Many catalysts used in petroleum processing are sensitive to small amounts of contaminants. One such material is carbon. To some types of synthetic catalysts, small amounts of carbon affect activity and/or selectivity appreciably; thus a rapid analytical procedure is needed to predict process controls. The search for a rapid procedure for determining total carbon on synthetic catalyst resulted in the development of a method which involves combustion followed by conductometric determination of the carbon dioxide formed.
Carbon on catalyst is generally determined by burning it in a resistance furnace and measuring the COs evolved by gravimetric or volumetric methods. These methods proved inadequate because carbon trapped in catalyst pores could not be burned without first grinding the sample. This was time-consuming and, in addition, grinding did not necessarily release all of the carbon.
High frequency induction heating has also been used to burn carbon and it offered the advantage of higher temperatures whereby the sample is melted and entrapped carbon is exposed to oxygen. PEPKOWlTZ 1 employed it in conjunction with a freeze-out technique for isolation of carbon dioxide, HOLLER et al. 2, absorbed the C02 in Ascarite, and SIMONS et al. 3, developed a high frequency combustion-volumetric method. All of these procedures were applied to metals and were not applicable directly to nonor low-conducting materials. In addition, the techniques used to measure the carbon dioxide involved were either time-consuming, too sensitive to operator error for control work, or not applicable in the range below o.1% carbon.
This paper describes a rapid and reasonably precise method for determining total carbon in non-conducting catalysts or other solids. The carbon dioxide evolved from the high frequency furnace is absorbed in dilute barium hydroxide. The change in conductivity of this solution is directly proportional to the amount of carbon dioxide absorbed, Apparatus A simple schematic diagram of the apparatus is shown in Fig. I and a photograph is shown in
Fig. 2. (i) High frequency induction furnace, equipped with "Vycor" glass combustion tube.
A Lindberg Model LI-5oi F was used for this work. Other suitable makes and models are available.
(2) Conductometric carbon determinator, Leco Model 515, was employed for the finishing step.