As mentioned in the lesson, the era of thermal refining was during 1910 to 1940. This refining process was used to increase the yield of gasoline, kerosene, and diesel from petroleum through conversion processes as the demand for these fuels increased (particularly for gasoline during World War I). The era of catalytic refining was during 1940 to 1970, spurred by the onset of World War II.

During this time, higher performance gasoline was necessary so thermal conversion processes (characterized by free radical reactions) were replaced by catalytic conversion processes (characterized by ionic reactions). These catalytic processes included cracking, reforming, alkylation, and polymerization. As mentioned in the lesson introduction video, something that I found very fascinating was that what was initially a very competitive market among oil companies before WWII suddenly changed when everyone (in the Allied forces) joined together in a combined effort to produce better refining processes. This in turn developed higher quality (higher octane) and more powerful fuel for the war effort.

Interestingly, the German opposition originally developed synthetic oil by utilizing processes such as the Fischer-Tropsch process and Bergius process through coal gasification. They developed aviation/jet fuel, oils, and rubber among other things throughout WWII. Source: http://en.wikipedia.org/wiki/Synthetic_fuel.

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).

Hydrocracking is essentially the combination of two processes: hydrogenation and cracking. Therefore, hydrocracking utilizes a bifunctional catalyst. The catalysts (highly active noble metals used for hydrogenation e.g. Pt and Pd) used in hydrocracking are very susceptible to poisoning and great care must be taken to remove sulfur from the feedstock. The process is typically accompanied by hydrotreating in order to remove heteroatom species (e.g. S, N and O). Additionally, while catalytic cracking is a carbon rejection process, hydrocracking is in a hydrogen addition process. Therefore, some complications from coking are avoided during the hydrocracking process. Several factors distinguish these two cracking processes; however, typically both processes are used in order to provide the most optimal yield of products in an economically efficient manner. The advantages of hydrocracking include its ability to handle a wide range of feedstock, as well as the selectivity of its distillates.

The primary objective of both cracking processes is to produce lighter saturated hydrocarbons with reduced molecular weights and boiling points from heavy oils. But due to the fact that aromatic rings cannot be cracked until they are fully saturated with hydrogen, the hydrocracking process allows for the processing of more aromatic feedstock, including the byproducts of catalytic cracking (e.g. light cycle oil). Furthermore, by modifying reactor configurations (e.g. fixed bed, ebullated bed, or expanded bed), catalysts, and hydrogen/carbon ratios, hydrocracking can be highly flexible, with the ability to process both relatively light feedstock as well as heavy vacuum residue into light and middle distillates.

Another difference between hydrocracking and catalytic cracking includes the change in enthalpy; while catalytic cracking is an endothermic process, hydrocracking is an exothermic process. The heat for catalytic cracking is supplied by the regeneration of catalysts. The evolution of the catalytic cracking (from Houdry to Thermafor to the modern fluid catalytic cracking) has continuously improved upon the thermal efficiencies of the process.

Although the hydrocracking process has several advantages over fluid catalytic cracking, hydrocracking is, in comparison, a more costly process. Therefore, it is not exclusively used, and refineries typically operate with both processes in order to produce the most desirable yield of products.

The most notable change in the supply of petroleum fuels for the United States is the drastic growth in domestic production of both natural gas and crude oil. The development of production in tight formations, or shale formations (particularly the now well-known Marcellus Shale in the Northeastern United States) combined with the technological advances (hydraulic fracturing and directional drilling), has had far-reaching effects, including decreased both dependency on and imports from other countries. The largest change is from Africa, with imports from that region decreasing by 90% from 2010 to 2014. For comparison, 2008 tight oil production accounted for only 12% of US production, while in 2012 the number rose to 35%. By 2019, we can expect half of US oil production to be from tight oil formations. This increased domestic production has also reduced costs, allowed prices to decrease, and making natural gas a viable and inexpensive alternative to coal in the generation of electricity. While increased use of natural gas in the electricity generation sector is partially environmental policy-driven, much of this growth can be attributed to the mechanics of a price competitive market. This change is beneficial, as when comparing these two sources of energy, combustion of natural gas produces far less carbon dioxide, nitrogen oxides, and sulfur emissions than coal. Natural gas also does not contain harmful particulate matter such as mercury. Furthermore, there have also been advances in other renewable sources of energy including wind and solar power. As these sources become more competitive as costs decrease, we can expect renewable electricity generation to account for 16% of total electricity generation in the United States by 2040.

There have been many positive changes regarding the environmental concerns from combustion of petroleum fuels in internal combustion engines. Though the total miles driven and vehicles used have increased (total vehicle miles traveled increasing by 0.9% each year), it has been more than offset by the increased fuel efficiency of engines. Strict regulations and standards set in place have forced manufacturers to develop better and cleaner vehicles. The EIA website states that light-duty vehicle fuel efficiency has increased by nearly 2% each year, and can be expected to reach 37.2 miles per gallon by 2040 from 21.5 mpg in 2012. Additionally, the entire nation has been slowly and gradually moving towards diesel fuels, biofuels, hybrid, and completely electric cars (most notably Tesla, with massive growth in recent years). Overall, I believe that the United States is moving in the right direction with regards to environmental policy and sustainability. However, this is a global issue and countries such as China and India must also follow suit (though India’s new prime minister has stated that the entire country will be moving towards solar powered homes, hoping that each home is powered by the year 2019).

http://ebf301.dutton.psu.edu/2014/05/25/supply-of-petroleum-fuels-in-the-united-states-and-petroleum-fuels-in-internal-combustion-engines/

As mentioned in the lesson, the separation process of crude oil provides insufficient yields for the desired products i.e. gasoline. To satisfy the demand for more desirable products, conversion processes are used to enhance the yield. Cracking is the process of breaking down large molecules into smaller ones. Free radicals are the active intermediate species in thermal cracking (as opposed to ions in catalytic cracking). Though radicals are more stable on ternary or secondary carbons, the weakest bond in a compound is broken and the radical is typically produced on a primary carbon. Additionally, due to the fact that beta-bond scission reactions proceed faster than isomerization in a radical during the thermal cracking process, the final product is primarily composed of straight-chain parrafins and negligible amounts of branched-chain paraffins. Straight-chain parrafins have a lower octane rating – or a higher tendency to knock (self ignite) – an undesirable effect in modern gasoline engines. Therefore, presently thermal cracking is rarely used to improve gasoline yields and instead used to convert heavy gas oils into light gas oils with some byproducts of gas, gasoline, and fuel oil. However, it is still used to improve diesel yields (where knocking is desirable) in countries that primarily rely on diesel fuel.

Vacuum distillation is necessary to separate the heavier components of crude. This is due to the temperature limit imposed in order to avoid cracking of hydrocarbons, an desirable precursor to accumulation of carbonaceous solids (coking) in the distillation column. The Vacuum Distillation Unit receives the residue of the Atmospheric Distillation Unit and operates between 10 to 30 mmHg. The presence of a vacuum essentially lowers the vapor pressure of the atmospheric residue, allowing fractional distillation of heavy distillates while still preventing cracking. The Watson Characterization Factor provides an upper temperature limit for vacuum distillation, but actual temperatures used are typically lower in order to avoid uncertainties and risks of coking. Higher values of the Watson Characterization Factor require lower temperatures and lower values of the characterization factor allow for higher temperatures. This is due to the nature of the hydrocarbons associated with the Watson Characterization Factor – values less that 10 indicate a highly aromatic composition, high stability, and a lower tendency to crack; values between 10 to 11 indicate a napthenic crude with moderate stability and moderate tendency to crack; and values ranging from 11 to 12.9 indicate a more paraffinic composition, which is relatively easier to crack and has the lowest stability among the three.

The three distillation methods introduced to us in this lesson include True Boiling Point Distillation (TBP), ASTM Distillation, and Equilibrium Flash Vaporization (EFV). These methods are commonly used to generate laboratory data on crude oil, and their distillation fractions have varying degrees of separation. The largest degree of separation can be obtained by TBP distillation – this method utilizes a high reflux ratio (100:1) and a high number of theoretical plates (>100) for liquid vapor contact. The temperature remains constant during evaporation of each component, providing the least overlap between distillation fractions. ASTM distillation provides the second best degree of separation – in contrast to TBP distillation, the ASTM method operates without plates, has a reflux ratio of essentially zero, and the temperature does not remain constant during this process. EFV is the final method of distillation and utilizes a flowing feed (rather than a batch feed), where separation of liquid and vapor occurs in a flash drum. Distillation occurs at various heater outlet temperatures, providing the least amount of separation between fractions of the three methods. TBP distillation is essentially used for crude assay; the ASTM method is used for determining properties of refinery products; and EFV conveniently provides data for flashing operations.