Introduction to Waxes

History:
Wax research was established as a scientific discipline in 1823. It became part of the new research area of soaps, oils, fats, and waxes. The real breakthrough of wax as an important raw material, in terms of quantity as well, occurred at the beginning of the Industrial Revolution. Ozocerite (fossil wax) was mined and refined to give ceresin (1875), Montan wax was obtained from Eocene lignite (1897), and paraffin waxes were obtained from crude petroleum.

In 1935 the first fully synthetic waxes were produced by the Fischer – Tropsch process. Polyethylene wax has been synthesized by the high pressure process since 1939, and became available by the low-pressure Ziegler process after 1953. On a laboratory scale polyolefin waxes can also be synthesized by using modern metallocene catalysts.

Composition:
Typically waxes do not consist of a single chemical compound, but are often very complex mixtures. Being oligomers or polymers in many cases, the components differ in their molar mass, molar mass distribution, or in the degree of side-chain branching. Functional groups (e.g., carboxyl, alcohol, ester, keto, and amide groups) can be detected in waxes, sometimes several different groups.

The academic definition still quoted in chemistry text books — that waxes are esters of long-chain carboxylic acids with long-chain alcohols — is no longer useful. It applies fairly well only to some classical waxes, such as beeswax; others (e.g., petroleum waxes) do not fall in this category.

Classification:

Typical Properties:


A drop point (mp) >40 °C
Their melt viscosity must not exceed 10 000 mPa · s at 10 °C above the drop point
They should be polishable under slight pressure and have a strongly temperature-dependent consistency and solubility
At 20 °C they must be kneadable or hard to brittle, coarse to finely crystalline, transparent to opaque, but not glassy, or highly viscous or liquid
Above 40 °C they should melt without decomposition
Above the mp the viscosity should exhibit a strongly negative temperature dependence and the liquid should not tend to stringiness
Waxes should normally melt between ca. 50 and 90 °C (in exceptional cases up to 200 °C)
Waxes generally burn with a sooty flame after ignition
Waxes can form pastes or gels and are poor conductors of heat and electricity (i.e. they are thermal and electrical insulators).
 

Uses:
 

Introduction to Petroleum Waxes:

The quantity of waxes obtained from crude petroleum has increased continuously for two reasons:

(1) the demand for lubricating oils with low pour points and

(2) the large proportion of paraffinic crudes in total crude oil production that have to be dewaxed for the production of lubricating oils

Depending on their natural occurrence and their crystalline nature, petroleum waxes are divided into:

1. Macrocrystalline waxes (paraffin waxes)

2. Microcrystalline waxes (micro waxes)

Classification of waxes from crude petroleum
 

Origin	light, medium, heavy lubricating oil distillates		residues from vacuum distillation		crude oil
Group	(macrocrystalline) paraffin waxes		microcrystalline waxes (microwaxes)		settling waxes
Subgroup	Paraffin waxes	Intermediate waxes	residue waxes		pipe waxes
					tank bottom waxes
Crude products	crude waxes (slack waxes)		petrolatum		raw waxes
Deoiled and refined products	scale waxes, deoiled slack waxes, filtered (decolorized) waxes, fully refined paraffin waxes		plastic microwaxes, hard microwaxes
Side products from deoiling	soft waxes		soft petrolatum (microwax slacks)

Macrocrystalline Waxes (Paraffin Waxes)

Paraffin waxes are obtained from light and middle lubricating oil cuts of vacuum distillation. Paraffin waxes also include waxes from heavy lubricating oil distillates, which are intermediates between macrocrystalline and microcrystalline waxes with regard to structure and composition (intermediate waxes).

Chemical Composition: Paraffin waxes consist predominantly of mixtures of straight-chain alkanes in a typical distribution of the homologous series whose molar masses depend on the boiling range of the lubricating oil distillate from which they are obtained. Long-chain, weakly branched isoalkanes are present in a much lower proportion, along with a very small fraction of monocyclic alkanes.

According to the European Wax Federation (EWF), paraffin waxes have a C-number distribution of n-alkanes from 18 to 45 and a total content of iso- and cycloalkanes of 0 – 40 %. Typical data for the intermediate waxes are an n-alkane C-number of 22 to 60 and a total content of iso- and cycloparaffins of 30 – 60 %.

Physical Properties: Paraffin waxes are insoluble in water and sparingly soluble in low molar mass aliphatic alcohols and ethers. They are more soluble in ketones, chlorohydrocarbons, petroleum spirit, solvent naphtha, benzene, toluene, xylene, and higher aromatics, especially at elevated temperature. The solubility decreases markedly with increasing molar mass (higher melting point) of the waxes.

Chemical Properties: Paraffin waxes are extremely unreactive under normal conditions. Oxidation reactions occur only at elevated temperatures (e.g., on storage and processing above 100 °C), particularly in the presence of oxygen and catalytically active metals. These reactions can be recognized from the burnt odor produced and the yellow to brown coloration of the waxes. Nevertheless, under certain thermally and catalytically controlled conditions, these waxes can undergo chemical reactions such as chlorination, oxidation, dehydrogenation, and cracking, of which chlorination and cracking are important in industry.

Division into Product Classes:

Depending on the degree of refining, paraffin waxes are divided into the following product classes:

1. Crude waxes, also known as slack waxes

2. Slack wax raffinates (scale waxes)

3. Deoiled slack waxes

4. Soft waxes

5. Semi-refined waxes

6. Filtered (decolorized) waxes

7. Fully refined waxes



Microcrystalline Waxes (Microwaxes)

Microcrystalline waxes originate from vacuum residues and from the sediments of paraffinic crude oil (settling waxes). Waxes that are liquid at room temperature are mostly contained in diesel oil or gas oil fractions and can be isolated from them.

Chemical Composition: Like paraffin waxes, microcrystalline waxes consist of a mixture of saturated hydrocarbons that are predominantly solid at room temperature, such as n- and isoalkanes, naphthenes, and alkyl- and naphthenes-substituted aromatics. Unlike paraffin waxes, isoparaffins and naphthenic compounds predominate here. The microcrystalline structure can be explained by the presence of strongly branched isoparaffins and naphthenes, which inhibit crystallization.

Physical Properties: Microcrystalline waxes are insoluble in water and most organic solvents at room temperature. They are moderately to readily soluble in solvents such as chlorohydrocarbons, benzene, toluene, xylene, solvent naphtha, and turpentine oil, especially at elevated temperature. Solubility decreases markedly as molar mass increases. Solvents and oils are retained very strongly by microcrystalline waxes and therefore evaporate very slowly. The quality of some consumer products, such as petroleum jellies or floor and shoe polish, is determined by this retention capacity of microwaxes.

Chemical Properties: Microwaxes are more reactive than paraffin waxes because of the higher concentration of complex branched hydrocarbons with tertiary and quaternary carbon atoms. These C–C bonds are not very thermally stable (i.e. the waxes darken and resinify) on prolonged heating. In addition, they form black tar like substances on contact with aggressive chemicals such as concentrated sulfuric acid or antimony pentachloride.

The reaction of microwaxes with oxygen at elevated temperature and in the presence of catalytically acting heavy-metal soaps is used for the production of oxidized microwaxes.

Division into Product Classes:

Depending on the degree of refining, microwaxes are divided into the following classes:

1. Bright stock slack waxes (petrolatum)

2. Plastic microwaxes

3. Hard microwaxes

More on Base Oils:

Mineral base oils are generally prepared from crude oils by Distillation, to adjust the viscosity and flash point; then refining, to improve viscosity temperature characteristic; followed by dewaxing, to improve the low temperature properties; and finally hydrofinishing; to remove undesirable impurities from petroleum distillates (such as Sulfur and Nitrogen compound and Olefins).

Base Stocks, obtained after above listed operations are called Solvent Neutral Base Oils (SN) which are distinguished with numbers according to their approximate SUS viscosity at 40 C°, such as SN90, SN150, SN350,SN500 etc.

In modernized refinery plant lube-cut obtained from domestic petroleum oil refinery, is used to produce virgin mineral base oils.

In addition to refining the lube-cut to produce Base oils, high quality low oil paraffin waxes are also produced by deoiling the wax.