103.    ---------------. [AUDIBERT, E] [Synthesis of Methyl Alcohol.]  Chim. et ind., vol. 20, 1928, pp. 1015-1022; British Chem. Abs., 1929, B. p. 162.

                 Résumé of the work carried out on the synthesis of MeOH from CO and H₂ under high pressure and reported at the 2d Conference on Bituminous Coal, Pittsburgh, 1928.  The conditions throughout the experiment were:  Pressure 150 atm., rate of circulation of gases over catalysts 5,000 cu. m. (n.t.p.) per m.³ of catalyst volume, and gas mixtures containing H₂ and CO in the ratio 5:1 (with catalysts having Cu as the chief constituent)) and 2:1 (with those of which ZnO is the basis); yields of MeOH are expressed in gm. per 1. of catalyst vol. per hr.  It was found that, in addition to the physical changes that occur in a catalyst as a result of prolonged use even with carefully purified gases, in the case of Cu catalysts a fouling of the solid took place owing to the deposition of C compounds of high molecular weight.  The rapidity of fouling is a function of the partial pressure of CO in the gas, and it is reduced to an unimportant value when the proportion does not exceed 1/6.  ZnO catalysts do not foul with gases containing 33% CO; such a proportion, in fact, gives the optimum yields of MeOH.  When ZnO and Cu catalysts are heated in H₂ at 550° for a number of hrs., each suffers a loss of activity, that of the ZnO catalyst being the greater.  The activity of a Cu catalyst is completely removed by the addition of small amounts of the oxides of Sn and Bi; those of B, Ti, and V have no immediate effect, although they accelerate the rate at which prolonged heating reduces the activity.  Al and Ce oxides, on the other hand, increase the activity.  The addition of Be and Cr oxides to a Zn oxide catalyst increases the activity, the presence of W oxide affects it adversely, while U oxide is without effect.  The yields of MeOH obtained with each catalyst under the conditions specified above at temperatures corresponding to the optimum amounts are compared in the cases of Cu and ZnO catalysts.  With Cu at temperatures not exceeding 275°, the yield was 1,100-1,150 gm. and with Zn oxide at 375°, 300-325 gm.  The effect of the pressure (p in atmosphere) on the yield, R, for a Cu catalyst is represented approximately by R=p.050p² and for ZnO by R=0.014p².  When the rate of flow over a ZnO catalyst is increased 5,000-10,000, the yield rises by 55% and 10,000-20,000 by 35%.  Small amounts of S present as CS₂ or thiophen in an otherwise pure gas mixture poison the Cu but are without effect on the activity of the ZnO catalysts.  Beside the desired reaction, which produces MeOH, a number of side reactions occur which result in the formation of H₂O, CO₂, and CH₄.  From a study of the relative rates of the main and side reactions, it is shown that the useful conversion of CO is much greater with a Cu catalyst than is the case with 1 of ZnO.  In deciding the relative value of the 2 types of catalyst, the poor yields from ZnO have to be considered in conjunction with the robustness and indifference to small traces of poisons, while the extra yields from Cu catalysts have to be offset against the much greater sensitiveness to poisoning.