Development of a method and algorithm for calculating the equilibrium of methanol synthesis under medium pressure

Abstract

The object of research is the synthesis of methanol under medium pressure, and the subject of research is the calculation of the equilibrium composition. A method and an algorithm for calculating the equilibrium composition of products are proposed. Calculations have been carried out using two mechanisms of methanol synthesis. First of all, the first approach to the mechanism of methanol synthesis was applied, which provides for the formation of methanol from a mixture of carbon oxides and hydrogen by the simultaneous reaction of methanol synthesis from carbon monoxide (IV) and steam reforming of carbon monoxide (II). The poor convergence of the system of two equations on the basis of this interaction mechanism is established, which complicates the selection of initial approximations and the choice of a real solution. At the second stage, the mechanism of the formation of methanol from carbon monoxide (II) with the simultaneous flow of steam reforming of CO in the opposite direction is considered. The degree of the equation describing the dependence of the equilibrium constant on the partial pressures of the reactants decreases in comparison with the first approach and causes much better convergence when solving the system of two equations. The use of a coefficient that takes into account the effect of pressure on the value of the equilibrium constant is proposed, and its dependence on temperature is approximated. The developed algorithm is implemented in MathCAD, while the relative maximum deviation for methanol is 8.53 %. The third approach is to use two coefficients that adjust the equilibrium constant depending on pressure. In this case, the relative maximum deviation of methanol is 16.25 %. The program according to the proposed algorithm takes into account the multiplicity of the initial data, namely the possibility of varying the composition of the initial mixture, pressure and temperature. The calculation was carried out according to the initial data of industrial implementation of methanol synthesis. Comparison of the equilibrium concentration of methanol with the real one at the outlet of the synthesis column established the degree of equilibrium reaching 39.4 %, which indicates the presence of a reserve of methanol synthesis and the possibility of increasing the practical yield of methanol.