Characterization of hydrotreating catalysts by reversed-flow gas chromatography

A flow perturbation gas chromatographic method, called reversed-flow technique, was introduced in 1980 and has been used to study the kinetics of various surface-catalyzed reactions, as well as for other physicochemical measurements. A review on the method has already been published. The new technique is based on reversing the direction of flow of the carrier gas from time to time. It uses a conventional gas chromatograph with any kind of detector, accommodating in its oven a so-called sampling cell. This consists of a sampling column and a diffusion column and is connected to the carrier gas inlet and the detector via a four-port or six-port valve. By switching the valve from one position to the other, the carrier gas is made to flow through the sampling column either from D{sub 2} to D{sub 1} or in the reversed direction. The sampling column can be filled with a catalyst whereby it plays the role of a catalytic reactor, or it filled with a usual chromatographic material acting as a conventional separation column, or it can contain both kinds of solids. Moreover, this column can be completely empty of any solid material, when it simply acts as a sampling volume to producemore » chromatographic signals without any separation process. The diffusion column, which was not used in the early papers, is employed either as a device for feeding catalytic or chromatographic beds with a gas diffusion stream, or as a means to study slow rate processes, normally occurring within a gas chromatographic column and usually being described as broadening factors.« less