The function of the de-waxing unit is to produce Paraffin and Waxes from different feed stocks in blocked out operation employing MIBK as the de-oiling solvent.
Lube Oil De-Waxing Process Overview
Normally, the two designed feed stocks used for the unit are: MVGO and HVGO obtained from Vacuum Unit.
Wax re-crystallization, such as wax sweating, separates wax into fractions and the process makes use of the different solubility of the wax fractions in a solvent such as ketone.
More generally, three main technologies are used in modern refinery technology:
(1) Solvent de-waxing in which the feedstock is mixed with one or more solvents, then the mixture is cooled down to allow the formation of wax crystals, & the solid phase is separated from the liquid phase by filtration.
(2) Urea de-waxing, in which urea forms adducts with straight-chain paraffin that was separated by filtration from the de-waxed oil.
(3) Catalytic de-waxing, in which straight-chain paraffin hydrocarbons are selectively cracked on zeolite-type catalysts, and the lower boiling reaction products are separated from the de-waxed lubricating oil by fractionation.
The solvent de-waxing plant using, for instance, Methyl Iso-butyl Ketone (MIBK) has its solvent recycled in the process. Typical solvent dewaxing plant shall have essentially three main units: De-waxing/de-oiling unit; Hydro-finishing Unit; and Washing Unit. The De-waxing / De-oiling Unit typically consists of six sections, Chilling Section; Filtration Section; De-waxed Oil Solvent Recovery Section; Slack Wax Solvent Recovery Section; Refrigeration Section; and Inert Gas System.
Paraffin is the common name for the hydrocarbons with general formula CnH2n+2 (Alkanes). It is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between 47 C to 64 C and having a density of around 0.9 g/cm³. It is insoluble in water, but soluble in ether, benzene and certain esters. Paraffin is unaffected by most common chemical reagents, but burns readily. It is an excellent electrical insulator, with an electrical resistivity of between 1013 and 1017 ohm meter.
Paraffin wax (C25H54) is an excellent material to store heat, having a specific heat capacity of 2.14-2.19 J g-1K-1 and a heat of fusion of 200-220 J g-1.
This property is exploited in modified dry wall for home building material. It is infused in the dry wall during manufacture so that, when installed, it melts during the day, absorbing heat, and solidifies again at night, releasing the heat. Paraffin wax is used in making Candles, Textiles, Cosmetic, Yarns, Plastic, Paper, Rope, Pencil, Waterproofing, Packaging and even in some food stuffs.
Semi Microcrystalline Waxes are derived from the refining of heavy distillates from lubricant oil production by de-oiling petrolatum (petroleum jelly) as a part of the petroleum refining process. Depending on the end use and desired specification, the product then may have its odour removed and colour removed. This is usually done by means of a filtration method or by hydro-treating the wax material.
In contrast to the more familiar paraffin wax which contains mostly un-branched alkanes, microcrystalline wax contains a higher percentage of iso-paraffinic (branched) hydrocarbons and naphthenic hydrocarbons. It is characterized by the fineness of its crystals in contrast to the large crystals of paraffin wax. It is generally darker, more viscous, denser, tackier, and more elastic than paraffin wax and has a higher molecular weight and melting point. The elastic and adhesive characteristics of micro crystalline waxes are related to the non-straight chain components which they contain. Typical semi microcrystalline wax crystal structure is small and thin, making them more flexible than paraffin wax. It is commonly used in cosmetic formulations.
Microcrystalline waxes can generally be put in two categories: “Laminating Grades” and “Hardening Grades”. The laminating grades typically have a melting point of 140-175ºF and needle penetration of 25 or above. The hardening grades ranges from about 175-200ºF and have a needle penetration of 25 or below.
Colour in both grades can range from brown to white, depending on the degree of processing done at the refinery level.
Distillate leaving the vacuum distillation unit contains such significant quantities of wax that they are solid at room temperature. Removal of the wax from the lubricating base oil is necessary for the base stocks to have the required low temperature properties. The solvent dewaxing process uses a mixture of MEK and toluene or other solvents such as MIBK to aid in the crystallization and filtration of wax from the lube oil stocks.
Again for bitumen process and lube oil production plants the targeting step include drawing a boundary around the facility.
Heat in and out, directly, and/or indirectly through steam consumption and/or generation, water production and/or generation, power consumption and/or generation are among the plant’s boundary are all identified.
Again heat integration between feed and product is common in such facilities; integration between reaction and separation section is highly recommended to achieve lower energy consummation targets. Complete pinch technology application for such plants will be included in later versions of this manual.