Recovery process, catalysts

Rhodium is an expensive metal, and the commercial viability of the rhodium-based hydroformylation process depends crucially on the efficiency of the catalyst recovery process. In the past this has been achieved either by a complicated recycle process or more commonly by energy-requiring distillation. A major advancement in catalyst recovery in recent years has been the introduc-... 

While the generation of ethylidene diacetate was problematic, it was not the biggest issue with this process. While catalyst precipitation was not normally a significant problem, the process produced a high boiling tarry by-product which binds Rh. A complex, proprietary catalyst recovery process was required to recover Rh. 

Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

Water formed in the reaction as well as some undesirable by-products must be removed from the acetic acid solvent. Therefore, mother Hquor from the filter is purified in a residue still to remove heavies, and in a dehydration tower to remove water. The purified acetic acid from the bottom of the dehydration tower is recycled to the reactor. The water overhead is sent to waste treatment, and the residue still bottoms can be processed for catalyst recovery. Alternatively, some mother Hquor from the filter can be recycled directiy to the reactor. 

Heterogeneous hydrogenation catalysts can be used in either a supported or an unsupported form. The most common supports are based on alurnina, carbon, and siUca. Supports are usually used with the more expensive metals and serve several purposes. Most importandy, they increase the efficiency of the catalyst based on the weight of metal used and they aid in the recovery of the catalyst, both of which help to keep costs low. When supported catalysts are employed, they can be used as a fixed bed or as a slurry (Uquid phase) or a fluidized bed (vapor phase). In a fixed-bed process, the amine or amine solution flows over the immobile catalyst. This eliminates the need for an elaborate catalyst recovery system and minimizes catalyst loss. When a slurry or fluidized bed is used, the catalyst must be separated from the amine by gravity (settling), filtration, or other means. 

In two processes under development as of 1997, the sulfur dioxide stream reacts with reduciag gas over a proprietary catalyst to form elemental sulfur. Both processes have achieved a sulfur recovery of 96% ia a single reactor. Multiple reactor systems are expected to achieve 99+% recovery of the feed sulfur. The direct sulfur recovery process (DSRP), under development at Research Triangle Institute, operates at high temperature and pressure. A similar process being developed at Lawrence Berkeley Laboratory is expected to operate near atmospheric pressure. 

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

What can drive the switch from existing homogeneous processes to novel ionic liquids technology One major point is probably a higher cost-effectiveness. This can result from improved reaction rates and selectivity, associated with more efficient catalyst recovery and better environmental compatibility. 

Reflux overhead vapor recompression, staged crude pre-heat, mechanical vacuum pumps Fluid coking to gasification, turbine power recovery train at the FCC, hydraulic turbine power recovery, membrane hydrogen purification, unit to hydrocracker recycle loop Improved catalysts (reforming), and hydraulic turbine power recovery Process management and integration... 

Catalytica (ref. 7) have reported a recovery process based on air and catalyst. Whilst the reagent is cheap, the process requires high capital investment. It is a clean process but only treats hydrogen bromide streams and cannot treat inorganic bromide streams directly. 

Cobalt catalysts such as HCo(CO)4 are widely used for hydroformyla-tion of higher alkenes, despite the higher temperatures and pressures required. The main reason for this is that these catalysts are also efficient alkene isomerization catalysts, allowing a mix of internal and terminal alkenes to be used in the process. Catalyst recovery is more of a problem here, involving production of some waste and adding significantly to the complexity of the process. A common recovery method involves treating the catalyst with aqueous base to make it water soluble, followed by separation and subsequent treatment with acid to recover active catalyst (4.3). 

Thermal operations such as distillation, decomposition, transformation, and rectification often cause thermal degradation. Furthermore, with these processes quantitative catalyst recovery is generally not possible, which results in loss of productivity. 

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. 

Catalysis in biphasic media is one of the most elegant and efficient means to solve the problem of catalyst recovery. Many excellent reviews are available and industrial processes are currently running.104-107 This method is (like all others) not applicable for all situations, and is particularly... 

The loss of expensive catalyst from the reactor system can be fatal for any process. Physical loss involves the removal of active catalyst from the closed loop of the process. This can include the plating out of metal or oxides on the internal surfaces of the manufacturing plant, failure to recover potentially active catalyst from purge streams and the decomposition of active catalyst by the process of product recovery. The first two can be alleviated to some extent by improvements in catalyst or process design, the last is an intrinsic problem for all manufacturing operations and is the subject of this book. 

RSRP [Richards sulphur recovery process] A proposed modification of the Claus process in which liquid sulfur is used to cool the catalyst bed. Developed jointly by the Alberta Energy Company and the Hudson s Bay Oil Gas Company, but not reported to have been commercialized. 

SARP [Sulphuric acid recovery process] A method for recovering sulfuric acid which has been used for alkylation, for re-use. The acid is reacted with propylene, yielding dipropyl sulfate, which is extracted from the acid tar with isobutane. It is not necessary to hydrolyze the sulfate to sulfuric acid because the sulfate itself is an active alkylation catalyst. 

Xi and coworkers [135-137] reported on the epoxidation of alkenes performed with (CP)3[P04(W03)4] catalyst. This insoluble catalyst formed soluble active species, (CP)3[P04 W02(02) 4], by the reaction with H202. When H202 was consumed completely, the catalyst became insoluble again. Therefore, the catalyst recovery was simple. When coupled with the 2-ethylanthraquinone/2-ethylanthrahydroquinone redox process for H202 production, 02 could be used as an oxidant for the epoxidation of propylene in 85% yield based on 2-ethylanthrahydro-quinone which was obtained without ary by-products (Figure 13.8). 

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