TOPIC :LIQUID-LIQUID EXTRACTION Prepared by : Siddharth parmar( ) Guided by : Mr.Yashwant p. Bhalerao

 CONTENTS: Introduction to Extraction Application of Extraction Types of Extractor Equipment Single Stage and Multi Stage

Introduction to Extraction Liquid-liquid extraction (also known as solvent extraction) involves the separation of the constituents (solutes) of a liquid solution by contact with another insoluble liquid. Solutes are separated based on their different solubilities in different liquids. Separation is achieved when the substances constituting the original solution is transferred from the original solution to the other liquid solution

Introduction

The simplest liquid-liquid extraction involves only a ternary (i.e.3 components) system. The solution which is to be extracted is called the feed, and the liquid with which the feed is contacted is the solvent. The feed can be considered as comprising the solute A and the "carrier" liquid C. Solvent S is a pure liquid. During contact, mass transfer of A from the feed to the solvent S occurs, with little transfer of C to S. The solvent (with the solute) is then permitted to separate from the carrier liquid.

Introduction The solvent-rich product of the operation is called the extract, and the residual liquid from which solutes has been removed is the raffinate In some operations, the solutes are the desired product, hence the extract stream is the desirable stream. In other applications, the solutes may be the contaminants that need to be removed, and in this instance the raffinate is the desirable product stream.

Application of Extraction Extraction processes are well suited to the petroleum industry because of the need to separate heat-sensitive liquid feeds according to chemical type (e.g. aliphatic, aromatic, naphthenic) rather than by molecular weight or vapour pressure. Other major applications exist in the biochemical or pharmaceutical industry, where emphasis is on the separation of antibiotics and protein recovery. In the inorganic chemical industry, they are used to recover high- boiling components such as phosphoric acid, boric acid, and sodium hydroxide from aqueous solutions.

Examples of Extraction Extraction of methylacrylate from organic solution with perchlorethylene. Extraction of benzylalcohol from a salt solution with toluene. Removing of H2S from LPG with MDEA. Extraction of caprolactam from ammonium sulfate solution with benzene. Extraction of methanol from LPG with water.

Liquid-Liquid Extraction Solvent Solution Extract(E) Raffinate(R)

Extraction – is the process by which a solute is transferred from one phase to a new phase. Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their relative solubility's in two different immiscible liquids, usually water and an organic solvent. Process of dissolved substance transferring from one phase to another phase, which are immiscible or restrictedly miscible, is named liquid-liquid –partition or partition between two phase of liquids.

Distribution law At equilibrium, the ratio of the concentrations of the solute in the two phases is given by CE/CR = K The distribution constant K, must be greater than 1 if the desired product is extract stream. The distribution constant K, must be lesser than 1 if the desired product is raffinate stream.

Typical Extraction System In Industry An extraction system always includes at least 1 distillation column (or other separation process) to recover solvent from the extract phase. If the solvent exhibits some degree of miscibility in the feed, then a second separation process (normally distillation) is required to recover solvent from raffinate.

Classification Of Extractor

Types Of Extractor Single Stage Multi Stage

Types of Extractor Equipment Single Stage 1.Mixer-Settler 2.Decanter Multi Stage 1.Mixer-settler Battery (MSB) 2.Mechanically Agitated Extractors i.Scheibel Extractor ii.Rotating Disk Contactor (RDC) iii.Pulse Extractors

Mixer-Settler Mixer-settlers are still widely used because of their reliability, operating flexibility, and high capacity. They can handle difficult-to-disperse systems, such as those having high interfacial tension and/or large phase density difference. They can also cope with highly viscous liquids and solid-liquid slurries. The main disadvantages are their size and the inventory of material held up in the equipment. For multiple unit operations, considerable capital costs may be needed for pumps and pipings. A mixer-settler device ordinarily consisted of two parts: a mixer for contacting the two liquid phases to bring about mass transfer, and a settler for their mechanical separation.

Mixer-Settler The mixer and settler can be integral or separate. The operation may be continuous or batchwise.

Decanter Settlers (or sometimes known as decanter), can be as simple as involving simple dispersion, where the entering liquid is dispersed into droplets. The droplets are then allowed to settle by gravity in the main part of the vessel. Most settlers consist of a horizontal vessel, because the separating efficiency is proportional to the area of the phase interface. To increase the size of the droplets and hence their settling rate, the dispersion may be passed through a coalescer (packing or wire mesh)

Decanter

Mixer-settler Battery (MSB) Mixer-settler can be single-stage or multi-stage (cascade). For multi- stage system, also known as mixer-settler battery (MSB), it is possible to achieve optimum selection of degree of dispersion because the mixers can be adjusted independently. System expansion is easy by the addition of extra stages to existing system.

Mixer-settler Battery (MSB)

Scheibel Extractor  This is probably the oldest of column having agitators. It operates on the mixer-settler principle. There are many versions of this design. The agitators are mounted at fixed intervals on a central vertical shaft, and wire-mesh packings are installed to improve coalescence and separation of the phases.  The main disadvantages of this column include : Poor dis-assembly characteristics Easy fouling of the separation zones Poor efficiency for large diameter column

Scheibel Extractor

Rotating Disk Contactor (RDC) In this system, horizontal disks are used as agitating elements, which are mounted on a centrally supported shaft. Mounted on the column wall and offset against the agitator disks are the stator rings, whose have aperture is greater than the agitator disk diameter. This device uses the shearing action of the rapidly rotating disks to inter-disperse the phases

Rotating Disk Contactor (RDC)

Pulse Extractors In this design, a reciprocating pump is used to create pulses of short amplitude that are superimposed on the usual flow of the liquid phases. The column itself may contain packing or perforated plates. The unique features of pulsed columns are low axial mixing and a relatively small increase in axial mixing with increase in column diameter. The pulsation causes the light liquid to be dispersed into the heavy phase on the upward stroke and the heavy phase to jet into the light phase on the downward stroke. Such columns have no moving parts, and found almost exclusive use in the processing of highly corrosive radioactive liquids.

Pulse Extractors