Example

Consider the process from Figure 1C - the effluent water stream from an industrial process contains 7% w/w of phenol, which needs to be removed through liquid-liquid extraction. The desired solvent, when added to the phenol-water system, must cause a phase split such that the solvent-rich phase will contain significantly more phenol than water while the water-rich phase will contain very little phenol or solvent. It should be possible to separate easily the solvent from phenol. That is, the solvent must not form azeotrope, it must have a reasonable difference in boiling point and vapour pressure from phenol, and it must have a density lower than that of water in order to have free convection flow in the extraction column. If the solvent has a high environmental impact, the loss of the solvent through the water-rich phase will have to be reduced. If the solvent is unable to remove enough phenol, more solvent may need to be used. It should pose a low risk of explosion (the flash point temperature should be as high as possible).

Table 2 Solvent selection problem formulation with properties

Property

Solvent design

L-L Extraction Extractive distillation

Azeotropic distillation

Solid separation Gas absorption

Simple General Simple General Simple General Simple General Simple General

Pure

Solubility parameter Surface tension Viscosity Boiling point Melting point Density

Vapour pressure Heat of fusion

Mixture Selectivity Solvent loss. Solvent power Distribution coefficient Phase split Azeotropes Mixture viscosity Henry's law constant Environmental

To ensure a minimal loss of the solvent to the water stream, the solvent should have very low miscibility in water and a high octanol-water partition coefficient. It should be possible to separate the solvent easily from phenol (must not form azeotrope, must

Table 3 Specific environmental concerns

Environmental property

Health concern

Safety concern

Environmental concern

Implicit Toxicity

Biological persistence Chemical stability Reactivity

Explicit

Biodegradability Vapour pressure Henry's law constant in water log P

Water solubility Flash point Biological oxygen demand Vapour density Evaporation rate LD50

Ozone depletion potential have a reasonable difference in boiling point and vapour pressure from phenol, and must have a density lower than that of water in order to have free convection flow in the extraction column). For the process in Figure 1C, the target properties and their target values are given in Table 4.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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