Palmitate coking inhibitor as well as preparation method and application thereof

Abstract

The invention discloses a palmitate coking inhibitor as well as a preparation method and application thereof, and belongs to the technical field of coking inhibitors. According to the technical scheme, palmitic acid reacts with a potassium compound to obtain the coking inhibitor, wherein the potassium compound is potassium hydroxide, potassium carbonate or potassium bicarbonate. The coking inhibitor has good oil solubility and can be directly added into cracking raw oil, injection equipment such as an inhibitor nozzle does not need to be additionally arranged independently, the unnecessary blocking risk is reduced, and the process complexity is reduced; and compared with the existing sulfur and phosphorus-containing oil-soluble inhibitor, the coking inhibitor provided by the invention has good decoking performance for middle and later-stage gas-phase coking.

Description

Technical Field

[0001] The invention relates to the technical field of coking inhibitors, and in particular to a palmitate coking inhibitor and a preparation method and application thereof. Background Art

[0002] More than 80% of the world's ethylene production uses tubular furnace steam cracking technology. Its hydrocarbon liquid raw materials often contain a large amount of aromatic components, which plays a vital role in the operating efficiency of the ethylene cracking furnace.

[0003] Hydrocarbon raw materials and steam undergo thermal cracking reaction in high-temperature furnace tubes to produce small molecular target products such as ethylene and propylene. At the same time, it is accompanied by a large number of side reactions. The dehydrogenation of aromatic components produces by-products such as tar and coke, which has brought many adverse effects on ethylene production, resulting in a series of adverse effects such as reduced yield of target products, decreased processing capacity of the device, increased energy consumption and shortened operation cycle.

[0004] The cracking coking mechanism of aromatics and its influencing factors are very complex, but the most recognized ones include: catalytic coking, gas phase coking and free radical coking. Gas phase coking is the main form of coking, which refers to the coke generated in the main body of the gas flow. Aromatics are very important intermediate substances in gas phase coking. Some of these aromatics come from the raw materials themselves, and some are generated through trimerization reactions. The coking process can be expressed as:

[0005]

[0006] In recent years, a variety of coking inhibition technologies have been developed to combat aromatic coking, including changing cracking reaction conditions, hydrothermal cracking, pretreatment of cracking raw materials, surface treatment of furnace tubes, and addition of coking inhibitors. The use of new cracking technologies and furnace tube surface treatment processes requires huge investments in replacing cracking furnaces and furnace tubes, which is difficult to achieve in a short period of time. In addition, chemical market prices change rapidly, and investment returns cannot be guaranteed.

[0007] Changing the dilution ratio and steam of cracking is helpful to reduce coking, but the effect is limited, and the increased dilution steam affects the processing capacity and output of the device and increases the energy consumption of the device. Therefore, adding coking inhibitors to the cracking raw materials is a generally recognized and most effective method.

[0008] The reported coking inhibitors mainly include sulfur and phosphorus compounds, metal salt compounds, and organic polysiloxane compounds. For example, Chinese invention patent CN101294100A discloses a method for inhibiting coking in a hydrocarbon steam cracking device, which requires the use of at least one of silica sol, aluminum sol and titanium sol to pretreat the furnace tube, and then inject sulfur and phosphorus compound inhibitors during the cracking process. Existing sulfur and phosphorus oil-soluble inhibitors are mainly used for catalytic coking before or at the initial stage of feeding. Sulfur and phosphorus inhibitors can form a layer of passivation on the surface of the furnace tube before the coking product is produced, slowing down the process of catalytic coking. However, as the cracking furnace runs to the middle and late stages, the catalytic coking weakens, the gas phase coking increases, and the coke layer will still gradually thicken. Sulfur and phosphorus oil-soluble inhibitors cannot eliminate the coke layer of gas phase coking.

[0009] Chinese invention patent CN1367225A discloses a method for inhibiting coking in a hydrocarbon steam cracking device. After the furnace tube is decoked, potassium, lithium silicate, borate, or potassium, magnesium, calcium, and barium nitrate inorganic salt coking inhibitor is added to the water vapor before resuming feeding, and the duration is 1-3 hours. However, inorganic salts are incompatible with hydrocarbon materials. During the addition process, it is very easy to cause the inhibitor to be unevenly distributed in the pipeline, resulting in the deposition of inorganic salts in the furnace tube, and even blocking the furnace tube, causing the cracking furnace to be shut down unplanned, seriously affecting the stable operation of production. In addition, the use method of the inhibitor is very important for the effect of inhibiting coking and the stable operation of the cracking furnace. If the injected inhibitor solution is not vaporized quickly, the liquid is sprayed onto the high-temperature furnace tube, and the furnace tube will be fatigued and damaged due to the creep stress of continuous shrinkage and thermal expansion; if too much inorganic salt inhibitor is injected, it may cause the deposition of the inhibitor in the furnace tube or the fall of large pieces of coke to block the furnace tube.

[0010] Therefore, it is necessary to develop a new coking inhibitor that can reduce the coking of light oil cracking furnaces while solving the problems of existing coking inhibitors. Summary of the invention

[0011] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a palmitate coking inhibitor and a preparation method and application thereof. The coking inhibitor of the present invention has good oil solubility and can be directly added to cracking feedstock oil without the need to separately add injection equipment such as inhibitor nozzles, thereby reducing unnecessary blockage risks and reducing process complexity. Moreover, compared with existing sulfur-phosphorus-containing oil-soluble inhibitors, the coking inhibitor of the present invention has good decoking performance for mid- and late-stage gas-phase coking.

[0012] The technical solution of the present invention is:

[0013] In a first aspect, the present invention provides a method for preparing a palmitate coking inhibitor, wherein palmitic acid is reacted with a potassium compound to obtain the coking inhibitor; wherein the potassium compound is an alkaline potassium salt such as potassium hydroxide, potassium carbonate or potassium bicarbonate.

[0014] Palmitic acid can be used as a surfactant and softener because it has a polar head group that can connect to metal potassium ions; it also has a non-polar chain that allows it to dissolve in organic solvents.

[0015] Preferably, the molar ratio of palmitic acid to potassium is 1:(1-1.1); in order to avoid super esterification, preferably, the molar ratio of palmitic acid to potassium is 1:(1.02-1.05).

[0016] In the second aspect, the present invention provides a coking inhibitor prepared by the above-mentioned preparation method, which is lipophilic and hydrophilic and can slow down the coking of light oil cracking furnace. The coking inhibitor can be directly added to oil raw materials or water, and its lipophilic group can capture and combine with the coking precursor to inhibit the further carbonization of the coking precursor. In addition, the coking inhibitor slows down the side reaction of generating coke, and will not have a negative impact on the target product yield and technical and economic indicators of the device.

[0017] The mechanism of action of the coking inhibitor is as follows: since the inhibitor contains both long-chain hydrocarbon lipophilic groups and polar head groups (metal cations), it can be dissolved in organic solvents. The long-chain hydrocarbon lipophilic groups of the coking inhibitor can combine with tar precursors and pull potassium groups that inhibit coking to form a mixture of tar and coking inhibitor. The mixture undergoes catalytic gasification of coke in the presence of hot steam, that is, the coking inhibitor releases alkali metal oxides, which can catalyze the conversion of coking precursors into carbon monoxide and hydrogen, thereby eliminating and slowing down the deposition of coke on the tube wall and extending the operating cycle of the cracking furnace.

[0018] The reaction mechanism of the coking inhibitor of the present invention in inhibiting coking is:

[0019]

[0020] The coking inhibitor can not only inhibit early coking, but also reduce and remove the existing coke layer. The application of the coking inhibitor in the steam cracking ethylene production unit solves the problems of short operation cycle, short service life of cracking furnace tubes, high energy consumption and low production efficiency in the prior art. It can significantly reduce the coke amount in the furnace tubes, reduce the tube wall temperature, and greatly extend the operation cycle of the cracking furnace.

[0021] The coking inhibitor of the present invention does not require the use of complicated auxiliary facilities such as nozzles, thereby preventing inhibitor deposition or fatigue damage caused by shrinkage, thermal expansion and creep of the furnace tube caused by the inhibitor.

[0022] In the third aspect, the present invention also provides the application of the above-mentioned palmitate coking inhibitor, which is used to slow down the coking of light oil cracking furnaces. Light oil includes hydrocarbons such as ethane, propane, liquefied gas and naphtha; heavy oil includes hydrocarbons such as diesel and tail oil. There are significant differences in the composition of light oil and heavy oil, so the composition of the coke in their cracking furnace tubes is also different. Compared with heavy oil, the coke of light oil is relatively light and has a higher saturation, and the carbon number of potassium palmitate is comparable to the average carbon number distribution of light oil, so it has a stronger binding force with the coke of light oil and a better decoking effect.

[0023] The coking inhibitor of the present invention is suitable for cracking furnaces SRT-III, SRT-IV, GK-VI, CBL industrial furnaces and simulated cracking test furnaces.

[0024] The coking inhibitor of the present invention is applicable to cracking raw materials such as ethane, light hydrocarbons, naphtha and other light oil raw materials. When the cracking furnace uses liquid hydrocarbon raw materials, the inhibitor can be added to the liquid hydrocarbon raw materials or to the dilution steam; when the cracking furnace uses gaseous raw materials, the inhibitor can be added to the dilution steam.

[0025] The specific method of using the coking inhibitor of the present invention is:

[0026] The coking inhibitor is injected into the cracking feedstock through a metering pump and enters the light oil cracking furnace together with the cracking feedstock. For example, the inhibitor can be injected into the cracking feedstock at the raw material pump inlet or outlet of the heating furnace, preferably at the raw material pump inlet, with the help of the mechanical stirring action of the raw material pump to obtain a good stirring and mixing effect; the inhibitor can also be pre-mixed with part of the cracking feedstock in advance, and then the mixture is injected into the cracking feedstock at the raw material pump inlet or outlet of the heating furnace through a pipeline.

[0027] The inhibitor can also be injected into the dilution steam in advance to form a mixture of inhibitor and steam, which then enters the light oil cracking furnace together.

[0028] Preferably, the injection amount of the coking inhibitor is 20-60 ppm of the input amount of the cracking raw material.

[0029] When the coking inhibitor of the present invention is used, the injection method of the coking inhibitor can be a continuous injection method or an intermittent injection method. Moreover, when the inhibitor is injected by the continuous injection method or the intermittent injection method, the injection concentration of the inhibitor, the start or stop of the injection of the inhibitor, all need to be determined according to the temperature of the tube wall of the radiation section of the cracking furnace.

[0030] Among them, the continuous injection method refers to the continuous injection of small doses of inhibitors at the beginning of the cracking reaction of hydrocarbon feedstock in the cracking furnace, which can inhibit the rapid rise in the furnace tube wall temperature in the initial stage of the cracking furnace feeding.

[0031] The intermittent injection method means that no inhibitors are injected in the early stage of the cracking furnace operation. After the coke layer is gradually generated in the tube wall of the radiation section, the thermal resistance of the tube wall increases, and the tube wall temperature rises to above 1000℃, the system starts to inject the inhibitor; the injection is continued for 24-120h. At this time, the coke layer on the tube wall is significantly thinned or reduced, and the thermal resistance of the tube wall is reduced. When the tube wall temperature drops significantly by about 30-50℃, the injection of the inhibitor is stopped; after a period of operation, when the tube wall temperature rises significantly to 1000℃ again, the inhibitor is injected again until the injection of the inhibitor cannot effectively reduce the tube wall temperature.

[0032] Compared with existing inorganic salt inhibitors or low molecular weight salt inhibitors, the coking inhibitor of the present invention has good oil solubility, can be directly added to the raw oil, and enters the cracking furnace tube with the raw oil, without the need to separately add injection equipment such as inhibitor nozzles.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. In the actual operation of industrial cracking furnaces, existing inorganic salt inhibitors or low molecular weight organic inhibitors have poor oil solubility and need to be equipped with inhibitor nozzles separately to help distribute them into the furnace tubes. In actual operation, since the nozzle of the inhibitor injection nozzle is relatively small, generally with a diameter of 0.5-5mm, once iron filings or other debris are mixed into the inhibitor storage tank and pipeline, the inhibitor injection nozzle will be blocked. Once blocked, the inhibitor injection will fail. In addition, multiple groups of inhibitor nozzles need to work in parallel at the same time. In actual operation, there is often a problem of too large or too small flow rate of a nozzle, resulting in uneven injection dosage of different nozzles. The temperature of the corresponding furnace tube with a smaller injection dosage is significantly higher than that of other groups, triggering the over-temperature shutdown of the cracking furnace, and the over-temperature of a single group of furnace tubes in the cracking furnace will inevitably affect the overall operation cycle. The coking inhibitor of the present invention has good oil solubility and can be directly added to the cracking feedstock oil and enter the cracking furnace tube along with the cracking feedstock oil. The process is mature and stable, and there is no need to separately add injection equipment such as inhibitor nozzles, thereby reducing unnecessary blockage risks and reducing the complexity of the process. At the same time, the inhibitor has good emulsification properties, and within the set concentration range, inhibitor deposition will not occur, and fatigue damage will not occur due to shrinkage, thermal expansion, and creep of the furnace tubes caused by injection, thereby increasing operational stability.

[0035] 2. Compared with the existing sulfur-phosphorus oil-soluble inhibitors, the coking inhibitor of the present invention has good decoking performance for gas phase coking in the middle and late stages. The existing sulfur-phosphorus oil-soluble inhibitors are mainly used for catalytic coking before or at the initial stage of feeding. The sulfur-phosphorus inhibitors can form a layer of passivation on the surface of the furnace tube before the coking product is produced, slowing down the process of catalytic coking. However, as the cracking furnace runs to the middle and late stages, the catalytic coking weakens, the gas phase coking increases, and the coke layer will still gradually thicken. The sulfur-phosphorus oil-soluble inhibitors cannot eliminate the coke layer of gas phase coking. In the operation of an actual industrial cracking furnace, the coking inhibitor of the present invention can be used in different stages of the cracking furnace, including the early, middle and late stages. The best application scenario is the middle and late stages of the operation of the cracking furnace, because at this time, part of the coke layer has accumulated in the furnace tube of the cracking furnace, and the purpose of removing the existing coke layer can be achieved by injecting the coking inhibitor of the present invention. Of course, the coking inhibitor of the present invention can also be injected in the early stage of the operation of the cracking furnace, which can also prevent the increase of the coke layer and extend the operation cycle of the cracking furnace.

[0036] 3. When the coking inhibitor of the present invention is used in a steam cracking ethylene production device, it can significantly reduce the coke content of the furnace tube and greatly extend the operation cycle of the cracking furnace.

[0037] 4. When the coking inhibitor of the present invention is used in a steam cracking ethylene production device, it can reduce the cracking furnace tube wall temperature and reduce the number of cracking furnace coking, thereby extending the life of the cracking furnace tube and saving the cracking furnace coking energy consumption and the cost of replacing the cracking furnace tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the thermal cracking device used in the embodiment of the present invention.

[0039] In the figure, 1, cracking furnace; 101, thermocouple; 2, quench cooler; 3, gas-liquid separation tank. DETAILED DESCRIPTION

[0040] In order to enable persons skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0041] The coking inhibitors in the following examples were prepared by the following method:

[0042] Palmitic acid reacts with potassium compounds to obtain a coking inhibitor.

[0043] The potassium compound is potassium hydroxide or potassium carbonate.

[0044] The coking inhibitor prepared in the following examples participates in the following thermal cracking process:

[0045] Use Figure 1The thermal cracking device shown has a cracking reaction temperature of 840°C, a cracking raw material of naphtha, a feed rate of 5kg / h, a dilution ratio of 0.5, and a residence time of 0.26s. The reaction materials need to be heated by the feed system and the cracking furnace 1, and then enter the quencher 2. The liquid phase product is collected from the product separation lower port of the gas-liquid separation tank 3, and the hydrocarbon composition of the cracked gas after the reaction and the content of carbon monoxide and carbon dioxide are analyzed from the venting port. When the tube wall temperature (TMT) of the cracking furnace 1 reaches the upper limit of 1100°C, the feed is stopped and the operation time is recorded as the evaluation basis for the length of the operation cycle.

[0046] The coking inhibitor in the embodiment of the present invention can be injected into steam or water from injection port 1, or injected into the cracking raw material from injection port 2. However, the inorganic salt inhibitor in the comparative example can only be injected into steam or water from injection port 1.

[0047] After injecting the coking inhibitor, the temperature of the cracking furnace 1 is raised to above 800°C, and air is mixed in and maintained at 800°C. The oxygen content of the coking gas at the outlet of the quencher 2 is detected by the coking controller. At the beginning, the carbon monoxide and carbon dioxide contents are relatively high, reaching the upper limit of the carbon monoxide and carbon dioxide gas analyzer detection of 25%; as the coking process continues, the carbon monoxide and carbon dioxide contents gradually decrease, and the oxygen content continues to increase until it reaches a level equivalent to the oxygen content of the air. At this time, the coking operation is completed and the total coking operation time is recorded. During the coking operation, the temperature indication of the thermocouple 101 in the furnace tube of the cracking furnace 1 must be continuously detected. It is required not to exceed the upper temperature limit of 1100°C of the 2520 material. It is generally set within 1000°C. Once it approaches this temperature, the inflow of coking air is reduced to control the coking reaction.

[0048] Example 1

[0049] The preparation method of the coking inhibitor of this embodiment is as follows: palmitic acid is reacted with potassium hydroxide, wherein the theoretical molar ratio of potassium hydroxide to palmitic acid is 1:1. However, considering the reversibility of the esterification reaction, in order to allow the palmitic acid to react completely, the amount of potassium hydroxide should be slightly larger. Therefore, in this embodiment, the molar ratio of potassium hydroxide to palmitic acid is 1.05:1, and the coking inhibitor is finally obtained.

[0050] Using the above Figure 1The thermal cracking process shown adopts a continuous injection method. When the cracking reaction of the hydrocarbon feedstock is fed into the cracking furnace 1, a coking inhibitor is continuously injected in small doses. The injection amount is 50ppm of the cracking hydrocarbon feedstock input to complete a feeding operation cycle: the cracking reaction temperature is 840°C, the cracking feedstock is naphtha, the feeding amount is 5kg / h, the dilution ratio is 0.5, and the residence time is 0.26s; when the TMT of the cracking furnace 1 reaches the upper limit of 1100°C, the feeding is stopped, and the operation time is recorded as 120h; the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively, and are 0.09% and 0.07% respectively after injection; the charring time is 0.40h.

[0051] Example 2

[0052] The difference from Example 1 is that this example adopts an intermittent injection method, and injects the coking inhibitor 25 hours in the middle of the cracking reaction of the hydrocarbon feedstock in the cracking furnace 1.

[0053] Complete a feeding operation cycle: cracking reaction temperature 840℃, cracking raw material is naphtha, feed amount is 5kg / h, dilution ratio is 0.5, residence time is 0.26s; when the cracking furnace 1TMT reaches the upper limit of 1100℃, stop feeding, and record the operation time as 110h; the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively before injection, and are 0.09% and 0.07% respectively after injection; the charring time is 0.42h.

[0054] Comparative Example 1

[0055] The difference from Example 1 is that in Comparative Example 1, no coking inhibitor is injected.

[0056] Complete a feeding operation cycle: cracking reaction temperature 840℃, cracking raw material is naphtha, feed amount is 5kg / h, dilution ratio is 0.5, residence time is 0.26s; when the cracking furnace 1TMT reaches the upper limit of 1100℃, stop feeding, record the operation time as 50h, carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively; charring time is 1.00h.

[0057] It can be seen from Examples 1-2 and Comparative Example 1 that when the coking inhibitor of the present invention is injected into the cracking furnace 1 by the continuous injection method, the operating cycle is extended by 2.4 times compared with Comparative Example 1 in which the coking inhibitor is not injected, and the coking time is reduced by 60%, indicating that the coking inhibitor of the present invention has an obvious coking inhibition effect when used by the continuous injection method. When the coking inhibitor of the present invention is injected into the cracking furnace 1 by the intermittent injection method, the operating cycle is extended by 2.1 times compared with Comparative Example 1 in which the coking inhibitor is not injected, and the coking time is reduced by 55%. Therefore, it can be seen from Examples 1-2 and Comparative Example 1 that the coking inhibitor of the present invention has an obvious coking inhibition effect in both the early and middle and late stages of operation.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that Comparative Example 2 uses a potassium carbonate inhibitor (ie, an inorganic potassium salt inhibitor).

[0060] A continuous injection method was adopted. Potassium carbonate was continuously injected in small doses at the beginning of the cracking reaction of the hydrocarbon raw material in the cracking furnace 1. The injection amount was 50ppm of the cracking hydrocarbon raw material input, and a feeding operation cycle was completed: the cracking reaction temperature was 840°C, the cracking raw material was naphtha, the feeding amount was 5kg / h, the dilution ratio was 0.5, and the residence time was 0.26s. During the experiment, the carbon monoxide and carbon dioxide contents were 0.12% and 0.08% respectively, which were significantly higher than those in comparative example 1. This shows that the inorganic potassium salt inhibitor also played a role in eliminating coke. However, because the inlet pressure of the cracking furnace 1 increased rapidly, it was judged that the furnace tube was blocked. Although the TMT of the cracking furnace 1 did not reach the upper limit of 1100°C, the feeding was also stopped. The recorded operation time was 60h and the charring time was 0.5h. The furnace tube of the cracking furnace 1 was disassembled, and white matter was found to be adhered to the tube wall at about 100mm from the inhibitor injection port. The white matter had strong adhesion and was distributed in an annular shape, causing the tube wall to narrow. The furnace tubes were cleared with pure water, and the composition of the aqueous solution was collected and analyzed. The result showed potassium carbonate, which indicated that the inorganic potassium salt inhibitor lacked oil solubility and was easily unevenly distributed, resulting in deposition in the furnace tubes and clogging the furnace tubes.

[0061] Comparative Example 3

[0062] The difference from Example 1 is that Comparative Example 3 uses a dimethyl disulfide inhibitor (ie, an organic sulfur-phosphorus inhibitor).

[0063] A continuous injection method is adopted. When the cracking reaction of hydrocarbon raw materials is started, dimethyl disulfide is continuously injected in small doses into the cracking furnace 1. The injection amount is 50 ppm of the cracking hydrocarbon raw material input to complete a feeding operation cycle: the cracking reaction temperature is 840°C, the cracking raw material is naphtha, the feeding amount is 5 kg / h, the dilution ratio is 0.5, and the residence time is 0.26 s; when the TMT of the cracking furnace 1 reaches the upper limit of 1100°C, the feeding is stopped, and the operation time is recorded as 70 hours. The operation cycle is extended by 0.4 times compared with the comparative example 1 in which the coking inhibitor is not injected, the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively, and the coking time is 0.7 hours.

[0064] Comparative Example 4

[0065] The difference from Comparative Example 3 is that Comparative Example 4 adopts an intermittent injection method, and dimethyl disulfide is injected 25 hours in the middle of the cracking reaction of the hydrocarbon feedstock in the cracking furnace 1.

[0066] Complete a feeding operation cycle: the cracking reaction temperature is 840℃, the cracking raw material is naphtha, the feeding amount is 5kg / h, the dilution ratio is 0.5, and the residence time is 0.26s; when the cracking furnace 1TMT reaches the upper limit of 1100℃, the feeding is stopped, the operation time is recorded as 55h, the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively, and the charring time is 0.95h. The operation cycle is extended by 0.1 times compared with the comparative example 1 without injecting the coking inhibitor, and the charring time is basically similar.

[0067] It can be seen from Comparative Examples 1, 3-4 that organic sulfur and phosphorus inhibitors are more effective in inhibiting coking in the early stage of operation. Catalytic coking can be prevented by covering a layer of sulfur and phosphorus passivates. However, in the middle and late stages of the operation of the cracking furnace, when a coke layer has been formed on the inner wall of the cracking furnace tube, sulfur and phosphorus passivates can no longer be produced, and they basically have no effect in inhibiting coking.

[0068] Comparative Example 5

[0069] The difference from Example 1 is that in Comparative Example 5, when preparing the coking inhibitor, the fatty acid is not a single palmitic acid, but a ternary mixed fatty acid composed of oleic acid, palmitic acid and stearic acid in a molar ratio of 1:1:1, which reacts with potassium hydroxide, wherein the theoretical molar ratio of potassium hydroxide to the mixed fatty acid is 1:1, but considering the reversibility of the esterification reaction, in order to allow the fatty acid to react completely, the amount of potassium hydroxide should be slightly larger, and therefore, in this embodiment, the molar ratio of potassium hydroxide to the mixed fatty acid is 1.05:1, and finally a ternary mixed fatty acid salt coking inhibitor is prepared.

[0070] A continuous injection method is adopted. When the cracking reaction of hydrocarbon raw materials is started, a ternary mixed fat coking inhibitor is continuously injected in small doses at the beginning of the cracking reaction of the cracking furnace 1. The injection amount is 50 ppm of the cracking hydrocarbon raw material input to complete a feeding operation cycle: the cracking reaction temperature is 840°C, the cracking raw material is naphtha, the feeding amount is 5 kg / h, the dilution ratio is 0.5, and the residence time is 0.26 s; when the TMT of the cracking furnace 1 reaches the upper limit of 1100°C, the feeding is stopped, and the recorded operation time is 90 hours, which is 0.8 times longer than that of comparative example 1; the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively before the injection, and are 0.07% and 0.04% respectively after the injection; the charring time is 0.5h, which is reduced by 50% compared with comparative example 1.

[0071] It can be seen from Example 1, Comparative Example 1 and Comparative Example 5 that the ternary mixed fatty acid salt coking inhibitor also has a good coking inhibition effect, but its coking inhibition effect is relatively poor relative to the potassium palmitate coking inhibitor. This is because the proportion of potassium palmitate that can act on light oil coke in the ternary mixed fatty acid salt coking inhibitor is reduced, resulting in the coking inhibition effect being worse relative to the potassium palmitate coking inhibitor.

[0072] Experimental Example 1

[0073] Without adding any inhibitors, Figure 1 In the thermal cracking process shown, the cracking reaction temperature is 840°C, the cracking raw material is naphtha, the feed rate is 5kg / h, the dilution ratio is 0.5, and the residence time is 0.26s; when the cracking furnace runs for 20h, the cracking products of the cracking furnace are collected, and the yield of the cracking products is analyzed by chromatography. The results are shown in Table 1.

[0074] Experimental Example 2

[0075] The potassium palmitate coking inhibitor of Example 1 was used as follows: Figure 1 The thermal cracking process shown adopts a continuous injection method. When the cracking reaction of the hydrocarbon feedstock is put into the cracking furnace 1, a coking inhibitor is continuously injected in small doses. The injection amount is 50ppm of the cracking hydrocarbon feedstock input. The cracking reaction temperature is 840°C. The cracking feedstock is naphtha, the feed amount is 5kg / h, the dilution ratio is 0.5, and the residence time is 0.26s. When the cracking furnace runs for 20h, the cracking products of the cracking furnace are collected, and the yield of the cracking products is analyzed by chromatography. The results are shown in Table 1.

[0076] Table 1 The yield of the pyrolysis products of Experimental Example 1 and Experimental Example 2

[0077]

[0078] It can be seen from Table 1 that under the same raw materials and process conditions, the cracking yields of Experimental Example 1 and Experimental Example 2 are very close, and the main technical and economic indicators of the device such as ethylene, propylene and triene yields of Experimental Example 2 are slightly higher than those of Experimental Example 1. This is because the coking inhibitor slows down the formation of other side reactions of coking, which is beneficial to the formation of target products such as ethylene. This proves that the coking inhibitor of the present invention will not have a negative impact on the technical and economic indicators of the device.

[0079] Example 3

[0080] The preparation method of the coking inhibitor of this embodiment is as follows: palmitic acid is reacted with potassium carbonate, wherein the theoretical molar ratio of potassium carbonate to fatty acid is 0.5:1. However, considering the reversibility of the esterification reaction, in order to allow the palmitic acid to react completely, the amount of potassium carbonate should be slightly larger. Therefore, in this embodiment, the molar ratio of potassium carbonate to palmitic acid is 0.52:1, and the coking inhibitor is finally obtained.

[0081] Using the above Figure 1The thermal cracking process shown adopts a continuous injection method. When the cracking reaction of the hydrocarbon feedstock is fed into the cracking furnace 1, a coking inhibitor is continuously injected in small doses. The injection amount is 50ppm of the cracking hydrocarbon feedstock, and one feeding operation cycle is completed: the cracking reaction temperature is 840°C, the cracking feedstock is naphtha, the feed amount is 5kg / h, the dilution ratio is 0.5, and the residence time is 0.26s; when the TMT of the cracking furnace 1 reaches the upper limit of 1100°C, the feeding is stopped, and the recorded operation time is 115h; the carbon monoxide and carbon dioxide contents are 0.09% and 0.07% respectively; the charring time is 0.46h.

[0082] Example 4

[0083] The difference from Example 3 is that this example adopts an intermittent injection method, and injects the coking inhibitor 25 hours in the middle of the cracking reaction of the hydrocarbon feedstock in the cracking furnace 1.

[0084] Complete a feeding operation cycle: cracking reaction temperature 840℃, cracking raw material is naphtha, feeding amount is 5kg / h, dilution ratio is 0.5, residence time is 0.26s; when the cracking furnace 1TMT reaches the upper limit of 1100℃, the feeding is stopped and the recorded operation time is 110h; the carbon monoxide and carbon dioxide contents are 0.05% and 0.03% respectively before injection, and are 0.09% and 0.07% respectively after injection; the charring time is 0.45h.

[0085] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, and all of these shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for preparing a palmitate coking inhibitor, characterized in that: The coking inhibitor is obtained by reacting palmitic acid with a potassium compound; wherein the potassium compound is potassium hydroxide, potassium carbonate or potassium bicarbonate.

2. The method for preparing the palmitate coking inhibitor according to claim 1, wherein The molar ratio of palmitic acid to potassium element is 1:(1-1.1).

3. A palmitate coking inhibitor prepared by the preparation method according to claim 1 or 2.

4. The use of the palmitate coking inhibitor as claimed in claim 3, characterized in that: The coking inhibitor is used to slow down the coking of light oil cracking furnaces.

5. The use of the palmitate coking inhibitor as claimed in claim 4, characterized in that: The coking inhibitor is injected into the light oil cracking raw material tank or pipeline and enters the light oil cracking furnace together with the cracking raw material; or the coking inhibitor is injected into the dilution steam generator or pipeline and enters the light oil cracking furnace together with the dilution steam.

6. The use of the palmitate coking inhibitor according to claim 4, characterized in that: The injection amount of coking inhibitor is 20-60ppm of the cracking raw material input.

7. The use of the palmitate coking inhibitor according to claim 4, characterized in that: The coking inhibitor is injected by a continuous injection method or an intermittent injection method.

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