Acetone recovery process

In an acetone-recovery process, a gas stream containing 20.0 mole% acetone and the remainder nitrogen leaves a chemical plant at 90°C and 1 atm. The stream is cooled at constant pressure in a condenser, enabling some of the acetone vapor to be recovered as a liquid. The nitrogen and uncondensed acetone are discharged to the atmosphere. 

Fig. 39. —Section, Plan, and details of an Absorption Tower used in Robertson and Kin tool s Acetone Recovery Process-...

Most by-product acetylene from ethylene production is hydrogenated to ethylene in the course of separation and purification of ethylene. In this process, however, acetylene can be recovered economically by solvent absorption instead of hydrogenation. Commercial recovery processes based on acetone, dimetbylform amide, or /V-metby1pyrro1idinone have a long history of successfiil operation. The difficulty in using this relatively low cost acetylene is that each 450, 000 t/yr world-scale ethylene plant only produces from 7000 9000 t/yr of acetylene. This is a small volume for an economically scaled derivatives unit. 

The demand for isoprene for Butyl rubber led to the development of a recovery process for this Cj diolefin. Extractive distillation with acetone was the first process used but it has been replaced with acetonitrile (ACN ). The first step in the process is the fractionation of steam cracker debutanizer bottoms in a conventional two tower system to produce a C5 cut containing 30% isoprene. The first tower rejects C and heavier while the second rejects C4 and lighter materials. 

Reaction of K3Co(CN) with PMMA. A 1.0 g sample of PMMA and 1.0g of the cobalt compound were combined in a standard vessel and pyrolyzed for 2 hrs at 375°C. The tube was removed from the oven and the contents of the tube were observed to be solid (PMMA is liquid at this temperature). The tube was reattached to the vacuum line via the break-seal and opened. Gases were determined by pressure-volume-temperature measurements on the vacuum line and identified by infrared spectroscopy. Recovered were 0.22g of methyl methacrylate and 0.11 g of CO and C02. The tube was then removed from the vacuum line and acetone was added. Filtration gave two fractions, 1.27g of acetone insoluble material and 0.30g of acetone soluble (some soluble material is always lost in the recovery process). The acetone insoluble fraction was then slurried with water, 0.11 g of material was insoluble in water. Infrared analysis of this insoluble material show both C-H and C-0 vibrations and are classified as char based upon infrared spectroscopy. Reactions were also performed at lower temperature, even at 260°C some char is evident in the insoluble fraction. 

For example, an ABE plant was established at Germinston, South Africa in 1937 and ran successfully until 1983, first producing solvent from starch but switching to molasses. The fermentation and distillation recovery process operated in batch mode. The fermentation produced approximately 20gl of mixed solvents from 55 to 60 g 1 of substrate with solvent yields of about 0.35 g g sugar. The butanol acetone molar ratio is typically 2 1 [178]. 

The nature of the wastes being treated by Hovione is shown in Figure 2.10. They arise from semi-synthetic tetracycline production of around 60 tonnes per annum. A separate plant, operated under GMP conditions, was constructed for the specific purpose of waste minimisation through treatment and recycling. The major items handled are solvent (acetone, methanol), a precious metal catalyst (rhodium) and an organic (triphenyl phosphine). All aspects of the recovery processes are carefully interfaced such that the whole operation is balanced. Solvent distillation is carried out continuously, whereas other unit operations are carried out batch-wise. 

Various solvents can be used as extraction agents, for example hexane, ethanol (96%) or hexane/ethanol mixtures. Benzene, cyclohexane, acetone, chloroform, and ether are also used however. The solvent destroys the cell wall of the alga and extracts the oil from the aqueous phase (medium) owing to the higher lipid solubility in organic solvents as compared to water. The solvent recovery process takes place in a subsequent distillation stage. 

For acetone-butanol-ethanol (ABE) fermentation, the broth contains about 25-35 g/1 of mixed solvents. Butanol concentration is usually less than 20 g/1, which makes its recovery by distillation expensive. This low butanol concentration in the fermentation broth is related to the inability of Clostridium species to produce more butanol due to solvent toxicity (Lee et al., 2008). Metabolic engineering and advanced fermentation techniques are ongoing to enhance the organisms abilities to produce and tolerate higher concentrations of butanol and increase productivity. Several integrated fermentation and recovery processes, such as fed-batch fermentation with pervaporation and continuous fermentation with gas stripping, have been reviewed elsewhere (Lee et al., 2008). 

The solvent used to form the dope is evaporated during the extrusion process and must be recovered. This is usually done by adsorption on activated carbon or condensation by refrigeration. For final purification, the solvent is distilled. Approximately 3 kg of acetone, over 99%, is recovered per kg of acetate yam produced. Recovery of solvent from triacetate extmsion is similar, but ca 4 kg of methylene chloride solvent is needed per kg of triacetate yam extmded. 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

The recovery area of the plant employs fractionation to recover and purify the phenol and acetone products. Also in this section the alpha-methylstyrene is recovered and may be hydrogenated back to cumene or recovered as AMS product. The hydrogenated AMS is recycled as feedstock to the reaction area. The overall yield for the cumene process is 96 mol %. Figure 1 is a simplified process diagram. 

The recovery of the product is described in outline in Figure 95. Essentially the process involves separating the broth and mycelium by filtration, extracting the mycelium with acetone and methylene chloride. Combining these extracts with the broth and re-extracting with methylene chloride. The extract is washed with 2% sodium bicarbonate, evaporated and re-dissolved in methylene chloride. The product is allowed to crystallise from the methylene chloride. 

The almost quantitative oxidation/complexation of palladium(O) in powder or foils by Me2dazdt 2I2 in THF, acetone, acetonitrile, and methylethylketone (MEK) to afford [Pd(Me2dazdt)2](I3)2 makes this synthetic route appealing for practical industrial applications. A selective process for Pd-recovery from model three-way car converters was simulated obtaining a Pd-extraction yield > 90%, and was proposed as an alternative to hydrometallurgical processes.62... 

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

A mixture of acetone and chloroform is to be separated into pure products [Hostrup et al. (1999)]. Since they also form an azeotrope, one alternative to satisfy the separation objective is to find a suitable solvent for separation by extractive distillation. This type of problem in product design is usually encountered during the purification or recovery of products, by-products, reactants or removal of undesirable products from the process. Also, it can be noted that failure to find a suitable solvent may result in the discard of the product. Alternatively, a functional chemical product manufacturer may be interested to find, design and develop a new solvent. In this case, the solvent is the chemical product. 

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