Application of gasoline upgrading combination technology

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Abstract: With the increasing heaviness and inferior quality of crude oil, as well as the increasingly stringent environmental regulations regarding energy conservation and emission reduction, energy production companies are actively seeking ways to improve the utilization rate of crude oil, reduce the yield of heavy-duty products, increase the yield of light oils, boost the production of high-value products, and thereby enhance their economic efficiency. Based on the actual conditions of its facilities, Lanzhou Petrochemical Company proposed an optimized gasoline production process framework of \"three optimizations to ensure one optimization\", that is, \"coordinately optimizing the production of catalytic cracking, gasoline etherification, and alkylation units to maximize efficiency.\" This combined process provides Lanzhou Petrochemical Company with new approaches to improving economic efficiency during gasoline upgrading; it has great applicability and serves as a good model, offering broad prospects for application. At present in our country, air pollution in large cities caused by vehicle exhaust emissions is extremely severe, posing a critical issue that needs to be addressed urgently for sustainable development. To ensure that vehicle exhaust emissions meet standards, one of the main measures is to establish strict fuel standards for vehicles in order to clean up the fuel. Table 1: Gasoline quality standards. Parameters: National Standard II, National Standard III, National Standard IV, National Standard V. Sulfur content: ug/g – ≤500, 150, 50, 10. Olefin content: vol% – ≤35, 30, 25, 25. Aromatic hydrocarbon content: vol% – ≤40, 40, 35, 35. Benzene content: vol% – ≤2.5, 11, 1. Oxygen content: wt% – ≤2.7, 2.7, 2.7, 2.7. Vapor pressure: kPa – ≤74/88, 72/88, 65/88, 60/88. As can be seen from the table, the quality requirements for gasoline become increasingly stringent as we move from National Standard II to National Standard V. With increasingly stringent standards for gasoline and diesel, as well as the growing demand for clean fuels around the world, the purification of fuels has become an unstoppable global trend. Producing clean fuels with low sulfur, low olefins, and low aromatics to reduce harmful emissions from vehicles has become a key focus in the modern refining industry. I. Domestic pathways for gasoline purification technologies In China, the key to producing automotive gasoline that meets emission standards of Grade IV and above is to address the high levels of sulfur and olefins in catalytically cracked gasoline. Hydrogenation technology is currently an effective method for desulfurization and deoxygenation. However, while hydrogenation units produce gasoline with acceptable levels of sulfur and oxygenates, the saturation of oxygenates reduces the octane rating of the hydrogenated gasoline. RON of IV gasoline in producing countries decreases by 0.5–2 units ； The RON value of V gasoline in the producing countries needs to be reduced by about 1 unit as well. Given the current shortage of means for producing high-octane components of gasoline in our country, developing and applying technologies that can significantly reduce the sulfur and olefin content in catalytic cracking gasoline while preventing excessive loss of octane is key to addressing the issue of clean fuel production in our country. (1) Develop technologies for the etherification, isomerization, and alkylation of light olefins, including C4 and C5 light olefin etherification as well as C5–C7 isomerization techniques. These approaches aim to increase the oxygen content in automotive gasoline, while reducing the olefin content and vapor pressure, thereby preventing the formation of photochemical smog and improving the octane rating of gasoline ； Conduct research on solid acid alkylation process technologies to reduce acid leakage pollution in existing alkylation units and increase their operational efficiency. (II) Improving the quality of catalytic cracking gasoline by developing a new generation of catalytic cracking catalysts that produce more light components and olefins, thereby providing sufficient raw materials for etherification and alkylation processes to manufacture high-octane gasoline blending components ； Increase the octane number and oxidation stability of catalytic cracking gasoline, reduce its sulfur content, and maintain an appropriate level of olefin content to ensure the octane number. (III) Increase the production capacity of wide-range reformate gasoline by expanding existing facilities or building new ones, and employ benzene separation processes to strictly control benzene content ； Gradually reduce the proportion of catalytically cracked gasoline in the gasoline pool, optimize the product structure, and promote a reasonable distribution of the octane number of automotive gasoline. II. Research on the Pathways for Cleaning Up Gasoline at Lanzhou Petrochemical Company (I) Optimizing the Pre-treatment Process To ensure the production of gasoline that meets National Standard IV, Lanzhou Petrochemical Company employed selective hydrogenation technology for gasoline to remove sulfur and olefins, thereby producing gasoline that complies with this standard. The gasoline production process is shown in Figure 1. Figure 1 shows the processing flow before the optimization of the gasoline purification production process. However, during operation, the selective hydrogenation technology for gasoline also leads to a loss in gasoline octane number and a decrease in gasoline yield, which affects the production of high-octane gasoline at Lanzhou Petrochemical Company and hinders the improvement of the company’s economic performance. (II) The optimization plan for the cleaner production of gasoline aims to achieve desulfurization and dealkylation of gasoline, improve its quality and reduce environmental emissions, while meeting the requirements of gasoline engines and maintaining a high octane rating for gasoline, thereby enhancing the company’s economic benefits. Lanzhou Petrochemical relies on the existing gasoline production processes (catalytic gasoline, gasoline hydrogenation, and gasoline etherification routes) ； (Catalytic C4, MTBE, selective hydrogenation of C4, alkylation processes), the entire process is optimized to leverage the synergistic effects of these processes, thereby increasing the proportion of low-sulfur, high-octane components in the gasoline blending pool. 1. Optimize the distribution of catalytic heavy oil products to increase gasoline production. As can be seen from the gasoline production process at Lanzhou Petrochemical Company, to improve both the quantity and quality of gasoline, it is necessary for the catalytic units to have the capability to crack heavy oils effectively, produce low levels of coke, and yield high amounts of light hydrocarbons. Additionally, it is important to optimize the composition of catalytic gasoline and liquid hydrocarbons by increasing the content of compounds such as propylene, isobutylene, and C5-C6 tertiary alkenes, thereby enabling refineries to optimize the production process for high-octane, clean gasoline. To meet this requirement, Lanzhou Petrochemical Company employed a new type of heavy oil cracking catalyst with high liquid yield and low residue. This agent exhibits excellent resistance to heavy metals, a high conversion rate of heavy oil, and the ability to reduce coke production. It avoids the problems associated with previous systems, where adjustments such as raising the reaction temperature or reducing the activity of the system’s equilibrium agents led to a decline in the catalyst’s performance in heavy oil cracking, resulting in a decrease in the overall liquid yield and an increase in coke production. It also prevents the increase in dry gas and coke production that occurs as the reaction temperature rises. Table 2 Material balance of the catalytic unit – Differences before and after application
Feedstock, %: Paraffin oil 53.51% → 56.80%, difference of 3.29%; Residue 43.72% → 43.20%, difference of -0.52%; Heavy compounds 1.50% → 0.00%, difference of -1.50%; Coked liquid hydrocarbons 1.27% → 1.30%, difference of 0.03%.
Product distribution, %: Dry gas 3.68% → 3.66%, difference of -0.02%; Liquid hydrocarbons 13.47% → 14.40%, difference of 0.93%; Gasoline 46.66% → 46.95%, difference of 0.29%; Diesel 21.68% → 22.22%, difference of 0.54%; Slurry 4.86% → 4.15%, difference of -0.71%; Coke (including losses) 9.65% → 8.62%, difference of -1.03%. Total liquid yield, %: 81.80% → 83.56%, increase of 1.76%. Residue blending ratio, %: 44.96% → 43.20%, decrease of 1.76%.

Table 3 Quality analysis of stabilized gasoline
Parameters – Before and after application
Boiling range, °C: Initial boiling point 34.5 → 32.5; 10% boiling point 48 → 46.5; 50% boiling point 95.5 → 93; 90% boiling point 169 → 171.5. Final boiling point 196 → 200. Octane number (RON): 90.8 → 92.3. Olefin content: 37.5 → 45.3.

Table 4 Quality analysis of liquid hydrocarbons
Composition, Vol% – Before and after application: <C3 0.22 → 0.05; Propane 9.94 → 9.58; Propylene 39.71 → 41.43; Isobutane 17.04 → 16.96; n-Butane 4.71 → 4.27; Butene-1 + Isobutylene 14.73 → 15.11; Trans-butene 7.93 → 8.09; cis-Butene 5.61 → 5.77. Content of C5 and higher hydrocarbons: 0.11 → 0.07.
As can be seen from the tables above, after the introduction of the new catalyst on an industrial scale, the yields of liquid hydrocarbons and gasoline in the catalytic unit increased by 0.93% and 0.29%, respectively. The yield of slurry decreased by 0.71%, while the total liquid yield increased by 1.76%. The coke production decreased by 1.03% (a reduction of 10.7%). Among them, the total amount of olefins in gasoline increased from 37.5% to 45.3%, and the octane rating (RON) rose from 90.8 to 92.3, providing a guarantee for optimizing the raw materials used in etherification. The overall content of olefins in liquid hydrocarbons is increasing; the levels of butene-1 and isobutylene have risen from 14.73% to 15.11%, while the content of isobutane remains relatively stable, which provides a guarantee for optimizing the raw materials used in alkylation processes. 2. Increase the yield of etherified gasoline and produce more high-octane blending components. The catalytic etherification of light gasoline is a supplementary technique for improving the quality of catalytic gasoline; as a high-octane blending component, etherified light gasoline is fully miscible with gasoline and can be blended with it in any proportion. The catalytic etherification of light gasoline is a process in which tertiary carbon alkenes present in catalytic light gasoline react with CH3OH to produce corresponding ethers. This method reduces the olefin content in gasoline while increasing its octane rating; moreover, it converts about 8%–10% (based on the amount of light gasoline) of methanol into components that make up gasoline. It is thus a process for increasing gasoline production, as well as a way to transform low-value methanol into high-value gasoline components, thereby helping enterprises improve their productivity. Lanzhou Petrochemical Company has built a 500,000-ton/year catalytic light gasoline etherification unit; by optimizing operations in Tonghua, it has continuously improved the economic efficiency of this unit, achieving good results. Table 5: Properties of the etherified products Time Before application After application Conversion rate of C5 tertiary alkenes, %: 70 71.38 Conversion rate of C6 tertiary alkenes, %: 46 46.11 Total ether content, %: 48.40 49.40 Octane number: 98 100.0 Yield of etherified products, %: 32.29 38.22 As can be seen from the data in the table, the conversion rate of C5 tertiary alkenes reached a maximum of 71.38%, while that of C6 tertiary alkenes reached a maximum of 46.11%. The total ether content in the products remained stable at 49.40%, an increase of 1 percentage point. The octane number of the etherified product remained stable at 100, with the average value increasing by 2 units. The main reasons are, on the one hand, the increase in the content of 1-butene + isobutylene in the raw materials as well as the rise in MTBE in the etherified products; on the other hand, while ensuring that the total ether content in the etherified products met the required quality standards, the bottom temperature of the etherification distillation tower was gradually reduced from 124±0.5°C to 120°C±0.5°C during operation. As a result, the yield of the etherified products increased significantly, from 32.29% to 38.22%, an increase of 5.93%, leading to a notable improvement in the efficiency of the plant. The etherification unit is designed to handle a maximum processing capacity of 66 t/h. By optimizing the operation of the unit and gradually increasing the processing volume, the capacity for processing light gasoline was raised to 70 t/h to enable normal production and maximize the efficiency of the etherification unit. To date, the facility has processed 1.0387 million tons of light gasoline, consumed 76,300 tons of methanol, and produced 405,500 tons of etherified products, providing high-quality blending components for the company’s production of high-octane gasoline. 3. Make full use of light C4 to increase the production of MTBE and isooctane. The MTBE plant and the alkylation plant are the devices for balancing light C4 in the refining system, with production capacities of 60,000 tons per year and 113,000 tons per year respectively. The MTBE plant consists of three sections: etherification, product separation, and methanol recovery. The raw material is light C4 from the gas separation unit, and it mainly produces MTBE ； The alkylation unit consists of four sections: reaction, refrigeration, purification, and distillation. The raw material is MTBE off-gas, and the main product is alkylated oil. After the introduction of new catalysts for industrial use in catalytic units, the olefin content in catalytically processed gasoline increased significantly, while both propylene and tetraolefins in catalytically processed liquid hydrocarbons also rose concurrently. Optimize the operating processes for MTBE production, selective hydrogenation of C4 hydrocarbons, and alkylation to maximize the balance of light C4 compounds and increase the production of MTBE and isooctane. Table 6 Key Performance Metrics of the MTBE Plant Item Before Optimization After Optimization Flow rate, t/h Yield, % Flow rate, t/h Yield, % Light C4 used in MTBE production 22.7/22.5 Isobutylene content in light C4 21.32/23.38 MTBE output 5.36/23.81 5.76/25.60 As can be seen from the table, the isobutylene content in light C4 increased by 2 percentage points after optimization, while the yield of MTBE rose from 23.81% to 25.60%, an increase of 1.79 percentage points ； MTBE production has been increasing year by year, reaching 57,200 tons in 2014, an increase of 13,400 tons compared to 2010. After being upgraded with long-cycle operation technology, the alkylation unit’s startup cycle was extended from 3 months to over 9 months; dual-reactor operation was adopted, which increased the unit’s processing capacity from 14.5 t/h to over 17 t/h, with the annual production of alkylated oil reaching up to 90,133 tons. The production of aviation isooctane was increased, with its proportion rising from 6.9% in 2010 to 13.17% in 2014, an increase of 6.27 percentage points, achieving good results. 4. The optimization plan for gasoline upgrading based on the principle of “using three processes to ensure one goal” – Lanzhou Petrochemical Company has, through continuous adjustments to its gasoline processing strategies, developed this optimization plan. It involves coordinating and optimizing the operations of catalytic cracking, gasoline etherification, and alkylation units (the three processes), with the aim of maximizing the efficiency of gasoline production (the one goal). The optimized gasoline processing process at Lanzhou Petrochemical Company is shown in Figure 2. Figure 2: The gasoline processing flow after optimization of the gasoline purification production plan. III. Conclusions (1) With the implementation of the optimized production process combining the three approaches to ensure high-quality gasoline, Lanzhou Petrochemical Company’s gasoline quality has met the National IV standard, thereby resolving the challenges associated with gasoline production. (II) With the implementation of the optimized production process for gasoline under the \"Three Transformations to Support One Transformation\" strategy, the company’s gasoline output increased steadily, and the proportion of gasoline in crude oil rose from 19.51% in 2010 to 22.05% in 2014 ； The proportion of high-octane gasoline increased significantly; the share of 97# gasoline rose from 4.1% in 2010 to 22.3% in 2014, achieving good results. Over four years, the production of high-octane gasoline increased by 1.3082 million tons, resulting in an additional profit of 322 million yuan. Selected Papers from the 2016 National Conference on Advanced Technologies in the Refining and Petrochemical Industry, Refinery of Lanzhou Petrochemical Company, China National Petroleum Corporation