Indirect hydration process

The indirect hydration, also called the sulfuric acid process, practiced by the three U.S. domestic producers, was the only process used worldwide until ICI started up the first commercial direct hydration process in 1951. Both processes use propylene and water as raw materials. Early problems of high corrosion, high energy costs, and air pollution using the indirect process led to the development of the direct hydration process in Europe. However, a high purity propylene feedstock is required. In the indirect hydration process, C -feedstock streams from refinery off-gases containing only 40—60 wt % propylene are often used in the United States. 

Process. A typical indirect hydration process is presented in Eigure 1. In the process, propylene reacts with sulfuric acid (>60 wt%) in agitated reactors or absorbers at moderate (0.7—2.8 MPa (100—400 psig)) pressure. The isopropyl sulfate esters form and are maintained in the Hquid state at 20—80°C. Low propylene concentrations, ie, 50 wt %, can be tolerated, but concentrations of 65 wt % or higher are preferred to achieve high alcohol yields. Because the reaction is exothermic, internal cooling coils or external heat exchangers are used to control the temperature. 

Fig. 1. Indirect hydration process for the manufacture of isopropyl alcohol CBM = constant boiling mixture (61,62).

Butanol is produced commercially by the indirect hydration of / -butenes. However, current trends are towards the employment of inexpensive Raffinate 11 type feedstocks, ie, C-4 refinery streams containing predominandy / -butenes and saturated C-4s after removal of butadiene and isobutylene. In the traditional indirect hydration process, / -butenes are esterified with Hquid sulfuric acid and the intermediate butyl sulfate esters hydroly2ed. DEA Mineraloel (formerly Deutsche Texaco) currentiy operates a 2-butanol plant employing a direct hydration of / -butenes route (18) with their own proprietary catalyst. 

There are two main processes for the synthesis of ethyl alcohol from ethylene. The eadiest to be developed (in 1930 by Union Carbide Corp.) was the indirect hydration process, variously called the strong sulfuric acid—ethylene process, the ethyl sulfate process, the esterification—hydrolysis process, or the sulfation—hydrolysis process. This process is stiU in use in Russia. The other synthesis process, designed to eliminate the use of sulfuric acid and which, since the early 1970s, has completely supplanted the old sulfuric acid process in the United States, is the direct hydration process. This process, the catalytic vapor-phase hydration of ethylene, is now practiced by only three U.S. companies Union Carbide Corp. (UCC), Quantum Chemical Corp., and Eastman Chemical Co. (a Division of Eastman Kodak Co.). UCC imports cmde industrial ethanol, CIE, from SADAF (the joint venture of SABIC and Pecten [Shell]) in Saudi Arabia, and refines it to industrial grade. 

In the indirect hydration process, ethylene lirst is absorbed in concentrated H SOj to form mono- and diethyl sulfates CH CH + H2S04 si CH,CH OSO,H and... 

Since the indirect hydration process has gradually been superseded by direct hydration, the economic data listed in Table 9.1 conoern only the latter process. 

FIGURE 26.10 Indirect hydration process for ethanol mannfactnre. (Ethanol is prodnced from ethylene by using sulfuric acid in a three-step process. The process involves the formation of ethyl sulfate, which is hydrolyzed to ethanol.)... 

Indirect Hydration (Esterification—Hydrolysis) Process. The preparation of ethanol from ethylene by the use of sulfuric acid is a three-step process (Fig. 1) ... 

Indirect hydration, the traditional route, took advantage of readily available refinery grade propylene and cheap sulfuric acid in a quick two-step to isopropyl alcohol. Persistent catalysis research has now resulted in a direct route involving a small amount of an arcane catalyst, less energy intensity, high conversion rate, and an overall cheaper process. 

The specifications for the feed to the indirect hydration route to IPA plant can be loose. Refinery grade propylene, even with some small amounts of ethane and ethylene can be used, because the C2S and propane don t react. They just pass through the process. As a matter of fact, the process acts as kind of a C3 splitter, since about 50% of the propylene gets converted to IPA in each pass through the reactor, leaving high purity propane behind. 

IPA in concentrations of 91% or 99% is recovered in the same manner described in the indirect hydration route. Approximately 5% DIPE forms as a by-product in this process and comes out the bottom of the propylene recovery column. 

You may wonder why boch these processes produce isopropyl alcohol instead of (normal) propyl alcohoL With the exception of ethylene, direct or indirect hydration of an aliphatic olefin always produces an alcohol with the hydroxyl group preferentially attached to the double-bonded carbon with the least number of hydrogen atoms. 

Which alcohols are made commercially by direct hydration and which ones can only be made by indirect hydration or more complicated processes Which ones can go either way ... 

Synthesis gas is also the precursor to MTBE via methanol. The process requires isobutylene as well. Ethyl alcohol is made by direct, catalyzed hydration of ethylene. The route to isopropyl alcohol historically used to be solely indirect hydration of propylene, which occurs at much lower pressures and temperatures than the direct method, but advances in catalysis now make the direct route competitive. 

Direct hydration Indirect hydration Other process... 

Isopropanol is manufactured in the United States by the indirect hydration of propylene in processes which may involve the use of concentrated or dilute sulfuric acid, whereas, in European countries and Japan, a direct hydration process is used in which propylene reacts with water in the presence of a catalyst. It is used mainly for the production of acetone, but also as a solvent and in the manufacture of other chemicals and in pharmaceutical and cosmetic formulations (lARC, 1977). 

Diethyl sulfate is manufactured from ethylene and sulfuric acid. It is used principally as an intermediate (ethylating agent) in the manufacture of dyes, pigments and textile chemicals, and as a finishing agent in textile production. It is an intennediate in the indirect hydration (strong acid) process for the preparation of synthetic ethanol from ethylene. No data were available on levels of occupational exposure to diethyl sulfate (lARC, 1992a). 

Indirect hydration, the traditional process, is still used in many factories.47-50 Counterflows of sulfuric acid and alkene react at elevated temperature and under pressure to form sulfate esters. The more reactive propylene requires milder reaction conditions than ethylene (70-85% H2S04, 40-60°C, 20-30 atm, vs. 95-98% H2S04, 65-85°C, 10-35 atm). The rate of absorption of alkenes is increased by agitation of the liquid. In the second step sulfate esters are hydrolyzed to alcohol ... 

In modern industrial ethyl alcohol plants, the compound is produced in two principal ways (I) by direct hydration of ethylene, or (2) by indirect hydration of ethylene. In the direct hydratiun process. H 0 is added to ethylene in the vapor phase in Lhe presence of a catalyst CH CH 4- H 0 CHiCHiOH. A supported acid catalyst usually is Used. Important factors affecting the conversion include temperature, pressure, the H 0/CH CH ratio, and the purity of (he ethylene, Further, some byproducts are formed by other reactions taking place, a primary side reaction being the dehydration of ethyl alcohol into diethyl ether 2C HjOH (C Hs)jO + HiO. To overcome these problems, a large... 

In view of the many limitations inherent in the direct acid-catalyzed hydration of alkenes, indirect hydration via hydroxymercuration-demeicuration has become a very valuable method for the preparation of alcohols. This process has recently been thoroughly reviewed.311... 

Table 9.4 gives economic data concerning the production of isopropanol by the indirect and direct hydration processes. 

The value of 2-butanol t ii° = 0 08, >,bpuol3 99.5 C) resides in the fact that 90 per cent of its total production is used for the synthesis of MEK. (methylethyiketone) by dehydrogenation. It is manufactured by the indirect hydration of n-butenes. of which the 1- and 2-isomers yield the same 2-butanoL They are absorbed in 80 per cent weight sulfuric acid, between 15 and 20 C, and 0.7.10 Pa absolute. The salfuric esters obtained are then hydrolysed between 25 and 35°C at 0.1.10 Pa absolute, with 65 to 75 per cent weight sulfuric add (Exxon. Maruzen and Shell processes). Despite considerable research work (Deutsche Texaco. Mitsubishi. Mitsui, Petrotex and Shell), the direct catalytic hydration of H-butenes has not yet reached the industrial stage. 

When PVA was added to the water-cement sample, the polymer shifted the hydration process to higher times and it has lower hydration final degree and maximum adiabatic temperature, because the gel formed by the polymer hinders the hydration of cement with water, as it was stated before. As consequence, the apparent activation energy for the modified cement-water sample is higher than for pristine cement-water. The E values for PVA and PVA+clay are similar, and it is an indirect indication that the polymer has covered the clay. 

Ethanol is manufactured by three main processes indirect hydration, direct hydration, and fermentation. 

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