Parameters ethylene oxide production

The kinetic parameters for the oxidation of a series of alcohols by ALD are shown in Table 4.1 (74). Methanol and ethylene glycol are toxic because of their oxidation products (formaldehyde and formic acid for methanol and a series of intermediates leading to oxalic acid for ethylene glycol), and the fact that their affinity for ALD is lower than that for ethanol can be used for the treatment of ingestion of these agents. Treatment of such patients with ethanol inhibits the oxidation of methanol and ethylene glycol (competitive inhibition) and shifts more of the clearance to renal clearance thus decreasing toxicity. ALD is also inhibited by 4-methylpyrazole. 

Arrhenius parameters (as far as available) for the ring-opening reactions of ethylene oxide, propylene oxide, and isobutylene oxide. Overall values of ftCi and fcHcl obtained for propylene oxide have been split into rate coefficients for attack at primary carbon and attack at secondary carbon, utilizing gas chromatographic product analysis data [152]. (It is interesting to note that the results for attack at primary carbon are of the same order of magnitude as the corresponding values for ethylene oxide.) First-order rate coefficients at a constant acid concentration for the acid catalyzed hydrolysis of various epoxides [153] are collected in Table 10. Rate coefficients of the uncatalyzed and acid catalyzed reactions of ethylene oxide with various nucleophiles [151, 154] can be found in Table 11. 

A complex system is one in which more than one reaction occurs. This can lead to ijiultiple products, some of which are more desirable than others from a practical standpoint. For example, in the air oxidation of ethylene the desired product is ethylene oxide, but complete oxidation to carbon -dioxide and—water—alse-0eeu-FS--The-im-perta-nt-per-for-ma-nee-factor-is-i he production rate of ethylene oxide and its purity in the reaction products, rather than the total amount of ethylene reacted. To characterize this performance two parameters are used yield and selectivity. The yield of a specific product is defined as the fraction of reactant converted to that product. The point selectivity is the ratio of the rate of production of one product to the rate for another product. With multiple products there is a separate selectivity based on each pair of products. The overall, or integrated, selectivity is the ratio of the amount of one product produced to the amount of another. Selectivity and yield are related to each other through the total conversion, i.e., the total fraction of reactant converted to all products. 

Both the time-on-stream and the reactant ratio are important chemical engineering parameters affecting the characteristics of the process. It was found that the increase in the time-on-stream at T = 673K can improve both the conversion of ethane and the yield of ethylene. The total yield of chloroorganic products therewith decreases, but the concentration of vinyl chloride passes through a maximum. We also observed an increase in the yield of deep oxidation products COx (see Table 2). 

Fig. 9. Influence of chlorine coverage on the kinetic parameters for selective ethylene oxidation over a Ag(llO) surface. Parameters for both the production of ethylene epoxide (EtO, circles) and the undesired side reaction to full combustion (C02, squares) are presented. Steady-state reaction orders in P02 and Pei and activation energies a versus chlorine coverage near 563 K, Pb = 20 torr, and P02 = 150 torr. From Ref. 118.

While for traditional processes the atom utilization is 25 %, in catalytic procedures it amounts to 100 %. According to this parameter, the former process resembles more to production of calcium chloride with ethylene oxide as the side product In other words, this process affords 3 kg of calcium chloride per 1 kg of ethylene oxide by 100 % yield. 

In a subsequent simulation study, two important industrial selective oxidation processes were addressed in detail, namely the partial oxidation of methanol to formaldehyde and the epoxidation of ethylene to ethylene oxide. In both cases secondary undesired reactions play a significant role, i.e. the combustion of the primary product in the formaldehyde process and the combustion of the ethylene reactant in the ethylene oxide process, so that the study also provided information on how the adoption of high conductivity monolith catalysts would alfect the selectivity of industrial partial oxidation processes for both a consecutive and a parallel reaction scheme. For both processes intrinsic kinetics applicable to industrial catalysts as well as design and operational parameters for commercial reactors were derived from simulation studies and experimental investigations collected in the literature. 

Treatment of Decalin with acetyl chloride and aluminum chloride in ethylene chloride as solvent gives a complex mixture of products as shown (15). By variation of the reaction parameters, however, it is possible to maximize the yield of the remarkable reaction product, 10 j3-vinyl-/m j-Decalin l/8,r oxide (5). This vinyl ether undoubtedly... 

The first mode of the high resolution C-NMR of adsorbed molecules was recently reviewed Q-3) and the NMR parameters were thoroughly discussed. In this work we emphasize the study of the state of adsorbed molecules, their mobility on the surface, the identification of the surface active sites in presence of adsorbed molecules and finally the study of catalytic transformations. As an illustration we report the study of 1- and 2-butene molecules adsorbed on zeolites and on mixed tin-antimony oxides (4>3). Another application of this technique consists in the in-situ identification of products when a complex reaction such as the conversion of methanol, of ethanol (6 7) or of ethylene (8) is run on a highly acidic and shape-selective zeolite. When the conversion of methanol-ethylene mixtures (9) is considered, isotopic labeling proves to be a powerful technique to discriminate between the possible reaction pathways of ethylene. 

Other steps used in the model assume that the heterogeneous conversion of methane is limited to the gas-phase availability of oxygen, O2 adsorption is fast relative to the rate of methane conversion, and heat and mass transports are fast relative to the reaction rates. Calculations for the above model were conducted for a batch reactor using some kinetic parameters available for the oxidative coupling of methane over sodium-promoted CaO. The results of the computer simulation performed for methane dimerization at 800 °C can be found in Figure 7. It is seen that the major products of the reaction are ethane, ethylene, and CO. The formation of methanol and formaldehyde decreases as the contact time increases. 

In fact, one important parameter is the water content of the medium, which causes the undesirable production of acetaldehyde by its reaction with ethylene in the presence of palladium chloride, or by the hydrolysis of the vinyl acetate formed. This operating variable can be adjusted to make the acetate production plant self-sufficient in terms of acetic acid. In this case, die acetaldehyde co-produced is oxidized to the arid in a separate section. It is the water content of the acetic arid employed, controlled by the degree of purification of the by-product arid which is recycled, which ultimately serves to determine the vinyl acetate to acetaldehyde ratio. Longer reridence time in the reactor or higher temperature also favors the formation of acetaldehyde. 

Transformation can take place in the presence of either air or oxygen. In both cases, it is important to avoid direct oxidation of the hydrocarbon, and this is achieved by introducing excess hydrochloric acid or ethylene. In fact, the latter appears to be prefer able, because it generates smaller amounts of by-products owing to the increase in temperature, a parameter to which the reactions involving HQ are more sensitive. 

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