A catalyst and a method for the coupled conversion of CO2 and polyolefins to prepare high-quality gasoline

Abstract

The present invention discloses a method for the coupled conversion of carbon dioxide and polyolefins to prepare high-quality gasoline, belonging to the technical field of the conversion and recycling of polyolefin plastics. The catalyst is a bifunctional catalyst composed of metal, metal oxide and molecular sieve. Using carbon dioxide and polyolefins as reaction raw materials, a conversion reaction is carried out under the action of the catalyst. The reaction process can not only realize the resource utilization of carbon dioxide at the same time, but also turn waste polyolefin plastics into valuable products, achieve high-value utilization, and generate high-octane gasoline. The reaction has high product yield and product selectivity. The yield of high-octane gasoline can reach 60-90%, the content of aromatics in gasoline is between 10-35%, and the catalyst can be reused after simple regeneration treatment. It is a new technology for the comprehensive utilization of polyolefin plastics and carbon dioxide emission reduction, and has good application prospects.

Description

Technical Field

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

[0002] Plastics are important organic synthetic polymers and are widely used in various fields such as packaging, agriculture, construction, and automobiles. As of 2019, the global annual plastic production has reached 460 million tons / year, making it one of the synthetic materials with the largest production. Among them, polyolefin plastics represented by polyethylene and polypropylene account for about 55% of the total plastic production. However, due to the chemical inertness of polyolefins, a large amount of polyolefins are disposable products and are difficult to recycle and reuse. Thus, the serious environmental pollution problems caused have attracted extensive attention from scientific researchers.

[0003] For polyolefins, the C(sp 3 )-C(sp 3 ) bonds on its backbone are very stable and not easily broken. Therefore, recycling polyolefins requires introducing additional energy to break the C-C bonds. However, in traditional polyolefin recycling technologies, such as pyrolysis and hydrocracking methods, the breaking of C-C bonds is random and irregular, and the obtained products are mostly pyrolysis oils mainly composed of long-chain alkanes or olefins. The product distillation range is wide, and the added value of the products is relatively low. It is impossible to prepare high-added-value products with high selectivity, which makes the plastic pyrolysis lack an economically viable driving force.

[0004] CO2 is a greenhouse gas, and how to reduce CO2 emissions has become an extremely important research direction. At the same time, using CO2 as a C1 resource and developing efficient catalytic technologies to convert CO2 into high-value chemicals is an important direction for the resource utilization of CO2. However, the linear geometric structure of the CO2 molecule and the high bond energy of the C=O double bond (~799 KJ / mol) make the catalytic conversion of CO2 very difficult. Therefore, realizing the efficient conversion and utilization of CO2 also has important academic significance. Although some studies have shown that high-added-value chemicals or liquid fuels (such as light olefins, aromatics, or higher alcohols) can be prepared by using CO2 and H2 under high temperature and pressure. However, at present, the acquisition of H2 resources highly depends on the consumption of fossil energy (coal, oil, and natural gas). Without a considerable "green hydrogen" acquisition technology, the large-scale use of H2 resources means more CO2 emissions. Therefore, realizing the resource utilization of CO2 under hydrogen-free conditions is more attractive and challenging.

[0005] Gasoline is C5-C 11Hydrocarbon mixtures are fuels with extremely high demand and are generally obtained by cracking and fractionating petroleum. Obtaining gasoline under mild conditions through catalytic pyrolysis using waste polyolefins as raw materials is an economically viable technical route. However, the products obtained from traditional polyolefin pyrolysis mainly consist of long-chain linear olefins or alkanes, with almost no high-octane aromatics and isohydrocarbons. This causes the octane number of gasoline to decrease and makes it unusable directly. Therefore, achieving the coupling conversion reaction of CO2 and polyolefins to produce high-value-added gasoline at relatively low temperatures, such as below 300 °C, remains a challenge to this day. Summary of the Invention

[0006] In view of the above problems, the present invention provides a catalyst and a method for the coupling conversion of CO2 and polyolefins to prepare high-octane gasoline. To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a catalyst for the coupling conversion of carbon dioxide and polyolefins to prepare high-octane gasoline. The catalyst is a bifunctional catalyst composed of a metal and a molecular sieve. Using carbon dioxide and polyolefins as reaction raw materials, a conversion reaction is carried out in a moving bed or fixed bed reactor under the action of the catalyst: 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; wherein the metal and metal oxide components play the role of activating CO2; the molecular sieve plays the role of activating polyolefins; the composite mode of the metal or metal oxide and the molecular sieve is physical mixing or loading; the molecular sieve is a molecular sieve with a ten-membered ring or twelve-membered ring topological structure;

[0008] 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, Pt; the mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1 wt% - 60 wt%, preferably 0.5 wt% - 50 wt%.

[0009] Based on the above technical solution, preferably, the metal can be directly supported on the molecular sieve, or can be dispersed on a metal oxide support and then physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide support is one or more of Al2O3, TiO2, CeO2, ZnO, MoO x 、MnO x or more.

[0010] Based on the above technical solutions, preferably, the framework elements of the molecular sieve with a ten-membered 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 with a ten-membered or twelve-membered ring topological structure is preferably at least one of Beta, ZSM-11, or ZSM-5.

[0011] Based on the above technical solutions, preferably, the molecular sieve with a ten-membered or twelve-membered ring topological structure contains medium-strong acid, and the amount of medium-strong acid sites is ≥0.1 mol / kg, more preferably ≥0.2 mol / kg, and even more preferably ≥0.25 mol / kg.

[0012] The acid strength is defined by the NH3-TPD peak, including three acidities: weak acid, medium-strong acid, and strong acid; this NH3-TPD is based on the desorption peak position of NH3. The position of the desorption peak refers to the test conditions where the ratio of the sample mass w to the carrier gas flow rate f (w / f) = 100 g·h / L and the heating rate is 10 °C / min. The TCD records the thermal conductivity signal of the desorbed NH3, plots the desorption curve, and divides the inorganic solid into three acid strength levels according to the peak position vertex of the curve; a weak acid refers to an acid site where the NH3 desorption temperature is less than 245 °C; a medium-strong acid is an acid site where the NH3 desorption temperature is between 275 - 500 °C; a strong acid is an acid site where the NH3 desorption temperature is greater than 500 °C. The molecular sieve can be synthesized in the laboratory or commercially purchased and meet the requirements of the present invention.

[0013] Based on the above technical solutions, preferably, the metal or metal oxide is compounded with the molecular sieve by impregnation, deposition precipitation, chemical vapor deposition, or physical mixing.

[0014] Based on the above technical solutions, preferably, the bifunctional catalyst needs to be pre-reduced. The reduction atmosphere is H2 or CO, etc., the reduction temperature is 300 °C - 500 °C, and the reduction time is 0.5 h - 10 h.

[0015] Based on the above technical solutions, the present invention also provides a method for the coupled conversion of carbon dioxide and polyolefin plastics to prepare high-octane gasoline. Using carbon dioxide and polyolefin as reaction raw materials, the conversion reaction is carried out in a moving bed or fixed bed reactor, and the catalyst given in the previous technical solutions is used.

[0016] Based on the above technical solutions, preferably, the polyolefin includes one or more of polyethylene, polypropylene, and polybutene, as well as plastic products processed from the above polyolefins or waste plastics after use.

[0017] Based on the above technical solutions, preferably, the pressure of carbon dioxide 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 the catalyst to polyolefin ≥ 1:500, preferably ≥ 1:100; the reaction space velocity ≥ 300 ml·g -1 ·h -1 , preferably 300–8000 ml·g -1 ·h -1 , more preferably 500–5000 ml·g -1 ·h -1

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Different from the traditional plastic pyrolysis technology, the technical solution of the present invention uses a composite catalyst to achieve the one-step coupling of CO2 and polyolefin with high selectivity to convert into high-octane gasoline. The addition of CO2 can not only be used as a raw material for the production of high-octane gasoline, but also consume the H species in the polyolefin to promote the formation of aromatics.

[0020] 2. Different from the mechanism of high-temperature pyrolysis 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 it is not easy to produce high-quality gasoline components of C5-C 11 . The present invention utilizes the hydrogen spillover between catalyst components, uses the strong acidic sites of molecular sieves to break the C-C bonds of polyolefins, and uses CO2 to consume the hydrogen overflowing from the hydrogen transfer aromatization of molecular sieves, breaking the original reaction equilibrium and promoting the formation of aromatics. Under relatively mild reaction conditions (reaction temperature below 300 °C), high-octane gasoline can be prepared with high selectivity, showing strong economic application prospects.

[0021] 3. The present invention uses polyolefins as raw materials, and the polyolefins can also be plastic products processed from polyolefins and polyolefins as raw materials, such as plastic bags, plastic barrels, food wraps, various films, waste food packaging, etc. The raw materials have a wide source and high utilization rate, and it is an effective polyolefin utilization scheme that can be scaled up.

[0022] 4. The present invention can not only be applied to the resource utilization of low-concentration CO2 waste gas generated in processes such as oil refining, cement production, steelmaking, and power generation, but also be used for the utilization of waste gas containing high-concentration CO2 generated from lime kilns, oilfield gas, and grain fermentation gas. The raw materials have a wide source and strong applicability, and can significantly promote the emission reduction of greenhouse gas CO2. Taking the tail gas in the steelmaking industry as an example, the CO2 content is about 6% - 18%. The gas can be transformed by this technology without separation and purification, greatly saving the separation cost.

[0023] 5. After the catalyst of the present invention is regenerated by air calcination - hydrogen reduction, it can be recycled, and there is no obvious catalyst loss phenomenon, which can significantly reduce the cost problem caused by catalyst deactivation.

[0024] 6. The preparation process of the nano - composite catalyst of the present invention is simple and the conditions are mild; moreover, in the reaction process, not only can the high - value utilization of polyolefins and CO2 be achieved simultaneously, but also it has a high space - time yield and selectivity of products. Among them, 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 implementation manners

[0025] The present invention will be further described below through examples, but the scope of the claims of the present invention is not limited by these examples. At the same time, the examples only give some of the conditions for achieving this purpose, but it does not mean that these conditions must be met to achieve this purpose.

[0026] I. Preparation of molecular sieve

[0027] The medium - strong acid described in the present invention can be tested by means such as the H - spectrum of solid nuclear magnetic resonance, NH3 - TPD, infrared, chemical titration, etc. However, the test methods for acidity are not limited to the above - mentioned test methods.

[0028] The molecular sieve with 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 method as an example for illustration.

[0029] 1) ZSM - 5 molecular sieve, the preparation process can refer to the following method:

[0030] Weigh the raw materials 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); deionized water. Stir and age at 30 °C. After 2 h, transfer it to a hydrothermal autoclave and crystallize at 180 °C for 48 h. Quench to room temperature in a water bath, wash by centrifugation repeatedly until the pH of the supernatant is 7 at the end of washing. The precipitate is dried at 110 °C for 17 h and then calcined in air at 600 °C for 3 h to obtain ZSM - 5 molecular sieve, marked as fraction 1.

[0031] 2) Beta molecular sieve, the preparation process can refer to the following method:

[0032] Weigh the raw materials according to the mass ratio of oxides SiO2:Al2O3:Na2O:R:H2O = 10:0.3:1:2:200: silica sol; aluminum isopropoxide; sodium hydroxide; TEAOH (R); deionized water. Stir overnight at room temperature, then place the gel in an oven at 65 °C, dry, crush it and put it into a crystallization kettle, pour in a certain amount of deionized water, crystallize at 170 °C for 3 days. The obtained product is filtered, washed, dried, ammonium-exchanged, and then calcined in a muffle furnace at 600 °C for 6 h to obtain Beta zeolite, labeled as fraction 2.

[0033] The framework element composition of the zeolite with a ten-membered or twelve-membered ring topological structure can also be at least one of Si-O, Si-Al-O, Si-Al-P-O, Si-Al-B-O, Si-Al-Ge-O;

[0034] Table 1 Preparation and performance parameters of zeolites with ten-membered or twelve-membered ring topological structures

[0035]

[0036] II. Preparation of bifunctional catalysts

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

[0038] The impregnation process can be carried out by either isovolumetric impregnation or excess impregnation, specifically as follows:

[0039] Dissolve the metal source in deionized water to prepare a precursor solution. Place it in the precursor solution and stir well to evenly disperse the precursor solution and its solute on the zeolite. Subsequently, obtain the metal oxide-modified zeolite through drying and calcination.

[0040] If the isovolumetric impregnation method is used, the pore volume V of the zeolite needs to be measured in advance p . The volume V0 of the precursor solution used = 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 Tables 2-3.

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

[0043]

[0044]

[0045] III. Catalytic Reaction Examples

[0046] This catalyst can be used in a moving bed or fixed bed reactor.

[0047] The reaction device is equipped with a gas mass flowmeter to control the gas flow rate, and gas chromatography is used for quantitative analysis of the products.

[0048] The following takes the fixed bed reactor as an example for illustration: A certain amount of catalyst and a certain amount of polyolefin are mixed and placed in the fixed bed reactor. The air in the reactor is replaced with CO2, and then it is heated to 180 - 300 °C in a CO2 atmosphere (containing 5% Ar as the internal standard for chromatographic analysis). The pressure of the CO2 gas is 0.5 - 10 MPa, and the space velocity of the reaction feed gas is adjusted to 300 - 12000 ml·g -1 ·h -1 for the reaction. The products are quantitatively analyzed by chromatography.

[0049] The gaseous products are analyzed using Ar as the internal standard and the yields are calculated.

[0050] By changing the reaction temperature, reaction pressure, and the reaction space velocity of CO2, the reaction performance can be changed.

[0051] 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%. The addition of CO2 can not only be used as a raw material for the production of high - octane gasoline, but also consume the H species in the polyolefin and promote the formation of aromatics.

[0052] Table 3 lists the specific applications of the catalyst and the data of their effects.

[0053] Table 3 Specific Applications of the Catalyst and the Data of Their Reaction Effects

[0054]

[0055]

[0056] In Comparative Example 1, the metal components and preparation method used in catalyst L are the same as those of catalyst A, and the molecular sieve component used is replaced with the commercially available F5 molecular sieve from Nankai University Catalyst Factory, which has three - dimensional eight - membered ring pores.

[0057] In Comparative Example 2, the metal components and preparation method used in catalyst M are the same as those of catalyst A, and the molecular sieve component used is replaced with the commercially available F6 molecular sieve from Nankai University Catalyst Factory, which has three - dimensional eight - membered ring pores.

[0058] The reaction results of Comparative Examples 1-2 show that molecular sieves with different topological structures significantly modulate the product selectivity. Molecular sieves 5 and 6 with a three-dimensional eight-membered ring pore structure are not conducive to the conversion of polyolefins and the formation of gasoline products. They are suitable for producing short carbon chain hydrocarbon products, but the yield of gasoline products is only 4%.

[0059] In Comparative Example 3, the metal components and preparation method used in catalyst P are the same as those in catalyst A, and the molecular sieve component used is replaced with molecular sieve 7, with a strong acid density of only 0.07 mmol / g. The reaction performance of Comparative Example 5 is poor, which may be due to the too low acid density resulting in poor ability to catalyze the cracking of plastics. Therefore, a certain medium strong acid density is very important.

[0060] In Comparative Example 4, catalyst Q is prepared by directly impregnating Pt on γ-Al2O3. As a result, CO2 and polyolefins are hardly converted, and almost no aromatics are formed.

[0061] In Comparative Example 5, the molecular sieve component used in catalyst R is the same as that in catalyst A (molecular sieve 1), but the difference is that it does not contain the metal Pt component. Since the molecular sieve hardly has the activity to catalytically activate 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, mainly long-chain alkanes are produced, and the CO2 conversion rate is only 1%, which is very low, and high-selectivity preparation of aromatics and CO2 emission reduction cannot be achieved.

[0062] Comparative Examples 4 and 5 show that when only one functional component of metal oxide or molecular sieve exists, the reaction effect is poor, and it does not have the excellent reaction performance described in the present invention at all.

[0063] In Comparative Example 6, the catalyst used is the same as that used in Example 1, which is catalyst A. However, in Comparative Example 6, no olefins are added. Experiments show that without the addition of polyolefins, CO2 cannot be effectively converted.

[0064] In Comparative Example 7, the catalyst used is the same as that used in Example 1, which is catalyst A. However, in Comparative Example 7, no CO2 is added, and N2 is used as the pressurizing atmosphere. Experiments show that without the introduction of CO2, polyolefins can be converted into gasoline by the bifunctional catalyst composed of metal and molecular sieve. The reaction results are similar to those of Comparative Example 5. The aromatic content in gasoline is not high, only 5%, the octane number of gasoline is not high, and it does not have the excellent reaction performance described in the present invention.

[0065] It can be seen from the reaction results of Comparative Examples 6-7 that the CO2 conversion reaction and the polyolefin conversion reaction are mutually coupled and mutually achieved. Without polyolefins, CO2 cannot be effectively converted; without CO2, polyolefins cannot be highly selectively converted into high-quality gasoline, the octane number of gasoline decreases, and the practicability decreases.

[0066] The catalyst used in Comparative Example 8 was the same as Catalyst A used in Example 1 respectively. However, the filling partial pressure of CO2 in Comparative Example 8 was relatively low, and at this time, the amount of CO2 was insufficient, and its promoting effect on the selective formation of aromatics was relatively small. Therefore, it is very important to ensure a sufficient amount of CO2 to promote the catalytic reaction.

[0067] It can be seen from the above table that the topological structure, acid properties of the molecular sieve, the feed ratio of CO2 to polyolefin waste plastics, and the matching between the metal or metal oxide and the molecular sieve all play crucial roles, directly affecting the selectivity of gasoline components, the conversion rate of CO2, and the quality (octane number) of gasoline.

Claims

1. A method for converting carbon dioxide and polyolefins into high-quality gasoline, characterized in that: Using carbon dioxide and polyolefin as reaction raw materials, the catalyst employed is a bifunctional catalyst, one of the functional components being composed of a metal, a metal oxide, or both, and the other functional component being composed of a molecular sieve; wherein the metal and metal oxide components play a role in activating CO2; the molecular sieve plays a role in activating polyolefin; the molecular sieve is a molecular sieve with a ten-membered ring or twelve-membered ring topological structure; the framework elements of the molecular sieve with 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, Si-O-Al-Ge; the molecular sieve with a ten-membered ring or twelve-membered ring topological structure contains medium-strength acids, and the amount of medium-strength acid sites is ≥ 0.1 mol / kg; the metal or metal oxide includes one or more of the elements Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir, Pt, and the mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1 wt% - 60 wt%; The pressure of the carbon dioxide is 0.2 - 6 MPa; the reaction temperature is 180 - 400 °C; the mass ratio of the catalyst to the polyolefin is ≥ 1:500; the gas hourly space velocity of the reaction is 300 – 12000 ml·g -1 ·h -1 .

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

3. The method according to claim 1, wherein: The metal or metal oxide is directly supported on the molecular sieve, or is dispersed on a metal oxide support and then physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide support is one or more of Al2O3, TiO2, CeO2, ZrO2, ZnO, MoO x , MnO x and the like.

4. The method according to claim 1, characterized in that: The molecular sieve with a ten-membered ring or twelve-membered ring topological structure is at least one of Beta, ZSM-11, or ZSM-5.

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

6. The method according to claim 1, wherein: The bifunctional catalyst needs to be pre-reduced, the reduction atmosphere is H2, CO, the reduction temperature is 300 °C - 500 °C, and the reduction time is 0.5 h - 10 h.

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

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