4. Preparation of Cobalt Catalyst.
The cobalt Catalyst used today differs only slightly from the one used in 1938 prior to the exchange of information between U.S. and German engineers.
Composition: Cobalt (Co) -------------------100 pts.
Magnesia (MgO) ------------- 10 pts.
Thoria (ThO2) -------------------5 pts.
Kieselguhr --------------------200 pts.
The same catalyst would also be used in the Kreislauf operation except for a higher Kieselguhr content (dilution).
The preparation of this catalyst up to the forming and drying of the filter cake was identical as in 1938. A new drier had been developed which would at the same time form the catalyst and give a minimum of abrasion loss in handling. The drier consisted of a drum of 2 m. long and 1.5 m. dia. The outside was studded with small toothed rails, which would serve as molds. The filter cake was pressed on to the drum and the identation of the mold filled to give small (3 mm.) cylinders. The drum rotated slowly (0.1 RPM). At the same time hot gases were passed through the cake filled molds drying the catalyst particles before they would reach the bottom position of the drum, where having contracted slightly during drying, they drop out by gravity. Air or superheated steam could be used for drying purposes.
This method of handling the catalyst made it possible to use a Kieselguhr which had been processed at 700°C. and was softer than the material treated at 1000° C. The softer Kieselguhr gave a more active catalyst (apparent density 130-150 gm/100 cc.)
The reduction of the catalyst is carried out with dry CO2 free gas (H2-N2 mixture or H2 alone). CH4 is not a detrimental component of the reducing gas. H2O, CO2, CO, NO2, are all undesirable. The presence of CO2 is detrimental due to the shift-reaction, which is catalyzed, forming small quantities of CO. This CO is further reduced to CH4 causing local over heating on the new and highly active catalyst.
The effect of CO2 in the reducing gas is quite pronounced: with 1 gm/m3 gas, the reduction is 50%. With no CO2 in the gas, reduction is 60-65%.
While reducing the catalyst, the necessary heat is supplied with the reducing gas. A temperature of 400° C is reached with ¾ hours and maintained for a very short time to complete the reduction. The CoO; CO; H2O; H2 equilibrium at 400° C governs the extent to which the oxide is reduced. Co. 60%-CoO 40% is the correct ratio in a good catalyst. The extent of reduction is determined by measuring the cm3 H2 evolved from a known weight of catalyst, upon addition of H2SO4.
For the production of olefins both RCH and Lurgi proposed to thin out the catalyst with more Kieselguhr, the catalyst otherwise being identical. About 250-300 pts. Kieselguhr would be used instead of 200 pts. for every 100 pts. of cobalt.