Olefins or alkeneswhich are unsaturated straight-chain or branched hydrocarbons, do not occur naturally in crude oil.
Olefins or alkeneswhich are unsaturated straight-chain or branched Catalytic cracking, do not occur naturally in crude oil. Diagrammatic example of the catalytic cracking of petroleum hydrocarbons The fluid catalytic cracking process breaks large hydrocarbon molecules into smaller molecules by contacting Catalytic cracking with powdered catalyst at a high temperature and moderate pressure which first vaporizes the hydrocarbons and then breaks them.
The cracking reactions occur in the vapor phase and start immediately when the feedstock is vaporized in the catalyst riser. Figure 2 is a very simplified schematic diagram that exemplifies how the process breaks high boiling, straight-chain alkane paraffin hydrocarbons into smaller straight-chain alkanes as well as branched-chain alkanes, branched alkenes olefins and cycloalkanes naphthenes.
The breaking of the large hydrocarbon molecules into smaller molecules is more technically referred to by organic chemists as scission of the carbon-to-carbon bonds.
As depicted in Figure 2, some of the smaller alkanes are then broken and converted into even smaller alkenes and branched alkenes such as the gases ethylenepropylenebutylenesand isobutylenes. Those olefinic gases are valuable for use as petrochemical feedstocks.
The propylene, butylene and isobutylene are also valuable feedstocks for certain petroleum refining processes that convert them into high-octane gasoline blending components.
As also depicted in Figure 2, the cycloalkanes naphthenes formed by the initial breakup of the large molecules are further converted to aromatics such as benzenetolueneand xyleneswhich boil in the gasoline boiling range and have much higher octane ratings than alkanes.
In the cracking process carbon is also produced which gets deposited on the catalyst catalyst coke. By no means does Figure 2 include all the chemistry of the primary and secondary reactions taking place in the fluid catalytic process. There are a great many other reactions involved.
However, a full discussion of the highly technical details of the various catalytic cracking reactions is beyond the scope of this article and can be found in the technical literature.
The desirable properties of an FCC catalyst are: Good stability to high temperature and to steam High activity Good resistance to attrition Low coke production A modern FCC catalyst has four major components: Zeolite is the primary active component and can range from about 15 to 50 weight percent of the catalyst.
The zeolite used in FCC catalysts is referred to as faujasite or as Type Y and is composed of silica and alumina tetrahedra with each tetrahedron having either an aluminum or a silicon atom at the center and four oxygen atoms at the corners.
It is a molecular sieve with a distinctive lattice structure that allows only a certain size range of hydrocarbon molecules to enter the lattice.
The acidic sites are provided by the alumina tetrahedra. Thus, the net charge of the alumina tetrahedra is -1 which is balanced by a sodium ion during the production of the catalyst.
Typically the nitrogen content of the feedstock is between and ppm.
Higher Nitrogen content results in significant depression of the conversion rate. The matrix component of an FCC catalyst contains amorphous alumina which also provides catalytic activity sites and in larger pores that allows entry for larger molecules than does the zeolite.
That enables the cracking of higher-boiling, larger feedstock molecules than are cracked by the zeolite. The binder and filler components provide the physical strength and integrity of the catalyst.
The binder is usually silica sol and the filler is usually a clay kaolin. Nickel, vanadium, iron, copper and other metal contaminants, present in FCC feedstocks in the parts per million range, all have detrimental effects on the catalyst activity and performance.
Nickel and vanadium are particularly troublesome.
There are a number of methods for mitigating the effects of the contaminant metals: This seriously hampers a refinery's flexibility to process various crude oils or purchased FCC feedstocks. Hydrodesulfurization of the FCC feedstock removes some of the metals and also reduces the sulfur content of the FCC products.
However, this is quite a costly option.39 Chapter 3 Catalytic Combustible Gas Sensors in a square. The source of the electrical current is con-nected, and between the other pair of opposite cor-ners, the output measurement circuit is connected.
Fluid bed catalytic cracking (FCC) is the most popular design in use today. In the FCC unit, the catalyst is a finely divided powder. When the catalyst is fluidized or “fluffed-up” with air or hydrocarbon vapor it behaves like a fluid and can . Fireside Corrosion. Load cycling and relatively quick ramp rates under staged conditions will have a negative impact on both fireside corrosion and circumferential cracking.
Petroleum refinery process in which heavy oil is passed through metal chambers (called catalytic crackers or cat crackers) under pressure and high temperature in the presence of catalysts such as alumina, silica, or zeolites. This boiling breaks up heavy, large, and more complex long-chain oil molecules into lighter, smaller, and simpler short-chain molecules such as those of gasoline.
Fluid catalytic cracking is a commonly used process, and a modern oil refinery will typically include a cat cracker, particularly at refineries in the US, due to the high demand for gasoline.
The process was first used around and employs a powdered vetconnexx.com WWII, the Allied Forces had plentiful supplies of the materials in contrast to the Axis Forces which suffered severe shortages. Definition of catalytic cracking: Petroleum refinery process in which heavy oil is passed through metal chambers (called catalytic crackers or cat crackers) under pressure and high temperature in the presence of catalysts such as.