Search

A comprehensive two-dimensional (2D) mathematical model has been proposed to simulate the burning process of a king-size cigarette. The characteristics of this model are including: 1) the use of kinetic models for the evaporation of water, the pyrolysis of tobacco and the oxidation of char, 2) the application of mathematical relationships between the release amounts of certain products (i.e., "tar" and CO) and different reaction variables (i.e., temperatures and oxygen concentrations), 3) the introduction of mass, heat and momentum transports, 4) the consideration of filtration effects of the cigarette filter on "tar". These characteristics were expressed in a set of coupled equations that can be solved numerically by FLUENT. The information about the char density field, temperature field, flow velocity field, "tar" and CO density fields and the filtration efficiency could be obtained from the model. This model was validated by comparing the predictions with experimental data on puff number, the temperatures at specific locations, the filtration efficiency and the yields of "tar" and CO under different puff intensities. The calculated results show a good agreement with the experimental data. The predicted puff number was 7.3, and the experimental puff number was 6.8. The standard root mean square error (NRMSE) between the experimental and the predicted temperatures at specific locations is < 18%. The predicted filtration efficiency for "tar" was 46.1%, and the experimentally determined filtration efficiency for nicotine was 44.5%. The maximum relative deviations of the yields of "tar" and CO under different puff intensities were 8.9% and 10.6%, respectively. [ABSTRACT FROM AUTHOR]

The reaction kinetics of 2,3-butanediol (2,3-BDO) and other key intermediates, including methyl ethyl ketone (MEK), 2-methylpropanal, acetoin, 2-butanol and 2-methyl-1-propanol, were investigated over acidic zeolites (ZSM-5, and Y-type zeolite), Cu/ZSM-5, Cu/Y and Cu/SiO 2 to elucidate the roles of acid and metal sites in the process of hydrodeoxygenation of 2,3-BDO to butene. Hydrogenation and dehydrogenation reactions occur on Cu sites, while dehydration reactions take place on acid sites. At low space time, 2,3-BDO can readily be converted to acetoin by dehydrogenation over supported Cu catalysts, however, with increasing space time, the formed acetoin is hydrogenated back to 2,3-BDO. DFT (density functional theory) calculations suggest that the cage structure of Y zeolite allows the formation of larger Cu clusters, potentially blocking acid sites and preventing access of C 4 alcohols (2-butanol, 2-methyl-1-propanol) to the acid sites for dehydration. This effect results in lower selectivity to butenes over Cu/Y than on Cu/ZSM-5. [ABSTRACT FROM AUTHOR]

In this study, three different types of mesoporous materials (Al-MCM-48, Al-SBA-15 and hierarchical ZSM-5 (meso-ZSM-5) where mesoporosity was introduced into ZSM-5 by sodium hydroxide treatment) were loaded with ∼20 wt% CuO and investigated in the conversion of 2,3-butanediol to butenes. The results showed that the introduction of mesopores on the catalysts (Al-MCM-48 and Al-SBA-15 types) could decrease the production of cracking products, especially C 3 = and C 5 = –C 7 = by comparison to the catalyst with ∼20 wt% CuO loaded on HZSM-5; meanwhile, the selectivity of C 8 = from oligomerization of butenes was found to increase with increasing pore size of the catalysts. In addition, Cu/meso-ZSM-5 catalyst has a performance with similarities to both Cu/ZSM-5 catalyst and mesoporous copper catalysts (Cu/Al-MCM-48 and Cu/Al-SBA-15) since both micropores (diameter of ∼0.55 nm) and mesopores (pore size of ∼23 nm) exist on meso-ZSM-5. Therefore, Cu/meso-ZSM-5 showed high activity for both cracking reactions (C 3 = and C 5 = –C 7 = ) and oligomerization (C 8 = ). [ABSTRACT FROM AUTHOR]

In this study, Cu/ZSM-5 catalysts were used to catalyze the hydrodeoxygenation of 2,3-butanediol to butenes in a single reactor in the presence of hydrogen. The carbon selectivity of butenes increased with increasing SiO 2 /Al 2 O 3 ratio (lowering acidity of zeolite) and H 2 /2,3-butanediol ratio. Cu/ZSM-5 with a SiO 2 /Al 2 O 3 ratio of 280 showed the best activity toward the production of butenes; however, Cu/ZSM-5 with SiO 2 /Al 2 O 3 of 23 was favorable for the dehydrogenation reaction of 2,3-butanediol even in the excess of hydrogen. On zeolite ZSM-5(280), the carbon selectivity of butenes increased with increasing copper loading and 19.2 wt% of CuO showed the highest selectivity of butenes (maximum 71%). The optimal reaction temperature is around 250 °C. Experiments demonstrated that methyl ethyl ketone (MEK) and 2-methylpropanal are the intermediates in the conversion of 2,3-butanediol to butenes. The optimal performance toward the production of butene is the result of a balance between copper and acid catalytic functions. [ABSTRACT FROM AUTHOR]

To demonstrate the difference in moisture adsorption properties of fibers and the influence on the moisture adsorption properties of the five plant fibers ( conifer, broadleaf, flax, grass and bamboo) and one regenerated fiber ( Tencel), as well as the adaptability between moisture adsorption properties of fibers and coating performance of reconstituted tobacco for heated tobacco products, were studied. The results showed that the moisture adsorption properties of the six fibers were different. Tencel fiber performed the best, followed by bamboo fiber, and flax fiber performed the worst. The maximum adsorption rate and desorption rate of the fibers increased significantly with the increase of relative humidity during moisture migration. The parallel exponential dynamic model (PEK) was used to fit the moisture migration, it indicated that the progress consisted of a fast and a slow sorption procedure which occurred simultaneously. The fast procedure dominated the water migration behaviour in the sheet. As the relative humidity increased, the equilibrium moisture absorption content of the fast procedure increased and its characteristic time decreased. Meanwhile, the characteristic parameters of the slow procedure had no obvious rule with relative humidity. The micro-structure morphology, environmental conditions and other factors strongly influenced the moisture adsorption properties of fibers, the hygroscopic properties of fibers were positively correlated with the relative humidity ( RH), negatively correlated with the crystallization of cellulose, while the temperature showed a weak effect on it. It was found that the reconstituted tobacco sheet showed outstanding coating performance including water and coating liquid with the application of excellent hygroscopic fibers under the condition of adding the same amount ratio during application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni/Nb 2 O 5 catalysts with reducible NbO x species were synthesized. • An exceedingly high cyclopentanone yield was achieved by using Ni/Nb 2 O 5 in H 2 O. • Superior performance resulted from close cooperation between Ni-NbO x sites and H 2 O. • NbO x sites facilitated furfural adsorption via flat configuration. • H 2 O mediated furfural activation and transferred active hydrogen. Selective aqueous hydrogenation of furfurals to valuable cyclopentanones is attractive for biomass utilization. Herein, Ni/Nb 2 O 5 catalysts with different calcination temperatures were synthesized and employed to study the effect of reducible NbO x species and water solvent on the aqueous hydrogenation-rearrangement of furfural. A significantly higher cyclopentanone (CPO) yield (>92 %) was achieved in water on Ni/Nb 2 O 5 -500, while no CPO was detected in heptane. Catalysts characterization indicated that the calcination temperature of Nb 2 O 5 determined the crystallinity and modulated reducible NbO x. Kinetic and isotopic experiments elucidated that the excellent catalytic performance of Ni/Nb 2 O 5 remarkably correlated with surface reducible NbO x species and H 2 O-mediated effect. NbO x species closely interacted with Ni sites, in which Ni was in charge of H 2 activation and NbO x facilitated furfural adsorption via flat configuration. Water helped furfural activation and active hydrogen transfer between Ni sites and adsorbed furfural on NbO x sites, thus significantly boosted aqueous hydrogenation of furfural to CPO. [ABSTRACT FROM AUTHOR]

Background: During the biomass-to-bio-oil conversion process, many studies focus on studying the association between biomass and bio-products using near-infrared spectra (NIR) and chemical analysis methods. However, the characterization of biomass pyrolysis behaviors using thermogravimetric analysis (TGA) with support vector machine (SVM) algorithm has not been reported. In this study, tobacco was chosen as the object for biomass, because the cigarette smoke (including water, tar, and gases) released by tobacco pyrolysis reactions decides the sensory quality, which is similar to biomass as a renewable resource through the pyrolysis process. Results: SVM algorithm has been employed to automatically classify the planting area and growing position of tobacco leaves using thermogravimetric analysis data as the information source for the first time. Eighty-eight single-grade tobacco samples belonging to four grades and eight categories were split into the training, validation, and blind testing sets. Our model showed excellent performances in both the training and validation set as well as in the blind test, with accuracy over 91.67%. Throughout the whole dataset of 88 samples, our model not only provides precise results on the planting area of tobacco leave, but also accurately distinguishes the major grades among the upper, lower, and middle positions. The error only occurs in the classification of subgrades of the middle position. Conclusions: From the case study of tobacco, our results validated the feasibility of using TGA with SVM algorithm as an objective and fast method for auto-classification of tobacco planting area and growing position. In view of the high similarity between tobacco and other biomasses in the compositions and pyrolysis behaviors, this new protocol, which couples the TGA data with SVM algorithm, can potentially be extrapolated to the auto-classification of other biomass types. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crystal plane regulative hydrogen spillover strategy was developed on Al 2 O 3. • Ni/Al 2 O 3 (1 1 1) exhibited a high turnover number in reductive amination. • Hydrogen migration prevented Ni sites from hydrogen poisoning. • Adsorption and activation of NH 3 for reductive amination was enhanced. • Ammonolysis of intermediate Schiff-base to primary amine was accelerated. Hydrogen spillover had played a significant role in catalytic processes involving reducible oxide supported metal catalyst and hydrogen molecule. Herein, crystal plane regulative hydrogen spillover strategy for the effective reductive amination on Ni/Al 2 O 3 was developed. A rod-like alumina supported Ni catalyst with primarily external (1 1 1) facets was prepared. In the presence of NH 3 and H 2 , Ni/Al 2 O 3 (1 1 1) exhibited a turnover number of 30.4 h−1, which was 136-fold higher than that of Ni/Al 2 O 3 (1 1 0) in the reductive amination of furfural to furfuryl amine. For the Ni/Al 2 O 3 (1 1 1) catalyst, Al 2 O 3 (1 1 1) facets exhibited strong Lewis acidity, resulting in an enhanced H affinity of Al 2 O 3 (1 1 1) and a positively charged of Ni through electronic interaction. It was revealed that strong H affinity of Al 2 O 3 (1 1 1) and positively charged Ni sites significantly promoted hydrogen migration from Ni surface to Al 2 O 3 (1 1 1) facets, which effectively prevented the Ni sites from hydrogen poisoning and enhanced the adsorption and activation of NH 3 and intermediates for reductive amination. Consequently, the activation energy of Schiff base reductive ammonolysis was obviously reduced, resulting in high inherent activity for furfural reductive amination to furfuryl amine. This work developed a new strategy for high efficiency reductive amination catalyst in terms of hydrogen spillover effect. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Converting renewable resources to a chemical that is a precursor for making fuels. • The catalytic conversion of methyl ethyl ketone to butene over several supported Cu catalysts as bifunctional catalysts. • The high selectivity (above 97%) to produce butene from MEK can be achieved over Cu supported on zeolite Y sodium. Abstract The direct conversion of methyl ethyl ketone (MEK) to butene over supported copper catalysts was investigated in a fixed bed reactor over Cu-Al 2 O 3 , Cu-zeolite Y sodium (Cu-ZYNa) and Cu-zeolite Y hydrogen (Cu-ZYH). In this reaction, MEK is hydrogenated to 2-butanol over metal sites which is further dehydrated on acid sites to produce butene. Experimental results showed that the selectivity of butene was the highest over Cu-ZYNa, and it was improved by finding the optimum reaction temperature, hydrogen pressure and the percentage of copper loaded on ZYNa. The highest selectivity of butene (97.9%) was obtained at 270 °C and 20 wt% Cu-ZYNa. Over Cu-Al 2 O 3 , the selectivity of butenes was less than Cu-ZYNa since subsequent hydrogenation of butene occurred to produce butane. It was also observed that with increasing H 2 /MEK molar ratio, butane selectivity increased. However, when this ratio was decreased, hydrogenation of butene was reduced, but dimerization to C 8 alkenes and alkane began to be favored. The main products over 20% Cu-Al 2 O 3 were butene and butane, and a maximum selectivity of butene (87%) was achieved at an H 2 /MEK molar ratio of five. The lowest selectivity of butene was obtained using Cu-ZYH, reaching ∼40%. All catalysts were characterized by (NH 3 -TPD), (CO 2 -TPD), XPS and TPR to probe catalyst acidity, basicity and the reducibility of Cu loaded on the supports. It was found that the amount of acidity in Cu-ZYH is much higher than in Cu-ZYNa. This could have caused the selectivity of butene to decrease as a result of dimerization, oligomerization and cracking reactions. [ABSTRACT FROM AUTHOR]