Azeotropes isopropanol/water mixtures

The azeotropic composition of a binary system is not only influenced by recycled third components added to the mixture and by the operating pressure, but also by the presence of an insoluble inert gas, which is favorable for the separation if the volatile components of the mixture diffuse at different velocities across the regions of inert gases. Figure 2-31 a shows an example using the binary isopropanol/water mixture. Steam diffuses faster across an air bolster than isopropanol vapor, and thus, the distillate of isopropanol mole fraction is more water-rich due to the presence of air between the liquid and the condensation surfaces (point A2), compared with the distillation under air exclusion (point A,). 

The shifting of A] A2 is of practical use in separating water rich isopropanol/water mixtures (Fig. 2-31 b). A feed/"is almost completely separated into water flow rate JV leaving column DCl and a isopropanol flow rate P leaving column DC2. Both columns are operated at ambient pressure. The overhead products AT, and JC2 are practically of azeotropic composition (point Aj, Fig. 2-31 a). In the condenser C, most of the condensed overhead products form the reflux / , or / 2, to the columns DCl or DC2, respectively. The remainder is then separated into a water rich fraction >i and an alcohol rich fraction >2 in the diffusion distillation unit DA (Fig. 2-31 c shows the diffusion separation unit). Some of the overhead product fluxes Kj and K2 are heating the unit while water is used for cooling. 

Separation of an isopropanol/water mixture by azeotropic rectification using toluolene, reduction of energy costs to 70% of these compared to conventional operation by means of a heat pump IPA Isopropanol P Power Q Heat flow... 

In Part 3 of this book an extrainer is added to the system so that liquid-liquid sphtting can appear in the top decanter and also maybe in the top few stages of the azeotropic column. The LLE behavior in the decanter, or the VLLE behavior in the top stages of flie azeotropic column, can be predicted by Aspen Plus. The system of separating an isopropanol-water mixture using cyclohexane as the entrainer will be used as an example to demonstrate the way to generate a LLE envelope in Aspen Plus. 

Example 4.5 2-Propanol (isopropanol) and water form an azeotropic mixture at a particular liquid composition that results in the vapor and liquid compositions being equal. Vapor-liquid equilibrium for 2-propanol-water mixtures can be predicted by the Wilson equation. Vapor pressure coefficients in bar with temperature in Kelvin for the Antoine equation are given in Table 4.113. Data for the Wilson equation are given in Table 4.126. Assume the gas constant R = 8.3145 kJ-kmol 1-K 1. Determine the azeotropic composition at 1 atm. 

Figure 3.9 highlights the key feature of a RCM by means of the mixture isopropanol, n-propanol, water, in which two binary azeotropes of water-alcohol occur ... 

We will start this chapter by explaining how the heterogeneous azeotropic distillation works in separating a mixture with an azeotrope. Three systems with different RCMs will be used as examples to illustrate the column sequence for the separation. After that, we will focus on the detailed design and control of the isopropanol-water system, which is a system that exhibits the most complex RCM. 

In liquid mixtures of type (2), the solutions of primary interest are azeotropic and other mixtures containing variable amounts of water in organics dehydration of organic solvents containing very small amounts of water. Removal of water from azeotropic mixtures of ethanol-water, isopropanol-water, etc., is extensively practiced using polymeric membranes (of crosslinked polyvinyl alcohol) that are highly polar and selective for water. On the other hand, the membranes that are used to remove VOCs selectively from aqueous solutions are usually highly nonpolar rubbery polymeric membranes, e.g. dimethyl siloxane (silicone rubber). 

Very little data exist on the separation efficiency of multilayer diffusion and capillary condensation. Asaeda and Du (1986) used a thin modified alumina membrane to separate alcohol/water gaseous mixtures at high relative pressures (near 1). The azeotropic point could be bypassed for water/ethanol and water/isopropanol mixture by employing eapillary condensation as a separation mechanism at a temperature of 70°C. By deereasing the pore size to the microporous range (pore diameter < 2 nm by plugging the pores with hydroxides), the separation faetors were inereased to above 60 (Asaeda and... 

Separation of the ternary mixture (isopropanol (A) - water (B) + benzene (E)) Binary azeotropic charge ( xbaz = [0.674,0.326,0]) is separated by the application of an entrainer ( ). The composition of the ternary IPA - water - benzene heteroazeotrope and those of its it-rich and 5-rich phases ... 

In this configuration the conventional reactive distillation column is taken but the top vapour is condensed and fed into a second column. In this column pure water is drawn off and an azeotropic mixture of water and isopropanol is recycled back to the reactive distillation column. 

In the conventional reactive distillation combined with azeotropic distillation an azeotropic distillation takes place in the second column. An entrainer is fed in order to obtain pure isopropanol at the bottom and a water/entrainer mixture at the top. The entrainer is chosen such that it forms an... 

The mode of operation and the dimensioning of a heteroazeotropic distillation as exemplified by the separation of the system water-acetic acid has been described by Wolf et al. [61b]. Morozova and Platonov [61c] analyzed the structure of phase diagrams of multicomponent mixtures using a digital computer. They studied the requirements for the separation of azeotropic mixtures. In order to achieve optimum column combinations Serafimov et al. [58 c] studied the ternary mi.xture isopropanol/ benzene/water on the basis of a mathematical treatment of the separation of heteroazeotropic mixtures. In another paper [58 d] a procedure was presented for the separation into its components of the water-containing mixture with acetone, ethanol, benzene and butyl acetate by means of the thermodynamic and topological analysis of the phase diagram structure. 

V. Pressure effects—Azeotropes. Switch the system to isopropanol and water. Use NRTL or NRTL-2 as the VLB package. We want to look at the analysis at different pressures. To do this, you need to set up a column (dimensions and so forth are arbitrary). Run the simulation so that Aspen Plus will let you use Analysis. Look at the T-y,x and y,x diagrams at p = 1.0 atm, p = 10.0 atm, and p = 0.1 atm Notice how the concentration of the azeotrope shifts. (In the Binary Analysis Results Table the azeotrope occurs when Ki p = 1.000. Record the azeotrope mole fractions). This shift maybe large enough to develop a process to separate azeotropic mixtures (see Chapter 81. 

This theoretical study is focused on the process combination of a distillation column and a pervaporation unit located in the side stream of the column. This hybrid membrane process can be applied for the separation of azeotropic mixtures such as acetone, isopropanol and water. Water is removed from the side stream of the column by pervaporation, while pure acetone and isopropanol are obtained at the top and bottom of the column. Detailed simulation studies show the influence of decisive structural parameters like side stream rate and recycle position as well as operational parameters like reflux ratio and mass flow on concentration profiles, membrane area and product compositions. 

The MAH contents of the xylene-soluble and xylene-insoluble fractions were determined by heating a 1-2 g sample in refluxing xylene to dissolve or swell the polymer and then, on conversion of succinic acid to anhydride units, to remove a xylene-water azeotrope in a Dean-Stark tube. The xylene solution or suspension was cooled to about 60 C and 0.5N methanolic KOH was added through the condenser. The mixture was refluxed for 1.5 hrs, cooled and titrated with a 0.25N isopropanolic HCl solution to a phenolphthalein end point. 

Figure 8.8c shows that for liquid isopropanol concentrations less than the azeotrope (which corresponds to Xa = 0.685), the vapor contains a higher percentage of isopropanol than the liquid, while at liquid isopropanol concentrations greater than the azeotrope the vapor contains less isopropanol than the liquid. At the azeotrope (where the equilibrium curve crosses the reference curve) the vapor and liquid have the same composition, and the boiling-point temperature of this mixture, 80.4°C, is less than the boiling point of either pure species or of any mixture of them with a different composition (at 1.00 atm). This type of azeotrope is common, and makes separation by distillation difficult. If we start with a liquid mixture of, say, 10 mol% isopropanol and attempt to separate it into pure isopropanol and pure water by distillation, we find that it is easy to get practically... 

Until about 1970 most of the acetone used was produced in the gas phase from the azeotropic mixture of isopropanol and water by a dehydrogenation process ... 

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