Heptane-toluene separation process

Axial flow pumps, 134, 136, 140 applicafion range, 150 Azeotrope separation, 387,388,420-426 Azeotropic distillation, 420-426 acetonitrile/water separation, 422 commercial examples, 421-424 design method, 424 ethanol/water/benzene process, 424 n-heptane/toluene/MEK process, 424 vapor-liquid equilibrium data, 421, 423, 425,426... 

An experimental apparatus for continuously processing an aqueous stream containing an organic contaminant was designed and constructed. The criteria for choosing the contaminant/surfactant/ extraction solvent are discussed along with the system operating parameters such as the heptane/water ratio, the hydrodynamic conditions of the ultrafilter and the overall efficiency of the toluene separation. A mathematical model of the continuous system was also developed and evaluated. 

The toluene production process is started by heating n-heptane from 65 to 800 °F in a heater. It is fed to a catalytic reactor, which operates isothermally and converts 15 mol% of the n-heptane to toluene. Its effluent is cooled to 65 °F and fed to a separator (flash). Assuming that all of the units operated at atmospheric pressme, determine the species flow rates in every stream. 

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).

Figure 19.12. Batch parametric processing of solid-liquid interactions such as adsorption or ion exchange. The bottom reservoir and the beef interstices are filled with the initial concentration before pumping is started, (a) Arrangement of adsorbent bed and upper and lower reservoirs for batch separation, (b) Synchronization of temperature levels and directions of flow (positive upward), (c) Experimental separation of a toluene and n-heptane liquid mixture with silica gel adsorbent using a batch parametric pump. (Reprinted from Wilhelm, 1968, with permission of the American Chemical Society), (d) Effect of cycle time r on reservoir concentrations of a closed system for an NaCl-H20 solution with an ion retardation resin adsorbent. The column is initially at equilibrium with 0.05M NaCl at 25°C and a = 0.8. The system operates at 5° and 55°C. [Sweed and Gregory, AIChE J. 17, 171 (1971)].

Some hydrocarbon separations can be effected azeotropically. Figure 13.28(b) shows an operation with methylethylketone which entrains n-heptane away from toluene. Hexane in turn is an effective entrainer for the purification of methylethylketone by distilling the latter away from certain oxide impurities that arise during the synthesis process. 

Therefore, in a mixture as complex as petroleum, the reaction processes can only be generalized because of the difficulties in analyzing not only the products but also the feedstock as well as the intricate and complex nature of the molecules that make up the feedstock. The formation of coke from the higher molecular weight and polar constituents of a given feedstock is detrimental to process efficiency and to catalyst performance. One method by which the process chemistry can be rationalized is to separate the resid and its conversion products into fractions using solubility/ insolubility in volatile liquids as well as adsorption/ desorption on solids. In this way a number of resids and resid conversion products were separated into coke (toluene insoluble), asphaltenes (toluene soluble/ n-heptane insoluble), resins (n-heptane soluble, adsorbs on alumina), aromatics (n-heptane soluble, does not adsorb on alumina), and saturates (n-heptane soluble, does not adsorb on alumina). 

Similar processes are used for separating other close boiling aromatics and paraffins such as the separation of toluene and n-heptane using as entrainer methyl ethyl ketone, which forms a minimum-boiling azeotrope with the heptane. The azeotrope is taken in the overhead and the toluene in the bottoms. 

The formation of the mesophase by this route has the disadvantage of requiring rather long processing times. An alternative route is the solvent route [18]. Isotropic aromatic pitches contain a separable fraction which, when heated at 230-400°C, develops an optically anisotropic liquid crystal phase in <10 minutes. This mesophase has been called a neomesophase since it is highly soluble in solvents such as pyridine or quinoline, while the mesophase derived by the thermal route is insoluble. The separable fraction of isotropic pitch is insoluble in solvents like benzene, toluene, or mixtures of toluene and heptane. Thus, it can be separated by solvent extraction from isotropic or heat soaked pitches (Figure 5, b and b ). 

Commercial Ziegler polyethylene processes are generally operated at pressures only slightly above atmospheric, namely 2-4 atmospheres and at temperatures of 50—75°C. Polymerization is conducted in the presence of Ziegler-Natta catalysts, the nature of which is discussed in Chapter 1. For the polymerization of ethylene the catalyst is usually based on titanium tetrachloride/aluminium alkyl (e.g., diethylaluminium chloride). The catalyst may be prepared in situ by adding the components separately to the reactor as solutions in diluents such as diesel oil, heptane or toluene or the components may be pre-reacted and the catalyst added as a slurry in a liquid diluent. These operations must be conducted in an inert atmosphere (usually of nitrogen) since oxygen and water reduce the effectiveness of the catalyst and may even cause explosive decomposition. In a typical process, ethylene and the catalyst and diluent are... 

HFCLM-based Perstraction Processes. Perstraction, the combination of permeation and extraction, is selective permeation of a species from a liquid feed through a membrane into a strip or sweep liquid which selectively extracts the permeating species (Sirkar (30) has a brief review). Cahn and Li (31) report separation of toluene and n-heptane through an aqueous ELM and kerosene as the strip liquid. Papadopoulos and Sirkar (32) explored the separation of a 2 vol% isopropanol-n-heptane mixture through a highly polar liquid membrane in a HFCLM... 

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