Petroleum Chemistry最新文献

A traditional technology for removing acid gases includes absorption by aqueous solutions of alkanolamines. Despite a high degree of gas flow purification and the high productivity of this process, there is a problem of thermo-oxidative degradation of the absorption solution. Degradation products are thermally stable and tend to accumulate within the system, resulting in significant operational problems. One of the promising approaches to the regeneration of alkanolamine absorbents is combining of membrane filtration and electrodialysis. This paper presents the first study of the effect of the pore size of a membrane used for prefiltration of an alkanolamine absorbent on the efficiency of the removal of heat-stable salts (HSS) by electrodialysis. Our findings indicate that both the initial HSS content and the effectiveness of their extraction vary depending on the alkanolamine type. Such variation is determined by the different mechanisms of a resin formation in absorbent solutions depending on the alkanolamine type. It was shown that decreasing the pore size and transition from microfiltration to nanofiltration enhances the degree of HSS extraction from 55 to 65% for classical electrodialysis and up to 87% for bipolar electrodialysis. To address the issue of fouling in ion-exchange membranes, a sequential washing with acid and alkaline solutions has been proposed. Our results indicate that this method makes it possible to restore the degree of HSS extraction from absorption solutions by 95%.

Catalytic systems based on SAPO-11 molecular sieves are known for their superior selectivity in the hydroisomerization of higher (C₁₆₊) n-paraffins. However, further improvement of SAPO-11-based catalysts is impeded by the lack of effective tools for controlling the morphology and size of silicoaluminophosphate crystals. The present study investigates the effects of the DPA/Al₂O₃ molar ratio in reaction gels on the nature of intermediate phases and on the physicochemical properties of SAPO-11 molecular sieves. SAPO-11 has been found to crystallize through the formation of different phases depending on the DPA/Al₂O₃ ratio: an AlPO₄·2H₂O intermediate at DPA/Al₂O₃ = 1.0, a mixture of AlPO₄·2H₂O and a layered silicoaluminophosphate at DPA/Al₂O₃ = 1.4, and a layered silicoaluminophosphate alone at DPA/Al₂O₃ = 1.8. Proper adjustment of this ratio provides an effective tool to control the crystal morphology, crystal size, and the porous structure characteristics of the SAPO-11 molecular sieves. It has been identified that, at DPA/Al₂O₃ = 1.0, cubic and lamellar SAPO-11 nanocrystals 200–400 nm in size are formed. These nanocrystals have the following textural properties: S_BET = 286 m²/g; V_micro = 0.06 cm³/g; and V_meso = 0.21 m³/g. Furthermore, the effects of the morphology and size of SAPO-11 molecular sieve crystals on their catalytic performance in the hydroisomerization of n-hexadecane have been demonstrated. Promising catalytic systems based on SAPO-11 nanocrystals have been proposed for the hydroisomerization of C₁₆₊ n-paraffins.

The article provides a comparative assessment of two design cases of heat input for a compact single-tube steam methane reformer operating at 10 bar and a feed flow rate of 1–3 Nm³/h, filled with a granulated nickel catalyst, and equipped with a 5–15 kW propane–butane burner. In the first design case, the catalyst-filled tube was heated with a flue gas as it was injected from the flame burner (at an excess air ratio of 2.3) through an annular channel that enclosed the tube. In the second design case, the heat was provided by a cylindrical IR burner panel (at an excess air ratio of 1.05) that enclosed the tube. Using mathematical modeling, the performance of both reformer cases was compared, with all other parameters being equal. The IR-burner-based reformer exceeded its flue-gas-heated counterpart in terms of methane conversion, heat recovery efficiency (about twofold for both parameters), the percentage of radiant heat transfer (by a factor of about 2.3), and fuel enthalpy increase (6–7% higher in the second case). When the operating load was tripled, the reformer integrated with the IR burner exhibited a lesser performance drop (regarding all the parameters mentioned above) than the conventionally heated reformer (in particular, the methane conversion declined by 8% in the second design case and by 18% in the first). The parametric calculations based on the permeable burner panel model showed that a Peclet number greater than five (Pe > 5) was able to prevent the panel inlet surface from heating to an extent that could otherwise cause emergency autoignition of the fuel–air mixture at the panel inlet.

The study investigates the effects of various functional groups contained in porous aromatic frameworks (PAFs) on the properties and performance of a series of rhodium catalysts developed for hydroformylation. Analytical methods such as TEM, FTIR spectroscopy, elemental analysis, XRD, and low-temperature nitrogen adsorption–desorption were used to characterize the catalysts before and after running. The catalysts based on PAFs with sulfo groups (PAF–SO₃H) exceeded those based on PAFs with imidazole substituents (PAF–Im⁺Cl^–) in terms of specific activity in the hydroformylation of 1-hexene. Both catalyst types exhibited high stability over five running cycles. An extra wash with sulfuric acid enhanced the specific activity of the PAF–SO₃H catalysts, although their metal retention capacity declined; the washing had no adverse effect on the stability of the PAF–Im⁺Cl^– catalysts. Rhodium in the catalysts was present as Rh⁰ (nanoparticles) and Rh³⁺, and the reduced Rh was found to most likely act as a precursor of the catalytically active hydridocarbonyl complexes.

A series of unsupported nickel phosphides were synthesized in situ in a reaction mixture under the conditions of hydrodechlorination of 1,4-dichlorobenzene. Triphenylphosphine and red phosphorus were used as phosphorus sources, beneficial in terms of environmental friendliness and cost effectiveness. Using X-ray fluorescence spectrometry, it was demonstrated that, with red phosphorus as a phosphorus source, a Ni₂P phase was formed even at a Ni/P molar ratio of 1 : 1. The effects of temperature and pressure on the catalytic activity were investigated. The nickel phosphides proved to be reusable in hydrodechlorination: their catalytic activity remained adequate over five reaction cycles. In contrast, an unphosphided nickel-based catalyst exhibited high activity only in the first to third reaction cycles, after which the dechlorination degree abruptly declined due to the formation of NiCl₂.

Though alumina and silica are well-known and widely used supports, they have notable drawbacks, such as the formation of the AlPO₄ phase and inadequate metal–support interactions with nickel phosphide. This study investigates the synergistic effects of silica and alumina on the physicochemical properties and catalytic performance of nickel phosphide catalysts. Catalysts supported by alumina (Al₂O₃), silica (SiO₂), and a composite silica-alumina (ASA) have been simultaneously prepared using a straightforward isopyknic co-impregnation method in order to eliminate the influence of preparation conditions. The results indicated that Ni₂P/SiO₂ exhibited poor dispersion, while Ni₂P/Al₂O₃ showed a larger particle size along with the formation of the AlPO₄ phase. The coordination between silicon and aluminum facilitated the reduction of nickel phosphate to nickel phosphide (Ni₂P) and inhibited the formation of AlPO₄. Ni₂P/ASA demonstrated an improved dispersion and smaller particle size. Therefore, a comparative study of the Ni₂P/SiO₂, Ni₂P/ASA, and Ni₂P/Al₂O₃ performance revealed the superior catalytic efficacy of the SiO₂–Al₂O₃ supported Ni₂P in the naphthalene hydrogenation.

This paper proposes a novel approach to the extraction of cluster structures from a ZSM-5 zeolite lattice. The approach involves transforming the zeolite crystalline structure into a directed molecular graph followed by identifying cycles from which cluster structures are generated. One advantage of this approach is the complete similarity of the resultant cluster structures at equal input data, making the DBSCAN clustering method applicable to the identification of unique structures. Furthermore, this approach is effective in identifying the active and extended regions within a multilevel ONIOM model for subsequent quantum-chemical calculations. Finally, the proposed approach makes it possible to automate the extraction of cluster structures from ZSM-5 crystals and to select the most important structures for further analysis. To validate its efficiency, the novel approach was applied to identify the most probable location of Zn²⁺ cation-exchange sites in ZSM-5.

Based on quantum-chemical computation, a solution with periodic boundary conditions (PBC) was employed within density functional theory (DFT) simulations in order to assign the chemical shifts in the ²⁷Al MAS NMR spectra of Al-BEA (HBEA) zeolite (Si/Al = 31) to the individual crystallographic T-sites calculated for polymorph B of an identical zeolite. The results were compared both to relevant published reports (Si/Al = 71 and 75) and to the experimental data previously obtained by the authors for a mixture of polymorphs (Si/Al = 25). Deconvolution of the ²⁷Al MAS NMR spectrum into Al signals at different T-sites of polymorph B was compared to a similar deconvolution for polymorph A.