In order to produce larger amount and high octane contain gasoline, catalytic cracking was developed during World War II. As moving alone with the time, the improvements of this process increase the thermal efficiency of the process. Fluid Catalytic Process (FCC) which was introduced in 1942 has the highest thermal efficiency among the catalytic cracking processes. Catalytic hydrocracking has shorter history than catalytic cracking and it was started in 1958. It is also known as a hydrogen addition process, but Fluid Catalytic Process is known as carbon rejection process. These two processes also have differences in feedstock, process objectives and their products.

For catalytic cracking, it used acid catalytic. Straight run atmospheric gas oil (AGO) and light vacuum gas oil (LVGO) are the typical feedstock for catalytic cracking. Compare to catalytic cracking, hydrocracking use metal catalytic on acid support and has a wider range of feedstock. It can process more aromatic feedstock which resists cracking such as light cycle oil (LCO). It can also process heavy vacuum residue under the extreme condition such as high hydrogen pressures. Those extreme conditions prevent the process from shut down which due to extensive coking on catalyst.

As we learned from lesson 7, the process objectives of two processes are also different. For hydrocracking, its main objective is to decrease both molecular weight and boiling point of heavy oils and produces saturated hydrocarbon from highly aromatic feedstock such as light cycle oil. Since the product of hydrocracking has low sulfur and nitrogen content, it also contributes to limit the sulfur emission and aromatic hydrocarbon in motor fuels. The main objectives of catalytic cracking are to increase the yield of gasoline and number of octane in the gasoline. At the same time, it also lower the yield of coke and achieve higher conversion, but prevent the over cracking.

From the products, we could also see the differences between these two processes. The products of catalytic cracking include light gas, gasoline with high octane component, light cycle oil, heavy cycle oil, slurry oil, and coke by-product. As we talked about the objective of catalytic cracking previously, the gasoline with high octane component is the main product of catalytic cracking. For hydrocracking, diesel, jet fuel, and gasoline with extreme low sulfur component are the main products. The process uses metal catalyst and hydrotreating to remove heteroatoms such as sulfur and nitrogen. The products of hydrocracking contain low sulfur and nitrogen component which is more environmental friendly. At the same time, hydrocracking produces high yield of valuable distillates without some undesirable byproduct such as heavy oils, gas and coke.

References:

1. Class website lesson 7

https://www.e-education.psu.edu/fsc432/content/lesson-7-catalytic-conversion processes-part-1

Blog 7

Write a blog post comparing catalytic cracking and catalytic hydrocracking processes with respect to feedstocks, process objectives, and products.

After all of the various physical separations have occurred to a crude oil, such as distillation, deasphalting, and dewaxing, there is a need to now change the composition of the crude oil using chemistry, breaking and creating bonds. The yields of this product after just undergoing the physical changes does not meet the demand required so further chemical separations must be pursued. The earliest discovered method for chemical separation is known as thermal cracking which uses brutal heat, heating the temperatures until the compounds crack and the chemical bonds are broken.

However the thermal cracking processes could not meet the demand for quality. This process delivered gasoline with a low octane number which was only acceptable for automobiles back in the day. Engines now have higher compression ratios and require a higher octane number in gasoline. They need a gasoline that does not ignite spontaneously with pressure when pressurized with air. This lead to the introduction of catalytic cracking.

Most catalytic conversion processes were developed right before and during Second World War for making higher quantities of better fuels with higher octane numbers. In catalytic cracking the reactive species are carbo cations that are produced on catalyst surfaces. Carbo cations go through isomerization reactions very quickly providing the opportunity to create isoparrafins. Almost all gasoline production in the U.S. is done through catalytic means.

There are a few different forms of catalytic cracking such as Houdry catalytic cracking, Thermafor catalytic cracking (TCC), and fluid catalytic cracking (FCC), however they are not all equally efficient. Fluid catalytic cracking is the most popular process and is the heart of the refinery. Catalytic cracking had a very flexible range of feedstocks that can be used from the gas oil boiling range all the way up to light vacuum gas oil. Cracking products after being fractionated can be separated into products such as gas, gasoline, light cycle oil (LCO) and heavy cycle oil (HCO).

For heavier aromatic feedstock materials such as heavy vacuum gas oil or vacuum distillation residue hydrogen must be introduced so that we can convert these heavy fractions without rejecting large quantities of Carbon. This is known as hydro cracking, which has the principal objective of upgrading products by decreasing the molecular weight and boiling point of heavy oils to produce products of saturated hydrocarbons, such as diesel and jet fuel. The hydrocracking process has two dimensions: Hydrogenation of aromatic rings and cracking of aliphatic compounds. Hydrocracking provides high yields of valuable distillates without producing low-grade byproducts such as heavy oils, gas, or coke, as experienced in carbon rejection processes such as coking. This method is less flexible with its feedstock range and also more costly than catalytic cracking.

Write a blog post comparing catalytic cracking and catalytic hydrocracking processes with respect to feedstocks, process objectives, and products.

Catalytic cracking is a process utilized by petroleum refineries which has been around for nearly a century. The reason this process became so popular is mainly due to its increased yield of gasoline with a higher octane rating, compared to a yield that would be achieved from thermal cracking. This process differs in a few ways from thermal cracking, as catalytic cracking incorporates the use of a catalyst, is more flexible in its feedstock, and does not require as high of temperatures and pressures as thermal cracking would.

Amongst the different types of catalytic cracking processes is Fluid Catalytic Cracking (FCC), introduced in 1942. This process in particular has seen a large use in the refining industry as it has a very flexible feedstock, which is usually straight-run atmospheric gas oil (AGO) and light vacuum gas oil (LVGO). Utilizing an acidic catalyst, long chains of n-alkanes are broken into shorter branched chains of isoalkanes, as well as cycloalkanes and aromatics. Different methods of catalytic cracking are used in refineries to produce LPG, cycle oils, and light hydrocarbons such as propane and butane, in addition to high-octane gasoline. Through alkylation and polymerization, these light hydrocarbons are used as feedstock to produce higher molecular weight isoalkanes and olefins which ultimately end up in the high-octane gasoline pool. Coking occurs during the cracking reactions, which works to deactivate the catalyst. When the coke is burned off with air, the temperature of the catalyst particles increases from the heat released by this, which provides the required energy for cracking to occur with minimal loss. This is what ultimately makes the cracking process so thermally efficient.

In 1958, the first commercial use of a process known as catalytic hydrocracking occurred. While catalytic cracking can support a wide range of feedstocks, hydrocracking is even more flexible and selective. Its main use in the refining industry is for its ability to produce light and middle distillates including large amounts of hydrogen, as well as its respect for environmental regulations that seek to limit the quantities of sulfur and aromatic hydrocarbon emissions. While these are all useful items, the overall goal of this process is to produce diesel and jet fuel from highly aromatic feedstocks such as residue and LGO from FCC. This is achieved by causing a decrease in the molecular weight and boiling point of heavy oils. The incorporation of bi-functional catalysts systems helps to keep coking under control. Hydrocracking involves a hydrogen-addition process, providing high yields of the desired distillates while avoiding the production of low-grade byproducts such as heavy oils, gas, and coke.