Method for preparing bio-oil by co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 catalyst

Abstract

The application discloses a method for preparing bio-oil by co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 as a catalyst, and high-quality bio-oil is prepared by co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 as a catalyst. Research shows that the addition of plastics can significantly improve the yield of hydrocarbons. The total hydrocarbon of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene increases by 6%, 78% and 45% respectively under the catalytic pyrolysis of Ni-Mo / HZSM-5, and waste plastics have a synergistic effect on the pyrolysis of black liquor solids. When black liquor solids and polyethylene are co-pyrolyzed, the yield of alkanes is the highest at 69.44% at a temperature of 650 DEG C. When black liquor solids and polypropylene are co-pyrolyzed, the yield of alkanes is the highest at 44.9% at a temperature of 550 DEG C. The obtained pyrolysis bio-oil is mainly composed of hydrocarbons, and is a kind of high-quality bio-oil.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bio-oil preparation, and particularly relates to a method for preparing bio-oil by co-pyrolysis of black liquor solids and waste plastics using Ni-Mo / HZSM-5 as a catalyst. BACKGROUND

[0002] As a renewable resource, biomass can be converted into liquid bio-oil, combustible gas and other biomass energy through pyrolysis, which can reduce dependence on fossil fuels and protect the environment. Black liquor is a byproduct produced during the pulping and cooking process of biomass, which has high chemical oxygen demand (COD) content, high pH value (12-13) and pungent odor, and is mainly composed of dissolved lignin degradation products and cellulose and hemicellulose degradation products produced by reaction with NaOH and Na2S aqueous solution. It is a low-calorific-value, high-moisture-content inferior fuel. However, the traditional method of treating black liquor involves evaporation and concentration of black liquor before combustion for power generation, which has problems such as low combustion efficiency of black liquor, high evaporation energy consumption, short operation cycle, and emission of large amounts of greenhouse gases during the combustion process, which is not consistent with the current energy-saving and carbon-reducing background. Catalytic pyrolysis is an efficient method for preparing platform products, which is widely used for upgrading inferior fuels. It can convert black liquor into high-value products such as bio-aromatics and bio-oil. However, similar to bio-oil prepared by catalytic pyrolysis of biomass, the oxygen content and water content of bio-oil produced by black liquor pyrolysis are high, the organic acid content is high, and the calorific value is generally low. At the same time, plastics are widely used in daily life and industrial sectors. Experts estimate that global plastic waste production will increase from 240 million tons / year in 2016 to 430 million tons / year in 2040 under normal circumstances. These plastic products generally have a short lifespan, only 9% are recycled, and most are incinerated or disposed of in landfills, which causes serious resource waste and environmental problems. Waste plastics are a high-hydrogen-containing hydrocarbon resource, which can act as a hydrogen source when co-pyrolyzed with biomass to improve the quality of bio-oil prepared from biomass and achieve resource utilization of waste. Black liquor is a special biomass resource, and research on its co-catalytic pyrolysis with waste plastics to prepare high-quality bio-oil is of great significance for the resource utilization of these two types of waste. However, no one has studied this so far. Therefore, studying the conversion mechanism of catalytic pyrolysis of black liquor and plastics can selectively regulate the quality of black liquor fuel, and is of great significance for the high-value, resource utilization and utilization of waste.

[0003] To improve the poor fuel properties of black liquor, many researchers have studied the preparation of bio-oil from pyrolysis of black liquor. For example, Heeres et al. used Ga-modified H-ZSM-5 catalysts for in-situ and ex-situ pyrolysis (T = 500-600 °C) of black liquor based on the organic fraction of black liquor, and up to 7 wt% bio-aromatics were obtained. Andersson et al. used black liquor and pyrolysis oil for co-gasification to produce methanol, and the gasification rate of pure black liquor and black liquor-pyrolysis oil mixture was as high as 50%. The above experiments confirmed that it is feasible to prepare bio-oil from pyrolysis of black liquor, but there are problems such as low yield of pyrolysis bio-oil and easy coking of black liquor during pyrolysis, so it is necessary to introduce a hydrogen source to improve the quality of black liquor bio-oil. At present, due to the problems of complex components, poor stability during storage, and low calorific value of bio-oil produced by biomass pyrolysis, which limits the use of bio-oil, therefore, some researchers have tried to introduce waste plastics for co-pyrolysis with biomass to improve the quality of bio-oil. WANG, LIKUN, BURRA et al. prepared high-quality fuel by co-pyrolysis of biomass and plastic waste, which solved the problems of plastic / rubber waste pollution, high oxygen content, poor stability, and low calorific value of bio-oil produced by biomass pyrolysis, and realized efficient utilization of solid waste. Jin et al. used black liquor lignin and waste plastics for co-pyrolysis, and found that co-pyrolysis of black liquor lignin and waste plastics could promote the formation of monomer aromatic hydrocarbons. Salvilla et al. evaluated the effect of temperature and biomass-plastic ratio on the rate synergy in the co-pyrolysis process, and found that the activation energy of plastic in the co-pyrolysis of plastic and biomass was significantly lower than that of pure plastic pyrolysis, which indicated the synergistic effect of biomass and plastic pyrolysis oil. Xu et al. found that there was obvious synergistic effect in the co-pyrolysis of biomass and plastic, and the yield and hydrogen content of bio-oil were higher when wood chips and polypropylene were co-pyrolyzed. The above experiments confirmed that there was obvious synergistic effect in the co-pyrolysis of biomass and waste plastics, and the quality of bio-oil produced by pyrolysis was significantly improved. Black liquor is a special biomass resource, and there is little research on the co-pyrolysis of black liquor and plastic. Co-pyrolysis of black liquor and waste plastics can make up for the shortcomings of the two in the pyrolysis process, and realize the high-value utilization of the two wastes.

[0004] The co-pyrolysis products of plastics and biomass are affected by the feeding method, the reactivity of the pyrolysis reactor and the product distribution, the effect of the catalyst and the operating parameters. At present, there are many types of molecular sieve catalysts used in the catalytic cracking of biomass to produce aromatic compounds. HZSM-5 molecular sieve catalyst has strong surface acidity and unique regular pore structure, and has good deoxygenation and aromatization capacity, and has been applied to the synthesis of refinery, fine chemicals, petrochemicals and fuel components. Microporous molecular sieve is more likely to break long-chain alkanes in the middle, the pyrolysis temperature of cellulose is between 325 and 400, the decomposition temperature of hemicellulose characterized by xylan is between 250 and 350, and lignin is relatively stable and can be pyrolyzed at 300 to 550 to increase the content of bio-oil and reduce the generation of volatile matter. The pore size of the catalyst is larger than that of the biomass component, which is beneficial to the flow of molecules in the pore, can avoid coking, and the separation of the catalyst and the carbon after pyrolysis is beneficial to the recycling of the catalyst. ZSM-5 doped with other metal elements can modify the strength and density of the zeolite acid center, thereby improving the catalytic efficiency. Qu et al. used MoO3 / ZSM-5 molecular sieve catalyst to catalyze the oil sludge, and found that at 500 DEG C, MoO3 / ZSM-5 catalyst effectively promoted the conversion of long-chain saturated hydrocarbons in the oil phase to aromatic hydrocarbons, and after catalytic pyrolysis, the mass fraction of aromatic hydrocarbons in the oil phase increased by 5.6%, the boiling range decreased by 300 DEG C, and the content of heavy oil was significantly reduced. Liu et al. used 5% Ni-Mo2N / HZSM-5 (Si / Al ratio of 25) catalyst to improve the yield of benzene, toluene and xylene, and to reduce the yield of naphthalene and methyl naphthalene. Sun et al. used Mo-modified ZSM-5 catalyst in the process of catalytic fast pyrolysis (CFP) of biomass to produce aromatic hydrocarbons, and the research showed that Mo / ZSM-5 catalyst could improve the yield of monocyclic aromatic hydrocarbons (MAHs). The above experiments show that HZSM-5-based catalyst loaded with transition metals such as Ni and Mo is beneficial to the upgrading of biomass pyrolysis and the selective generation of high-value platform products. SUMMARY

[0005] In order to improve the fuel properties of black liquor, solve the environmental pollution problem caused by black liquor and waste plastics, and realize the high-value conversion of black liquor and waste plastics, the present study intends to use Mo-Ni / HZSM-5 catalyst to co-pyrolyze waste plastics and black liquor to prepare high-quality bio-oil, so as to increase the content of hydrocarbon substances in the pyrolysis bio-oil, which can be directly used as fuel or mixed with other fossil fuels after upgrading. The separation process is expected to replace the traditional alkali recovery process and realize the resourceization and high-value of black liquor, thereby increasing the value for papermaking enterprises.

[0006] The object of the present application is achieved by the following technical solutions:

[0007] The method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics with Ni-Mo / HZSM-5 catalyst comprises the following steps:

[0008] 1) The dilute black liquor is dried at 105 DEG C to form black liquor solids, and the drier is used for standby, and the black liquor solids are selected and uniformly mixed with polypropylene or polyethylene, and the mass ratio of the mixture is 1:1, which is used as the raw material for co-pyrolysis experiment;

[0009] 2) Preparation of catalyst:

[0010] After the HZSM-5 molecular sieve is cleaned and dried, it is dehydrated in an oven at 105 DEG C, and then calcined in a muffle furnace at 550 DEG C for 4h, and a Ni-Mo / HZSM-5 catalyst is prepared by vacuum impregnation, 10g of HZSM-5 molecular sieve is taken in a 250ml beaker, then 5% of ammonium molybdate and 5% of nickel nitrate corresponding to the mass of the HZSM-5 molecular sieve are added respectively, and then 20 times the mass of deionized water corresponding to the mass of the HZSM-5 molecular sieve is mixed, vacuum impregnation is carried out for 12h, then the sample is dried, ground and sieved after drying at 100 DEG C, and the catalyst is placed in a muffle furnace and calcined at 600 DEG C for 4h, and then reduced at 450 DEG C for 6h with 10% H2 / Ar mixed gas to obtain the Ni-Mo / HZSM-5 catalyst;

[0011] 3) Co-pyrolysis:

[0012] The GCMS-QP2020 type Py-GC / MS (Shimadzu Corporation) is used for rapid pyrolysis experiment, the peak area normalization scanning method is used for qualitative and quantitative analysis of the pyrolysis products, the effects of pyrolysis temperature, catalyst and waste plastic on the distribution of rapid pyrolysis organic products of black liquor solids are discussed, the black liquor solids, waste plastic and catalyst are uniformly mixed according to the mass ratio of 10:10:1, and then dispersed on quartz wool, placed in a stainless steel crucible, and helium is used to maintain an inert atmosphere;

[0013] The gas chromatography detection conditions are as follows: SH-Rxi-5Sil MS capillary column (30mx0.25 mmx0.25 um), carrier gas is helium, flow rate is 1.0mL / min: initial column temperature is 50 DEG C, and maintained for 2min, then increased to 250 DEG C at a rate of 10 DEG C / min, and maintained for 8min; injection temperature is 250 DEG C, injection amount is 1ul, split ratio is 30:1.

[0014] In the present application:

[0015] The HZSM-5 molecular sieve in step 2) is selected from the catalyst factory of Nankai University, and the Si / Al is 50.

[0016] In step 2), the HZSM-5 molecular sieve is calcined in a muffle furnace at 550 DEG C for 4h, and the heating rate is 10 DEG C / min.

[0017] Step 3) the inert atmosphere is maintained using helium at a flow rate of 50 mL / min.

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

[0019] The application discloses a method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics by using Ni-Mo / HZSM-5 catalyst, and the high-quality bio-oil is prepared by co-pyrolyzing black liquor solids (black liquor solids) and waste plastics (polypropylene and polyethylene) by using the Ni-Mo / HZSM-5 catalyst. Research finds that the addition of plastics can significantly improve the yield of hydrocarbons. The total hydrocarbon increases by 6%, 78% and 45% respectively under the catalytic pyrolysis of the Ni-Mo / HZSM-5 catalyst compared with no catalyst when the black liquor solids, the black liquor solids and polypropylene, and the black liquor solids and polyethylene are used. The waste plastics have a synergistic effect on the pyrolysis of the black liquor solids (black liquor solids). When the black liquor solids and polyethylene are co-pyrolyzed, the yield of alkanes is the highest at 69.44% at a temperature of 650 DEG C. When the black liquor solids and polypropylene are co-pyrolyzed, the yield of alkanes is the highest at 44.9% at a temperature of 550 DEG C. The obtained pyrolysis bio-oil is mainly composed of hydrocarbons and is a high-quality bio-oil. Compared with traditional bio-oil, the content of hydrogen compounds in the co-pyrolysis bio-oil is high, and the performance is good. The research helps to realize the synergistic high-value utilization of the black liquor and the waste plastics, is expected to replace the traditional alkali recovery process and solve the environmental pollution problem caused by the waste plastics for a long time, realizes the resource utilization and high-value utilization of the black liquor and the waste plastics, and increases the value of a papermaking enterprise. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 FIG. 1 is an SEM spectrum of the Ni-Mo / HZSM-5 catalyst used in the method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics by using the Ni-Mo / HZSM-5 catalyst according to the embodiment of the present application;

[0021] Figure 2 FIG. 2 is an XRD spectrum of the Ni-Mo / HZSM-5 catalyst used in the method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics by using the Ni-Mo / HZSM-5 catalyst according to the embodiment of the present application;

[0022] Figure 3 FIG. 3 is a TG and DTG curve graph of the black liquor solids, polyethylene and polyethylene at 20 DEG C / min used in the method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics by using the Ni-Mo / HZSM-5 catalyst according to the embodiment of the present application;

[0023] Figure 4 FIG. 4 is a material component GCMS analysis analysis graph of the pyrolysis product of each raw material used in the method for preparing bio-oil by co-pyrolyzing black liquor solids and waste plastics by using the Ni-Mo / HZSM-5 catalyst according to the embodiment of the present application;

[0024] Figure 5is a graph of selectivity of different catalysts of the method for preparing bio-oil by catalyzing co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 to black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene at the same temperature;

[0025] Figure 6 is a graph of the effect of temperature of the method for preparing bio-oil by catalyzing co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 on pyrolysis of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application are further described below in conjunction with the examples.

[0027] Embodiment:

[0028] The method for preparing bio-oil by catalyzing co-pyrolysis of black liquor solids and waste plastics with Ni-Mo / HZSM-5 includes the following steps:

[0029] 1) Dry the dilute black liquor at 105°C to form black liquor solids, and place the black liquor solids in a dryer for standby. Select black liquor solids and polypropylene or polyethylene, and uniformly mix them with a mass ratio of 1:1 as co-pyrolysis experimental raw materials;

[0030] 2) Preparation of catalyst:

[0031] After the HZSM-5 molecular sieve (selected from the catalyst factory of Nankai University, Si / Al is 50) is cleaned and dried, it is then dehydrated at 105°C in an oven, and then calcined at 550°C for 4h in a muffle furnace (the temperature rising rate is 10°C / min). The Ni-Mo / HZSM-5 catalyst is prepared by vacuum impregnation method. Take 10g of HZSM-5 molecular sieve in a 250ml beaker, then add 0.5g of ammonium molybdate and 0.5g of nickel nitrate, and mix with 200mL of deionized water. After vacuum impregnation for 12h, the sample is dried at 100°C, ground and sieved, and then the catalyst is placed in a muffle furnace and calcined at 600°C for 4h. Then, the catalyst is reduced at 450°C for 6h with 10% H2 / Ar mixed gas to obtain the Ni-Mo / HZSM-5 catalyst;

[0032] 3) Co-pyrolysis:

[0033] The GCMS-QP2020 type Py-GC / MS (Shimadzu Corporation) was used for rapid pyrolysis experiment, and the peak area normalization scanning method was used for qualitative and quantitative analysis of the pyrolysis products. The effects of pyrolysis temperature, catalyst and waste plastics on the distribution of rapid pyrolysis organic products such as black liquor solids were discussed. The black liquor solids, waste plastics and catalyst were mixed uniformly according to the mass ratio of 10:10:1, and then dispersed on the quartz wool, placed in a stainless steel crucible, and helium gas (50 mL / min) was used to maintain an inert atmosphere. The gas chromatography detection conditions were as follows: SH-Rxi-5Sil MS capillary column (30 m x 0.25 mm x 0.25 um), carrier gas was helium, flow rate was 1.0 mL / min: initial column temperature was 50℃, maintained for 2 min, then increased to 250℃ at a rate of 10℃ / min, maintained for 8 min; injection temperature was 250℃, injection amount was 1 μL, split ratio was 30:1.

[0034] Experimental example:

[0035] 1. Method of the reference example

[0036] 2. Materials and methods

[0037] 2.1 Experimental raw materials

[0038] The dilute black liquor was taken from the kraft eucalyptus pulp production line of a company in Guangxi. Before the experiment, the dilute black liquor was dried at 105℃ to form black liquor solids, and placed in a dryer for standby. The plastics selected were polyethylene and polypropylene, both taken from Hengfa Plastic Factory, and the particle size was 1000 mesh. The ratio of black liquor to polypropylene and polyethylene was 1:1, and the mixture was used as the co-pyrolysis experimental raw material. The main physical property parameters and elemental analysis of the raw materials are shown in Table 1. The quartz wool was purchased from Aladdin Reagent Co., Ltd., and the plastics were dried overnight in an oven (105℃) before the experiment.

[0039] Table 1 Main elemental analysis (wt.%) of black liquor solids and different plastics.

[0040]

[0041]

[0042] 2.2 Experimental method

[0043] 2.2.1 Preparation of catalyst

[0044] HZSM-5 molecular sieve (selected from Nankai University Catalyst Factory, Si / Al is 50) was cleaned and dried, then dehydrated in an oven at 105°C, and then calcined in a muffle furnace (heating rate is 10°C / min) at 550°C for 4h. The Ni-Mo / HZSM-5 catalyst was prepared by vacuum impregnation method. 10g of HZSM-5 molecular sieve was taken in a 250ml beaker, then a certain amount of ammonium molybdate and nickel nitrate (metal ion mass accounts for 5% of the mass of the molecular sieve, bimetallic atom 1:1) and deionized water were added and mixed in a certain proportion, vacuum impregnated for 12h, then the sample was dried at 100°C, ground and sieved. The catalyst was calcined in a muffle furnace at 600°C for 4h, and then reduced with 10% H2 / Ar mixed gas at 450°C for 6h to obtain the Ni-Mo / HZSM-5 catalyst.

[0045] 2.2.2 Catalytic pyrolysis experiment

[0046] The GCMS-QP2020 type Py-GC / MS (Shimadzu Corporation) was used for rapid pyrolysis experiment, and the peak area normalization scanning method was used for qualitative and quantitative analysis of the pyrolysis products, to explore the effects of pyrolysis temperature, catalyst and waste plastics on the distribution of black liquor solid organic products in rapid pyrolysis. The black liquor, waste plastics and catalyst were mixed uniformly in a certain proportion and dispersed on quartz wool, placed in a stainless steel crucible, and helium gas (50mL / min) was used to maintain an inert atmosphere. The gas chromatography detection conditions: SH-Rxi-5Sil MS capillary column (30mx0.25 mmx0.25 um), carrier gas is helium, flow rate 1.0mL / min: initial column temperature 50°C, maintain for 2min, then increase to 250°C at a rate of 10°C / min, maintain for 8min; injection temperature 250°C, injection volume: 1μL, split ratio is 30:1.

[0047] 2.3 Separated product detection and characterization

[0048] The Elemantar:Vario EL cube type elemental analyzer was used to determine the element content in polypropylene, polyethylene and black liquor solids. The MINFLEX600 type X-ray diffractometer was used to analyze the crystal structure of the catalyst; the ESCALAB 250XI+ type X-ray photoelectron spectrometer was used to analyze the valence state of the catalyst; the FEI TECNAI G2 F30 type 300KV field emission transmission electron microscope was used to analyze the apparent morphology of the catalyst; the ASAP 2460 type specific surface area and porosity analyzer was used to analyze the pore size of the catalyst.

[0049] 2.4 Separation effect or extraction rate evaluation

[0050] The products from pyrolysis were directly introduced into GC / MS for on-line analysis and detection. The detected compounds were classified according to functional groups, and semi-quantitative analysis was performed using area normalization method. Since liquid products cannot be collected in the process of Py-GC / MS, the total peak area and relative peak area of compounds were used to calculate the yield of target hydrocarbon substances (W x , %)

[35] , as follows.

[0051] W x = (S x / ∑S i )*100% (1)S x - the peak area of a certain compound

[0052] S i - the peak area of various compounds

[0053] W x - the content percentage (%) of a certain compound

[0054] (2) The content of hydrocarbon substances in pyrolysis compounds was calculated, and the selectivity of various hydrocarbons was calculated, as follows.

[0055] W total = (S aromatichydrocarbon +S alkane +S olefin ) / ∑S i (2)S aromatic - the peak area of aromatic hydrocarbon compounds

[0056] S alkane - the peak area of alkane compounds

[0057] S olefin - the peak area of olefin compounds

[0058] S i - the total peak area of various compounds

[0059] 3. Results and discussion

[0060] 3.1 Characterization and analysis of catalysts

[0061] 3.1.1 Analysis of apparent morphology of Mo-Ni / HZSM-5

[0062] Figure 1 (a) and (b) SEM images of Ni-Mo / HZSM-5 and (c) STEM image of Ni-Mo-HZSM-5 catalyst and corresponding elemental mapping analysis (Ni, Mo).

[0063] The micro-morphology of the samples was observed by scanning electron microscopy (SEM). From the SEM images, it can be seen that the Mo-Ni / HZSM-5 catalyst has a uniform morphology, and the Mo-Ni / HZSM-5 catalyst has a uniform morphology.Figure 1 a, b, it can be seen that the Ni and Mo atoms are mainly supported on the surface of HZSM-5 in the form of small particles, and these nanoparticles promote the interaction between the catalyst and the reactants, thereby improving the performance of the catalytic reaction. The surface of the Ni-Mo / HZSM-5 catalyst is rough, but still maintains the same morphological characteristics as the carrier, showing a hexagonal shape. Energy dispersive spectroscopy analysis of the Ni-Mo / HZSM-5 catalyst found that the Ni and Mo atoms were uniformly distributed on the carrier. In addition, a clear layered structure was formed on the surface of the catalyst, which can provide more sites for catalytic reactions.

[0064] 3.1.2 Surface chemical composition of Mo-Ni / HZSM-5

[0065] Figure 2 XRD pattern of Ni-Mo / HZSM-5 catalyst

[0066] Figure 2 The XRD pattern of the Ni-Mo / HZSM-5 catalyst is shown. As can be seen from the figure, the Ni-Mo / HZSM-5 catalyst shows complete peaks, which indicates that the structure of the HZSM-5 molecular sieve is maintained during the preparation of the Ni-Mo / HZSM-5 catalyst, and that the framework structure of the HZSM-5 is not affected after impregnation of Ni and Mo. The Ni-Mo / HZSM-5 catalyst contains Ni and Mo metal nanoparticles. Based on the JCPDS NO 00-004-0850 card, the metal nanoparticle Ni shows a characteristic peak at 2θ of 44.51, as shown in Figure 2 Based on the JCPDS NO 00-004-0850 card, the metal nanoparticle Mo shows a characteristic peak at 2θ of 44.51, but it is not shown in the figure. Combined with the analysis of the electron microscope image, the possible reason is that the metal Mo nanoparticles are well dispersed in the HZSM-5.

[0067] 3.2 Effect of main catalytic process on pyrolysis products and their conversion rate

[0068] In order to realize the high-value utilization of black liquor and waste plastics, this study first analyzes the catalytic conversion characteristics of black liquor and two typical plastics, analyzes the effect of waste plastic addition on black liquor pyrolysis, and explores the effect of temperature and catalyst on the co-pyrolysis of black liquor solids and plastics. Secondly, the pyrolysis bio-oil is compared with the traditional bio-oil and the advantages of pyrolysis bio-oil are analyzed, and finally the catalytic mechanism is analyzed.

[0069] 3.2.1 Catalytic conversion characteristics of different raw materials

[0070] The TG and DTG curves of black liquor solids, polypropylene, and polyethylene under N2 atmosphere at a heating rate of 20℃ / min are shown in Figure 3 Figure 3 ​It can be seen that the pyrolysis temperature range of black liquor solid is very wide, from 30℃ to 1000℃, while the pyrolysis temperature range of polyethylene and polypropylene is narrow (from 0℃ to 498℃), and the pyrolysis of polypropylene is completed earlier than that of polyethylene, and the required pyrolysis temperature is the lowest, but they are both completely pyrolyzed at nearly 500℃, while at this time, nearly 47% of the components of black liquor solid are not decomposed, and the solid residue produced after the complete pyrolysis of black liquor solid is about 10.67%, which may be the residual alkali components in black liquor solid that are not easy to decompose. Figure 3 It can be seen that at 477℃, the maximum mass loss rate of polyethylene pyrolysis is -0.0280% / ℃, and the maximum mass loss rate of polypropylene is -0.020% / ℃ at 454℃. In the pyrolysis process, the temperature required to reach the maximum mass loss rate is polyethylene > polypropylene > black liquor solid, while the maximum mass loss rate is polyethylene < polypropylene < black liquor solid. When the pyrolysis temperature exceeds 500℃, polyethylene and polypropylene are completely pyrolyzed and no solid residue is produced.

[0071] 3.2.2 Analysis of the effect of adding waste plastics on black liquor pyrolysis

[0072] Figure 4 Material composition GCMS analysis of raw material pyrolysis products [a) content of each pyrolysis component of black liquor solid, content of each pyrolysis component of black liquor solid and polypropylene, content of each pyrolysis component of black liquor solid and polyethylene; b) GCMS analysis of the content of each pyrolysis component in the process of pyrolysis of polypropylene and polyethylene alone].

[0073] In order to study the promoting effect of waste plastics on black liquor pyrolysis products, the raw materials were separately pyrolyzed at 550℃ and mixed pyrolyzed (the mixing ratio of plastics to black liquor solid was 1:1). The main products analyzed from the ion chromatogram are as follows Figure 4a, the black liquor solid, the black liquor solid with polypropylene, and the black liquor solid with polyethylene thermal decomposition mainly produces oxygen-containing compounds, such as aldehydes, ketones, alcohols, phenolic esters, carboxylic acids and other substances (other substances mainly refer to some unidentified and heteroatomic compounds containing N and S elements) and the like. The black liquor solid pyrolysis products are mainly composed of phenolic compounds, hydrocarbons and ketone compounds, among which the phenolic compounds produced by pyrolysis are the most, accounting for 37.29% of the total content, mainly from lignin and its fragments; followed by hydrocarbon substances. As can be seen from the figure, a small amount of alcohol, ketone, aldehyde, acid substances are produced by black liquor pyrolysis. These substances may be produced by the pyrolysis of carbohydrates in the black liquor. When polyethylene is co-pyrolyzed with black liquor solids, the phenolic compounds decrease from 37.29% to 17.86%, and the hydrocarbon compounds increase from 14.92% to 35.39%. This is because polyethylene mainly produces aliphatic alkanes and alkenes after pyrolysis, so the hydrocarbon compounds increase significantly. At the same time, the alcohol, acid, aldehyde and ester substances also increase, which shows that polyethylene promotes the pyrolysis of black liquor solids. This is because the oxygen-containing groups produced by the pyrolysis of black liquor solids are transferred to the small molecules of polyethylene depolymerization, resulting in a decrease in hydrocarbon compounds and an increase in oxygen-containing groups when polyethylene is co-pyrolyzed with black liquor solids. When polypropylene is co-pyrolyzed with black liquor solids, the phenolic compounds decrease from 37.29% to 10.34%, and the hydrocarbon compounds increase from 14.92% to 25.92%. At the same time, the alcohol, acid, aldehyde and ester substances also increase, which also shows that polypropylene promotes the pyrolysis of black liquor solids. However, as can be seen from the figure, the content of alcohol, acid, aldehyde and ester produced by co-pyrolysis of polypropylene and black liquor solids is higher than that of polyethylene and black liquor solids. This is because the pyrolysis temperature of polypropylene is slightly lower than that of polyethylene (as can be seen from the thermogravimetric curve). Under high temperature conditions, the carbohydrates in the black liquor are preferentially pyrolyzed, and these carbohydrate-derived free radicals initiate the chain scission of polypropylene polymer in the early stage of co-pyrolysis. Therefore, the hydrogen proton is transferred from the polypropylene chain to the carbohydrate-derived free radical, thereby stabilizing the degradation products of the carbohydrate. This mechanism helps to increase the yield of hydrocarbons and limit the formation of coke. The main products of polypropylene and polyethylene pyrolysis at 550°C are as follows Figure 4The main products of polypropylene pyrolysis are aromatic hydrocarbons and alkanes, while the main products of polyethylene pyrolysis are alkanes, olefins and alicyclic hydrocarbons. In the pyrolysis process, they are mainly decomposed from long carbon chains into short carbon chain substances, so there is no generation of oxygen-containing substances. As can be seen from the figure, the aromatic hydrocarbons generated by pyrolysis of polypropylene are greater than those of polyethylene, indicating that polypropylene is more prone to aromatization than polyethylene. The possible reason is that the thermal decomposition temperature of polypropylene is lower than that of polyethylene, so the degree of depolymerization of polypropylene is greater, and therefore the content of aromatic hydrocarbons and alkanes generated is more. Therefore, after adding polypropylene or polyethylene, the black liquor solids pyrolysis generates more hydrocarbon substances and oxygen-containing group substances, and the pyrolysis is more complete, indicating that the addition of polypropylene or polyethylene promotes the pyrolysis of black liquor solids.

[0074] 3.2.3 Effect of catalyst on pyrolysis of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene

[0075] The raw materials were selected to carry out separate catalytic pyrolysis and mixed catalytic pyrolysis (the mixing ratio of plastics and black liquor solids was 1:1, and the catalyst amount was 10% of the black liquor solids) at 450°C, and the catalytic effect of the catalyst was analyzed.

[0076] Figure 5 The selectivity of different catalysts to the pyrolysis products of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene at the same temperature is shown.

[0077] a, d, g) respectively represent the content of each pyrolysis product of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene. b, e, h) respectively represent the hydrocarbon content and composition in the pyrolysis products of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene. c, f, i) respectively represent the selectivity of various hydrocarbons in the pyrolysis products of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene.

[0078] The main products, hydrocarbon content and selectivity of various hydrocarbons from ion chromatogram analysis are shown in Figure 5 As can be seen from the figure, the main components of black liquor solids pyrolysis are phenolic compounds, alcohol compounds and hydrocarbon compounds Figure 5a) Without catalyst, the pyrolysis of alcohol and phenolic substances has high content, and their components respectively account for 26.8% and 40.21%. Under the catalysis of HZSM-5, the hydrocarbon substances increase from 11.38% to 15.94%, while the phenolic and alcohol substances decrease obviously, and the acid substances increase. This is because the deoxidation and alkylation of HZSM-5 lead to the transfer of oxygen-containing groups, so more hydrocarbon and acid substances are generated, and some substances with insufficient volatility cannot be detected by gas chromatography. The pyrolysis effect is more obvious with the addition of Mo-Ni / HZSM-5 catalyst. First, the hydrocarbon substances increase from 11.38% and 15.94% to 23.63%. This is because the small-molecule oxygen-containing compounds (such as furan, smaller aldehyde and water) after the depolymerization of carbohydrates in black liquor penetrate the catalyst pores and undergo a series of reactions (dehydration, dehydrogenation, decarboxylation, decarbonylation, oligomerization and isomerization) to form monocyclic aromatic hydrocarbons and olefins, so the content of hydrocarbon substances increases, and it also indicates that the Mo-Ni / HZSM-5 catalyst has obvious hydrogenation deoxidation effect. From Figure 5 b and Figure 5 c It can be seen from the analysis that with the addition and improvement of the catalyst, the content and selectivity of alkanes and olefins are increasing, and the yield of aromatic hydrocarbons is decreasing, which indicates that Mo-Ni / HZSM-5 promotes the catalytic cracking of lignin and its oligomers, and promotes the further deoxidation and ring-opening of lignin to fatty hydrocarbons. From Figure 5 d It can be seen that the main components of black liquor solids and polyethylene pyrolysis are phenolic and hydrocarbon compounds. Without catalyst, the main pyrolysis products are phenolic, acid and hydrocarbon substances, among which acid accounts for the largest proportion, accounting for 33.4%. Under the catalysis of HZSM-5, the hydrocarbon substances increase from 25.84% to 27.58%, increasing by 1.74%, while the acid substances decrease obviously, and the phenolic substances increase. This may be because the co-feeding of polyethylene ensures the existence of olefins in the pyrolysis reaction, and the Diels-Alder reaction between furan and olefins will form Diels-Alder adducts, and after dehydration, aromatic hydrocarbons are produced, so the content of aromatic hydrocarbons increases. After adding Mo-Ni / HZSM-5 catalyst, the phenolic substances produced by pyrolysis decrease from 29.48% to 15.9%, and the hydrocarbon substances increase to 37.36%. Compared with the same condition without catalyst, the hydrocarbon substances increase by 1.45 times, indicating that Mo-Ni / HZSM-5 promotes the pyrolysis of black liquor solids in the catalytic pyrolysis process. From Figure 5 e, f It can be seen from the analysis that after adding Mo-Ni / HZSM-5 catalyst, the content and selectivity of aromatic hydrocarbons and alkanes are first increased and then decreased, while the content and selectivity of olefins are increasing. The possible reason may be that the pyrolysis temperature of polypropylene is high, and the pyrolysis is not sufficient, which does not better cooperate with the pyrolysis of black liquor solids. From Figure 5As can be seen from the data, the main components of black liquor solids and polypropylene pyrolysis are phenols, alcohols, and hydrocarbons. Without a catalyst, the main pyrolysis products are alcohols, phenols, acids, and hydrocarbons, with similar proportions. Under HZSM-5 catalysis, the hydrocarbon content increased from 18.04% to 22.41%, while alcohols decreased significantly and acids increased. This is because the addition of polypropylene leads to more complete black liquor solids pyrolysis, and HZSM-5 promotes the transfer of oxygen-containing groups from carbohydrates in the black liquor solids, thus generating more hydrocarbons and acids. After adding the Mo-Ni / HZSM-5 catalyst, the phenolic compounds produced during pyrolysis decreased from approximately 18.76% and 19.38% to 9.17%, while hydrocarbon compounds increased significantly, rising from 18.04% and 22.41% to 32.16%. Compared to the same conditions without a catalyst, hydrocarbon compounds increased by 1.78 times, indicating that the Mo-Ni / HZSM-5 catalyst promoted the co-pyrolysis of polypropylene and black liquor solids. Simultaneously, from Figure 5 Analysis of the .h,i model shows that the content and selectivity of aromatic hydrocarbons and olefins decrease after the addition of the Mo-Ni / HZSM-5 catalyst, while the content and selectivity of alkanes increase. This indicates that Mo-Ni / HZSM-5 promotes the alkylation reaction of unsaturated substances in the pyrolysis process, and promotes their further hydrogenation, deoxygenation and ring-opening to transfer to saturated hydrocarbons.

[0079] 3.2.4 Figure 6 The effect of temperature on the pyrolysis of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene;

[0080] To analyze the effect of pyrolysis temperature on pyrolysis products, the raw material was selected and subjected to individual and mixed catalytic pyrolysis at Ni-Mo / HZSM-5 catalyst at pyrolysis temperatures of 450℃, 550℃, and 650℃ (the mixing ratio of plastic and black liquor solids was 1:1, and the catalyst amount was 10% of the black liquor solids). The main products, hydrocarbon content, and selectivity of various hydrocarbons were analyzed from ion chromatograms as follows: Figure 6 As shown. From Figure 6 As shown in .a, during the temperature increase, the production of alcohols and hydrocarbons from the pyrolysis of black liquor solids decreases, while the production of acids increases. The yields of liquid and gaseous products from the pyrolysis of black liquor samples increase with increasing temperature. Higher temperatures promote the depolymerization of carbohydrates in the black liquor solids; therefore, at 550℃, alcohols are mainly produced, and at 650℃, depolymerization is more pronounced, mainly producing acids and aldehydes. Phenolic compounds have the highest content at 550℃, accounting for 52.52%, while hydrocarbons account for 20.38% at this temperature. Temperatures that are too low or too high will affect the yield of phenols. Figure 6b, c, it can be seen that the content and selectivity of aromatic hydrocarbons and olefins first increase and then decrease, and the content of alkanes decreases, which is mainly due to the promotion of lignin depolymerization at high temperature. Lignin polymer preferentially depolymerizes into monomers, and the methoxy group of lignin side chain is initially likely to be cracked by high temperature and acidity of the catalyst, which leads to the transfer of phenolic compounds to aromatic hydrocarbons. From Figure 6 , d, it can be seen that during the temperature rise, the alcohol, phenolic and ketone substances produced by the catalytic pyrolysis of black liquor solids and polyethylene decrease with the increase of reaction temperature, and the hydrocarbon substances increase with the increase of temperature, which shows that the increase of temperature promotes the pyrolysis of polyethylene. Therefore, the content of hydrocarbon substances in the pyrolysis products is the most at 650℃, accounting for 69.44%. This is because the pyrolysis temperature of polyethylene is high (known from the thermogravimetric curve). When the temperature continues to rise, the low molecular substances produced by the pyrolysis of polyethylene play a dispersing and promoting role in the pyrolysis process of black liquor solids. Increasing the pyrolysis temperature is beneficial to the formation of small molecular organic oxygen fragments that can enter the pores of the zeolite catalyst. On the other hand, higher temperature leads to the increase of small gas phase components, especially carbon oxides. Under the action of the catalyst, the oxygen-containing substances produced by pyrolysis undergo alkylation transfer reaction, so there are more hydrocarbon substances. From Figure 6 .e and Figure 6 .f, it can be seen that the content of aromatic hydrocarbons first decreases and then increases with the increase of temperature. This is because the stability of these intermediates produced by lignin pyrolysis is not as good as that of phenols, and they can be fragmented into smaller units under harsh conditions to enter the pores of the zeolite catalyst for actual aromatization. Figure Figure 6 .f shows that the content of olefins increases with the increase of temperature, the selectivity of alkanes and aromatic hydrocarbons decreases, and the selectivity of alkanes increases. From Figure 6 , g, it can be seen that during the temperature rise, the alcohol, hydrocarbon substances produced by the catalytic pyrolysis of black liquor solids and polypropylene first increase and then decrease with the increase of reaction temperature, and the acid substances first decrease and then increase. The increase of temperature promotes the pyrolysis of polypropylene, so the content of hydrocarbon substances in the pyrolysis products is the most at 550℃, accounting for 44.9%. When the temperature continues to rise, the low molecular substances produced by the pyrolysis of polypropylene combine with the oxygen-containing substances produced by the pyrolysis of black liquor solids, so the content of alcohol and acid increases. From Figure 6 .h and Figure 6 .i, it can be seen that the content of alkanes, olefins and aromatic hydrocarbons first increases and then decreases with the increase of temperature, the selectivity of alkanes and olefins decreases, and the selectivity of aromatic hydrocarbons increases.

[0081] ​Ni-Mo / HZSM-5 catalyzed co-pyrolysis of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene at different temperatures. a, d, g) represent the content of each pyrolysis product of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene, respectively. b, e, h) represent the content and composition of hydrocarbons in the pyrolysis products of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene, respectively. c, f, i) represent the selectivity of various hydrocarbons in the pyrolysis products of black liquor solids, black liquor solids and polyethylene, and black liquor solids and polypropylene, respectively.

[0082] 3.3 Comparison of pyrolysis products and typical bio-oil

[0083] Under the optimal process, the ratio of black liquor solids to polypropylene raw material was 1:1, the pyrolysis temperature was 550°C, and Ni-Mo / HZSM-5 was selected as the catalyst. The black liquor and waste plastic were catalytically pyrolyzed to prepare biofuels. From the components of the pyrolysis products, there were phenols, alcohols, ethers, aldehydes, acids, ketones, esters, and hydrocarbons in the pyrolysis products, among which hydrocarbons and alcohols were the most, accounting for 44.9%. (The main components of traditional bio-oil are benzene ring-containing substances, hydrocarbons, aldehydes, carboxylic acids, and sugars, accounting for 15-30%, 1-10%, 15-25%, 5-20%, and 15-30%, respectively. From the component analysis, the biofuel prepared by catalytic pyrolysis of black liquor and plastic belongs to or is similar to bio-oil. However, due to the high content of hydrocarbons in the pyrolysis products, the hydrogen content is high. Therefore, from the component analysis of the pyrolysis products, the bio-oil prepared by catalytic pyrolysis of black liquor and waste plastic is a high-quality bio-oil.

[0084] CONCLUSION

[0085] It is of great significance to solve the problem of black liquor in paper mill and reduce plastic solid waste pollution by studying the synergistic high-value utilization of black liquor and waste plastics. In this paper, the preparation of high-quality bio-oil by co-pyrolysis of black liquor and waste plastics with Ni-Mo / HZSM-5 catalyst was studied. The co-pyrolysis mechanism of polypropylene, polyethylene and black liquor solids was studied, and the effects of catalyst type and temperature on the yield of pyrolysis bio-oil were discussed. The results showed that waste plastics had a synergistic effect on the pyrolysis of black liquor solids (black liquor solids), and the addition of plastics could effectively increase the yield of hydrocarbons, thus facilitating the production of high-quality bio-oil. Ni-Mo / HZSM-5 played a role in hydrogenation and deoxidation during the pyrolysis of black liquor solids, black liquor solids and polypropylene, and black liquor solids and polyethylene. Increasing the temperature appropriately could promote the co-pyrolysis of black liquor solids and polypropylene, and black liquor solids and polyethylene, and increase the yield of hydrocarbons. Compared with traditional bio-oil, the hydrogen content in co-pyrolysis bio-oil was high, and the performance was better. This study helps to realize the synergistic high-value utilization of black liquor solids and waste plastics, and is expected to replace the traditional alkali recovery process and solve the environmental pollution problem caused by waste plastics for a long time, realize the resourceization and high-value utilization of black liquor and waste plastics, and increase the value of papermaking enterprises and help to achieve "carbon neutralization". Follow-up studies will be carried out on scale-up experiments, and the technology will be evaluated from the aspects of energy consumption, economy, and environmental impact, in order to guide actual production.

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[0146] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing bio-oil by co-pyrolysis of black liquor solids and waste plastics using Ni-Mo / HZSM-5 catalyst, characterized in that: It comprises the following steps: 1) The dilute black liquor is dried at 105°C to form black liquor solids, which are stored in a dryer for later use. The black liquor solids are mixed with waste plastics in a mass ratio of 1:1, and the waste plastics are waste polypropylene or polyethylene, as co-pyrolysis experimental raw materials; 2) Preparation of catalyst: The HZSM-5 molecular sieve is cleaned and dried, then dehydrated at 105°C in an oven, and then calcined at 550°C for 4h in a muffle furnace. A Ni-Mo / HZSM-5 catalyst is prepared by vacuum impregnation. 10g of HZSM-5 molecular sieve is placed in a 250ml beaker, then 5% of ammonium molybdate and 5% of nickel nitrate, which are equivalent to the mass of the HZSM-5 molecular sieve, are added, and then 20 times the mass of deionized water, which is equivalent to the mass of the HZSM-5 molecular sieve, is added. After vacuum impregnation for 12h, the sample is dried at 100°C, ground and sieved, and then placed in a muffle furnace at 600°C for calcination for 4h. Then it is reduced at 450°C for 6h using 10% H2 / Ar mixed gas to obtain the Ni-Mo / HZSM-5 catalyst; 3) Co-pyrolysis: A GCMS-QP2020 type Py-GC / MS is used for rapid pyrolysis experiment. The pyrolysis products are qualitatively and quantitatively analyzed by peak area normalization scanning method. The black liquor solids, waste plastics and catalyst are mixed in a mass ratio of 10:10:1 and evenly dispersed on quartz wool, placed in a stainless steel crucible, and a helium gas is used to maintain an inert atmosphere; Gas chromatography detection conditions: SH-Rxi-5Sil MS capillary column 30mx0.25mmx0.25um, carrier gas is helium, flow rate is 1.0mL / min: initial column temperature is 50°C, maintained for 2min, then increased to 250°C at a rate of 10°C / min, maintained for 8min; injection temperature is 250°C, injection volume is 1μL, split ratio is 30:

1.

2. The method for preparing bio-oil by co-pyrolysis of black liquor solid and waste plastics with Ni-Mo / HZSM-5 catalyst according to claim 1, characterized in that: The HZSM-5 molecular sieve in step 2) is selected from the catalyst factory of Nankai University, and the Si / Al ratio is 50.

3. The method of claim 1 for the production of bio-oil by co-pyrolysis of black liquor solids and waste plastics using Ni-Mo / HZSM-5 catalyst, characterized in that: In step 2), the calcination in the muffle furnace at 550°C for 4h is at a heating rate of 10°C / min.

4. The method of claim 1 for producing bio-oil by co-pyrolysis of black liquor solids and waste plastics using Ni-Mo / HZSM-5 catalyst, characterized in that: In step 3), the helium gas is used to maintain an inert atmosphere, and the helium gas flow rate is 50mL / min.

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