Asen I. Anastasov

An investigation of the kinetic parameters of the o-xylene oxidation process carried out in a fixed bed of high-productive vanadia-titania catalyst

The behavior of a reactor of a fixed bed composed by high-productive V2O5–TiO2 (anatase) supported catalysts for oxidation of o-xylene into phthalic anhydride is theoretically and experimentally investigated. A two-dimensional heterogeneous mathematical model, as well as experiments obtained in an industrial multitube fixed bed reactor, is used. The kinetic parameters in the kinetic relations suggested by Calderbank et al. (Chem. Eng. Sci. 32 (1977) 1435) for description of the oxidation process are corrected in a proper way. New formal values of the parameters mentioned are determined. They interpret well the temperature regime and the yields of phthalic anhydride and the main side product (phthalide) obtained in the industrial reactor during the initial periods of the catalyst life.

Deactivation of an industrial V2O5–TiO2 catalyst for oxidation of o-xylene into phthalic anhydride

A quantitative description of the observed deactivation in the process of oxidation of o-xylene (o-XL) into phthalic anhydride (PA) is given in this paper. Experimental temperature profiles along the length of the fixed bed obtained in an industrial reactor during various periods of the catalyst life are studied. With the help of a two-dimensional heterogeneous mathematical model the degree of the catalyst deactivation along the bed is determined as a function of time. The activation profiles obtained interpret very well the magnitude and the location of the hot spot, the PA yield and the content of the main undesired product phthalide (PH). A terraced change of the catalyst activity along the bed is found out, while a maximum decrease of the activity is registered in the hot spot zone. Optimal temperature regimes valid for different periods of the catalyst life are determined.

A study of the influence of the operating parameters on the temperature of the hot spot in a fixed bed reactor

The influence of the operating parameters (coolant temperature, inlet temperature of the reaction mixture, initial reagent concentration and gas flow rate) of the process of oxidation of o-xylene into phthalic anhydride taking place in a fixed bed reactor on the hot spot temperature is investigated in this study. Using a two-dimensional heterogeneous mathematical model and physical experiments in a pilot reactor the admissible deviations from the industrial values of the parameters are determined. There is no risk the catalyst to be overheated or a runaway of the hot spot to occur under the variations determined. Two states of the catalyst are investigated—a catalyst which is completely pretreated and calcined, but not pretreated catalyst.

Influence of the inlet temperature on the performance of a fixed-bed reactor for oxidation of o-xylene into phthalic anhydride

The influence of the inlet gas temperature on the performance of a fixed-bed reactor for realization of highly exothermic catalytic process is investigated. The important industrial process of oxidation of o-xylene into phthalic anhydride is used as an example. A wide interval of inlet gas temperatures (from 120 to 450°C) is studied by means of a two-dimensional heterogeneous mathematical model. The results obtained are verified by experiments carried out in a pilot non-isothermal, non-adiabatic integral reactor. It is shown that the highest yield of phthalic anhydride, as well as the lowest content of the by-product, is achieved at a low inlet gas temperature. A minimum of the hot-spot temperature as a function of the inlet temperature is observed.

A new approach to the oxidation of o-xylene into phthalic anhydride in a fixed bed of vanadium-titanium catalyst

Abstract A new approach is proposed to feeding in the input mixture for the highly exothermic processes of partial oxidation. It is shown experimentally, by oxidating o -xylene into phthalic anhydride in a pilot non-isothermal integral reactor with a fixed bed of catalyst, that an additional feed-in of o -xylene beyond the hot spot considerably increases the productivity of the process. It is also shown that, if there is more than one feed-in, the use of two beds of industrial catalysts of different activity also increases the productivity with a lower expenditure on catalyst.

Oxidation of o-xylene into phthalic anhydride in a reactor with two fixed beds of vanadium-titania catalyst

Abstract The process of partial oxidation of o-xylene into phthalic anhydride carried out in two catalyst beds is investigated for the first time. The activity of the second bed is lower than that in the first. It is shown experimentally in a pilot non-isothermal non-adiabatic integral reactor that the use of two beds of industrial catalyst (fresh catalyst in the first bed and spent in the second), in combination with more than one feed-in of o-xylene into the reactor, improves the selectivity and the quality of the phthalic anhydride, as well as the productivity.