A method for preparing sweet and fragrant substances by catalyzing low-temperature pyrolysis of tobacco biomass

Abstract

The present invention relates to the field of pyrolysis technology, and more particularly to a method for preparing a burnt sweet aroma substance by catalyzing the low-temperature pyrolysis of tobacco biomass, comprising the following steps: (1) preparing metal oxide nanocubic crystals using a hydrothermal method, and then loading the nanocubic crystals onto the surface of a catalyst matrix to obtain a metal-based catalyst material; (2) mixing tobacco biomass powder with the metal-based catalyst material and pyrolyzing the mixture at low temperature; and (3) separating and analyzing the burnt sweet aroma substances in the gaseous phase products obtained by pyrolysis, including various furan compounds such as 5-methylfurfural. The burnt sweet aroma substance prepared by the present invention can improve the problem of insufficient tobacco aroma in cigarette products, increase the burnt sweet aroma, and improve the smoking quality.

Description

Technical Field

[0001] The invention relates to the technical field of biomass energy utilization, and in particular to a method for preparing burnt sweet and fragrant substances by catalyzing low-temperature pyrolysis of tobacco biomass. Background Art

[0002] With the increasing global emphasis on environmental sustainability, the application prospects of lignocellulosic biomass are constantly expanding. Therefore, the utilization and treatment of lignocellulosic biomass has become more important. Tobacco, as an important renewable lignocellulosic biomass resource, has significant industrial value. The process of processing tobacco into cigarette products usually produces more than 70% of tobacco waste, mainly including low-grade tobacco leaves, moldy tobacco leaves, short stems, stem fragments, smoke dust, and other by-products. Currently, agrochemical, biochemical, physical, and thermochemical conversion methods have been widely used to decompose biomass and waste. Among these methods, catalytic fast pyrolysis has become an effective technology for the thermochemical conversion of biomass and its waste into energy products due to its advantages such as low cost, convenient operation, and high liquid fuel yield.

[0003] Biomass pyrolysis is the process of thermal degradation of biomass under anaerobic or low-oxygen conditions, producing bio-oil, combustible gases, and solid biomass carbon. Tobacco biomass pyrolysis for the production of aroma compounds is a cutting-edge technology in the field of tobacco biomass thermochemical conversion and utilization. This technology selectively produces high-value-added target chemicals (such as phenols, furans, and oxygenates) through catalytic pyrolysis of biomass, converting low-quality tobacco biomass into high-quality aroma compounds. Heating tobacco biomass between 200 and 350°C releases a large number of flavor compounds while reducing the formation of toxic and harmful compounds such as nitrosamines, volatile compounds, and phenolic compounds (typically formed at 800 to 900°C). Therefore, controlling tobacco biomass pyrolysis under low-temperature conditions can result in a more favorable product composition. Among the many high-value-added bioproducts produced by the pyrolysis of tobacco biomass, caramel-sweet flavor compounds are important aroma compounds, widely used in heat-processed foods such as bread, coffee, cigarettes, and tea. They enhance the aroma of baked and sweet foods, adding sweetness and improving the aftertaste of these heat-processed foods. Typical caramel-sweet flavor compounds include methylcyclopentanone, maltol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and 2,3-dihydroxy-2,5-dihydro-6-methyl-4H-pyran-4-one (DDMP). In the cigarette industry, caramel-sweet flavor compounds can be inherently produced by the pyrolysis of tobacco polysaccharides and monosaccharides, or added externally to enhance specific flavors. They can enhance the caramel flavor and sweetness of cigarette products. Therefore, the targeted catalytic low-temperature pyrolysis of tobacco biomass to produce caramel-sweet flavor compounds not only enhances the flavor and quality of bio-flavor compounds, but also improves the safety of cigarette products. Summary of the Invention

[0004] The purpose of the present invention is to provide a new method for preparing burnt sweet and fragrant substances by catalyzing the low-temperature pyrolysis of tobacco biomass.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass comprises the following steps:

[0007] Step 1: dissolving a soluble metal salt in distilled water, performing a hydrothermal reaction under alkaline conditions, and calcining the resulting solid product at high temperature to produce metal oxide nanocubic crystals; uniformly dispersing and mixing the metal oxide nanocubic crystals and a catalyst matrix in a solvent, removing the solvent, vacuum drying, and reducing calcining to obtain a metal-based catalyst material;

[0008] Step 2: mixing tobacco biomass powder with the metal-based catalyst material and then pyrolyzing the mixture in situ under a nitrogen atmosphere;

[0009] Step 3: Online collection, separation and analysis of the sweet and fragrant substances in the pyrolysis products.

[0010] Preferably, in step 1, the soluble metal salt comprises a hydrate of at least one of cerium nitrate, zinc nitrate and magnesium nitrate.

[0011] Preferably, in step 1, the alkaline condition is to add at least one base selected from NaOH, ammonia and Ca(OH)2 to the reaction solution. - The concentration is 1~20mol / L.

[0012] Preferably, in step 1: the temperature of the hydrothermal reaction is 120-240°C, the reaction time is 12-24 hours; the temperature of the high-temperature calcination is 300-600°C, the reaction time is 1-2 hours, and the atmosphere is air; the temperature of the reduction calcination is 350-450°C, the time is 1-3 hours, and the atmosphere is nitrogen.

[0013] Preferably, in step 1, the catalyst matrix includes at least one of reduced graphene oxide, Al2O3 and HZSM-5, and the mass ratio of the catalyst matrix to the metal oxide nanocubic crystals is 1:1 to 20.

[0014] Preferably, in step 2, the raw material of the tobacco biomass powder includes at least one of tobacco stalks, tobacco, tobacco stems and tobacco flakes, and the raw material is crushed to a particle size of 100 to 400 meshes to obtain tobacco biomass powder.

[0015] Preferably, in step 2, the mass ratio of the tobacco biomass powder to the metal-based catalyst material is 1:0.2-1.5.

[0016] Preferably, in step 2, the pyrolysis temperature is 200-500° C., and the pyrolysis time is 60-180 s.

[0017] Preferably, in step 3, the caramelized sweet aroma substance includes at least one of oxygen-containing heterocyclic compounds such as furfural, furfuryl alcohol, furanone, cyclopentenone, and ethyl maltol.

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

[0019] 1. The present invention discloses a method for preparing a caramelized, sweet, and fragrant substance by catalyzing the low-temperature pyrolysis of tobacco biomass. First, metal oxide nanocubic crystals (such as cubic nanocrystalline cerium oxide) with more oxygen vacancies and acidic sites are prepared, and then dispersed on the surface of a catalyst matrix (such as reduced graphene oxide). This achieves dual functionalization of acid active centers and metal active centers, reduces the agglomeration effect of the metal oxide crystals, and enables them to be evenly dispersed, thereby providing more reaction sites and stronger catalytic performance.

[0020] 2. The metal-based catalyst material prepared by the preparation method of the present invention is used to perform low-temperature catalytic rapid pyrolysis of tobacco biomass, which can promote the dehydration and decarbonylation process of cellulose and hemicellulose pyrolysis at a lower pyrolysis temperature, and quickly and efficiently produce methylcyclopentanone, furfuryl alcohol, 5-methylfurfural, DDMP and other burnt sweet and fragrant substances (BSFSs).

[0021] 3. The burnt-sweet aroma substance prepared by the present invention can improve the problem of insufficient tobacco aroma in cigarette products, increase their burnt-sweet aroma, and improve the smoking quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 TEM images ((a) to (d) in the figure) and SEM images ((e) to (h) in the figure) of the catalysts obtained in Example 1, Comparative Example 1, and Comparative Example 2, as well as the GO raw materials used, wherein (a) (e) correspond to GO raw materials, (b) (f) correspond to Comparative Example 1, (c) (g) correspond to Example 1, and (d) (h) correspond to Comparative Example 2.

[0023] Figure 2 These are the XRD ((a) in the figure) and FTIR ((b) in the figure) analysis diagrams of the catalysts obtained in Example 1, Comparative Example 1, Comparative Example 2, and the GO raw materials used.

[0024] Figure 3 This is the SPI-TOF-MS mass spectrum of tobacco biomass pyrolysis products (Comparative Example 3). DETAILED DESCRIPTION

[0025] The following embodiments of the present invention are described in detail. The following embodiments are implemented based on the technical solutions of the present invention, and provide detailed implementation methods and specific operating procedures. However, the protection scope of the present invention is not limited to the following embodiments.

[0026] In the following examples, tobacco biomass (tobacco stems) was obtained from Anhui China Tobacco Industrial Co., Ltd., dried, pulverized, and passed through a 100-mesh sieve before use. Pyrolysis was performed using resistance heating in a tubular furnace. Volatile products from the catalytic pyrolysis of tobacco biomass were detected by online SPI-TOF-MS, and product content was calculated using the signal intensity values ​​corrected for ethylene gas.

[0027] 1. Preparation of catalyst for catalyzing low-temperature pyrolysis of tobacco biomass to produce sweet and fragrant substances

[0028] Example 1

[0029] This embodiment provides a method for preparing a catalyst for catalyzing low-temperature pyrolysis of tobacco biomass to produce a burnt sweet and fragrant substance, comprising the following steps:

[0030] (1) Dissolve 0.868 g of Ce(NO3)3·6H2O and 9.6 g of NaOH in 5 mL and 35 mL of distilled water, respectively. Slowly mix the two solutions and transfer them to a Teflon bottle and stir for 30 minutes until a milky white slurry is formed. Place the Teflon bottle in a stainless steel high-pressure reaction vessel, seal it, and transfer it to an electric oven at 180°C for 24 hours. After hydrothermal treatment, perform solid-liquid separation, and wash the precipitate several times with distilled water and anhydrous ethanol. Freeze-dry the solid product at -80°C overnight to obtain a freeze-dried powder. Finally, calcinate the freeze-dried powder at 450°C in air for 2 hours to obtain nano-cubic CeO2.

[0031] (2) 20 mg of GO was ultrasonically dispersed in 20 mL of ethanol. Then, 100 mg of nanocubic CeO2 prepared in step (1) was slowly added to the dispersion under vigorous stirring and continued to stir vigorously for 1 h.

[0032] (3) The dispersion from step (2) was centrifuged to remove the ethanol solution and then vacuum dried at 60°C for 4 h to obtain a gray-black solid. After drying, the solid was calcined and reduced at 400°C in a nitrogen atmosphere for 1 h to obtain a cerium-based catalyst supported on reduced graphene oxide, which was designated as Ce-RGO.

[0033] Comparative Example 1

[0034] This comparative example provides a method for preparing a catalyst for catalyzing low-temperature pyrolysis of tobacco biomass to prepare a burnt sweet and fragrant substance, comprising the following steps:

[0035] (1) Dissolve 0.868 g of Ce(NO3)3·6H2O and 9.6 g of NaOH in 5 mL and 35 mL of distilled water, respectively. Slowly mix the two solutions and transfer them to a Teflon bottle and stir for 30 minutes until a milky white slurry is formed. Place the Teflon bottle in a stainless steel high-pressure reaction vessel, seal it, and transfer it to an electric oven at 180°C for 24 hours. After hydrothermal treatment, perform solid-liquid separation, and wash the precipitate several times with distilled water and anhydrous ethanol. Freeze-dry the solid product at -80°C overnight to obtain a freeze-dried powder. Finally, calcinate the freeze-dried powder at 450°C in air for 2 hours to obtain nano-cubic CeO2.

[0036] Comparative Example 2

[0037] This comparative example provides a method for preparing a catalyst for catalyzing low-temperature pyrolysis of tobacco biomass to prepare a burnt sweet and fragrant substance, comprising the following steps:

[0038] (1) Dissolve 0.868 g of Ce(NO3)3·6H2O and 9.6 g of NaOH in 5 mL and 35 mL of distilled water, respectively. Slowly mix the two solutions and transfer them to a Teflon bottle and stir for 30 minutes until a milky white slurry is formed. Place the Teflon bottle in a stainless steel high-pressure reaction vessel, seal it, and transfer it to an electric oven at 180°C for 24 hours. After hydrothermal treatment, perform solid-liquid separation, and wash the precipitate several times with distilled water and anhydrous ethanol. The solid product is freeze-dried at -80°C overnight to obtain a freeze-dried powder. Finally, the freeze-dried powder is calcined at 450°C in an air atmosphere for 2 hours to obtain nanocubic CeO2. The CeO2 freeze-dried powder is further mixed with an equal mass of Zn(NO3)2·6H2O and calcined at 450°C in an air atmosphere for 2 hours.

[0039] (2) 20 mg of GO was ultrasonically dispersed in 20 mL of ethanol. Then, 100 mg of the bimetallic oxide prepared in step (1) was slowly added to the dispersion under vigorous stirring and continued to stir vigorously for 1 h.

[0040] (3) The dispersion obtained in step (2) was centrifuged to remove the ethanol solution and then vacuum dried at 60°C for 4 h to obtain a gray-black solid. After drying, the solid was calcined and reduced at 400°C in a N2 atmosphere for 1 h to obtain a cerium-zinc bimetallic oxide supported on reduced graphene oxide, which was designated as CeZn-RGO.

[0041] The catalysts obtained in Example 1 and Comparative Examples 1 and 2 were characterized as follows:

[0042] 1. TEM and SEM tests were performed on Example 1 (Ce-RGO), Comparative Example 1 (CeO2), Comparative Example 2 (CeZn-RGO) and the raw material GO used in the synthesis process. The results are as follows: Figure 1 shown.

[0043] from Figure 1 It can be seen that the loading of metal oxides onto RGO does not change the original thin layer morphology of RGO, but the magnetic aggregation of metal oxides is significantly improved due to the loading of RGO. The regular cubic CeO2 particles on Ce-RGO have been successfully distributed on the RGO lamellar structure; while smaller, more irregular particles (ZnO) are also present on Ce / Zn-RGO.

[0044] 2. XRD and FTIR analysis were performed on Example 1 (Ce-RGO), Comparative Example 1 (CeO2), Comparative Example 2 (CeZn-RGO) and the raw material GO used in the synthesis process. The results are as follows: Figure 2 shown.

[0045] from Figure 2 It can be seen that the peak position of Ce / RGO matches that of CeO2, indicating that CeO2 particles are loaded on the RGO surface. The peak of the CeZn / RGO image matches both standard PDF data for CeO2 (34-0394) and ZnO (36-1451), confirming that both Ce and Zn oxides are loaded onto the RGO. The FTIR spectrum also shows characteristic peaks corresponding to each substance.

[0046] 3. BET and NH3-TPD analyses were performed on Example 1 (CeZn-RGO), Comparative Example 1 (CeO2), Comparative Example 2 (CeZn-RGO) and the raw material GO used in the synthesis process, and the parameter information was shown in Table 1.

[0047] Table 1 BET and NH3-TPD analysis parameters of GO and several catalysts

[0048]

[0049] BET data show that the catalysts are non-porous or macroporous materials. Compared with CeO2, Ce / RGO and CeZn / RGO have larger BET specific surface areas and higher total acid content. Although Ce / RGO and CeZn / RGO have similar densities of strong acid sites, Ce / RGO has slightly more weak acid sites.

[0050] 2. Application and Implementation of Catalytic Pyrolysis of Tobacco Biomass

[0051] Example 2

[0052] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0053] 20 mg of tobacco biomass powder and 10 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor. Pyrolysis was carried out under a nitrogen atmosphere at 300°C for 120 seconds, with a catalyst to tobacco biomass ratio of 1:2. The total strength of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0054] Comparative Example 3

[0055] This comparative example provides a method for preparing a sweet and fragrant substance by low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0056] 20 mg of tobacco biomass powder was directly charged into a reactor and pyrolyzed under a nitrogen atmosphere at 300°C for 120 seconds. Online SPI-TOF-MS was used to measure the total intensity of burnt sweet flavor substances (BSFSs) in the tobacco biomass pyrolysis products under non-catalytic conditions.

[0057] Comparative Example 4

[0058] This comparative example provides a method for preparing a sweet and fragrant substance by catalyzing the low-temperature pyrolysis of tobacco biomass, the specific steps of which are:

[0059] 20 mg of tobacco biomass powder and 10 mg of the catalyst (CeO2) prepared in Comparative Example 1 were placed in a reactor. Pyrolysis was carried out under a nitrogen atmosphere at 300°C for 120 seconds, with a catalyst to tobacco biomass ratio of 1:2. The summed intensity of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0060] Comparative Example 5

[0061] This comparative example provides a method for preparing a sweet and fragrant substance by catalyzing the low-temperature pyrolysis of tobacco biomass, the specific steps of which are:

[0062] 20 mg of tobacco biomass powder and 10 mg of the catalyst (CeZn-RGO) prepared in Comparative Example 2 were loaded into a reactor. Pyrolysis was carried out under a nitrogen atmosphere at 300°C for 120 seconds, using a catalyst to tobacco biomass ratio of 1:2. The total strength of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0063] Example 3

[0064] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0065] 20 mg of tobacco biomass powder and 20 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor. Pyrolysis was carried out under a nitrogen atmosphere at 335°C for 140 seconds, with a catalyst to tobacco biomass ratio of 1:1. The summed intensity of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0066] Example 4

[0067] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0068] 20 mg of tobacco biomass powder and 17.5 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor and pyrolysis was carried out under a nitrogen atmosphere at 400°C for 180 seconds. The total strength of burnt sweet flavor substances (BSFSs) in the tobacco biomass pyrolysis products was determined using online SPI-TOF-MS.

[0069] Example 5

[0070] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0071] 20 mg of tobacco biomass powder and 17.5 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor and pyrolysis was carried out under a nitrogen atmosphere at 300°C for 120 seconds. The total strength of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0072] Example 6

[0073] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0074] 20 mg of tobacco biomass powder and 17.5 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor and pyrolysis was carried out under a nitrogen atmosphere at 200°C for 180 seconds. The total strength of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0075] Example 7

[0076] This embodiment provides a method for preparing a sweet and fragrant substance by catalyzing low-temperature pyrolysis of tobacco biomass, the specific steps of which are as follows:

[0077] 20 mg of tobacco biomass and 5.0 mg of the catalyst (Ce-RGO) prepared in Example 1 were placed in a reactor and pyrolysis was carried out under a nitrogen atmosphere at 300°C for 180 seconds. The total strength of burnt sweet flavor substances (BSFSs) in the catalytic pyrolysis products of tobacco biomass was determined using online SPI-TOF-MS.

[0078] The volatile products of the catalytic pyrolysis of tobacco biomass in the above examples and comparative examples were detected by online SPI-TOF-MS. The mass spectra of the products are shown in FIG. Figure 3 As shown, 33 volatile products were primarily identified from the pyrolysis of tobacco biomass. The compound names and aroma characteristics are shown in Table 2. These products include 13 ketones, 6 phenols, 5 heterocyclic compounds, 4 alcohols, 3 aldehydes, and 2 hydrocarbons. Among these products were 12 burnt sweet flavor substances (BSFSs), with m / z values ​​ranging from 84 to 144. Most of these substances are oxygen-containing heterocyclic compounds with furanic structures and are often attributed to high-value-added chemicals produced by biomass pyrolysis. Of the 33 volatile products detected, BSFSs accounted for over 60% of the total intensity. Therefore, BSFSs were ultimately selected as target compounds for evaluating the catalytic effect of TB pyrolysis in this experiment.

[0079] Table 2 Volatile products of tobacco biomass catalytic pyrolysis (catalyst: Ce / RGO, temperature: 300°C)

[0080]

[0081]

[0082] The total BSFSs intensity values ​​in the products of Example 2, Comparative Examples 3-5, and Examples 3-7 are shown in Table 3. Compared to Comparative Example 3 (no catalyst), the yield of BSFSs in the products obtained from the rapid pyrolysis of tobacco biomass using the three catalysts under the same conditions (same pyrolysis temperature and time) was significantly increased, with Example 2 (Ce-RGO) achieving the best results, increasing the BSFSs yield by 33.6% over that in Comparative Example 3. The results from the different comparative examples show that BSFSs yield initially increases and then decreases with increasing temperature and catalyst dosage, indicating that increasing temperature promotes the pyrolysis of tobacco biomass at low temperatures. As the temperature approaches 400°C, the BSFSs yield decreases slightly over time.

[0083] Table 3 Results of BSFSs content in tobacco biomass catalytic pyrolysis products under different conditions

[0084]

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing sweet and fragrant substances by catalyzing low-temperature pyrolysis of tobacco biomass, characterized in that: The steps include: Step 1: dissolving a soluble metal salt in distilled water, hydrothermally reacting the mixture at 120-240° C. under alkaline conditions for 12-24 hours, and calcining the resulting solid product at 300-600° C. under air atmosphere for 1-2 hours to obtain metal oxide nanocubic crystals; uniformly dispersing and mixing the metal oxide nanocubic crystals and a catalyst matrix in a solvent, vacuum drying after removing the solvent, and reducing and calcining the mixture at 350-450° C. under nitrogen atmosphere for 1-3 hours to obtain a metal-based catalyst material; the soluble metal salt comprises a hydrate of at least one of cerium nitrate, zinc nitrate, and magnesium nitrate; the catalyst matrix comprises at least one of reduced graphene oxide, Al2O3, and HZSM-5, and the mass ratio of the catalyst matrix to the metal oxide nanocubic crystals is 1:1-20; Step 2: After mixing the tobacco biomass powder with the metal-based catalyst material, in situ pyrolysis is performed at 200-500° C. for 60-180 s under a nitrogen atmosphere; Step 3: Online collection, separation and analysis of the sweet and fragrant substances in the pyrolysis products.

2. The method according to claim 1, characterized in that In step 1, the alkaline condition is to add at least one of NaOH, ammonia and Ca(OH)2 to the reaction solution until OH - The concentration is 1~20mol / L.

3. The method according to claim 1, characterized in that In step 2, the raw material of the tobacco biomass powder includes at least one of tobacco stalks, tobacco stems and tobacco flakes, and the raw material is crushed to a particle size of 100-400 mesh to obtain tobacco biomass powder.

4. The method according to claim 1, wherein In step 2, the mass ratio of the tobacco biomass powder to the metal-based catalyst material is 1:0.2-1.

5.

5. The method according to claim 1, wherein In step 3, the caramelized sweet aroma substance includes at least one of furfural, furfuryl alcohol, furanone, cyclopentenone and ethyl maltol.

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