Reaction and Catalyst Extraction

The most important point is the complete separation of the catalyst and the products. The Union Carbide process proposal for the hydroformylation of higher olefins solves this problem [36, 37]. The catalyst leaching is lower than 20 ppb of 

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Figure 5.6. Process flowsheets of biphasic reaction A+B - C+D and extraction l, Simultaneous reaction and extraction within the reactor 2, Separate reaction and catalyst extraction...

Fig. IS Successive reaction and catalyst extraction (after solvent distillation).

The simultaneous reaction and catalyst extraction shown in Figure 6 (a) is not favorable, due to the fact that the catalyst leaves the reaction medium during the reaction. The successive reaction and catalyst extraction shown in Figure 6 (b), where reaction and extraction are carried out in two different units, is however much... 

Figures Simultaneous (a) and successive (b) reaction and catalyst extraction.

C. Usually the polymerisation is carried out in the presence of Ziegler-Natta catalysts based on titanium tetrachloride and aluminium alkyl. The catalyst may be either prepared or formed in the reactor. Usually, the polymerisation is carried out in presence of a hydrocarbon solvent. The polymer is insoluble in the solvent. The reaction is terminated by addition of an alcohol and catalyst extracted with alcoholic hydrochloric acid. Catalyst removal is important for electrical insolution used. The Polymer chain obtained by this process is essentially linear. 

The phase transfer catalysis not only promotes the reactions between the reagents which are mutually insoluble in immiscible phases, but also offers a number of process advantages such as, increase in rate of reactions, increase in product specificity, lowering of energy requirement, use of inexpensive solvents and catalysts, extraction of cations or even neutral molecules from one phase to another etc. 

A fluorous surfactant covalently tethered to silica provides a thin film of perfluorinated solvent for reactions and/or extractions. This material was used for the small-scale hydrocyclization of 6-bromo-1-hexene with NaBH and a catalytic amount of a fluorous tin bromide in 1-butanol. The yield of methylcyclopentane was modest, however, and this technology is a long way from being viable on an industrial scale. The same idea has been more successfully employed with fluorous silica-supported tin Lewis acid catalysts for Baeyer-Villiger oxidations. ... 

Figure 4 shows simultaneous reaction and product extraction, also called in situ extraction. The reaction of A and B runs in the reactor which contains the polar (e.g., aqueous) catalyst phase. The nonpolar extractant absorbs the organic products which are separated from the polar catalyst phase in the following separation step. The procedure is more costly because a further distillation is necessary in a third unit to separate the products from the low-boiling extractant, which is then recycled to the reactor. 

An important alternative is the successive reaction and product extraction procedure shown in Figure 5. First the reaction of A and B is carried out in a single polar homogeneous phase containing the catalyst. Downstream, the products are extracted with a nonpolar solvent or solvent mixture. In the third unit, the distillation, the low boiling extractant is distilled off and recycled to the extraction unit. Two examples will demonstrate the practicability of this concept. 

In 2002 we predicted that non-synthetic applications would have a great chance to be among the first technical ionic liquid applications. This assumption has held true as Chapter 9 clearly proves. Non-synthetic applications are particularly attractive due to their often much shorter development times. Usually, the improvement over existing technology is only based on one or very few specific properties of the ionic liquid, whereas, for most synthetic applications a complex mixture of physicochemical properties in dynamic mixtures has to be considered. This point is well illustrated by the fact that all liquid-liquid biphasic catalysis involves both a reaction and an extraction step. Hence, the ionic liquid catalyst solution has to ftilfil at the same time aU of the requirements to work as a superior reaction medium as well as its role as a suitable extraction medium. The result is a significantly more complex set of material requirements which prolongs the specific ionic liquid development and testing times. 

Some economic aspects, including rhodium catalyst cost, are treated in section 8.2. Catalyst performance aspects are treated in sections 8.3 (activity, selectivity) and 8.4 (stability, loss routes for Rh and ligand). In 8.5 and 8.6, several commercial processes are described. Four generic, industrially used process types are described in 8.5, viz. processes using a stripping reactor, a liquid recycle, a two-phase reaction, and an extraction after a one-phase reaction. In 8.6, interesting, current developments in a few petrochemical product areas are shortly discussed. 

In a typical procedure, a solution of 0.175 mmol of L- -amino acid and 0.175 mmol of NaOH in 1 ml of water was added to a solution of 0.100 mmol of Cu(N03)2in 100 ml of water in a 100 ml flask. Tire pH was adjusted to 6.0-6.5. The catalyst solution was cooled to 0 C and a solution of 1.0 mmol of 3.8c in a minimal amount of ethanol was added, together with 2.4 mmol of 3.9. The flask was sealed carefully. After 48 hours of stirring at 0 C the reaction mixture was extracted with ether, affording 3.10c in quantitative yield After evaporation of the ether from the water layer (rotary evaporator) the catalyst solution can be reused without a significant decrease in enantioselectivity. 

Other uses include use as a reaction and extraction solvent in pharmaceutical production as an intermediate for the preparation of catalysts, antioxidants (qv), and perfumes and as a feedstock in the production of methyl isopropenyl ketone, 2,3-butanedione, and methyl ethyl ketone peroxide. Concern has also arisen at the large volume of exported MEK which has been covertly diverted and used to process cocaine in Latin American countries... 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Competitive Extraetion of Anions. The successful extraction of the necessary anion into the organic phase is cmcial for PTC. Often three anions compete for the catalyst cation the one that is to react, the one formed in the reaction, and the one brought in originally with the catalyst. Table 1 hsts the widely differing values of tetra-rr-butylammonium salts. The big difference in the halide series is noteworthy and preparatively important. Hydroxide is 10 times mote difficult to extract than chloride (11) and the divalent and trivalent anions and PO " are stiU more hydrophilic. Thus... 

Hydrolysis by Steam. High pressure steam, 4.5—5.0 MPa (650—725 psi), at 250°C in the absence of a catalyst hydroly2es oils and fats to the fatty acids and glycerol (20). The reaction is commonly carried out continuously in a countercurrent method. The glycerol produced during the reaction is continuously extracted from the equiUbrium mixture with water. A yield of 98% can be achieved. Currentiy, the preferred method to produce soaps is steam hydrolysis of fats followed by alkaU neutrali2ation of the fatty acids. 

A solution containing 741 g (5.0 mols) of 1-phenyl-2-propylidenylhydrazine, 300 g (5.0 mols) of glacial acetic acid and 900 cc of absolute ethanol was subjected to hydrogenation at 1,875 psi of hydrogen in the presence of 10 gof platinum oxide catalyst and at a temperature of 30°C to 50°C (variation due to exothermic reaction). The catalyst was removed by filtration and the solvent and acetic acid were distilled. The residue was taken up In water and made strongly alkaline by the addition of solid potassium hydroxide. The alkaline mixture was extracted with ether and the ether extracts dried with potassium carbonate. The product was collected by fractional distillation, BP B5°C (0.30 mm) yield 512 g (68%). 

The major advantage of the use of two-phase catalysis is the easy separation of the catalyst and product phases. FFowever, the co-miscibility of the product and catalyst phases can be problematic. An example is given by the biphasic aqueous hydro-formylation of ethene to propanal. Firstly, the propanal formed contains water, which has to be removed by distillation. This is difficult, due to formation of azeotropic mixtures. Secondly, a significant proportion of the rhodium catalyst is extracted from the reactor with the products, which prevents its efficient recovery. Nevertheless, the reaction of ethene itself in the water-based Rh-TPPTS system is fast. It is the high solubility of water in the propanal that prevents the application of the aqueous biphasic process [5]. 

Reactive distillation is one of the classic techniques of process intensification. This combination of reaction and distillation was first developed by Eastman Kodak under the 1984 patent in which methyl acetate was produced from methanol and acetic acid. One of the key elements of the design is to use the acetic acid as both a reactant and an extraction solvent within the system, thereby breaking the azeotrope that exists within the system. Likewise, the addition of the catalyst to the system allowed sufficient residence time such that high yields could be obtained, making the process commercially viable. Other examples in which reactive distillation may enhance selectivity include those of serial reactions, in which the intermediate is the desired product, and the reaction and separation rates can be systematically controlled to optimize the yield of the desired intermediate. ... 

The catalyst anion has also been shown to have a large influence on the reaction rate. The extraction constant of tetra-n-butylammonium salts between water and chloroform decreases with different anions as follows picrate CIO4 > T > toluene sulphonate > NO.-i > Br > benzoate > Cf > acetate > OH (Esikova, 1997 Dehmlow, 1993). 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

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