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Relevant reference

Hydrogenation/hydrodesulphurisation/hydrodenitrogenation hydrogenation of dimethyl maleate hydrogenation of Methyl acetylene and butyne (in C3 and C4 fractions from naphtha cracker)

hydrodenitrogenation of petroleum fraction as feed to hydrocracking

[99]

Acetalization/ketalization reaction of acetaldehyde, acetone with methanol, ethanol

(Photochemical) chlorination chlorination of toluene: selectivity for benzyl chloride

[100]

Separation of close boiling compounds m/p- cresol and 2,6 xylenol: preferential reaction with amine: reactive extractive distillation mixture of cyclohexene and cyclohexane: through hydration/esterification of cyclohexene

1,4 dichloro 2-butene to 1,2 dichloro 3-butene cyclohexanone oxime to epsilon-caprolactum epichlorohydrin from glycerol dichlorohydrin aniline production (V-l-1)

[103]

Cracking dicyclopentadiene to cyclopentadiene

Impurities removal carbonyl compounds removal from phenol removal of minute amount of ethyl acetate in aqueous solution of ethanol removal formaldehyde, acetaldehyde impurities from crude acetone by reaction with diamine

[106]

Etherification: MTBE, ETBE, and TAME

Gasoline reformulation using ethers such as MTBE, ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) as octane boosters and oxygenates has been driven by the Clean Air Act in USA in late seventies, which boosted MTBE production to a new level in the early 1980s; TAME and ETBE also emerged as promising fuel additives. In addition to its antiknock property, enhancing the octane number of the fuel, MTBE improves the water tolerance limit of the fuel and has a higher calorific value than other additives such as methanol. The RD process can exceed the equilibrium limitation and offer more than 99% conversion. The process is shown in Fig. 1.2. Another important aspect of carrying out the etherification to near complete conversion, is its efficient use in separating the iso-olefins from the refinery stream containing both normal and secondary butenes (C4 or C5), which otherwise are very difficult to isolate. The RD column can handle the mixed olefins quite effectively and exploits the presence of inert butenes to improve its own performance. This separation is necessary because n-butenes are required in the pure form for producing pure butene-1, as a co-monomer for polymerization of ethylene, feed for acrylates, and for the oxidative production of butadiene.

The decision to ban MTBE in California from 2003 will force refiners to look for a new fuel additive and will probably have adverse implications for the existing and proposed production units for MTBE and other fuel ethers. Nevertheless, MTBE has been mainly responsible for the initiation of research and development in RD and its high status today. In the last two decades, especially in the 80s, the patents and published literature on RD have been mainly focussed on its application for MTBE and other ethers.

The conventional processes for the manufacture of MTBE uses a catalytic reactor with a slight excess of methanol (methanol/isobutylene = 1.05 to 2). The products correspond to the near-equilibrium conversion of 90-95 %. The reaction mixture is separated using distillation, but this is complicated by the formation of the binary azeotropes methanol-MTBE and isobutylene-methanol. The unreacted isobuty-lene is difficult to separate from other volatile C4 products. In the RD process,

Process Ethermax

Fig. 1.2 Process for MTBE production: an adiabatic reactor and an RD

on the other hand, almost complete conversion of isobutylene is obtained, thereby eliminating the separation and recycling problems. The RD column consists of three sections, of which the middle section is the reactive zone packed with a solid catalyst. The top non-reactive rectifying section performs the separation of inert gases and excess methanol, and the bottom section separates out MTBE in almost pure form. The boiling point of MTBE is 328 K and that of methanol is 337.5 K. Surprisingly, MTBE is the bottom product while unreacted high-boiling methanol is collected through distillate. This behavior is caused by the formation of the isobutylene-methanol low-boiling azeotrope, which lifts methanol from the stripping section of the column.

The pioneering work to commercialize this technology was performed by Smith from the Chemical Research and Licensing Company (CR&L), who has been awarded several patents for different catalyst structures, internal column design, and flow schemes [1]. Some patents have been assigned to the researchers from Elf who describe using alternating catalytic and non-catalytic zones to carry out the etherification. The efforts in these studies were directed towards minimizing the pressure drop in the catalyst bed and providing maximum residence time for the liquid in the catalytic zone. This was achieved by providing separate free passage to the upflowing vapor stream either by packing the catalyst in the down-coming stream or by providing annular space in the catalyst bed, thereby isolating reaction and distillation zones in a single column. UOP, Koch Engineering, and Hills AG have jointly developed the Ethermax process for producing ethers by RD. The process uses Koch Engineering's Katamax packing where a solid acid catalyst is confined in screen envelopes.

The existence of multiple steady states has attracted the attention of several researchers [2]. Simulation studies indicated that the same column configuration operating under similar conditions can give rise to different steady-state conversions. Bravo and co-workers reported the only experimental evidence of multiple steady states in the synthesis of TAME in the pilot plant of Neste Oy [3]. The MTBE system also shows oscillatory behavior, as reported by Sundmacher and Hoffmann [2].

The use of RD in the manufacture of other ethers such as ETBE, TAME, and so on, has been demonstrated to be beneficial and several patents and investigations have emerged [3, 4]. UOP describes a process for the manufacture of DIPE (di-iso-propyl ether), which uses propylene and water feedstock. It is a two-stage RD process associated with simultaneous hydration and etherification [5]. The ethers, being the heaviest components, are collected in the bottom stream.

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