Wars cause the “tides” to shift and facilitate humans’ potential (and industry) to the next level. An increase in demand for gun & engine lubricators, chemicals for making bombs, and gasoline forced the petroleum industry to attempt satisfying the decade long dream of breaking carbon bonds to reduce the size of the molecule and ultimately increase yield. World War II presented the petroleum industry with an unheard of opportunity that would not have resulted in the same process we use today. Competing refineries all across the World, from the United States, France, Great Britain, and Poland, collaborated in order to create the best possible chemistry and operations so that the Allies fighting against The Nazi Regime would prevail. They became obsessed with increasing the octane number of their gasoline products so much that they started adding TEL to their blend. Little did they know, they were setting themselves up for a “battle” twenty some years down the road with Clair Patterson who proved that the lead burned from their high octane gasoline in automobiles was poisoning humans and the environment. We could say, in an abstract way, that World War II indirectly lead to us discovering the toxicity of lead when burned in engines. The War also pushed the automobile industry to create more fuel efficient vehicles to match the quality of gasoline being produced from the catalytic cracking’s ionic reactions compared to thermal cracking’s free radical reactions. If wars are so influential to the petroleum industry, as history has proved, it makes me wonder what kind of changes would be made if a third world war were to break out within the next year.

Sources:

F. Self, E. Ekholm, and K. Bowers, Refining Overview – Petroleum, Processes and Products, AIChE, 2000, Chapter 6. [6.] M.R. Riazi, S. Eser2, J. L. Peña Díez, and S. S. Agrawal, “Introduction” In Petroleum Refining and Natural Gas Processing, Editors: M. R. Riazi, S. Eser, J. L. Peña, S. S. Agrawal, ASTM International, West Conshohocken, PA, 2013, p.6

http://www.space.com/25579-cosmos-recap-earth-age-lead-poisoning.html

There are a number of reasons why refineries treat their wastewater right on site instead of sending it off to a municipal treatment plant, but for the most part, it has to do with the contaminants present in the samples. Wastewater from processes such as desalting, distillation, thermal and catalytic cracking, and coking possibly contain benzene (toxic aromatic compound), H₂S, NH₃, heteroatoms, and acids. Requirements for wastewater in municipal treatment plants vary from state to state so refineries are just playing it safe by treating their water in-house. The refineries have the equipment and knowledge to detect the exact amount of contaminant species, therefore they should be the ones who treat it. On top of all this, you can’t combine the four different types of wastewater (cooling water, process water and steam, storm water, and sanitary sewage water) so transporting it to the municipal plant would require four different vehicles, a bunch of unneeded money spending, and communication of specifics. Even though industrial wastewater treatment plants are capable of removing chemicals and acids, it is not safe to use the facilities for water that has came in contact with petroleum fractions. The contaminants found in this water is basically human poison and is best left to the people who know where the all the water has came from.

Sources:

Petroleum Refining, by J. H. Gary, G. E. Handwerk, M. J. Kaiser, 5th Edition, CRC Press NY, 2007, Chapter 13, Supporting Processes, pp. 290-293.

http://en.wikipedia.org/wiki/Industrial_wastewater_treatment#Oils_and_grease_removal

http://10statesstandards.com/wastewaterstandards.html#52

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.

The methods of cracking chain molecules in petroleum have expanded over the past century just as every other invention and process has been modified for the benefit of the consumer. Thermal cracking was developed one hundred years ago as a way to salvage more useful products (gasoline, naphtha, diesel) from the tower residues and heavy fractions. This was the first commercial conversion process. By using hydrogen abstraction and beta scission, engineers were able to “chop up” the long chain alkanes that are the responsible for the heaviness of the residue into shorter C-H chains. Although the first scientists may not have completely known the chemistry of the reaction, they knew that this process was going to be a crucial part of petroleum refineries, especially with the boom of automobiles in the early 20^th century. The influx of automobiles may have been responsible for the beginning of the use of thermal cracking, but it also may have been its demise. The process is barely ever used for increasing the yield of lighter products since it proved to produce low octane numbers (compared to its more chemically accurate counterpart, catalytic cracking). Thermal cracking is still used in today’s refineries, yet most of the time it is utilized for the production of ethylene.

Dewaxing is a separation process that takes advantage of deasphalted oil (DAO) and heavy vacuum gas oil (HVGO) from the vacuum distillation tower as feedstocks in producing lubricating oil base stock and, to some extent, distillate fuels such as gasoline. The goal of dewaxing is to remove hydrocarbons that would potentially increase the pour point of the lube oil base stock to a desirable range of -9^o – 14^o F. There is two different processes that result in this marketable lube oil: solvent dewaxing and catalytic dewaxing.

Solvent dewaxing is a physical process that uses refrigeration, scraping techniques, and methyl ethyl ketone (MEK) and propane solvents to separate the feedstocks and produce a valuable product. The MEK solvent and the deasphalted oil combine in the first phase and go through a series of refrigeration processes at different temperatures to form wax crystals, which are then transported to a rotary filter where a filter cloth separates the wax from the oil + solvent. The wax goes on to produce candle wax and petroleum jelly while the dewaxed oil purifies into the desirable lube oil base stock. Issues that arise from this process come from choosing which type of solvents to use. Most refineries use MEK even though propane can be used from multiple aspects of the process, save money, increase filtration rates.

Catalytic dewaxing is a chemical process that, by nature, is actually a conversion process. It uses catalytic cracking of n-paraffins, but since the purpose is to remove wax, it is classified as a separation process. There is not much detail to this process although it does use hydrogen addition to prevent coking. It is obviously the best way to dewax the feedstocks because it results in a product with lower pour points, high yield, and high stability. Catalytic dewaxing also allows for the production of light distillates such as gasoline since the n-paraffins are cracking.

In reality, distillation can never achieve absolute separation of the different hydrocarbons liquids that enter the Light Ends Unit (LEU) as feedstock. Theoretically, there is a way to achieve a degree of separation that proves suitable for the refinery’s needs by distilling small fractions of the liquid using a number of ‘theoretical plates’. The feedstock that enters the LEU has components of low molecular weight and high volatility. These characteristics allow refineries to analyze the feedstock on a molecular level and define the degree of separation in terms of specific hydrocarbon concentrations. Once a stage of distillation is complete, the new condensate, enriched in the more volatile component, is taken past the next plate and redistilled in a different section. This process proceeds for however many theoretical plates are calculated until almost-pure components are left. For the Light Ends Unit, the feed is separated into two fractions, the distillate and the bottoms.

Solvent extraction out of the vacuum distilled residue pulls the asphaltenes out of the one-phase material. The strength of a specific compound, determined by the two Hildebrande Parameters, indicates the solubility of said compound in a solvent. The first parameter depends upon the surface tension and molar volume of the non-polar solvent while the second parameter uses the solvent’s energy of vaporization and molar volume. With these different characteristics in mind, it is easy to see how each component of the vacuum distilled residue has their own solubility properties. Aromatic hyrdocarbons have higher density than aliphatic hyrdrocarbons, which means that they also have a lower molar volume. This results in the increase of the second Hildebrande Paramenter (and consequently the increase of compound strength) since molar volume is the denominator in the equation. On the same line, higher carbon number paraffins have a larger molar volume, resulting in a lower strength value. Using this information, refineries add a large amount of low strength paraffin solvent to the vacuum dissolved residue to basically ‘cancel out’ the asphaltene’s solubility and yield solid particles that can be filtered out.

The three most commonly used distillation methods are true boiling point distillation, American Society of Testing and Materials (ATSM) Distillation, and Equilibrium Flash Vaporization. Each has its own benefits and drawbacks, but for the most part, the degree of separation between distillation fractions greatly decreases with the order of methods I just mentioned. True Boiling Point distillation consists of at least 100 theoretical plates and boasts a high reflux ratio of 100, making this method great for characterizing crude oils and constituting a significant component of crude. When processing binary mixed crudes, the temperature remains constant until the higher percentage compound is evaporated. Contrary to TBP distillation, ATSM distillation contains zero theoretical plates and has a reflux rate of zero. These characteristics of this method prove that it is perfect for refinery products and property calculations & correlations in distillate fractions. Finally, the least effective and most different from the other two methods, Equilibrium Flash Vaporization heats a flowing feed and separates the liquid and vapor in a flash drum, which is installed between the feed heat exchangers and the atmospheric furnace. Since EFV has the produces the lowest degree of separation, it is mostly used for data collection in finishing operations.

Increasing the furnace outlet temperature further in the atmospheric distillation unit in order to process the heavier fractions of crude oil would result in the breaking of chemical bonds (thermal cracking) causing loss of product and equipment problems due to coking. Since boiling point decreases with a lowered pressure, transferring the heavy crudes to a vacuum distillation tower allows the refinery to separate these at lower temperatures, thereby reducing the amount of energy invested into the process. Pressures in the vacuum tower range from 25mmHg – 40mmHg, but can be lowered to 10mmHg by the addition of steam into the furnace. It is ideal for the difference in pressures at the top and bottom of the tower to be at a minimum so special packing materials are used instead of trays to improve fractionation. With all this change in pressure, it is also important to keep check on the exact temperatures being used. The Watson Characterization Factor (K_w) is used to estimate the upper temperature limit. Graphing K_w versus Temperature creates a band with an upper and lower line. It is necessary to stay below the top line, although if you need to be extremely careful (especially with paraffinic oils) it is best to stay below the bottom line as well.