Process synthesis ethanol dehydration

The most important contribution in the field of simultaneous dehydrogenation, condensation, and dehydration made by Russian chemists is the synthesis of butadiene from ethanol over a double oxide catalyst by the method of Lebedev. Much has been published on this process. Lebedev s interest in rubber synthesis began with his researches on conversions of dienes in 1908 and his method of synthesis of butadiene was reported in 1927. An experimental synthetic rubber plant was founded for research in the field and the studies on the mechanism of formation of butadiene and of polymerization were continued after Lebedev s death by his students (103,104,105,188,190,378). A survey of the properties and methods of preparation of butadiene was published by Petrov (289). 

New processes currently being developed could rehabilitate the dehydration of ethanol by making use of non-petroleum raw materials. These include the direct production of ethanol from synthesis gas or its indirect manufacture from the same gas, passing through methanol. The former process was developed by Union Carbide on a rhodium catalyst ... 

An important principle of synthesis is to avoid mixtures of isomers wherever possible minimizing separations increases recovery of products. Bimolecular dehydration is a random process. Heating a mixture of ethanol and methanol with acid will produce all possible combinations dimethyl ether, ethyl methyl ether, and diethyl ether. This mixture would be troublesome to separate. 

In the presence of catalysts such as are used for the synthesis of methanol from mixtures of hydrogen and carbon monoxide and which have been promoted by the addition of an alkali oxide, ethanol may be dehydrated to form butanol in a high pressure process. Catalyst mixtures composed of chromium and zinc oxides to which either barium hydroxide or potassium oxide has been added have been specified.6 ... 

By a similar mechanism to that proposed for the formation of ethyl ether by dehydration of ethanol, it is possible that the reaction occurs stepwise with the intermediate dehydration of one ethanol molecule to form ethylene which then reacts with another ethanol molecule to form butanol. It is thus possible that higher alcohols may be built up by the reaction of olefins with the lower alcohols. Mixed oxide type of catalysts are used in the process of a nature similar to those which have been found effective in alcohol synthesis from hydrogen and carbon monoxide. It should lie noted here that catalysts which promote the union of carbon atoms must be used, and since potassium oxide promoted catalysts composed of mixtures of zinc, copper, or chromium oxides have been found to be effective in the syuthesis of higher alcohols, such catalysts should be useful in promoting the addition of olefins to alcohols or other oxygenated organic molecules.77... 

According to a recent conference given by Prof. Kita [162], the classical synthesis method currently used by Mitsui allows to produce about 250 zeolite membranes per day. Both the LTA and T types (Na K) membranes are now commercial and more than 80 pervaporation and vapor permeation plants are operating in Japan for the dehydration of organic liquids [163]. A typical pervaporation system, similar to the one described in [8], is shown in Fig. 11. One of the most recent applications concerns the production of fuel ethanol from cellulosic biomass by a vapour permeation/ pervaporation combined process. The required heat is only 1 200 kcal per liter of product, i.e. half of that of the classical process. Mitsui has recently installed a bio-ethanol pilot plant based on tubular LTA membranes in Brazil (3 000 liters/day) and a plant with 30 000 liters/day has been erected in India. The operating temperature is 130 °C, the feed is 93 % ethanol, the permeate is water and the membrane selectivity is 10 000. 

Metal oxides are widely used as catalyst supports but can also be catalytically active and useful in their own right. Alumina, for example, is used to manufacture ethene from ethanol by dehydration. Very many mixed metal oxide catalysts are now used in commercial processes. The best understood and most interesting of these are zeolites that offer the particular advantage of shape selectivity resulting from their narrow microporous pore structure. Zeolites are now used in a number of large-scale catalytic processes. Their use in fine chemical synthesis is discussed in Chapter 2. 

Sodium benzenesulfinate resin 43 can also be used to prepare a traceless solid-phase synthesis for 3,4-dihydropyrimidine-2-ones 54 and 55 (Scheme 12.13). This strategy highlighted the sulfinate acidification to yield resin-bound benzenesulfinic acid 52, followed by the condensation of urea or thiourea with aldehydes and sulfinic acid. A one-pot cyclization-dehydration process with 1,3-dicarbonyl compounds or )8-ketoesters (generated in situ by treating the latter reagents with KOH/EtOH) afforded 54, while cyclization with a mixture of pyrrolidine and /8-ketoacid in ethanol followed by the addition of TsOH HaO gave the ester form of 55. When THF was used as a solvent, the free carboxylic acid form of 55 was obtained in comparable yields. 

Williamson s synthesis 1. A method of preparing simple ethers by dehydration of alcohols with concentrated sulfuric acid. The reaction is carried out at 140 C under reflux with an excess of the alcohol 2ROH ROR + H2O The concentrated sulfuric acid both catalyzes the reaction and displaces the equilibrium to the right. Also the ether may be distilled off during the reaction (in which case it is called Wilkinson s continuous process). The product, ether, is termed simple , because the R groups are identical. There are two possible mechanisms for the process, depending on the nature of the alcohol. In the case of primary alcohols, there is a hydrogensulfate formed. For example, with ethanol ... 

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