methanol.

Methanol Dehydration to Dimethyl Ether over Silica Derived from Rice Husk as the Component-Based Catalysts

Dimethyl Ether (DME) an alternative fuel was synthesized by methanol dehydration over the silica-based catalysts. Silica extracted from both rice husk (A) and rice-husk ash (B) was used as the precursors for preparing the catalysts. The SiO2/Al2O3 and the SAPO catalysts prepared from that silica were analyzed using X-ray diffraction (XRD), N2 adsorption (BET surface area), X-ray fluorescence (XRF), NH3 temperature-programmed desorption (NH3-TPD), and thermal gravimetric analysis (TGA). The effects of reaction temperature on the methanol selectivity and conversion to dimethyl ether were investigated. The methanol dehydration reactions were carried out in a packed-bed reactor at the reaction temperature of 250-350°C. DME was the major product and formed with selectivity of 57% over SAPO-B. An increasing of the reaction temperatures resulted in the enhancing of methanol conversion. The highest methanol conversion of 93% was achieved at 325°C. The method of silica extraction had an effect on the selectivity to DME due to the higher BET surface area.

On the impact of co-feeding aromatics and olefins for the methanol-to-olefins reaction on HZSM-5

The impact of adding various aromatic molecules (benzene, toluene, and xylenes) or olefins (ethene, propene, 1-butene, 1-pentene, and 1-hexene) to methanol over a HZSM-5 catalyst on activity and selectivity was systematically studied. Addition of a low concentration of aromatic molecules (16–32C%), which are free of diffusion constraints, significantly enhanced the aromatics-based catalytic cycle and greatly suppressed the olefin-based cycle. This led to enhanced methane and ethene formation and methylation of aromatic rings at the expense of propene and C4+ higher olefins. The ratio of propene to ethene is controlled by the concentration of the aromatic molecules added. Co-feeding the same molar concentration of benzene, toluene and p-xylene influenced the methanol conversion to a nearly identical extent, as none of them experience transport constraints and the methylation rapidly equilibrates the aromatic molecules retained in the pores. In stark contrast, addition of small concentrations (10–40C%) of C3–6 olefins with 100C% methanol does not selectively suppress the catalytic cycle based on aromatic molecules. This led to unchanged selectivities to ethene and higher olefins (C3+). Within the C3+ fraction, the selectivity to propene decreased and the selectivity to butenes were enhanced with increasing concentration of the co-fed olefin. Because of the relatively fast rates in methylation and cracking of C3–6 olefins in the olefin-based cycle, the product distributions at high methanol conversion were identical when co-feeding C3–6 olefins with the same carbon concentrations. This work provides further insights into the two distinct catalytic cycles operating for the methanol conversion to produce ethene and propene over HZSM-5 catalysts.

Hierarchically tetramodal-porous zeolite ZSM-5 monoliths with template-free-derived intracrystalline mesopores

In this work, we report a unique synthesis of hierarchical zeolite ZSM-5 monoliths using polyurethane foam (PUF) as a rigid scaffold through a simple steam-assisted crystallization (SAC) method. The resultant monolithic ZSM-5 with a well crystalline structure possesses unique tetra-modal porosity (macropore/macropore/mesopore/micropore). The first modes of macroporosity (pore size of ∼33 μm) is formed after the removal of the PUF scaffolds. The second set of macropores with a size of 0.2–1.7 μm originate from the aggregation of ZSM-5 nanocrystals (crystal size of ∼500 nm) inside the macropores of the PUF scaffolds. The third level of porosity stems from the intracrystalline mesopores (∼53 nm) in each ZSM-5 crystal, along with the fourth intrinsic microporosity of zeolites. The mesopores are derived from the voids formed in the initial dry precursors, which are transformed and preserved as intracrystalline mesopores in each zeolite crystal. This type of ZSM-5 monolith possesses a high macroporosity (75.2%) and mechanical stability (1.2 MPa). The total surface area of the monolithic ZSM-5 is ∼226 m2 g−1 and the total pore volume is ∼0.21 cm3 g−1. The ZSM-5 monolith as a structured catalyst for methanol to propylene (MTP) conversion shows excellent catalytic performance with high methanol conversion (above 95%) and propylene selectivity (above 40%) at a high weight hourly space velocity (WHSV, 3.6 h−1). Importantly, the diffusion efficiency of catalyst is remarkably improved. After reaction for 5 h, the selectivity of propylene reaches a steady state.

Effects of micro and nano-sized SAPO-34 and SAPO-5 catalysts on the conversion of methanol to light olefins

In the present study, SAPO-34 and SAPO-5 catalysts with different crystallite size were synthesized under hydrothermal conditions and partially characterized by XRD, SEM, EDX, BET and NH3-TPD. Crystallite sizes in the range of 450 nm–8 μm were obtained. To elucidate the effects of crystallite size on their catalytic performance, especially in terms of the conversion, life time and selectivity, the performance of the methanol-to-olefin reaction over these two SAPO catalysts was investigated. The SAPO-34 catalyst with small crystals showed a longer catalyst lifetime and higher conversion of methanol as well as more than 50 % selectivity toward light olefins. Synthesized catalysts with larger crystals showed significantly shorter life time and lower selectivity toward light olefins. The overall results of this study demonstrate that not only the phase (SAPO-34 or SAPO-5) but also the crystal size are critical factors governing the MTO conversion and selectivity.

Effect of acidic promoters on the titania-nanotubes supported V2O5 catalysts for the selective oxidation of methanol to dimethoxymethane

The effect of acidic promoters on the titania-nanotubes (TNT) supported V 2 O 5 catalysts (VTNT) was investigated. The structure of TNT was quite stable after the treatment with sulfuric, phosphoric, and phosphotungstic acids, respectively. The acid-modified VTNT catalysts were tested for the selective oxidation of methanol to dimethoxymethane (DMM). It was found that only the VTNT modified with sulfuric acid followed by calcination at 673 K exhibited the significantly enhanced selectivity to DMM with high methanol conversions. The calcination created some sulfate groups strongly interacted with vanadium species, which enhanced the strengths of surface acidity without weakening the redox ability of vanadium sites. The addition of phosphoric and phosphotungstic acids might enhance the surface acidity of V 2 O 5 /TiO 2 , but weakened its redox ability, and therefore had the negative effect for the target reaction. Addition of sulfate groups followed by calcination at 673 K strengthened the surface acidity of V 2 O 5 /TiO 2 and thus promoted the selectivity to dimethoxymethane at the high methanol conversions, while the addition of phosphoric and phosphotungstic acids in any case or the addition of sulfate groups without a high temperature calcination had the negative effect because they decreased either the surface acidity or redox ability of V 2 O 5 /TiO 2 .

CFD analysis of the effects of the flow distribution and heat losses on the steam reforming of methanol in catalytic (Pd/ZnO) microreactors

A three-dimensional computational fluid dynamics (CFD) simulation study of the effects of the flow distribution and the heat losses on the performance of microchannels and microslits reactors for the steam reforming of methanol (SRM) over Pd/ZnO is presented. Several flow distributing headers covering a wide range of the flow diffuser expansion angle (α) have been considered. Large values of α lead to flow maldistribution characterized by jet flow resulting in negative effects on the SRM conversion and hydrogen yield, especially for the microslits at high reaction temperatures and space velocities. Simulations have also evidenced that heat losses constitute a critical issue for microreactors operation, particularly at low space velocities. Heat losses may reach very high values, above 80–90% of the energy supplied to the microreactor, with the consequence that it may be necessary to provide up to 9times the heat of the SRM reaction to achieve high methanol conversions.

Experimental study on the performance of hydrogen production from miniature methanol–steam reformer integrated with Swiss-roll type combustor for PEMFC

A miniature plate-type hydrogen production reactor using methanol as fuel was designed and tested. This reactor is composed of a catalytic combustor, vaporizer, reformer, and methanator. All components were fabricated on one piece of rectangular quartz glass plate 50mm×44mm×7mm in size. The combustor was fabricated on one side of the glass plate with a Swiss-roll type channel in which the Pt/Al2O3 particles were loaded in segmented form to catalyze the combustion. A spiral channel was fabricated on the other side of the plate and divided into three sections: a vaporizer for liquid methanol–water mixture vaporization, a reformer for methanol–steam reforming catalyzed by CuO/ZnO/Al2O3 particles and a methanator for carbon monoxide (CO) removal catalyzed by Ru/Al2O3 particles.The test results indicated that this reactor successfully produced H2 and had thermal efficiency ranging from 13% to 35%. The reactor performance depends on the feed rates to the combustor and reformer, respectively. High methanol conversion can be obtained from either a low feed rate to the reformer or a high feed rate to the combustor. However, both cases also produce high CO concentrations. The CO methanation reaction was used to reduce the CO concentration. It was found that the methanation reaction depends greatly on the reactor temperature with high temperature not being favorable to this reaction. High CO conversion and low H2 consumption with low methanol conversion result when the reaction temperature is low. Thermal management for producing suitable temperature and catalyst activity improvement in high reaction temperature for the methanator are both needed in the integrated reactor design to reduce the CO concentration down to acceptable levels for fuel cell operation.

Steam reforming of methanol over gadolinium doped ceria (GDC) and metal loaded GDC catalysts prepared via sol–gel route

Gadolidium doped ceria-10 (GDC10, Ce0·9Gd0·1O1·95) and metal (Ni and Cu) loaded GDC10 catalysts are successfully prepared via a novel sol–gel route using cerium glycolate complex as precursor. The effect of sol–gel parameters, namely hydrolysis molar ratio h, acid molar ratio A and metal types, is investigated. It is found that all the parameters affected the gel formation. The optimal conditions to prepare the catalysts are to use the hydrolysis molar ratio of 29, the acid molar ratio of 0·3 and the calcination temperature of 500°C for 7 h. Various techniques are employed to characterise the obtained products. X-ray diffractograms show a fine crystalline cubic fluorite structure, while scanning electron microscope–energy dispersive X-ray spectra show good dispersion of each element. Steam reforming of methanol is carried out over the synthesised catalysts, and among the catalysts studied, 20%Ni/GDC10 exhibits the highest methanol conversion, over 70% at 400°C.

Numerical study of methanol–steam reforming and methanol–air catalytic combustion in annulus reactors for hydrogen production

This study presents the numerical simulation on the performance of mini-scale reactors for hydrogen production coupled with liquid methanol/water vaporizer, methanol/steam reformer, and methanol/air catalytic combustor. These reactors are designed similar to tube-and-shell heat exchangers. The combustor for heat supply is arranged as the tube or shell side. Based on the obtained results, the methanol/air flow rate through the combustor (in terms of gas hourly space velocity of combustor, GHSV-C) and the methanol/water feed rate to the reformer (in terms of gas hourly space velocity of reformer, GHSV-R) control the reactor performance. With higher GHSV-C and lower GHSV-R, higher methanol conversion can be achieved because of higher reaction temperature. However, hydrogen yield is reduced and the carbon monoxide concentration is increased due to the reversed water gas shift reaction. Optimum reactor performance is found using the balance between GHSV-C and GHSV-R. Because of more effective heat transfer characteristics in the vaporizer, it is found that the reactor with combustor arranged as the shell side has better performance compared with the reactor design having the combustor as the tube side under the same operating conditions.