Process for preparing second-generation biodiesel and biological aviation fuel through hydrogenation

Abstract

The invention discloses a process for preparing second-generation biodiesel and biological aviation fuel through hydrogenation. The process comprises the following steps: pre-treated waste grease is mixed with high-pressure hydrogen after being pressurized and heated, the mixture enters a fluidized bed hydrogenation feeding heating furnace to be heated to 200-300 DEG C and then sequentially enters a first-stage fluidized bed hydrogenation reactor and a second-stage fluidized bed hydrogenation reactor for hydrogenation reaction, and a reaction product obtained by refining enters a fractionating tower for fractionating, and respectively obtaining biological aviation fuel and second-generation biodiesel. The invention provides a two-stage fluidized bed hydrogenation process aiming at the defects of a fixed bed hydrogenation process for producing second-generation biodiesel and biological aviation oil, solves the problems and limitation of a conventional fixed bed hydrogenation process, and has unique technical advantages. The two-stage fluidized bed hydrogenation process hardly limits the indexes such as the metal content and the carbon residue content in the waste grease; reaction coking materials can be taken out of a fluidized bed hydrogenation reaction system on line, and a hydrogenation bed layer and equipment cannot be blocked; in the fluidized bed reactor, the material is in a fluidized state, the reaction temperature is uniform, and the local overheating phenomenon can be effectively avoided.

Description

Technical Field

[0001] The present invention relates to a process for preparing biodiesel, in particular to a process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation. Background Art

[0002] Waste oil contains many toxic and harmful components. The amount of waste oil discharged each year at home and abroad is huge. If these waste oils are discharged directly without treatment or flow back to the dining table, they will pose a serious threat to the ecological environment and national food safety. The production of second-generation biodiesel and bio-aviation fuel using waste oil as raw materials is of great significance for reducing carbon emissions, improving air quality and the ecological environment, increasing the proportion of green and clean fuel applications, and achieving carbon peak and carbon neutrality. At present, the production of second-generation biodiesel and bio-aviation fuel at home and abroad is mainly achieved through fixed-bed hydrogenation technology. However, the fixed-bed hydrogenation process still has the following problems and limitations in terms of raw materials, catalysts and production processes: the fixed-bed reactor adopts graded loading of catalysts, and has strict restrictions on the metal and residual carbon content of the raw materials, requiring metal content ≯5.0μg / g and residual carbon content ≯0.85%. However, the acid value, metal (especially Fe, Na, Ca), oxygen, nitrogen, sulfur, phosphorus and other heteroatom contents of waste oils and fats far exceed the limit, which is extremely challenging for the existing fixed-bed hydrogenation process and cannot be carried out normal production; at the same time, fixed-bed catalysts are easily affected by reaction water generation, reaction coking, etc., resulting in the pressure drop of the catalyst bed exceeding the bearing capacity, making it difficult to achieve long-term operation; in addition, the overall fixed-bed hydrogenation process is difficult to adjust, and waste oils and fats may release a large amount of heat in certain specific catalyst areas during the reaction, causing coking, which brings safety risks. Summary of the Invention

[0003] The present invention provides a process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation.

[0004] The present invention provides the following technical solution: a process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation, wherein pretreated waste oil is pressurized and heated, mixed with high-pressure hydrogen, and then enters a fluidized bed hydrogenation feed heating furnace to be heated to 200-300°C. The waste oil then enters a first-stage fluidized bed hydrogenation reactor and a second-stage fluidized bed hydrogenation reactor in sequence for hydrogenation reaction. The refined reaction products enter a fractionating tower for fractionation to obtain bio-aviation fuel and second-generation biodiesel, respectively.

[0005] During the pretreatment, the water content, mechanical impurities and other invalid components in the waste grease are removed, and the water content in the waste grease is reduced to below 0.05%w.

[0006] The reaction temperature of the first stage fluidized bed hydrogenation reactor is 250-320℃, the reaction pressure is 8.0-16.0MPa, and the hydrogen-to-oil ratio is 800-1200Nm 3 / Nm 3, volume space velocity 0.3~1.0h -1 .

[0007] The reaction temperature of the two-stage fluidized bed hydrogenation reactor is 300-380°C, the reaction pressure is 8.0-16.0 MPa, and the hydrogen-to-oil ratio is 800-1200 Nm 3 / Nm 3 , volume space velocity 1.0~1.5h -1 .

[0008] Furthermore, both the first-stage and second-stage fluidized bed hydrogenation reactors are equipped with an online catalyst injection system, which can continuously replenish catalyst online to ensure catalyst activity. At the same time, an online reaction coke discharge system is set up to continuously discharge impurities such as polymers and metals produced by condensation during the reaction process from the reaction system, preventing blockage of the hydrogenation bed and equipment, and ensuring long-term stable operation of the first-stage and second-stage fluidized bed hydrogenation reactors. Since the reaction is exothermic, the reactor temperature will rise, and each reactor is equipped with a cold hydrogen port to control the reaction temperature.

[0009] In the present invention, the reaction product from the first-stage fluidized bed hydrogenation reactor is treated in a first hot high-pressure separator and then enters a second-stage fluidized bed hydrogenation reactor; the reaction product from the second-stage fluidized bed hydrogenation reactor is separated in a second hot high-pressure separator and enters the hot high-pressure separator for gas-liquid separation, the hot high-fraction gas is heat-exchanged with mixed hydrogen and cooled by air and then enters a cold high-pressure separator, in which gas, oil and water are separated into three phases, the cold high-fraction oil passes through a cold low-pressure separator and enters a product fractionation tower for fractionation; the hot high-fraction oil enters a hot low-pressure separator, the hot low-fraction oil enters a product fractionation tower for fractionation, the hot low-fraction gas enters a cold low-pressure separator for treatment, and then the cold low-fraction oil enters a product fractionation tower for fractionation.

[0010] The product fractionation tower is equipped with two side-stream towers: a bio-aviation fuel stripper and a second-generation biodiesel stripper. The overhead effluent from the product fractionation tower is cooled in the product fractionation tower overhead cooler, then pressurized by an overhead reflux pump. A portion of the effluent is sent to the bio-naphtha product tank as bio-naphtha product, and a portion is returned to the top of the product fractionation tower as reflux. Bio-aviation fuel is drawn from the product fractionation tower side-stream and enters the bio-aviation fuel stripper for stripping. After stripping, the bio-aviation fuel is pressurized by the bio-aviation fuel product pump, heat exchanged with a heat exchanger, cooled, and then sent to the bio-aviation fuel product tank. Second-generation biodiesel is drawn from the product fractionation tower side-stream and enters the second-generation biodiesel stripper for stripping. After stripping, the second-generation biodiesel is pressurized by the second-generation biodiesel product pump, heat exchanged with a heat exchanger, cooled, and then sent to the second-generation biodiesel product tank.

[0011] The present invention addresses the shortcomings of a fixed-bed hydrogenation process in producing second-generation biodiesel and bio-aviation fuel. The present invention provides a two-stage fluidized bed hydrogenation process, which solves the problems and limitations of conventional fixed-bed hydrogenation processes and has unique technical advantages. The two-stage fluidized bed hydrogenation process has almost no restrictions on indicators such as the metal content and residual carbon content in waste oils and fats; reaction coke can be removed from the fluidized bed hydrogenation reaction system online without causing blockage of the hydrogenation bed and equipment; and in the fluidized bed reactor, the materials are in a fluidized state, the reaction temperature is uniform, and local overheating can be effectively avoided.

[0012] 1. Simplified raw material pretreatment process

[0013] The two-stage fluidized bed hydrogenation process has very broad requirements for raw materials, and can eliminate the complex and energy-intensive raw material pretreatment process required by the conventional fixed-bed hydrogenation process. The raw material pretreatment of the two-stage fluidized bed hydrogenation process only needs to consider the dehydration factor, and there are no strict restrictions on the content of impurities such as metals and residual carbon in waste oils and fats.

[0014] 2. The reaction temperature is uniform and stable, easy to operate and control, and low energy consumption

[0015] The two-stage fluidized bed hydrogenation process is in a fluidized state in the reactor, with good heat and mass transfer properties. The heat released by the reaction will not accumulate locally in the bed. The entire reactor is basically in a constant temperature reaction state. The temperature difference in the reactor is ≯50°C, and the amount of cold hydrogen required is small. The heat released by the reaction can basically be used to heat the raw materials. In the fixed bed hydrogenation process, waste oil may release a large amount of heat in certain specific catalyst areas during the reaction. The temperature difference in the reactor sometimes exceeds 100°C, making the operation difficult to control and posing a safety risk.

[0016] 3. The pressure drop of the hydrogenation bed is small, which will not cause blockage of the bed and equipment

[0017] The two-stage fluidized bed hydrogenation process is equipped with an online reaction coke discharge system to achieve continuous discharge of polymers, metals and other impurities produced by condensation during the reaction process from the reaction system. Compared with conventional fixed-bed reactors, the bed pressure drop is smaller. The normal fluidized bed hydrogenation bed pressure drop is ≯50KPa, while the bed pressure drop of conventional fixed-bed reactors can even reach 800KPa. The two-stage fluidized bed hydrogenation process slows down the growth rate of the catalyst bed pressure drop and extends the operation cycle of the device.

[0018] 4. The process can achieve long-term operation

[0019] The two-stage fluidized bed hydrogenation process is equipped with an online catalyst filling system, which can continuously replenish the catalyst online to ensure the activity of the catalyst. It has a high ability to remove metal, oxygen, nitrogen and other impurities in the raw materials, greatly extending the operation cycle of the device. The conventional fixed bed hydrogenation process has a continuous operation time of 5 to 10 months, and the two-stage fluidized bed hydrogenation process has a continuous operation time of ≥24 months.

[0020] Table 1 Main comparison between two-stage fluidized bed hydrogenation process and conventional fixed bed hydrogenation process

[0021] project Conventional fixed bed hydrogenation process Two-stage fluidized bed hydrogenation process Reaction pressure, MPa 8～16 8～16 Reaction temperature, °C 300～380 250～380 <![CDATA[Space velocity, h -1 > 0.15～1.0 0.3～1.5 <![CDATA[Metal content, μg·g -1 > ≯5.0 No restrictions Residual carbon content, μg·g-1 ≯0.85 No restrictions Solid impurity particle size, μm ＜25 No restrictions Continuous operation time of the device, months 5～10 ≥24 BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flow chart of raw material pretreatment process for conventional fixed-bed hydrogenation process.

[0023] Figure 2 This is a flow chart of raw material pretreatment of the present invention.

[0024] Figure 3 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be fully described below in conjunction with the drawings in the embodiments of the present application, so as to fully understand the purpose, effect and application prospects of the present invention. The following examples are only used to illustrate the present invention and are not intended to limit the scope of application of the present invention.

[0026] Example 1

[0027] (1) First, the waste grease enters the pretreatment device 1 to remove the water, mechanical impurities and other invalid components in the waste grease, and reduce the water content in the waste grease to below 0.05%w.

[0028] (2) The pre-treated waste oil enters the raw material buffer tank 2, is pumped out by the reaction feed pump and pressurized, and then is first heat-exchanged with the hydrogenation reaction product, and then mixed with high-pressure hydrogen. It then enters the fluidized bed hydrogenation feed heating furnace 3 and is heated to 200-300°C. It then enters the reactor from the bottom of the first-stage fluidized bed hydrogenation reactor 4, so that the catalyst particles are fluidized and move violently under the action of the airflow. The first-stage fluidized bed hydrogenation reaction temperature is 250-320°C, the reaction pressure is 8.0-16.0 MPa, and the hydrogen-to-oil ratio is 800-1200 Nm 3 / Nm 3, volume space velocity 0.3~1.0h-1. The fluidized bed hydrogenation reactor has good heat and mass transfer performance. In the fluidized bed hydrogenation reactor, the raw materials, hydrogen and catalyst are fully mixed to form a high back-mixing system. Under this system, the catalyst is in full contact with the reaction raw materials to avoid coking caused by large amounts of heat release in local areas, while slowing down the growth rate of the catalyst bed pressure drop and extending the operation cycle of the device. Hydrogenation, decarboxylation and decarbonylation reactions are carried out in the first-stage fluidized bed hydrogenation reactor 4. At the same time, the metal and residual carbon content and other impurity contents of the reaction products of the first-stage fluidized bed hydrogenation reactor 4 are effectively removed. The first-stage fluidized bed hydrogenation reactor 4 is provided with a catalyst online injection system, which can continuously replenish the catalyst online to ensure the activity of the catalyst; at the same time, an online reaction coke discharge system is provided to realize the continuous discharge of impurities such as polymers and metals produced by condensation during the reaction process from the reaction system, which will not cause blockage of the hydrogenation bed and equipment, and ensure the long-term stable operation of the first-stage fluidized bed hydrogenation system. The product of the first stage fluidized bed hydrogenation reaction is separated in the first hot high-pressure separator 5 to obtain a bio-oil intermediate product, which is then sent to the second stage fluidized bed hydrogenation reactor 6 for further hydrogenation and refining. The second stage fluidized bed hydrogenation reaction temperature is 300-380°C, the reaction pressure is 8.0-16.0 MPa, and the hydrogen-to-oil ratio is 800-1200 Nm 3 / Nm 3 The second-stage fluidized bed hydrogenation system is equipped with an online catalyst injection system and an online reaction coke removal system to ensure long-term stable operation. Since the reaction is exothermic, the reactor temperature will rise. Each reactor is equipped with a cooling hydrogen port to control the reaction temperature.

[0029] (3) The reaction products from the first-stage fluidized bed hydrogenation reactor 4 are treated in the first hot high-pressure separator 5 and then enter the second-stage fluidized bed hydrogenation reactor 6.

[0030] The reaction products coming out of the second-stage fluidized bed hydrogenation reactor 6 are separated by the second hot high-pressure separator 7 and enter the second hot high-pressure separator 7 for gas-liquid separation. The hot high-fraction gas coming out of the second hot high-pressure separator 7 is heat exchanged with the mixed hydrogen and cooled by air and then enters the cold high-pressure separator 16. In the cold high-pressure separator 16, the three-phase separation of steam, oil and water is carried out. The cold high-fraction oil passes through the cold low-pressure separator 15 and enters the product distillation tower 9 for fractionation; the hot high-fraction oil enters the hot low-pressure separator 8 for further flash evaporation, and the hot low-fraction oil enters the product distillation tower 9 for fractionation. The hot low-fraction gas is condensed and enters the cold low-pressure separator 15 together with the cold high-fraction oil.

[0031] To prevent the ammonium salts generated by the reaction from crystallizing at low temperatures and clogging the tubes of the hot high-fraction gas air cooler, demineralized water is injected before the hot high-fraction gas air cooler to wash away the ammonium salts. The cold high-fraction gas exiting the cold high-pressure separator 16 first passes through a circulating hydrogen desulfurization tower to remove hydrogen sulfide. It then passes to the circulating hydrogen compressor 17, where it is re-pressurized, mixed with compressed new hydrogen, and returned to the reaction system.

[0032] (4) The cold low-pressure oil from the cold low-pressure separator 15 and the hot low-pressure oil from the hot low-pressure separator 8 are heated in the product fractionation tower feed heating furnace and then enter the product fractionation tower 9, which has two side-line towers: a bio-aviation fuel stripping tower 10 and a second-generation biodiesel stripping tower 11. The top flow of the product fractionation tower 9 is cooled in the product fractionation tower top cooler and then pressurized by the top reflux pump. A portion of the top flow is sent to the bio-naphtha product tank 14 as a bio-naphtha product, and a portion is returned to the top of the product fractionation tower 9 as reflux. Bio-aviation fuel is extracted from the product fractionation tower side line and enters the bio-aviation fuel stripping tower 10 for stripping. The stripped bio-aviation fuel is pressurized by the bio-aviation fuel product pump, heat-exchanged with the heat exchanger, cooled, and then sent to the bio-aviation fuel product tank 12. The second-generation biodiesel is extracted from the side line of the product distillation tower and enters the second-generation biodiesel stripping tower 11 for stripping. The stripped second-generation biodiesel is pressurized by the second-generation biodiesel product pump, heat-exchanged and cooled with the heat exchanger, and then sent to the second-generation biodiesel product tank 13.

[0033] Process conditions of the fractionation tower: top operating pressure 0.03~0.10MPa, top operating temperature 105~145℃, bottom operating temperature 265~330℃

[0034] Process conditions of cold low-pressure separator: operating pressure 0.5~1.0MPa, operating temperature 30~50℃

[0035] Process conditions of hot low-pressure separator: operating pressure 0.5~1.0MPa, operating temperature 300~380℃

[0036] The process conditions of the first hot high-pressure separator are: operating pressure 8.0-16.0 MPa, operating temperature 250-320°C

[0037] The process conditions of the second hot high-pressure separator are: operating pressure 8.0-16.0 MPa, operating temperature 300-380°C

[0038] The above embodiment merely represents one embodiment of the present invention. While the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and all such modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation, characterized in that: The pretreated waste oil is pressurized and heated, mixed with high-pressure hydrogen, and enters the fluidized bed hydrogenation feed heating furnace to be heated to 200-300°C. It then enters the first-stage fluidized bed hydrogenation reactor and the second-stage fluidized bed hydrogenation reactor in sequence for hydrogenation reaction. The refined reaction products enter the distillation tower for fractionation to obtain bio-aviation fuel and second-generation biodiesel, respectively.

2. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 1, characterized in that: The pretreatment is to remove invalid components such as moisture and mechanical impurities from the waste grease, and reduce the water content of the waste grease to below 0.05%w.

3. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 1, characterized in that: The reaction temperature of the first stage fluidized bed hydrogenation reactor is 250-320°C, the reaction pressure is 8.0-16.0 MPa, and the hydrogen-to-oil ratio is 800-1200 Nm 3 / Nm 3 , volume space velocity 0.3~1.0h -1 .

4. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 1, characterized in that: The reaction temperature of the two-stage fluidized bed hydrogenation reactor is 300-380°C, the reaction pressure is 8.0-16.0 MPa, and the hydrogen-to-oil ratio is 800-1200 Nm 3 / Nm 3 , volume space velocity 1.0~1.5h -1 .

5. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 1, characterized in that: The first-stage fluidized bed hydrogenation reactor and the second-stage fluidized bed hydrogenation reactor are both provided with an online catalyst filling system for continuously replenishing the catalyst online; and an online reaction coke discharge system is also provided.

6. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 1, characterized in that: The reaction product from the first-stage fluidized bed hydrogenation reactor is treated by a first hot high-pressure separator and then enters a second-stage fluidized bed hydrogenation reactor; the reaction product from the second-stage fluidized bed hydrogenation reactor is separated by a second hot high-pressure separator and enters a hot high-pressure separator for gas-liquid separation, the hot high-fraction gas is heat exchanged with mixed hydrogen and cooled by air and then enters a cold high-pressure separator, in which gas, oil and water are separated into three phases, the cold high-fraction oil passes through a cold low-pressure separator and enters a product fractionation tower for fractionation; the hot high-fraction oil enters a hot low-pressure separator, the hot low-fraction oil enters a product fractionation tower for fractionation, the hot low-fraction gas enters a cold low-pressure separator for treatment, and then the cold low-fraction oil enters a product fractionation tower for fractionation.

7. The process for preparing second-generation biodiesel and bio-aviation fuel by hydrogenation according to claim 6, characterized in that: The product fractionation tower is equipped with two side-line towers, a bio-aviation fuel stripping tower and a second-generation biodiesel stripping tower. The top effluent of the product fractionation tower is cooled by the product fractionation tower top cooler, then pressurized by the top reflux pump, and a portion is sent to the bio-naphtha product tank as a bio-naphtha product, and a portion is returned to the top of the product fractionation tower as reflux. Bio-aviation fuel is extracted from the side line of the product fractionation tower and enters the bio-aviation fuel stripping tower for stripping. The stripped bio-aviation fuel is pressurized by the bio-aviation fuel product pump, then heat exchanged with a heat exchanger, cooled, and then sent to the bio-aviation fuel product tank. Second-generation biodiesel is extracted from the side line of the product fractionation tower and enters the second-generation biodiesel stripping tower for stripping. The stripped second-generation biodiesel is pressurized by the second-generation biodiesel product pump, then heat exchanged with a heat exchanger, cooled, and then sent to the second-generation biodiesel product tank.

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