Ahmed Al Shoaibi

Elemental mercury adsorption on sulfur-impregnated porous carbon - a review.

The presence of elemental mercury in wellhead natural gas is an important industrial problem, since even low levels of mercury can damage cryogenic aluminium heat exchangers and other plant equipment. Mercury present in the natural gas stream will also dramatically shorten the useful life of precious metal catalysts. The present work reviews the overall process of elemental mercury removal in practice using non-regenerative adsorbents (e.g. sulfur-impregnated porous carbon), addressing the various influencing parameters such as the method of sulfur impregnation, the impregnation temperature, the sulfur to carbon ratio, the impregnation time, the impact of flue gas constituents, the effect of processing temperature, and the nature of any carbon-containing functional groups present. The distribution of elemental sulfur is found to be the key to developing an effective adsorbent, rather than quantity of sulfur impregnated. Modifying or developing an adsorbent for elemental mercury removal from natural gas needs a detail physical and chemical characteristics assessment of the adsorbent.

Kinetic Modeling of Ethane Pyrolysis at High Conversion

The primary objective of this study is to develop an improved first-principle-based mechanism that describes the molecular weight growth kinetics observed during ethane pyrolysis. A proper characterization of the kinetics of ethane pyrolysis is a prerequisite for any analysis of hydrocarbon pyrolysis and oxidation. Flow reactor experiments were performed with ~50/50 ethane/nitrogen mixtures with temperatures ranging from 550 to 850 °C at an absolute pressure of ~0.8 atm and a residence time of ~5 s. These conditions result in ethane conversions ranging from virtually no reaction to ~90%. Comparisons of predictions using our original mechanism to these data yielded very satisfactory results in terms of the temperature dependence of ethane conversion and prediction of the major products ethylene and hydrogen. However, there were discrepancies in some of the minor species concentrations that are involved in the molecular weight growth kinetics. We performed a series of CBS-QB3 analyses for the C(3)H(7), C(4)H(7), and C(4)H(9) potential energy surfaces to better characterize the radical addition reactions that lead to molecular weight growth. We also extended a published C(6)H(9) PES to include addition of vinyl to butadiene. The results were then used to calculate pressure-dependent rate constants for the multiple reaction pathways of these addition reactions. Inclusion of the unadjusted rate constants resulting from these analyses in the mechanism significantly improved the description of several of the species involved in molecular weight growth kinetics. We compare the predictions of this improved model to those obtained with a consensus model recently published as well as to ethane steam cracking data. We find that a particularly important reaction is that of vinyl addition to butadiene. Another important observation is that several radical addition reactions are partially equilibrated. Not only does this mean that reliable thermodynamic parameters are essential for an accurate model, but also that the reaction set describing molecular weight growth chemistry must include a final product that is sufficiently stable to shift the equilibrium toward this product despite the decrease in entropy that accompanies molecular weight growth. Another reaction, H addition to olefins, was found to inhibit molecular weight growth by leading to the production of a lower olefin plus methyl radicals.

Implementation of Novel Error Propagation Based Reduction Approach in H 2 S/O 2 Reaction Mechanism

Presence of hydrogen sulfide in oil and gas refinery process is of critical importance since this gas must be removed prior to its utilization in the fuels. Hydrogen sulfide has very harmful effect on the human health and environment so that it must be removed in an effective and efficient manner. Claus process is the most commonly used process for hydrogen sulfide treatment. This process is basically based on the oxidation of hydrogen sulfide. The importance of Claus process has prompted the interest to study the oxidation chemistry of hydrogen sulfide. Simplification of the reaction mechanism enables one to understand the properties of chemical processes that occur during the treatment hydrogen sulfide. A novel error-propagationbased approach has been utilized in this paper that furthers our previous efforts on the reduction of detailed mechanism of H2S/O2 reactions. Direct elementary reaction error approach (DERE) has been used in order to reduce the reaction mechanism. The results obtained from the resulting reduced mechanism showed very good agreement with the detailed chemistry results under different reaction conditions. Some discrepancies were found for some species, especially for the mole fractions of H2 and H2O. The reduced mechanism revealed a superior performance over our previously developed mechanism especially when the reaction takes place under stoichiometric and fuel-lean conditions. The new reduced mechanism is also capable to track the difference in chemical kinetics that occurs with the change in reaction conditions.

Reaction Mechanism for m-Xylene Oxidation in the Claus Process by Sulfur Dioxide

In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation.

PRODUCTION AND CHARACTERIZATION OF POROUS CARBON FROM DATE PALM SEEDS BY CHEMICAL ACTIVATION WITH H3PO4: PROCESS OPTIMIZATION FOR MAXIMIZING ADSORPTION OF METHYLENE BLUE

The potential of date palm pits to be a suitable precursor for preparation of porous carbon was explored in the present work, utilizing phosphoric acid as the activating agent. Experimental methods reported in the literature were chosen with certain modifications in order to simplify the process. Process optimization was performed using the popular response surface methodology (RSM) adopting a Box-Behnken design. Process optimization was intended to maximize the porous carbon yield and the methylene blue (MB) adsorption capacity, with the process variables being the activation temperature, impregnation ratio (IR), and activation time. The structural characteristics were assessed based on nitrogen adsorption isotherms, SEM, and FT-IR, while the adsorption capacity was estimated using MB adsorption. The optimized experimental conditions were identified to be an activation temperature of 400°C, IR of 3, and activation time of 58 min, with the resultant porous carbon having a yield of 44% and MB adsorption capacity of 345 mg/g. The structural characteristics of the porous carbon reveal the BET surface area to be 725 m2/g, with pore volume of 1.26 cc/g, an average pore diameter of 2.91 nm, and total micropore volume of 0.391 cc/g. The popular Langmuir and Freundlich adsorption isotherm models were tested, and a maximum monolayer adsorption capacity of MB was estimated to be 455 mg/g, which compares with the highest for MB reported in literature, evidencing the suitability of porous carbon for adsorption of macromolecular compounds. The low activation temperature and activation time with highest yield render the process technically and economically attractive for commercial use.

ASPEN PLUS SIMULATION OF POLYETHYLENE GASIFICATION UNDER EQUILIBRIUM CONDITIONS

The gasification process of polyethylene (PE) was successfully modeled using a combination of various unit operation modules available in the Aspen Plus simulation package. The study presents significant insight into the effect of various process parameters on the polyethylene gasification process under equilibrium conditions that has not been reported elsewhere. The simulation tool was used to predict the product composition and temperature for varying cases of steam and airflow rates and pressure. Based on the simulation results, the behavior of the conversion process was characterized according to the combined and individual fractional efficiencies. Finally, the optimum conditions that would yield a maximum conversion for the PE gasification process have been identified and reported.

Kinetic Analysis of C4 Alkane and Alkene Pyrolysis: Implications for SOFC Operation

Pyrolysis experiments of isobutane, isobutylene, and 1-butene were performed over a temperature range of 550–750 °C and a pressure of ∼ 0.8 atm. The residence time was ∼ 5 s. The fuel conversion and product selectivity were analyzed at these temperatures. The pyrolysis experiments were performed to simulate the gas phase chemistry that occurs in the anode channel of a solid-oxide fuel cell. The experimental results confirm that molecular structure has a substantial impact on pyrolysis kinetics. The experimental data show considerable amounts of C5 and higher species (∼2.8 mole % with isobutane at 750 °C, ∼7.5 mole % with isobutylene at 737.5 °C, and ∼7.4 mole % with 1-butene at 700 °C). The C5 + species are likely deposit precursors. The results confirm that hydrocarbon gas phase kinetics have substantial impact on SOFC operation.Copyright

Impact of process conditions on preparation of porous carbon from date palm seeds by KOH activation

Date palm seed being one of the major waste biomass produced in UAE, is assessed for its potential to be an appropriate precursor for preparation of porous carbon by utilizing KOH as an activating agent through application of process optimization. Process optimization was performed using the popular response surface methodology adopting a Box–Behnken design, to maximize porous carbon BET surface area and % yield, by altering activation temperature, activation time and impregnation ratio. The chemical reactions involved during the impregnation and the carbonization processes for these hydroxide/lignocellulose mixtures present in date palm seed have been proposed. A deep insight has been obtained concerning the possible reactions mechanism. The adsorption capacity was estimated using Iodine adsorption, which infers micropore nature of the porous carbon and it can be utilized for an effective waste water treatment with smaller molecular size substrates.

KOH-based porous carbon from date palm seed: preparation, characterization, and application to phenol adsorption

The date palm seed being one of the major forms of biomass produced from the date industry in UAE, its potential to be an appropriate precursor for the preparation of porous carbon utilizing KOH as an activating agent is assessed in the present work. The porous carbon is prepared at an activation temperature of 600 °C, impregnation ratio of 2, and activation duration of 1 hour, in an inert atmosphere using a conventional horizontal furnace. The resultant porous carbon has a Brunauer-Emmett-Teller surface area of 892 m(2)/g, pore volume of 0.45 cm(3)/g, and an average pore diameter of 1.97 nm. This porous carbon was used for adsorption studies at different initial concentrations (100-400 mg/l) and temperatures (30-50 °C). The adsorption isotherm parameters for the Langmuir and Freundlich models were determined using experimental adsorption data and it was found that both Langmuir and Freundlich isotherms described well the adsorption behavior of phenol on porous carbon. The mono layer adsorption capacity was observed to be 333 mg/g, which is highest for the reported date pam seed biomass-based porous carbon. From the data obtained, it was concluded that the removal of phenol from aqueous solution by porous carbon prepared from data palm seed is a low-cost process with an extremely high performance.

Prominent catalytic activity of mesoporous molecular sieves in the vapor phase dehydration of cyclohexanol to cyclohexene

Abstract Cerium incorporated KIT-6 mesoporous materials were synthesized through direct hydrothermal method and characterized by using X-ray diffraction (XRD), nitrogen sorption isotherm (BET), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma – atomic emission spectroscopy (ICP-AES), diffuse reflectance ultraviolet visible spectroscopy (DRS-UV-Vis), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. It appeared that stable cerium ions were inserted into the silica framework of KIT-6, thus generating acid properties in their host materials. The catalytic activity of Ce-KIT-6 materials was evaluated in the vapor phase dehydration of cyclohexanol to cyclohexene and dicyclohexyl ether at different temperatures with various Si/Ce molar ratios. Ce-KIT-6 (25) showed higher activity with 54% cyclohexanol conversion and 64% selectivity to cyclohexene. The catalytic results indicated that Ce-KIT-6 mesoporous materials could be used as versatile and stable acid catalysts.