Miscellaneous Refinery Processes
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Miscellaneous refinery processes Lubricant base stock and wax processes Lubricating oils and waxes are refined from var ious fractions of atmospheric and vacuum distillation. With the invention of vacuum distillation, it was discovered that the waxy residuum made a better lubricant than any of the animal fats that we re then in use, which was the beginning of modern hydrocarbon lubricant refining technology, whose primary objective is to remove undesirable products, such as asphalts, sulphonated aromatics and paraffinic and iso-paraffinic waxes from the residual fractions in order to produce high-quality lubricants. This is done by a series of processes including de- asphalting, solvent extraction and separation and treatment processes such as dewaxing and hydrofinishing. (See figure 18) Figure 18. Lubricating oil & wax manufacturing process OIL10F15 In extraction processing, reduced c rude from the vacuum unit is propane de-asphalted and combined with straight-run lubricating-oil feedstock, preheated and solvent extracted to produce a feedstock called raffinate. In a typical extraction process which uses phenol as the solvent, the feedstock is mixed with phenol in the treating section at temperatures below 204 °C. Phenol is then se parated from the raffinate and recycled. The raffinate may then be subjected to another extraction proc ess which uses furfural to separate aromatic compounds from non-aromatic hydrocarbons, producing a lighter- coloured raffinate with improved viscosity index and oxidation and thermal stability. Dewaxed raffinate may also be subject t o further processing to improve the qualities of the base stock. Clay adsorbents are used to remove dark-coloured, unstable molecules from lubricating-oil base stocks. An alternate process, lube hydrofinishing, passes hot dewaxed raffinate and hydrogen through a catalyst that slightly changes the molecular structure, resulting in a lighter-coloured oil with improved characteristics. The treated lube oil base stocks are then mixed and/or compounded with additives to meet the required physical and chemical characte ristics of motor oils, industrial lubricants and metal- working oils. The two distinct types of wax der ived from crude oil are paraffin wax, produced from distillate stocks, and microcrystalline wax, manufactured from residual stocks. Raffinate from the extract ion unit contains a considerable amount of wax, which can be r emoved by solvent extraction and crystallization. The raffinate is mixed with a solvent, such as propane, methyl ethyl ketone (MEK) and toluene mixture
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Transcript of Miscellaneous Refinery Processes
8/11/2019 Miscellaneous Refinery Processes
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Miscellaneous refinery processes
Lubricant base stock and wax processes
Lubricating oils and waxes are refined from various fractions of atmospheric and vacuum distillation.With the invention of vacuum distillation, it was discovered that the waxy residuum made a betterlubricant than any of the animal fats that were then in use, which was the beginning of modernhydrocarbon lubricant refining technology, whose primary objective is to remove undesirable products,such as asphalts, sulphonated aromatics and paraffinic and iso-paraffinic waxes from the residualfractions in order to produce high-quality lubricants. This is done by a series of processes including de-asphalting, solvent extraction and separation and treatment processes such as dewaxing andhydrofinishing. (See figure 18)
Figure 18. Lubricating oil & wax manufacturing process
OIL10F15
In extraction processing, reduced crude from the vacuum unit is propane de-asphalted and combinedwith straight-run lubricating-oil feedstock, preheated and solvent extracted to produce a feedstockcalled raffinate. In a typical extraction process which uses phenol as the solvent, the feedstock is mixedwith phenol in the treating section at temperatures below 204 °C. Phenol is then separated from theraffinate and recycled. The raffinate may then be subjected to another extraction process which usesfurfural to separate aromatic compounds from non-aromatic hydrocarbons, producing a lighter-coloured raffinate with improved viscosity index and oxidation and thermal stability.
Dewaxed raffinate may also be subject to further processing to improve the qualities of the base stock.Clay adsorbents are used to remove dark-coloured, unstable molecules from lubricating-oil base stocks.An alternate process, lube hydrofinishing, passes hot dewaxed raffinate and hydrogen through a catalystthat slightly changes the molecular structure, resulting in a lighter-coloured oil with improvedcharacteristics. The treated lube oil base stocks are then mixed and/or compounded with additives to
meet the required physical and chemical characteristics of motor oils, industrial lubricants and metal-working oils.
The two distinct types of wax derived from crude oil are paraffin wax, produced from distillate stocks,and microcrystalline wax, manufactured from residual stocks. Raffinate from the extraction unitcontains a considerable amount of wax, which can be removed by solvent extraction and crystallization.The raffinate is mixed with a solvent, such as propane, methyl ethyl ketone (MEK) and toluene mixture
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or methyl isobutyl ketone (MIBK), and precooled in heat exchangers. The crystallization temperature isattained by the evaporation of the propane in the chiller and filter feed tanks. The wax is continuouslyremoved by filters and cold solvent washed to recover retained oil. The solvent is recovered from thedewaxed raffinate by flashing and steam stripping, and recycled.
The wax is heated with hot solvent, chilled, filtered and given a final wash to remove all traces of oil.Before the wax is used, it may be hydro-finished to improve its odour and eliminate all traces ofaromatics so the wax can be used in food processing. The dewaxed raffinate, which contains smallamounts of paraffins, naphthenes and some aromatics, may be further processed for use as lubricating-oil base stocks.
Control of treater temperature is important to prevent corrosion from phenol. Wax can clog sewer or oildrainage systems and interfere with waste water treatment. The potential exists for exposure to processsolvents such as phenol, propane, a methyl ethyl ketone and toluene mixture or methyl isobutyl ketone.Inhalation of hydrocarbon gases and vapours, aromatic naphtha containing benzene, hydrogen sulphideand hydrogen-rich process gas is a hazard.
Asphalt processing
After primary distillation operations, asphalt is a portion of residual matter which requires furtherprocessing to impart characteristics required by its final use. Asphalt for roofing materials is produced byair blowing. Residual is heated in a pipe still almost up to its flashpoint and charged to a blowing towerwhere hot air is injected for a predetermined period of time. The dehydrogen ation of the asphalt formshydrogen sulphide, and the oxidation creates sulphur dioxide. Steam is used to blanket the top of thetower to entrain the contaminants, and is passed through a scrubber to condense the hydrocarbons.
Vacuum distillation is generally used to produce road tar asphalt. The residual is heated and charged toa column where vacuum is applied to prevent cracking.
Condensed steam from the various asphalt processes will contain trace amounts of hydrocarbons. Any
disruption of the vacuum can result in the entry of atmospheric air and subsequent fire. In asphaltproduction, raising the temperature of the vacuum tower bottom to improve efficiency can generatemethane by thermal cracking. This creates vapours in asphalt storage tanks which are in the flammablerange, but not detectable by flash testing. Air blowing can create some polynuclear aromatics (i.e.,PAHs). Condensed steam from the air blowing asphalt process may also contain various contaminants.
