In chemical separation terminology, the raffinate (from French ''raffiner'', to refine) is a product which has had a component or components removed. The product having the removed materials is referred to as the

extract An extract is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures, absolutes or in powder form. The aromatic principles of many spices, nuts ...

. For example, in solvent extraction, the raffinate is the liquid stream which remains after solutes from the original liquid are removed through contact with an

immiscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appli ...

liquid. In metallurgy, raffinating refers to a process in which impurities are removed from liquid material. In

pressure swing adsorption Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases (typically air) under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at ne ...

the raffinate refers to the gas which is not adsorbed during the high pressure stage. The species which is desorbed from the adsorbent at low pressure may be called the "extract" product.

Types

Raffinate-1 or C4R1

In naphtha cracking process, C4R1 refers to C4 residual obtained after separation of

1,3-butadiene 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two v ...

from C4 raffinate stream and which, mainly consists of

isobutylene Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula . It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value. Producti ...

40~50 wt% and ''cis''- or ''trans''-

2-butene But-2-ene is an acyclic alkene with four carbon atoms. It is the simplest alkene exhibiting ''cis''/''trans''-isomerism (also known as (''E''/''Z'')-isomerism); that is, it exists as two geometric isomers ''cis''-but-2-ene ((''Z'')-but-2-ene) and ...

30~35 wt%. Normally C4R1 is a side product in 1,3-butadiene plant and feed to ''tert''-butyl alcohol plant.

Raffinate-2 or C4R2

In naphtha cracking process, C4R2 refers to C4 residual obtained after separation of 1,3-butadiene and isobutylene from C4 raffinate stream and which mainly consists of ''cis''- or ''trans''-2-butene 50~60 wt%,

1-butene 1-Butene (or 1-Butylene) is the organic compound with the formula CH3CH2CH=CH2. It is a colorless gas that is easily condensed to give a colorless liquid. It is classified as a linear alpha-olefin. It is one of the isomers of butene (butylene). ...

10~15 wt%, and ''n''-

butane Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name but ...

~20 wt%. Normally C4R2 is a side product in ''tert''-butyl alcohol plant if C4R1 is used for feed.

Raffinate-3 or C4R3

In naphtha cracking process, C4R3 refers to C4 residual obtained after separation of 1,3-butadiene, isobutylene, and 1-butene from C4 raffinate stream which mainly consists of ''cis''- or ''trans''-2-butene, ''n''-butane, and unseparated 1-butene. Normally C4R3 is being process through a selective hydrogenation unit (SHU) and CDHydro deisobutenizer unit to produce isobutylene as a feed to ''tert''-butyl alcohol plant.

Raffinate-4 or C4R4

In naphtha cracking process, C4R4 refers to C4 residual obtained after separation of 1,3-butadiene, isobutylene, 1-butene, and ''cis''- or ''trans''-2-butene from C4 raffinate stream which mainly consists of ''n''-butane. Normally C4R4 is a side product in ''tert''-butyl alcohol plant if C4R3 is used for feed.

References