Heavy oil solids test

　　Abstract: Through the comparison and optimization of four test methods used at home and abroad to determine the solid content of oil slurry in catalytic unit, it is found that the enterprise standard centrifugal method is fast and can be well matched with the production of the unit, and the carbonization burning method is accurate and can provide reliable data for the catalytic unit。

　　1、introduction

　　Oil slurry is the tail material in the production process of catalytic cracking unit in petrochemical industry, and the solid content of oil slurry refers to the amount of catalyst lost in the oil slurry, which directly reflects the stability of the operation of the unit. Secondly, the main component of catalytic cracking oil slurry is dense aromatic hydrocarbons, which can be further processed to produce high-quality petroleum coke, carbon black and rubber filling oil. Heavy fuel oil can also be prepared, but if there is a high concentration of catalyst particles in the oil slurry, the comprehensive utilization of the oil slurry has brought difficulties, directly used as industrial fuel oil, easy to cause nozzle wear and furnace ash, when it is used as a coking raw material to produce petroleum coke, the ash content of the product is difficult to meet the quality requirements. Therefore, the solid content of the oil slurry in the heavy oil catalytic cracking unit of Yumen Refinery is strictly controlled at 6g/L, so it is very important to accurately measure the solid content of the oil slurry。

　　2、research contents

　　2.1Centrifugal method for determination of solids in oil slurry used for many years in Yumen Refinery

　　To determine the solid content of the oil slurry in the catalytic cracking unit, Yumen Refinery has used the enterprise standard Q/SY YM 0153-2003 method for the determination of the solid content of the oil slurry (centrifugal method) for many years. The basic method is to first heat and melt the oil slurry to 70℃, and violently shake the oil slurry for 1 minute while it is hot. Immediately pour the oil slurry into 25ml of the centrifuge test tube (pre-add 25ml of the preheated solvent oil - usually a line of oil in the centrifuge test tube), and the process of oil to the oil does not exceed 12 seconds. The centrifuge tube is immersed in a 70℃ water bath, held for 3 minutes, removed and shaken for 30-60 seconds, so that the solvent and catalyst are evenly mixed, and then put into the centrifuge. Start the centrifuge, turn the speed control knob, when the speed reaches 800-1000 RPM, centrifuge separation for 5 minutes. Remove the centrifuge tube from the centrifuge, immerse in 70℃ water bath for 2 minutes, remove the centrifuge tube reading. Repeat the steps until the difference between the two readings is within 0.05 ml, the reading is accurate to 0.05 ml, and finally look up Table 1 according to the milliliter number of the catalyst volume in the centrifugal test tube to calculate the solid content (g/L), through many years of experiments, we found that there is a certain error in this method, often resulting in large results。

　　2.1.1The error of the experimental method itself

　　In this method, solvent oil and regular oil are used as solvents, and the dissolved oil slurry is fully shaken by heating and then centrifuged. However, in practice, the oil slurry is often too heavy, and most of the recombination components in it cannot be dissolved even after being heated and fully shaken, resulting in the oil slurry being centrifuged, and the recombination components adhering to the catalyst particles are mixed together and centrifuged at the bottom. After we poured out the upper liquid after centrifugation, we used a glass rod to take out the lower material. It was observed that the material at the bottom of the centrifuge tube was not only catalyst particles, but also some undissolved substances. Therefore, during the experiment, these substances were taken as solid particles by the experimenter and the solid content in the oil slurry was obtained by looking up the table, which inevitably caused the analysis data to be too large。

　　2.1.2 Human error of the experimenter

　　This method first requires the experimenter to shake the centrifugal tube several times, in order to make the solvent oil and the normal first-line oil fully dissolve the restructured substances in the oil slurry. However, due to the different shaking strength of each operator, it is difficult to ensure that the shaking situation is the same each time, which will cause the repeatability and reproducibility of the experimental results is not good. The slurry and catalyst are not easy to stratify or tilt the layers, and the volume number is difficult to be accurately read by the analyst with visual observation or empirical reading. Therefore, the human error of the experimenter is also one of the reasons that affect the accuracy of the experimental results。

　　2.2 Comparison between high temperature ash combustion method and centrifugal method

　　Through the study of centrifugal method, we found the cause of inaccuracy in determining the solid content of oil slurry in Yumen Refinery, so we considered using other simple and feasible experimental methods for determination. In this regard, we consulted the data and considered using high temperature ash burning method for accurate analysis of oil slurry. The basic method is to heat the sample to 70℃, directly add it to the crucible with constant weight, use ash-free filter paper as the lead, ignite and burn until only ash and residual carbon are left. The carbon residue is heated and transformed in the Muffle furnace at 775℃ until all the slurry residue is burned off, and finally cooled and weighed. We found in repeated tests that if the slurry is weighed in large quantities, it takes a longer time to burn all the slurry, and even if the burning time is extended, sometimes it is difficult to burn all the slurry, and there are still black substances in the crucible. Therefore, we optimized the optimal weighing amount for many tests, and determined that the oil slurry of 5-10 grams was weighed and burned at about 775 ° C for more than 2.0 hours. At the same time, the results of centrifugal method and high temperature ash burning method were compared. The results are shown in the table 1

　　Table 1 Comparison test between centrifugal method and high temperature ash burning method to determine solid content of oil slurry

　　According to the data analysis in Table 1, the results of the high temperature ash burning method for the determination of solids content in the slurry are obviously small, which can better reflect the actual situation of solids content in the slurry of Yumen Refinery. However, this method also has some shortcomings. First, the burning at a high temperature of 775℃ will cause a small amount of carbon deposited on the catalyst surface to be burned off, resulting in small data. Secondly, the high temperature ash burning method takes a long time to experiment, and the total time of the constant weight crucible and the experiment is roughly 4-6 hours, which is difficult to timely cooperate with the smooth operation of the device, and the centrifugal method to determine the solid content of the oil slurry although there is a certain error, but the measurement time is only about half an hour, which can provide data for the device in time. Therefore, it is recommended to use centrifugal analysis in daily cooperation, and use burning method regularly to correct the results。

　　2.3 Other methods for determination of solid content of oil slurry at home and abroad are introduced

　　2.3.1 Standard test method for determination of total residue in residual oil

　　This method is ASTM D4870-94. The experimental instrument used is the standard instrument produced by PETROLAB company in the United States. The analysis diaphragm and control diaphragm are glass fiber diaphragm with filtration accuracy of 1.6μm and diameter of 47㎜ produced by Whatman Company in the United States. The diaphragm is constant weight at 110℃, the oil slurry is preheated for half an hour, and after mixing, 11 grams of sample is weighed, the diaphragm is fixed, and the steam generator is turned on. The sample was placed on the electric heating plate, heated at 100℃, the vacuum pump was turned on, the sample was poured into the filter, and washed with 85% n-heptane and 15% toluene to ensure that all solids were transferred to the diaphragm. The prepared analytical diaphragm and control diaphragm were dried at 110℃ to constant weight, and the actual sample weight was obtained. The solid contaminant content was calculated according to the weight gain of the diaphragm and the weight of the sample before and after filtration. Because our center does not have the instruments used in this method, and a large amount of n-heptane and toluene are used to wash at 100℃ in the experiment, which is bound to cause certain harm to the health of the experimenters. Therefore, this method is not suitable for large-scale promotion and adoption in Yumen Refinery。

　　2.3.2 Carbonized burning method

　　The method is to carbonize a certain amount of oil slurry sample in a specific heating furnace at 500-600℃ (under nitrogen purging), and then purge with air at 600℃, so that the residual carbon is completely burned off, and the remaining powder is cooled and weighed and calculated. According to our research, this method is the most accurate for the determination of solid content in oil slurry, but we do not have the specific heating furnace and equipment required by this method, so it is difficult to carry out the research work of this method。

　　3、conclusion

　　3.1 The centrifugal method used in Yumen Refinery for many years for the determination of solid content in oil slurry has some errors in the experimental method itself and the experimenter's human error, resulting in high results。

　　3.2The results of high temperature ash burning method for determination of solid content in oil slurry are obviously small, which can better reflect the actual situation of solid content in oil slurry in Yumen refinery。

　　3.3It is suggested that centrifugal analysis should still be used in daily cooperation, and burning method should be used regularly to correct the results。

　　3.4Other methods to determine the solid content of oil slurry at home and abroad are difficult to be popularized in Yumen Refinery due to lack of analytical instruments and many other reasons。

　　references

　　company standard Q/SY YM 0153-2003  Determination of solids in oil slurry (centrifugal method)

　　About the author: Yang Chunzhen, female, oil analysis technician, engaged in oil analysis work for many years, has high theoretical knowledge and practical experience in oil analysis work, especially in the research of test methods has unique insights。