Residua and Asphalt

The importance of residua and asphalt to the environmental analyst arises from spillage or leakage in the refinery or on the road. In either case, the properties of 

Environmental Analysis and Technology for the Refining Industry, by James G. Speight Copyright 2005 John Wiley Sons, Inc. 

1-trichloroethane has been used in recent years as solvents for the determination of asphalt (and residua) solubility (ASTM D2042). 

The residua from which asphalt are produced, once considered the garbage of a refinery, have little value and little use other than as a road oil. In fact, the development of delayed coking (once the so-called refinery garbage can ) was with the purpose of converting residua to liquids (valuable products) and coke (fuel). 

The properties of asphalt emulsions (ASTM D977, D2397) allow a variety of uses. As with other petroleum products, sampling is an important precursor to asphalt analysis, and a standard method (ASTM D140) is available that provides guidance for the sampling of asphalts, liquid and semisolid, at point of manufactnre, storage, or delivery. 

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The character of fuel oil generally renders the usual test methods for total petroleum hydrocarbons (Chapters 7 and 8) ineffective since high proportions of the fuel oil (specifically, residual fuel oil) are insoluble in the usual solvents employed for the test. In particular, the asphaltene constituents are insoluble in hydrocarbon solvents and are only soluble in aromatic solvents and chlorinated hydrocarbons (chloroform, methylene dichloride, and the like). Residua and asphalt (Chapter 10) have high proportions of asphaltene constituents, which render any test for total petroleum hydrocarbons meaningless unless a suitable solvent is employed in the test method. 

The softening point of residua and asphalt is the temperature at which asphalt attains a particular degree of sofmess under specified conditions of test. 

Typical refinery producfs include (1) nafural gas and liquefied petroleum gas (LPG), (2) solvent naphtha, (3) kerosene, (4) diesel fuel, (5) jet fuel, (6) lubricating oil, (7) various fuel oils, (8) wax, (9) residua, and (10) asphalt (Chapter 3). A single refinery does nof necessarily produce all of fhese producfs. Some refineries are dedicated to particular products (e.g., the production of gasoline or the production of lubricating oil or the production of asphalt). However, the issue is that refineries also produce a variety of waste products (Table 4.1) that must be disposed of in an enviromnentally acceptable manner. 

The most outstanding development resulting from these investigations is the use of liquid propane for the selective precipitation of resins and asphalts. The development of the propane deasphalting process is a very important contribution to petroleum technology in the refining of residual oils and provides a method for substantially complete separation of lubricating oils from the asphaltic materials contained in the residua derived from any crude source. 

Methanol as Source ofSNG. Methanol can be produced from a large range of feedstocks by a variety of processes. Natural gas. liquefied petroleum gas (LPG), naphthas, residua] oils, asphalt, oil shale, and coal are in the forefront as feedstocks to produce methanol, with wood and waste products from farms and municipalities possible additional feedstock sources, hi order to synthesize methanol, the main feedstocks are converted to a mixture of hydrogen and carbon oxides (synthesis gas) by steam reforming, partial oxidation, or gasification. The hydrogen and carbon oxides are then converted to methanol over a catalyst. 

Figure 1-5 Simplified relationship between petroleum, two residua, and propane asphalt. 

Nevertheless, there have been some successful attempts to define the behavior of residua (and heavy oils) during the hydrodesulfurization process in terms of physical composition, which has also led to the development of process modifications to suit various heavy feedstocks. This line of investigation arose because of the tendency, over the years, to classify all residua (and heavy oils) as the same type of refinery discard which was, effectively, useless for further processing. The only exception is the production of asphalt from certain residua. It was only when... 

Residua and heavy oils, like any other petroleum, can be fractionated by a variety of techniques (Speight, 1999) to provide broad general fractions termed asphaltenes, resins, aromatics, and saturates (Figure 6-6). By convention, the asphaltene and resin fractions are often referred to as the asphaltic fraction because of their insolubility in liquid propane and subsequent separation from a liquid propane solution of residua as asphalt. 

Muller et al. used SCS derivatives to study the effects of hydrodesulfurization (HDS) on polycyclic aromatic sulfur heterocycles (PASHs) in bitumen residua. Their experiments concentrated on PASHs, which is a predominant class of SCS in vacuum residue bottoms. Asphaltenes were removed by precipitation, followed by the separation of aromatic fractions from saturated fractions by the saturates, aromatics, resins, and asphalts (SARA) method. Several methods can be deployed as the SARA method depending on the type of petroleum sample, one of the more common for more viscous oils is a combination of two methods ASTM D2007 and ASTM D893. Pentane-insoluble (PI) method ASTM D893 is used first to identify the asphaltene content then ASTM D2007 is used to calculate the saturates, aromatics, and resins. 

The vacuum residua or vacuum bottoms is the most complex fraction. Vacuum residua are used as asphalt and coker feed. In the bottoms, few molecules are free of heteroatoms molecular weights range from 400 to >2000, so high that characteri2ation of individual species is virtually impossible. Separations by group type become blurred by the sheer mass of substitution around a core stmcture and by the presence of multiple functionahties in a single molecules. Simultaneously, the traditional gc and ms techniques require the very volatiUty that this fraction lacks. 

Asphalt (qv) is prepared from petroleum and often resembles bitumen. When asphalt is produced simply by distillation of an asphaltic cmde, the product can be referred to as residual asphalt or straight-mn petroleum asphalt. If the asphalt is prepared by solvent extraction of residua or by light hydrocarbon (propane) precipitation, or if blown or otherwise treated, the term should be modified accordingly to qualify the product, eg, propane asphalt. 

Propane is usually used in this process although propane—butane mixtures and pentane have been used with some variation in process conditions and hardness of the product. Propane deasphalting is used primarily for cmde oils of relatively low asphalt content, generally <15%. Asphalt produced from this process is normally blended with other asphaltic residua for making paving asphalt. 

Fig. 10. The relationship between a cmde oil, two residua from the cmde oil, and the propane asphalt.

Asphalt Manufacture Saleable asphalts are produced from the residua of selected crudes. The residuum itself may be sold as straight reduced cuts to make it easier to handle, producing the so called cut-back asphalts. Another variation is air blown or oxidized asphalts for improved tenacity, greater resistance to weathering, and decreased brittleness. Emulsified asphalts are made for application at relatively low temperatures. 

The classic definition of asphaltenes is based on the solution properties of petroleum residua in various solvents. The word asphaltene was coined in France by J.B. Boussingault in 1837. Boussingault described the constituents of some bitumens (asphalts) found at that time in eastern France and in Peru. He named the alcohol insoluble, essence of turpentine soluble solid obtained from the distillation residue "asphaltene", since it resembled the original asphalt. 

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). 

Obviously to remove large amounts of asphaltic materials, substantial quantities of clay would be required in both the percolation and hot contacting methods, and the adsorption process then may become uneconomical in the treating of raw residua. With the exception of residual oils containing low concentrations of asphalts, oils to be treated with clay generally receive some pretreatment—for example, with sulfuric acid followed by neutralization of the acid oil, or selective solvent extraction. 

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