GASOLINE AND OTHER COMMON FUELS CHEMICAL PROPERTIES BASIC INFORMATION

Gasoline is a mixture of the lighter liquid hydrocarbons that distills within the range of 38 to 204 OC (100 to 400 OF). Commercial gasolines are a mixture of straight -run, cracked, reformed, and natural gasolines.

It is produced by the fractional distillation of petroleum; by condensation or adsorption from natural gas; by thermal or catalytic decomposition of petroleum or its fractions; by the hydrogenation of producer gas or by the polymerization of hydrocarbons of lower molecular weight Gasoline produced by the direct distillation of crude petroleum is known as straight-run gasoline.

It is usually distilled continuously in a bubble tower, which separates the gasoline from the other fractions of the oil having higher boiling points, such as kerosene, &el oil, lubricating oil, and grease. The range of temperatures in which gasoline boils and is distilled off is roughly between 38 and 205 OC (100 and 400 OF).

The yield of gasoline from this process varies from about 1 percent to about 50 percent, depending on the petroleum. Straight-run gasoline now makes up only a small part of gasoline production because of the superior merits of the various cracking processes. The flash point of gasoline is well below -17.8 OC (0 OF) at atmospheric pressure. In atmospheric burning smoke production normally occurs.

In some instances natural gas contains a percentage of natural gasoline that may be recovered by condensation or adsorption. The most common process for the extraction of natural gasoline includes passing the gas as it comes from the well through a series of towers containing a light oil called straw oil.

The oil absorbs the gasoline, which is then distilled off. Other processes involve adsorption of the gasoline on activated alumina, activated carbon, or silica gel. High-grade gasoline can be produced by a process known as hydrofining, that is, the hydrogenation of refined petroleum oils under high pressure in the presence of a catalyst such as molybdenum oxide.

Hydrofining not only converts oils of low value into gasoline of higher value but also at the same time purifies the gasoline chemically by removing undesirable elements such as sulfur. Producer gas, coal, and coal-tar distillates can also be hydrogenated to form gasoline.


Kerosene or sometimes referred to as Fuel Oil # 1 is a refined petroleum distillate. Kerosenes usually have flash points within the range of 37.8 OC to 54.4 OC (100 OF to 130 OF).

Therefore unless heated, kerosene will usually not produce ignitable mixtures over its surface. In atmospheric burning smoke production normally occurs. In some applications it is treated with sulfuric acid to reduce the content of aromatics, which burn with a smoky flame. It is commonly used as a fire and a solvent.


Diesel or sometimes referred to Fuel Oil #2 is the fraction of petroleum that distills after kerosene; which is in the family of gas oils. In atmospheric burning smoke production normally occurs. Several grades of diesel are produced depending on the intended service.

The combustion characteristics of diesel fbels are expressed in terms of a centane number, which is a measure of ignition delay. A short ignition delay, i.e., the time between injection and ignition is desirable for a smooth running engine.

GLYCEROL CHEMICAL PROPERTIES BASIC INFORMATION

WHAT ARE GLYCEROL?


Glycerol (glycerin, melting point: 18oC, boiling point: 290oC, density: 1.2620, flash point: 177oC) is a clear, nearly colorless liquid having a sweet taste but no odor.

Glycerol may be produced by a number of different methods, such as:

1. The saponification of glycerides (oils and fats) to produce soap.
2. The recovery of glycerin from the hydrolysis, or splitting, of fats and oils to produce fatty acids.
3. The chlorination and hydrolysis of propylene and other reactions from petrochemical hydrocarbons.

Natural glycerol is produced as a coproduct of the direct hydrolysis of triglycerides from natural fats and oils in large continuous reactors at elevated temperatures and pressures with a catalyst. Water flows countercurrent to the fatty acid and extracts glycerol from the fatty phase.

The sweet water from the hydrolyzer column contains about 12% glycerol. Evaporation of the sweet water from the hydrolyzer is a much easier operation than with evaporation of spent soap lye glycerin in the kettle process.

The high salt content of soap lye glycerin requires frequent soap removal from the evaporators. Hydrolyzer glycerin contains practically no salt and is readily concentrated.

The sweet water is fed to a triple-effect evaporator where the concentration is increased from 12% to 75 to 80% glycerol. After concentration of the sweet water to hydrolyzer crude, the crude is settled for 48 hours at elevated temperatures to reduce fatty impurities that could interfere with subsequent processing. Settled hydrolyzer crude contains approximately 78% glycerol and 22% water.

The settled crude is distilled under vacuum at approximately 200oC. A small amount of caustic is usually added to the still feed to saponify fatty impurities and reduce the possibility of codistillation with the glycerol.

The distilled glycerin is condensed in three stages at decreasing temperatures. The first stage yields the purest glycerin, usually 99% glycerol and lower-quality grades of glycerin are collected in the second and third condensers. Final purification of glycerin is accomplished by carbon bleaching, followed by filtration or ion exchange.

There are several synthetic methods for the manufacture of glycerol. One process involves chlorination of propylene at 510oC (950oF) to produce allyl chloride in seconds in amounts greater than 85 percent of theory (based on the propylene). Vinyl chloride, some disubstituted olefins, and some 1,2 and 1,3-dichloropropanes are also formed.

Treatment of the allyl chloride with hypochlorous acid at 38oC (100oF) produces glycerin dichlorohydrin (CH2ClCHClCH2OH), which can be hydrolyzed by caustic soda in a 6% Na2CO3 solution at 96oC. The glycerin dichlorohydrin can be hydrolyzed directly to glycerin, but this takes two molecules of caustic soda; hence a more economical procedure is to react with the cheaper calcium hydroxide, taking off the epichlorohydrin as an overhead in a stripping column. The epichlorohydrin is easily hydrated to monochlorohydrin and then hydrated to glycerin with caustic soda.

CH3CH=CH2 + C12 → CH2ClCH=CH2 + HCl
CH2ClCH=CH2 + HOCl → CH2ClCHClCH2OH
CH2ClCHClCH2OH + 2NaOH → CH2OHCHOHCH2OH + 2NaCl