Blog 8

Write a blog post discussing the objectives of catalytic reforming and limits on catalytic reforming capacity in the U.S. refineries.

Alkylation, polymerization, catalytic reforming, and isomerization are all catalytic conversion processes performed to produce a high octane number gasoline. This is essential for obtaining high performance and high power. Catalytic reforming developed during the Second World War with a feed stock coming from the Light Ends Unit. The heaviest product of this, the heavy naphtha is used. This is heavy because it has a lot of naphthenes or cycloalkanes in its composition. Catalytic reforming’s objective is to convert these naphthenes or cycloalkanes into aromatics with very high octane numbers. Dehydrogenation of naphthenes using precious metal catalysts is straight forward for a clean heavy naphtha feedstock. However, if sulfur is associated it must have pre hydro treatment to avoid poisoning from occurring with platinum.

After the crude has been distilled and the heavy naphtha has been obtained and treated, if necessary, it is separated in a naphtha fractionator. The light naphtha will be withdrawn and sent to the gasoline pool while the true heavy naphtha will go through a catalytic reformer which will then produce the high octane number reformate and a byproduct of hydrogen gas.  The most important reactions of interest within this process are converting naphthenes to aromatics and the isomerization of n-paraffins to i-paraffins. Reforming a heavy naphtha that contains a higher n-paraffin content requires more severe conditions within the reactor. The desired catalytic reforming reactions within catalytic reforming are dehydrogenation, dehydroisomerization, dehydrocyclization, and isomerization. High temperature, low hydrogen pressure, low space velocity, and a low H2/HC ratio all strongly promote the occurrence of these chemical reactions.

Up until the 1990s catalytic reforming was one of the most popular processes in the refinery for producing high number gasoline. With the introduction of the Clean Air Act amendments the amount of benzene aromatics became limited. This made catalytic reforming undesirable. However, the valuable byproduct of hydrogen gas has become very essential since it is needed in the hydro treating and hydro cracking processes. This being said, catalytic reforming became the cheapest way of obtaining hydrogen.

As we learned from lesson 8, catalytic reforming is known as a conversion process in the refineries. The main objectives of catalytic reforming is to convert heavy naphtha into high-octane reformate and produce hydrogen as significant by-product. The product of catalytic reforming is also low in sulfur and is a major blending product of gasoline. Platinum (Pt) and palladium (Pd) are contained in most catalyst of reforming. From this process, hydrogen which is one significant byproduct is produced for further hydrotreating and hydrocracking process. Especially the hydrotreating process is necessary for naphtha feedstock before it go through reforming process, because platinum catalyst needs to be protected by poisoning from sulfur and nitrogen.

There are some limits on catalytic reforming capacity in the U.S. Refineries. Firstly, as lesson 8 mentioned, due to regulations and limitations on benzene and total aromatics for gasoline in U.S. and Europe, the amount of reformate can be used is limited. As we mention in reforming’s objectives, hydrogen is still an important byproduct from catalytic reforming to be used in refineries. Secondly, in order to maintain the yield of hydrogen and reformate, hydrocracking is an undesired reaction in reforming process.  It would consume hydrogen to produce gaseous hydrocarbon to lower the yield of hydrogen and reformate. Some conditions such as pressure at 50 to 350 psig, hydrogen/feed ratio of 3–8 mol H₂/mol feed, and liquid hourly space velocities of 1–3 h^-1 are used to prevent hydrocracking during reforming. Thirdly, coke deposition during reforming process deactivated catalyst even with the usage of hydrogen. Semi-regenerative process was introduced in 1946 and it need to be shut down every 3 to 24 months for catalyst regeneration. Cyclic process expands the on-stream time up to 5 years, but it is not a favorite process by the industries. Continuous process which is introduced in 1971 allows remove and replace catalyst during operation to keep its high activity. However, it is expensive to operate.

Reference

1. F SC class website lesson 8

https://cms.psu.edu/section/content/default.asp?WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=F20C6357261A4AE2A750C141B721E8C1

Write a blog post discussing the objectives of catalytic reforming and limits on catalytic reforming capacity in the U.S. refineries.

Catalytic reforming is another catalytic conversion process utilized by many petroleum refineries. This was introduced in a similar time frame as catalytic cracking – during World War II. Of course, there was a huge increase in the demand for high-octane gasoline during this time frame due to the necessity of fuel demanded from US aircraft.

There are four different reactions of catalytic reforming which all achieve the same objective of increasing the octane number. Dehydrogenation, dehydroisomerization, and dehydrocyclization are all highly endothermic reactions which produce aromatic compounds and hydrogen gas in large yields. These reactions require high temperatures and relatively low pressures, however the hydrogen pressure must be significantly high enough in order to avoid deactivating the catalyst surfaces due to coke deposition.

Hydrogen is the most valuable byproduct obtained from catalytic reforming. This is because this element can be used to essentially ‘clean up’ fuels further through processes of hydrotreating and hydrocracking. There are a couple of limits posed on catalytic reforming. Usually the feedstock must be hydrotreated before reforming can take place since the platinum catalyst used in reforming can be hindered by exposure to sulfur, nitrogen, or other heteroatom contaminants. Also, the United States and Europe hold a limit on the levels of benzene and the total aromatics for gasoline, therefore placing a limit on the amount of reformate able to be used in the blending of gasoline. The overall goal of catalytic reforming is to obtain high-octane-number gasoline while also acting as the sole internal source of the byproduct hydrogen.

Another limit pertaining to catalytic reforming is the occurrence of the undesirable side reaction of hydrocracking. This process consumes the valuable hydrogen byproduct while forming gaseous hydrocarbons which in turn decrease the yield of reformate. The principal approach to achieve high yields and high quality of reformate is increasing the selectivity of desirable reactions by means of finding the proper balance between acidic and metallic sites.