A CoAlO x Method for preparing low-polymer polyvinyl alcohol by hydrogenation of SAPO-34 and CO2

Abstract

This invention discloses a CoAlO x A method for preparing low-polymerization polyvinyl alcohol using SAPO-34 composite catalyst and CO2 hydrogenation. The method first involves wet impregnation of CoAlO2 prepared by a hydrothermal method. x CoAlO was mixed with SAPO-34, dried, and then calcined in air to obtain CoAlO. x The SAPO-34 catalyst was then activated by high-temperature reduction under a 2% H2 / Ar atmosphere; subsequently, the catalyst was reacted with a CO2 / H2 mixture at 240°C and 3.2 MPa to efficiently produce low-polymerization-degree polyvinyl alcohol. This invention is the first to achieve CoAlO x The coupled reaction of SAPO-34 with CO2 hydrogenation has the characteristics of efficient reaction pathway and controllable product selectivity.

Description

Technical Field

[0001] This invention relates to the field of CO2 hydrogenation preparation technology, specifically to a CoAlO x / A method for preparing low-polymerization polyvinyl alcohol by hydrogenation of SAPO-34 with CO2. Background Technology

[0002] Against the backdrop of addressing global climate change and promoting sustainable development, the capture, conversion, and utilization of carbon dioxide (CO2) has become a key direction for scientific research and industrial development. Among these, the hydrogenation of CO2 into high-value-added chemicals and fuels can achieve carbon recycling and reduce greenhouse gas emissions, while also converting inert CO2 molecules into economically valuable chemical products, thus possessing significant environmental and economic benefits. Currently, research on this technological pathway mainly focuses on syngas, methanol, low-carbon olefins, aromatics, and high-carbon hydrocarbons (such as gasoline and diesel). However, precisely controlling the reaction pathway to avoid generating worthless byproducts (such as CO) and synthesizing high-value-added oxygen-containing compounds with well-defined structures and abundant functional groups remains a technological bottleneck in this field.

[0003] Polyvinyl alcohol (PVA), a widely used water-soluble polymer, is extensively applied in industries such as textiles, food, pharmaceuticals, construction, and polymer chemicals. Currently, industrial PVA synthesis relies on fossil fuels, using routes such as polyvinyl acetate alcoholysis or acetylene synthesis. This approach suffers from high energy consumption, cumbersome procedures, dependence on non-renewable resources, and associated safety hazards. In contrast, direct synthesis of PVA using CO2 as a C1 feedstock achieves atom economy and aligns with green chemistry principles, but it presents significant technical challenges. This process requires not only a catalyst capable of efficiently activating CO2 and H2 to complete multi-step hydrogenation and C / C bond growth, but also precise molecular-level control over the initiation, growth, and termination of the polymerization chain. This places extremely high demands on the multifunctional synergistic effect of the catalyst system (such as hydrogenation / chain growth at metal sites and polymerization regulation at molecular sieve acid sites).

[0004] Currently, there are very few publicly available reports, both domestically and internationally, on the direct synthesis of polyvinyl alcohol (PVA), especially low-polymerization-degree PVA, from CO2. This area remains a technological gap and belongs to the forefront of research. Therefore, developing a novel, efficient, and stable catalytic material and process to achieve the direct and highly selective conversion of CO2 into high-value polymers such as low-polymerization-degree PVA is of significant scientific research value and broad industrial application prospects for overcoming the technological bottlenecks in CO2 resource utilization, improving process economics, and expanding the raw material sources for polymer synthesis chemistry. Summary of the Invention

[0005] To address the shortcomings of existing methods for preparing polymers via CO2 hydrogenation, the present invention aims to provide a highly efficient method for producing CoAlO₂.x A method for preparing low-polymerization-degree polyvinyl alcohol by hydrogenation of SAPO-34 and CO2 is proposed, realizing the one-step generation of high-value-added product polymers using CO2.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A high-efficiency CoAlO x A method for preparing low-polymerization polyvinyl alcohol by hydrogenation of SAPO-34 with CO2 includes the following steps:

[0008] (1) The activated CoAlO x The SAPO-34 catalyst was placed in a stainless steel autoclave and a certain amount of H2O was added before sealing. Then, CO2 was introduced to purge and release the gas, removing air and dissolved oxygen from the autoclave and the water.

[0009] (2) After the mixed gas CO2 / H2 is introduced to a certain pressure, the temperature is raised and the mixture is stirred to react. After the reaction liquid is separated by an organic filter membrane, it is left to stand for a period of time. The resulting precipitate is low-polymerization polyvinyl alcohol.

[0010] Furthermore, CoAlO x The SAPO-34 catalyst was prepared using the following steps: S1, CoAlO was synthesized via a hydrothermal method. x The precursor was calcined at high temperature to obtain CoAlO x Solid, and grind; S2, CoAlO x The solid is dispersed in deionized water, SAPO-34 powder is added, and the mixture is stirred, reacted, filtered, washed, dried, and then calcined at high temperature to obtain the final product.

[0011] Furthermore, in S1, a precursor solution is prepared using cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and excess urea, and then CoAlO is synthesized using a hydrothermal method. x The precursor, wherein the molar ratio of Co to Al is 3:1; the pH value of the precursor solution is 8-10; the hydrothermal temperature is 120 ℃, the heating rate is 2-5 ℃ / min, and the time is 12h.

[0012] Furthermore, in S1 and S2, high-temperature calcination refers to calcination at 500 ℃ for 5 h in an air atmosphere.

[0013] Furthermore, in S2, CoAlO x The mass ratio of SAPO-34 to SAPO-34 is 19:1, and the particle size is above 100 mesh.

[0014] Furthermore, the activated CoAlO x / SAPO-34 catalyst refers to CoAlO₂ catalyst prepared under a mixed atmosphere of 2 mmol %H₂ / Ar (i.e., 0.02 mmol H₂ / mmol Ar). x The SAPO-34 catalyst was reduced at 650 °C for 3 h at a gas flow rate of 60 mL / min.

[0015] Furthermore, per 200mg CoAlO x Add 3~5 ml of H2O to the SAPO-34 catalyst.

[0016] Further, a CO2 / H2 mixture is introduced, wherein the pressure ratio of CO2 to H2 is 1:3 and the total pressure is 3.2 MPa.

[0017] Furthermore, the heating and stirring reaction refers to reacting at 240 °C for 12 h with a stirring rate of 800 rpm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This study is the first to propose the synthesis of polyvinyl alcohol (PVA) via CO2 hydrogenation using the synergistic catalysis of metal oxides and molecular sieves. This fills the gap in the conversion of CO2 hydrogenation into polymer synthesis. Traditional PVA synthesis routes suffer from high energy consumption, cumbersome steps, reliance on non-renewable resources, and safety hazards. In contrast, the direct synthesis of PVA from CO2 achieves atom economy and conforms to green chemistry principles.

[0020] 2. The operation method of the present invention is simple, and the synthesized polyvinyl alcohol can be separated by simple filtration, which reduces the operating cost.

[0021] 3. CO2 is a greenhouse gas, and polyvinyl alcohol is a high-value polymer. Converting inexpensive CO2 into polyvinyl alcohol has high economic value. Attached Figure Description

[0022] Figure 1 CoAlO in Example 1 x CoAlO x XRD diffraction patterns of the SAPO-34 catalyst and the reduced catalyst.

[0023] Figure 2 CoAlO in Example 1 x CoAlO x SEM images of the SAPO-34 (19:1) catalyst before and after activation, where a1-a2 are CoAlO x SEM images at different magnifications (5 μm, 1 μm); a3-a4 are CoAlO xSEM images of SAPO-34 (19:1) at different magnifications (5 μm, 1 μm); b1-b2 are CoAlO x -650 SEM images at different magnifications (2 μm, 1 μm); b3-b4 are CoAlO x SEM images of / SAPO-34(19:1)-650 at different magnifications (2 μm, 1 μm).

[0024] Figure 3 The image shows the XRD diffraction pattern of the polyvinyl alcohol produced in Example 1.

[0025] Figure 4 The image shows the FTIR spectrum of the polyvinyl alcohol produced in Example 1.

[0026] Figure 5 The image shows the Raman spectrum of the polyvinyl alcohol produced in Example 1. Detailed Implementation

[0027] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this disclosure and should not be regarded as specific limitations on this application.

[0028] The technical terms “first”, “second”, etc. in this application are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0029] The reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0030] The technical term "and / or" in this application is only a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0031] In addition, the character " / " in this application generally indicates that the objects before and after it are in an "or" relationship.

[0032] In this application, "multiple" means two or more (including two), and "at least one" means one or more.

[0033] It should be noted that, unless otherwise specified in the examples, the conditions should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] CoAlO x It is a common catalyst for the hydrogenation of CO2 to alcohols, in which the Co group plays an important role in C-C coupling. Compared with other works, this invention is the first to combine it with SAPO-34 molecular sieve and react it with CO2 hydrogenation, thereby enabling the hydrogenation of CO2 in CoAlO2. x The methanol and ethanol produced by hydrogenation at the site can be further converted into polyvinyl alcohol, which provides a possibility for the preparation of polymers through CO2 hydrogenation.

[0035] This invention utilizes X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the morphology and surface structure of the catalyst, and uses XRD and FTIR Raman spectroscopy to characterize the structure of polyvinyl alcohol.

[0036] Example 1

[0037] (1) Preparation of CoAlO x solid

[0038] CoAlO x The solid was synthesized using a hydrothermal method. Specifically, 6.5 g of cobalt nitrate hexahydrate, 2.81 g of aluminum nitrate nonahydrate, and 13.5 g of urea were first dissolved in 75 mL of deionized water and stirred to form a homogeneous precursor solution. This precursor solution was then transferred to a high-pressure reactor and subjected to a hydrothermal reaction at 120 °C with a heating rate of 2 °C / min for 12 h. After filtration, washing, and drying, CoAlO was obtained. x Precursor. Finally, the precursor was calcined at 500 °C for 5 h in air at a heating rate of 2 °C / min. The resulting solid was ground and sieved to obtain CoAlO with a particle size of over 100 mesh. x Solid. Its XRD and SEM results are as follows: Figure 1 and Figure 2 .

[0039] (2) Preparation of CoAlO x / SAPO-34 catalyst

[0040] The obtained CoAlO x The solid was dispersed in deionized water, and then processed according to the CoAlO4 standard. xCommercially available SAPO-34 powder was added at a mass ratio of 19:1 to SAPO-34. After stirring for 24 hours, the product was filtered, washed, and dried. Then, it was calcined at 500 °C for 5 hours in air at a heating rate of 2 °C / min. The resulting solid was ground and sieved to obtain CoAlO with a particle size of over 100 mesh. x / SAPO-34 catalyst.

[0041] (3) CoAlO x / SAPO-34 catalyst activation

[0042] Before testing the activity, the obtained CoAlO x The SAPO-34 catalyst was reduced at 650 °C for 3 h in a 2% H2 / Ar mixed atmosphere.

[0043] (4) CoAlO x / SAPO-34 catalyst reacts with CO2

[0044] 100 mg of CoAlO after activation in step (3) x The SAPO-34 catalyst was placed in a stainless steel autoclave, and 3 mL of H2O was added before sealing. Then, CO2 at 1 MPa was purged 10 times to remove air and dissolved oxygen from the water. After purging, a mixed gas of 3.2 MPa (P(CO2) / P(H2) = 1:3) was introduced, and the airtightness of the apparatus was checked. Once the airtightness was ensured, the reaction temperature was set to 240 °C, the reaction time to 12 h, and the reaction speed to 800 rpm. The reaction solution was separated through an organic filter membrane to obtain a colorless and transparent liquid. After standing for a period of time, a slightly yellow precipitate formed, which was the target product, low-polymer polyvinyl alcohol. The precipitate was dried and weighed, and the yield of low-polymer polyvinyl alcohol was calculated to be 10.1 mg (the average of three test data).

[0045] XRD of the target product, such as Figure 3 As shown, the FTIR spectrum is as follows Figure 4 As shown, the Raman spectrum is as follows Figure 5 As shown.

[0046] Figure 3 The XRD diffraction patterns of the synthesized polyvinyl alcohol sample and the standard sample PVA-1788 are shown for comparison. It can be seen that their spectra are similar; the PVA structure consists of a carbon backbone with hydroxyl groups attached to the carbon atoms of methane. This polymer exhibits high crystallinity, stemming from the strong interactions between chains formed by intermolecular hydrogen bonds, and it shows a distinct characteristic peak at 2θ = 20°, indicating the successful synthesis of polyvinyl alcohol.

[0047] Figure 4The FTIR spectra of the generated polyvinyl alcohol sample and the standard sample PVA-1788 are compared. It can be seen that the spectra of the two are similar in the 4000-500 cm⁻¹ range. -1 The stretching vibration of OH was observed in the wavelength range (3400 cm). -1 Left and right), in-plane bending vibration (1600 cm) -1 (left and right) and out-of-plane bending vibration (700 cm) -1 Symmetrical and asymmetric stretching vibrations of CH2 (3000 cm⁻¹) -1 -2800 cm -1 ) and bending vibration (1400 cm) -1 Left and right), stretching vibration of CO (1000 cm) -1 (Approximately 1000 ppm), which further demonstrates the successful synthesis of polyvinyl alcohol.

[0048] Figure 5 The Raman spectra of the generated polyvinyl alcohol sample and the standard sample PVA-1788 are compared, showing that the 1440 cm⁻¹... -1 and 1360cm -1 The peak at 1145 cm⁻¹ is attributed to the bending vibration of CH in the polyvinyl alcohol species. -1 The peak at 920 cm⁻¹ is attributed to the bending vibration of CO in the polyvinyl alcohol species. -1 and 850cm -1 The peak at 1145 cm⁻¹ is attributed to the stretching vibration of the C-C group of polyvinyl alcohol species. The main difference between the generated sample and PVA-1788 is reflected in the peak at 1145 cm⁻¹. -1 The presence of this information indicates that the synthesized polyvinyl alcohol has a low hydroxyl content, i.e., a low degree of polymerization.

[0049] Example 2

[0050] The other steps in this embodiment are the same as in embodiment 1, except that in step (1), the hydrothermal reaction at 120°C for 12 h is changed to the hydrothermal reaction at 120°C for 5 h.

[0051] After drying the precipitate, it was weighed, and the yield of low-polymerization degree polyvinyl alcohol was calculated to be basically unchanged, the same as in Example 1.

[0052] Example 3

[0053] The other steps in this embodiment are the same as in embodiment 1, except that in step (4), 3 mL H2O is replaced with 5 mL H2O.

[0054] After drying the precipitate, it was weighed, and the yield of low-polymerization degree polyvinyl alcohol was calculated to be 9.5 mg.

[0055] Example 4

[0056] The other steps in this embodiment are the same as in embodiment 1, except that in step (4), 100 mg of CoAlO x / The SAPO-34 catalyst was changed to 200 mg.

[0057] After drying the precipitate, it was weighed, and the yield of low-polymerization degree polyvinyl alcohol was calculated to be 14.5 mg.

[0058] Comparative Example 1

[0059] CoAlO was prepared according to step (1) of Example 1. x Solid, then CoAlO x The solid was reduced at 650 °C for 3 h in a 2% H2 / Ar mixed atmosphere to obtain activated CoAlO. x The catalyst, its XRD and SEM are as follows: Figure 1 and Figure 2 .

[0060] According to step (4) of Example 1, only CoAlO x / SAPO-34 catalyst replaced with CoAlO x When the catalyst reacted with CO2, no precipitate was formed, meaning the yield of low-polymerization-degree polyvinyl alcohol was 0.

[0061] Comparative Example 2

[0062] Commercial SAPO-34 powder was reduced at 650 °C for 3 h in a 2% H2 / Ar mixed atmosphere to obtain activated SAPO-34 catalyst.

[0063] According to step (4) of Example 1, only CoAlO x When the SAPO-34 catalyst was replaced with another SAPO-34 catalyst and reacted with CO2, no precipitate was formed, meaning the yield of low-polymerization polyvinyl alcohol was 0.

[0064] Comparative Example 3

[0065] CoAlO was prepared according to step (1) of Example 1. x Solid, then according to CoAlO x Commercially available SiO2 powder was added at a mass ratio of 19:1 to SiO2 and reduced at 650 °C for 3 h in a 2% H2 / Ar mixed atmosphere to obtain activated CoAlO2. x / SiO2 catalyst.

[0066] According to step (4) of Example 1, only CoAlO x / SAPO-34 catalyst replaced with CoAlO xWhen the SiO2 catalyst reacted with CO2, no precipitate was formed, meaning the yield of low-polymerization polyvinyl alcohol was 0.

[0067] The solid catalysts prepared in Example 1 and Comparative Example 1 are respectively labeled as CoAlO x CoAlO x The catalyst obtained after hydrogen activation with SAPO-34 (19:1) is denoted as CoAlO. x -650, CoAlO x / SAPO-34(19:1)-650 and XRD analysis was performed on them to analyze their structure.

[0068] Figure 1 CoAlO x CoAlO x / SAPO-34 (19:1), CoAlO x -650 and CoAlO x The XRD diffraction pattern of / SAPO-34(19:1)-650 shows that CoAlO x CoAlO x / SAPO-34 (19:1) mainly exhibits Co6Al2O 11 The crystal phase of Co3O4 indicates that the Co species in the catalyst at this point mainly exist in the oxidation state, followed by CoAlO x -650, CoAlO x In the SAPO-34(19:1)-650 catalyst, it can be seen that oxidized Co species are transformed into metallic Co.

[0069] Figure 2 CoAlO x CoAlO x / SAPO-34 (19:1), CoAlO x -650 and CoAlO x The SEM images of / SAPO-34 (19:1)-650 show that the catalysts all exhibit a stacked morphology, with CoAlO x ( Figure 2 The a1-a2 particles exhibit a relatively dense rod-like structure on their surface, with uniformly distributed particles that have a smooth surface and clear boundaries; CoAlO x / SAPO-34 (19:1) Figure 2 The a3-a4 components exhibit a nanoparticle aggregate structure, CoAlO x ( Figure 2 The surface nanoparticles (b1-b2) are uniformly dispersed in CoAlO x / SAPO-34 (19:1)-650 ( Figure 2The b3-b4 components exhibit an aggregated nanostructure, further demonstrating the successful preparation of the catalyst.

[0070] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A CoAlO x A method for preparing low-polymerization polyvinyl alcohol by hydrogenation of SAPO-34 and CO2, characterized in that... Includes the following steps: (1) The activated CoAlO x The SAPO-34 catalyst was placed in a stainless steel autoclave and a certain amount of H2O was added before sealing. Then, CO2 was introduced to purge and release the gas, removing air and dissolved oxygen from the autoclave and the water. (2) After the mixed gas CO2 / H2 is introduced to a certain pressure, the temperature is raised and the mixture is stirred to react. After the reaction liquid is separated by an organic filter membrane, it is left to stand for a period of time. The resulting precipitate is low-polymerization polyvinyl alcohol.

2. The method as described in claim 1, characterized in that, CoAlO x The SAPO-34 catalyst was prepared using the following steps: S1, CoAlO was synthesized via a hydrothermal method. x The precursor was calcined at high temperature to obtain CoAlO x Solid, and ground; S2, CoAlO x The solid is dispersed in deionized water, SAPO-34 powder is added, and the mixture is stirred, reacted, filtered, washed, dried, and then calcined at high temperature to obtain the final product.

3. The method as described in claim 2, characterized in that, In S1, a precursor solution was prepared using cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, and excess urea, followed by the hydrothermal synthesis of CoAlO. x The precursor has a molar ratio of Co to Al of 3:1; and / or, the pH of the precursor solution is 8 to 10; and / or, the hydrothermal reaction temperature is 120 °C; and / or, the hydrothermal reaction heating rate is 2 to 5 °C / min; and / or, the hydrothermal reaction time is 12 h.

4. The method as described in claim 2, characterized in that, In S1 and S2, high-temperature calcination refers to calcination at 500℃ for 5 hours in an air atmosphere.

5. The method as described in claim 2, characterized in that, In S2, CoAlO x The mass ratio of SAPO-34 to SAPO-34 is 19:1; and / or the particle size is 100 mesh or larger.

6. The method as described in claim 1, characterized in that, Activated CoAlO x / SAPO-34 catalyst refers to CoAlO₂ catalyst produced under a 2% H₂ / Ar mixed atmosphere. x The SAPO-34 catalyst was reduced at 650 °C for 3 h at a gas flow rate of 60 mL / min.

7. The method as described in claim 1, characterized in that, 200 mg CoAlO x Add 3~5ml of SAPO-34 catalyst to H2O.

8. The method as described in claim 1, characterized in that, A CO2 / H2 mixture is introduced, with a CO2 to H2 pressure ratio of 1:3 and a total pressure of 3.2 MPa.

9. The method as described in claim 1, characterized in that, A heated and stirred reaction refers to a reaction at 240 °C for 12 h; and / or a stirring rate of 800 rpm.

Images