The strong acidity and remarkable molecular sieving effect of zeolites makes them especially important materials in industrial reactions and separation processes. The use of zeolites as membranes combines the advantages of inorganic membranes (high temperature stability and solvent resistance) with the zeolitic properties. Such zeolite membranes have potential uses as separation and reaction membranes, and as simultaneous reaction/separation membranes. A number of approaches have proved effective for modifying the properties of zeolite membranes, including the use of nano-crystalline zeolites for membrane preparation, regioselective deactivation of acid sites, and modification of zeolitic pore size. This review describes the synthesis of nano-crystalline zeolites by an emulsion method and the regioselective deactivation of acid sites by the catalytic cracking of silane (CCS) method. The effects of the crystal size and CCS treatment on the performance of the zeolite membrane are reviewed.
Palladium membrane reactors have the potential to achieve higher conversion as well as larger recovery of purified hydrogen in the steam reforming reaction, even at lower temperatures. However, increasing feed rate resulted in larger deviation from the ideal analytical model assuming plug flow and isothermal conditions. This study developed a computational fluid dynamics (CFD) model, which takes into account the concentration, temperature and velocity distributions due to mass, heat transfer and flow resistances in the membrane reactor. The CFD model clearly showed that large temperature and concentration distributions were formed in both the radial and axial directions, so reducing the reactor performance compared to the ideal reactor. The correctness of the model was verified for the dehydrogenation of cyclohexane in a single tube type as well as a multi-tube type of palladium membrane reactor. Furthermore, the multi-tube model was applicable for simulation of changes in the reactor design such as the membrane dimension. World-leading potentials of palladium membrane reactors in Japan are evaluated by introducing major projects.
Biodiesel fuel (BDF) is a clean burning alternative to petroleum diesel, and is produced from renewable resources such as vegetable oils and animal fats. BDF is nontoxic, biodegradable, and reduces the emissions of unburned hydrocarbon, carbon monoxide and sulfur oxides compared to petroleum diesel. Damage to the global environment and the increase of crude oil prices have emphasized research on BDF production in recent years. This review describes an overview of our work on BDF production methods, which include (i) homogeneous synthesis of BDF at room temperature in the presence of cosolvents such as dimethyl ether, diethyl ether, t-butyl methyl ether, and tetrahydrofuran; (ii) rapid synthesis of BDF using a microtube reactor; (iii) synthesis of BDF using an electrolysis method; (iv) development of solid alkaline catalysts for BDF production from waste cooking oil; and (v) simultaneous BDF production and separation in a trickle bed reactor. The advantages and future challenges in our methods for BDF production are presented and discussed.
Colloidal gas aphron (CGA) fluids, consist of gas bubbles with diameters ranging from 10 to 100 μm, surrounded by a thin aqueous surfactant film. This fluid combines certain surfactants and polymers to create the systems of microbubbles. The function of surfactant in CGA is to produce the surface tension to contain the aphrons. Also a biopolymer needs to be considered in the formulation as a viscosifier as well as stabilizer. The aphron-laden fluid appears to be particularly well suited for drilling through depleted zones. The unique feature of aphron based fluids is to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion by means of air microbubbles. This microenvironment seal readily cleans up with reservoir flow back as production is initiated, thereby reducing cost associated with stimulation processes. This paper presents a comprehensive, comparative study of rheological behavior and filtration properties of CGA based drilling fluids with various concentrations of polymer and surfactant. Laboratory evaluations showed that the CGA based fluid is one of the ideal engineering materials which can control fluid loss or loss circulation during drilling operation, save cost and increase productivity which rheological characteristics and filtration properties of them are greatly influenced by the level of polymer and surfactant concentration.
The dispersion state of Pt nano-particles supported on Al2O3 was investigated by gas chemisorption. The amount of H2 chemisorption was larger than that of CO over the entire range of Pt dispersion. Pt dispersion beyond 100 % was estimated for Pt/Al2O3 with nano-sized Pt particles by H2 chemisorption. FT-IR measurements of hydrogen species adsorbed on Pt/Al2O3 with different Pt dispersions revealed that hydrogen species dissociatively adsorbed on Pt nano-particles and spilled over onto Al2O3. Hydrogen species dissociatively adsorbed on Pt nano-particles were highly reactive with NO at room temperature, leading to the formation of N2. In contrast, hydrogen species spilled over onto the fringes of Pt particles reacted with NO to form N2O.
In a series of studies of powdered diamond (O-Dia)-supported catalyst, performance of Mn co-loaded Co/O-Dia for Fischer-Tropsch synthesis was examined. The addition of Mn to Co/O-Dia greatly increased CO conversion with a slight decrease in the selectivity to higher hydrocarbons (C5+). The fraction of olefin in the C5+ liquid product largely increased. The higher activity of Co–Mn/O-Dia catalyst is ascribed to the higher dispersion of active Co particles on O-Dia with the addition of Mn. The optimal ratio of Mn to Co is in the range of 0.05 to 0.1 at a Co loading of 5 wt%. At a reaction temperature of 230 °C, CO conversion of 85 % with a chain propagation probability of 0.81 at SV of 4500 mL · h−1 · g-cat−1 were obtained. On O-Dia Mn-co-loaded catalyst precursor CoOx could easily be reduced under moderate H2 pretreatment conditions to give well-dispersed metallic Co particles ranging from 3 to 11 nm in diameter (average size 7.1 nm). In contrast, without Mn, the particle size distribution of Co was broad, ranging from 4 to 30 nm (average 14.9 nm) at a Co loading of 5 wt%. The role of Mn is to prevent sintering of Co during H2 reduction.
n-Butane dehydrogenation was investigated over alumina-supported Pt catalysts modified with Sn. Preparation of this catalyst by conventional co-impregnation method with H2PtCl6 and SnCl2 mixed solution (Pt–Sn/Al2O3 catalyst), resulted in considerable loss of amount of Sn during calcination. Therefore, SnO2–Al2O3 was prepared by the sol-gel method and Pt was then deposited on this support (Pt/SnO2–Al2O3 catalyst). This procedure prevented loss of Sn at the calcination step. In addition, Pt/SnO2–Al2O3 demonstrated a remarkable promotion effect of Sn compared with Pt–Sn/Al2O3. CO adsorption was higher on Pt/SnO2–Al2O3 than on Pt–Sn/Al2O3. Sn present in the oxidized state was dispersed on the support surface of Pt/SnO2–Al2O3. XRD measurements suggested that an inactive PtSn2 phase was formed and particle growth occurred in Pt–Sn/Al2O3. XRD peaks from Pt were not observed for Pt/SnO2–Al2O3, suggesting the formation of highly dispersed Pt3Sn. This study showed that highly dispersed tin oxides on the support surface retarded side reactions and formation of Sn-rich PtSn2 particles, resulting in high activity for n-butane dehydrogenation.
A paper in press with this journal and accessible via Science Direct and Scopus1) that compared four solvent extraction gives a description in its ‘results and discussion’ about DME extraction2). The authors of Ref. 1) have the following to say about DME extraction: Several hundreds of times more DME needs to extract oil from microalgae. This is very difficult to follow, and I am confused by the description of DME amount cited from a laboratory-scale test2). Next, extraordinary Fig. 2 is ‘pulled out of a hat.’ In the cited study, we used an extraction column (diameter, 11.6 mm; length, 190 mm)2). Moreover, we described ‘microalgae were loaded into the lower half of the extraction column,’ and ‘DME flow rate was 10 cm3 · min−1.’ It should be emphasized that the test was conducted by a very short fix-bed extractor. It goes without saying that in practical applications, DME should be circulated in the liquid state until the extracted oil become sufficiently inspissated in the same manner as other common industrial practices in the field of extraction. Maybe the authors of Ref. 1) did not know counter-current multiple extraction? DME was not circulated but was used one time only, which resulted in considerable DME consumption. The discussion in Ref. 1) takes no note of these and is therefore difficult to accept. Moreover, there is no description supporting the comparison and all that can be said is that a reader cannot be expected to attach any importance to them.
2,2’,6,6’-tetra-t-butyl-4,4’-biphenol (TBBP), playing a role as an anti-oxidant, is oxidized to the corresponding diphenoquinone (TBBPO) prior to the oxidative degradation of lubrication oil. To extend the life of lubrication oil, a possibility of reducing TBBPO to TBBP was examined using a bifunctional palladium membrane electrode that enabled simultaneous hydrogen production by water electrolysis and catalytic hydrogenation. It was demonstrated that TBBPO in the lubricant could be reversibly reduced to TBBP.