Cat cracking

Solvent Deasphalting This is the solvent extraction of virgin residuum to remove asphaltenes or other tarry constituents. The deasphalted oil may be further processed into lubricating oils and greases, or used as cat cracking feed. 

The cat products become feed to other units, such as alkylation and polymerization plants. High boiling liquid products are used to make lubes, and the gas goes into the refinery fuel systems. Cat cracking feed stocks come from atmospherie and vacuum stills, phenol extraction plants, hydrotreaters, deasphalters and cokers. 

An important part of any cat crackings correlations package is an accurate feed characterization technique. Feed characterization is vital since it quantifies... 

Correlations have been used as a tool for catalyst selection studies. Predictions of the product yields and qualities possible with various catalysts can provide the necessary information for a refiner to study the economics of switching catalysts, for instance. With a good idea of the profitability of changing catalyst types, the refinery can justify such a change in his cat crackings operation. 

Another important use of correlations is the optimization of existing unit operations. Cat cracking correlations can provide the refiner with valuable information for optimizing reactor temperature level, gasoline/distillate cut point, and feed and recycle rates. The practical application of this information can mean increased profitability for the cat cracking operation. 

Fluid cat cracking required identifying stable operating regimes for beds of fine catalyst at high gas flow rates. Highly efficient cyclone and electrostatic systems had to be developed for catalyst recovery. Finally, the principles of pressure... 

Fluid coking is very insensitive to poor gas-solids contacting, but has one problem not faced by cat cracking or hydroforming. If the heavy residual oil is fed too fast to the reactor, the coke particles will become wetted and stick together in large unfluidizable lumps. Correct control of feed rate is necessary to prevent this bogging. 

Fluid bed processes have been subject to many problems and uncertainties in development and scale up from bench-scale reactors. The fluidization behavior of each process seems different and very often does not meet expectations based on experience with earlier plants. With hindsight fluid cat cracking seems to be an ideal system from the point of view of easy operation and straightforward scale up. 

Refiners process many different types of crude oil. As market conditions and crude quality fluctuate, so does cat cracking feedstock. Often the only constant in FCC operations is the continual change in feedstock quality. 

FCC feed characterization is one of the most important activities in monitoring cat cracking operation. Understanding feed properties and knowing their impact on unit performance are essential. Troubleshooting, catalyst selection, unit optimization, and subsequent process evaluation all depend on the feedstock. 

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. 

Although desulfurization is not the goal of cat cracking operations, approximately 50% of sulfur in the feed is converted to HjS. in addition, the remaining sulfur compounds in the FCC products are lighter and can be desulfurized by low-pressure hydrodesulfurization processing. 

FCC catalysts are in the form of fine powders with an average particle size in the range of 75 microns. A modern cat cracking catalyst has four major components ... 

The carbonium ion s charge is not stable and the acid sites on the catalyst are not strong enough to form many carbonium ions. Nearly all the cat cracking chemistry is carbenium ion chemistry. 

One of the benefits of catalytic cracking is that the primary and secondary ions tend to rearrange to form a tertiary ion (a carbon with three other carbon bonds attached). As will be discussed later, the increased stability of tertiary ions accounts for the high degree of branching associated with cat cracking. 

Cracking, isomerization, and hydrogen transfer reactions account for the majority of cat cracking reactions. Other reactions play an important role in unit operation. Two prominent reactions are dehydrogenation and coking. 

Dehydrogenation. Under ideal conditions (i.e., a clean feedstock and a catalyst with no metals), cat cracking does not yield any appreciable amount of molecular hydrogen. Therefore, dehydrogenation reactions will proceed only if the catalyst is contaminated with metals such as nickel and vanadium. 

Although cat cracking reactions are predominantly catalytic, some nonselective thermal cracking reactions do take place. The two processes proceed via different chemistry. The distribution of products clearly confirms that both reactions take place, but that catalytic reactions predominate. 

Hsich, C. R. and English, A. Ar., Two Sampling Techniques Accurately livaluate Fluid-Cat-Cracking Products, Oil Gas Journal, June 23, 1986. pp, ts-43. 

Cat cracking has been, and will continue to be, a big money maker for the refining industry. It is unlikely that any new cat crackers will be built (especially in the U.S.) in the near future. Therefore, emphasis will be placed on finding ways to improve the operational reliability and profitability of the existing FCC s. 

Aniline Point is the minimum temperature for complete miscibility of equal volumes of aniline and the hydrocarbon sample. In cat cracking, aniline solution is used to determine aromaticity of FCC feedstocks. Aromaticity increases with reducing aniline point. 

Resid refers to a process, such as resid cat cracking, that upgrades residual oil. 

Since 1977, Reza Sadeghbeigi has been involved in various aspects of cat cracking at major and independent oil companies focusing on technical services, troubleshooting, process design, and project management—including major FCC revamps. 

The first edition of this book was published nearly five years ago. The book was well received and the positive reviews were overwhelming. My main objective of writing this second edition is to provide a practical transfer of experience to the readers of the knowledge that 1 have gained in more than 20 years of dealing with various aspects of the cat cracking process. 

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