Direct Oxidation Of Ethylene Research Articles

Influence of Noble Metals on the Direct Oxidation of Ethylene to Acetic Acid over NM/WO3-ZrO2 (NM = Ru, Rh, and Pd) Catalysts

Abstract Ru-, Rh-, and Pd/WO3-ZrO2 catalysts were studied for the direct oxidation of ethylene to acetic acid. The catalytic activity and selectivity depended strongly on the noble metals used. Rh/WO3-ZrO2 gave the highest conversion of ethylene, whereas Ru/WO3-ZrO2 was almost inactive. The higher catalytic activity was attributed to a better metal dispersion. Pd/WO3-ZrO2 gave the highest selectivity for acetic acid (75%), with the selectivity of the other two catalysts being rather low (∼10%). Temperature-programmed oxidation and H2 reduction experiments were used to show that the strength of the noble metal–oxygen bond played an important role in product distribution. A weak metal–oxygen bond favored the formation of acetic acid, while a strong metal–oxygen bond favored the combustion of ethylene to COx.

Kinetic Studies on the Promotional Effect of Te in Pd–Te–H4SiW12O40/SiO2 for Direct Oxidation of Ethylene to Acetic Acid

The role of Te in Pd–Te–H4SiW12O40/SiO2, a highly active and selective catalyst for direct oxidation of ethylene to acetic acid, was investigated. Kinetic studies of ethylene oxidation over Pd–H4SiW12O40/SiO2 and Te-promoted Pd-H4SiW12O40/SiO2 demonstrated that doping with Te enhanced the rate of reaction of ethylene to acetaldehyde but reduced direct formation of CO2 from ethylene. In contrast, the successive reaction of acetaldehyde to acetic acid was not influenced to a significant extent by the addition of Te.

Effect of Support and Acidity of Catalyst on the Direct Oxidation of Ethylene to Acetic Acid

The selective oxidation of ethylene to acetic acid was investigated on Pd-acid/ support catalyst system. The catalytic activity is influenced strongly by the acidity of the catalyst. The stronger the catalyst acidity the higher the catalytic activity. The nature of the support also influences the activity of the catalyst substantially. The catalyst has highest activity when it exhibits highest acidity on silica.

A new process for acetic acid production by direct oxidation of ethylene

A new process for acetic acid production by direct oxidation of ethylene which was established and commercialized is described. The catalyst system consisting of Pd and heteropoly acid exhibits excellent activity and selectivity. The addition of Se or Te to the catalyst system is effective to suppress the formation of carbon dioxide. This new process is applicable to a plant of a wide range of size corresponding to the local demand. Because this new process produces little waste water, it is very friendly to the environment.

Epoxidation of ethylene over silver catalysts modified by sodium chloride

the selectivity of epoxide synthesis in the direct oxidation of ethylene is increased to 85–87% by addition of sodium chloride to the silver catalyst; this selectivity corresponds to the maximum expected by mechanistic studies.

Ethylene Oxidation—Exploratory Research

Abstract The steps involved in developing commercially successful catalysts and the ways in which the techniques and technologies utilized have changed over time are described, primarily from the standpoint of the author's experiences during 20 years at Halcon/Scientific Design. The discussion is limited to the direct oxidation of ethylene to ethylene oxide in the vapor phase over catalysts containing silver.

The mechanism of the action of alkaline earth compounds as additives to silver catalysts in the direct oxidation of ethylene

The mechanism of the action of SrO 2, CaO 2, SrCO 3, barium formate and barium oxalate used as additives to silver catalysts (2–20 mole %) in the oxidation of ethylene to ethylene oxide and CO 2 + H 2O has been studied. Two methods of preparation were employed, i.e., mixing of the components (AgO + additive) in alcohol (type I) and acetone (type II), respectively, and the characteristic differences are discussed. In a stream of ethylene/air the additives in presence of silver transform into their respective carbonates of increased surface area, the actual catalyst matrix consisting of the carbonates highly doped with Ag atoms and covering with a thin layer the network structure of metallic silver. The processes occurring during the conditioning period are favored if the components are vibrated in alcohol (type I) instead of acetone (type II). The resulting catalysts have largely increased activity but lower selectivity than have properly defined standard pure silver catalysts. The two principal mechanisms, i.e., a primary effect with additives stable to decomposition (SrCO 3), and a secondary effect with additives that transform into their carbonates in a stream of ethylene/air at 300 °C have been well established. The data of different catalyst series have been correlated by a normalization method discussed in the Appendix.

A Study of the Oxidation of Ethylene to Ethylene Oxide on a Silver Catalyst

A study has been made of the direct oxidation of ethylene to ethylene oxide in a flowing system under the catalytic action of silver. Various catalysts were prepared and one containing 10 per cent. barium carbonate, having a high and sustained activity, was selected for a detailed examination of the influence of reaction conditions on the yield of ethylene oxide. It has been found that the percentage ethylene in the reaction mixture can be varied widely without greatly changing the yield of ethylene oxide, but that the conversion is decreased by increasing the ethylene content. The yield increases with increasing oxygen content until the latter reaches 20 per cent. after which further enrichment with oxygen has little effect. The presence of water vapour slightly increases the yield, hut considerably decreases conversion. The yield is much decreased by diminishing the reaction pressure. Highest yields (73 per cent.) were obtained when small amounts of ethylene dichloride were added to the reactants but at the expense of low conversion. Propylene and isobutylene yielded only carbon dioxide and water when oxidized in the presence of a silver catalyst. The results are discussed in relation to the reaction mechanism suggested by Twigg(1).