Solvents & Solvent Drying

What is a Solution ?

Solute Solvent Solution

Sugar Water Solution

Example:

SOLUTION

What is a Solvent?• The liquid in which a solute is dissolved to form a

solution.• The term “solvents” refers to liquid organic

chemicals used to dissolve solid materials. • A solvent is a substance that dissolves a solute,

resulting in a solution.• A solvent is usually a liquid but can also be a

solid or a gas. • The maximum quantity of solute that can

dissolve in a specific volume of solvent varies with temperature.

Liquid-liquid separation is a useful method to separate components (compounds) of a mixture

Let's see an example.

Suppose that you have a mixture of sugar in vegetable oil (it tastes sweet!) and you want to separate the sugar from the oil.

You observe that the sugar particles are too tiny to filter and you suspect that the sugar is partially dissolved in the vegetable oil.

What will you do?

How about shaking the mixture with water

Will it separate the sugar from the oil? Sugar is much more soluble in water than in vegetable oil, and, as you know, water is immiscible (=not soluble) with oil.

Did you see the result? The water phase is the bottom layer and the oil phase is the top layer, because water is denser than oil.

*You have not shaken the mixture yet, so sugar is still in the oil phase.

By shaking the layers (phases) well, you increase the contact area between the two phases. The sugar will move to the phase in which it is most soluble: the water layer

Now the water phase tastes sweet,because the sugar is moved to the water phase upon shaking.**You extracted sugar from the oil with water.**In this example, water was the extraction solvent ;the original oil-sugar mixture was the solution to be extracted; and sugar was the compound extracted from one phase to another. Separating the two layers accomplishes the separation of the sugar from the vegetable oil

Why only water ?

Polar solvents have large dipole moments (aka “partial charges”); they contain bonds between atoms with very different electro negativities, such as oxygen and hydrogen.

Non polar solvents contain bonds between atoms with similar electro negativities, such as carbon and hydrogen (think hydrocarbons, such as gasoline).

Bonds between atoms with similar electro negativities will lack partial charges; it’s this absence of charge which makes these molecules “non-polar”.

Polar & Non-Polar Solvents

Molecules with a hydroxyl group (-O-H) are generally soluble in water.

Other substances, like fats, are non-polar . They will not dissolve in water.

These substances are neutral and there is no excess charge at one end of the molecule. Examples are, benzene (C6H6), and carbon tetra-chloride (CCl4). Benzene will dissolve in carbon tetra-chloride.

Molecules that are hydrocarbons (mostly C and H) will dissolve in other hydrocarbons.

A basic rule is: Like dissolves in Like .

This means that, in general, polar substances will dissolve in other polar substances, and that non-polar substances will dissolve in other non-polar substances.

Polar substances will not dissolve non-polar substances.

A solvent is a liquid that serves as the medium for a reaction.

It can serve two major purposes:

(Non-participatory) to dissolve the reactants.

Remember “like dissolves like” ?

Polar solvents are best for dissolving polar reactants (such as ions); nonpolar solvents are best for dissolving nonpolar reactants (such as hydrocarbons).

Participatory: as a source of acid (proton), base (removing protons), or as a nucleophile (donating a lone pair of electrons).

Remember water & oil example ?

• Think of how oil and water don't mix. Water is polar and oil is non-polar.

• A polar molecule has poles, basically some areas are charged negatively and some are charged positively.

• A soap is a salt of a fatty acid, it has a polar end that "likes" water and a long non-polar chain that "likes" oil.

Uses of Solvents

As a Solvent• Dissolution• Extraction• Degreasing• Inks, dyes, paints,

coatings• Dilution, dispersal• Dry cleaning

As Something Else• Fuels• Feedstocks• Drugs of abuse• Beverages• Antifreeze• Explosives• Pollutants

Removing water from Solvents

There are various ways of removing water and other impurities from a solution. This can become a major task once the used reagents are alsosensitive towards water.

The drying agents commonly used in the organic laboratories are the anhydrous forms of calcium chloride (CaCl2), sodium sulfate (Na2SO4) Calcium sulfate (CaSO4 and magnesium sulfate (MgSO4).

Pore sizes in adsorbents may be distributed throughout the solid. Pore sizes are classified generally into 3 ranges:

macropores have "diamaters" in excess of 50-nm, mesopores (also known as transitional pores) have "diameters" in the range 2 - 50-nm, and micropores have "diameters" which are smaller than 2-nm.

Types

3A Molecular Sieves : 3A (pore size 3 ): Adsorbs NH3, H2O, (not C2H6), good for drying polar liquids 4A Molecular Sieves : 4A (pore size 4 ): Adsorbs H2O, CO2, SO2, H2S, C2H4, C2H6, C3H6, ethanol. Will not adsorb C3H8 and higher hydrocarbons. Good for drying nonpolar liquids and gases. 5A Molecular Sieves : 5A (pore size 5 ): Adsorbs normal (linear) hydrocarbons to n-C4H10, alcohols to C4H9OH, mercaptans to C4H9SH. Will not adsorb isocompounds or ring structures with more than four carbon atoms. 10X Molecular Sieves : 10x (pore size 8 ): Adsorbs branched hydrocarbons and aromatics. Used for drying gases. 13X Molecular Sieves : 13x (pore size 10 ): Adsorbs di-n-butylamine (not tri-n-butylamine).

Why is acetone, instead of water, used to extract chlorophyll and other green leaf pigments?

The pigments and the rest of the leave stuff will just stick together in water. Acetone is an organic solvent that can separate the aqueous impurities from the pigments in leaves.

Applications

Drying of Acetone. Acetone has been dried with a widespectrum of desiccants. Thus, alumina, calcium chloride,phosphorus pentoxide, and 4A molecular sieves, as well ascalcium and (anhydrous) cupric sulfate, have all been used.

Ethanol is used in perfumes & after shaves.

Acetone is used in Chlorophyll Extraction because it is an organic solvent.

It can split the aqueous impurity from the pigment in leaves unlike when water is used.

Isopropyl Alcohol used as a solvent in bulk drug API mfg.

Applications

Solvents in Rubber & Polymers

Making better products...

Solvents are used in many different processes within the polymer manufacturing industry, e.g. in the production of rubber or tyres and in polyolefin's manufacturing.

Dearomatised aliphatic hydrocarbon solvents are applied in the production of tyres to ‘glue’ together the many different pieces and layers of rubber, ensuring they are safe and durable. Methyl isobutyl ketone (MIBK) is used as a raw material in the manufacture of rubber antiozonants.

In the shoe industry, a major breakthrough occurred in 1928 when polychloroprene was first introduced.

The first, simple formulation is still manufactured and is usedworldwide because the glue can be easily prepared by simply making a solution of the polymer.

This gives a product with good adhesion to various substrates.

Many new products are available today as potential replacements. Hot melt adhesives can be used in some applications but they still require solvents for cleaning, degreasing, and swelling.

Water-based adhesives are the most likely replacement product.

REPRESENTATIVE TYPES OF SOLVENTS BEING RECOVERED

AcetatesAcetoneBenzene(MIBK)ChloroformCyclohexanoneEthanolEtherFreons

GasolineHeptaneHexaneIsopropyl Alcohol (IPA)MethanolMethyl Ethyl Ketone (MEK)Methyl Isobutyl KetoneMethylene Chloride

Mineral SpiritsPentanePerchloroethylenePropanolsTetrahydrofuran (THF)TolueneTrichloroethaneTrichloroethyleneXylene

MOLECULAR SIEVES FOR SOLVENT DRYING:

This market includes the drying of solvents used for cleaning and/or purification of a material. This type of drying is found in chemical plants, refineries, manufacturing plants, etc. where a material is rinsed by a hydrocarbon stream, then recycled, dried, and returned to cleanse the material.

For example, an acetone liquid stream is used to wash a thread used for making tea bags

TO DRY USE ONE OF THE FOLLOWING DRYING AGENTS

Alcohols Anhydrous forms of potassium carbonate; anhydrous magnesium or calcium sulphate; quicklime.

Alkyl halidesAryl halides

Anhydrous calcium chloride; anhydrous forms of sodium sulphate, magnesium sulphate, or calcium sulphate; sodium pentoxide.

Saturated andAromatic hydrocarbons

Anhydrous calcium chloride or sulphate; metallic sodium; phosphorus pentoxide.

Aldehydes Anhydrous sodium sulphate; anhydrous magnesium or calcium sulphate.

Ketones Anhydrous sodium sulphate; anhydrous magnesium or calcium sulphate; anhydrous potassium carbonate.

Organic bases(amines) Solid potassium or sodium hydroxide; quicklime; barium oxide.

Organic acids Anhydrous sodium sulphate; anhydrous magnesium or calcium sulphate.

Solvent drying guide

Solvent BP Molecular SieveAcetone 56 3AAcetonitrile 82 3A / 4A SILICABenzene 80 4A / 5ACTC 77 4AChloroform 62 4ACyclohexane 81 4ADichloromethane 40 4A / 3ADiethyl ether 34 4ADMF 153 4ADMSO 189 3A1,4 Dioxane 101 4AEthanol 79 3AEthyl acetate 77 4AHexane 69 4AMethanol 65 4A2 propanol 82 3APyridine 116 4ATHF 66 4A / 3ATolune 111 4A / 5AXylene 137 4A

Solvent drying using Molecular Sieves