Wastewater that comes into contact petroleum fractions cannot be treated at municipal water treatment facilities. This is because municipal water treatment does not have the equipment to clean the pollutants that are added to the water during petroleum processing. It is also not the job of the municipal water treatment to clean the many poisons that were added to the water during petroleum processing. Municipal water treatment facilities clean the water of sewage and storm run off. The kind of toxic chemicals found in the petroleum refining waste water contain poisonous compounds which under normal circumstances would never come into contact with any water stream. For instance, a multitude of hydrocarbons, aromatic compounds, such as benzene and heteroatom compounds like mercaptans, amines, phenols, cyanide’s. These polluted streams of water also contain dissolved gases like H2S and NH3, acids such as H2SO4 and HF. All of which a municipal waste water facilities is not capable of removing to a safe level for release back into the environment.

While similar in nature, a municipal wastewater treatment facility and an industrial wastewater treatment facility such as one located onsite in petroleum processing plants may not be able to handle mixing input streams. This would especially be the case for adding industrial wastewater to a municipal treatment outfit because they are designed for specific types of pollutants. These pollutants include food wastes, microorganisms, viruses, bacteria, certain nutrients such as Nitrogen and Phosphorous, and household organic products such as pharmaceuticals and soaps.¹ Beyond these contaminants, municipal treatment also controls levels of suspended solids and biochemical oxygen demand (BOD) among other things which do exist in industrial wastewater, however the problems is there are more than just these pollutants coming from refineries. For example, BOD, Nitrogen, Phosphorous, and suspended solids are accompanied by contaminants like oils, hydrocarbons, mercaptans, phenols, toxic compounds such as cyanides and H₂S or even strong acids such as sulfuric acid and hydrofluoric acid. Municipal installations are simply not built to handle these types of pollutants and would therefore either slowly destroy the municipal plant or allow the toxins to flow directly into the clean water supply. A report by the EPA said that refineries may use one to two and a half gallons of water for every gallon of product they produce³ which would lead to an enormous amount of pollutants entering our water supply.

1. Velegol, Stephanie . “CE 370 – Module #7a: Wastewater Components.” Penn State College of Engineering . N.p., n.d. Web. 23 July 2014. http://www.engr.psu.edu/mediaportal/flvplayer.aspx?FileID=4b42d423-1a7d-4e05-accd-9
2. Eser, Semih. “Wastewater Treatment.” F SC 432: Petroleum Processing. N.p., n.d. Web. 23 July 2014. <https://cms.psu.edu/section/content/default.asp?WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=F20C6357261A4AE2A750C141B721E8C1>
3. “Water & Energy Efficiency by Sectors, Oil refineries.” EPA. Environmental Protection Agency, n.d. Web. 23 July 2014. <http://www.epa.gov/region9/waterinfrastructure/oilrefineries.html#water>.

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.

Sources:

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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