A combined catalyst and sorbent for enhancing hydrogen production from coal or biomass

Future large-scale production of H2 for use as a clean fuel will likely depend upon gasifying coal or biomass followed by steam reforming the resulting gas mixture and separating the CO2 byproduct. The process of steam reforming and CO2 separation can be greatly simplified by utilizing a new material that combines a reforming catalyst with a sorbent for CO2. Such a material was prepared in the form of small pellets with cores made of calcium and magnesium oxides and shells made largely of alumina impregnated with a nickel catalyst. Subsequent laboratory performance tests of the material showed that CO, CH4, and toluene, which are representative products of gasification, were largely converted to H2 by reacting the material with steam in the presence of the catalyst/sorbent, so that CO2 was absorbed as it was produced. The sorbent was easily regenerated by raising its temperature, which made it possible to reuse the catalyst/sorbent repeatedly

Development of a novel combined catalyst and sorbent for hydrocarbon reforming

A combined catalyst and sorbent was prepared and utilized for steam reforming methane and propane in laboratory-scale systems. The material was prepared in the form of small spherical pellets having a layered structure such that each pellet consisted of a highly reactive lime or dolime core enclosed within a porous but strong protective shell made of alumina in which a nickel catalyst was loaded. The material served two functions by catalyzing the reaction of hydrocarbons with steam to produce hydrogen while simultaneously absorbing carbon dioxide formed by the reaction. The in situ removal of CO 2 shifted the reaction equilibrium toward increased H 2 concentration and production. The concept was proved by using both a thermogravimetric analyzer and a fixed-bed reactor loaded with the material to reform hydrocarbons. Tests conducted with the fixed-bed reactor at atmospheric pressure and with temperatures in the range of 520-650°C produced a product containing a large concentration of H 2 (e.g., 94-96 mol %) and small concentration of CO and CO 2. Therefore, the results achieved in a single step were as good as or better than those achieved in a conventional multistep reaction and separation process

Application of a combined catalyst and sorbent for steam reforming of methane

The performance of a combined catalyst and sorbent material designed for reforming hydrocarbons was evaluated by reacting methane with steam at different temperatures and pressures in a reactor packed with the material. The combined material was in the form of small spherical pellets comprised of a sorbent core of lime encased in a porous shell made largely of sintered alumina that supported a nickel catalyst. On the basis of previous research, two shell formulations were included in the study. One shell formulation contained a small quantity of CaO for strengthening of the shells, whereas the other contained a similar quantity of La2O3. Reaction testing of the combined catalyst and sorbent over a temperature range of 550-650 °C and a pressure range of 1.0-10.0 atm showed that pellets with either shell formulation were capable of producing H2 at or near thermodynamic equilibrium levels during a period when CO2 was being rapidly absorbed by the core material. Limited lifecycle testing of the combined catalyst and sorbent was also conducted at 650 °C and 1.0 atm over 10 cycles of H2 production and sorbent regeneration. A product stream with 98 mol % H 2 (dry basis) was produced during the rapid CO2 absorption period of each cycle. However, the length of this period declined with each cycle

Steam reforming of bio-oil fractions: Effect of composition and stability

The efficacy of steam reforming of the aqueous species in bio-oils produced from the fast pyrolysis of biomass is examined. A fractionating condenser system was used to collect a set of fractions of fast pyrolysis liquids with different chemical characteristics. The water-soluble components from the different fractions were steam-reformed using a nickel-based commercial catalyst in a fixed-bed reactor system. When reforming at 500 °C, an overall positive effect in hydrogen yields was observed for the fractions with higher concentrations of lower molecular-weight oxygenates, such as acetic acid and acetol, while the heavier compounds, such as the carbohydrates, showed an opposite effect. In general, higher selectivity toward hydrogen correlated to a lower tendency toward carbon deposits. Overall, the bio-oil fraction corresponding to the light end performed the best with the highest activity toward hydrogen. A range of steam/carbon ratios was examined. Carbon accumulation in the reactor was clearly a main issue during steam reforming of all of the bio-oil fractions studied. Chemical changes caused by aging of aqueous bio-oil were found to have a detrimental effect on hydrogen production

Development of a CaO-based CO2 sorbent with improved cyclic stability

The carbonation of CaO is an attractive method for removing CO2 from hot gas mixtures. However, regeneration and reuse of a CaO-based sorbent causes a gradual decline in absorption capacity, which ultimately limits the life of the material. Various methods have been proposed for increasing the life cycle performance of a CaO-based sorbent. Two of these methods were selected for further investigation. One method incorporates an “inert” material in the sorbent, while a second method stabilizes the sorbent through controlled sintering. Promising results were achieved with both methods when they were applied separately to a sorbent derived from a natural limestone. In one case MgO was finely dispersed within the sorbent, where it served as an “inert” material in the sense that it did not absorb CO2. A concentration of approximately 20 wt % appeared to be nearly optimal. In a second case the sorbent was stabilized by calcining the material at 1100 °C for 5 h. Although neither method produced a completely stable material, the stability of the sorbents was improved sufficiently so that by the end of a 1200-cycle test the absorption capacity of either of the treated sorbents was 45% greater than that of an untreated sorbent and the rate of decline was very small

Production of benzaldehyde: a case study in a possible industrial application of phase-transfer catalysis

The conventional method of producing benzaldehyde by direct oxidation of toluene has a major drawback: low conversion to achieve high selectivity. Phase-transfer catalysis (PTC) may be used as an alternative route for benzaldehyde production. In the present study, routes to produce benzaldehyde from benzyl chloride in the liquid phase by using PTC have been examined based on the kinetic data obtained. Using the results of this study and the available information on the conventional route, process design simulations have been carried out for all the routes. While PTC-based processes offer advantages, the study shows that the conventional route appears to be the preferred one for this relatively large-scale organic intermediate with current conversions, selectivities, and chemical costs. However, even minor improvements in one or two PTC steps can greatly enhance the prospects of the PTC route. In general, as the processes get increasingly chemistry intensive, the PTC route becomes increasingly the preferred candidate

Phase-transfer catalysis: a new rigorous mechanistic model for liquid-liquid systems

A general kinetic model for phase-transfer catalyzed reactions involving two liquid phases and a homogeneous catalyst has been developed. The proposed new model introduces the separation of the contributions of the phase-transfer catalysis (PTC)-enhanced reaction and the non-PTC reaction toward the overall conversion. The common approach in the past was that the non-PTC reaction was either ignored or incorporated in the PTC-enhanced reaction. Even more significantly, the model also incorporates terms for explaining the variability of catalyst phase distribution with changes in electrolyte composition in the aqueous phase, which subsequently affects the amount of inorganic nucleophile that reacts in the organic phase. The industrially important reaction, synthesis of benzaldehyde from benzyl chloride, has been used to validate the model. Three reaction steps, i.e. esterification, hydrolysis, and oxidation, as well as combinations thereof, were considered. It was found that the model was able to fit the experimental data well. Model verification was done, not by parameter estimation by regression, but by determining them from separate sets of experiments. This lends greater credibility to multiparameter models (like that in the present case). Further analysis showed that the parameter values of the individual reactions can be used to classify the reactions, based on an approach proposed earlier by Starks et al. (Phase Transfer Catalysis, Chapman and Hall, New York, USA, 1994) and extended by Satrio et al. (Chem. Eng. Sci. 55 (2000) 5013)