In the routine analysis of catalytic feedstocks

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A preliminary study on the relationship between distillables (total distillate) in the routine analysis of catalytic feedstocks and reaction coking. In recent production operations, significant reaction coking has occurred, preventing an increase in processing capacity. By analyzing past production data, it was found that there is a direct relationship between distillables (total distillate) in the routine analysis of catalytic feedstocks, reaction coking, and the yield of light liquids in the product. Table-1: Statistics on raw materials and light liquid yield in January 2005
Date | Density | Residual Carbon | Total Distillation Volume | Light Liquid Yield (%)
1.40 | 0.91 | 1805.03 | 711197 | 80.1
1.11 | 0.93 | 035.54 | 681034 | 78.7
1.18 | 0.91 | 1926.21 | 681067 | 81.1
1.21 | 0.92 | 166.05 | 108278 | 78.5
1.25 | 0.90 | 0704.75 | 107775 | 75.9
1.28 | 0.92 | 158.54 | 104071 | 71.6
The overall light liquid yield for the entire month of 2005 was 77.5%. As can be seen from Table-1, the density and residual carbon of the raw materials processed on January 18th and 21st were higher than those of the raw materials processed on January 25th and 28th, but the light liquid yield was 4.5% higher than that on January 25th and 28th. Among these, the overall distillation yield dropped from 68% and 63% on January 18th and 21st, with an average of 65.5%, to 55% and 45% respectively, giving an average of 50%. This is the main reason for the increased coking rate during the reaction as well as the decline in the yield of light liquids; this constitutes Analysis 1. Table-2: Statistics on raw materials and light liquid yield for January 2006 Date Density Residual carbon Total distillation volume Light liquid yield % 1.60 0.92 374.61 55 108574.7 1.10 0.91 774.69 56 108075.7 1.17 0.92 636.44 53 104973.9 1.24 0.92 865.72 52 105374.2 1.27 0.92 256.07 55 104572.5 The overall light liquid yield for January 2006 was 75.18%. Average density of the raw materials used in processing: 0.9237; average residual carbon content: 5.51; average total distillate content: 54%. The average yield of light liquids from the product is 74.2%, and the average processing volume is 1,062 tons. Table-3: Statistics on raw materials and light liquid yield in September 2006. Date, Density, Residual Carbon, Total Distillation Volume, Light Liquid Yield (%): 9.10, 89.99, 4.96, 41.37, 0.81; 9.50, 0.90, 30.59, 16.91, 28.58; 79.69, 0.80, 0.90, 74.53, 61.22; 279.89, 0.15, 0.90, 68.51, 60.13; 132.17, 0.19, 0.91, 100.49, 68.12; 244.79, 0.5. The overall light liquid yield for September 2006 was 79.29%. Average density of the raw material: 0.9054; average residual carbon: 5.22; average total distillate content: 64%. Average yield of light fractions from the product: 80.04%; average processing volume: 1,288 tons. As analyzed from Tables 2 and 3, the difference in average density of the raw materials is 0.0183, the difference in average residual carbon is 0.29, the difference in average total distillate content is 10%, the difference in the average yield of light fractions in the products is 5.84%, and the difference in average processing volume is 226 tons. Of course, a high density of the feedstock (low hydrogen-to-carbon ratio) and high residual carbon content (it is stated that residual carbon multiplied by 1.5 equals the amount of coke formed) directly lead to increased coke formation during the reaction. Among the feedstocks processed over these two months, the biggest difference was observed in those with a full distillation value, with a difference of 10 units. The full distillation value represents the number of milliliters of the distillable components obtained after heating 100 ml of the feedstock; it can also be expressed as a percentage. What remains are heavy aromatic hydrocarbons, as well as non-volatile hydrocarbons such as tar and asphaltenes. Due to their low hydrogen content, these compounds easily form coke and adhere to the catalyst during catalytic cracking reactions, thereby increasing the rate of coke formation, saturating the catalyst’s ability to burn off coke, reducing its processing capacity, and lowering the yield of light fractions in the products. This is Analysis Two. Table-4: Comparison of raw material values before and after maintenance. Dates: before shutdown, after restart. Density, full distillation residue carbon, light liquid yield. 3.20, 0.907867; 4.31, 18.14; 4.17, 0.905857; 5.47, 8.55; 3.60, 0.914773; 4.69, 80.9; 4.20, 0.902856; 4.92, 79.23; 3.90, 0.911169; 4.89, 81.64; 4.25, 0.899255; 5.82, 78.73; 3.13, 0.907166; 4.02, 79.64; 4.28, 0.890455; 5.78, 78.9. Table-4 shows the production statistics for 15 days each before and after the shutdown for maintenance this year; the average light liquid yield in March was 81.29%. The average light liquid yield in April was 78.53%, which is partly due to the low production volume resulting from the shutdown of some distillation units. However, based on an analysis of the raw materials, the average density of these materials in March before the shutdown was higher than it was after the restart: 0.0108. Yet the overall distillation ratio was 13.8% higher in April. The analysis shows that the level of the overall distillation ratio, as determined by the raw materials, has a significant impact on the yield of light liquids in the final product. Based on the above analysis, for the raw materials used in catalytic processing, it is generally agreed that they should have a low density and low residual carbon. In cases where the analytical data are incomplete, the total distillation range should be considered as an important reference value. Another issue to note is that coker wax oil has a high total distillation range but is difficult to crack, and it can also cause catalyst deactivation. However, by testing the alkaline nitrogen content and freezing point (since coker wax oil is produced through thermal cracking, its freezing point is usually high), it is possible to determine whether the raw material contains coker wax oil. From a production perspective, when purchasing raw materials, it is advisable to choose those with a low density, low residual carbon, high total distillation range, and low freezing point (a low freezing point indicates a high paraffin content in the raw material, which facilitates catalytic cracking), in order to maximize the company’s profitability.