Cracker Residues

The oil furnace process uses aromatic petroleum oils and residues as feedstock and in the oil furnace process (Fig. 1), a highly aromatic feedstock oil (usually a refinery catalytic cracker residue or coal tar-derived material) is converted to the desired grade of carbon black by partial combustion and pyrolysis at 1400 to 1650°C in a refractory (mainly alumina) -lined steel reactor. 

The SVR of the vacuum residues and bitumens (samples 2-13) has a mean x = 96.6 wt% ( y = 2.27 %). Again sample 1 stands out from this group with SVR = 82 wt%. The atmospheric residues demonstrate a mean SVR of x = 69.8 wt% ( +V= 3.74 %). For the substances from conversion processes the SVR again depends on the degree of distillation. There SVR spreads over a range from 54.5 wt% (waxy distillate, sample 23) up to 98.5 wt% (cat-cracker residue, sample 20). 

The data of (G /SVR) 100 for the atmospheric residues (samples 14- 17) do not demonstrate any uniformity. The products from conversion processes generally show higher values. The extremely high value for the waxy distillate is extraordinary and obviously due to the low SVR (54.5 wt%). The high values for cracker residues, which have been distilled exhaustively (samples 20, 21, 22) ai e understandable. 

Methylnaphthalenes are also found in petroleum-derived feedstocks, such as pyrolysis tar from ethylene production and cat-cracker residues (see Chapter 9.2.2). The l-/2-methylnaphthalene isomer ratio, which is around 1 2.5 for methyl-naphthalenes in coal tar, is higher in this case, because of the lower temperature exposition of the raw material, and is close to 1 1. Recovery of methylnaphthalenes from these sources is generally only carried out on a small scale, since it can be extremely intricate to separate co-boiling compounds petroleum-derived methylnaphthalenes has served as a feedstock for naphthalene production by dealkylation, especially in the USA in the 1960 s and 70 s. 

During the course of the pyrolysis of a petroleum-derived residue (pyrolysis tar, cat-cracker residue) or a filtered coal tar pitch it is possible to observe, under the polarisation microscope and at a certain temperature, the formation of anisotropic spherules, which grow as the reaction time lengthens and the temperature increases, coalesce and, at around 500 to 600 °C, are transformed into a semi-coke phase with marked anisotropy. Figure 13.2 shows photomicrographs of a filtered coal tar pitch pyrolyzed at 400 °C with the formation of spherulitic mesophases after reaction times of 2, 6,10 and 16 hours. 

Table 13.3 summarizes the major characteristics of binder and impregnating pitches. Eletrode binders are produced exclusively from coal tar whereas impregnating pitches can be produced from low-QI tar or by air blowing and heat-treatment of cat-cracker residues. 

In the furnace process, which today dominates carbon black production, oils rich in aromatics from naphtha or gas oil pyrolysis, cat-cracker residues (decant oils) together with mixtures of aromatics from coal tar, are used as feedstock. Table 13.5 summarizes the characteristic data for decant oil, pyrolysis oil from naphtha cracking and a carbon black feedstock derived from coal tar. 

Feedstocks. Feedstocks for the oil-fumace process are heavy fuel oils. Preferred oils have high aromaticity, are free of suspended solids, and have a minimum of asphaltenes. Suitable oils are catalytic cracker residue (once residual catalyst has been removed), ethylene cracker residues, and distilled heavy coal tar fractions. Other specifications of importance are freedom from solid materials, moderate to low sulfur, and low alkali metals. The ability to handle such oils in tanks, pumps, transfer lines, and spray nozzles is also a primary requirement. 

The nature of the matrix eontinued to be changed to cope with ever increasing amounts of cracker residues added to the gas oil feedstock. Better porosity was needed to allow larger residue molecules access to the active matrix pores, where they could crack into smaller fragments that, in turn, could enter the small zeohte pores. Alumina, and kaolin, fired at high temperature and then acid extracted were successful components of an active matrix. The alumina in the matrix could also absoib poisons from the residues, such as the metals nickel and vanadium and some sodium compounds. 

Most refineries produce sufficient gas oil to meet the cat crackers demand. However, in those refineries in which the gas oil produced does not meet the cat cracker capacity, it may be economical to supplement feed by purchasing FCC feedstocks or blending some residue. The refinery-produced gas oil and any supplemental FCC feedstocks are generally combined and sent to a surge drum, which provides a steady flow of feed to the charge pumps. This drum can also separate any water or vapor that may be in the feedstocks. 

The teed to the cat cracker in a typical refinery is a blend of gas oils from such operating units as the crude, vacuum, solvent deasphalting, and coker. Some refiners purchase outside FCC feedstocks to keep the FCC feed rate maximized. Other refiners process atmospheric or vacuum residue in their cat crackers. In recent years, the trend has been toward heavier gas oils and residue. Residue is most commonly defined as the fraction of feed that boils above 1,050°F (565 C). Each FCC feed stream has different distillation characteristics. 

One area of cat cracking not fully understood is the proper determination of carbon residue of the feed and how it affects the unit s coke make. Carbon residue is defined as the carbonaceous residue formed after thermal destruction of a sample. Cat crackers are generally limited in coke burn capacity, therefore, the inclusion of residue in the feed produces more coke and forces a reduction in FCC throughput. Conventional gas oil feeds generally have a carbon residue less than 0,5 wt for feeds containing resid, the number can be as high as 15 wt lf. 

DO is the heaviest product from a cat cracker. DO is also called slurry oil, clarified oil, bottoms, and FCC residue. Depending on the refinery location and market availability, DO is typically blended into No. 6 fuel, sold as a carbon black feedstock (CBFS), or even recycled to extinction. 

Hydrotreating Hydrogenation Catalytic Remove impnrities, satnrate HCs Residuals, cracked HCs Cracker feed, distillate, lube... 

At the end of the 1970s Statoil cracked a North Sea atmospheric residue for the first time in M. W. Kellogg s circulating pilot nnit in Texas [1]. This pilot unit was qnite large, with a capacity of one barrel a day. The test in this pilot nnit was very snccess-ful and showed that North Sea atmospheric residnes were very suitable feedstocks for a residue fluid catalytic cracker, and that North Sea atmospheric residnes gave very promising prodnct yields. 

Some years later Statoil decided to start a project within catalytic cracking in order to learn more abont residue fluid catalytic cracking in general, and particnlarly abont catalysts suitable for this process. The project started as a prestudy for the residue fluid catalytic cracker unit (FCCU) that Statoil was planning to bnild at the Mongstad refinery in Norway. The intention was to crack North Sea atmospheric residue directly, without first using a vacuum gas distillation tower followed by cracking... 

The feeds used in all experiments presented in this paper are North Sea atmospheric residues originating from the atmospheric distillation tower at the Statoil Mongstad refinery in Norway. After the start-up of the residue fluid catalytic cracker at this refinery in 1989, the same feed has been used both in the commercial FCCU and in the ARCO pilot unit at Chalmers. Typical data for some North Sea atmospheric residue feeds used in the ARCO pilot unit are shown in Table 3.1. 

A paraffinic North Sea atmospheric residue was used as feed, see Table 4.1. This feed is representative for the feedstock used in the catalytic cracker at the Mongstad refinery. 

C4 Hydrorefining. The main components of typical C4 raw cuts of steam crackers are butanes (4-6%), butenes (40-65%), and 1,3-butadiene (30-50%). Additionally, they contain vinylacetylene and 1-butyne (up to 5%) and also some methylacetylene and propadiene. Selective hydrogenations are applied to transform vinylacetylene to 1,3-butadiene in the C4 raw cut or the acetylenic cut (which is a fraction recovered by solvent extraction containing 20-40% vinylacetylene), and to hydrogenate residual 1,3-butadiene in butene cuts. Hydrogenating vinylacetylene in these cracked products increases 1,3-butadiene recovery ratio and improves purity necessary for polymerization.308... 

Safeguards. All materials will be tested at levels no higher than those found in natural products, e.g., beta-damascenone occurs in apples at 100 times its threshold and will not be used at a level higher than 100 times its average reported threshold. Total intake will be limited to 1 ng per day (less than in an apple) in situations where swallowing is necessary. Rinse water and crackers will be provided to help dissipate any unpleasant residual sensations. Exposure will be limited to six sessions per day. 

C4 raw cuts of stream crackers typically contain butanes (4-6%), butenes (40-65%) and 1,3-butadiene (30-50%), as well as some vinylacetylene, 1-butyne, propadiene and methylacetylene. First, acetylenes are selectively hydrogenated and the 1,3-butadiene is extracted resulting in butene cut (or raffinate I). Isobutylene is next removed to produce raffinate II which contains linear butenes and some residual 1,3-butadiene. The latter needs to be removed to achieve maximum butene yields. The methods and catalysts for this process are chosen according to the final use of butenes. The demand for polymer-grade... 

The high-boiling distillates, such as the atmospheric and vacuum gas oils, are not usually produced as a refinery product but merely serve as feedstocks to other processes for conversion to lower-boiling materials. For example, gas oils can be desulfurized to remove more than 80% of the sulfur originally in the gas oil with some conversion of the gas oil to lower-boiling materials (Table 6-11). The treated gas oil (which has a reduced carbon residue as well as lower sulfur and nitrogen contents relative to the untreated material) can then be converted to lower-boiling products in, say, a catalytic cracker where an improved catalyst life and volumetric yield may be noted. 

A number of different types of laboratory scale units have been developed to simulate commercial catalytic crackers. These include fixed bed (MAT), fluidized bed, and riser units.(1,2,3) In particular, for simulating commercial riser FCC units which process residue, a riser pilot plant is the preferred choice. 

A number of refiners have processed residue containing feedstocks in commercial FCC units. Feeds with as much as 5.1%w RCR ( 6.5%w CCR) and 85 ppm Ni + V have been processed in Phillips Borger Refinery.(4) Ashland has processed feedstocks of up to 7.1%w RCR ( 8.5%w CCR) and 85 ppm Ni + V in their RCC (Reduced Crude Conversion) process.(5,6) A commercial scale ART (Asphalt Residual Treating) unit has processed residues containing levels of contaminants as high as 13.5%w RCR and 300 ppm Ni + V (7,8). However, in typical day-to-day operation of residue cat crackers, feedstock quality is not as extreme as those illustrated above. 

Selective solvent extraction of volatiles will remove volatiles with very high yields although the extracts are always contaminated with non-volatile components. For example, acetonitrile extraction followed by co-extraction with pentane was used by Vemin (38). In our experiments the direct extraction of crushed crackers with Freon 113 or ethyl acetate contained too much residual lipid. Distillation of the solvent yielded a lipid concentrate low in aroma volatiles. Attempts to use gel filtration (Bio-Beads S-X12 from Bio-RAD) to remove the lipids but retain the odorous substances were also unsuccessful. 

This chapter describes the preparations and characteristics of highly aromatic and highly anisotropic pitches from the distillate fraction of catalytic cracker bottoms (CCB). CCB is the aromatic residue from a catalytic cracking process. 

Aromatic Pitches from the Distillate Fraction of Catalytic Cracker Bottoms and Residue Fractions... 

Catalytic Cracker Bottoms (CCB) which is the heavy residue from the catalytic cracking of petroleum distillate is a common aromatic feedstock used for synthetic carbons and pitch production. CCB, like other heavy aromatic feedstock, is composed of alkyl-substituted polycondensed aromatics with a very wide molecular weight distribution. 

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