The increasing demand needed for World War 2 aided the development of petroleum refinery processes. The changes were brought about by the demand for higher grade fuels and the transitions and developments in the combustion engines. Environmental regulations also played a role in the innovations of petroleum refining. The introduction of the new processes encompassed the refinery processes that we know as separation, conversion, finishing, and support.

From this world war, thermal cracking refineries were needed for quicker and easier production of petroleum based products. This war brought together a sort of alliance for a combined effort of petroleum refining for more powerful fuels. The new developments brought about by this alliance was able to increase the yield as well as produce a multitude of products. It also aided the finishing processes for stabilizing and purifying the products of thermal cracking. Boosting the octane numbers of the petroleum fuel allowed for more power for the machinery needed for not only war but also for automobiles which were becoming an increasingly demanding notion. There was still a need for kerosene at this time as well because of the slow electrification outside the urban areas. The high demand of the light and medium distillates made this an important task to experiment and develop new ideas of petroleum refining.

Heavily polluted wastewater streams come in direct contact with petroleum fractions and require serious treatment processes for purification. Hydrocarbons such as aromatic compounds and heteroatoms can be found in wastewater streams from distillation and different forms of cracking. There is a set of quality parameters to measure the treatment required for the wastewater processes including amount of suspended solids, hydrocarbon content, nitrogen content, phenols content, and acidity. Municipal wastewater treatment cannot handle treating the pollutants because the different streams need to be kept separate to reduce the load on the treatment units. The wastewater treatment constitutes a very significant supporting process for safe operation. Most municipal wastewater treatment facilities can only handle cooling water and sanitary sewage water after it has had minor treatments. The amount of refinery equipment and treatment processes require expensive machinery as well as many units for the processes that municipals may not be able to afford. Primary treatments are physical whereas secondary treatments are biological processes. Primary treatment of sour water contaminated with oils and solid particles involve the stripped of dissolved H2S using steam, separators, and settling tanks. After primary treatments are conducted typically water can be sent to municipalities for further treatment processes because they are at a acceptable level for municipalities to handle. Secondary treatments utilize microorganisms to further remove organic contaminants.

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 cracking has been widely used since the early 1900’s for production of a range of fuels, predominantly light distillates, gasoline. Three types of Catalytic cracking exist, Houdry Catalytic Cracking, Thermafor Catalytic Cracking, and Fluid Catalytic Cracking. Fluid Catalytic Cracking has been widely adopted because of its thermal efficiency compared to the other two processes as well as its little to no down time during running. Catalytic cracking generally uses gas oil as a feed for the cracking processes. The gas oil is run through a column where steam is introduced and uses catalysts such as a zeolite or aluminum/silica catalysts for the separation process. The catalysts tend to build coke an inherently become deactivated requiring activation by heated air and/or steam. The products that come from these processes are Gas, Gasoline, Light Cycle Oil, and Heavy Cycle Oil. For the Fluid Catalytic Cracker, a product is also Decant Oil which can be used for fuel oil or for feedstock to produce needle coke or carbon black. Light Cycle Oil can be processed to produce diesel fuel. The Fluid Catalytic Cracker is used not only for its efficiencies but also because of its use of better catalysts and reactivation of the catalysts. These processes have a downfall in handling a wide range of feedstocks, primarily the heavier factions.

Hydrocracking has begun to be used in the late 50’s because of this growing demand for middle and light distillates as well as its flexibility to handle wide range of feedstocks. The hydrocracking plants have the ability to crack aromatics to produce paraffinic compounds without losing carbon, which increases the yields of the desired distillates without producing low-grade byproducts, such as coking. This is a major issue that wasted time and energy in the catalytic cracking plants. The catalyst used were typically metals such as nickel and copper as well as silica/alumina as in catalytic cracking. Since the process is bi-functional it also required highly active noble metals such as platinum and palladium. This process sheds the unwanted heteroatoms and increasing the H/C ratio. Hydrocracking can be used to treat the products that were resistive to cracking from the Fluid Catalytic Cracking plant such as Light Cycle Oil.

Hydrocracking costs more to perform which leads to the reasoning of performing both the Fluidized Catalytic Cracking for what it can do and using the Hydrocracking for what the FCC cannot do to supply the necessary amounts of fuels in demand. Although Hydrocracking is more flexible with feed, produces less coke, and gives use to the byproduct produced hydrogen, Fluidized Catalytic Cracking still serves its purpose for a cost effective way to produce light distillates such as gasoline, as well as coke that can be used for heating in plants and other purposes.

Thermal cracking was initially developed to attempt to solve an energy source issue for the automobile and for aircrafts. Gasoline is produced by cracking gas oils at high temperature and initially at high pressures for hydrogen abstraction, then at low pressures for the cracking or breaking of the bonds. The heavy and light gas oils are separated to avoid heating the reactive longer alkane chains to maintain coke formations. This was a great means for our country to produce light middle distillates and heavier ends by excessive heating. The US has since discovered catalytic cracking which allows for a conversion process that produces higher yields of gasoline and higher octane number. Although the process of thermal cracking is in the past for the US, other countries still use this conversion process as a principal application of petroleum refining for diesel fuel production.

Visbreaking is known as a mild thermal cracking process which reduces the viscosity of the vacuum distillation residue to produce fuel oil, which is converted to lighter distillates. Thermal severity is a measurement of temperature and time and is an index number that helps describe how viscosity will change in visbreaking. Thermal severity can inform a refinery on how asphaltene and carbon content of feedstocks are characteristics to be aware of when considering possibilities of coking in the visbreaker reactor.

Dewaxing is a process that is carried out to remove wax, long chain paraffins, from a feedstock for production of candles, cosmetics purposes, petroleum jelly and other lubricating oils. There are to different types of dewaxing, one being solvent based and the other involves catalytic cracking of the compounds. Solvent based dewaxing involves refrigeration of the feedstock after it is mixed with the solvent. Depending on the desired production the temperature is set accordingly to allow for a range of lube oils produced based upon a pour point. The solvent/feedstock mixture are chilled to a certain temperature and ran through a rotary filter to allow for the separation of the wax from the feedstock. There are two main solvents used for solvent dewaxing, propane and methyl ethyl ketone (MEK). In most U.S. refineries methyl ethyl ketone is used over propane for its characteristic changes of the feedstock. MEK has a small difference between filtration temperatures and pour points of dewaxed oils, has a fast chilling rate, and although propane is slightly better still has good filtration rates.

Dewaxing is considered a separation process, but because Catalytic dewaxing involves breaking and making bonds it is usually referred to as a conversion process of n-paraffins.  Catalytic dewaxing is still considered dewaxing because of its ability to remove long chain n-paraffins. Contrary to solvent dewaxing, catalytic dewaxing uses a molecular sieve catalysts with a pore opening size small enough that iso- structures, such as i-paraffins, are unable to go through the sieves. The increase of i-paraffins that this causes helps to lower the pour point of the feedstock. When cracking a molecule it is important to supply hydrogen so the radical chains do not bond to the catalyst surface active sites inhibiting there use, also known as coking. Cracking n-paraffins can lead to the production of distillate fuels as a by-product, such as gasoline. Catalytic dewaxing produces lube base stock with a lower pour point and a in higher yield than that of a product from solvent dewaxing. Both dewaxing processes have low capital investments. Catalytic dewaxing is also useful for the production of both lube oil base stock and light distillates.

Distillation is different from deasphalting in the sense that distillation is a separation by boiling points. Deasphalting is a process by which a solvent is used to fractionate feedstock, atmospheric or vacuum distillation with respect to the solubility/insolubility of molecular components in a given solvent. Vacuum Distillation Residue (VDR) is completely dissolved in aromatic solvents such as toluene. VDR is typically a solid at room temperature so the aromatic solvents are used to create a liquid mixture at which point a light paraffin solvent is mixed with the liquid to precipitate the VDR component asphaltene. The light paraffin used will determine the separated asphaltene from the solubilized product based on what portion of the VDR is soluble or not. The VDR component that is soluble in this light paraffin is referred to as a maltene and is classified with a prefix of the paraffin used such as n-heptane maltenes. This separation process can continue by using the product from each step of VDR component mixed with a lighter and lighter solvent to precipitate an insoluble product. This process allows for specific separated products depending on what is needed. This procedure can be carried out to start with a low H/C ratio and eventually make a high H/C ratio by-product, although is not typically high value.

The solubility of the VDR compounds for solvent extraction depends on the strength of the solvent measured by the Hildebrand Solubility Parameters (HSP) for non-polar solvents. There are two parameters that affect this solubility. The first parameter is a relationship between surface tension and molar volume where, increasing surface tension would depend on decreasing molar volume. The second HSP is the relationship of the heat energy required to evaporate a solvent under constant volume conditions and the molar volume. The relation here is a decreasing molar volume will correspond to an increasing energy of vaporization. These two parameters demonstrate why aromatics have a higher solvent power than aliphatic hydrocarbons. An aromatic has a lower molar volume or higher density than an aliphatic hydrocarbon. The molar volume is inversely proportional to the parameter thus the parameter will have a higher value signifying a higher solvent power.

Michael H Bufalini, May 1^st, 2014

The US Energy Information Association is the most notable source for our countries energy supply and demand. Using the most recent data of supply and disposition the determination of our major fuel sources and import and export business can be analyzed. The Petroleum and Other Liquids data sheet illustrates the break down how the produced crude oil and petroleum products are used for energy consumption per thousand barrels of distillate liquid.

According to the supply data the US produces approximately 11,000 barrels of crude oil and petroleum products per day while importing 9,240 barrels per day. This data table also involves the net production based on these two values while subtracting the production from renewable fuel sources and oxygenate plant production such as Fuel Ethanol. The production value is 75% crude oil production with the other 25% being natural gas liquids and liquefied refinery gases. The crude oil production is expected to have a higher value because it supplies the majority of the vehicles on the road with our combustible fuel, gasoline. Although not a major contribution, natural gas still holds a high percentage because of the growing use of electricity generation, some use for transportation and in home heating.

The finished petroleum use about 50% of the products for the internal combustion engine in vehicles around the country. Another large percent of the finished petroleum products are used for distillate oils. Approximately 4,800 barrels per day are produced of distillate fuel oils for the use of diesel fuel, domestic heating, and in some cases outdoor portable stoves and heaters.

While we are importing 9,240 barrels a day of crude and petroleum we are also exporting about 40% of that amount of the same products. The majority of the US export business is finished petroleum products in the distillate fuel oil category. This is an expected leader of export because outside of the United States, countries use larger transportation methods and more vehicles run on diesel fuel. The largest distillate fuel export is also 15ppm sulfur content or lower which shows a greater reduction of harmful SOx emissions.  Petroleum Coke is also a high exported fuel source of the finished petroleum products. This is most likely used for a source of fuel for other countries power plants.

The refining process follows regulations with how much a certain fuel needs to be refined for permissible amounts of emissions. Certain fuels need more refining to reduce the carbon, sulfur, and nitrogen emissions. The majority of our distillate fuel oil is refined to be under 15ppm of sulfur and our gasoline is blended with additives such as ethanol and other oxygenates to boost octane and meet air quality requirements. With ethanol being in the fuel it ensures higher percentage of carbon dioxide in the emissions rather than carbon monoxide. Ethanol is being produced by hydrolysis from ethylene, which is manufactured in cracker plants from natural gas liquids.