Sulfur content, feedstocks importance

Sulfur Content. Another important feedstock physical property related to delayed coking is the sulfur content. The sulfur present in the feedstock tends to concentrate in the coke, where the sulfur level is usually equal to or higher than that of the feedstock. Sulfur levels as high as 4 weight % in today s feedstocks can cause unacceptably high levels of sulfur in the coke product. The resulting coke may not be acceptable for metallurgical use and may be a problem when burned as fuel. 

Aromaticity is the most important property of a carbon black feedstock. It is generally measured by the Bureau of Mines Correlation Index (BMCI) and is an indication of the carbon-to-hydrogen ratio. The sulfur content is limited to reduce corrosion, loss of yield, and sulfur in the product. It may be limited in certain locations for environmental reasons. The boiling range must be low enough so that it will be completely volatilized under furnace time—temperature conditions. Alkane insolubles or asphaltenes must be kept below critical levels in order to maintain product quaUty. Excessive asphaltene content results in a loss of reinforcement and poor treadwear in tire appHcations. 

Of the two types of SOx catalysts, the SOx additive has proven to be the more popular. Its main advantage is that it can be added to the unit at any time, and it need be added only in amounts required to give the desired degree of SOx reduction. This is especially important for units using feedstocks which vary in sulfur content. Also, use of an SOx additive does not Interfere with the... 

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

The physical properties of a certain feedstock that determine the yields and product qualities include gravity, characterization factor, carbon residue, sulfur content and metals content. The last three properties are of specific importance. 

The crude oil feedstock heavily influences the product slate for the refinery and the downstream processing required to meet the refinery s product goals. Fuels are blended to meet product specifications of volatility, sulfur content, and octane number. Most important, refiners constantly seek to optimize their blending programs to meet product goals without giving up product. 

Sulfur is present in a variety of forms, in its elementary form, as a bound molecule, but also in an oxidized state. High sulfur contents import certain acidity to industrial carbon blacks. Nitrogen, when present, is usually included in the graphite grid. One thing to bear in mind is that sulfur and nitrogen content are contingent primarily on feedstock type and quality. 

Hydrodesulfurization of petroleum feedstocks is one of the important processes in the petroleum industry to produce clean fuels. The C0M0/AI2O3 catalyst is widely used. Recently, the need for fuels of lower sulfur content due to the serious problems of global-scale air pollution because of burning petroleum feedstocks initiated to develop hydrodesulfurization catalysts, which are of higher activity than commercial C0M0/AI2O3. 

Source of Supply. The traditional source of fuel oil for the U.S. East Coast has been Venezuelan imports. Under the impact of the newer sulfur-content specifications, an increasing portion of this fuel is being taken from African crudes, and it is possible that the Middle East may also become an important supplier in this market. For these reasons, as well as from a national security standpoint—particularly as we become more dependent on fuel oil for basic energy—the refiner will be faced with the problem of handling a range of feedstocks. 

For specific projects petroleum coke can be an important alternative feedstock. A number of plants have been designed for coal and have later taken up petroleum coke because of its low price. The most important differences between these feedstocks lie in the low quantity and high melting point of the ash and the high sulfur content. 

The data of Table 10-20 clearly show that the most important change produced by hydrotreating is the reduction in sulfur content. Olefins if present also are reduced, but aromatics are unaffected. Further, the boiling point of the feedstock is essentially unchanged. 

Methanol is acknowledged as a highly suitable liquid feedstock for H production due to its high H/C ratio, low sulfur content, wide availability, and easy storage and transportation [60]. Cu/ZnO-based catalysts are important for industrial-scale catalytic production of H from methanol [61]. Lin et al. designed a core-shell... 

Today, petroleum is our primary hydrocarbon feedstock. It is estimated [1] that at the beginning of 2004, worldwide reserves were 1.27 trihion barrels of oil. At current usage this supply is projected to last -50 years. The other important hydrocarbon feedstocks are coal and natural gas. Methane, CH4, is the major component of natural gas (75-90%) and as shown in Fig. 7.2, is one of the most abundant hydrocarbons on the planet and is widely distributed. Current estimates are that natural gas reserves (6,100 trillion cubic feet) are comparable to oil on an energy content basis. If the estimates of natural gas in methane hydrate deposits in the deep oceans are considered, the amount of methane on the planet could far exceed the known oil reserves Given the abundance, wide distribution, hi er hydrogen to carbon ratio and low sulfur content compared to oil and coal, methane could become the hydrocarbon feedstock of choice that could lead to a Methane Economy" for the next several decades. 

The procedure is carried out at the decomposition temperature of the sulfiding agent. Activation with spiking agents generally requires much lower temperatures ( 160°C-260°C) than that with nonspiked oil ( 300°C-350°C) (Hallie, 1982). It is important to keep an adequate sulfur concentration in the sulfiding feedstock in order to control the heat release of sulfiding reactions. A sulfur content of 0.5-2.0wt% in the feedstock is typically recommended, whereas in spiked feeds sulfur concentration must be below 1 wt%. 

Sulfttr Content. The amount of sulfur in crude is important in terms of handling the crude within the refinery and the undesirable effects of sulfur in finished products. High-sulfur crudes require special materials of construction for refinery equipment because of their corrosiveness. Certain refinery processes require desulfurization of sour charge stocks prior to use as a feedstock, not only because of their corrosiveness, but also because of the effect of sulfur-bearing compounds on expensive catalysts, From the standpoint of the consumer, sulfurous gasoline has an unforgettably offensive odor unless specially sweetened and it may corrode the fuel system and engine parts, as well as pollute the atmosphere after it has been burned,... 

Residua and heavy oils contain impurities other than sulfur, nitrogen, and oxygen, and the most troublesome of these impurities are the organometallic compounds of nickel and vanadium. The metal content of a residuum or heavy oil can vary from several parts per million (ppm) to more than 1000 parts per million (Table 6-15), and there does seem to be more than a chance relationship between the metals content of a feedstock and its physical properties (Reynolds, 1997 Speight, 1999). In the hydrodesulfurization of the heavier feedstocks the metals (nickel plus vanadium) are an important factor since large amounts (over 150 ppm) will cause rapid deterioration of the catalyst. The free metals, or the sulfides, deposit on the surface of the catalyst and within the pores of the catalyst, thereby... 

Feedstock Characteristics. Several important feed characteristics considered in H-Oil desulfurization are (1) the character of the residuum, i.e., whether vacuum, atmospheric, deasphalter bottoms, cracked tars, or blends (2) the asphaltene and metal content (3) the sulfur level and degree of desulfurization required. These feed characteristics ultimately infiuence the selection of operating temperature, hydrogen partial pressure, space velocity, and catalyst type and usage. 

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