NOTES
Rapid Indirect Method for Determination of Hydrogen and Carbon in Hydrocarbons Willem Entermad and Herman C. E. van Leuven KoninklijkeJSheIl-Laboratorium (Shell Research N.V.) Amsterdam
RAPID AND ACCURATE determination of hydrogen and carbon is, particularly in the petrochemical field, of major importance. This note describes a technique, first published in 1959 (I), which, in essence, measures the amounts of oxygen consumed in the formation of water and carbon dioxide on combustion of a hydrocarbon sample. In contrast to most other methods, the technique is inherently insensitive toward water present in the sample and this feature makes it particularly suitable for the analysis of coke on moist catalysts. Using a modernized version of the apparatus, we were able to speed up the procedure appreciably. Since carbon and hydrogen are measured in an identical way, the method is also suitable for the precise and rapid determinations of the carbon-to-hydrogen ratios of liquid and gaseous hydrocarbons. EXPERIMENTAL
The apparatus (Figure 1) consists of a quartz combustion tube, a rotating-type gas circulation pump, absorption traps for water and carbon dioxide, and an electric pressure transducer with digital read-out. In order to promote complete oxidation of the sample, the combustion tube is partly filled with platinum gauze and kept at a temperature of 950 "C. Solid materials (e.g., catalysts) are introduced by means of a ladle-and-magnet system. Liquid or gaseous samples are injected from a hypodermic syringe through a rubber septum into a vertical combustion tube. The two absorption traps are filled with magnesium perchlorate and soda asbestos, respectively. The capacity of each trap is approximately 80 ml and the charges will last for 50-100 determinations. The carbon dioxide trap can temporarily be by-passed via pressure-actuated membrane valves. Pressures can be measured to an accuracy of approximately 0.1 Torr. The procedure takes about 5 minutes: at the start of a determination, oxygen is admitted to the system and purified by pumping it through both absorption traps, after which the pressure ( A ) is read. With the oxygen circulating again and the carbon' dioxide trap bypassed the sample is introduced. Circulation is maintained for a few minutes and the second pressure ( B ) noted. Then the gases are also pumped through the carbon dioxide trap after which the final pressure (C) is read. The two pressure drops are proportional to the amounts of organic hydrogen and carbon in the sample. The pressures are measured with the pump switched off. To ensure that all pressures refer to the same volume, the carbon dioxide trap is opened just before the second reading is taken. In the case of catalyst samples, where absolute percentages are required, the system has to be calibrated. This is done by burning known quantities of a standard compound, e.g., Present address, Centraal Laboratorium TNO, Delft, The Netherlands. ( 1 ) R. T. Longman, T. A. Hiett, et al., 24th Mid-year Meeting, the American Petroleum Institicte, Dlv. Refining, New York, N.Y., May 1959, Preprint: 17 pp.
PRESSURE TRANSDUCER
COMBUSTION ITUBE
m
/ P L ~ T I N U M GAUZ SILVER G A U Z E A T A P P R O X . 500% Figure 1. Set-up of apparatus for analysis of coke deposits on catalysts
Table I. Analyses of 100-Milligram Catalyst Samples %C from Sample H found C found titration 1.38-1.39 1.43 Catalyst I
