Azeotropic distillation process

Historically azeotropic distillation processes were developed on an individual basis using experimentation to guide the design. The use of residue curve maps as a vehicle to explain the behavior of entire sequences of heterogeneous azeotropic distillation columns as weU as the individual columns that make up the sequence provides a unifying framework for design. This process can be appHed rapidly, and produces an exceUent starting point for detailed simulations and experiments. 

Doherty MF and Perkins JD (1979) The Behaviour of Multi-component Azeotropic Distillation Processes, IChemE Symp Ser, 56 4.2/21. 

Bauer, M. H. and J. Stichlmair. Design and Economic Optimization of Azeotropic Distillation Process Using Mixed-Integer Nonlinear Programming. Comput Chem Eng 22 1271-1286 (1998). 

Figure 13.29. Composition profiles and flowsketches of two azeotropic distillation processes (adapted by King, 1980). (a) Separation of ethanol and water with benzene as entrainer. Data of the composition profiles in the first column were calculated by Robinson and Gilliland, (1950) the flowsketch is after Zdonik and Woodfield (in Chemical Engineers Handbook, McGraw-Hill, New York, 1950, p. 652). (b) Separation of n-heptane and toluene with methylethylketone entrainer which is introduced in this case at two points in the column (data calculated by Smith, 1963).

Bauer MJ, Stichlmair J. Superstructurers for the mixed integer optimization of nonideal and azeotropic distillation processes. Comp Chem Eng 1997 20 25. 

Azeotropic distillation has often been discussed in recent literature (I, 2, 3). Methods for providing phase equilibria for azeotropic and extractive distillation have been studied extensively (I, 4, 5, 6, 7, 8, 9). Some have discussed the design (10) or calculation of azeotropic distillations (2, 3) others only discussed choosing the entrainer for azeotropic distillation processes (11). 

To calculate phase equilibria suitable for most azeotropic distillation problems, the methods should be applicable to three-phase equilibria. Vapor-liquid and liquid-liquid equilibria are usually required. A suitable method for this purpose has already been discussed (5). It is applied here to calculate completely all phase equilibria involved in the usual azeotropic distillation process. 

This production expansion was made possible in no small degree by a sharp reduction in the cost of manufacture. From an original market price of 1.45 a pound in 1926, cellulose acetate dropped steadily to. 50 a pound in 1936, and further to. 30 in 1940. In addition to a lower cost as a result of the increasing quantity of production, these reductions in price were aided greatly by reductions in the cost of raw materials. Acetic acid became much cheaper during this period, and the cost of conversion of the acid to its anhydride was aided by improved process development. Recovery of acetic acid from aqueous solution also became cheaper with the adoption of extraction and azeotropic distillation processes, replacing the original recovery by evaporation of neutralized solutions. In addition, technical developments in the acetylation process increased the economy of plant unit operations. 

M.5 The process of azeotropic distillation is widely used to separate mixtures that are difficult or impossible to separate by simple fractional distillation. An example of an azeotropic distillation process is the separation of ethanol from water using, as... 

The hydrogen bonding grouping provides insight for screening suitable entrainers in the development of a feasible azeotropic distillation process. Selected entrainers are then tested experimentally for their quantitative effect on VLE. 

In certain systems where solubility considerations permit, it is possible to use a salt dissolved into the liquid phase as the separating agent in place of the normal liquid. The attraction of the salt-effect distillation technique lies in its potential for greatly reduced energy requirements compared with conventional extractive and azeotropic distillation processes. 

The combination of distillation and decantation is used in the well-known azeotropic distillation process shown in Fig. 11.4-1. The separation of the homogeneous azeotropic feed (e.g., ethanol/water) is achieved by the admixture of an entrainer (e.g., toluene) which forms a large mixing gap with one of the feed components (here water). In colunrn C-1, water is recovered as bottoms B. The azeotropic overhead fraction t> is mixed with the fraction S2 (toluene-rich) from the decanter. In colunrn C-2 pure ethanol is recovered as bottoms B2. The overhead fraction D2 is condensed, subcooled, and split into the fractions 51 (water-rich) and 52 (toluene-rich) in the decanter. Both fractions are recycled within the pro-... 

BASF has recently patented a reactive azeotropic distillation process to produce esters from methacrylic acid and alcohols, involving a total of 3 columns. Although the patent example is for butyl methacrylate, they claim methyl methacrylate as well. 

In Chapters, the steady-state design of a heterogeneous azeotropic distillation process for the dehydration of ethanol using benzene as a light entrainer was studied. The process consisted of two distillation columns, one decanter and two recycle streams. One of the recycle streams was successfully closed, but the second would not converge using steady-state Aspen Plus. 

The heterogeneous azeotropic distillation process provides an excellent example of the utility of distillation simulation to both design and control of a very complex nonideal system. 

This chapter examines quantitatively, using rigorous simulations, how this design parameter affects the energy and capital investment of the entire system. The focus is the distillate composition trade-off. The example used is the heterogeneous azeotropic distillation process, but the same issue applies in any of the other methods (e.g., extractive distillation) in which a preconcentrator column is used. 

In addition to heterogeneous azeotropic distillation, several alternative methods are available for ethanol dehydration such as extractive distillation, adsorption, and pervapo-ration. A comprehensive review of the subject, including 302 references, has been presented by Vane. A recent paper by Kiss and Paul claims that the heterogeneous azeotropic distillation process is more economical than adsorptive drying because of the large amount of energy required to regenerate the adsorbent. 

W. L. Luyben, Control of a multi-unit heterogeneous azeotropic distillation process, AIChE Journal 51, 115-134 (2006). 

Fig. 1-24. Influence of an auxilliary component on the azeotropic point in an azeotropic distillation process.

The reaction requires an initial heat-up. Typical heat-up rates are 70 - 90 °C per hour initially followed by a phase where water distillation starts and further heats up at rates of around 15 - 25 °C per hour. Heating is continued until a predetermined batch temperature above 200 °C is reached. The equilibrium is shifted to the right by reaction water removal. For this purpose, the reactor is equipped with a distillation column (for the purpose of separating glycols and reaction water), a condenser and a receiver to collect the reaction water. Water removal is facilitated by applying nitrogen as the inert gas or a vacuum. Alternatively, an azeotropic distillation process may be applied. A solvent is used for water removal, e.g. xylene. In a separator, the xylene-water mixture is separated, the xylene is recirculated back into the reactor and the reaction water is collected in the receiver. 

Acetic Acid 80 195 91 G G — — plus 2-3 percent formic acid. 3-5 percent propionic acid, ethylacetate, small amount water (ethylacetate>acetic acid azeotrope distillation process). Alloy C > 4.0 mpy. I126-hr. test. 

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