Weight Hourly Space Research Articles

Vapor phase nitration of toluene using dilute nitric acid and molecular modeling studies over beta zeolite

The regio-selective nitration of toluene to para-nitrotoluene with dilute HNO 3 has been studied over catalyst beta zeolite. The effect of reaction temperature, concentration of HNO 3 and molar ratio of toluene to HNO 3 is reported. The maximum conversion of 55% (toluene to HNO 3 ratio, 1.7:1), selectivity to para-nitrotoluene of 70%, and catalyst life of 75 h (weight hourly space velocity (WHSV)=0.2) were obtained using 20% nitric acid at temperature of 120 °C. The catalyst deactivated faster when the concentration of acid and the temperature of reaction and WHSV was increased. The physicochemical characterization of the deactivated catalyst showed the structural stability of beta zeolite under the reaction conditions, but the para-nitrotoluene, and other oxidation products 4-nitrobenzoic acid, benzaldehyde, benzoic acid and anthraquinone were found deposited on the catalyst surface. Even then, the selectivity for para-nitrotoluene remains nearly constant. The molecular modeling study revealed that para-nitrotoluene encounters the least resistance for diffusion in the beta zeolite. These observations indicate that the shape selective nitration of toluene takes place inside the zeolite pores. The catalyst with alumina binder was found to be more active than the catalyst without binder because of higher acidity. The deactivated catalyst can almost be regenerated by washing the catalyst with organic solvents.

Alkylation of phenol with methanol over ion-exchanged Y-zeolites

Alkylation of phenol with methanol was carried out over Lewis acid ion exchangedY-zeolites, FeY, ZnY, CdY and LaY at temperatures of 523, 573, 623, 673 and 698 K. The products obtained wereo-cresol, 2,6-xylenol and anisole. The effects of phenol to methanol mole ratio and Weight Hourly Space Velocity (WHSV) were examined for high phenol conversion and product selectivity. Phenol conversion decreased with increase of temperature over all the catalysts due to coke deposition. Selectivity too-cresol decreased with increase of temperature as it, once formed, became the reactant for formation of 2,6-xylenol. Selectivity to 2,6-xylenol increased with increase of temperature indicating high activation energy for its formation. Selectivity to anisole, although formed less than 10% over all the catalysts, decreased with increase of temperature due to its conversion too-cresol and then to 2,6-xylenol. In addition, selectivity to anisole also decreased with decrease of phenol to methanol feed ratio and WHSV. The study of time on stream showed preferential blocking of strong acid sites by coke deposits and hence these site dependent formations ofo-cresol and 2,6-xylenol were greatly reduced but free weak acid site dependent anisole formation increased with time.

Pd/δ-Al2O3 Catalysts for Isoprene Selective Hydrogenation: Regeneration of Water-Poisoned Catalysts

Water-containing isoprene was partial hydrogenated over δ-alumina-supported eggshell Pd catalysts with a weight-hourly space velocity (WHSV) of 18 h-1 (grams of feed per hour × grams of catalyst) at 40 °C and 30 atm (30.39 kg/cm2) total pressure. The isoprene conversion decreased with time on stream and became almost time invariant at about 50 h, with a value of 20%. The activity of the water-poisoned catalysts was only slightly recovered after the water-free isoprene was introduced; by this, the conversion was increased only to 24%. In contrast, by hydrogen treatment prior to the introduction of water-free feed, the water-poisoned catalyst was greatly reactivated. The improvement in activity was also influenced by temperature. The number of Pd sites available for CO chemisorption was increased and, thus, the catalyst activity was improved by a raise in temperature to 200 °C, then declined. At nearly steady state, the isoprene conversion by catalysts reactivated at 200 °C is about 93% of that by catalysts...

Separation, characterization and catalytic cracking kinetics of aromatic fractions obtained from FCC feedstocks

A modified ASTM-D-2549 method was used to separate and characterize the aromatic fraction contained in a fluid catalytic cracking (FCC) unit feedstock. The total aromatic fraction was firstly separated in many other fractions which were subsequently characterized and analyzed using a GC/MS system. The results of the separation scheme were found to be satisfactory. The total aromatic fraction, obtained by the above separation, and an FCC gasoline fraction from a commercial unit, were used as feedstocks in kinetic experiments. These experiments were carried out in a microactivity (MAT) reactor at relatively short residence times using an equilibrium cracking catalyst. From these experiments the cracking products distribution was measured as a function of Weight Hourly Space Velocity (WHSV) and time on stream. Based on these experimental results, a lump kinetic model was developed for gasoline and the aromatics fraction. The kinetic constants of this reaction scheme were estimated using a sequential step regression method.

Mechanistic study of the selective hydrogenolysis of CCI2F2 (CFC‐12) into CH2F2 (HFC‐32) over palladium on activated carbon

AbstractThe influence of process parameters such as temperature (400‐560K), H2/CCl2F2 ratio (2.2‐20), and Weight Hourly Space Velocity (WHSV) (0.3‐1.0 g/(g · h)) on the hydrogenolysis of CCl2F2 into CH2F2 over palladium on activated carbon has been investigated. The reactivity of CHCIF2 and CH2F2 and the influence of HCl were also examined. In the reaction of CCl2F2, the main product is CH2F2. Significant amounts of CHCIF2 and CH4 are also found. The catalyst shows a remarkably high selectivity to CH2F2, in the range of 70‐90 mol%, at all conversion levels in a broad range of process conditions. A mechanism is proposed in which the reaction proceeds mainly via parallel reaction pathways. One route results in CH2F2 and CHCIF2, while the other route yields CH4. The selectivity to CH2F2 and CHCIF2 is determined by the amount of adsorbed chlorine on the catalytic surface and a constant selectivity for CH4 was found. High selectivity for CH2F2 can be achieved at high H2/CCl2F2 ratios and low HCl concentration. The postulated mechanism is supported by thermodynamic data.

Fuels and chemicals from sewage sludge: 3. Hydrocarbon liquids from the catalytic pyrolysis of sewage sludge lipids over activated alumina

Toluene-extracted lipids (obtained by extraction with boiling toluene) from a dried raw Atlanta sewage sludge were pyrolysed over activated alumina at 450 °C and atmospheric pressure. Pyrolysis yielded low-viscosity liquids (10.7–67.5 wt%), non-condensable gases (12.1–15.6 wt%), semi-solids (only at higher weight-hourly space velocity) and water. The liquid products were hydrocarbon mixtures which contained predominantly alkanes. Infrared spectra, as well as proton-decoupled 13C nuclear magnetic resonance, confirmed the absence of carbonyl groups in the pyrolysed liquid products; showing that even the carboxylic acids, the major component of the separated lipid fraction, did not survive the pyrolysis reaction. Gas chromatography of the liquid products showed a uniform hydrocarbon distribution across the C6–C20 mass range. Non-condensable gases consisted of carbon dioxide, carbon monoxide, methane, ethane, ethene and C3–C5 compounds. This process resulted in rejection of both nitrogen and sulfur. The lipid extract only contained 1 wt% of the nitrogen and 16 wt% of the sulfur in the sludge. But these elements were reduced by a further 84% in the liquid product with respect to the lipid. The pyrolysed liquid contained 0.08 wt% nitrogen and 0.22 wt% sulfur. This liquid has a great potential to be used as diesel fuel, heating fuel and chemical feedstocks.

ChemInform Abstract: Oxidative Coupling of Methane Over Sodium Promoted Praseodymium Oxide

Unpromoted and alkali-promoted lanthanide oxides were evaluated in the oxidative coupling of methane to higher hydrocarbons. Methane conversion was carried out catalytically and in a redox mode by cycling methane and air independently over the lanthanide oxides. The sodium-promoted nonstoichiometric oxide, 4% Na on Pr6On, was most active and selective, giving in the redox mode 21% methane conversion and 76% C+2 selectivity at 800 °C and 1.4 WHSV (weight hourly space velocity, g CH4g cat. hr). At comparable conversion catalytic methane conversion had a C+2 selectivity of 64%. This selectivity deficit with respect to redox is attributed to an additional destructive route of the methyl radical, namely the reaction with molecular oxygen to yield a methylperoxy intermediate. Process variable studies support a mechanism whereby methane is activated at the metal oxide surface to form a methyl radical and in the gas phase C+2 hydrocarbon building occurs.

The Conversion of Light Naphtha Into Aromatics by Using Promoted Zeolite Catalysts

Zeolites of the ZSM-5 family are poor for converting liquid paraffins into aromatics, but commercially available H-ZSM-5 can be effectively promoted with zinc or gallium. A gallium-promoted zeolite was used for the conversion of pentane and a natural-gas condensate into aromatic-rich liquid products. Optimum performance was obtained at temperatures of 475�C and weight-hourly space velocity of 1 h-1. The aromatic products were principally benzene, toluene and xylene, with the benzene content increasing with increasing conversion temperature. Operation of the catalyst at high severity (high temperature, low space velocity) produced a liquid product containing over 90% of aromatics. Lower severity produced less aromatics but higher overall liquid yield.

Oxidative coupling of methane over sodium promoted praseodymium oxide

Unpromoted and alkali-promoted lanthanide oxides were evaluated in the oxidative coupling of methane to higher hydrocarbons. Methane conversion was carried out catalytically and in a redox mode by cycling methane and air independently over the lanthanide oxides. The sodium-promoted nonstoichiometric oxide, 4% Na on Pr 6O n, was most active and selective, giving in the redox mode 21% methane conversion and 76% C + 2 selectivity at 800 °C and 1.4 WHSV (weight hourly space velocity, g CH 4 g cat. hr). At comparable conversion catalytic methane conversion had a C + 2 selectivity of 64%. This selectivity deficit with respect to redox is attributed to an additional destructive route of the methyl radical, namely the reaction with molecular oxygen to yield a methylperoxy intermediate. Process variable studies support a mechanism whereby methane is activated at the metal oxide surface to form a methyl radical and in the gas phase C + 2 hydrocarbon building occurs.

Carbon deactivation of Fischer-Tropsch ruthenium catalyst

Carbon deactivation of a 0.5 wt % Ru/..gamma..-Al/sub 2/O/sub 3/ surface-impregnated catalyst was studied by using a Berty continuous-stirred, gas-solid reactor (CSGSR)-gas chromatograph setup. The experimental variables were as follows: temperature, 473-573 K; pressure, 2-6 atm; weight hourly space velocity, 0.85, 16.5 h/sup -1/; H/sub 2//CO feed ratio, 3 and 2; and synthesis time, 0.5-5 h. Carbon deposited in a synthesis run was measured by integrating the methane evolution profile during catalyst reduction at 723 K in H/sub 2/. Significant amounts of carbon were deposited, increasing to several monolayers during 5-h synthesis periods. The methanation rate decreased as the synthesis continued, while the selectivity for C/sub 2/-C/sub 4/ hydrocarbons showed a maximum during the initial stages of deactivation. The kinetic data could be correlated by assuming both hydrogen-assisted CO dissociation and hydrogenation of surface carbon to be rate determining. The turnover numbers for methanation (N/subCH/4/sub) and carbon deposition (N/C/Ru/sub) are given.

Gas-phase isomerization of ethylbenzene over PT-heteropoly acid/zeolite catalysts

The catalytic performance and availability of heleropoly compounds in vapor phase isomerizalion of elhylbenzene to xylene have been studied. 12-molybdophosphoric acid and its salts of four first row transition metals (Cr. Fe, Co and Ni) were chosen as heteropoly compounds, and they were supported together with platinum over Y-zeolite. The experiments were carried out at 400‡C, 18 kg/cm2 of H2 pressure, 4.6 of H2/ethylbenzene mole ratio and 1.5 gr-feed/hr gr-cal of LWHSV (Liquid Weight Hourly Space Velocity). As the results of experiments, heleropoly acid enhances the activity and selectivity of isomerization and the activity of isomerization is strongly affected by the method of catalyst preparation. In case of 12-molybdophosphates, their acidities vary with the kind of countercalions and it seems that the acidity is closely related to the electro negativity of the corresponding countercation. The pretrealment with hydrogen shows an echanced activity and selectivity.