It has been a long history since petroleum refinery started in 1855 in U.S. During 1910 to 1940, thermal refinery was the major refinery process to produce light and middle distillate petroleum products. However, the new chemistry was introduced and catalytic refinery process was developed in 1930s. Compare to thermal refinery, catalytic refinery produces higher yield of petroleum products with higher octane number that reduce knocking. During the World War II, the U.S need higher yield of petroleum products and require higher octane number to run more powerful engines. The pressure from the war provides stimulus to urgently develop catalytic technologies. The World War II helped to start the catalytic age of refinery which between 1940 and 1970.

During the catalytic cracking, reforming, alkylation, polymerization was introduced and they changed the way of making high octane number gasoline. Hydrotreatment was also invented to protect platinum catalyst that used in reforming. During the World War II, intense activities of development of catalytic refinery happened. Visbreaking, alkylation, isomerization and fluid catalytic cracking were invented. All four technologies contribute to increase the yield of petroleum products which with higher octane number. These technologies are still important in the refinery process today. The catalytic age of refinery was end in 1970 not because the new chemistry was introduced. It is due to the 1973 and 1979 oil crises and environmental concerns. The World War II helped to start the catalytic age of refinery. Even the catalytic age of refinery ended, the lessons and experience we learned from catalytic age helped us go even further in the age of heavy end conversion refinery.

References

1. F SC 432 class website Lesson 11

https://www.e-education.psu.edu/fsc432/content/catalytic-refinery-1940-1970

2. Katrina C. Arabe, “How Oil Refining Transformed U.S. History & Way of Life”  January 17th, 2003.

http://news.thomasnet.com/IMT/2003/01/17/how_oil_refinin/

3.Congressional Research Service, “The U.S. Oil Refining Industry: Background in Changing Markets and Fuel Policies”

Click to access R41478.pdf

According to the lessons we have learned so far, various processes involve with hydrogen consumption and would produce wastewater. Cooling water, process water and stream, storm water, and sanitary sewage water are the four types of wastewater that were introduced in lesson 10. Process water and stream is the most polluted wastewater among four since it directly contact with petroleum fraction. Storm water could also be toxic due to exposure to pollutants and spills by accident. The pollutants that found in wastewater include toxic aromatic compounds, heteroatom compounds, strong acids, dissolved gases, suspended and dissolved solids. Compare to process water and storm water, cooling water and sanitary sewage water are less toxic and need less treatment to directly send to public treatment plants.

Refinery wastewater cannot be treated in municipal wastewater treatment plants mainly due to its capacity of treating heavy toxic chemical wastewater. Most public wastewater facilities are building to treat household wastewater and wastewater from industrial. There are some heavy chemical wastewater plants, but not many of them. As we talked about refinery wastewater previously, it contains different types of heavy toxic chemical such as H2S that municipal wastewater treatment plants hardly to treat and probably will harm the plants. It is important that refinery wastewater go through primary treatment which is physical treatment to strip H2S and remove oil and solids. Refinery wastewater also needs to go through the secondary treatment which uses microorganisms to further remove organic contaminants. After these two treatments, refinery wastewater became more applicable for public treatment facilities.

References:

1. F SC 432 class website lesson 10

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

2.EPA. Washington, DC (2004). “Primer for Municipal Waste water Treatment Systems.”

Click to access primer.pdf

3. The Washington State Department of Ecology, “Water Pollution Prevention Opportunities in Petroleum Refineries” Ecology Publication No.02-07-017

Click to access 0207017.pdf

As we learned from lesson 8, catalytic reforming is known as a conversion process in the refineries. The main objectives of catalytic reforming is to convert heavy naphtha into high-octane reformate and produce hydrogen as significant by-product. The product of catalytic reforming is also low in sulfur and is a major blending product of gasoline. Platinum (Pt) and palladium (Pd) are contained in most catalyst of reforming. From this process, hydrogen which is one significant byproduct is produced for further hydrotreating and hydrocracking process. Especially the hydrotreating process is necessary for naphtha feedstock before it go through reforming process, because platinum catalyst needs to be protected by poisoning from sulfur and nitrogen.

There are some limits on catalytic reforming capacity in the U.S. Refineries. Firstly, as lesson 8 mentioned, due to regulations and limitations on benzene and total aromatics for gasoline in U.S. and Europe, the amount of reformate can be used is limited. As we mention in reforming’s objectives, hydrogen is still an important byproduct from catalytic reforming to be used in refineries. Secondly, in order to maintain the yield of hydrogen and reformate, hydrocracking is an undesired reaction in reforming process.  It would consume hydrogen to produce gaseous hydrocarbon to lower the yield of hydrogen and reformate. Some conditions such as pressure at 50 to 350 psig, hydrogen/feed ratio of 3–8 mol H₂/mol feed, and liquid hourly space velocities of 1–3 h^-1 are used to prevent hydrocracking during reforming. Thirdly, coke deposition during reforming process deactivated catalyst even with the usage of hydrogen. Semi-regenerative process was introduced in 1946 and it need to be shut down every 3 to 24 months for catalyst regeneration. Cyclic process expands the on-stream time up to 5 years, but it is not a favorite process by the industries. Continuous process which is introduced in 1971 allows remove and replace catalyst during operation to keep its high activity. However, it is expensive to operate.

Reference

1. F SC class website lesson 8

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

In order to produce larger amount and high octane contain gasoline, catalytic cracking was developed during World War II. As moving alone with the time, the improvements of this process increase the thermal efficiency of the process. Fluid Catalytic Process (FCC) which was introduced in 1942 has the highest thermal efficiency among the catalytic cracking processes. Catalytic hydrocracking has shorter history than catalytic cracking and it was started in 1958. It is also known as a hydrogen addition process, but Fluid Catalytic Process is known as carbon rejection process. These two processes also have differences in feedstock, process objectives and their products.

For catalytic cracking, it used acid catalytic. Straight run atmospheric gas oil (AGO) and light vacuum gas oil (LVGO) are the typical feedstock for catalytic cracking. Compare to catalytic cracking, hydrocracking use metal catalytic on acid support and has a wider range of feedstock. It can process more aromatic feedstock which resists cracking such as light cycle oil (LCO). It can also process heavy vacuum residue under the extreme condition such as high hydrogen pressures. Those extreme conditions prevent the process from shut down which due to extensive coking on catalyst.

As we learned from lesson 7, the process objectives of two processes are also different. For hydrocracking, its main objective is to decrease both molecular weight and boiling point of heavy oils and produces saturated hydrocarbon from highly aromatic feedstock such as light cycle oil. Since the product of hydrocracking has low sulfur and nitrogen content, it also contributes to limit the sulfur emission and aromatic hydrocarbon in motor fuels. The main objectives of catalytic cracking are to increase the yield of gasoline and number of octane in the gasoline. At the same time, it also lower the yield of coke and achieve higher conversion, but prevent the over cracking.

From the products, we could also see the differences between these two processes. The products of catalytic cracking include light gas, gasoline with high octane component, light cycle oil, heavy cycle oil, slurry oil, and coke by-product. As we talked about the objective of catalytic cracking previously, the gasoline with high octane component is the main product of catalytic cracking. For hydrocracking, diesel, jet fuel, and gasoline with extreme low sulfur component are the main products. The process uses metal catalyst and hydrotreating to remove heteroatoms such as sulfur and nitrogen. The products of hydrocracking contain low sulfur and nitrogen component which is more environmental friendly. At the same time, hydrocracking produces high yield of valuable distillates without some undesirable byproduct such as heavy oils, gas and coke.

References:

1. Class website lesson 7

https://www.e-education.psu.edu/fsc432/content/lesson-7-catalytic-conversion processes-part-1

Thermal cracking was first developed by William Merriam Burton in 1913 which operated under the temperature 700 F -750 F and pressure at 90 psi. It is probably the first commercialized cracking process. By this time, it is also the history of cracking of heavy crude oil fraction to light fraction started. However, as we learned from lesson 5, thermal cracking produces short straight chain alkanes from longer straight chains found in gas oils and the reactions were governed by the free radicals. The process actually produces gasoline that contain lower octane number than that of gasoline which produced by catalytic cracking. It is due to isomerization of free radicals is not favored. During 1920, the petroleum refining industry was facing a challenge called engine knock. In order to solve the problem, it needed more powerful and stranger engines, but that means it also require gasoline which contain higher octane number. By 1930, gasoline had achieved the octane ring around 60 and 70. The newer and more powerful engine required higher octane gasoline which up to about 100, but thermal cracking could not raise its octane number any higher. It is also the reason that thermal cracking is not common process in U.S refineries. Thermal cracking once was the primary process for distillate fuel production. Even it is not anymore, it still remain as an important process in refineries to produce diesel fuel and ethylene.

Dewaxing is a separation process that removes wax from feedstock such as DAO from deasphalting and HVGO from vacuum distillation in refining process. Wax is a desirable by-product which is necessary to remove for producing lubricating oil base stock with low pour points. Solvent dewaxing and catalytic dewaxing are the two commercial methods of dewaxing that generally used in refining process. Solvent dewaxing is a physical process which involves freezing and solvent transport. Methyl ethyl ketone (MEK) and propane are the two main solvents used in this process. In US, MEK is the most common solvent used in process because it has advantages such as lower capital investment, energy saving and higher filtration rates. The process need to freeze the feedstock in a several stage. Wax crystals will be formed by solidifying wax compounds thought the refrigeration. In a rotary filter, crystals will be dissolved in solvent and separated. Eventually, the layer of wax will go through the steam stripping unit to separate solvent from the product. Unlike solvent dewaxing, catalytic dewaxing is a chemical process which involves reactions of long-chain n-alkenes. A selective catalytic cracking of n-paraffins take place in this process. In the pores of molecular sieve catalysts (zeolites), the pores only open 0.6 nm to filter i-paraffin out. Through this process, the ratio of i-paraffins and n-paraffins will increase to lower the pour point. In order to prevent coking on the surface, hydrogen is used alone the process. This cracking process produces some by-products such as gasoline. Overall, two dewaxing achieve the goal to lower the pour points and separate wax. However, catalytic dewaxing produce lube base stock with even lower pour point and in higher yield. Solvent dewaxing produce lube base stock in a lower yield because to separate the wax from oil in this process is hard.

In lesson 4, we learned that distillation is a separation process which depends on the boiling point of compounds. Compare to distillation, solvent fractionation fractionate the feedstock or vacuum distillation residue (VDR) depend on the solubility of the compound in the given solution. Use graph from lesson 5 on class website as an example, it showed us a simple flow of the process. Asphaltenes, which are compounds that have highest molecular weight of VDR, is soluble in aromatic solution such as benzene and toluene. They can be separated by using precipitation under the condition that paraffin solvent was mixed in. Maltenes is the part of VDR which is soluble in paraffin solvent and also known as a solvent in the separation process. For further separation of n-heptane soluble, a lighter and weaker solvent n-pentane is used. That gives us an insoluble fraction (hard resin) and soluble fraction (n-pentane). Even lighter solvent propane is used to separate soluble fraction (n-pentane) to soft resin and oil products.

Since there is a large difference in structure of asphaltenes and oil fractions in VDR, it is normal for us to see a suspension of discrete asphaltene particles rather than a solution in VDR. However, VDR normally appear as a solution (one-phase material). The gradient solubility model is a general acceptable hypothesis that explains what we observed. In this model, the strength of solvent influences the solubility of a compound in given solvent. Hildebrand Solubility Parameters (HSP) measures the strength of solvent in this model. There two types of parameters used in the measurement and they correlate well to each other. 1^st Hildebrand Parameter depends on surface tension and molar volume of the given solvent. 2^nd Hildebrand Parameter depends on energy of evaporation and molar volume of given solvent. From the equations of two parameters, we can see that solubility increase with increasing surface tension, increasing energy evaporation and decreasing molar volume. As we know, aromatic solvent are stronger solvent than aliphatic hydrocarbon and it is explained by two types of Hildebrand parameters. That also explains why increasing carbon number make the solvent power of paraffin solvent increase.

Atmospheric Distillation (CDU) separates the heavy and light crude In Atmospheric Distillation (CDU), it process with a network of heater to heat the crude to about 550 F. Then in the further process the temperature will be raised to about 750 F in furnace. In flash zone, the vapor fraction would go toward the top of the column and the liquid fraction would be send to vacuum distillation (VDU).  The vacuum distillation (VDU) is needed due to the unwanted high temperature. Such high temperature will cause cracking and coking on the surface. In order to lower the temperature, a vacuum chamber is designed to lower the pressure which to lower the temperature.

From the temperature vs Watson Characterization Factor plot that post on class website, it provides us a range of temperature which helps to avoid coking.  The risk of coking is negligible when the operation temperature is low than the band of temperature that showed on plot. However, when it operates under the temperature that is within the area of band, it is possible to cause coking during the process. From the plot, we can also see that higher Watson K factor leads to lower temperature band. Refer to what we learned in lesson 2, Watson K factor is calculate depend on physical properties. Paraffinic has higher Watson K factor than naphthenic and aromatic. It means paraffinic is easier to cause coking than naphthenic and aromatic at high temperature.

Three distillation methods that introduced in lesson 4 are True Boiling Point Distillation (TBP), ASTM Distillation (ASTM) and Equilibrium Flash Vaporization (EFV). Since the method of each distillation is different, each of them has their own utility, application in refining and separation performance.

The best possible separation is achieved in True Boiling Point Distillation (TBP). True Boiling Point Distillation (TBP) used more than 100 theoretical plates and a high reflux ratio (R/P) of 100 in the separation process. Since it has such outcome, it is usually used to characterize crude oils and constitute a significant component of crude essay.

Compare to True Boiling Point Distillation (TBP), ASTM distillation (ASTM) also used batch operation. However, the operation incorporates exclude contact plate and a reflux ration of 0. A slight reflux may involve due to the condensation of vapor on the tube. In petroleum refining, the method is used to refine products, calculate properties and correlate distill fractions.

Equilibrium Flash Vaporization (EFV) probably provides the lowest degree of separation among the three distillation methods. It contains a heater to heat a flowing feed. In the flash drum, the separation of liquid and vapor take place. In refinery, Equilibrium Flash Vaporization (EFV) always provides clear and useful data for flashing operation for us to interpret.