Glossary of Key Wax Terms
Glossary of Key Wax Terms
Additive: a substance added to petroleum products to impart some desirable property, e.g. polymer may be added to a petroleum wax to increase tackiness, or food grade butylated hydroxytoluene added to prevent oxidation in storage.
Alkanes: hydrocarbon having the general Formula Cnttzn+z, also called a paraffin.
Aromatics: hydrocarbons with an unsaturated ring structure, e.g. benzene.
ASTM: American Society for Testing Materials, an organization which sets standards for the testing of industrial products.
Asphaltenes: one of the principal components of asphalt, the black or brown solid material precipitated from asphalt with normal pentane. It is an arbitrary fraction defined by the method of analysis.
Base Oil: a finished petroleum lubricant stock that when blended with other materials (additives) produces special purpose products such as engine oils.
Blending: mixing two or more base stock components to achieve targeted specifications. "Blending" usually refers to mixing homologous materials, i.e. two base oils or two petroleum waxes; "Compounding" refers to mixing base products with additives.
Catalytic Dewaxing: a catalytic hydrocracking process that uses molecular sieve catalysts to selectively hydrocrack waxes present in a feedstock into lighter hydrocarbon fractions.
Ceresin: an almost white wax produced by purification of ozokerite; a native mineral wax used in the manufacture of candles, shoe polishes, electrical insulation and floor waxes. Also known as ceresin wax, cerin, cerosin, purified ozokerite.
Clay: granular or finely divided mineral materials used for treating petroleum. Clays used in petroleum processing include fuller's earth, bauxite, bentonite, and montmorillonite. Most common clay used in the decolorization of petroleum waxes is bauxite.
Cloud Point: the temperature at which the first signs of wax precipitation appear in an oil.
Color: the color of most waxes is measured only while molten, because occluded air and surface finish can cause the color of solid samples of the same wax to vary significantly. Although some commercial standards for particular waxes, e.g. carnauba, are based on the color of the solid wax, the two most widely used color standards for waxes are ASTM D1500, used to measure dark-brown to off-white color, and ASTM D156, used to measure off-white to pure white waxes.
Compounding: mixing additives with oils, particularly lubricating oils, to impart oxidation resistance, rust resistance, detergency, or other desirable characteristics.
Crystallization: in dewaxing operations, formation of a solid phase (wax), prior to separation by filtration.
Deoiling: the separation process used to refine slack wax into finished petroleum waxes. The predominant process operates by chilling a mixture of feed and solvent to crystallize the wax, then separating the wax from the oil and solvent mix by filter or centrifuge. Solvent deoiling may be conducted as an integral part of a dewaxing/deoiling plant or operate as an independent plant. Alternate processes for deoiling include "sweating" the oil from the wax and fractional crystallization.
Dewaxing: the separation process used to refine waxy gas oils into wax-free oil. Solvent dewaxing, in which a mixture of feed and solvent is chilled to crystallize the waxy portion for removal by filter or centrifuge, produces low-pour lube base stocks and slack wax. The slack wax may be deoiled to reduce oil content and produce fully-refined wax. Alternate technologies for dewaxing include wax hydroisomerization, in which wax molecules are branched in a catalytic reaction and converted into high VI lubricants, and catalytic dewaxing, in which wax molecules are destroyed and become lighter, fuels products.
Differential Scanning Calorimetry (DSC): a test widely used to characterize waxes, DSC measure the amount of energy consumed under controlled heating and cooling rates. Curves of heat flow versus temperature provide insight into the thermal characteristics of wax, including crystalline transitions such as solid-to-solid, solid-to-liquid, and liquid-to-solid. Common values obtained from the curves include the initial and ending temperatures for heat flow and heat of fusion, measured in joules per gram. Also called Thermographic Analysis (TGA)
Gas Chromatography: another test used to characterize waxes, most useful for relatively simple structures of vegetable and insect waxes. GC has limited utility on petroleum and synthetic waxes. Good resolution can be had on products with one preponderant structure, e.g. paraffins with a preponderance of primary alkanes. Products such as microcrystalline wax, which contain several different branched isomers for each carbon number plus some cyclic compounds cannot be completely resolved, but useful information can still be had.
Gel Permeation Chromatography: method used to measure the molecular weight distribution for synthetic polyethylene waxes. Though it cannot match the resolution available through GC, GPC can discern molecular weights and molecular weight distribution for products too heavy for GC.
Hydrocracking: a catalytic refining process in which large molecules are broken into smaller molecules, conducted at high temperatures, high pressure and in the presence of hydrogen.
Hydrofining: a catalytic refining process, less severe than hydrocracking, in which impurities such as sulfur and nitrogen are removed from hydrocarbon streams by reaction with hydrogen.
Hydrofinishing: a mild hydrofining process used particularly to replace or supplement clay treating of lube oils and waxes.
Hydrogenation: chemical reaction with hydrogen. Most common reactions in a petroleum context is saturation of double bonds to convert olefins to paraffins, and aromatics to naphthenes, and the removal of sulfur, nitrogen and oxygen impurities from hetero-molecules.
Infrared Spectroscopy (IR): Infrared absorption curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxylic acids, alcohols and esters. The IR curves are typically used in combination with other analytical methods such as DSC or GS/GPC to characterize waxes.
Melt Point: the temperature at which a material changes phase from solid to liquid. Petroleum waxes usually do not melt at sharply defined temperatures because they are mixtures of hydrocarbons with different melting points. Paraffin waxes are relatively simple mixtures and can have narrower melting ranges than microcrystalline waxes and petrolatums which are more complex in composition and melting behavior. Paraffin waxes are usually marketed on the basis of melting point determined from the plateau in the cooling curve measured in ASTM D87. Other methods of melt point determination are available, depending on the composition of the wax. Drop melting point (ASTM D126) is used for amorphous waxes, e.g. microcrystallines, but is not reliable for higher viscosity synthetic wax, for which ring-and-ball softening point (ASTM D36) should be used. Open or closed capillary tubes are used to measure the melting point of many natural waxes. The congealing point (ASTM D938) is the temperature at which a melted wax ceases to flow, and is more consistent than melting points for some waxes.
Microcrystalline Wax: hydrocarbons of molecular weight higher than 450 and less than 800.
Naphthene: a type of hydrocarbon, characterized by saturated ring structures, e.g. cyclohexane, naphthalene, etc.
Naphthenic acids: organic acids occurring naturally in petroleum.
Nuclear Magnetic Resonance Analysis (NMR): used in the polymer industry to measure properties such as amount and type of branching, polymerized ethylene oxide content and hydroxyl content. The same techniques are applicable to natural waxes, and are used for both characterization and quality control.
Oil Content: ASTM D721 measures the amount of residual oil left in petroleum wax after refining. Oil content is determined as that percentage of wax soluble in methyl ethyl ketone at -31.7°C. The method is applicable to waxes containing not more than 15% oil. A similar method, D3235 Test for Solvent Extractables in Petroleum Wax uses a 1:1 mixture of methyl ethyl ketone and toluene and may be used on waxes having levels of extractables as high as 50%.
Olefins: open chain hydrocarbons containing one or more double bonds, e.g. ethylene, propylene, etc.
Paraffins: open chain, saturated hydrocarbons, e.g. hexane, isooctane, etc.
Paraffin Wax: hydrocarbons of molecular weight higher than 350 and lower than 520 which are solid at room temperature.
Paraffin Wax - Fully Refined: paraffin wax that has been refined to a residual oil content no more than 1%, usually lower than 0.5% and generally meeting FDA food grade standards.
Penetration: the standard test for hardness of wax is ASTM D1321, which measures the depth in tenths of a millimeter that a needle of certain configuration, under a given weight, penetrates the surface of a wax at a given temperature. A series of penetrations measured at different temperatures, rather than a single temperature is preferred. Penetration of softer waxes and petrolatums may be measured using a cone rather than a needle.
Resins: any of a class of solid or semi-solid organic products of natural or synthetic origin with no definite melting point. Generally of higher molecular weight, most resins are polymers.
Saponification Number: ASTM D1387 reports the milligrams of potassium hydroxide which react with one gram of sample under elevated temperatures, and indicates the amount of free carboxylic acid plus any ester materials which may be saponified. Both the acid number and the saponification number are generally provided to give an indication of the free carboxylic acid and ester content of vegetable and insect waxes and synthetic waxes containing carboxylic acids or esters.
Scale Wax: a semi-refined paraffin wax with an oil content of 1 - 3%
Slack Wax: generic term for the mixture of wax and oil recovered in a dewaxing process; may contain 2 - 35% oil. Typical dispositions are to further process for finished wax, to process for fuels or to sell into certain end-use markets.
Total Acid Number: ASTM D1386 reports the milligrams of potassium hydroxide necessary to neutralize one gram of sample, and indicates the amount of free carboxylic acid present. The test is widely used for vegetable and insect waxes, and synthetic waxes containing carboxylic acid groups.
Viscosity: ASTM D88 is used to measure the time in seconds required for a specified quantity of wax at a specified temperature to flow by gravity through an orifice of specified dimensions. Viscosity is expressed as Saybolt Universal Seconds (SUS) at the temperature of the test. The SI unit for kinematic viscosity is mm2/s (centistokes).