The zeolites used in catalytic cracking are chosen to give high percentages of hydrocarbons with between 5 and 10 carbon atoms - particularly useful for petrol (gasoline). It also produces high proportions of branched alkanes and aromatic hydrocarbons like benzene.
Note: If you are interested in other examples of catalysis in the petrochemical industry, you should follow this link. It will lead you to information on reforming and isomerisation (as well as a repeat of what you have just read about catalytic cracking).
Economic Reasons For Catalytic Cracking Of Alkanes
Download: https://shoxet.com/2vA1KS
Thermal cracking doesn't go via ionic intermediates like catalytic cracking. Instead, carbon-carbon bonds are broken so that each carbon atom ends up with a single electron. In other words, free radicals are formed.
Fluid Catalytic Cracking (FCC) is the conversion process used in petroleum refineries to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum (crude oils) into gasoline, olefinic gases, and other petroleum products.[1][2][3] The cracking of petroleum hydrocarbons was originally done by thermal cracking, now virtually replaced by catalytic cracking, which yields greater volumes of high octane rating gasoline; and produces by-product gases, with more carbon-carbon double bonds (i.e. olefins), that are of greater economic value than the gases produced by thermal cracking.
Oil refineries use fluid catalytic cracking to correct the imbalance between the market demand for gasoline and the excess of heavy, high boiling range products resulting from the distillation of crude oil.
FCC units are less common in EMEA because those regions have high demand for diesel and kerosene, which can be satisfied with hydrocracking. In the US, fluid catalytic cracking is more common because the demand for gasoline is higher.
In 1922, a French mechanical engineer named Eugene Jules Houdry and a French pharmacist named E. A. Prudhomme set up a laboratory near Paris to develop a catalytic process for converting lignite coal to gasoline. Supported by the French government, they built a small demonstration plant in 1929 that processed about 60 tons per day of lignite coal. The results indicated that the process was not economically viable and it was subsequently shut down.[12][13][14]
In 1933, Houdry and Socony-Vacuum joined with Sun Oil Company in developing the Houdry process. Three years later, in 1936, Socony-Vacuum converted an older thermal cracking unit in their Paulsboro refinery in New Jersey to a small demonstration unit using the Houdry process to catalytically crack 2,000 barrels per day (320 m3/d) of petroleum oil.
This fluid catalytic cracking process had first been investigated in the 1920s by Standard Oil of New Jersey, but research on it was abandoned during the economic depression years of 1929 to 1939. In 1938, when the success of Houdry's process had become apparent, Standard Oil of New Jersey resumed the project, hopefully in competition with Houdry, as part of a consortium of that include five oil companies (Standard Oil of New Jersey, Standard Oil of Indiana, Anglo-Iranian Oil, Texas Oil and Royal Dutch Shell), two engineering-construction companies (M. W. Kellogg Limited and Universal Oil Products) and a German chemical company (I.G. Farben). The consortium was called Catalytic Research Associates (CRA) and its purpose was to develop a catalytic cracking process which would not impinge on Houdry's patents.[12][13][14]
Chemical engineering professors Warren K. Lewis and Edwin R. Gilliland of the Massachusetts Institute of Technology (MIT) suggested to the CRA researchers that a low velocity gas flow through a powder might "lift" it enough to cause it to flow in a manner similar to a liquid. Focused on that idea of a fluidized catalyst, researchers Donald Campbell, Homer Martin, Eger Murphree and Charles Tyson of the Standard Oil of New Jersey (now Exxon-Mobil Company) developed the first fluidized catalytic cracking unit. Their U.S. Patent No. 2,451,804, A Method of and Apparatus for Contacting Solids and Gases, describes their milestone invention. Based on their work, M. W. Kellogg Company constructed a large pilot plant in the Baton Rouge, Louisiana refinery of the Standard Oil of New Jersey. The pilot plant began operation in May 1940.
Based on the success of the pilot plant, the first commercial fluid catalytic cracking plant (known as the Model I FCC) began processing 13,000 barrels per day (2,100 m3/d) of petroleum oil in the Baton Rouge refinery on May 25, 1942, just four years after the CRA consortium was formed and in the midst of World War II. A little more than a month later, in July 1942, it was processing 17,000 barrels per day (2,700 m3/d). In 1963, that first Model I FCC unit was shut down after 21 years of operation and subsequently dismantled.[12][13][14][15]
A refiner's choice of crude oil will be influenced by the type of processing units at the refinery. Refineries fall into three broad categories. The simplest is a topping plant, which consists only of a distillation unit and probably a catalytic reformer to provide octane. Yields from this plant would most closely reflect the natural yields from the crude processed. Typically only condensates or light sweet crude would be processed at this type of facility unless markets for heavy fuel oil (HFO) are readily and economically available. Asphalt plants are topping refineries that run heavy crude oil because they are only interested in producing asphalt.
The last level of refining is the coking refinery. This refinery processes residual fuel, the heaviest material from the crude unit and thermally cracks it into lighter product in a coker or a hydrocraker. The addition of a fluid catalytic cracking unit (FCCU) or a hydro cracker significantly increases the yield of higher-valued products like gasoline and diesel oil from a barrel of crude, allowing a refinery to process cheaper, heavier crude while producing an equivalent or greater volume of high-valued products.
A hydrocracking unit, or hydrocracker, takes gas oil, which is heavier and has a higher boiling range than distillate fuel oil, and cracks the heavy molecules into distillate and gasoline in the presence of hydrogen and a catalyst. The hydrocracker upgrades low-quality heavy gas oils from the atmospheric or vacuum distillation tower, the fluid catalytic cracker, and the coking units into high-quality, clean-burning jet fuel, diesel, and gasoline.
Five oil sources were selected for the TEA: camelina, pennycress, jatropha, castor bean, and yellow grease. The five sources were selected for the following reasons: non-food feedstocks (pennycress and castor bean), promising for the US agro-climatic conditions (camelina, pennycress, and castor bean), low cost and readily available (yellow grease), receiving global attention (jatropha), and high yield among terrestrial plants (jatropha and castor bean). Additionally, some of these sources were less studied as potential jet fuel feedstock (e.g., pennycress and castor bean), thus we saw an opportunity for this study to improve the knowledge base for these feedstocks. Moreover, alternative jet fuel (AJF) produced from camelina oil, jatropha oil, and yellow grease has been tested in aircrafts, which indicated market interest in these sources [24]. Algae was also considered a promising biofuel feedstock but it was not included in our analysis because there have been many other studies on algae productivity and economics over the years [25,26,27,28,29,30,31]. Below is a brief description of the five selected oil sources.
The resource analysis indicates that oil crops currently grown in the US (such as soybean) have relatively low oil yield when compared to oil crops grown in other, mainly tropical, parts of the world (e.g., palm, coconut, and jatropha). Higher-yielding oil crops such as canola and camelina are increasingly grown in the country but they are facing competition with the food industry; thus it is unclear what the future holds for these resources. While receiving a lot of attention, pennycress and jatropha are slow to develop for various reasons (e.g., agronomic, economic, and social). Non-terrestrial oil sources such as animal fats and greases have relatively lower prices than terrestrial oil crops and thus are increasingly used for biofuels production. With inputs from resource analysis on feedstock compositions profiles, oil prices, and availability, TEA is performed for five selected oil feedstocks using the HEFA process concept. The five selected oils are camelina, pennycress, jatropha, castor bean, and yellow grease. Please note that there are no mature feedstock markets at the moment available for the four oilseeds analyzed, and the feedstock prices are still quite volatile in the current market. For instance, the MJSP for these five resources ranges between $3.8 and $11.0 per gallon jet blendstocks, mainly due the variation of oil feedstock prices. If feedstock price can be assumed the same, the MJSP variation is small. Feedstock is the main component of MJSP for HEFA. Jet fuel generally comprises around 60% of output for the oil feedstocks studied in this work. Sensitivity analysis indicates that the key cost drivers are feedstock price, conversion plant capacity, fatty acid profile, addition of hydrocracker, and type of hydroprocessing catalysts. Both edible and non-edible oils are promising alternative fuel feedstocks not only because they are renewable and can be produced locally and in environmentally friendly ways, but also because they can be cost competitive with strategic process design and integration, taking into consideration oil prices, resources, and feedstock composition profiles. Because there are currently no mature feedstock markets available for the four oilseeds analyzed, uncertainty analysis will be conducted in the future.
The subject of the cracking mechanism was discussed from the early days of catalytic cracking.33 It is now generally accepted that catalytic cracking involves the formation of carbenium ions.34 As depicted in Fig. 9, there is variety of ways these can be created:35,36 2ff7e9595c
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