Semicontinuous, middle‐vessel distillation of ternary mixtures

Abstract

IntroductionTraditionally, distillation processes have been designed to operate in a batch column, in which a still is charged and distilled, or to operate continuously, in which a stream is fed to a column and distillate and bottoms products are withdrawn continuously. Batch distillation is usually preferred for low throughputs, when fine or specialty chemicals are produced, or when there is intermittent or seasonal chemicals production. In contrast, continuous distillation is favored for larger-scale throughputs and continuous upstream feeds.In this article, the design, control, and operation of a semi-Ž . continuous, middle-vessel column SCMVC to separate nearly-ideal ternary mixtures is investigated. The middle-vessel permits semicontinuous operation to be an attractive policy for the separation of multicomponent mixtures. The MVC is a distillation column with a large vessel between the rectifying and stripping sections. One MVC configuration is shown in Figure 1 Ž . In a brief companion article Phimister and Seider, 2000a , simulation studies of a SCMVC are presented for the separation of azeotropic mixtures in processes comparable to continuous extractive and azeotropic distillations. The MVC is shown to reduce capital investment, as compared with continuous processing. An MVC operated semicontinuously avoids column dumping and repeated startups, and allows for column automation, as compared with batch operation. In Table 1, several features of distillation processes are listed to compare a SCMVC with batch and continuous columns.In this article, recent work on middle-vessel columns is reviewed. Then, the semicontinuous process is reviewed for the separation of three alkanes. Next, shortcut design procedures are adapted for semicontinuous columns. Several PI control configurations are examined, and for a DB configuration, the decoupling effect of the PI-composition controllers is shown. Finally, the three-alkane separation is considered in greater detail, with a column designed using the shortcut procedures and a DB-control configuration. MV DistillationWithin the past decade, there has been much interest in the performance of alternative distillation configurations, including the MVC multivessel columns, series of heat-integrated, batch-distillation columns, and semicontinuous distillation configurations.Although the MVC was initially suggested by Robinson and Ž . Gilliland 1950, p. 388 , few papers appeared until the 1990s. Ž . One of the first articles, by Hasebe and coworkers 1992 , reintroduced the MVC, presenting a campaign policy with simulation results. The simulations involve ideal mixtures, with the heavy and light impurities removed in the bottoms product and distillate, respectively, while the desired product concentrates in the middle vessel. In a subsequent article, Ž . Hasebe and coworkers 1996 conclude that a batch MVC consistently provides superior performance compared to batch rectification followed by batch stripping. Meski and Ž . Morari 1995 also conclude that MVC performance is superi...

Control of Reactive Distillation Column: A Review

“…Semicontinuous processes have been introduced in recent years as a process intensification technique that allows multiple separations to be performed in one separation column ( (Phimister & Seider 2000a;2000b;2000c;Adams II & Seider 2006a;2008;) Several semicontinuous processes have been explored for a variety of design scenarios, Semicontinuous distillation with chemical reactions in middle vessels (MV) where streams are continuously exchanged between the middle vessels and columns is advantageous over conventional reactive distillation column for several reasons (Adams II & Seider 2006a): First, because the two reaction products have intermediate boiling points and the reaction is highly reversible, it is difficult to recover the product in a sidedraw. Second, because one of the reagents leaves in the distillate (acetaldehyde) and one leave in the bottoms product (propylene glycol), the reaction is shifted to the left.…”

Separation of acetonitrile/methanol/benzene ternary azeotrope via triple column pressure-swing distillation

“…Modla [11] introduced a new triple column configuration applied in pressure-swing batch distillation for separation of chloroform/acetone/toluene. Phimister and Seider [12] investigated the operation of a semicontinuous, middle-vessel column to separate a nearly-ideal ternary mixture. Huang et al [8] studied direct and indirect sequence ideal heart-integrated distillation column to separate a simple close-boiling ternary mixture.…”

“…There are some methods for separation of ternary azeotropic system such as membrane [7], continuous distillation [8,9], and batch distillation [6,[10][11][12][13]. The concentration of water was improved at 94.9 wt% for the purification of ethyl acetate/ethanol/water ternary azetropic mixtures using membrane by Xia et al [7].…”

The energy consumption in a batch stripper and a batch rectifier

“…In this column, the feed is charged to a middle vessel, so it can also be called "a middle vessel column". It has gained lots of attention and been studied by many authors [3][4][5][6][7][8][9][10][11].…”