A study of propane aromatization on a zeolite-containing catalyst with different Si/Al ratios

Abstract

79Aromatic hydrocarbons are an important feedstock for producing a significant part of the products of organic synthesis and the petrochemical industry. At present, their industrial production is based mainly on the hydroconversion of liquid pyrolysis products and the catalytic reforming of gasoline fractions. Under conditions of constant shortage of benzene, the devel opment of catalytic aromatization processes for vari ous hydrocarbon materials is of current concern.To date, a few process technologies for the aroma tization of light hydrocarbons have been developed. The Cyclar process for the conversion of low molecu lar weight paraffins (mostly propane and butanes) to aromatic hydrocarbons is based on the dehydrocy clodimerization of light paraffins using the technology of continuous regeneration of a spherical catalyst, which consists of a high silica zeolite, a base metal as a promoter, and an inert binder.A metallosilicate catalyst, which provides the selectivity of formation of aromatic hydrocarbons, is used in the Z forming process for producing a ben zene-toluene-xylene (BTX) fraction and hydrogen from liquefied petroleum gases and light naphtha. The above described conversion processes, which are based on the use of a fixed or moving catalyst bed, provide the production of aromatic hydrocarbons at a level of 50-60% of propane feedstock and 56-66% of butane feedstock involving the recycling of the unconverted residue.The Arben process is based on the conversion of a liquefied gas in a fluidized bed of a microspherical cat alyst with its continuous air regeneration; it is per formed in one isothermal reactor with an embedded regenerator. We also know the Alifar process for pro ducing aromatic hydrocarbons from individual pro pane and butanes or from their mixtures.For the competent use of low molecular weight hydrocarbons, studies in the field of production of the BTX fraction from the С 2 -С 4. fraction are carried out in OAO Nizhnekamskneftekhim.Effective catalysts for producing aromatic hydro carbons through the conversion of paraffins or С 2 -С 12 olefins are high silica zeolites of the pentasil group: ZSM 5, ZSM 11, TsVM, TsVN, etc.; most of the researchers attribute the catalytic activity of these cat alysts to the acid-base properties of their surface resulting from the presence of protic (Brönsted) and aprotic (Lewis) acid sites [1][2][3][4]. The ratio of Lewis and Brönsted sites depends on the zeolite structure, the composition of the frame, the thermal stability of the hydroxyl cover, and the chemical nature of the sub stances used to modify the internal and external sur face of the catalysts [5][6][7]. It is assumed that the con tent of Brönsted sites is roughly proportional to the number of aluminum atoms in the zeolite unit cell [8]. The content of Lewis sites is also proportional to the amount of aluminum contained in the zeolite [4].One of the important factors that affect the level and pattern of conversion of lower paraffins on zeolite containing catalysts is the content of aluminum and t...

Kinetic Features of the Process of Conversion of Propane to Aromatic Hydrocarbons

“…The published results of studies of the process of C 2 -C 4 hydrocarbons aromatization prove the efficiency of used bifunctional systems. They are characterized by the presence of acid sites of the zeolite carrier and active metal-containing sites formed when introducing of dehydrating promoters into the catalyst [1][2][3][4][5][6]. However, in most papers devoted to the study of the mechanisms of reactions over high-silica zeolites, the kinetic data are not fully presented, which is caused by certain difficulties arising from attempts to determine the degree of influence of diffusion processes on the reaction rate [7][8][9].…”

Catalytic aromatization of ethane on zinc-modified zeolites of various framework types

“…Aromatization of gaseous hydrocarbons occurs in the presence of various cata lytic systems, of which high silica zeolites of the pen tasil family are considered the most effective [1][2][3][4][5]. These are ZSM 5, ZSM 8, and ZSM 11 zeolites and their domestic analogs, such as zeolites of the TsVK, TsVM, TsVN, and other brands [6,7]. Among poten tial catalysts for aromatization of light hydrocarbons, metal-zeolite systems command the major attention as they exhibit higher activity and selectivity compared with the unmodified zeolite supports.…”