The objective of catalytic reforming is to convert low octane straight-run naphtha streams into high a high octane, low sulfur reformate which is used as the major blending product for gasoline. To get a higher octane number of gasoline, the aromatic and branched iso-paraffins concentrations have to be increased. Hydrogen is a useful by product produced by catalytic reforming. The hydrogen gas can be used for the hydro treating and hydrocracking processes. The naptha feedstock is usually hydro treated before reforming to protect the catalyst used. The majority of reforming catalysts used in the process contain either platinum, palladium, or bi/tri metallic formulations of platinum with Rhenium, Tin or Iridium supported on alumina. Limits on catalytic reforming capacity in American and European refineries have been placed to regulate the amount of benzene and aromatics sold in gasoline.

The main reactions of interest in catalytic reforming are the dehydrogenation of naphthenes to aromatics, isomerization of straight chain n-paraffins to branched iso-paraffins, dehydroisomerization of alkyl-C₅ naphthenes and dehydrocyclization of n-paraffins to aromatics. The aromatics in the feed should remain unchanged under the right conditions. In addition, varying the reactor conditions can control side reactions such as the hydrogenation of aromatics. Considering the reactions are endothermic, the most suitable reactor conditions would be high temperatures, low hydrogen pressures, low space velocity, and low H₂/HC ratio. It is important to note that the hydrogen pressure should be high enough to inhibit coke deposition on the catalyst surfaces.

Another objective in catalytic reforming is to inhibit the undesired reaction of hydrocracking in the reactor. Hydrocracking consumes hydrogen in the reaction, thus decreasing the yield of reformate. The reaction is favored at high temperatures and high hydrogen pressures; thus, hydrocracking in the reactor must be taken into consideration when choosing the optimum reactor conditions. Also, it is important to note that the balance between acidic and metallic sites must be controlled to catalyze specific reactions; for example, the platinum surface metals catalyze dehydrogenation reactions compared to the acidic alumina support sites that catalyze isomerization and cracking reactions.

In addition, the process’s coke deposition produced deactivates the coke; hence, the catalysts must be regenerated periodically to maintain a maximum yield. There are 3 types of catalyst regeneration for catalytic reforming and they are: semi-regenerative, cyclic and continuous.

Other reactions have been developed to further increase the octane number. For instance, alkylation is a process whereby light iso-paraffins are combined with C₃–C₄ olefins, to produce a mixture of higher molecular weight iso-paraffins. Alkylation requires a strong acid catalyst such as sulfuric acid and hydrofluoric acid. However, the latter is preferred because it is less sensitive to temperature fluctuations. Furthermore, the polymerization process combines propenes and butenes to produce olefins, which contribute to a higher octane number, but the process has been largely replaced by alkylation.

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The desirable reactions in catalytic reforming include dehydrogenation of naphthenes to aromatics, dehydroisomerization of alkyl-C5-naphthenes, dehydrocyclization of n-paraffins to aromatics, and isomerization of n-alkanes to i-alkanes. Of these chemical reactions, the first three produce the valuable by-product of hydrogen. The primary objective of catalytic reforming is to produce high-octane gasoline. Gasoline, the leading choice of fuel in the transportation sector of the United States, requires higher-octane numbers in order to prevent the undesirable knocking effects in modern, powerful gasoline engines. The feedstock includes the heavy naphtha from the Light Ends Units, and contains many cycloalkanes to be converted into aromatics.

However, there are several limits imposed on these reactions and care must be taken to avoid complications. Firstly, though coke deposition is less favorable with higher pressure, hydrocracking (an undesirable chemical reaction that produces low-octane n-alkanes) also occurs at higher pressures. Therefore, catalytic reformers are typically run at low but sufficient pressure to inhibit hydrocracking while limiting coke deposition.

Dehydrogenation processes that utilize Platinum/Palladium catalysts are also subject to sulfur poisoning. Thus, feedstock typically requires hydrotreatment to remove contaminants before any processing is carried out.

Additionally, in recent years, aromatics such as benzene and toluene have been considered carcinogenic, and restrictions have been enforced on their composition in gasoline. Thus, alkylation – combining smaller molecules into larger ones (the counterpart to cracking) – is alternatively used to produce i-alkanes and higher-octane gasoline without aromatics. Drawbacks with alkylation include the requirement of highly acidic catalysts and the dangers associated with its use.

Another method of creating high-octane gasoline is polymerization. Though similar to alkylation, this process utilizes alkenes exclusively, as opposed to the alkane i-butane in alkylation. One advantage of this method is the use of less acidic catalysts (i.e. phosphoric acid) instead of those used in alkylation (i.e. sulfuric acid and hydrofluoric acid).

Catalytic reforming converts low octane straight run naphtha fractions, especially heavy naphtha that is rich in naphthenes, into a high octane, low sulfur reformate, which is a major blending product for gasoline. Hydrogen is the most valuable byproduct from catalytic reforming and is used for the increasing demand for hydrogen in hydro treating and hydrocracking processes. The feedstock for the catalytic reforming is straight run heavy naphtha that is separated in the naphtha fractionator of the Light Ends Unit. The naphtha feedstock needs to be hydro treated before reforming to protect the catalyst from being deactivated by depositing nitrogen and sulfur on the surface of the platinum. This naphtha from the fractionator, inherently has a low octane number and can be sent directly to the gasoline pool after being hydro treated or sent to an isomerization process.  A Platinum or bimetallic catalyst on a metal oxide support is used for the reforming process. The United States and Europe are setting regulations for a total limit of aromatics and benzene that is allowed to be in fuels. The amount of reformate that can be used in gasoline has also been limited. These regulations have led to the use of alkylate as an octane booster over catalytic reforming. Alkylate does not contain any olefinic or aromatic hydrocarbons.

The main purpose of this process is to increase the octane number of heavy naphthtas. In doing so, the conversion of napthenes to aromatics and isomerization of n-paraffins to i-paraffins must be performed to increase the octane number. The higher octane allows engines to run at higher compression ratios that produce more energy for car engines as well as aviation engines. The desirable outcomes of the catalytic reforming reactions are dehydrogenation, dehydroisomerization, dehydrocyclization, and isomerization. The first three reactions will promote the production or separation of hydrogen as well as aromatize the compounds to boost the octane number. The fourth, isomerization, is where the n-paraffin rearranges itself from a straight chain to an i-paraffin.

Catalytic reforming is a process used in oil refining with many positive results. The main objective of catalytic cracking is to convert heavy, low-octane, straight-run naphtha fractions that are specifically rich in napthenes convert it into a high-octane low sulfur reformate. This reformate and product of catalytic reforming is responsible for a large portion of major blending products for gasoline, in the gasoline pool. As a secondary positive outcome of catalytic reforming, the production of hydrogen as a byproduct is largely beneficial to the refinery in order to provide the hydrogen necessary for the important hydrotreating and hydrocracking processes used in the refinery as well.

The process of catalytic cracking is a chemical process with many steps. Since the main goal of the process is to maximize the octane number of the naphtha, the two most imperative reactions in the process are the conversion of napthenes to aromatics, as well as the isomerization of n-paraffins to i-paraffins. A catalyst is needed for catalytic reforming to take place, which can also pose a problem since the catalyst used in catalytic reforming contains platinum, palladium, and even bimetallic formulations of platinum with Iridium or Rhenium supported on alumina. When the platinum catalyst supported on a alumina is used, the process is referred to as platforming.

Even with the near perfection in execution of the chemistry in catalytic reforming performed by many companies, like Chevron and Exxon, the process still does have its limitations in the U.S. Those limitations stem from environmental regulations on the hydrocarbon contents of gasoline. The government has placed restrictions on the amount of benzene and aromatics contained in gasoline, and it is for this reason that alkylation has started to take strides putting it ahead of catalytic reforming in terms of productivity in increasing octane numbers of gasolines because alkylate, the product of alkylation, does not contain any aromatic or olefinic components.

References:

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

The goal of Catalytic reforming process is to convert heavy naphtha, which contains high levels of naphthenes, into a high-octane reformate. This reformate is very low in sulfur and is an important product for blending in gasoline. This process produces hydrogen that can be used for hydro treating and hydro cracking processes. This hydrogen is used to hydrotreat the naptha feedstock. This needs to be done to protect the platinum catalyst from poisoning by sulfur or nitrogen species. Even with the hydrogen usage catalysts are still deactivated by coke deposition. The commercial catalytic processes are identified based on the type of catalyst regeneration that is used. The first type of reforming process that was used commercially is called semi-regenerative. This process was first used in 1949. These reactors need to be shut down every 3 to 24 months because the catalysts need to be regenerated because the catalysts are deactivated by coke deposition. The second type of catalytic reforming process is called cyclic. It was first introduced in 1960 and involves a swing reactor. Three of the four are in operation at one time. They use the extra reactor when one is offline for catalyst regeneration. The third type of catalytic reforming process is called continuous. This type of process was introduced in 1971. The catalyst is removed and replaced without stopping the process. This allows the catalysts to maintain a high level of activity, although this process is very expensive. There are three types of processes within catalytic reforming are Alkylation, polymerization, and isomerization. Alkylation combines light iso-paraffins with olefins to produce very high molecular weight iso-paraffins to blend with gasoline. Polymerization combines propenes and butenes to also produce higher olefins with high octane numbers to blend with gasoline. Isomerization has been used since the need for lead free gasoline has been relevant. This process isomerizes n-butane to iso-butane. Then also uses alkylation to produce high octane gasoline stocks.

The catalytic reforming process was somewhat of a “late addition” to the whole petroleum-refining scene. The 1940’s and 1950’s opened up a new world of high compression engines (automobiles & aircraft) and families with multiple automobiles, so naturally the demand for high octane number gasoline skyrocketed. Catalytic reforming solved this issue by taking the heavy straight run naphtha fractions from the atmospheric distillation tower and converting it into a high octane product that proved to be the main fraction of the gasoline blending pool. Beyond the production of high octane number reformates, this process also yields high amounts of hydrogen, which can be separated out and transferred to other processes in the refinery such as hydrocracking and hydrotreating.

This process is fairly complex, in terms of the chemistry, compared to other refining processes. Since this process uses catalysts that contain platinum, the feedstock must first be hydrotreated to eliminate the probability of poisoning. There are desired reactions and undesired reactions that could take place all depending on four variables such as temperature, pressure, H₂/hydrocarbon ratio, and space velocity. The overall reactions that should take place are naphthenes converted to aromatics and n-paraffins converted to i-paraffins, but the four specific reactions are dehydrogenation, dehydroisomerization, dehydrocyclination, and isomerization. Each has their own range of octane number increases but the conditions in which these reactions are favored are all similar. A reactor with high temperature, low pressure, and low H₂/hydrocarbon ratio favors these reactions against undesired hydrocracking. The main problem with controlling conditions is that hydrocracking AND the desired reactions both thrive in a reactor with low space velocity; this aspect of the process is where the refinery has to control the activity of the catalysts and the balance of acidic versus metal sites to have high yield and high quality results. Despite the specifics of these reactions and refinery’s firm grasp of the chemistry of each particular process, regulations on limiting benzene and aromatics in automobile gasoline have limited the catalytic reforming process in the United States.

Catalytic reforming is a process which is born out the the necessity for high octane fuels which are used in transportation such as gasoline and aviation fuel.. This process takes the low octane straight run naphtha that is rich in naphthenes into high octane and low sulfur fuel which is used heavily in gasoline. Using this process a higher yield of gasoline can be achieved. In order to do this a few chemical reactions which increase the octane number of naphtha, convert the naphthenes to aromatics, and insomerize n-paraffins to i-paraffins must be completed. The catalysts used to bring these reactions to completion are generally platinum, palladium, or bimetallic formulation of platinum with Iridium or Rhenium with alumina. The process creates a large volume of hydrogen, which is a very valuable bi-product because it is in high demand for hydro-treating and hydro-cracking processes. The catalytic reformer is fed by the heavy naphtha line from the naphtha splitter. The naphtha splitter is fed by the straight run naphtha. The most desirable chemical reactions in the catalytic reforming process is dehydrogenation of naphthenes to aromatics, dehydroisomerization of alkyl-c5-naphthenes, Dehydrocyclization of n-paraffins to aromatics, and isomerization of n-alkanes to i-alkanes. These reactions increase the Research Octane Number (RON) from 75 to 110, 83 to 100, 0 to 110, and -19 to 90 respectively. 
All of these reactions except for the isomerization of n-alkanes produces hydrogen. If sufficient hydrogen is not produced coking my begin.

The catalytic reforming process is not without its limits. The United States and Europe limits the amount of benzene and other aromatics which can be found in gasoline. Because these compounds are carcinogenic and are harmful to the environment in many cases, catalytic reforming is limited. The high demand for high octane fuels and the hydrogen by product makes the process very valuable to refineries despite the production of aromatics.