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Normally there is no advantage to employing more than 30 weight percent metal oxide based on the catalyst. by bringing it into contact at said temperature with an oxide of one of the metals of Group VB and Group VIB of the Pen'odic Table having a valence V of 4 V 7, the oxide being supported on an activated alumina carrier, the metal being in said valence state in the oxide to confer Lewis acid properties on the combination, said carrier containing 3 to 30 weight percent of said oxide based on the total. The process of claim 1 wherein the cyclic trimerization temperature is 25 C. A postulated mechanism for the functioning of these catalysts is that the presence of cations of 5 or greater valence on large surface area give maximum exposure of strong Lewis acid sites for attachments of acetylene molecules. to C., wherein the alumina support has a surface area of 30 to 400 square meters per gram and wherein the Group VB-Group VI-B metal oxide is present in amount of 5 to 25 weight percent based on the total. The process of claim 1 wherein the alumina has a surface area of 100 to 350 square meters per gram, wherein the Group VB-Group VI-B metal oxide is employed in an amount of 5 to 25 weight percent based on the total, and wherein said oxide is present in combination with 1 to 5 weight percent based on the total of C00. In radiocarbon dating by low-level liquid scintillation counting using benzene as the scintillator, wherein organic matter to be dated is burned to form carbon dioxide which contains carbon 14, the carbon dioxide being converted into acetylene, which then is converted into benzene by cyclic trimerization, the step of producing the benzene by the process of claim 1. The process of claim 3 wherein the C00 is present in an amount of 3.2 weight percent and the oxide conferring Lewis acid properties is present in an amount of 10 weight percent. The process of claim 3 wherein the oxide conferring Lewis acid properties is V 0 '7. United States Patent 3,365,510 LOW TEMPERATURE CONVERSEON 0F ACETYLENE TO PURE BENZENE John E. In dating organic matter by its carbon 14 content, the successfully in 1954. This pretreatment was limited to the elimination of associated water so that no water would be present in the formed benzene, the catalyst being heated for two hours under vacuum at 200 C. One such variable is the dehydration period and another variable is the flow rate. DEHYDRATION OF Mo-Co CATALYST Conditions: Catalyst: XIIMo-Co cat. The water content was attributed to atmospheric moisture and incomplete catalyst dehydration and was eliminated by collecting the benzene in an inert atmosphere and dehydration for four hours. This discovery of carbon 14 in nature led to its development as an archaeological and geological calendar. PROCEDURE In order to prepare the benzene using the foregoing catalysts, the catalysts were first dehydrated. Results obtained by the use of these promoters in accordance with the procedures set forth were as follows: Based on the results obtained as shown in Table II, cobalt molybdate catalysts were selected for use in studying other variables in this benzene synthesis process. Analysis of a number of benzene samples showed the benzene purity to vary from 98-100% with acetone being the primary contamination and trace amounts of water and ethyl benzene also present.The rate of acetylene gas introduction over the preheated catalyst is related to both the temperature and the benzene synthesis yield. Normally the catalyst involved is heated at an elevated temperature (300 C. Recent studies have shown that the catalyst will react if not dehydrated, but the dehydration step increases benzene synthesis and enables pure benzene to be extracted devoid of any water. Investigation of the reaction shows that the catalyst reaction temperature and the acetylene flow rate are directly related, whereas the benzene yield and the acetylene flow rate are inversely related. The catalyst is then cooled and stored under nitrogen gas until ready for use. Purity is therefore of primary importance, and of secondary importance is the greater chance in known methods for carbon isotope fractionation. The percent C abundance calculations using the mass ratio data is reliable for three significant figures.According to the practice of the invention a process is provided for synthesizing pure benzene from acetylene by passing the acetylene over the surface of an alumina based promoter at a temperature below 150 C., and as low as room temperature (25 C.) The promoter, in part is activated alumina, that is, aluminum oxide which has been calcined, or otherwise heated with steam or air, etc., to raise its surface area above 29 say, 30 to 400 square meters per gram or higher, preferably to 350. Thus according to this invention a low temperature method is provided for the quantitative synthesis of a pure benzene which has no energy quenching products present and which does not require purifying distillation procedures.
Impure benzene cannot be tolerated for liquid scintillation counting and radiocarbon dating. The calculated percent C abundances for acetylene and benzene to be 1.07 percent.
With recent improvements in liquid scintillation spectrometry, such as summation counting, and the development of wide response quartz-faced phototubes (3000 A.- 4500 A.), counting efiiciencies approaching 90 percent haveb'een realized with benzene samples. The catalytic acetylene reaction was exothermic and was accompanied by a darkening of the catalyst material. Infra-red analyses were made with a Beckman IR-l O model using a Ca F cell with a 200 length light path.