CN118048169A

CN118048169A - Heavy oil catalytic cracking method for improving yield of liquid products and low-carbon olefin

Info

Publication number: CN118048169A
Application number: CN202410280065.XA
Authority: CN
Inventors: 景文珩; 袁灿; 严雷; 邢卫红
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2024-03-12
Filing date: 2024-03-12
Publication date: 2024-05-17

Abstract

The invention discloses a heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins, which comprises the following specific steps: taking methanol solution as a disperse phase, heavy oil as a continuous phase, adopting a continuous membrane emulsification method, and taking a membrane as a disperse medium to prepare methanol solution/heavy oil emulsion with uniform particle size distribution; and (3) conveying the prepared emulsion serving as a raw material into a reaction tube of an FCC system, and reacting to obtain a final product. According to the invention, the methanol solution is used as a disperse phase, the heavy oil is used as a continuous phase, the continuous membrane emulsification method is adopted to efficiently prepare the methanol solution/heavy oil emulsion, the methanol solution/heavy oil emulsion is used as FCC feed to realize synchronous yield increase of FCC liquid products and low-carbon olefin, and the emulsion droplet size is regulated and controlled by changing the concentration of the methanol solution and then changing the interfacial tension between the disperse phase and the continuous phase.

Description

Heavy oil catalytic cracking method for improving yield of liquid products and low-carbon olefin

Technical Field

The invention belongs to the technical field of catalytic cracking, and particularly relates to a heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins.

Background

Fluid Catalytic Cracking (FCC) is one of the main conversion technologies in most petroleum refineries. In addition to producing gasoline, catalytic cracking units are an important production route for lower olefins and play an important role in providing raw materials for petrochemical processes. In a riser reactor of a catalytic cracking unit, an atomized feedstock is vaporized after contacting hot catalyst particles in a fluidized state, and then cracked to produce light products (light oils, light olefins, etc.) and coke. Since the cracking reaction is carried out in the gas phase, how to efficiently atomize the feedstock into fine droplets to increase the vaporization rate is one of the key problems in obtaining a high-yield light product.

In the field of diesel engine combustion, it has been widely studied to incorporate a low boiling point phase in the oil and then to carry out the emulsification in order to improve the atomization of the fuel by introducing the puffing and micro-explosion effects of the emulsion at high temperatures. This also provides a concept for improving the atomization effect of the feedstock in the catalytic cracking process. Researchers prepare water/heavy oil emulsion with water content of 1.5% -5% by using a high-speed shearing machine, and improve atomization effect of catalytic cracking raw materials by using micro-explosion effect of the emulsion, so that light oil yield after heavy oil catalytic cracking is improved by 2%, and coke yield is respectively reduced by 1.23% [ Chem end Process 2016, 109:90-96 ]. However, the conventional mechanical emulsification methods such as ultrasonic homogenizers have limited emulsification amounts, which limit their practical application in industry. Meanwhile, the micro-explosion performance of the emulsion is closely related to the quality (water content and water drop size) of the emulsion. Therefore, how to efficiently prepare an emulsion having excellent micro-explosion performance quality has become a key to further improve the distribution of heavy oil products after industrial catalytic cracking.

In recent years, the membrane emulsification technology has been widely focused on due to low energy consumption, controllable emulsion droplet size and high emulsification flux, which also provides a key technology for emulsifying heavy oil. In the prior art, stable water/heavy oil emulsion is prepared by continuous membrane emulsification, and the quality of the emulsion can be changed by changing the emulsification parameters, so that the micro-explosion performance of the emulsion is controlled. Finally, the light oil yield was increased by 10.8% and the coke yield was also reduced by 5.9%, but with the negative effect of reduced olefin yield [ Fuel 2024,358:130122].

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide a heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins, which adopts a continuous membrane emulsification method to efficiently prepare a methanol-in-heavy oil emulsion, and controls the technological parameters and membrane parameters of the emulsification process to controllably prepare the disperse phase content and the size of the emulsion, and the prepared emulsion is used as an FCC raw material, and simultaneously, the micro-explosion effect and the MTO reaction of the emulsion are introduced to improve the yields of heavy oil FCC liquid products and low-carbon olefins. Meanwhile, as the reaction of preparing olefin (MTO) from methanol is one of the most important reactions in C1 chemistry, a new way is provided for producing low-carbon olefin. In view of the high selectivity of MTO to low olefins and the similarity of FCC and MTO processes, heavy oil and methanol can be simultaneously fed from a catalytic cracker in a conventional catalytic cracking process to improve the selectivity of low olefins. Since the MTO process is an exothermic process and the heavy oil cracking process is an endothermic process, the coupling of the two may form a thermal complement. The coke produced by the heavy oil can not only improve the conversion rate of methanol in the MTO process, but also improve the proportion of ethylene to propylene, and the methanol can improve the selectivity of low-carbon olefin in the heavy oil catalytic cracking process.

In order to achieve the above object, the present invention adopts the following technical scheme:

a heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins comprises the following specific steps:

s1, taking a methanol solution as a disperse phase, taking heavy oil as a continuous phase, adopting a continuous membrane emulsification method, and taking a membrane as a disperse medium to prepare the methanol solution/heavy oil emulsion with uniform particle size distribution.

S2, conveying the prepared emulsion serving as a raw material into a reaction tube of an FCC system, and reacting to obtain a final product.

Preferably, the concentration of the methanol solution in the aforementioned step S1 is 10 to 100%.

Preferably, the emulsified dispersion medium in the step S1 is a porous membrane material, and the average pore diameter is 0.1 to 1 μm.

Preferably, in the step S1, the content of the continuous phase of the methanol solution/heavy oil emulsion is 1-15%, the temperature of the continuous phase is 40-70 ℃, and the emulsification flux is 1000-2000L/m ²/h; the size of the dispersed phase liquid drops is 1-15 mu m, and the content of the dispersed phase is 5-15 vol%.

Preferably, in the foregoing step S1, the heavy oil is preheated before being added to the continuous membrane emulsification system, and the specific steps are as follows: the heavy oil is circularly heated to 100-150 ℃ in a pipeline for 10-30 min, and then the temperature of the heavy oil is stabilized at 40-70 ℃.

Preferably, in the aforementioned step S2, the reaction steps of the FCC system are as follows: preheating the prepared emulsion serving as a raw material, entering a reaction tube after preheating to start reaction, stripping and purging after the reaction is finished, cleaning the residual product in the reaction tube, and condensing and collecting a liquid product.

Preferably, the preheating temperature of the emulsion raw materials is 50-80 ℃, the agent-oil ratio is 4-9, and the reaction temperature is 480-540 ℃; the stripping time is 10-30 min, and the condensing temperature is 0-10 ℃.

Preferably, in the step S2, the catalyst in the FCC system is a USY-type molecular sieve, and the USY-type molecular sieve includes a fresh agent and a balancing agent in a mass ratio of 1:2-1:4.

The invention has the advantages that:

(1) Compared with the traditional mechanical emulsification mode, the membrane emulsification has the advantages of low energy consumption, simple operation, high emulsification efficiency and the like, can rapidly prepare a large amount of high-quality heavy oil emulsion, and has the potential of large-scale industrial production;

(2) According to the invention, the interfacial tension between the disperse phase and the continuous phase is regulated by changing the concentration of the methanol solution, so that the regulation and control of the size of the disperse phase of the emulsion can be realized; by changing the proportion of methanol and water in the heavy oil emulsion disperse phase, the micro-explosion and MTO reaction of the heavy oil emulsion in the FCC device can be regulated and controlled, and the optimal FCC product distribution is obtained;

(3) The invention not only realizes the micro-explosion effect of introducing emulsion into the heavy oil FCC process and methanol MTO reaction, improves the yield of liquid products and low-carbon olefin, but also provides guidance for the application of the MTO reaction on the FCC device, saves the cost of constructing the MTO device and relieves the operation burden of the existing MTO device.

Drawings

FIG. 1 is a schematic diagram of a membrane emulsification system of the present invention;

FIG. 2 is a schematic diagram of an FCC system according to the present invention;

FIG. 3 is a product profile for various FCC feedstocks of example 3 (where the purple, green and blue dashed lines are the liquid product, coke and light olefin yields for pure heavy oil as FCC feedstock);

FIG. 4 is a graph showing the pore size distribution of a SiC ceramic membrane used in the present invention;

FIG. 5 is a microscopic image of a methanol solution/heavy oil emulsion prepared from a methanol solution having a concentration of 20% and a water droplet size distribution chart.

Meaning of reference numerals in the drawings: 1. the device comprises a storage tank, 2, a temperature controller, 3, a raw material tank, 4-5, a pressure gauge, 6, a membrane component, 7, a constant flow pump, 8, a flowmeter, 9, a measuring cylinder, 10 and a gear pump; 11. the device comprises a heating belt, v _1-6, a one-way valve, 12, a computer, 13, a gas chromatograph, 14, a liquid collecting bottle, 15, a gas collecting bottle, 16, a condensing tube, 17, an incubator, 18, a thermocouple, 19, a micro peristaltic pump, 20, an electronic balance, 21, a thermocouple, 22, a reaction tube, 23, nitrogen, 24 and a water vapor generator.

Detailed Description

The invention is described in detail below with reference to the drawings and the specific embodiments.

Aiming at the problem of easy coking caused by difficult atomization of high-viscosity raw oil in the feeding process in the conventional industrial heavy oil FCC device, the invention provides a method for improving the secondary atomization effect of the raw oil in the FCC device by utilizing the micro-explosion effect generated by the rapid vaporization of the dispersed phase water in the emulsion so as to improve the distribution of FCC products. Meanwhile, methanol is introduced into the disperse phase of the emulsion, and the selectivity of heavy oil FCC low-carbon olefin is improved by utilizing the MTO reaction of methanol and the promotion effect of heavy oil FCC products on the MTO reaction of methanol. Finally, a continuous membrane method is adopted to prepare a methanol solution/heavy oil emulsion with even emulsion drop distribution as an FCC raw material, and the influence of different methanol concentrations on the distribution of FCC products is explored, so that the purposes of increasing the yield of liquid products and low-carbon olefins are achieved. In addition, thermal complementarity can be formed between the MTO reaction and the micro-explosion effect, so that the temperature stability of the local reaction in the FCC device is maintained. The method has the advantages of simple operation, capability of amplifying, device cost saving and the like, can provide key technical guidance for industrial large-scale application, and has high social benefit and economic benefit.

The heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins adopts a continuous membrane emulsification method to efficiently prepare the heavy oil methanol-in-oil emulsion, the dispersion phase content and the size of the emulsion are controllably prepared by controlling the technological parameters and the membrane parameters of the emulsification process, the prepared emulsion is used as an FCC raw material, and the micro-explosion effect and the MTO reaction of the emulsion are introduced at the same time, so that the yields of the heavy oil FCC liquid products and the low-carbon olefins are improved in one step.

The specific technical scheme comprises the following steps:

(1) Methanol and water are prepared into a uniform and stable methanol solution according to a certain proportion; the heavy oil as a continuous phase was added to a continuous membrane emulsification system for preheating, and the heavy oil used was vacuum residuum, the properties of which are shown in table 1.

TABLE 1 Properties of vacuum residuum

The preheating step of heavy oil is divided into two steps: firstly, the heavy oil is circularly heated to 100-150 ℃ in a pipeline and is stabilized for about 10-30 min so as to remove a small amount of water remained in the heavy oil, and then the temperature of the heavy oil is stabilized at 40-70 ℃, so that the heavy oil can be ensured to have good fluidity, and the methanol solution is not vaporized in advance in the emulsification process.

And taking the methanol solution as a disperse phase, adopting a constant flow pump to press the methanol solution through the ceramic membrane holes at a constant flow, taking heavy oil at the other side as a continuous phase to pass through the membrane surface at a certain speed under the action of a gear pump, and taking the disperse phase liquid drops at the membrane holes away from the membrane surface by the provided shearing force to form uniform methanol solution/heavy oil emulsion.

Wherein the average pore diameter of the selected ceramic membrane is 0.1-1 mu m; the flux of the emulsification process is 1000-2000L/m ²/h, the droplet size of the prepared emulsion disperse phase is 1-15 mu m, and the content of the disperse phase is 5-15 vol%.

(2) Placing the prepared emulsion serving as a raw material in a preheating box of an FCC system, wherein the preheating temperature is 50-70 ℃, and maintaining a certain temperature to ensure that the emulsion has good fluidity; when the temperature of the reaction tube of the FCC system is heated to the target temperature of 480-540 ℃, feeding is started, the reading of an electronic balance is recorded, the feeding amount of raw materials is controlled, the catalyst-to-oil ratio of the reaction is 4-9, and the reaction temperature is 480-540 ℃.

(3) After the feeding is finished, steam with the flow rate of 600-1400 mL/min is continuously used for stripping for 10-30 min, and inert gas is used for purging at the flow rate of 100-400 mL/min after the steam stripping is finished, so that the residual product in the reaction tube is cleaned; analyzing the liquid product collected by the secondary condenser tube at 0-10 ℃ to calculate the yield; and analyzing the mass change of the catalyst after being burnt for 2-4 hours at 600-800 ℃ by a muffle furnace, and calculating the coke yield.

The process flow of the present invention is shown in fig. 1 and 2. Referring to fig. 1, the preparation of the heavy oil emulsion is first performed, and the specific flow operation is as follows: adding a proper amount of heavy oil into a raw material tank 3, opening one-way valves v3 and v6, closing v1, and simultaneously opening a temperature controller 2 and a gear pump 10 to circularly preheat and remove water from the heavy oil in a pipeline. When the heavy oil reaches the target temperature, the gear pump 10 is closed, porous ceramic membrane materials are filled into the membrane component, the constant flow pump 7 is opened to convey the disperse phase to pass through the surface of the membrane at constant flow, then the one-way valve v3 is closed, the valve v1 is opened, the gear pump 10 is opened again for continuous membrane emulsification, and the prepared emulsion enters the storage tank 1.

The heavy oil emulsion FCC (fig. 2) was then carried out, and the specific flow operation was as follows: a certain amount of heavy oil emulsion is put into an incubator 17, a micro peristaltic pump 19 and a steam generator 24 are started, and heavy oil is conveyed to the bottom of a reaction tube 22 to react with the catalyst in a fluidized state. After the reaction is finished, collecting the produced gas in the gas collecting bottle 15 and carrying out component analysis by using a meteorological chromatograph; and then analyzing the liquid and coke yield.

Example 1

This example prepares an FCC feedstock by continuous membrane emulsification, as shown in fig. 1, the heavy oil catalytic cracking process comprising the specific steps of:

(1) Heating heavy oil to remove residual water, and then reducing the temperature to 60 ℃ for standby; 100mL of pure methanol solution is taken as a disperse phase, and is conveyed through a membrane hole by a constant flow pump at a constant flow rate of 89 mL/min; after the pressure of the disperse phase side is stable, a gear pump is started and heavy oil is conveyed at a flow rate of 800mL/min, the heavy oil flows through the surface of the membrane to shear out disperse phase liquid drops at the membrane holes to form emulsion, the emulsion flux is 1770L/m ²/h, and the average size of the prepared emulsion liquid drops is 3.63 mu m.

(2) 50ML of heavy oil emulsion is taken as a raw material and placed in an incubator of an FCC system (figure 2) to keep good fluidity, 20g of USY-type catalyst (fresh agent: balancing agent=1:3) is weighed and filled into a reaction tube, then the reaction tube is installed in the FCC system, when the temperature of the reaction tube approaches the target temperature of reaction, a micro peristaltic pump is started to convey the raw material to the reaction tube, and specific reaction parameters are shown in table 2.

(3) After the end of the feed, the gas was stripped for 20min, followed by a nitrogen purge, the gas and liquid products were collected and the yield was calculated. After the temperature of the reaction tube is reduced, the reaction tube is disassembled, the catalyst with coking is removed, and the coke mass is calculated after the catalyst is burnt for 2 hours at 650 ℃ in a muffle furnace.

TABLE 2 Process parameters for heavy oil FCC

Operating parameters	Numerical value
		Reaction temperature (. Degree. C.)	530
Raw material amount (g)	4.00
		Ratio of agent to oil (g/g)	5
Nitrogen flow (mL min ^-1)	200
		Water vapor flow rate (mL min ^-1)	1000

Example 2

According to the specific procedure in example 1, methanol solutions of different concentrations, 100%, 80%, 60%, 40%, 20%, 0, respectively, were set, and the effect of the methanol solutions of different concentrations on the average droplet size of the prepared methanol solution/heavy oil emulsion was compared, and the results are shown in table 3.

TABLE 3 average droplet size of methanol solution/heavy oil emulsion

From table 3, it can be seen that the smaller the concentration of the methanol solution, the larger the average droplet size of the methanol solution/heavy oil emulsion, because the interfacial tension between the dispersed phase and the continuous phase can be adjusted by changing the concentration of the methanol solution, thereby achieving the regulation of the dispersed phase size of the emulsion.

Example 3

According to the specific procedure in example 1, methanol solutions of different concentrations, 100%, 80%, 60%, 40%, 20%, 0 respectively, were set as FCC raw materials, and compared with methanol solutions/heavy oil emulsions prepared by using methanol solutions of different concentrations as the dispersed phase, the effect on the yields of light olefins, liquid products and coke was found in fig. 3.

As shown in fig. 3, as the methanol concentration in the dispersed phase of the emulsion was reduced from 100% to 0%, the yield of the liquid product was increased from 32.21% to 44.49%, and the total low-carbon olefin (ethylene+propylene+butene) yield was reduced from 16.27% to 13.16%, mainly because the change in the methanol concentration affected the micro-explosion effect of the emulsion and the proportion of MTO reaction, and as the methanol concentration was reduced, the micro-explosion performance of the emulsion was increased, MTO reaction was impaired, resulting in a gradual increase in the yield of the liquid product, and a gradual decrease in the yield of the low-carbon olefin and coke. As shown in table 4, the product distribution after the emulsion passed through FCC was optimized at a methanol concentration of 20%: the yield of the low-carbon olefin is 14.03%, the yield of the coke is 14.50%, the yield of the liquid product is 44.23%, the lowest coke amount is achieved, and the yield of the low-carbon olefin and the liquid product is good. Compared with pure heavy oil FCC, the liquid phase product yield is improved by 10.88%, the low carbon olefin yield is improved by 0.26%, and the coke yield is reduced by 6.95%.

TABLE 4 comparison of product compositions after FCC of different feeds

Example 4

This embodiment is different from embodiment 1 described above in that: the pure heavy oil is directly used as FCC raw material without emulsifying the heavy oil. The distribution of the product after FCC was: the yield of the low-carbon olefin is 13.16%, the yield of the coke is 14.64%, and the yield of the liquid product is 44.49%.

Example 5

This embodiment is different from embodiment 1 described above in that: pure methanol is directly used as FCC feed.

As is clear from examples 1,4 and 5, 10vol% of methanol/heavy oil emulsion (referred to as heavy oil: methanol solution=9:1), heavy oil and methanol were used as the raw materials of FCC, respectively, and the yields of low-carbon olefins after passing through FCC were compared, as shown in table 4. The results demonstrate that methanol can undergo MTO reactions in the FCC unit and is more selective for lower olefins than heavy oils. In addition, the heavy oil FCC and methanol MTO reaction can mutually promote, and the selectivity of the low-carbon olefin is improved.

TABLE 5 production of lower olefins

Note that the calculated values represent the ratio of methanol to heavy oil in the methanol/emulsion, respectively, multiplied by the sum of the olefin yields after catalytic cracking alone, respectively.

The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be appreciated by persons skilled in the art that the above embodiments are not intended to limit the invention in any way, and that all technical solutions obtained by means of equivalent substitutions or equivalent transformations fall within the scope of the invention.

Claims

1. The heavy oil catalytic cracking method for improving the yield of liquid products and low-carbon olefins is characterized by comprising the following specific steps of:

S1, taking a methanol solution as a disperse phase, taking heavy oil as a continuous phase, adopting a continuous membrane emulsification method, and taking a membrane as a disperse medium to prepare a methanol solution/heavy oil emulsion with uniform particle size distribution;

2. The heavy oil catalytic cracking method according to claim 1, wherein the concentration of the methanol solution in step S1 is 10 to 100%.

3. The method for catalytic cracking of heavy oil according to claim 1, wherein the emulsified dispersion medium in step S1 is a porous membrane material, and the average pore diameter is 0.1-1 μm.

4. The method for catalytic cracking of heavy oil according to claim 1, wherein in the step S1, the continuous phase content of the methanol solution/heavy oil emulsion is 1% -15%, the continuous phase temperature is 40% -70 ℃, and the emulsion flux is 1000% -2000 l/m ²/h.

5. The method according to claim 1, wherein in the step S1, the droplet size of the dispersed phase is 1 to 15 μm, and the content of the dispersed phase is 5 to 15 vol%.

6. The method for catalytic cracking of heavy oil according to claim 1, wherein in step S1, the heavy oil is preheated before being added to the continuous membrane emulsification system, and the specific steps are as follows: and (3) circularly heating the heavy oil in a pipeline to 100-150 ℃, stabilizing for 10-30 min, and stabilizing the temperature of the heavy oil at 40-70 ℃.

7. The method for catalytic cracking of heavy oil according to claim 1, wherein in said step S2, the reaction steps of the FCC system are as follows: preheating the prepared emulsion serving as a raw material, entering a reaction tube after preheating to start reaction, stripping and purging after the reaction is finished, cleaning the residual product in the reaction tube, and condensing and collecting a liquid product.

8. The heavy oil catalytic cracking method according to claim 6, wherein the preheating temperature of the emulsion raw material is 50-80 ℃, the catalyst-to-oil ratio is 4-9, and the reaction temperature is 480-540 ℃; the stripping time is 10-30min, and the condensing temperature is 0-10 ℃.

9. The heavy oil catalytic cracking method according to claim 1, characterized in that: in the step S2, the catalyst in the FCC system is a USY-type molecular sieve.

10. The heavy oil catalytic cracking method according to claim 9, characterized in that: the USY type molecular sieve comprises a fresh agent and a balancing agent in a mass ratio of 1:2-1:4.