1-Hexene Isomerization Over Nano-crystalline Zeolite Beta: Effects of Metal and Carrier Gases on Catalytic Performance

The paper presents the possibility of using carbon dioxide as a carrier gas in capillary gas chromatography (with a stationary liquid phase) to analyze semi-volatile compounds (boiling points of up to 400 °C). Based on the experiments carried out for compounds from the group of organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), the maximum volumetric flow rate (2.4 mL/min for CO2) was determined, enabling the correct separation of the tested standard mixtures (except for two compounds from the OCP group: 4,4′-DDD and Endrin aldehyde and two other pairs of compounds with Rs slightly less than 1.5). Compared to using helium as a carrier gas (and makeup), carbon dioxide produces wider (about 1.6 times) and lower (about 1.8 times) peaks of analytes; these values can vary depending on the separation efficiency of the column. Carbon dioxide can also be effectively used as a makeup gas for the FID detector. The signal increase is comparable to that obtained with helium used as makeup (on average 40–50% depending on the carrier gas). When high sensitivity and high resolution are not required, CO2 can be an alternative carrier and makeup gas to helium under the same flow conditions. The paper also describes practical aspects related to the implementation of CO2 as a carrier and makeup gas in GC.

Performance evaluation of desalination processes based on the humidification/dehumidification cycle with different carrier gases

Enthalpy and entropy of adsorption of light hydrocarbons C1-C4 have been measured for three monoliths of different polarity and for five different carrier gases: helium, hydrogen, nitrogen, carbon dioxide and dinitrogen oxide. Using carrier gas helium the highest values of enthalpy and entropy were observed for monolith based on ethylenedimethacrylate and the lowest values were observed for monolith based on silica, while monolith based on divinylbenzene demonstrated intermediate values. Entropy-enthalpy correlations were observed with carrier gas helium for all thee monoliths and possess similar slope indicating similar adsorption mechanism on all monoliths studied. Comparing different carrier gases entropy-enthalpy correlations within a homological series of solutes were observed for light carrier gases (He, H2 and N2) and were not observed for heavy carrier gases (CO2 and N2O). Instead, entropy-enthalpy correlations for heavy carrier gases were observed with pressure as variable and the higher the carrier gas pressure the lower the values of enthalpy and entropy observed. The observed changes in entropy-enthalpy correlations were explained by competitive adsorption of heavy carrier gas on monoliths.

Behavior of short silica monolithic columns in high pressure gas chromatography

A simple gas chromatographic technique for the determination of the solubility of gases in low-volatile liquids was proposed. The procedure is based on the introduction of a certain volume of the liquid saturated with the gas at atmospheric pressure into a gas chromatograph. The solubility of carrier gases (helium, hydrogen, nitrogen, methane, and carbon dioxide) in various stationary liquid phases (SLP), such as pentadecane, polydimethylsiloxane PMS-100, and polyethylene glycol PEG-600, was studied. The carrier gases studied can be arranged in the following series by solubility in SLP: He<H2<N2<CH4<CO2. This order coincides with the series reflecting change in the retention values in GLC for different carrier gases.

Biomass is a promising energy source due to its abundant, carbon-fixing, and carbon-neutral properties. Torrefaction can be employed to improve the properties of biomass in an oxygen-free or nitrogen atmosphere. This study investigates the product yields and the solid product characteristics from corncob waste torrefaction at the temperatures of 250 °C and 300 °C for 1 h. Nitrogen, carbon dioxide, and a gas mixture of air and carbon dioxide are employed as the carrier gases. The solid product characteristics approach those of coal at the higher temperature, regardless of what the carrier gases are. The fixed carbon, higher heating value, and solid and energy yields using carbon dioxide as a carrier gas at 300 °C are close to those using nitrogen. The product safety and storage properties before and after torrefaction are revealed by the measurements of ignition temperature and hygroscopicity. A higher torrefaction temperature leads to a higher ignition temperature of treated biomass, except using the mixture of air and carbon dioxide as the carrier gas. Carbon dioxide is a better carrier gas than nitrogen for biomass torrefaction, from the storage and transportation points of view.

Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.

Influence of geometry-limited diffusion on the selective catalytic reduction of NO by hydrocarbons over Cu-exchanged zeolite

Adsorption at ppm concentrations of propane, n-butane and dichlorodifluoromethane (Freon-12) gases and their mixtures from carrier gases helium, nitrogen, and carbon dioxide was measured on activated carbon at atmospheric pressure and 290 K. The experimental data are compared with predictions for an ideal-adsorbed-solution based upon single-gas (SG) and single-solute (SS) standard states. The SG standard states underestimate the adsorption of trace components with an average error of 25%. Average errors from SS standard states are only 8%, but new experimental isotherms are required for each trace component if the carrier gas is changed. Adsorbed-phase non-idealities observed for these systems can be explained by differences in size between large trace-gas molecules and small carrier-gas molecules.

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

The dependence of retention values (capacity factor, relative retention, Kovats' retention index) of some organic compounds (different chemical classes) on average column pressure has been experimentally studied for three carrier gases (hydrogen, nitrogen, and carbon dioxide). Linear equations for the relative retention dependence on average pressure were theoretically deduced. The equations obtained conformed well to the experiment. Even at low pressures (2–5 atm), carrier gas pressure influence on relative retention values is usually greater than experimental error. © 1996 John Wiley & Sons, Inc.

The dependence of retention values (capacity factor, relative retention, Kovats' retention index) of some organic compounds (different chemical classes) on average column pressure has been experimentally studied for three carrier gases (hydrogen, nitrogen, and carbon dioxide). Linear equations for the relative retention dependence on average pressure were theoretically deduced. The equations obtained conformed well to the experiment. Even at low pressures (2–5 atm), carrier gas pressure influence on relative retention values is usually greater than experimental error. © 1996 John Wiley & Sons, Inc.

Adsorption-controlled diffusion in catalytic reduction of NO with hydrocarbons over zeolite catalysts

Here, we present a new fluoride-deficient synthesis approach to beta nanozeolites that results in synergistic effects of mineralizers on the crystallization kinetics, attained at intermediate fluoride and hydroxide concentrations (controlled by the ratio of hydrofluoric acid (HF) to organic structure-directing agent (OSDA) in hydroxide form). This approach represents an improved methodology as compared to the traditional hydroxide and fluoride routes, and it is likely transferable to other zeolites with different framework topologies. The method affords not only improved kinetics but also a control of the crystal size, reaching the nanoscale regime (≤100 nm) and framework defect concentration (≤3.5 per unit cell). Upon loading with Pd species, the resulting Pd/beta catalysts are active for wet methane combustion and their performance is dependent on the concentration of zeolite defects, crystal size, and zeolite Si/Al ratio. The 3.0 wt% Pd catalyst supported on Na+-post-exchanged 500 °C-calcined beta zeolite with a Si/Al ratio of 45 and a crystal size of ca. 75 nm, obtained at a synergistic mixture HF/OSDA ratio of 0.50, is the best among those studied: it shows a light-off temperature of 300 °C, together with excellent catalyst stability (over 90% methane conversion at 350 °C even after 100 h on stream), in the presence of 10% water vapor. This study provides an example where the performance of zeolite-supported metal catalysts can be significantly improved by controlling both the zeolite crystal size and defect concentration.

Comparative microwave catalytic pyrolysis of cellulose and lignin in nitrogen and carbon dioxide atmospheres