Catalyst and method for preparing high-quality gasoline by means of coupling conversion of co 2 and polyolefin

Abstract

The present invention belongs to the technical field of the conversion and recycling of polyolefin plastics, and disclosed is a method for preparing high-quality gasoline by means of the coupling conversion of carbon dioxide and a polyolefin. The catalyst is a bifunctional catalyst composed of a metal, a metal oxide and a molecular sieve, and carbon dioxide and polyolefin as reaction raw materials are subjected to a conversion reaction under the action of the catalyst. The reaction process can not only achieve the resource utilization of carbon dioxide at the same time, but can also transform waste polyolefin plastics into wealth, thus achieving high-value utilization and generating high-octane gasoline; and the reaction has a high product yield and product selectivity, the yield of the high-octane gasoline can reach 60-90%, the content of aromatic hydrocarbons in the gasoline is 10-35%, and the catalyst can be repeatedly used in a simple regeneration treatment, and thus the method is a new technology for comprehensive utilization of polyolefin plastics and carbon dioxide emission reduction, and has good application prospects.

Description

A catalyst and a method for producing high-quality gasoline by coupling conversion of CO2 and polyolefins Technical Field

[0001] The present invention relates to the production of high-quality gasoline by coupling conversion of CO2 and polyolefins, and specifically to a catalyst and a method for producing high-quality gasoline by coupling conversion of CO2 and polyolefins. Background Art

[0002] Plastics are important organic synthetic polymer materials, widely used in a variety of fields, including packaging, agriculture, construction, and automotive. As of 2019, global plastic production reached 460 million tons per year, making it one of the largest synthetic materials by volume. Polyolefin plastics, represented by polyethylene and polypropylene, account for approximately 55% of total plastic production. However, due to their chemical inertness, a large amount of polyolefins are disposable, making them difficult to recycle and reuse. The resulting serious environmental pollution has attracted widespread attention from researchers.

[0003] For polyolefins, the C(sp 3 )-C(sp 3 ) bonds are very stable and difficult to break. Therefore, recycling polyolefins requires the introduction of additional energy to break the C-C bonds. However, traditional polyolefin recovery technologies, such as pyrolysis and hydrogenolysis, break C-C bonds randomly and irregularly, resulting in pyrolysis oils primarily composed of long-chain alkanes or alkenes. These products have a wide distillation range and relatively low added value, making it impossible to selectively produce high-value-added products. This has led to a lack of economically viable drivers for plastic pyrolysis.

[0004] CO2 is a greenhouse gas. With my country's stated goals of achieving carbon peak and carbon neutrality ("dual carbon"), reducing CO2 emissions has become a crucial research topic. Furthermore, developing efficient catalytic technologies to convert CO2 into high-value chemicals, using CO2 as a C1 resource, is a key area of ​​CO2 resource utilization and holds significant significance for achieving the dual carbon goals and sustainable social development. However, the linear geometry of the CO2 molecule and the high bond energy of the C=O double bond (~799 kJ / mol) make catalytic CO2 conversion very difficult. Therefore, achieving efficient CO2 conversion and utilization is of great academic significance. Although some studies have demonstrated the ability to produce high-value-added chemicals or liquid fuels (such as light olefins, aromatics, or higher alcohols) from CO2 and H2 under high temperature and pressure, the current availability of H2 resources is heavily dependent on the consumption of fossil fuels (coal, oil, and natural gas). In the absence of promising "green hydrogen" production technologies, the extensive use of H2 resources means increased CO2 emissions. Therefore, achieving CO2 resource utilization in the absence of hydrogen is both more attractive and more challenging.

[0005] Gasoline is C5-C 11 A mixture of hydrocarbons, a fuel in high demand, is typically obtained from petroleum through cracking and fractionation. Using waste polyolefins as raw materials, obtaining gasoline under mild conditions through catalytic pyrolysis is an economically viable technical route. However, the products obtained from traditional polyolefin cracking are mainly long-chain linear olefins or alkanes, with almost no high-octane aromatics or isomers. This reduces the octane number of gasoline, making it unusable directly. Therefore, achieving a coupled conversion reaction of CO2 and polyolefins to produce high-value-added gasoline at lower temperatures, such as below 300°C, remains a challenge.

[0006] Summary of the Invention

[0007] To address the above issues, the present invention provides a catalyst and a method for producing high-octane gasoline by coupling CO2 with polyolefins. To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] The present invention provides a catalyst for the coupled conversion of carbon dioxide and polyolefin to prepare high-octane gasoline. The catalyst is a bifunctional catalyst composed of a metal and a molecular sieve. Carbon dioxide and polyolefin are used as reaction raw materials. Under the action of the catalyst, a conversion reaction is carried out in a moving bed or fixed bed reactor. The catalyst is a bifunctional catalyst, one of the functional components is composed of a metal, a metal oxide or both, and the other functional component is composed of a molecular sieve. The metal or metal oxide component activates CO2; the molecular sieve activates polyolefin. The metal or metal oxide and the molecular sieve are composited by physical mixing or loading. The molecular sieve has a ten-membered ring or twelve-membered ring topological structure.

[0009] Based on the above technical solution, preferably, the metal or metal oxide contains one or more of the elements Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir, and Pt; the mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1wt%-60wt%, preferably 0.5wt%-50wt%.

[0010] Based on the above technical solution, preferably, the metal can be directly supported on the molecular sieve, or can be dispersed on the metal oxide carrier and then physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide carrier is Al2O3, TiO2, CeO2, ZnO, MoO x 、MnO x One or more of the following.

[0011] Based on the above technical solution, preferably, the framework element of the molecular sieve having a ten-membered ring or twelve-membered ring topology structure comprises at least one of Si-O, Si-O-Al, Si-O-Al-P, Si-O-Al-B, and Si-O-Al-Ge; and the molecular sieve having a ten-membered ring or twelve-membered ring topology structure is preferably at least one of Beta, ZSM-11, or ZSM-5.

[0012] Based on the above technical solution, preferably, the molecular sieve having a ten-membered ring or twelve-membered ring topology contains a medium-strong acid, and the amount of the medium-strong acid site is ≥0.1 mol / kg, more preferably ≥0.2 mol / kg, and more preferably ≥0.25 mol / kg.

[0013] The acid strength is defined by the NH3-TPD peak, including three types of acidity: weak acid, medium acid, and strong acid. The NH3-TPD is based on the position of the NH3 desorption peak. The position of the desorption peak refers to the thermal conductivity signal of the desorbed NH3 recorded by the TCD under standard test conditions, with a sample mass w and carrier gas flow rate f ratio (w / f) = 100g·h / L and a heating rate of 10°C / min. The desorption curve is plotted and the inorganic solid is divided into three acid strengths according to the peak position of the curve. Weak acid refers to an acidic site with an NH3 desorption temperature of less than 245°C; medium acid refers to an acidic site with an NH3 desorption temperature between 275-500°C; and strong acid refers to an acidic site with an NH3 desorption temperature greater than 500°C. The molecular sieve can be laboratory synthesized or commercially purchased and meet the requirements of the present invention.

[0014] Based on the above technical solutions, preferably, the metal or metal oxide is compounded with the molecular sieve by impregnation, deposition precipitation, vapor deposition, or physical mixing.

[0015] Based on the above technical solution, preferably, the bifunctional catalyst needs to be pre-reduced, the reducing atmosphere is H2 or CO, the reduction temperature is 300°C-500°C, and the reduction time is 0.5h-10h.

[0016] Based on the above technical solution, the present invention also provides a method for producing high-octane gasoline by coupling carbon dioxide with polyolefin plastics. The reaction is carried out in a moving bed or fixed bed reactor using the catalyst described in the above technical solution, using carbon dioxide and polyolefin as the reaction materials.

[0017] Based on the above technical solution, preferably, the polyolefin includes one or more of polyethylene, polypropylene, and polybutene, and plastic products made from the above polyolefins as raw materials or used waste plastics.

[0018] Based on the above technical solution, preferably, the carbon dioxide pressure is 0.2-6 MPa, preferably 0.5-3 MPa; the reaction temperature is 180-400°C, preferably 230-300°C; the mass ratio of catalyst to polyolefin is ≥1:500, preferably ≥1:100; the reaction space velocity is ≥300 mL·g -1 ·h -1 , preferably 300-8000mL·g -1 ·h -1 , more preferably 500-5000mL·g -1 ·h -1

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention differs from traditional plastic pyrolysis technology by utilizing a composite catalyst to achieve a one-step, highly selective conversion of CO2 and polyolefins into high-octane gasoline. The addition of CO2 not only serves as a feedstock for high-octane gasoline but also consumes hydrogen species in the polyolefins, promoting the production of aromatics.

[0021] 2. Different from the high-temperature pyrolysis mechanism of polyolefins, at low temperatures (reaction temperature below 300°C), polyolefin pyrolysis is more likely to produce long-chain alkanes with a carbon chain length greater than 20, and is less likely to produce C5-C 11 This invention utilizes hydrogen overflow between catalyst components, exploits the strong acidic sites of the molecular sieve to break the C-C bonds of polyolefins, and uses CO2 to consume hydrogen overflow from the molecular sieve during hydrogen transfer aromatization, thereby disrupting the original reaction equilibrium and promoting aromatics production. Under relatively mild reaction conditions (reaction temperature below 300°C), this method achieves highly selective production of high-octane gasoline, demonstrating strong economic application prospects.

[0022] 3. The present invention uses polyolefin as raw material. The polyolefin can also be polyolefin or plastic products made from polyolefin as raw material, such as plastic bags, plastic barrels, plastic wrap, various films, waste food packaging, etc. Its raw material sources are wide and the raw material utilization rate is high. It is an effective and scalable polyolefin utilization solution.

[0023] 4. This invention can be applied not only to the resource utilization of low-concentration CO2 waste gas generated by processes such as oil refining, cement production, steelmaking, and power generation, but also to the utilization of high-concentration CO2 waste gas generated by lime kilns, oilfield gas, and grain fermentation gas. With a wide range of raw material sources and strong applicability, it can significantly contribute to the reduction of greenhouse gas CO2 emissions, in line with my country's "dual carbon" policy. For example, the CO2 content in steelmaking exhaust gas is approximately 6%-18%. This technology can convert this gas without the need for separation and purification, significantly saving separation costs.

[0024] 5. The catalyst of the present invention can be recycled after regeneration treatment by air roasting-hydrogen reduction, without obvious catalyst loss, which can significantly reduce the cost problem caused by catalyst deactivation.

[0025] 6. The preparation process of the nanocomposite catalyst of the present invention is simple and the conditions are mild. The reaction process can not only realize the high-value utilization of polyolefins and CO2 at the same time, but also has a high product space-time yield and selectivity. The yield of high-octane gasoline can reach 60-90%, and the content of aromatics in gasoline is between 10-35%. Compared with the traditional polyolefin pyrolysis process under inert gas conditions, it has a higher octane number. DETAILED DESCRIPTION

[0026] The present invention will be further described below by way of examples, but the scope of the claims of the present invention is not limited by these examples. Meanwhile, the examples only provide some conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0027] 1. Preparation of molecular sieves

[0028] The medium-strong acid described in the present invention can be tested by solid-state nuclear magnetic resonance (NMR) H spectroscopy, NH3-TPD, infrared spectroscopy, chemical titration, etc. However, the acidity test method is not limited to the above test methods.

[0029] The molecular sieve having a ten-membered ring or twelve-membered ring topological structure described in the present invention can be prepared by a variety of methods and conditions. This patent takes the preparation by hydrothermal synthesis as an example.

[0030] 1) ZSM-5 molecular sieve, the preparation process can refer to the following method:

[0031] The raw materials were weighed according to the mass ratio of oxides SiO2:Al2O3:Na2O:R:H2O = 5:0.02:2:1.5:200: silica sol 30% (mass concentration), aluminum sulfate, sodium hydroxide, tetrapropylammonium hydroxide (R), and deionized water. The mixture was stirred and aged at 30°C for 2 hours. After that, it was transferred to a hydrothermal kettle and crystallized at 180°C for 48 hours. It was quickly cooled to room temperature in a water bath and repeatedly centrifuged and washed until the pH of the supernatant was 7 at the end of the washing. The precipitate was dried at 110°C for 17 hours and then calcined in air at 600°C for 3 hours to obtain ZSM-5 molecular sieve, which is marked as fraction 1.

[0032] 2) Beta molecular sieve, the preparation process can refer to the following method:

[0033] The raw materials, silica sol, aluminum isopropoxide, sodium hydroxide, TEAOH(R), and deionized water, were weighed in a mass ratio of SiO2:Al2O3:Na2O:R:H2O = 10:0.3:1:2:200. The mixture was stirred overnight at room temperature. The gel was then placed in a 65°C oven, dried, crushed, and placed in a crystallization kettle. A certain amount of deionized water was added and crystallized at 170°C for 3 days. The resulting product was filtered, washed, dried, and ammonium exchanged before being calcined in a muffle furnace at 600°C for 6 hours to produce Beta molecular sieve, labeled as fraction 2.

[0034] The skeleton element composition of the molecular sieve having a ten-membered ring or twelve-membered ring topology structure may also be at least one of Si-O, Si-Al-O, Si-Al-PO, Si-Al-BO, and Si-Al-Ge-O.

[0035] Table 1 Preparation and performance parameters of molecular sieves with ten-membered ring or twelve-membered ring topology

[0036] 2. Preparation of bifunctional catalysts

[0037] The metal is combined with the molecular sieve to form a bifunctional catalyst by impregnation, deposition, vapor deposition, or physical mixing. Here, the bifunctional catalyst prepared by impregnation is taken as an example.

[0038] The impregnation process can be implemented by either equal volume impregnation or excess impregnation, as follows:

[0039] The metal source is dissolved in deionized water to prepare a precursor solution, which is then placed in the precursor solution and stirred thoroughly to uniformly disperse the precursor solution and the solute therein on the molecular sieve, followed by drying and calcination to obtain the desired metal oxide-modified molecular sieve.

[0040] If the equal volume impregnation method is used, the pore volume V of the molecular sieve needs to be determined in advance. p The volume of the precursor solution used is V0 = V p If the excess impregnation method is used, the V0 of the precursor solution used <V p .

[0041] The specific catalyst preparation and its parameter characteristics are shown in Table 2-3.

[0042] Table 2 Catalysts prepared by impregnation method and their parameter characteristics

[0043] 3. Catalytic Reaction Examples

[0044] The catalyst can be used in a moving bed or fixed bed reactor.

[0045] The reaction apparatus was equipped with a gas mass flowmeter to control the gas flow, and gas chromatography was used for quantitative analysis of the products.

[0046] The following is an example of a fixed bed reactor: a certain amount of catalyst and a certain amount of polyolefin are mixed and placed in a fixed bed reactor. The air in the reactor is replaced with CO2. The temperature is then raised to 180-300°C in a CO2 atmosphere (containing 5% Ar as an internal standard for chromatographic analysis). The CO2 pressure is 0.5-10 MPa, and the space velocity of the reaction raw gas is adjusted to 300-12000 mL·g -1 ·h -1 The reaction was carried out and the product was quantitatively analyzed by chromatography.

[0047] The gaseous products were analyzed using Ar as an internal standard and the yields were calculated.

[0048] Changing the reaction temperature, reaction pressure, and reaction space velocity of CO2 can change the reaction performance.

[0049] The performance is as follows: the total selectivity of high-octane gasoline can reach 60-90%, the content of aromatics in gasoline is between 10-35%, and the addition of CO2 can not only serve as a raw material for the production of high-octane gasoline, but also consume H species in polyolefins and promote the production of aromatics.

[0050] Table 3 lists the specific applications of the catalyst and its effect data.

[0051] Table 3 Specific application of catalyst and its reaction effect data

[0052] The metal components and preparation method used in catalyst L used in comparative example 1 are consistent with those of catalyst A, and the molecular sieve component used is replaced by commercially available 5 molecular sieve from the catalyst factory of Nankai University, which has a three-dimensional octahedral pore channel.

[0053] The metal components and preparation method used in the catalyst M used in Comparative Example 2 are consistent with those of catalyst A, and the molecular sieve component used is replaced by the commercially available 6 molecular sieve from the Nankai University Catalyst Factory, which has a three-dimensional octahedral pore channel.

[0054] The reaction results of Comparative Examples 1 and 2 demonstrate that different molecular sieve topologies significantly alter product selectivity. The three-dimensional octahedral pore structures of Fraction 5 and Fraction 6 are not conducive to polyolefin conversion and gasoline production, but are suitable for producing short-chain hydrocarbons, but the gasoline yield is only 4%.

[0055] Catalyst P, used in Comparative Example 3, uses the same metal components and preparation method as Catalyst A. The molecular sieve component is replaced with a 7-point molecular sieve, and the strong acid density is only 0.07 mmol / g. The poor reaction performance of Comparative Example 5 may be due to the low acid density, resulting in poor catalytic plastic cracking ability. Therefore, a certain medium-strong acid density is very important.

[0056] The catalyst Q used in Comparative Example 4 is Pt directly impregnated on γ-Al2O3. As a result, CO2 and polyolefins are almost not converted, and almost no aromatics are generated.

[0057] The molecular sieve component used in the catalyst R used in Comparative Example 5 is the same as that of catalyst A (point 1), except that it does not contain the metal Pt component. Since the molecular sieve has almost no activity in catalytic activation of CO2, only olefins react during the catalytic reaction process, that is, olefins can be directly cracked by the molecular sieve. However, the aromatic content in gasoline is not high, the octane number of gasoline is not high, and long-chain alkanes are mainly produced. The CO2 conversion rate is only 1%, which is very low, and it is impossible to achieve highly selective preparation of aromatics and CO2 emission reduction.

[0058] Comparative Examples 4 and 5 show that when only one functional component, metal oxide or molecular sieve, is present, the reaction effect is poor and the excellent reaction performance described in the present invention is completely lacking.

[0059] The catalyst used in Comparative Example 6 is the same as the catalyst used in Example 1, Catalyst A. However, no olefin is added in Comparative Example 6. Experiments show that without the addition of polyolefin, CO2 cannot be effectively converted.

[0060] The catalyst used in Comparative Example 7 is the same as the catalyst used in Example 1, Catalyst A. However, in Comparative Example 7, no CO2 is added and N2 is used as the pressurized atmosphere. Experiments show that without the introduction of CO2, polyolefins can be converted into gasoline by a bifunctional catalyst composed of metal and molecular sieve. The reaction results are similar to those in Comparative Example 5. The aromatic content in the gasoline is not high, only 5%, and the octane number of the gasoline is not high, and it does not have the excellent reaction performance described in the present invention.

[0061] It can be seen from the reaction results of Comparative Examples 6-7 that the CO2 conversion and polyolefin conversion reactions are mutually coupled and mutually beneficial. Without polyolefin, CO2 cannot be effectively converted; without CO2, polyolefin cannot be highly selectively converted to produce high-quality gasoline, the octane number of gasoline decreases, and the practicality decreases.

[0062] The catalyst used in Comparative Example 8 is consistent with Catalyst A used in Example 1, but the filling partial pressure of CO2 in Comparative Example 8 is lower. At this time, the amount of CO2 is insufficient, and its effect on promoting the selective formation of aromatics is small. Therefore, it is very important to ensure a sufficient amount of CO2 to promote the catalytic reaction.

[0063] It can be seen from the above table that the topological structure of the molecular sieve, the acid properties, the feed ratio of CO2 to polyolefin waste plastics, and the matching between the metal or metal oxide and the molecular sieve all play a vital role, directly affecting the selectivity of gasoline components, the conversion rate of CO2 and the quality of gasoline (octane number).

Claims

1. A method for converting carbon dioxide and polyolefins into high-quality gasoline, characterized in that: Carbon dioxide and polyolefin are used as reaction raw materials, and the catalyst used is a bifunctional catalyst, one of the functional components is composed of metal, metal oxide or both, and the other functional component is composed of molecular sieve; the metal and metal oxide components play the role of activating CO2; The molecular sieve acts to activate the polyolefin; The molecular sieve is a molecular sieve having a ten-membered ring or twelve-membered ring topology structure; The metal or metal oxide includes one or more of the elements Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir, and Pt.

2. The method according to claim 1, characterized in that: The pressure of the carbon dioxide is 0.2-6MPa; the reaction temperature is 180-400°C; the mass ratio of the catalyst to the polyolefin is ≥1:500; the reaction gas space velocity is 300-12000mL·g -1 ·h -1 .

3. The method according to claim 1, characterized in that: The conversion reaction is carried out in a moving bed or fixed bed reactor.

4. The method according to claim 1, characterized in that: The mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1 wt%-60 wt%.

5. The method according to claim 1, characterized in that: The metal or metal oxide can be directly supported on the molecular sieve, or dispersed on the metal oxide carrier and physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide carrier is Al2O3, TiO2, CeO2, ZrO2, ZnO, MoO x 、MnO x One or two or more of the following.

6. The method according to claim 1, characterized in that: The framework elements of the molecular sieve having a ten-membered ring or twelve-membered ring topological structure include at least one of Si-O, Si-O-Al, Si-O-Al-P, Si-O-Al-B, and Si-O-Al-Ge; the molecular sieve having a ten-membered ring or twelve-membered ring topological structure is preferably at least one of Beta, ZSM-11, or ZSM-5.

7. [Corrected 04.12.2023 in accordance with Rule 26] The method according to claim 1, characterized in that: The molecular sieve having a ten-membered ring or twelve-membered ring topology structure contains medium-strong acid, and the amount of medium-strong acid sites is ≥0.1 mol / kg.

8. The method according to claim 1, characterized in that: The metal or metal oxide is compounded with the molecular sieve by impregnation, deposition precipitation, vapor deposition, or physical mixing.

9. The method according to claim 1, characterized in that: The bifunctional catalyst needs to be pre-reduced in a reducing atmosphere of H2 and CO, at a reducing temperature of 300°C-500°C and for a reducing time of 0.5h-10h.

10. The method according to claim 1, characterized in that: The polyolefin includes one or more of polyethylene, polypropylene and polybutene, and plastic products made from the above polyolefins as raw materials or waste plastics after use.

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