Hydrogenation of carbon monoxide in the presence of solvent under low pressure of 0.5 MPa was developed to easily evaluate catalysts, and was used to examine novel carbon–oxide composite supported cobalt catalysts. CO conversion increased in the order 16Co63C21TiO2 = 16Co63C21Al2O3 < 16Co63C21SiO2 < 16Co63C21ZrO2 (16Co: 16 wt% Co; 63C: 63 wt% carbon in PEG; 21TiO2, Al2O3, SiO2 or ZrO2 : 21 wt% TiO2, Al2O3, SiO2 or ZrO2). This reaction was performed for easy evaluation of catalysts under high temperature and low pressure conditions, which are not usually used for Co catalysts, so most product was methane for all cobalt catalysts. 16Co63C21ZrO2 catalyst showed the highest conversion of 31 % at 340 °C, probably because 16Co63C21ZrO2 catalyst consists of only mesopores which have advantages for mass transfer and was unchanged after the reaction. Furthermore, cobalt metal species did not change and were detected by XRD after the reaction, which would also maintain the higher activity. Novel carbon–oxide composite supported iron catalysts were similarly prepared and reactivity for the hydrogenation of carbon monoxide in the presence of solvent was examined. CO conversion increased in the order 16Fe63C21SiO2 = 16Co63C21TiO2 < 16Fe63C21Al2O3 < 16Fe63C21ZrO2 (calcined at 500 °C) < 16Fe63C21ZrO2 (calcined at 700 °C). Most product was methane for all iron catalysts under low pressure in the presence of solvent, but 16Fe63C21ZrO2 calcined at 700 °C also produced C2-C6 hydrocarbons. These results may be related to the increased surface area and pore volume for ZrO2 supported catalysts with higher calcination temperature and the decreased iron particle sizes after the reactions, specifically from 42 to 7.2 nm for the catalyst calcined at 700 °C.
Removal of water from water-in-crude oil (W/O) emulsions was investigated using poly[(acrylic acid)-co-(sodium acrylate)］as water-absorptive-polymer (WAP) at 15-70 °C and under 0.1-1.5 MPa employing a batch or a flow separation system. The W/O emulsions with water content of 1-5 mass% were prepared from Upper Zakum (UZ) crude oil reserved at a domestic oil stockpiling base and distilled water. In each separation system, water absorption rates of both granular and fibrous WAPs from W/O emulsions under ambient conditions were much faster than that of zeolite 4A, indicating an effectiveness of WAPs for water separation. Removal of water from W/O emulsions was enhanced at high temperatures (50-70 °C) and under high pressures (1.0-1.5 MPa). It was found that regeneration of used WAPs was possible by rinsing them in toluene followed by drying. These results indicate that absorption of water from W/O emulsion using WAP is considered as one of the promising physical demulsification methods such as centrifugal separation, thermal treatment, and gravitational sedimentation without using chemical demulsifier.
Methane reforming is an important process for the production of hydrogen and synthesis gas. In this study, in- situ analyses of dry reforming and partial oxidation of methane over 1 wt% Ni/Al2O3 were conducted using an yttria-stabilized zirconia oxygen sensor. The oxygen sensor with five sensing points was inserted in the catalyst bed along the gas flow direction. The concentrations of species in the gas flow channel were estimated from the oxygen partial pressure detected by the sensor. The progress of reactions was successfully monitored at the respective points in both reforming reactions under the conditions investigated. The reaction temperature was also measured at three points using thermocouples during the partial oxidation of methane. The plausible reaction mechanism for the partial oxidation of methane over Ni/Al2O3 was proposed based on the distributions of gas species and temperature in the catalyst layer. Monitoring in the stability test indicated that the catalyst deactivation tendency was different depending on the position in the catalyst bed.
Accelerated deterioration tests for selective CO methanation over Ni/TiO2 catalysts were performed to investigate the catalyst degradation factors. The accelerated deterioration test treated the catalyst in the reaction gas flow at the specified temperature (200, 250 or 300 °C) for 24 h. After the accelerated deterioration test, the Ni/TiO2 selectivity in CO methanation was reduced due to the enhancement of an undesirable reverse water-gas shift reaction. Powder X-ray diffraction found no change in the TiO2 structure between the fresh and spent catalysts. In-situ X-ray absorption spectroscopy demonstrated that the Ni species reduced by H2 were present as metallic Ni and remained unchanged in the fresh and spent catalysts. The number of surface Cl species for the spent catalyst was much smaller than that for the fresh catalyst. Therefore, disappearance of surface Cl components during the accelerated deterioration test caused the degradation of Ni/TiO2 catalysts for selective CO methanation.
Microwave chemistry and microwave material processing have attracted the interest of scientists and engineers in the last decades, but applications have remained limited to vulcanizing of rubber, pre-drying of ceramics, drying of foods, etc., which all depend on the special heating mode independent of thermal conduction. Recently, researches in microwave technology have again investigated the possibility of a new technique of reaction control resulting in higher reaction rates, shorter reaction times, and energy saving. The huge demand for highly efficient recycling of carbon and hydrogen sources has emphasized the importance of R&D on green chemical processes for the production of energy carriers and conversion of carbon resources. To overcome the constraints of thermal equilibrium, development of chemical and separation methodology will be important based on the irreversibility or high selectivity enabled by controlling the kinetics or non-equilibrium state. Microwave technology has a potential to realize such processes.
This special issue includes both review papers and regular papers covering inorganic chemistry, organic chemistry, materials science, catalysis, and biomass chemistry. Invited articles describe the characteristics of "microwave special effects" which have long been attractive but mysterious subjects of controversy and discussion. All authors were invited from academia and corporate members belonging to the 188 Committee (Electromagnetic Field-Excited Reaction Fields) of the University-Industry Research Committees supported by the Japan Society for Promotion of Science of which I am a current chair. I hope that this issue will inform the members of the Japan Petroleum Institute and related researchers/engineers of the current situation in microwave technology. Finally, I express my sincere thanks to the editorial board of the journal and the secretariat of the society.
Microwave processing was used to fabricate nanoparticles having a desired particle size and morphology by a simple method, carbothermal reduction method. By microwave processing, Ti4O7 nanoparticles (∼60 nm) maintaining the morphology of a pristine material were fabricated at 950 °C for 30 min. Since grain growth was observed in conventional processing, rapid heating (250 °C/min∼) and rapid cooling, which are features of the microwave processing, are also effective in maintaining the particle diameter even though this carbothermal reduction reaction proceeds in the high temperature region. In addition, we successfully synthesized spherical AlN nanoparticles with high nitridation rate, maintaining the morphology of pristine material by microwave processing. It is considered that the crystal structure of transition alumina (which is advantageous for formation of intermediate AlON but phase transition over 1200 °C) was maintained over 1300 °C by microwave rapid heating. In addition, by optimizing the nitrogen flow rate, spherical AlN nanoparticles having a nitridation ratio of 0.88 could be fabricated at 1200 °C for 180 min and a nitrogen flow rate of 0.2 L/min.
Two microwave special effects are reported to be phenomena at the interface of solids induced under microwave irradiation in chemical reaction systems. Nonequilibrium local heating is the heat generation observed at contact points between solids and intersurfaces of solids under microwave irradiation. Nonequilibrium local heating was detected in cobalt metal particles dispersed in DMSO by in-situ observation with Raman spectroscopy under microwave irradiation. Nonequilibrium local heating can enhance dehydration of alcohol in the pores of zeolite by preparing zeolite particles with carbon cores. Acceleration of electron transfer at the interface of solids under microwave irradiation was observed for photoreduction of violegen derivatives by cadmium sulfide and water oxidation at the surface of hematite electrodes.
An ultrahigh-speed heating method of greater than 100 °C/s was developed using the microwave irradiation. This method was achieved with a single-mode cavity and absorbent materials that can concentrate the microwave energy. We report a new fuel reforming using bioethanol and microwave heating. By the steam reforming of ethanol using microwave, only a catalyst layer is preferentially heated from the inside for a short time, and so it becomes possible to quickly reform with a simple setup and provide a high energy efficiency. 4.7 mole of hydrogen from one mole of ethanol could be constantly produced within 20 s. Full conversion of 100 % was obtained at low temperatures and high gas space velocities. Activation energies for the microwave process decreased about 30 % compared to the conventional one. Advantages of the microwave over conventional one became clear. This innovative microwave process will be used for on-board vehicles and contribute to CO2-free technologies.
Recent studies on microwave processing of biomass for bioenergy production are reviewed. Statistical review of published research papers related to microwave and biomass was used to classify microwave processing used in bioenergy production. Microwaves have potential for use in various processing methods such as pretreatment, gasification, pyrolysis, transesterification, extraction, liquefaction and drying, to achieve low energy consumption, rapid reaction time, and high production yield. Microwave-assisted processing technologies for the second generation biomass (lignocellulosic biomass) and third generation biomass (algae and seaweeds) are described, as first generation biomass (food crops such as sugar canes, corns and grains) is often discussed as a "fuel versus food" issue. Scale-up strategies and discussions on energy consumption, cost, and efficiency of the microwave processing are also described with reference to specific examples of microwave reactors. Understanding of dielectric properties of biomass mixture is crucially important for designing an efficient and robust microwave reactor. Microwave processing is a future promising technology for renewable energy production, although its industrialization is still unfulfilled.
Microwave irradiation is widely applied to organic synthesis. Many advantages of microwave irradiation, including drastic shortening of reaction time, suppression of side reactions, and/or higher chemical yield, have been proposed. Generally, these effects have been understood merely as a simple thermal effect, since microwave irradiation rapidly raises the temperature of the reaction mixture. However, some observed results could not be understood only by the thermal effect. Recently our group reported that several enantioselective reactions were accelerated under microwave irradiation without loss of enantioselectivity. As these extraordinary results could not be explained by the simple thermal effect, the concept of the "microwave-specific effect" should be considered. We describe our recent experimental results to elucidate the microwave-specific effect. Investigations are described on enantioselective ring-opening reactions of biaryl lactone derivatives, racemization of an optically pure biaryl lactone derivative, enantioselective Claisen rearrangement reaction, enantioselective Conia-ene reaction and ring-closing metathesis reaction. These reactions or racemization of optically pure compounds were accelerated under microwave conditions. Such reaction acceleration of enantioselective reactions was observed without loss of enantioselectivity.
Microwave heating is widely utilized not only in domestic microwave ovens for cooking and heating foods, but also for many other applications in different industrial fields. For example, in the field of organic chemistry, microwave irradiation for promoting organic reactions has been investigated. The author has conducted experimental and simulation studies on the microwave processing of metals and/or ceramic materials, which generally requires much higher heating temperature than applications in organic chemistry. The present article introduces selected studies on material processing and reactions, in which solid state materials are involved. The processes are carbothermic reduction of metal oxides, fabrication of ceramic/metal composite materials and controlling of self-propagating high temperature synthesis (SHS) reactions. Some specific phenomena occurring in these processes and characteristics and effects on the processes are also discussed.
Multifunctional phthalocyanine metal complexes are very useful for many applications, such as electroconductivity, electrochromism and liquid crystalline formation, so the syntheses of phthalocyanine derivatives have attracted much interest in recent years. Previously, we noticed that no template effect was observed for the microwave-assisted synthesis of phthalocyanine copper complex, which we thought might be due to dielectric loss coefficient of the added metal salt. However, the dielectric loss coefficient of metal salt in a dilute solution is very difficult to directly measure. Since the heat quantity is proportional to the dielectric loss coefficient from basic microwave theory, the maximum temperature of a solution containing a metal salt heated by microwave irradiation can be an indirect index of the dielectric loss coefficient. In this study, glycerin solutions containing one of twelve different metal salts (MCl2, MSO4, M(OAc)2: M = Co, Ni, Cu, Zn) were heated by microwave irradiation. The maximum temperature of the solution reached was measured for each of the metal salts. Then, the corresponding phthalocyanine metal complexes (C8S)8PcM (M = Co, Ni, Cu, Zn) were prepared using these twelve different metal salts by microwave heating. The findings showed a proportional relationship between the yields and the maximum temperatures reached by microwave irradiation. This relationship may provide a useful guideline in microwave-assisted synthesis of organic metal complexes.
A Belousov-Zhabotinsky reaction in a liquid-liquid system was observed under non-stirring conditions to evaluate control of the non-equilibrium reaction by microwave irradiation through color changes of the solution. Irradiation power and time, and droplet size were important factors to control the oscillatory reaction in the droplet. During irradiation, the oscillatory period of any droplet sizes became shorter because the reaction rate became faster. In smaller droplets (2 mm), this behavior can be explained by the non-thermal effect because the temperature was equal to the temperature of the surrounding oil. Moreover, the oscillatory behaviors of the reaction in smaller droplets did not change after the irradiation even under higher power and longer irradiation time. On the other hand, shorter oscillatory period was observed in larger droplets (7 mm) after the irradiation, and the special microwave effect persisted. Overall, microwave irradiation was useful for controlling the non-linear reaction in a liquid-liquid system because of activation of the interface through the oil phase.
Microwave Chemical Co., Ltd. (MWCC) will innovate the chemical/energy industry by utilizing novel microwave chemical platform technology. Since the rise of the chemical industry 150 years ago, the industry has relied on transmission of energy through external and indirect means of heating an entire object. Microwaves, which are also used in microwave ovens, transmit energy internally and directly to specific molecules only. We took this technology and developed a unique manufacturing process to design a chemical reaction at a molecular level that is an "energy-saving," "highly efficient," "compact" and "new property" production. We will spread this microwave chemical process throughout the chemical and energy industry. In 2014, the world first MW-chemical reactor/process in commercial scale was demonstrated by MWCC, at their mother factory in Osaka, Japan. This factory is producing fatty acid butyl ester with capacity of 3200 t/year. The product is sold to Toyo Ink Co., Ltd. and other several ink producers. Second commercial-scale MW-chemical reactor/process, built under JV between MWCC and Taiyo Kagaku Co., Ltd., will be commissioned in 2016. This process will have 1000 t/year capacity to produce sucrose ester. For MW process, the applicable reaction type is broad, such as, condensation, esterification, polymerization, distillation/extraction, and some other unique synthesizes. Process does not select reaction system, applicable for liquid-solid, gas-solid and emulsion system; systems with high-viscosity, slurry and powder. Microwave Chemical Co., Ltd. was established in 2007 to realize our desire to "spread innovative technologies from Japan to the world," "establish a new technology venture in Japan" and "start a business that contributes to environmental protection." We are committed to the challenge of promoting a new industry in the area where the diverse fields of chemistry, microwaves, and engineering intersect.
Recently, the magnetron has been used for internal microwave heating of chemical reactions. However, microwave chemical reactors with magnetrons cannot easily control the temperature distribution in the reactor due to instability in frequency and phase coherency. In contrast, the semiconductor microwave source has excellent frequency and phase stability so that microwave heating can be more easily concentrated in the reactor. The electromagnetic distribution field of the substance to be heated in the reactor can be controlled by changing the relative phase of the microwaves in a microwave chemical reactor with semiconductor microwave sources using multiple input ports, resulting in control of the thermal distribution of the target substance. We describe a microwave chemical reactor using multiple semiconductor microwave sources with GaN amplifier modules, and demonstrate local concentration of heating in the reactor by phase control of the microwaves, and experiments to promote chemical reactions in the region of concentrated microwave heating.