Waxes are organic substances that tend to be solid at ambient temperature and become free-flowing at elevated temperatures. While the chemical composition of waxes may be complex, normal alkanes are present. Also, the molecular weight distributions of waxes tend to be wide. The main commercial source of wax is crude oil, but not all crude oil refiners produce wax. Mineral waxes can also be produced from lignite. Plants, animals and even insects produce materials sold in commerce as wax.
Paraffin and microcrystalline waxes are derived from petroleum. They are easy to recover and offer a wide range of physical properties that can often be tailored by refining processes. Most producers offer two distinct types of petroleum waxes: paraffins, which are distinguished by large, well formed crystals; and microcrystallines, which are higher melting waxes with small, irregular crystals. Microcrystalline wax contains substantial proportions of branched and cyclic saturated hydrocarbons in addition to normal alkanes.
Some producers also sell “intermediate” wax, in which the boiling range is cut where the transition in crystal size and structure occur. Petroleum wax producers also characterize wax by degree of refinement; fully refined paraffin has oil content generally less than 0.5%, and fully-refined micro-crystalline less than 3%. Slack wax, precursors to the fully refined versions in either case, tend to have oil content above 3%, and as high as 35% by weight. Paraffin wax produced from petroleum is essentially a pure mixture of normal and iso-alkanes without the esters, acids, etc. found in the animal and vegetable-based waxes.
Synthetic waxes have entered the wax market in the recent past. Polyethylene waxes are low molecular weight polyethylenes (less than 10,000 Mn) having wax-like properties made by either high-pressure or low-pressure (Zeigler-type catalyst) polymerization. All such waxes have the same basic structure, but the various production processes yield products with distinctly different properties, and these have a major impact on the use of products. Products from one manufacturer may satisfy one particular application, while product from a similar process will not work well.
Fischer-Tropsch (FT) wax is a synthetic wax produced by the polymerization of carbon monoxide under high pressure, a technology used in the emerging natural gas to liquid (GTL) projects. The hydrocarbon product of FT reaction is distilled to separate the mix into fuels products and waxes with melting points ranging from about 45-106° C. It has been estimated that recent synthetic wax consumption in North America was 420 million lbs., of which FT wax accounts for about 195 million lbs.
Alpha olefin waxes are synthetically derived from ethylene via a Ziegler-Natta catalyst. The process results in a Schulz-Flory distribution of alpha olefins ranging from C4 through C30+. These are distilled into the individual carbon fractions or carbon fraction blends. Due to the high melting points of the waxes, C20 and higher carbon numbers are fractionated into blends. Because of the linear double bond present in normal alpha olefins, these waxes can be functionalized or reacted to create other derivatives. They can also be used for their physical properties such as hardness and melting point. End uses for alpha olefin waxes include lube oil additives, PVC lubricants, candles, oilfield chemicals and personal care applications.
Montan wax is derived by solvent extraction of lignite. The earliest production of montan wax on a commercial scale was in Germany during the latter half of the nineteenth century. Germany continues to lead the world in production of montan wax; although some montan wax is produced in the United States from the Ione lignite bed in California. The composition of montan wax varies geographically with production, but includes varying amounts of wax, resin and asphalt. Other mineral waxes include peat waxes, ozokerite and ceresin waxes.
Congealing point is a wax property that is of interest to many petroleum wax consumers. The congealing point represents the temperature at which a sample being cooled develops a “set” or resistance to flow. At that temperature, the wax may be at or close to the solid state, or it may be semisolid and quite unctuous, depending on the composition of the wax or petrolatum being tested. In the case of petrolatum, the congealing property is associated with the formation of a gel structure as the sample cools.
Historically, the congealing point of waxes has been determined by manually conducting standardized test procedures, such as ASTM Test Method D938, Standard Test Method for Congealing Point of Petroleum Waxes, Including Petrolatum, or TAPPI Test Method T-662, Congealing Point of Petroleum Waxes Including Petrolatum. As is known by those skilled in the art, ASTM Test Method D938 is an alternative to ASTM Test Method D127. The results obtained using ASTM Test Method D938 are usually lower than the results obtained by Test Method D127, the amount of the deviation varying with the nature of the petroleum wax.
ASTM Test Method D938 and TAPPI Test Method T-662 are manual test methods that require an operator to be exposed to multiple risks. These risks include the handling of hot glassware for an extended period, often three to eight consecutive minutes, depending on the sample; the use of a liquid-in-glass thermometer for an extended period; and the possibility of incurring a repetitive stress injury (RSI) risk, if multiple samples are to be tested. This is due to the fact that the operator must constantly reset his or her wrists to rotate an Erlenmeyer flask.
Therefore, what is needed is an automated test apparatus for determining the congealing point of a sample that reduces exposure to hot glassware, liquid-in-glass thermometers, and RSI risks, while yielding an acceptable level of test precision.