Hydratropaldehyde by Oxo Process from Styrene:
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(Rhodium: "Catalytic Hydratropic Aldehyde", Methods Discourse)Post 476616
(roger2003: "Hydratropaldehyde", Methods Discourse)and in "Ullmanns"
As shown , rhodium-based processes can be classified into three types. The most important of these on an industrial scale uses the so-called phosphine-modified catalyst system. The unmodified rhodium carbonyl complex is used for the reaction of special olefins.
Low-Pressure Oxo (LPO) Process. In the mid-1970s Union Carbide and Celanese succeeded in using rhodium – triphenylphosphine catalysts for the hydroformylation of olefins on an industrial scale. Since then some other companies have developed modifications of this process. The most important of these, however, is the low-pressure oxo (LPO) process jointly developed by Union Carbide, Davy McKee, and Johnson Matthey. A detailed description of this specific low-pressure route follows with the conversion of propene to butyraldehyde as an example.
Figure (5) shows a schematic of hydroformylation with the LPO gas-recycle process [8], [36].
The reaction takes place in a stirred-tank reactor made of stainless steel. The reactants and supplementary catalyst to make up for catalyst lost in production are fed in from below. Due to the sensitivity of the rhodium catalyst system toward catalyst poisons, the olefin and synthesis gas or hydrogen used as makeup gas must first be carefully purified . The reactor contains the catalyst dissolved in high-boiling reaction byproducts. In order to maintain catalyst activity a portion of the solution must be continuously removed and reprocessed separately , and the noble metal and the phosphine returned to the process. From time to time, all of the catalyst must be removed via line and reprocessed externally [12] , [16]. The hydroformylation reaction takes place at < 20 bar and 85 – 115 °C. The reactor jacket is cooled to remove the heat of reaction. The reaction products and unreacted gaseous reactants (conversion of about 30 % per pass) are forced out of the reactor by the recycled gas and pass through the demister and the condenser into the separator
Unreacted starting materials and part of the propane formed as byproduct are recycled to the reactor by means of the compressor. The level of propane in the circulating gas is adjusted by means of the outlet . The liquid reaction products are freed from residual olefin in a stripping column , and are worked up by multistage distillation. Residual olefin from the stripping column is recycled. To limit the buildup of inerts in the recycled gas stream and to reduce losses by venting, other treatment steps may be applied. These include extraction of propene with the aldehyde products, stripping the olefin from the aldehydes with synthesis gas and recycling both to the reactor [55], and washing the off-gas with stripped catalyst solution [56].
The LPO gas-recycle process has been partly replaced by a liquid-recycle variant, in which the catalyst solution and the aldehyde products leave the reactor as a liquid. The catalyst solution is separated from the aldehydes in several distillation steps and recycled. Combinations of gas and liquid recycle have also been described and are claimed to give increased propene conversion [53], [54].
Ruhrchemie – Rhône-Poulenc (RCH – RP) Process. Another industrial low-pressure process for olefin hydroformylation is based on a water-soluble rhodium catalyst [37][38][39][40][41][42][43]. As with the LPO process, the RCH – RP process has found its greatest importance in the hydroformylation of propene.
The use of a water-soluble catalyst system is associated with substantial advantages for industrial practice, because the catalyst can be considered to be heterogeneous. Since the catalyst is insoluble in the organic phase formed, separation of the aqueous catalyst phase and the butanal is greatly simplified by phase separation, and losses of the noble metal in the crude aldehyde stream are negligible. High-boiling byproducts do not dissolve in the aqueous catalyst phase, dispensing with the need for continuous catalyst regeneration. In the LPO process, however, these byproducts are retained in the catalyst phase and lead to catalyst problems, unless the catalyst system is continuously regenerated.
The process is explained by means of the simplified flow sheet . The reaction takes place in a stirred-tank reactor , which contains the catalyst solution; the reactants are introduced from below. Before entering the reactor, the synthesis gas is first passed through a stripping column in countercurrent to the crude aldehyde stream in order to recover the unreacted propene. Furthermore, purification of the reactants can be avoided by this procedure [42]. The crude aldehyde product leaves the top of the reactor and passes through the trap into the phase separator where it is separated from the entrained catalyst solution. The catalyst solution is returned to the reactor via the heat exchanger .
Because of the higher temperature compared to the LPO process , the heat of reaction can be used for steam generation in the heat exchanger . The crude aldehyde from the phase separator is distilled. Part of the water is retained in the crude aldehyde in homogeneous solution. This loss of water is compensated for via inlet . Part of the off-gas which escapes via the separator can be recirculated; part must be drawn off to maintain a constant propane level in the gas. Depending on the purity of the olefin used, the off-gas may contain considerable amounts of olefin. The RCH – RP process may then, for example, be combined with a cobalt high-pressure process to convert the residual olefin [44].
Rhodium High-Pressure Process. If unmodified rhodium carbonyl hydride is used as a hydroformylation catalyst, the reaction product consists of roughly equal amounts of branched and straight-chain aldehydes . For this reason this catalyst is only applicable if the n/i ratio is not important (i.e., both aldehydes are valuable products) or if the formation of a branched aldehyde is impossible (e.g., in the hydroformylation of ethylene to give propanal) [45]. Anhydrous propanal can be obtained by this process.
[8] Winnacker-Küchler 4th ed., 5, 537.
[36] F. Heinrich, M. Bernard, 27th DGMK-Haupttagung, Aachen Oct. 6 – 8, 1982, Compendium 82/83, p. 189.
[12] P. E. Garrou, Chem. Rev. 85 (1985) no. 3, 171.
[16] P. E. Garrou, R. A. Dubois, W. J. Chu, CHEMTECH 1985, no. 2, 123.
[55] Union Carbide Chemicals and Plastics Company,
Patent EP048976
, 1991 (K. D. Sorensen).
[56] Union Carbide Chemicals and Plastics Company,
Patent EP0404193
, 1991 (D. L. Bunning).
[53] Union Carbide,
Patent EP0188246
, 1986 (D. L. Bunning, M. A. Blessing).
[54] Davy Powergas,
Patent GB1387657
, 1973 (R. Fowler).
[37] Rhône-Poulence Industries,
Patent DE2627354
, 1976 (E. Kuntz).
[38] Rhône-Poulenc Chimie de Base,
Patent EP0104967
B 1, 1982 (J. L. Sabot).
[39] Rhône-Poulenc Recherches,
Patent EP0133410
A 1, 1984 (J. Jenck, D. Morel).
[40] Rhône-Poulenc Recherches,
Patent EP0158572
A 1, 1985 (C. Barre, M. Desbois, J. Nouvel).
[41] Rhône-Poulenc Industries, FR 8 005 488, 1980 (J. Jenck).
[42] Ruhrchemie AG,
Patent EP0103810
, 1983 (B. Cornils et al.).
[43] Ruhrchemie AG,
Patent EP0158246
A2, 1985 (B. Cornils et al.).
[44] Ruhrchemie AG,
Patent EP0111257
B 1, 1983 (B. Cornils et al.).
[45] Ullmann, 4th ed., 19, 443.