Vacuum distillation hydrocarbons

Mass spectrometry allows analysis by hydrocarbon family for a variety of petroleum cuts as deep as vacuum distillates since we have seen that the molecules must be vaporized. The study of vacuum residues can be conducted by a method of direct introduction which we will address only briefly because the quantitative aspects are ek r metiy difficult to master. Table 3.6 gives some examples the matrices used differ according to the distillation cut and the chemical content such as the presence or absence of olefins or sulfur. 

Coumarone—Indene Kesins. These should be called polyindene resins (17) (see Hydrocarbon resins). They are derived from a close-cut fraction of a coke-oven naphtha free of tar acids and bases. This feedstock, distilling between 178 and 190°C and containing a minimum of 30% indene, is warmed to 35°C and polymeri2ed by a dding 0.7—0.8% of the phenol or acetic acid complex of boron trifluoride as catalyst. With the phenol complex, tar acids need not be completely removed and the yield is better. The reaction is exothermic and the temperature is kept below 120°C. When the reaction is complete, the catalyst is decomposed by using a hot concentrated solution of sodium carbonate. Unreacted naphtha is removed, first with Hve steam and then by vacuum distillation to leave an amber-colored resin. It is poured into trays, allowed to cool, and broken up for sale. 

The injection of superheated steam at the base of the vacuum fractionator column further reduces the partial pressure of the hydrocarbons in the tower, facilitating vaporization and separation. The heavier fractions from the vacuum distillation column are processed downstream into more valuable products through either cracking or coking operations. 

Atmospheric Distillation and Vacuum Distillation Heater stack gas (CO, SO, NO, hydrocarbons and PM), vents and fugitive emissions (hydrocarbons) Steam ejector emissions (hydrocarbons), heater stack gas (CO, SO, NO, hydrocarbons and PM), vents and fugitive emissions (hydrocarbons). 

The atmospheric reduced crude is the feedstock for the vacuum distillation unit. To prevent thermal decomposition (cracking) of the higher boiling point hydrocarbons in the crude oil, the pressure in the vacuum distillation fractionation column is reduced to about one-twentieth of an atmosphere absolute (one atmosphere pressure is 14.7 psia or 760 mm Fig). This effectively reduces the boiling points of the hydrocarbons several hundred degrees Fahrenheit. The components boiling below about 1050°F (565°C) are vaporized and removed as vacuum gas... 

Vacuum distillation increases the amount of the middle distillates and produces luhricating oil base stocks and asphalt. The feed to the unit is the residue from atmospheric distillation. In vacuum distillation, reduced pressures are applied to avoid cracking long-chain hydrocarbons present in the feed. 

The residue from a large scale atmospheric pressure distillation of trimethyl phosphate exploded violently. This was attributed to rapid decomposition of the ester, catalysed by the acidic degradation products, with evolution of gaseous hydrocarbons. It is recommended that only small batches of alkyl phosphates should be vacuum distilled and in presence of magnesium oxide to neutralise any acid by-products, and to suppress the acid catalysed reaction. 

Demex [Demetallization by extraction] A process for removing metal compounds from heavy petroleum fractions, after vacuum distillation, by solvent extraction and supercritical solvent recovery. The solvent is typically a mixture of octanes and pentanes. Developed jointly by UOP and the Institute Mexicano del Petroleo seven units were operating in 1988. Hydrocarbon Process., 1988, 67(9), 66. 

Atmospheric and vacuum distillation units (Figures 4.3 and 4.4) are closed processes, and exposures are expected to be minimal. Both atmospheric distillation units and vacuum distillation units produce refinery fuel gas streams containing a mixture of light hydrocarbons, hydrogen sulfide, and ammonia. These streams are processed through gas treatment and sulfur recovery units to recover fuel gas and sulfur. Sulfur recovery creates emissions of ammonia, hydrogen sulfide, sulfur oxides, and nitrogen oxides. 

The analysis involves gas chromatographic methods such as purge and trap, vacuum distillation, and headspace (Askari et al., 1996). On the other hand, samples for the determination of semi- and nonvolatile hydrocarbons need not be collected in such a rigorous manner. On arrival at the laboratory, they require extraction by techniques such as solvent or supercritical fiuid. Some cleanup of... 

Residua are the dark-colored nearly solid or solid products of petroleum refining that are produced by atmospheric and vacuum distillation (Figure 11.1 Chapter 3). Asphalt is usually produced from a residuum and is a dark brown to black cementitious material obtained from petroleum processing that contains very high-molecular-weight molecular polar species called asphaltenes that are soluble in carbon disulfide, pyridine, aromatic hydrocarbons, and chlorinated hydrocarbons (Chapter 3) (Gruse and Stevens, 1960 Guthrie, 1967 Broome and Wadelin, 1973 Weissermel and Arpe, 1978 Hoffman, 1983 Austin, 1984 Chenier, 1992 Hoffman and McKetta, 1993). 

To produce fuel, propane is mixed with the refinery bottoms to separate heavy hydrocarbons from middle distillates remaining in the bottoms. These middle distillates can be processed through vacuum distillation to produce gasoline, diesel, and marine diesel [8]. 

The atmospheric bottom, also known as reduced oil, is then sent to the vacuum unit where it is further separated into vacuum gas oil and vacuum residues. Vacuum distillation improves the separation of gas oil distillates from the reduced oil at temperatures less than those at which thermal cracking would normally take place. The basic idea on which vacuum distillation operates is that, at low pressure, the boiling points of any material are reduced, allowing various hydrocarbon components in the reduced crude oil to vaporize or boil at a lower temperature. Vacuum distillation of the heavier product avoids thermal cracking and hence product loss and equipment fouling. 

Secondary vacuum distillation to separate the various lubricating nil fractions, which in some eases, may include the iwir/uum. Since hydrocarbons tend to undergo thermal decomposition above fiOO F (3 Ih O. the distillation is generally curried oul under vacuum to enable Ihe higher-boiling fractions lo be distilled. 

Distillation concentrates the metallic constituents in the residua (Table 3-5) some can appear in the higher-boiling distillates but the latter may, in part, be due to entrainment. Nevertheless, there is evidence that a portion of the metallic constituents may occur in the distillates by volatilization of the organometallic compounds present in the petroleum. In fact, as the percentage overhead obtained by vacuum distillation of reduced crude is increased, the amount of metallic constituents in the overhead oil is also increased. The majority of the vanadium, nickel, iron, and copper in residual stocks may be precipitated along with the asphaltenes by low-boiling alkane hydrocarbon solvents. Thus, removal of the asphaltenes with n-pentane reduces the vanadium content of the oil by up to 95% with substantial reductions in the amounts of iron and nickel. 

---