Extraction azeotropic isopropanol

Much research has been devoted to working out optimum parameters of producing different protein concentrates from fish and krill (Lanier, 1994). While the products have high nutritional value and many are tasteless and odorless, some, manufactured in denaturing conditions, lack the desired functional properties. A good example is the fish protein concentrate obtained by hot azeotropic isopropanol extraction. On the other hand, a concentrate of myofibrillar proteins known as surimi, produced mainly from fish and to a lesser extent from poultry and meat, is highly functional. 

Kao [48] has reported an elaborate, extractive process to produce 96 wt% MAP containing only 2.3% phosphoric acid and <1% each of DAP and unreacted alcohol. The process uses a fivefold molar excess of polyphosphoric acid (105%) to alcohol, thereby minimizing unreacted alcohol in the product. Because of the high viscosity of the intermediate product, the reaction is carried out in hydrocarbon (hexane) solvent. On completion of the reaction, additional hexane is added and the mixtnre is extracted with isopropanol. The hexane and aqueous layers are then separated. The hexane layer containing the MAP ester is extracted for the second time with aqueous isopropanol, then any residual water and isopropanol are removed by azeotropic distillation with continuous hexane addition. The hexane fraction is cooled, allowing the monoalkyl ester to crystallize. It is filtered and the residual hexane is distilled for recycle. The water-isopropanol extracts containing phosphoric acid are then stripped to recover the phosphoric acid for recycle. This batch process can be adapted to a continuous operation. Several refinements of this process have been published [49-51]. 

Figure 8-4. A flow diagram for the hydration of propylene to isopropanol (1) propylene recovery column, (2) reactor, (3) residual gas separation column, (4) aqueous - isopropanol azeotropic distillation column, (5) drying column, (6) isopropyl ether separator, (7) isopropyl ether extraction.

Considerable research was carried out in the 1980s using ethanol and isopropanol as oil extraction solvents. Ethanol is unusual because its oil solvating capacity is temperature and moisture-dependent. Oil solubility is relatively low at room temperature and moisture contents above the water alcohol azeotrope. Thus, the moisture content of the flakes must be in equilibrium with the alcohol (e.g., 2% for 95% ethanol and 7% for 91% isopropanol) (Wan Wakelyn, 1997), otherwise the solvency changes. Differences in oil solubility afford inexpensive means of oil separation from the solvent by merely cooling the miscella to separate an oil-rich phase without evaporating the bulk solvent. 

The vapor-liquid equilibrium (VLB) and liquid-liquid extraction (LLE) correlations in Aspen Plus are not always as accurate as possible. This can cause significant errors, particularly near pinch points in distillation columns. If data is available, Aspen Plus will find values of the parameters for any of the VLB or LLE correlations by doing a regression against the data you input. This is illustrated to obtain an improved fit for the non-random two-liquid (NRTL) VLB correlation for the binary system water and isopropanol (IPA). VLB data for water and isopropanol is listed in Table B-1. This system has a minimum boiling azeotrope at 80.46°C. The Aspen Plus fit to the data with NRTL is not terrible, but can be improved. 

There are many important industrial applications of azeotropic separations, which employ a variety of methods. In this book we discuss several of these chemical systems and demonstrate the application of alternative methods of separation. The methods presented include pressure-swing distillation, azeotropic distillation with a light entrainer, extractive distillation with a heavy entrainer (solvent), and pervaporation. The chemical systems used in the numerical case studies included ethanol-water tetrahydrofuran (THF)-water, isopropanol-water, acetone-methanol, isopentane-methanol, n-butanol-water, acetone-chloroform, and acetic acid-water. Economic and dynamic comparisons between alternative methods are presented for some of the chemical systems, for example azeotropic distillation versus extractive distillation for the isopropanol-water system. 

ISO standard 893 covers analysis of alkanesulfonates, specifying assay by gravimetry, alkane monosulfonates by titration or extraction (Sections 2(a) and 2(c), below), neutral oil by petroleum ether extraction of an isopropanol/water solution, pH of a 5% aqueous solution, water by Karl Fischer titration or azeotropic distillation, sulfate by titration with lead nitrate, sulfite by iodometric titration, and chloride by potentiometric titration (99). The value for neutral oil can be checked for losses due to evaporation by confirming that the weight of the sulfonates and other salts in the 2-propanol/water phase plus the water content and weight of neutral oil is equal to 100%. 

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