I
J. F. SHULTZ, F, J. SCHOENEWEIS, and Central Experiment Station,
U. S.
R. B. ANDERSON
Bureau of Mines, Bruceton, Pa.
Compressed Carbon Monoxide In this simple system, CO is separated from Hn and liquid CO evaporated directly into cylinders C O M M E R C I A L L Y available compressed carbon monoxide contains sufficient impurities, including sulfur compounds, to render its use in many catalytic reactions undesirable. Thompson (2) described an apparatus for preparing very pure carbon monoxide by the decomposition of formic acid in hot phosphoric acid. This method is laborious and requires relatively complicated apparatus for generating, storing, and compressing the carbon monoxide. At this laboratory, mixtures of hydrogen and carbon monoxide of high purity (7) are prepared by reforming natural gas and then compressing it into conventional gas cylinders for use in catalyst studies. A simple system was developed for separating carbon monoxide from hydrogen at liquid-nitrogen temperatures and evaporating liquid carbon monoxide directly into a gas cylinder. As this method obviates the necessity for a gasholder and a compressor, the cost of the apparatus and installation was less than $500. About 100 cubic feet of pure carbon monoxide at 1000 pounds per square inch gage can be prepared from 1Ha 3CO gas by one man in about 6 hours. The preparation requires 25 to 30 liters of liquid nitrogen. A flow diagram of the apparatus is given in Figure 1. A 2-liter condensation vessel was made from Schedule 80 stainless steel, Type 304, by welding caps of the same material to a short section of tubing. This steel has high impact strength at low temperatures and is less likely to form carbonyls than carbon steels. A 1-liter purification vessel was fabricated from Schedule 80 carbon steel with provision for replacing adsorbents. All components of the system were designed to withstand 3000 pounds per square inch at room temperature. The purification vessel was filled with about equal parts of activated carbon, Ascarite, and silica gel. The principal function of the adsorbents is removal of traces of water and carbon dioxide i o prevent plugging of the inlet or outlet tubes of the condensation vessel; their secondary function is removal of traces of impurities such as sulfur compounds, if present. Before the apparatus is used, the system is purged with synthesis gas by alternately increasing and lowering the pressure. The carbon monoxide cylinder
+
1
3-woy valve
A
Plywood
Figure 1.
Flow diagram of carbon monoxide separation from synthesis gas
either contains carbon monoxide or has been evacuated. The three-way needle valve, A-D, is closed. Needle valve B is open to the synthesis gas cylinder, while pressure is being built up in the system. Valve B is closed, and liquid nitrogen is slowly poured into the Dewar flask. When the flask is filled, valve B is carefully opened to introduce additional synthesis gas slowly, so that the liquid nitrogen does not boil too rapidly. When the hydrogen pressure decreases the rate of condensation of carbon monoxide, residual hydrogen is slowly purged through valve A . The volume of gas thus removed is determined by a wettest meter, and indicates when the condensation vessel is filled with liquid carbon monoxide. At that time, valve C is closed, and the pressure in the condensation bomb is decreased to atmospheric by opening valve A. The liquid nitrogen bath is then lowered from the condensation vessel and enough liquid carbon monoxide is evaporated to purge residual hydrogen from the condensation vessel through valve A . A is closed and the pressure in the condensation vessel is allowed to increase above the pressure in the cylinder containing carbon monoxide. Valve D and the valve at the cylinder containing carbon monoxide are opened, and carbon monoxide is evaporated into storage cylinders. When the pressure in this part of the system becomes con-
stant, D is closed and the condensation and evaporation procedures are repeated until the desired pressure is attained in the cylinder containing carbon monoxide. Mass spectrometric analysis of product gas showed 99.8y0 carbon monoxide, 0.15% hydrogen, and 0.05% methane. The efficiency of the process is about 80% based on synthesis gas and 1870 based on liquid nitrogen. In the evaporation cycle, failure to open valve D or a plug in the tubing from the condensation vessel would result in excessive pressures in the condensation vessel. Fox this reason, the apparatus is installed in an area assigned to high-pressure experimentation during the evaporation cycle, and the operation is regulated from behind a protective barricade. Acknowledgment
The authors wish to thank A. M. Whitehouse and R. W. Hiteshue for their assistance in the design and construction of this apparatus, Literature Cited (1) Clark, E. L., Kallenberger, R. H., Browne, R. Y., Phillips, J. R., Chem. Eng. Progr. 45, 651 (1949). (2) Thompson, J. G., IND.END.CHEM.21,
389-(1929),
RECEIVEDfor review October 19, 1955 ACCEPTED March 23,1956 VOL. 48,
NO. 8
AUGUST 1956
1365
