Vapor-hydrate phases equilibrium of （CH4＋C2H6） and （CH4＋C2H4） systems

Separation of the (C₁ + C₂) hydrocarbon system is of importance in natural gas processing and ethylene production. However it is the bottleneck because of its high refrigeration energy consumption, and needs to be urgently addressed. The technology of separating gas mixtures by forming hydrate could be used to separate (C₁ + C₂) gas mixtures at around 0 °C and has attracted increasing attention worldwide. In this paper, investigation of vapor-hydrate two-phase equilibrium was carried out for (C₁ + C₂) systems with and without tetrahydrofuran (THF). The compositions of vapor and hydrate phases under phase equilibrium were studied with model algorithm when structure I and structure II hydrates coexisted for the (methane + ethane) system. The average deviation between the modeled and actual mole fractions of ethane in hydrate and vapor phases was 0.55%, and that of ethylene was 5.7% when THF was not added. The average deviation of the mole fraction of ethane in vapor phase was 11.46% and ethylene was 7.38% when THF was added. The test results showed that the proposed algorithm is practicable.     

Ethylene oligomerization in the presence of ZrO(OCOR)<Subscript>2</Subscript>-Al(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>Cl-Modifier catalytic system

The kinetics of ethylene oligomerization and molecular-mass distribution of resulted oligomers on ZrO(OCOR)₂-Al(C₂H₅)₂Cl and ZrO(OCOR)₂-Al(C₂H₅)₂Cl-modifier catalyst systems, where the modifier was CCl₄, vinyl acetate, or zinc stearate, were studied depending on the modifier: ZrO(OCOR)₂ and Al(C₂H₅)₂Cl: ZrO(OCOR)₂ molar ratios, ethylene pressure, temperature, and modifier nature.     

Conversion of lower alcohols into C<Subscript>2</Subscript>–C<Subscript>4</Subscript> olefins over acid-base catalysts

The conversion reactions of methanol, ethanol, and their ethers in the presence of acid-base catalysts based on mesoporous ZSM-5 and ZSM-11 zeolites, microporous SAPO zeolites, heteropoly acids, and perfluorinated sulfonated cation exchangers are discussed. The set of reactions reflects the formation of olefins beginning from ethylene to butenes. The heats of reaction were estimated from the calculated values of the equilibrium constants and enthalpies at 700 K. It was assumed that the available experimental data for all three types of catalysts should be described by a complex mechanism of transformations of alcohols and ethers. The reaction sequence includes fast dehydration of alcohols into ethers. It is likely that, at temperatures of 512–573 K, the initial reactions have a common initiation mechanism for all three types of catalysts, which involves the formation of the protonated forms of substrate molecules that trigger the olefin synthesis reactions. For thermally stable catalysts (zeolites), the mechanism with participation of free radicals and olefins generated from the alkoxylated hydroxyl groups of zeolites is possible above 573 K. As the degree of conversion of ethers increases, carbenium and arenonium ions begin to play a progressively increasing role as active intermediates instead of the alkoxy groups. This crossover may be responsible for changes in both the kinetic parameters of the substrate transformation and the direction of the reaction over zeolites at 573–623 K. The schemes proposed in some published works for the conversion of oxygen-containing organic compounds and olefins with participation of superacid centers of the catalysts in question should be considered speculations in light of the effect of water leveling the strength of Brönsted sites.     

Kinetics of (TBAF + CO2) semi-clathrate hydrate formation in the presence and absence of SDS

In this communication, the impacts of adding SDS (sodium dodecyl sulfate), TBAF (tetra-n-butylammonium fluoride) and the mixture of SDS + TBAF on the main kinetic parameters of CO₂ hydrate formation (induction time, the quantity and rate of gas uptake, and storage capacity) were investigated. The tests were performed under stirring conditions at T = 5 ℃ and P = 3.8 MPa in a 169 cm³ batch reactor. The results show that adding SDS with a concentration of 400 ppm, TBAF with a concentration of 1–5 wt%, and the mixture of SDS + TBAF, would increase the storage capacity of CO₂ hydrate and the quantity of gas uptake, and decrease the induction time of hydrate formation process. The addition of 5 wt% of TBAF and 400 ppm of SDS would increase the CO₂ hydrate storage capacity by 86.1% and 81.6%, respectively, compared to pure water. Investigation of the impact of SDS, TBAF and their mixture on the rate of gas uptake indicates that the mixture of SDS + TBAF does not have a significant effect on the rate of gas uptake during hydrate formation process.     

Conversion of dimethyl ether into C<Subscript>2</Subscript>-C<Subscript>4</Subscript> olefins on zeolite catalysts

The effect of the nature of the metal introduced into HZSM-5 on the properties of the catalysts for the synthesis of olefins from dimethyl ether was studied. By means of the ammonia temperature-programmed desorption technique, it was shown that a decrease in the total amount of acid sites increases the selectivity for lower olefins. As the ratio of the medium to strong acid sites increases, the yield of olefins increases. The effect of the nature of gaseous additives in the feedstock on the selectivity for lower olefins was studied at T = 340°C, p = 0.1 MPa, and ν ₀ = 2000 h^?1.     

Cycloaddition of cage and polycyclic diazo compounds to C<Subscript>60</Subscript> fullerene catalyzed by Pd(acac)<Subscript>2</Subscript>-2PPh<Subscript>3</Subscript>-4Et<Subscript>3</Subscript>Al

Spirohomofullerenes were synthesized by cycloaddition of cage and polycyclic diazoalkanes generated in situ by oxidation of hydrazones of camphor, 2-adamantanone, and cholestane-3-one to C₆₀ fullerene in the presence of the Pd(acac)₂-2PPh₃-4Et₃Al three-component catalyst. It was found that the spiro-homofullerenes obtained from hydrazones of 2-adamantanone and cholestane-3-one and C₆₀ fullerene do not undergo thermal isomerization to the corresponding spiro-methanofullerenes.     

Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr<Subscript>3</Subscript>)<Subscript>2</Subscript>]BF<Subscript>4</Subscript>/BF<Subscript>3</Subscript>OEt<Subscript>2</Subscript> catalytic systems

Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr₃)₂]BF₄ + BF₃OEt₂ catalytic systems, where R = C₆H₅, o-CH₃C₆H₄, p-CH₃C₆H₄, or o-CH₃OC₆H₄, has been studied. Under the optimal conditions (B/Pd = 8, T = 75°C, R = C₆H₅), the conversion of styrene to the products exceeds the conversion for the known analogs and reaches 1.5 tons of styrene/g-atom of palladium with amounts of dimers and trimers of 91 and 9%, respectively. The dimers consist of up to 100% 1,3-diphenylbutene-1 with a trans/cis isomer ratio of 95/5.     

Study of a mass transfer-reaction model for SO<Subscript>2</Subscript> absorption process using LAS/H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution

A regenerative absorption process for removal of SO_x from FCC off-gas using LAS/H₂SO₄ solution as absorbant was studied and pilot-plant experiments were carried out. A mass transferreaction model for the SO₂ absorption process was established based on pilot-plant experiments, and the concentration distribution of components in the liquid film, and the partial pressure and mass transfer rate of SO₂ along the height of the absorption tower, was calculated from this model. The numerical simulation results were compared with the experimental results and proved that the model can be used for describing the SO₂ absorption process.     

Effect of CO<Subscript>2</Subscript> on the oxidation of cyclohexene by H<Subscript>2</Subscript>O<Subscript>2</Subscript> using Co<Subscript>1.5</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst

Oxidation of cyclohexene by cheap and environmentally friendly oxidants, namely H₂O₂ and CO₂ has been catalyzed by Co_1.5PW₁₂O₄₀. It has been found that the main products of the oxidation are 2-cyclohexen-l-one (enone), 2-cyclohexen-l-ol (enol) and 1, 2-cyclohexanediol (diol) with the enone as the major product. Oxidation by CO₂ along with H₂O₂ remarkably increased the conversion compared to that by CO₂ and H₂O₂ separately. This might be due to the fact that CO₂ increases the percarbonate species (HCO₄ ^?) responsible of the oxidation by oxygen transfer, which indicated that the CO₂/H₂O₂ mixture is a useful reagent system. The decrease of both the selectivity of the enone and epoxide in favor of that of diol at higher conversions indicated that the diol was formed from the epoxide by consecutive reaction and/or directly from cyclohexene.     

Catalytic hydroxycarbonylation of isobutylene with carbon monoxide and polyhydric alcohols in the presence of the Pd(acac)<Subscript>2</Subscript>-PPh<Subscript>3</Subscript>-TsOH system

The reaction of isobutylene hydroalcoxycarbonylation with CO and polyhydric alcohols (ethylene glycol, glycerol) in the presence of the catalytic system Pd(aacac)₂-PPh₃-TsOH has been investigated. It was found that carbonylation of isobutylene with CO in the presence of ethylene glycol yields a mixture of mono-and diglycol esters of isovaleric acid, irrespective of the initial reactant ratio. During the hydroalcoxycarbonylation of isobutylene with glycerol, either mono- and di- or mono-, di-, and triglycerides of isovaleric acid are formed depending on the reactant ratio.     

Kinetic study of methane hydrate formation in the presence of carbon nanostructures

The effect of synthesized nanostructures,including graphene oxide,chemically reduced graphene oxide with sodium dodecyl sulfate(SDS),chemically reduced graphene oxide with polyvinylpyrrolidone,and multi-walled carbon nanotubes,on the kinetics of methane hydrate formation was investigated in this work.The experiments were carried out at a pressure of 4.5 MPa and a temperature of 0 ℃ in a batch reactor.By adding nanostructures,the induction time decreases,and the shortest induction time appeares at certain concentrations of reduced graphene oxide with SDS and graphene oxide,that is,at a concentration of 360 ppm for reduced graphene oxide with SDS and 180 ppm for graphene oxide,with a 98% decrease in induction time compared to that in pure water.Moreover,utilization of carbon nanostructures increases the amount and the rate of methane consumed during the hydrate formation process.Utilization of multi-walled carbon nanotubes with a concentration of 90 ppm showes the highest amount of methane consumption.The amount of methane consumption increases by 173% in comparison with that in pure water.The addition of carbon nanostructures does not change the storage capacity of methane hydrate in the hydrate formation process,while the percentage of water conversion to hydrate in the presence of carbon nanotubes increases considerably,the greatest value of which occurres at a 90 ppm concentration of carbon nanotubes,that is,a 253% increase in the presence of carbon nanotubes compared to that of pure water.