A method for preparing aromatics by coupling CO with polyolefins

Abstract

The application discloses a method for preparing aromatic hydrocarbons by coupling conversion of carbon monoxide and polyolefins, and belongs to the technical field of polyolefin plastic conversion and recycling. The method uses carbon monoxide and polyolefin plastics as reaction raw materials, and a bifunctional catalyst composed of metals, metal oxides and molecular sieves as a catalyst to perform a conversion reaction. Since the carbon monoxide can come from carbon resources such as coal, biomass and natural gas, the reaction process can not only realize optimal utilization of carbon resources, but also change waste polyolefin plastics into treasure, realize high-value utilization, generate high-value-added aromatic hydrocarbon products, has high product yield and product selectivity, the aromatic hydrocarbon yield can reach 50-80%, the proportion of benzene, toluene and xylene in the aromatic hydrocarbons is greater than 60%, and the catalyst can be reused after simple regeneration treatment. The method is a new technology for comprehensive utilization of polyolefin waste plastics and utilization of carbon monoxide, and has good application prospect.

Description

Technical Field

[0001] This invention pertains to the production of high-value aromatics from the coupling conversion of CO and polyolefins, specifically relating to a catalyst and a method for preparing aromatics from the coupling conversion of CO and polyolefins. Background Technology

[0002] Plastics are important organic synthetic polymer materials, widely used in packaging, agriculture, construction, automobiles, and many other fields. As of 2019, global annual plastic production reached 460 million tons, making it one of the largest-producing synthetic materials. Polyolefin plastics, represented by polyethylene and polypropylene, account for approximately 55% of total plastic production. However, due to the chemical inertness of polyolefins, a large amount of them are used in single-use products and are difficult to recycle, causing serious environmental pollution problems that have attracted widespread attention from researchers.

[0003] For polyolefins, the C(sp) on their backbone 3 )-C(sp 3 C-C bonds are very stable and not easily broken. Therefore, recycling polyolefins requires the introduction of additional energy to break these bonds. However, in traditional polyolefin recycling technologies, such as pyrolysis and hydrogenolysis, the breaking of C-C bonds is random and irregular. The products obtained are mostly pyrolysis oils composed of long-chain alkanes or olefins, with a wide distillation range and relatively low added value. This makes it difficult to selectively produce high-value-added products, which makes plastic pyrolysis lack an economically viable driving force.

[0004] Carbon monoxide (CMon) molecules are unsaturated metastable molecules, chemically stable in terms of decomposition. At room temperature, CMon reacts not with acids or bases, but when mixed with air, it forms explosive mixtures. It can ignite and explode upon contact with open flames or high temperatures, classifying it as a flammable and explosive gas. Because the carbon element in the CMon molecule has a oxidation state of +2, it can be oxidized to +4, exhibiting reducing properties; it can also be reduced to a lower oxidation state, exhibiting oxidizing properties. As a major component of syngas and various coal gases, CMon is an important raw material for synthesizing a series of basic organic chemical products and intermediates. From CMon, almost all basic chemicals can be produced, such as ammonia, phosgene, as well as alcohols, acids, anhydrides, esters, aldehydes, ethers, amines, alkanes, and alkenes. Furthermore, utilizing the property of CMon reacting with transition metals to form carbonyl complexes or carbonyl complex derivatives, various homogeneous reaction catalysts required for organic chemical production can be prepared. In addition, CMon can be used as a terminator in polyethylene polymerization. Although some studies have shown that high-value-added chemicals or liquid fuels (such as low-carbon olefins, aromatics, or higher alcohols) can be produced from CO and H2 under high temperature and pressure, current H2 resource acquisition heavily relies on the consumption of fossil fuels (coal, oil, and natural gas). Without substantial "green hydrogen" acquisition technologies, large-scale use of H2 resources means greater CO2 emissions. Therefore, achieving CO resource utilization under hydrogen-free conditions is both more attractive and more challenging.

[0005] Aromatic hydrocarbons, especially benzene, toluene, and xylene (BTX), are essential organic chemical raw materials with extremely high demand. They are generally obtained from naphtha through catalytic reforming and distillation. Using waste polyolefins as raw materials, obtaining aromatic hydrocarbons under mild conditions via catalytic pyrolysis is an economically feasible technical route. Zhang et al. from the University of California, Santa Barbara, used a Pt / γ-Al₂O₃ catalyst to convert polyolefins into long-chain alkyl aromatic hydrocarbons at 280 °C, achieving an aromatic hydrocarbon yield exceeding 70%. Although this method can achieve conversion at a relatively mild temperature of 280 °C, the products contain almost no benzene, toluene, and xylene with higher added value (Fan Zhang et al. Science 370 (2020) 437–441). At lower temperatures, such as below 300 °C, there are no reports of achieving high-value aromatic hydrocarbons through the coupled conversion of CO and polyolefins. Summary of the Invention

[0006] To address the above problems, this invention provides a catalyst and a method for the coupled conversion of CO with polyolefins to prepare aromatics. To achieve the above objective, the technical solution of this invention is as follows:

[0007] This invention provides a catalyst for the coupled conversion of carbon monoxide and polyolefins to produce aromatics. The catalyst is a bifunctional catalyst composed of a metal and a molecular sieve. Carbon monoxide and polyolefins are used as reactants, and the conversion reaction is carried out in a batch reactor under the action of the catalyst. The catalyst is a bifunctional catalyst, with one functional component consisting of a metal, a metal oxide, or both, and the other functional component consisting of a molecular sieve. The metal and metal oxide components activate CO2, while the molecular sieve activates the polyolefin. The molecular sieve has MFI, MEL, and MWW topologies.

[0008] Based on the above technical solutions, 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 metal or metal oxide accounts for 0.1wt% - 60wt% of the mass fraction of the bifunctional catalyst, preferably 0.5wt% - 50wt%.

[0009] Based on the above technical solutions, preferably, the metal or metal oxide can be directly supported on the molecular sieve, or it 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 Al2O3, TiO2, CeO2, ZnO, or MoO. x MnO x One or more of them.

[0010] Based on the above technical solutions, preferably, the framework elements of the molecular sieve with MFI, MEL and MWW topologies 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 MFI, MEL and MWW topologies is preferably at least one of MCM-22, ZSM-11 or ZSM-5.

[0011] Based on the above technical solutions, preferably, the molecular sieve with MFI, MEL and MWW topologies contains a moderately strong acid, and the amount of the moderately 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, encompassing three acidities: weak acid, moderately strong acid, and strong acid. The NH3-TPD is based on the desorption peak position of NH3. This desorption peak position refers to the position of the desorbed NH3 thermal conductivity signal recorded by a TCD under standard test conditions: a sample mass w to carrier gas flow rate f ratio (w / f) = 100 g·h / L, and a heating rate of 10℃ / min. The desorption curve is plotted, and the inorganic solid is classified into three acid strengths based on the peak position of the curve: weak acid refers to acidic sites with an NH3 desorption temperature below 245℃; moderately strong acid refers to acidic sites with an NH3 desorption temperature between 275-500℃; and strong acid refers to acidic sites with an NH3 desorption temperature above 500℃. The molecular sieve can be laboratory-synthesized or commercially purchased and meets the requirements of this invention.

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

[0014] Based on the above technical solutions, preferably, the bifunctional catalyst needs to be pre-reduced, with the reduction atmosphere being H2 or CO, the reduction temperature being 300 ℃ - 500 ℃, and the reduction time being 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 monoxide and polyolefins to prepare aromatics. Carbon monoxide and polyolefins are used as reactants, and the conversion reaction is carried out in a batch reactor using the catalyst described in the preceding technical solutions.

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

[0017] Based on the above technical solutions, preferably, the pressure of the carbon monoxide is 0.2-6 MPa, more preferably 0.5-3 MPa; the reaction temperature is 180-400 ℃, more preferably 230-300 ℃; and the mass ratio of the catalyst to the polyolefin is ≥1:500, more preferably ≥1:100.

[0018] Based on the above technical solutions, preferably, when the reaction is carried out in a batch reactor, the residence time of the reactants is 0.5-20 h, more preferably 1-10 h, and even more preferably 2-10 h.

[0019] Based on the above technical solutions, preferably, when the reaction is carried out in a moving bed reactor, the gas space velocity of the reaction is 20-2000 ml·g. -1· h -1 Preferably 20-1000 ml·g -1 · h -1 More preferably 80-1000 ml·g -1 · h -1 .

[0020] The beneficial effects of this invention are as follows:

[0021] 1. The technical solution of this invention differs from traditional plastic pyrolysis technology. It employs a composite catalyst to achieve a one-step, highly selective conversion of CO into high-value-added aromatics such as benzene, toluene, and xylene through coupling with polyolefins. The addition of CO not only serves as a raw material for aromatic hydrocarbon generation but also reacts with H species generated during hydrogen transfer in the aromatization process, inhibiting alkane formation and improving the selectivity of aromatic components.

[0022] 2. Unlike the high-temperature pyrolysis mechanism of polyolefins, at low temperatures (reaction temperatures below 300 °C), polyolefins cannot generate aromatics through dehydrogenation aromatization (Equation 1), but can only generate aromatics through hydrogen transfer aromatization (Equation 2). Therefore, the yield of aromatics at low temperatures is limited by its reaction mechanism and cannot exceed 50%.

[0023] (1)

[0024] (2)

[0025] This invention utilizes hydrogen overflow between catalyst components and uses CO to consume the hydrogen overflowing from the molecular sieve hydrogen transfer aromatization, preventing the formation of alkanes and breaking the original reaction equilibrium. Under relatively mild reaction conditions (reaction temperature below 300 °C), it achieves highly selective preparation of high-value-added aromatic products, which has strong economic application prospects.

[0026] 3. This invention uses polyolefins as raw materials. The polyolefins can also be plastic products made from polyolefins and polyolefins, such as plastic bags, plastic buckets, cling film, various films, and waste food packaging. The raw materials are widely available and have a high utilization rate, making it an effective and scalable polyolefin utilization solution.

[0027] 4. This invention can be applied not only to the resource utilization of CO waste gas in the production processes of coking and ironmaking in the oil refining and metallurgical industries, but also to the utilization of waste gas containing high concentrations of CO in the production processes of synthetic ammonia and methanol in the chemical industry, and even waste gas containing both CO and CO2. It has a wide range of raw material sources and strong applicability, and can significantly promote the utilization of CO and reduce CO2 emissions.

[0028] 5. The catalyst of the present invention can be recycled after being regenerated by air roasting-hydrogen reduction, without significant catalyst loss, which can significantly reduce the cost problem caused by catalyst deactivation.

[0029] 6. The preparation process of the nanocomposite catalyst of the present invention is simple and mild; and the reaction process can not only realize the high-value utilization of polyolefins and CO at the same time, but also has a high product space-time yield and selectivity. The yield of mixed aromatics can reach 50-80%, and the proportion of benzene, toluene and xylene in the aromatics is greater than 60%. Compared with the traditional polyolefin pyrolysis process under inert gas conditions, the aromatic yield is more than twice that of the traditional process. Detailed Implementation

[0030] The present invention will be further illustrated below by way of embodiments, but the scope of the claims of the present invention is not limited to these embodiments. Furthermore, the embodiments only provide some conditions for achieving this objective, but do not imply that these conditions must be met to achieve this objective.

[0031] I. Preparation of Molecular Sieves

[0032] The moderately strong acids described in this invention can be tested using methods such as solid-state NMR spectroscopy (H-N), NH3-TPD, infrared spectroscopy, and chemical titration. However, the methods for testing acidity are not limited to those described above.

[0033] The molecular sieves with MFI, MEL and MWW topologies described in this invention can be prepared by various methods and conditions. This patent uses hydrothermal synthesis as an example.

[0034] 1) Molecular sieves with MFI topology can be prepared using the following method:

[0035] Raw materials were weighed according to the oxide ratio of SiO2:Al2O3:Na2O:R:H2O = 5:0.02:2:1.5:200 (mass ratio): 30% silica sol (mass concentration); aluminum sulfate; sodium hydroxide; tetrapropylammonium hydroxide (R); and deionized water. The mixture was aged by stirring at 30°C for 2 hours, then transferred to a hydrothermal reactor and crystallized at 180°C for 48 hours. The mixture was then rapidly 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 process. The precipitate was dried at 110°C for 17 hours and then calcined in air at 600°C for 3 hours to obtain the topologically structured ZSM-5 molecular sieve, labeled as Fen 1.

[0036] 2) Molecular sieves with MEL topology can be prepared using the following method:

[0037] The following raw materials were weighed according to the oxide ratio of SiO2:Al2O3:Na2O:R:H2O = 10:0.3:1:2:200 (mass ratio): silica sol; aluminum isopropoxide; sodium hydroxide; TBAOH(R); and deionized water. The mixture was stirred overnight at room temperature. The gel was then dried and crushed in an oven at 65°C and placed in a crystallization vessel. A certain amount of deionized water was added, and the mixture was crystallized at 170°C for 3 days. The resulting product was filtered, washed, dried, and subjected to ammonium exchange before being calcined in a muffle furnace at 600°C for 6 hours to obtain the ZSM-11 molecular sieve with a MEL topology, labeled as Fen 2.

[0038] The framework element composition of the molecular sieve with MFI, MEL and MWW topologies can also be at least one of Si-O, Si-Al-O, Si-Al-PO, Si-Al-BO, and Si-Al-Ge-O.

[0039] Table 1. Preparation and performance parameters of molecular sieves with MFI, MEL and MWW topologies.

[0040]

[0041] II. Preparation of Bifunctional Catalysts

[0042] The metal is combined with the molecular sieve by impregnation, deposition, vapor deposition, or physical mixing to form a bifunctional catalyst. Here, we take the bifunctional catalyst prepared by impregnation as an example.

[0043] The impregnation process can be implemented by either equal-volume impregnation or excessive impregnation, as detailed below:

[0044] The metal source is dissolved in deionized water to prepare a precursor solution. The precursor solution and solute are placed in the precursor solution and stirred thoroughly to ensure that the precursor solution and solute are uniformly dispersed on the molecular sieve. Then, the desired metal oxide modified molecular sieve is obtained by drying and calcination.

[0045] If the equal-volume impregnation method is used, the pore volume V of the molecular sieve needs to be measured in advance. p The volume of the precursor solution used, V0 = V p If an excessive impregnation method is used, the V0 of the precursor solution used will be... <V p .

[0046] The specific catalyst preparation and its parameter characteristics are shown in Table 2-3.

[0047] Table 2 Catalysts prepared by impregnation method and their parameter characteristics

[0048]

[0049] III. Examples of Catalytic Reactions

[0050] This catalyst can be used in batch reactors.

[0051] The reaction apparatus is equipped with a gas mass flow meter to control the gas flow rate, and gas chromatography is used for quantitative analysis of the products.

[0052] The following description uses a batch reactor as an example: 2g of the catalyst of this invention is mixed with 40g of polyolefin and placed in a batch reactor. The air in the reactor is replaced with CO, and CO gas (containing 5% Ar as an internal standard for chromatographic analysis) at (0.2-6 MPa) is introduced. The temperature is raised to 180ºC-300ºC to carry out the reaction. The product is quantitatively analyzed by chromatography.

[0053] The gaseous products were analyzed using Ar as an internal standard, and the yield was calculated. The liquid products were collected and analyzed using n-undecane as an internal standard, and the yield was calculated.

[0054] The reaction performance can be altered by changing the reaction temperature, reaction pressure, and the feed mass ratio of CO to polyolefin.

[0055] The performance is as follows: the total selectivity of aromatics can reach 60-80%, and benzene, toluene and xylene (BTX) account for more than 60% of the aromatics; the addition of CO can not only serve as a raw material for the generation of aromatics, but also react with hydrogen species generated by hydrogen transfer during the aromatization process, thereby inhibiting the generation of alkanes and improving the selectivity of aromatic components.

[0056] Table 3 lists the specific applications of the catalysts and their effect data.

[0057] Table 3. Specific applications of catalysts and their reaction effects.

[0058]

[0059] The metal components and preparation method used in catalyst L in Comparative Example 1 are the same as those in catalyst A. The molecular sieve component used is replaced with commercially available 5 molecular sieve from Nankai University Catalyst Factory, which has three-dimensional eight-membered ring channels.

[0060] The metal components and preparation method used in catalyst M in Comparative Example 2 are the same as those in catalyst A. The molecular sieve component used is replaced with a commercially available 6-membered molecular sieve from Nankai University Catalyst Factory, which has three-dimensional twelve-membered ring channels.

[0061] The metal components and preparation method used in catalyst N in Comparative Example 3 are the same as those in catalyst A. The molecular sieve component used is replaced with commercially available 7 molecular sieve from Nankai University Catalyst Factory, which has one-dimensional pores with coexisting eight-membered and twelve-membered rings.

[0062] The metal components and preparation method used in catalyst O in Comparative Example 4 are the same as those in catalyst A. The molecular sieve component used is replaced with commercially available 8 molecular sieve from Nankai University Catalyst Factory, which has one-dimensional ten-membered ring channels.

[0063] The reaction results of Comparative Examples 1-4 show that molecular sieves with different topologies significantly modulate the product selectivity. SAPO-34, with its three-dimensional eight-membered ring channel structure, is unfavorable for the conversion of polyolefins and the formation of aromatic products, but is suitable for generating short-chain hydrocarbons; however, the aromatic yield is only 4%. USY molecular sieves, with their three-dimensional twelve-membered ring channels, have large pores, leading to the easy formation of heavier aromatics (such as naphthalene) and carbon deposition / deactivation. Therefore, the yields of heavy aromatics and carbon deposits are high, with heavy aromatics accounting for 68% of all aromatic products. Commercially available MOR molecular sieves, with a coexistence of one-dimensional eight- and twelve-membered rings, and SAPO-11 molecular sieves, with one-dimensional ten-membered ring channels, are unfavorable for aromatization processes. The products are mainly cracked gasoline products with low aromatic content and an aromatic yield of only 21%.

[0064] Comparative Example 5 used catalyst P with the same metal composition and preparation method as catalyst A, but the molecular sieve component was replaced with 9-molecular sieve, and the strong acid density was only 0.07 mmol / g. Comparative Example 5 exhibited extremely poor reaction performance, likely due to its low acid density leading to poor aromatization ability. Therefore, a certain medium-strong acid density is crucial.

[0065] Comparative Example 6 used catalyst Q, which was Pt directly impregnated on γ-Al2O3. As a result, CO was hardly converted, the conversion rate of polyolefins was very low, and the yields of aromatics and BTX were also very low.

[0066] The molecular sieve composition used in catalyst R in Comparative Example 7 is the same as that in catalyst A (part 1), except that it does not contain the metal Pt component. Since the molecular sieve has almost no catalytic activity for activating CO, only olefins react in the catalytic reaction process. That is, olefins can be directly aromatized by the molecular sieve, but the aromatic yield is not high (38%), mainly producing long-chain alkanes, and the CO conversion rate is only 0.02 g·g⁻¹. （聚烯烃） ·h -1 The efficiency is very low, making it impossible to achieve highly selective preparation of aromatics and CO.

[0067] Comparative Examples 6 and 7 show that when only one functional component, metal oxide or molecular sieve, is present, the reaction effect is poor and it does not possess the excellent reaction performance described in this invention.

[0068] The catalyst used in Comparative Example 8 was the same as that used in Example 1, which was catalyst A. However, no olefins were added in Comparative Example 8. Experiments showed that without the addition of polyolefins, CO could not be effectively converted.

[0069] The catalyst used in Comparative Example 9 is the same as that used in Example 1, namely catalyst A. However, no CO was added in Comparative Example 9, and N2 was used as the pressurized atmosphere. The experiment showed that without the introduction of CO, polyolefins can be converted into aromatics by a bifunctional catalyst composed of metal and molecular sieve. The reaction results were similar to those in Comparative Example 7, with a low yield of aromatics of only 36%, which did not have the excellent reaction performance described in this invention.

[0070] The reaction results of Comparative Examples 8-9 show that the CO conversion and polyolefin conversion reactions are coupled and mutually reinforcing. Without polyolefins, CO cannot be effectively converted; without CO, polyolefins cannot be selectively converted to aromatics, and the number of alkane byproducts increases.

[0071] The catalyst used in Comparative Example 10 was the same as that used in Example 1, but the partial pressure of CO in Comparative Example 10 was lower. At this time, the amount of CO was insufficient, and its promoting effect on the selective formation of aromatics was small. Therefore, it is very important to ensure a sufficient amount of CO to promote the catalytic reaction.

[0072] As can be seen from the table above, the topology of the molecular sieve, acid properties, the feed ratio of CO to polyolefin waste plastics, and the matching between the molecular sieve and the metal or metal oxide are all crucial factors that directly affect the selectivity of mixed aromatics, the conversion rate of CO, and the content of benzene, toluene, and xylene in the aromatics.

Claims

1. A process for the coupled conversion of carbon monoxide and polyolefins to aromatic hydrocarbons, characterized in that: 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 molecular sieve is a molecular sieve with MFI, MEL and MWW topological structure; The metal element in the metal or metal oxide includes one or two or more of Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir and Pt; The pressure of carbon monoxide is 0.2-6 MPa, and the reaction temperature is 180-400 ℃; The aromatic hydrocarbon yield reaches 50-80%, and the proportion of benzene, toluene and xylene in the aromatic hydrocarbon is greater than 60%.

2. The method of claim 1, wherein: The mass ratio of catalyst to polyolefin is ≥1:

500.

3. The method of claim 1, wherein: The metal or metal oxide accounts for 0.1wt%-60wt% of the mass fraction of the bifunctional catalyst; the metal or metal oxide is directly loaded on the molecular sieve, or is dispersed on a metal oxide carrier and then physically mixed with the molecular sieve to form the bifunctional catalyst; the metal oxide carrier is one or two or more of Al2O3, TiO2, ZrO2, CeO2, ZnO, MoO x , and MnO x .

4. The method of claim 1, wherein: The framework element of the molecular sieve with MFI, MEL and MWW topological structure includes 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 MFI, MEL and MWW topological structure is at least one of MCM-22, ZSM-11 or ZSM-5.

5. The method of claim 1, wherein: The molecular sieve with MFI, MEL and MWW topological structure contains medium-strong acid, and the amount of medium-strong acid sites is ≥0.1 mol / kg.

6. The method of claim 1, wherein: The compounding mode of the metal or metal oxide and the molecular sieve is physical mixing or loading; the loading is loading the metal or metal oxide on the molecular sieve by impregnation, deposition precipitation or gas phase deposition.

7. The method of claim 1, wherein: The metal or metal oxide component in the catalyst activates CO; the molecular sieve activates polyolefin.

8. The method of claim 1, wherein: The bifunctional catalyst needs to be pre-reduced, the reducing atmosphere is H2 or CO, the reduction temperature is 300 ℃-500 ℃, and the reduction time is 0.5 h-10 h.

9. The method of claim 2, wherein: When the reaction is carried out in a tank reactor, the residence time of the reactants is 0.5-20 h; when the reaction is carried out in a moving bed reactor, the gas space velocity of the reaction is 20-2000 ml-g -1 · h -1 .

10. The method of claim 1, wherein: The polyolefin includes one or two or more of polyethylene, polypropylene and polybutene, and plastic products processed from the above polyolefin or waste plastics after use.

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