Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts

This work investigates the catalytic activity of geopolymers produced using two different alkali components (sodium or potassium) and four treatment temperatures (110 to 700 \ub0C) for the methyl transesterification of soybean oil. The geopolymers were prepared with metakaolin as an aluminosilicate source and alkaline activating solutions containing either sodium or potassium in the same molar oxide proportions. The potassium-based formulation displayed a higher specific surface area and lower average pore size (28.64-62.54 m\ub2/g; 9 nm) than the sodium formulation (6.34-32.62 m\ub2/g; 17 nm). The reduction in specific surface area (SSA) after the heat treatment was more severe for the sodium formulation due to the higher thermal shrinkage. The catalytic activity of the geopolymer powders was compared under the same reactional conditions (70-75 \ub0C, 150% methanol excess, 4 h reaction) and same weight amounts (3% to oil). The differences in performance were attributed to the influences of sodium and potassium on the geopolymerization process and to the accessibility of the reactants to the catalytic sites. The Na-based geopolymers performed better, with FAME contents in the biodiesel phase of 85.1% and 89.9% for samples treated at 500 and 300 \ub0C, respectively. These results are competitive in comparison with most heterogeneous base catalysts reported in the literature, considering the very mild conditions of temperature, excess methanol and catalyst amount and the short time spent in reactions

Permeability and nanoparticle filtration assessment of cordierite-bonded porous SiC ceramics

Cordierite bonded porous SiC ceramics having pore fractions (epsilon) between 0.33 and 0.72 and pore sizes of 6-50 mu m, flexural strength of 5-54 MPa, and elastic modulus of 6-42 GPa were prepared by oxide bonding at 1350 degrees C in air compacts of SiC, Al2O3 and MgO powders with petroleum coke (PC) as the sacrificial pore former. To test the applicability of the porous ceramics in the fluid flow field, air permeation behavior was studied with fluid superficial velocity from 0.083 to 0.90 m s(-1) and at 26-750 degrees C. The Darcian, k(1), and the non-Darcian, k(2), permeability coefficients were evaluated by fitting Forchheimer's equation to the experimental results. The temperature dependence of the permeability coefficients was explained from structural changes occurring during test conditions. The collection efficiency of filter ceramics (epsilon = 0.62-0.68) operating on removal of nanosized aerosol particles with sizes varying from 7 to 300 nm was determined by counting particles before and after filtration at a fluid superficial velocity of 0.1 m s(-1). Experimental results showed variation of collection efficiency from 96.7 to 99.9%. The size-selective fractional collection efficiency at different porosity levels was derived by using the well-known single-collector efficiency model considering some boundary conditions, and the model data were validated with experimental results. The test results were used for examination of the applicability of the filter ceramics in nanoparticle filtration processes

Investigation on sacrificial pore former removal and mullite binder phase transformation in powder formulations used for preparation of oxide bonded porous SiC ceramics

Sacrificial pore former removal and mullite binder phase transformation the two major stages of processing of oxide bonded porous SiC ceramics similar to were studied by conducting thermal analysis of the precursor powders (SiC +20 wt% Al2O3 +15-41 vol% petroleum coke pore former). Kinetic computation of reactions occurring in these stages was done by fitting the non-isothermal DTA data to empirical models. The ceramics prepared from the precursor powders were characterized by the combined approach of chemical and XRD analyses and electron microscopy and the results in combination with the kinetic data were used to explain the formation of the pore phase and the mullite binder phase of the ceramics

Permeation Behavior of Oxide Bonded SiC Ceramics at High Temperature and Prediction of Pressure Drop in Candle Filters

Oxide-bonded silicon carbide supports of porosity ranging from 33% to 47% were prepared by heating powder compacts (SiC, clay and alumina) at 1400 degrees C in air with graphite acting as a pore former. The supports were spray-coated with an aqueous slurry of fine SiC powder (d(50)=15 mu m), then sintered to produce a filtering layer with thickness ranging from 116 to 200 mu m and average pore size ranging from 5 to 20 mu m. Airflow tests were performed on both supports and coated filters at temperatures ranging from 25 degrees to 700 degrees C and superficial velocities ranging from 0.02 to 0.9 m.s(-1). Experimental permeability coefficients were used to simulate the pressure drop behavior of hypothetical candle filters for industrial combustion/gasification processes (biomass combustion in water-tube steam boilers (BCSB), pressurized fluidized-bed combustion (PFBC) and integrated gasification combined cycle (IGCC)). The simulated permeation properties of the hypothetical candles were compared to those of commercial hot gas filters

Effect of processing parameters on mullite bonded SiC membrane for turbid water filtration

A water-filtration membrane made of SiC possesses some excellent properties, but its application is limited by high fabrication cost. In this study, two sets of mullite bonded porous SiC ceramics membranes were prepared at reduced temperature by oxidation bonding method using different processing conditions. Dead-end filtration mode was utilized for the determination of permeability and their efficiency towards removal of turbidity. It was found that all the membranes prepared using different composition, pore formers (graphite, PVC and PMMA) and sintering temperature exhibited high turbidity removal efficiency (> 99%). This study provides an efficient method to prepare porous SiC ceramics with excellent permeability and turbidity removal efficiency, which will be helpful for the design of low cost SiC ceramic filters for water treatment

Evaluation of air permeation behavior of porous SiC ceramics synthesized by oxidation-bonding technique

Porous SiC ceramics were synthesized by oxidation bonding of compacts of commercial -SiC powder at 1300 degrees C. Different volume fractions of petroleum coke powder were used for variation of porosity of ceramics from 36% to 56%. The material exhibited variations of pore size from 3 to 15m, flexural strength from 5.5 to 29.5 MPa, and elastic modulus from 3.3 to 27.6 GPa. Air permeation behavior was studied at 26-650 degrees C. At room temperature Darcian (k(1)) and non-Darcian (k(2)) permeability parameters vary from 1.64 to 18.42x10(-13)m(2) and 0.58 to 2.95x10(-7)m, respectively. Temperature dependence of permeability was explained from structural changes occurring during test conditions

Microstructural, physical, and fluid dynamic assessment of spinel-based and phosphate-bonded investments for dental applications

This work reports the experimental evaluation of physical and gas permeation parameters of four spinel-based investments developed with or without inclusion of sacrificial fillers. Data were compared with those of three commercial formulations. Airflow tests were conducted from 27 to 546°C, and permeability coefficients were fitted from Forchheimer's equation. Skeletal densities found for spinel- (ρs = 3635 ± 165 kg/m3) and phosphate-bonded (ρs = 2686 ± 11 kg/m3) samples were in agreement with the literature. The developed investments were more porous and less permeable than commercial brands, and the differences were ascribed to the different pore morphologies and hydraulic pore sizes of ceramic matrices. The inclusion of both fibers and microbeads resulted in increases of total porosity (42.6–56.6%) and of Darcian permeability coefficient k1 (0.76 × 10−14–7.03 × 10−14 m2). Air permeation was hindered by increasing flow temperatures, and the effect was related to the influence of gas viscosity on ΔP, in accordance with Darcy's law. Casting quality with molten titanium (CP Ti) was directly proportional to the permeability level of the spinel-based investments. However, the high reactivity of the silica-based investment RP and the formation of α-case during casting hindered the benefits of the highest permeability level of this commercial brand