Carbon Residue, Asphaltene Content

The carbon residues of petroleum and petroleum products serve as an indication of the propensity of the sample to form carbonaceous deposits (thermal coke) under the influence of heat. 

Tests for Conradson carbon residue (ASTM D-189, IP 13), Ramsbottom carbon residue (ASTM D-524, IP 14), the microcarbon carbon residue (ASTM D4530, IP 398), and asphaltene content (ASTM D-893, ASTM D-2006, ASTM D-2007, ASTM D-3279, ASTM D-4124, ASTM D-6560, IP 143) are sometimes included in inspection data on petroleum. The data give an indication of the amount of coke that will be formed during thermal processes as well as an indication of the amount of high-boiling constituents in petroleum. 

The determination of the carbon residue of petroleum or a petroleum product is applicable to relatively nonvolatile samples that decompose on distillation at atmospheric pressure. Samples that contain ash-forming constituents will have an erroneously high carbon residue, depending on the amount of ash formed. All three methods are apphcable to relatively nonvolatile petroleum products that partially decompose on distillation at atmospheric pressure. Crude oils having a low carbon residue may be distilled to a specified residue with the carbon residue test of choice then applied to that residue. 

In the Conradson carbon residue test (ASTM D-189, IP 13), a weighed quantity of sample is placed in a crucible and subjected to destructive distillation for a fixed period of severe heating. At the end of the specified heating period, the test crucible containing the carbonaceous residue is cooled in a desiccator and weighed and the residue is reported as a percentage (% w/w) of the original sample (Conradson carbon residue). 

In the Ramsbottom carbon residue test (ASTM Test Method D524, IP 14), the sample is weighed into a glass bulb that has a capillary opening and 

---

The INT-R1 catalyst has been tested with extremely difficult feedstocks regarding their metal, Conradson Carbon and asphaltene content. Pentane and hexane deasphalted oils from extra heavy crude oils, and atmospheric residue of these crudes were among the feedstocks tested [6,7]. 

Residual Fuel. The residual fuel produced by both the pilot and refinery meets all government specifications for low sulfur, high pour point 6 fuel oil. The residual fuels are in fact very "clean" as shown in Table VIII by the high hydrogen and low sulfur, metals, carbon and asphaltenes content. This stock is better utilized as cat cracker feed than residual fuel, since higher value gasoline and kerosene fuel can be easily produced via catalytic processing. 

The physical and chemical properties of various heavy crude oils with API gravity ranging from 10° to 21° are presented in Table 1.9. It is clearly seen that the heavier the crude oil (lower API gravity), the higher the content of impurities (sulfur, nitrogen, carbon residue, asphaltenes, metals). Viscosity, which is commonly provided... 

Figure 6-4 Variation of carbon residue with asphaltene plus resin content of feedstocks.

The Demex process is a solvent extraction demetallizing process that separates high metal vacuum residuum into demetallized oil of relatively low metal content and asphaltene of high metal content (Table 8-5) (Houde, 1997). The asphaltene and condensed aromatic contents of the demetallized oil are very low. The demetallized oil is a desirable feedstock for fixed-bed hydrodesulfurization and, in cases where the metals and carbon residues are sufficiently low, is a desirable feedstock for fluid catalytic cracking and hydrocracking units. 

Density or specific gravity, total sulfur, aniline point, total nitrogen, viscosity, cloud point, pour point, trace metals (Fe, Ni, V), and carbon residue would normally be determined on this fraction. If the fraction is to be used as catalytic cracker feedstock, asphaltenes would also be determined by precipitation with normal-heptane (ASTM Test Method D3279, Heptane Insolubles). Wax content determination by solvent reflux [24] might be included in a lube stock evaluation. Hydrocarbon-type analysis by mass spectrometry or other means is an important part of lube stock evaluation, but this is beyond the scope of this chapter. 

Atmospheric and vacuum residues, to remove as much sulfur as possible to provide low-suUur fuel oils. It is also used to hydrogenate asphaltenes and porphyrins to reduce both Conradson carbon and metal contents. 

Schabron, J.F., Speight, J.G. 1997. An evaluation of the delayed-coking product yield of heavy feedstocks using asphaltene content and carbon residue. Rev. I Institut Frangais du Pitrole 52(l) 73-85. 

Specific gravity 60/60°F of crude oils and residua was measured by using a pycnometer according to ASTM D-70 method. Energy-dispersive x-ray fluorescence spectrometry technique was used for sulfur content measurements (ASTM D-4294) with a model SLFA-2100 HORIBA spectrometer. Coke-forming tendency of the feedstocks was measured as Ramsbottom Carbon (ASTM D-524), which determines the amount of carbon residue left after evaporation and pyrolysis of oil. The amount of asphaltenes was measured as insolubles in n-heptane according to ASTM D-3279 method. Atomic absorption was used for determining Ni and V contents with a model AA Series Solar spectrometer. Distillation curve of stabilized feeds (TBP distillation) was obtained by means of ASTM D-2892 method. 

The INT-RI catalyst can be used in fixed bed hydrotreating units to improve the residue quality, from a high sulfur residual to a low sulfur fuel oil [6]. Tests were performed to demonstrate the technical feasibility of directly processing these residues, using atmospheric residue of Cerro Negro and Iranian Gach Saran crude oils as feedstocks. These residues are characterized by a higher content of asphaltenes and Conradson Carbon than the deasphalted oils [5,6]. Therefore, the effect of these two variables on the performance of the catalyst, can be evaluated. 

Table 4 presents results obtained when processing a metal-rich vacuum residue of 7° API. Deasphalting this residue with pentane produce a 74% of low asphaltene DAO, which is hydrotreated to obtain a 18°API product with low metal and sulfur content. This product is mixed with virgin VGO to obtain, from the long residue, 30% wt of additional feedstock to FCC that meets metal, nitrogen and Conradson carbon specifications. This operation scheme is economically attractive due to high DAO yield. 

The catalyst used was Topsoe TK-751. It is a general purpose HDS catalyst for residual feedstocks. Their functions are desulphurization, demetallation and asphaltenes and Conradson carbon reduction. It is recommended for HDS of residua with moderate metals content and for 2 stage catalyst in composite fillings. It has good HDS activity, good HDM selectivity and capacity for metals uptake. It is Ni/Mo type. 

---