Vol 11, No 2 (2019)

The staged crystallization of aluminophosphate AlPO₄-11 from a commercially available aluminum source based on boehmite is studied for the first time by means of X-ray diffraction, ²⁷Al and ³¹P magic-angle spinning nuclear magnetic resonance, low-temperature nitrogen adsorption–desorption, and scanning election microscopy. It is shown that the synthesis of AlPO₄-11 proceeds via the formation of an intermediate phase based on crystalline aluminophosphate with a layered structure. It is found that AlPO₄-11 with a high degree of crystallinity and phase purity forms in 6–24 h at 200°C. Lengthening the time of crystallization at 200°C to more than 48 h results in the transformation of AlPO₄-11 into nonporous cristobalite. The results can be used to develop means for directional control of the phase purity and degree of crystallinity of commercially important silicoaluminophosphate molecular sieves SAPO-11 with desired properties. These can be used as a base for the synthesis of promising domestic catalysts for the commercial hydroisomerization of higher n-paraffins.

Different ways of increasing the selectivity of catalysts are described for converting oxygenate to liquid hydrocarbons. Analysis of reports suggests that the main factors affecting the selectivity of zeolite-containing catalysts are the structural type and acidic properties of the zeolites. It is shown that the strength and distribution of acid sites depend on the structural type and chemical composition of the zeolite framework, and on the chemical nature of the exchange cations. Different ways of changing the acidic properties of zeolites are discussed, e.g., modifying them with cations of various elements and subjecting them to postsynthesis acidic, alkaline, and steam heat treatment.

The catalytic systems based on metal porphyrin complexes used for promoting the reactions of olefin oxides with carbon dioxide were reviewed. The metal porphyrin complexes were shown to be effective catalysts for carboxylation of epoxides. The catalyzed reactions of oxiranes with carbon dioxide in the presence of homogeneous and heterogeneous metal porphyrin complexes, including the reactions with the use of various promoting additives, were considered.

The possibility of the efficient catalytic synthesis of hydrocarbons on a zeolite-containing catalyst modified with zinc oxide for several reaction–regeneration cycles is studied. An estimate of the interregeneration run time shows that it could be at least 130–150 h, which is quite long for such a high-temperature process. The dependences of the conversion of gases rich in C₃–C₄ within the composition of the associated petroleum gas on the temperature and time of the reaction are established.

The effect of the main parameters (temperature, pressure, and dilution of the reaction medium with an inert gas) of such catalytic processes as the cracking of vacuum gasoil and the hydrogenless refining and cracking of gasoline fractions on the ratio of the selectivity of the cracking and intermolecular hydrogen-transfer reactions is studied. Control over the ratio of these reactions allows products to be obtained according to the requirements for processing feedstocks. An increase in the time of feedstock–catalyst contact, a reduction in the degree of diluting the reaction mixture with an inert gas, and a rise in pressure result in greater selectivity for hydrogen-transfer reactions. Experiments are performed on setups with fixed and recycled beds of zeolite-containing catalysts. The transformation of feedstocks containing deuterated compounds is investigated.

Using a mathematical model that describes the process of methylbutene dehydrogenation to isoprene, a comparative analysis of energy efficiency is performed for two upgrading variants: (1) a system of two serially arranged axial fixed-bed reactors and (2) an adiabatic fixed-bed reactor. A mathematical analysis is performed to determine the dependence of yield Y and selectivity S on quantity Q of thermal energy supplied by means of steam in each case. For the two-reactor system, the best performance characteristics (Y = 53.1% and S = 82.9%) are attained at Q = 9.0 MJ/kg and contact time t = 0.8 s. However, the best performance characteristics in the radial reactor (Y = 42.0% and S = 86.1%) are observed at Q = 7.8 MJ/kg and t = 0.8 s. It follows that the thermal energy required for the methylbutenes dehydrogenation reaction in the radial reactor is 13.0% lower than for the axial reactors.

Review focuses on the modern applications of bacterial lipolytic enzymes in biotechnology and covers the scope of their properties including their activity and functional stability at different temperatures, pH, substrate specificity, and activity in the presence of different chemicals. The recent data on the production of genetically engineered strains producing the bacterial lipolytic enzymes and approaches to improving their productivity are presented. The applications of bacterial lipases in biotechnological processes used in the production of biofuel, chemicals and detergents, in the food industry, and in wastewater treatment are considered.