Petroleum refining has been around since the 1850s, when a single pot batch distillation was first done to produce kerosene as the major product, and since then it has evolved in many ways into an integrated, complex process that we use today to produce a vast amount of products and fuels. During its existence, petroleum refining has been influenced by many historical events that the world has seen. One of these historical events that greatly influenced petroleum refining, is the Second World War

In the late thirties, new catalytic technologies were being investigated by scientists in the US and around the world. When World War II came around in the forties, countries and scientists were put under intense pressure to make strides in the advancement of petroleum refining, thus providing the stimulus needed to urgently develop catalytic technologies. This catalytic age took place from 1940 to 1970 and was thoroughly fueled by World War II. The historical timeline of petroleum refining shows a clear influx of process development during the age of World War II.

The catalytic refinery of the 1940s largely resembles that of which we use today, in that the goal is to produce high yields of gasoline. This age saw the introduction of catalytic cracking, reforming, alkylation, and polymerization, all of which have contributed to revolutionizing the production of high octane number gasoline. These revolutions largely contributed to the war effort as well. The Catalytic refinery also saw the development of hydrotreatment, which was essential to protect the platinum catalysts used in reforming.

References:

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

In petroleum refining, a large amount of water is used in the refining process. This water is processed using wastewater treatment techniques. Since the amount of water used in refining is so vast, waste water treatment is an integral part of the refining process. There are four different types of waste water; cooling water, process water and steam, storm water and sanitary sewage water. These four types of water carry large amounts of pollutants as well. Pollutants like, liquid hydrocarbons, suspended and dissolved solids, mercaptans, phenols, amines, and cyanides. All of these pollutants are a direct result of the water’s use in the refinery.

There are two types of measurement systems that are used to measure the level of contamination in waste water. Those two types are the Biochemical Oxygen Demand and the Chemical oxygen demand. Biochemical Oxygen Demand measures the amount of oxygen consumed by microorganisms in decomposing organic matter, and the Chemical Oxygen Demand measures the total oxygen consumption by organic and inorganic chemicals present in water.

Refinery waste water however, can’t be treated in municipal waste water treatment plants. This is because the municipal water treatment plants are not capable of processing the contaminants that arise from water that is used in petroleum refining. It is also important to keep the different wastewater streams segregated as the different types of wastewater have different levels of different contaminants. This making the combining of the streams undesirable as the treatment of the water would be much more difficult, placing to high of a strain on the water treatment machinery.

References.

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

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

In petroleum refining there is a strong need to “crack” heavy, long chain alkane feedstocks into lighter, shorter chain alkane feedstocks. This can be done in a variety of ways. As mentioned in earlier lessons, one of these ways is through the process of thermal cracking. Another way this can be achieved is through the process of catalytic cracking, which will be the focus of this blog post.

Compared to thermal cracking, catalytic cracking occurs at lower temperatures and pressures, is more selective and flexible, and incorporates a catalyst. Catalytic cracking processes have evolved over the years, and are an exemplary display of chemical engineering. The most recent catalytic cracking technique was developed in 1942 and is called Fluid Catalytic Cracking. Even more recent is the addition of Catalytic Hydrocracking in refineries, which was developed by Chevron in 1958. These two most recent developments are useful in their own way yet very different in many others.

From a feedstock stand point, both catalytic cracking and catalytic hydrocracking use very different compounds. One of hydrocracking’s main advantages over catalytic cracking is its ability to cope with a much wider range of feedstocks. Hydrocracking processes are able to handle the upgrading of heavier crude oil fractions such as heavy vacuum gas oil and vacuum distillation residue. The heaviest fractions of crude oil, heavy vacuum gas oil and vacuum distillation residue, may not be easily processed by catalytic cracking because of potential problems with coking on the catalysts. For this reason, hydrocracking is able to handle much heavier feedstocks than catalytic cracking.

As for the processes themselves, there are many differences as well. The basis of catalytic cracking is carbon rejection, while hydrocracking is a hydrogen addition process. Catalyst cracking uses an acid catalyst, while hydrocracking uses a metal catalyst on acid support. Another differnce is that catalyst cracking is an endothermic process while hydrocracking is an exothermic process.

There are two main processes associated with hydrocracking, and they are; hydrotreating and hydrocracking. Hydrotreating is for the removal of heteroatoms, while hydrocracking is for the increase of the H/C ratio of the hydrocarbons and to decrease their molecular weight. This is done by hydrogenation and cracking, respectively. Hydrocracking is a very versatile process and can be adjusted according to its wide range of feedstocks.

In catalytic cracking, the process is a little different, and has evolved over time. The first process was the McAfee process which was a batch reaction process that involved a lewis acid to be incorporated in the batch. The next process was the first commercial process called the Houdry process which consisted of a continuous feedstock flow with multiple fixed-bed reactors. The incorporation of the reactor was what allowed the process to be used commercially. The process which followed the Houdry process was the Thermafore Catalytic Cracking process which adopted the use of moving-bed catalysts. Finally the last an most recent process is the afore mentioned Fluidized Catalytic Cracking which uses a fluidized bed catalyst. All of the processes were adapted and modified to increase the thermal efficiency of the process and have been increasing in order of appearance.

The last difference between hydrocracking and catalytic cracking is the products which they produce. The products of catalytic cracking can be described using the acronym PIANO, to represent the Paraffins, Iso-paraffins, Aromatics, Naphthenes, and Olefins produced in catalytic cracking. Catalytic cracking’s most important product is high octane gasoline which is a direct result of the branching alkanes produced in the process. As for hydrocracking, it provides a sizable amount of the diesel fuel production. This is due to straight-run light gas oil being a preferred stock for FCC to produce gasoline as the principal product. Catalytic cracking produces more gas and more coke than hydrocracking, but the liquid yield is higher for hydrocracking. Hydrocracking is more desireable in many areas when compare to catalytic cracking, but cost is not one of them as it is much more expensive to run.

References:

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

Another separation process in petroleum refining is, the process of dewaxing. What dewaxing is, is exactly what one might guess, and that is the removal of wax from a feedstock in an oil refinery. That feedstock can either be, deasphalted oil from deasphalting or heavy vacuum gas oil from vacuum distillation. The wax that is removed from the feedstock is long chain paraffin moleculues that solidify readily within the feedstock and once removed can be sold as a marketable by-product. Once a feedstock has undergone dewaxing, it can be used as the basis for lubricating oils, this is the most desired product of dewaxing.

Dewaxing however, can be accomplished using one of two different methods. Those methods are known as solvent dewaxing, and catalytic dewaxing. These two types of dewaxing have their obvious differences.

The first type, solvent dewaxing, is a physical process that includes the refridgeration of a feedstock after it has be mixed with a solvent. What happens is, once the feedstock is refrigerated, the wax within it solidifies and forms crystals. These crystals are then carried to a large rotating drum covered by a filter cloth. It is on the cloth that the wax will accumulate, thus removing it from the feedstock until it is removed from the surface of the drum using a large blade. This product is called slack wax and it then further undergoes steam stripping to recycle and remove the solvent. This wax product can then be used for things like candle wax and petroleum jelly.

Catalytic dewaxing is the second technique used and this is a chemical process. Catalytic dewaxing is the selective cracking of the long chain paraffins or wax into smaller chain alkanes. This is done by way of using a sieve catalyst to filter out the i-paraffins and filter the n-paraffins into cracking reactions. This is accomplished by way of using catalysts with very small pores, as small as 0.6 nm, that only allow n-paraffin’s long chain structure to pass through while blocking the bulky i-paraffins. Catalytic dewaxing is the cheaper of the two processes, as well as it is more flexible because it can be used to produce either lube oil base stock or light distillates.

Solvent fractionation is a further form of distillation that takes place in the Light Ends Unit (LEU). The feedstock for solvent fractionation is the residue that is left over from previous Vacuum Distillation, aptly called, vacuum distillation residue (VDR). VDR is a very heavy viscous compound that is solid at ambient temperatures. The reason vacuum distillation residue is so dense, is because of its high aromaticity along with its high asphaltene concentration. Asphaltenes are the highest molecular weight compounds contained in VDR, and appear in solution. What solvent separation is, is when the asphaltenes within VDR are precipitated from the solution using a light paraffinic solvent. The portion of the VDR that is soluble in the paraffin is called maltenes. The first paraffin used is typically n-heptane. The n-heptane soluables can further be separated using n-pentane, which is a lighter an weaker solvent. The result of this step is an insoluable compound called hard resin and n-pentane soluables. Finally, the lightest of the solvents, propane, is used. This final stage yields soft resin and oil products. In refining, this is done by skipping to the final step and only using propane, which yields asphalt and deasphalted oil.

The solubility of compounds in different solvents can be measured. For non-polar solvents, solvents are measured using Hildebrand Solubility Parameters (HSP). What the Hildebrand Solubility Parameters are, are two parameters used to accurately determine the solubility power for non-polar solvents. The first of the two parameters pertains to the surface tension and the molar volume of the solvent, while the second pertains to the energy of vaporization and the molar volume of the solvent. In general, the solubility parameter increases with increasing density of the solvent, as well as increasing surface tension or energy of vaporization of the solvent. With this knowledge we are able to understand why using too large of a volume of a solvent will interfere with the solubility of asphaltenes.

In petroleum refining, there are many processes that are import to achieving the overall fuels necessary for a refinery to sell. One of the main processes crude must undergo is distillation, where the crude is heated to a desired temperature in order to separate the crude into desired feedstock to undergo different treatments to get out different products. There are two types of distillation, the first is atmospheric distillation which is done at atmospheric pressure. The second is vacuum distillation.

The reason that vacuum distillation is so vital to the process of refining is due to the fact that if the temperature used in atmospheric distillation were to be raised any higher, it would cause thermal cracking which is not ideal. The reason thermal cracking is not desired is because it would compromise the ending product or fuel in many cases, and lead to coking. In order to avoid thermal cracking, and changing the chemical composition of the feedstock, vacuum distillation is used in succession to atmospheric distillation. The atmospheric residual oil is further distilled in the vacuum distillation column. This distillation must be performed at very low pressures, as low as 10-40 mmHg, in order to further distil the oil without the presence of thermal cracking and eventual coking. Vacuum distillation towers are very large, as tall as 164 feet with a 46 foot diameter. The reason they are so large is due to the expansion of the oil under such low pressures.

In order to complete vacuum distillation, you must know what temperature to perform the distillation at. This is done with the use of the Watson Characterization Factor. The factor is the ratio of mean average boiling point and specific gravity of the oil. This factor is used to further determine the chemical makeup of an oil. Higher characterization factors such as 12.5 or greater indicate a compound is mostly paraffinic, while a lower factor tells us it is naphthenic or aromatic. Once this has been determined, you can better select the temperature at which to Vacuum distil.

 References:

http://en.wikipedia.org/wiki/Vacuum_distillation

http://petrowiki.org/Crude_oil_characterization

One of the many claims to fame of the process is the production of high-performance fuels for internal combustion engines. The process also addresses the environmental concerns of the emissions produced in the combustion of theses fuels in such engines. This will be the topic of this blog post.

In reading the most recent data provided by the environmental protection agency for the week ending May, 16 2014, the United States crude oil refinery inputs were approximately 15.9 million barrels per day. The refineries operated at 88.7% capacity, with gasoline production coming out to 9.6 million barrels per day. As for the products supplied, the last four week period saw an average of 18.9 million barrels per day. Of the 18.9 million barrels, gasoline products were responsible for 8.9 million barrels. The number of gasoline products supplied is up 5.3% from last this time last year. This type of an increase is a direct correlation of the importance of oil refining for the gasoline provided for internal combustion engines.

The refining process uses many tools to improve on the environmental emissions produced by the gasoline burned in an internal combustion engine. The government has set strict and imperative environmental regulations on the oil these processes produce which causes the importance of improving these stages of utmost importance to oil companies.

During the refining process, the petroleum undergoes many stages to improve the emission contents of such liquid. The separation process separates the physical constituents within the oil, removing wax, solids and other impurities. While the conversion process is more for the purpose of adjusting the chemical composition, the finishing process plays a large role in the environmental improvement as well. It is here that hydro treating takes place with the intent to remove the main culprits of pollution from emissions, and that is the sulfur and nitrogen components of the oil. As we know, these elements are what create NOx and SOx, both of which are strictly controlled in government regulations.

These processes described above will become more and more imperative to be improved as the demand for high performance fuels increases along with the number of cars that are on the road. As the weather gets warmer in these coming months, we can also expect to see a rise in cars on the roads. This increase in travel is only adding to the need that is always prevalent in the oil refining industry. As the US looks to become an exporter of oil rather than its norm of being an importer the need to produce a quality oil becomes even more important with competing markets.

References:

1. Lesson 1: Introduction to Petroleum Refining and Crude Oil Composition: https://cms.psu.edu/section/content/default.asp?WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=F20C6357261A4AE2A750C141B721E8C1
2. This Week in Petrolium: http://www.eia.gov/oog/info/twip/twip.asp
3. http://www.eia.gov/oog/info/twip/twip_gasoline.html
4. Weekly Petroleum Status Report Highlights: http://www.eia.gov/petroleum/supply/weekly/