Method for preparing ammonia and carbon monoxide by recycling waste hydrocarbon-based plastic

Abstract

The invention provides a method for preparing ammonia and carbon monoxide by recycling waste hydrocarbon-based plastics, which comprises the following steps: carrying out catalyst pretreatment in an argon-filled glove box, mixing an iron-based catalyst with cobalt and potassium accelerators, filling the mixture into a ball-milling tank, and removing residual argon through nitrogen inflation and deflation circulation; then putting the pretreated catalyst and the waste plastic into a ball-milling tank together in a glove box, carrying out mechanical ball-milling treatment in a nitrogen or argon atmosphere to realize the reaction of the waste plastic and nitrogen to prepare ammonia, and fixing a carbon element into a metal carbide at the same time; and carrying out heat treatment on the generated metal carbide in a CO2-containing mixed atmosphere at 500 DEG C to co-produce carbon monoxide and regenerate the catalyst. According to the invention, a mechanochemistry and thermochemistry coupling mode is adopted, the problems of high energy consumption, carbon emission and low added value of products in existing waste plastic treatment are solved, the waste plastic can be upgraded and converted into high-value ammonia and carbon monoxide, and the method is applied to the fields of chemical fertilizers, chemical engineering and energy and has remarkable economic and environmental benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of waste resource utilization, and particularly relates to a method for preparing ammonia and carbon monoxide by using waste hydrocarbon-based plastics. BACKGROUND

[0002] With the acceleration of industrialization and the growth of global population, the production of waste hydrocarbon-based plastics (referred to as "waste plastics") continues to rise, causing great pressure on the environment. The traditional incineration and landfill methods not only occupy a large amount of land resources, but also may cause secondary pollution. Therefore, upgrading and recycling waste plastics into high-value-added chemicals not only can realize efficient recycling of resources, but also provides a promising, environmentally sustainable and potentially economically feasible new way for environmental protection.

[0003] At present, one of the most widely used upgrading and recycling methods is to obtain hydrogen by steam reforming after pyrolysis of waste plastics. However, this method has significant shortcomings. First, the product is highly complex. The steam reforming process inevitably produces a variety of gas mixtures including CO2 and CO. These complex gas components require additional and high-cost separation and purification processes, thereby increasing the recycling cost and operational complexity. Second, the catalyst is easily deactivated. During the reforming process, coke deposition phenomenon easily occurs under high temperature, which causes poisoning and deactivation of the used catalyst. This makes the catalyst need to be regenerated or even replaced frequently, seriously affecting the continuity, stability and economic benefit of the process. Third, hydrogen is difficult to store and transport. Although hydrogen is considered as a clean energy carrier, the low density (0.071 g cm -1 ) and low boiling point (-252.9℃) of liquid hydrogen bring high cost and safety challenges to its large-scale storage and long-distance transportation.

[0004] Ammonia is a promising hydrogen storage carrier due to its high hydrogen content (17.6wt%) and mature global storage and transportation infrastructure. In addition, according to the production calculation, it has always ranked among the top ten chemicals in the world. However, the traditional thermochemical Haber-Bosch method for synthesizing ammonia requires high temperature and high pressure reaction conditions (450℃, 200bar), and requires centralized large-scale manufacturing facilities to meet economic feasibility, which makes it difficult to be associated with dispersed sustainable energy complexes. This limitation prompts people to find alternative and more sustainable decentralized ammonia synthesis methods. On the other hand, the gray hydrogen used in the Haber-Bosch process is mainly derived from natural gas steam reforming, which leads to more than 90% CO2 emissions of this process. Under this condition, using waste plastics as a solid hydrogen source can avoid the safety hazards brought by highly flammable hydrogen.

[0005] In addition, to maximize the value of waste plastics, in addition to recycling hydrogen elements, the carbon therein should also be fully utilized. CO is an important chemical raw material, widely used in metal carbonylation, Fischer-Tropsch synthesis and other industrial processes. If the carbon in the plastic can be converted to CO while using plastic to produce ammonia, the atomic economy and economic benefit of the entire process will be greatly improved.

[0006] Therefore, it is of great significance to develop a new method for directly synthesizing ammonia with zero carbon emission and co-producing CO in a mild and environmentally friendly manner by comprehensively utilizing the carbon and hydrogen resources in waste plastics, which is of great significance to solve the problem of plastic pollution and promote the development of green industry. SUMMARY

[0007] In order to overcome the shortcomings of the prior art, the present application provides a method for preparing ammonia and carbon monoxide by recycling waste hydrocarbon-based plastics, comprising the following steps:

[0008] a. Catalyst pretreatment: first, a mixture of metal powder containing iron Fe catalyst and at least one promoter is loaded into a ball mill jar containing bearing steel balls in an argon-filled glove box, then the ball mill jar is subjected to multiple nitrogen filling and discharging cycles to completely remove residual argon; the ball milling process is carried out in a pure nitrogen atmosphere, and a working cycle mode of 1 hour of operation and 10 minutes of rest is adopted to effectively control the heat accumulation in the ball mill jar;

[0009] b. Mechanical chemical ammonia synthesis: in the glove box, the pretreated catalyst and the previously prepared waste hydrocarbon-based plastics are loaded into the ball mill jar and subjected to mechanical ball milling treatment in a nitrogen or argon atmosphere to generate ammonia and solid metal carbide;

[0010] c. Thermal chemical treatment: the solid metal carbide generated in step b is subjected to thermal treatment at a temperature of 500°C in a mixed gas atmosphere containing CO2 to generate carbon monoxide and pure metal iron.

[0011] Preferably, in step a, the promoter comprises cobalt Co, potassium K or a combination thereof, wherein Co is used to activate the C-H bond in the waste hydrocarbon-based plastics and promote its decomposition, and K is used as an electronic promoter to enhance the nitrogen dissociation rate and promote ammonia desorption.

[0012] Preferably, the waste hydrocarbon-based plastics are selected from at least one of polyethylene PE, polypropylene PP and polystyrene PS.

[0013] Preferably, in step c, the mixed gas atmosphere is a gas mixture composed of 99.0% argon Ar, 0.3% carbon dioxide CO2 and 0.7% carbon monoxide CO.

[0014] Preferably, the pretreatment time of the catalyst pretreatment process is 10 to 40 hours.

[0015] Preferably, the rotation speed of the mechanochemical ammonia synthesis process is 350 rpm to 550 rpm.

[0016] Preferably, the solid-state metal carbide generated in step b includes iron carbide.

[0017] Preferably, the iron carbide is Fe7C3.

[0018] The purpose of the present application is to provide a continuous process for efficiently upgrading waste hydrocarbon-based plastics to produce ammonia and CO. By combining the three core steps of mechanochemical pretreatment, mechanochemical ammonia synthesis, and thermochemical treatment, the continuous and efficient synthesis of ammonia and CO is achieved using waste hydrocarbon-based plastics, nitrogen, and CO2 as raw materials.

[0019] The technical effects of the present application are:

[0020] a. Significant ammonia synthesis effect: Under mild conditions, through the action of mechanical force, the efficient synthesis of waste plastics to ammonia is realized. In the gaseous product, the concentration of ammonia can reach up to 89.8 vol%, realizing the efficient recovery of hydrogen resources in waste plastics.

[0021] b. Efficient utilization of carbon resources and catalyst closed-loop regeneration: In the ammonia synthesis process, the carbon in the hydrocarbon-based plastics is fixed as solid-state metal carbide, realizing zero CO2 emission in the ammonia synthesis process. Subsequently, in the thermal treatment process, the fixed carbon can be efficiently converted into industrial raw material CO, while realizing the complete regeneration of the catalyst, constituting the closed-loop utilization of the catalyst.

[0022] c. Environmental friendliness and sustainability: The present application starts from the key principles of green chemistry, with significant environmental benefits. The method has high atom economy (about 100% when only stoichiometric reactants are considered), indicating the minimization of waste at the molecular level. The process shows a favorable E factor of 0.051 kg waste per kg product, highlighting its efficiency in reducing waste. The use of catalysts, although long-term, is reduced due to their complete regenerability, reducing their long-term impact on the environment. The process quality intensity of 1.05 indicates the efficient use of materials, and the carbon efficiency of 96.5% indicates that most of the carbon atoms in the starting material are incorporated into the desired product. In addition, the process is carried out without using any solvent or auxiliary substances, and its inherent design reduces the risk of accidents, meeting the needs of sustainable development.

[0023] d. Low energy consumption and high yield: First, from the perspective of energy consumption, the energy consumption of the present application on a laboratory scale is competitive. The energy consumption for producing one ton of ammonia is calculated to be 1.2 x 10 13J mt -1 At the laboratory scale, it is lower than the energy consumption of the Haber-Bosch process (3.9 x 10 13 J mt -1 ). Secondly, compared with the electrochemical method, its energy for direct synthesis of ammonia is 2.1 x 10 12 J mt -1 , lower than our method. However, the energy consumed in its separation process (2.3 x 10 14 J mt -1 ) is much higher than that consumed in the synthesis process, which is mainly due to the ammonia production in its aqueous electrolyte is only 10 ppm. In contrast, the high concentration of ammonia output of the present application greatly reduces the energy consumption of subsequent separation, indicating that it has higher overall yield and lower overall energy consumption in actual industrial applications. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Chemical reaction schematic diagram involved in the present application.

[0025] Figure 2 Process flow diagram of the method of the present application.

[0026] Figure 3 Influence of catalyst pretreatment atmosphere and mechanical-chemical ammonia synthesis atmosphere on ammonia yield and selectivity.

[0027] Figure 4 Comparison chart of ammonia production from waste plastics by iron-cobalt-potassium catalyst and other catalyst methods.

[0028] Figure 5 Comparison chart of ammonia production from different plastics.

[0029] Figure 6 Effect of different nitrogen fixation times on ammonia yield.

[0030] Figure 7 Effect of different PE addition amounts on ammonia synthesis performance.

[0031] Figure 8 Effect of ball milling speed on ammonia yield and selectivity in the process of mechanical-chemical ammonia synthesis.

[0032] Figure 9 X-ray diffraction (XRD) characterization of catalyst regeneration effect before and after thermochemical treatment.

[0033] Figure 10 Mossbauer spectroscopy characterization of catalyst regeneration effect before and after thermochemical treatment.

[0034] Figure 11 Comparison chart of catalyst regeneration effect at 500℃.

[0035] Figure 12 Catalyst cycle stability test. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0037] The present application provides a method for preparing ammonia and carbon monoxide using waste hydrocarbon-based plastics for recycling. Figure 1 The core idea of the present application is shown from the perspective of chemical reaction equation. Figure 2 Further, the overall method flow of the present application is intuitively shown in the form of a flow chart, including three core steps of catalyst pretreatment (nitrogen fixation), mechanical chemical ammonia synthesis and thermal chemical treatment.

[0038] Figure 3 Further, the influence of different reaction atmospheres (such as nitrogen and argon) on ammonia yield and selectivity in the two key steps of catalyst pretreatment and mechanical chemical ammonia synthesis is compared. The results clearly indicate that the two-step mechanical chemical method for synthesizing ammonia gas according to the present application is the key to obtaining high ammonia yield. Figure 4 The experimental results show that the iron-cobalt-potassium (FeCoK) ternary catalyst system used in the present application exhibits the highest ammonia yield in the waste plastic ammonia synthesis reaction compared to single iron catalyst or catalyst containing only one promoter, proving the superiority of the catalyst combination. Subsequent embodiments will further detail the specific parameters and effects of the method of the present application.

[0039] Example 1: Investigation of the influence of catalyst pretreatment time on ammonia yield.

[0040] 1. Catalyst pretreatment (nitrogen fixation process): In order to prevent metal oxidation, 20.00 g of 100 mesh iron powder, 0.05 g of potassium and 0.40 g of cobalt were loaded into a ball mill tank with a volume of 250 ml in an argon-filled glove box, and 500 g of bearing steel balls with a diameter of 5 mm were pre-loaded into the tank. The sealed ball mill tank was subjected to multiple nitrogen charging and discharging cycles to remove residual argon, and then 9 bar of nitrogen was charged; the planetary ball mill was set to a rotation speed of 400 rpm, and an intermittent ball milling mode was adopted, with 1 hour of ball milling and 10 minutes of rest for each ball milling, and four groups of experiments were performed, with a cumulative ball milling time of 10 hours, 20 hours, 30 hours and 40 hours, to form a catalyst containing active nitrogen species;

[0041] 2. Mechanochemical ammonia synthesis: After the catalyst pretreatment, 0.30 g of high-density polyethylene HDPE powder was added into each ball mill tank in an argon glove box; the ball mill tank was resealed and 5 bar of nitrogen was flushed in as a protective atmosphere. The reaction was carried out at a rotation speed of 550 rpm for 11 hours.

[0042] After the reaction, the gas products of each group of experiments were collected. As shown in Table 1, the volume fraction of ammonia in the mixed gas was 72.5%, 80.3%, 86.2% and 89.8% when the catalyst pretreatment time was 10, 20, 30 and 40 hours, respectively. This shows that prolonging the catalyst pretreatment time is beneficial to improving the final ammonia yield. Figure 6

[0043] Example 2: Investigation of the applicability of different waste plastic raw materials.

[0044] 1. Raw material pretreatment: The high-density polyethylene HDPE from waste packaging boxes and bottle caps, as well as waste polypropylene PP and polystyrene PS, were cut into small pieces and ground at a rotation speed of 25000 rpm for 30 minutes using a grinding machine. The obtained powder was sieved through an 80-mesh sieve for standby use. Meanwhile, a mixture of the above-mentioned plastics was prepared.

[0045] 2. Catalyst pretreatment: Same as Example 1, but the cumulative ball milling time was 20 hours.

[0046] 3. Mechanochemical ammonia synthesis: After pretreatment, 0.30 g of different plastic powder obtained in step 1 was added into the above ball mill tank in an argon glove box. The ball mill tank was resealed and 5 bar of nitrogen was flushed in as a protective atmosphere. The rotation speed was set to 550 rpm and the reaction was carried out for 11 hours.

[0047] After the reaction, the gas products were collected. As shown in Table 2, the ammonia yield was 4.9 mmol, 6.5 mmol, 6.2 mmol, 6.8 mmol and 5.1 mmol when waste HDPE packaging boxes, bottle caps, PP, PS and mixed plastics were used as raw materials, respectively. The results confirm that the method of the present application has wide applicability in treating diversified waste plastics. Figure 5 Example 3: Investigation of the effect of plastic addition amount on ammonia yield.

[0048] 1. Catalyst pretreatment: Same as Example 1, but the cumulative ball milling time was 40 hours.

[0049]

[0050] ​​2. Mechanochemical ammonia synthesis: After catalyst pretreatment, four sets of experiments were conducted. High-density polyethylene (HDPE) powder of 0.15 g, 0.30 g, 0.45 g, and 0.60 g was added to the ball mill jar in an argon glove box, respectively. The jar was resealed and purged with 5 bar of nitrogen gas. The rotation speed was set to 550 rpm, and the reaction was continued for 11 hours.

[0051] After the reaction is complete, collect the gaseous products. For example... Figure 7 As shown in the figure, the volume fractions of ammonia in the mixed gas obtained by ion chromatography were 88.1%, 89.8%, 79.5%, and 75.0% when the HDPE addition amounts were 0.15 g, 0.30 g, 0.45 g, and 0.60 g, respectively. The results indicate that under the experimental conditions, there exists an optimal range of plastic addition amounts to obtain the highest ammonia concentration.

[0052] Example 4: Investigating the effect of rotation speed in mechanochemical ammonia synthesis on ammonia yield.

[0053] 1. Catalyst pretreatment: Same as in Example 1, but with a cumulative ball milling time of 40 hours.

[0054] 2. Mechanochemical ammonia synthesis: After catalyst pretreatment, 0.30g of high-density polyethylene (HDPE) powder was added to the ball mill jar in an argon glove box; the ball mill jar was resealed; and nitrogen gas at 5 bar was introduced as a protective atmosphere. The reaction was carried out at speeds of 350, 400, 450, 500 and 550 rpm, respectively. By controlling the reaction time at each speed, the total number of ball milling revolutions was ensured to be 360,000 revolutions.

[0055] After the reaction is complete, collect the gaseous products. For example... Figure 8 As shown, the volume fractions of ammonia in the resulting mixed gas, determined by ion chromatography at reaction speeds of 350, 400, 450, 500, and 550 rpm, were 22.9%, 50.2%, 67.9%, 80.1%, and 89.8%, respectively. The results indicate that increasing the reaction speed significantly improves the ammonia yield.

[0056] Example 5: Verification of the effect of thermochemical treatment and catalyst regeneration.

[0057] 1. Thermochemical treatment (CO synthesis and catalyst regeneration): Take 0.40 g of the solid metal carbide generated after the reaction under the conditions of Example 3 (with the addition of 0.30 g HDPE) and place it in the quartz tube of the fixed-bed reactor; under argon protection, at 2 °C for min... -1The fixed bed is heated to 500℃ at a certain rate; after reaching the target temperature, the gas source is switched, and a mixed gas containing 0.3% CO2, 0.7% CO and 99.0% Ar is introduced into the reaction bed and kept at the temperature; the composition of the outlet gas is monitored online by gas chromatography until the concentration of CO stabilizes, indicating that the reaction is complete.

[0058] 2. Characterization and analysis of regeneration effect: This process not only converts fixed carbon into high-value-added CO, but also regenerates the catalyst; Figure 9 The X-ray diffraction (XRD) pattern confirmed that the Fe7C3 phase after the reaction was transformed back into α-Fe after this thermochemical treatment. Figure 10 Mössbauer The spectrum further confirmed the phase transformation of the iron. Figure 11 The regeneration effects of solid metal carbides and iron powder-carbon black physical mixtures in this invention at 500°C were compared. The results showed that the catalyst regeneration process of this invention (i.e., the reaction of Fe7C3 with CO2) was more efficient, proving the effectiveness of this regeneration path. Figure 12 The results of the catalyst stability test are shown. After multiple cycles of "ammonia synthesis-catalyst regeneration", the ammonia production did not decrease significantly, indicating that the catalyst of the present invention has excellent recycling performance.

[0059] The reaction mechanism of this invention is as follows: Under the high-speed impact and shearing action of a planetary ball mill, the catalyst lattice undergoes severe plastic deformation, resulting in a large number of dislocations, vacancies, and other defects within the lattice, and accumulating significant strain energy. At this point, the catalyst lattice is in a high-energy, non-equilibrium metastable state. This non-equilibrium metastable state spontaneously relaxes to a lower-energy stable or equilibrium state through the rearrangement of lattice parameters and atomic positions. During this process, the transferred energy mainly includes the Poisson response (ΔE) around the adsorption intermediate. Poisson response ) and atomic relaxation (ΔE) atomrelaxation This dynamic energy transfer can lower the energy barrier of the reaction, promoting the breaking and desorption of chemical bonds in the adsorbate intermediates.

[0060] This invention, based on key principles of green chemistry, offers significant environmental benefits. Table 1 compares the green chemistry indicators of this invention with those of the Haber process and electrochemical methods for ammonia production. It is evident that the combination of this invention's high atom economy, low waste generation, catalyst renewability, solvent-free operation, efficient material use, and high carbon efficiency contributes to achieving a highly environmentally friendly process.

[0061] Table 1 Comparison of various indicators in green chemistry

[0062]

[0063] a. The green chemistry indicator for the Haber process was calculated based on industrial hydrogen production via steam methane reforming. In the calculation, we assumed 100% conversion and yield for steam methane reforming.

[0064] b. This is an indicator that measures the efficiency of a chemical reaction, defined as how many atoms in the reactants are incorporated into the target product.

[0065] c. This refers to the proportion of carbon atoms in the reactants that are incorporated into the target product.

[0066] d. The environmental impact of a chemical process is assessed by quantifying the amount of waste produced relative to the amount of target product.

[0067] e. This is a key green chemistry indicator that measures the ratio of the total mass of all materials used in the chemical process to the mass of the target product.

[0068] f. This is a green chemistry indicator that assesses the efficiency of the mass of reactants incorporated into the target product. Since the catalyst is renewable, the catalyst loading is not considered in the calculation of some green chemistry indicators.

[0069] g. The process mass intensity of the Haber process cannot be calculated at present due to the lack of industrial selectivity and conversion data.

[0070] From the perspective of energy consumption and yield, Table 2 shows that the reaction energy consumption and yield of the present application have great advantages compared with the Haber process and the electrochemical method.

[0071] Table 2 Reaction energy consumption and yield comparison

[0072]

[0073] The above examples are the preferred embodiments of the present disclosure, but the embodiments of the present disclosure are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present disclosure are equivalent replacement methods and are included in the protection scope of the present disclosure.

Claims

1. Process for the preparation of ammonia and carbon monoxide using waste hydrocarbon-based plastics for recycling, characterized in that, The method comprises the following steps: a. Catalyst pretreatment: firstly, a mixture of metal powders containing an iron Fe catalyst and at least one promoter is loaded into a ball mill jar containing bearing steel balls in an argon-filled glove box, and then the ball mill jar is subjected to multiple nitrogen filling and venting cycles to completely remove residual argon; the ball milling process is carried out in a pure nitrogen atmosphere and adopts a working cycle mode of 1 hour of operation and 10 minutes of rest to effectively control the heat accumulation in the ball mill jar; b. Mechanical-chemical ammonia synthesis: in the glove box, the pretreated catalyst is loaded into the ball mill jar together with the pre-prepared waste hydrocarbon-based plastic, and mechanical ball milling is carried out in a nitrogen or argon atmosphere to generate ammonia and solid metal carbide; c. Thermal chemical treatment: the solid metal carbide generated in step b is subjected to thermal treatment at a temperature of 500°C in a mixed gas atmosphere containing CO2 to generate carbon monoxide and pure iron metal.

2. The method for preparing ammonia and carbon monoxide from waste hydrocarbon-based plastics according to claim 1, characterized in that, In step a, the promoter comprises cobalt Co, potassium K or a combination thereof, wherein Co is used to activate the C-H bond in the waste hydrocarbon-based plastic and promote its decomposition, and K acts as an electronic promoter to enhance the nitrogen dissociation rate and promote ammonia desorption.

3. The method of claim 1 or 2, wherein the method of producing ammonia and carbon monoxide from waste hydrocarbon-based plastics comprises, The waste hydrocarbon-based plastic is selected from at least one of polyethylene PE, polypropylene PP, and polystyrene PS.

4. The method of claim 1 or 2, wherein the method of producing ammonia and carbon monoxide from waste hydrocarbon-based plastics comprises, In step c, the mixed gas atmosphere is a gas mixture composed of 99.0% argon Ar, 0.3% carbon dioxide CO2, and 0.7% carbon monoxide CO.

5. The method of claim 1 or 2, wherein the method of producing ammonia and carbon monoxide from waste hydrocarbon-based plastics comprises, The pretreatment time of the catalyst pretreatment process is 10 to 40 hours.

6. The method of claim 1 or 2, wherein the method of producing ammonia and carbon monoxide from waste hydrocarbon-based plastics comprises, The rotational speed of the mechanical-chemical ammonia synthesis process is 350 rpm to 550 rpm.

7. The method of claim 1 or 2, wherein the method of producing ammonia and carbon monoxide from waste hydrocarbon-based plastics comprises, The solid metal carbide generated in step b comprises iron carbide.

8. The method for preparing ammonia and carbon monoxide from waste hydrocarbon-based plastics according to claim 7, characterized in that, The iron carbide is Fe7C3.

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