Nano-Tubular Cellulose for Bioprocess Technology Development

Delignified cellulosic material has shown a significant promotional effect on the alcoholic fermentation as yeast immobilization support. However, its potential for further biotechnological development is unexploited. This study reports the characterization of this tubular/porous cellulosic material, which was done by SEM, porosimetry and X-ray powder diffractometry. The results showed that the structure of nano-tubular cellulose (NC) justifies its suitability for use in “cold pasteurization” processes and its promoting activity in bioprocessing (fermentation). The last was explained by a glucose pump theory. Also, it was demonstrated that crystallization of viscous invert sugar solutions during freeze drying could not be otherwise achieved unless NC was present. This effect as well as the feasibility of extremely low temperature fermentation are due to reduction of the activation energy, and have facilitated the development of technologies such as wine fermentations at home scale (in a domestic refrigerator). Moreover, NC may lead to new perspectives in research such as the development of new composites, templates for cylindrical nano-particles, etc

The impact of urea on the performance of metal exchanged zeolites for the selective catalytic reduction of NO_x: Part I. Pyrolysis and hydrolysis of urea over zeolite catalysts

Urea-SCR over metal exchanged zeolites is one of the leading catalytic technologies to abate NOx emissions in diesel exhaust. Ideally, urea injected into the diesel exhaust upstream of the SCR catalyst decomposes only to the gaseous products CO2 and NH3, where the latter gas can react with NOx emissions to form harmless N2 and H2O. However, solid by-products can be formed as well, and if deposited on the catalyst harm the long-term catalytic performance. In order to identify the impact of various urea decomposition products on the catalytic activity, we studied the pyrolysis and hydrolysis of neat urea and of urea over different zeolites (H-Y, Cu-Y, H-Beta, Na-Beta, and Fe-Beta). The experiments were run in dry and steam-containing N2 between 20 and 750 ° C by using simultaneous thermogravimetric analysis (TGA), differential thermoanalysis (DTA), and online GC/MS evolved gas analysis. Solid intermediate products at different decomposition temperatures were identified by means of ATR-FTIR and luminescence spectroscopy. As for neat urea, CO2, NH3 and HNCO could be detected as major gaseous products. At 270 ° C significant amounts of cyanuric acid and ammelide and at 500 ° C of melem and melon were identified as solid intermediates. Above 625 °C, all solid residues decomposed to cyanogen and isocyanic acid. Furthermore, it could be shown clearly that the investigated zeolites significantly accelerate the pyrolysis of urea and cyanuric acid, and the hydrolysis of HNCO, by shifting the decomposition processes to lower temperatures and by inhibiting the formation of solid by-products. In addition, the presence of steam in the feed gas can prevent even further the formation of solid residues and the high temperature adsorption of gaseous products

Catalytic and adsorption studies for the hydrogenation of CO₂ to methane

CO₂ methanation has been evaluated as a means of storing intermittent renewable energy in the form of synthetic natural gas. A range of process parameters suitable for the target application (4720 h⁻¹ to 84,000 h⁻¹ and from 160 °C to 320 °C) have been investigated at 1 bar and H₂/CO₂ = 4 over a 10% Ru/γ-Al₂O₃ catalyst. Thermodynamic equilibrium was reached at T ≈ 280 °C at a GHSV of 4720 h⁻¹. Cyclic and thermal stability tests specific to a renewable energy storage application have also been conducted. The catalyst showed no sign of deactivation after 8 start-up/shut-down cycles (from 217 °C to RT) and for total time on stream of 72 h, respectively. In addition, TGA-DSC was employed to investigate adsorption of reactants and suggest implications on the mechanism of reaction. Cyclic TGA-DSC studies at 265 °C in CO₂ and H₂, being introduced consecutively, suggest a high degree of short term stability of the Ru catalyst, although it was found that CO₂ chemisorption and hydrogenation activity was lowered by a magnitude of 40% after the first cycle. Stable performance was achieved for the following 19 cycles. The CO₂ uptake after the first cycle was mostly restored when using a H₂-pre-treatment at 320 °C between each cycle, which indicated that the previous drop in performance was not linked to an irreversible form of deactivation (sintering, permanent poisoning, etc.). CO chemisorption on powder Ru/γ-Al₂O₃ was used to identify metal sintering as a mechanism of deactivation at temperatures higher than 320 °C. A 10% Ru/γ-Al₂O₃//monolith has been investigated as a model for the design of a catalytic heat exchanger. Excellent selectivity to methane and CO₂ conversions under low space-velocity conditions were achieved at low hydrogenation temperatures (T = 240 °C). The use of monoliths demonstrates the possibility for new reactor designs using wash-coated heat exchangers to manage the exotherm and prevent deactivation due to high temperatures