EFFECT OF LINEAR FLOW VELOCITY ON SYNTHESIS FROM CARBON MONOXIDE AND WATER VAPOR

S. I. Smolyaninov, V. M. Mironov, A. G. Zilberman

(Presented by the scientific-methodological seminar of the CTF)

The linear velocity of the reactant flow, which determines the hydrodynamic regime in the contact apparatus, is one of the most important macrokinetic factors, often governing the observed rate of a heterogeneous process, which substantially affects the choice of optimal parameters of an industrial process and the design of reaction devices.

For the synthesis of organic compounds from carbon monoxide and water vapor at atmospheric pressure, the influence of the rate of external mass transfer was determined earlier [1]. In the present work, a study is proposed of this influence on synthesis at an excess pressure of \(0.98\ \text{MN}/\text{m}^2\) (\(10\ \text{atm}\)).

The synthesis process according to the hypothetical equation

\[ 3\mathrm{CO}+\mathrm{H}_2\mathrm{O}=(-\mathrm{CH}_2-)+2\mathrm{CO}_2 \tag{1} \]

was carried out on an iron-copper reduced catalyst at temperatures from 473 to 523°K, in the range of fictitious reaction times from 60 to 360 sec and with contact-layer lengths from 32 to 240 cm.

Changing the length of the catalyst layer made it possible to increase the linear velocity of the synthesis-gas flow by almost an order of magnitude, without affecting the residence time of the reactants in the reaction zone.

As a result of the study, values were obtained for the degree of conversion of carbon monoxide to organic compounds (hydrocarbons), determined by equation (1), and values for the degree of conversion of CO to hydrogen, according to the overall equation

\[ \mathrm{CO}+\mathrm{H}_2\mathrm{O}=\mathrm{CO}_2+\mathrm{H}_2. \tag{2} \]

The sum of these quantities determines the total (summative) degree of conversion of carbon monoxide.

In view of the difficulty of calculating the true values of the linear flow velocity in the contact layer, it was possible to use fictitious velocities; as their conventional unit, the velocity of the synthesis-gas flow in a catalyst layer 32 cm long at a fictitious contact time of 720 sec was adopted, i.e., that determined by the minimum conditions of the experiment.

Figure 1 presents the dependence of the degree of conversion of CO to hydrocarbons on the fictitious linear velocity of the synthesis gas at various process temperatures. The analogous dependence for the degree of conversion of carbon monoxide to hydrogen is given in Fig. 2. From the indicated dependences it is clearly evident that changing the conditions of external diffusion of the reactants

Fig. 1. Dependence of the degree of conversion of carbon monoxide on the fictitious linear velocity of synthesis gas: 1 — fictitious contact time 60 s; 2 — fictitious contact time 360 s. Process temperature: x — 473 K; o — 488 K; △ — 503 K; ● — 523 K.

Fig. 2. Dependence of the degree of conversion of carbon monoxide to hydrogen on the fictitious linear velocity of synthesis gas. 1 — fictitious contact time 60 s; 2 — fictitious contact time 360 s. Process temperature: x — 473 K; o — 488 K; △ — 503 K; ● — 523 K.

and of the reaction products significantly affects synthesis from carbon monoxide and water vapor at medium pressure; moreover, for the degree of conversion of CO to hydrocarbons, an increase in the linear velocity leads to an increase in the degree of conversion, more sharply at high values of the fictitious reaction time, whereas the degree of conversion of CO to hydrogen is characterized by the presence of a maximum.

For comparison, we note that for the process at atmospheric pressure these dependences are expressed more strongly, which indicates a weakening of the influence of external mass transfer on the rate of the surface reaction with increasing total pressure of the synthesis gas.

Conclusions

1. A study has been carried out of the linear flow velocity of synthesis gas on the synthesis of organic compounds from carbon monoxide and water vapor at medium pressure.

2. It has been shown that, with increasing linear velocity, the degree of conversion of CO to hydrocarbons increases. The indicated dependence for the degree of conversion of carbon monoxide to hydrogen is characterized by the presence of a maximum.

3. An increase in the total pressure of the reaction mixture diminishes the influence of external-diffusion transfer on the process under study.

LITERATURE

1. S. I. Smol’yaninov, V. M. Mironov, A. V. Kravtsov. Khim. i tekhnol. topliv i masel, No. 8, 12–16, 1962.