CN115895736B - A method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin - Google Patents

Abstract

The invention discloses a method for preparing low-carbon olefin and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin. The method comprises the following steps: pyrolysis gasification: mixing the pretreated waste plastic with alkali lignin, and performing pyrolysis gasification to generate a gas-phase product, a liquid-phase product and a solid-phase product; adding a catalyst into the liquid phase product to perform catalytic conversion to obtain an olefin product; the gas phase product is subjected to chemical chain reforming with an oxygen carrier and then reacts with water vapor to obtain hydrogen; calcining the reacted oxygen carrier in air atmosphere, and then entering a step S3 for cyclic reaction. According to the invention, the alkali lignin and the waste plastics are mixed for pyrolysis gasification, and the pyrolysis gasification of the alkali metals such as Na, al and the like in the alkali lignin is utilized to generate a catalytic synergistic effect on the waste plastics, so that the recovery yield of olefins in the waste plastics is improved, the added value of products is improved, the synergistic resource utilization of wastes is realized, and the efficient, clean and high-value utilization of the waste plastics is realized.

Description

A method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin

Technical Field

The present invention belongs to the technical field of waste plastic recycling, and more specifically, relates to a method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastic with alkali lignin.

Background technique

Plastics are important organic synthetic polymer materials with a wide range of applications. Waste plastics are a general term for plastics that have been eliminated or replaced in industrial production and people's daily lives, including waste plastic films, plastic threads and woven products, plastic packaging boxes and containers, plastic bags and ground films, etc. In addition, plastics used in automobiles, electronic appliances and home appliances in my country have also become one of the important sources of waste plastics. The rapid increase in the output of waste plastics has caused a series of social problems, and it is imperative to vigorously develop the waste plastic recycling industry.

Alkali lignin is a byproduct of the papermaking industry after separating cellulose from plants. It is rich in lignin, alkaline metals and inorganic salt components. my country's alkali lignin production is huge. The papermaking industry separates about 30 million tons of cellulose from plants every year, and obtains about 10 million tons of alkali lignin byproducts. The calorific value of alkali lignin directly used as fuel is not high, and it is easy to corrode boilers and pipeline equipment. There is a bottleneck in the treatment of alkali metals in the recycling process. At present, only a small part of alkali lignin is made into high-value-added products such as water reducers and dispersants through oxidation, sulfonation and other reaction processes. Most of the alkali lignin is discarded or concentrated as auxiliary fuel, which not only causes a huge waste of resources but also poses an environmental threat.

On the other hand, low-carbon olefins (ethylene, propylene, butene) are important platform compounds, important raw materials and intermediates for fine chemicals such as syngas detergents and pharmaceuticals, and are widely used. Hydrogen energy is a clean and efficient secondary energy source and an important chemical raw material. It is rich in resources, has a wide range of sources, is clean and efficient, and is known as the energy of the 21st century.

The Chinese invention patent "A method for dechlorinating waste plastic cracking oil" discloses that the waste plastic cracking oil is reacted with hydrogen under the action of a hydrogenation catalyst, and the hydrogenation product oil is obtained after oil and gas separation, and then mixed with an adsorbent to obtain an oil product after adsorption and dechlorination. The Chinese invention patent "A waste plastic pyrolysis carbonization system" discloses that the waste plastic is crushed and then incinerated and pyrolyzed to improve the pyrolysis efficiency. The Chinese invention patent "An efficient waste plastic recycling granulator and granulation method" discloses a machine frame, a plasticizing device, a cooling device and a particle forming device, which simplifies the waste plastic granule production process and reduces energy consumption. The Chinese invention patent "A sealed automatic feeding device and method for a waste plastic pyrolysis treatment system" discloses a pretreatment system, a liquefaction tank, a multi-stage liquid cyclone, a plastic pyrolysis system, a waste heat recovery system, a flue gas purification system, an oil-water separation system, etc. The Chinese invention patent "A method and system for producing low-carbon olefins and aromatics from waste plastic oil" discloses that the waste plastic oil is separated by adsorption and desorption to obtain residual oil and desorbed oil, and then subjected to multiple catalytic cracking to obtain low-carbon olefins and aromatics products.

The above patents involve recycling processes such as granulation, pyrolysis and carbonization of waste plastics, but do not involve further high-value utilization processes of waste plastics, making it difficult to fundamentally increase the added value of the products. In the recycling of waste plastics, it is often necessary to obtain mixed products of low-carbon olefins and aromatics from waste plastic oil through multiple cracking processes.

Summary of the invention

In view of the above-mentioned existing technical problems, the purpose of the present invention is to provide a method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin, wherein alkali lignin and waste plastics are mixed for pyrolysis and gasification, and alkali metals such as Na and Al in alkali lignin are used to produce catalytic synergy on the pyrolysis and gasification of waste plastics, thereby improving the recovery yield of olefins in waste plastics, increasing the added value of products, realizing coordinated resource utilization of wastes, and realizing efficient, clean and high-value utilization of waste plastics.

In order to achieve the above object, the present invention is implemented by the following technical solutions:

A method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin comprises the following steps:

S1. Pyrolysis and gasification: The pretreated waste plastics are mixed with alkali lignin and pyrolyzed and gasified at 190-1000°C to generate gas phase products, liquid phase products and solid phase products;

S2. Preparation of olefins: adding a catalyst to the liquid product in step S1 and performing catalytic conversion at 300 to 1000° C. to obtain an olefin product; the catalyst component is selected from one or more of Si, O, Ca, A, Na, K or Cu;

S3. Chemical loop reforming: The gas phase product in step S1 is chemically loop reformed with an oxygen carrier at 800-1000° C.; the active component of the oxygen carrier is selected from one or more of Fe, Mn, Co, Ce, Cu, Ca, Al, Si or La;

S4. Hydrogen preparation: reacting the oxygen carrier obtained by chemical chain reforming in step S3 with water vapor at 700 to 1000° C. to obtain hydrogen;

S5. Regeneration of oxygen carrier: calcine the oxygen carrier after the reaction in step S4 in an air atmosphere at 800-1000°C, and the oxygen carrier after the reaction enters step S3 for a cyclic reaction.

The present invention uses waste plastics coupled with alkali lignin, and then performs pyrolysis and gasification, and utilizes alkali metals such as Na and Al in alkali lignin to produce catalytic synergy on the pyrolysis and gasification of waste plastics. Alkali metals such as Na and Al exist in the form of Na ₂ CO ₃ /γ-Al ₂ O ₃ in the reaction, showing strong decarboxylation and bond breaking effects, as well as strong selectivity for olefins and alkanes. Under the catalysis of the alkali metals, the distribution and selectivity of liquid products produced in the pyrolysis and gasification process of waste plastics are further improved and enhanced, and finally solve the technical problems of low olefin product yield, low product added value, low resource conversion rate, and alkali metal treatment in the recycling of alkali lignin in the traditional waste plastic regeneration process. The alkali lignin added in the present invention, after pyrolysis and gasification with the waste plastics, produces gas phase products, liquid phase products and solid phase products, the liquid phase products can be used to prepare low-carbon olefins, the gas phase products can be used to prepare high-purity hydrogen, and the solid phase products are burned by a burner for heat recovery. The present invention can not only cleanly and efficiently convert waste plastics and alkali lignin directly into olefins and high-purity hydrogen, but also co-produce carbon black for combustion and heating. After being processed by the processing process of the present invention, the product has less ash content and can be used as a binder for coal briquette gasification, a grinding aid for cement production, and a bonding agent for ceramic and refractory material production.

The low-carbon olefins described in the present invention are olefins with carbon atoms between 2 and 4, that is, a general term for small molecule olefins such as ethylene, propylene and butene.

Specifically, the composition of the alkali lignin used in the present invention is: carbon element accounts for 43.99%, N element accounts for 0.29%, and hydrogen element accounts for 4.77%.

Preferably, in step S1, the reaction temperature of the pyrolysis and gasification is 190-1000°C.

Further preferably, in the step S1, the reaction temperature of the pyrolysis and gasification is 550-750°C.

Preferably, in step S2, catalytic conversion is carried out at 500-600°C.

Specifically, in step S2, the catalyst is a catalyst component conventionally used in the art.

Specifically, in step S3, the oxygen carrier is an oxygen carrier component conventionally used in the art.

Preferably, the mass ratio of the alkali lignin to the pretreated waste plastic is in the range of (0.10-0.99): 1. Within this ratio range, the alkali lignin and the waste plastic have a good catalytic synergistic effect. The inventors have found through long-term research that when the ratio of alkali lignin to waste plastic is lower than the above mass ratio range, the catalytic synergistic effect is not obvious; and when the ratio of alkali lignin to waste plastic exceeds the above mass ratio range, although it has a certain catalytic synergistic effect, the alkali lignin introduces too many impurities, which affects the material fluidity and selectivity of olefin products during the pyrolysis and gasification of waste plastics, and reduces the olefin yield.

Further preferably, the mass ratio of the alkali lignin to the pretreated waste plastic is in the range of (0.60-0.99):1.

Preferably, the particle size of the alkali lignin is in the range of 40 to 200 meshes. Alkali lignin in this particle size range is easier to feed, and is also convenient for heat and mass transfer during the reaction to fully react.

Preferably, the particle size of the oxygen carrier is in the range of 20 to 80 meshes.

Preferably, in step S1, a gasifying agent is further added, and the gasifying agent is water vapor and/or air. The gasifying agent can promote the conversion efficiency of the raw material.

Preferably, in step S1, an inhibitor is also added, and the inhibitor is a Ca-based inhibitor, specifically calcium oxide. The inhibitor can inhibit the generation of chlorine-containing pollutants during the pyrolysis and gasification of waste plastics and reduce the formation of chlorine-containing precursors.

Preferably, in step S1, the reaction time of the pyrolysis and gasification is 0.5 to 10 hours.

Preferably, in step S3, the reaction time of the chemical chain reforming is 10 to 40 minutes.

Preferably, in step S5, the oxygen carrier is calcined in an air atmosphere at 800-1000° C. for 60-80 min.

Preferably, in the step S2, the liquid phase product is further subjected to a refining process before being added to the catalyst, and the refining process includes a denitrification refining process, a dechlorination refining process and a desiliconization refining process.

Preferably, in step S3, the gas phase product is purified by spraying with alkali solution and then chemically reformed with the oxygen carrier. The reformed tail gas obtained after chemically reforming can continue to be burned to provide heat for the system.

Preferably, the pretreatment includes pulverization and/or magnetic separation; the pulverization is to pulverize the waste plastic to obtain waste plastic particles with a particle size range of 5 to 50 mm; the magnetic separation is to remove metallic foreign matter from the waste plastic.

More preferably, before the crushing process, the waste plastics are further subjected to drying process to reduce the moisture content of the waste plastics to below 15%.

Preferably, in step S1, a mechanical stirring feeding device is used to transport the mixture of waste plastics and alkali lignin to the gasification reactor to achieve continuous feeding of the mixture. The mechanical stirring feeding device is a lower rotary stirring feeding device; a water-cooled variable pitch screw is provided to achieve self-sealing of the material during the transportation process, thereby ensuring the control of the oxygen content in the pyrolysis system.

Specifically, the solid phase product is usually carbon black, which can be subsequently used for combustion heating, industrial boiler heating or industrial filler (such as filler in rubber).

Compared with the prior art, the present invention has the following beneficial effects: the present invention uses waste plastics coupled with alkali lignin for pyrolysis and gasification, and utilizes alkali metals such as Na and Al in alkali lignin to produce catalytic synergy for the pyrolysis and gasification of waste plastics, thereby solving the technical problems of low olefin product yield, low product added value, low resource conversion rate, and alkali metal treatment in the traditional waste plastic regeneration process, as well as alkali lignin recycling. The present invention can directly convert waste plastics and alkali lignin into low-carbon olefins and high-purity hydrogen in a clean and efficient manner, and can also co-produce carbon black for combustion and heating. The present invention has the advantages of simple process, low cost and high product added value.

Detailed ways

The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

In addition, unless otherwise specified, the reagents and materials used in the following examples are commercially available.

Example 1

A method for preparing low-carbon olefins and co-producing high-purity hydrogen by coupling waste plastics with alkali lignin comprises the following steps:

(1) Crushing: After the waste plastics are initially sorted and screened to remove metal, glass, soil and other debris, they are dried to reduce the moisture content of the waste plastics to less than 15%. The dried waste plastics are fed into a crusher and crushed into waste plastic particles with a particle size range of 5 to 15 mm.

(2) Magnetic separation: waste plastic particles enter the conveyor belt, and the metal foreign matter in the waste plastic particles is screened and separated in the magnetic separation area to prevent the subsequent metal foreign matter from interfering with the waste plastic molding process. The equipment used in the magnetic separation process includes drum screens, magnetic separators, belt conveyors, etc.

(3) Pyrolysis and gasification: The waste plastic particles after magnetic separation are mixed with alkali lignin with a particle size of 100 mesh at a mass ratio of 0.02:1 and enter the pyrolysis and gasification process. The reaction is carried out at 500°C for 3 hours to generate gas phase products, liquid phase products and solid phase products. In the pyrolysis and gasification process, the waste plastic particles enter the gasification reactor through a stirring feeding device to achieve continuous feeding of the waste plastics. At the same time, a water-cooled variable pitch screw is set in the screw feeder to achieve self-sealing of the material during the transportation process. The inhibitor CaO is added;

(4) Olefin preparation: After the liquid product is purified by denitrification, chloride and silicide, it enters the catalytic conversion stage. Under the action of the catalyst, it reacts at 450°C for 30 minutes to obtain olefin products and a small amount of liquid phase, which is circulated and refluxed for reaction; the active components of the catalyst include Si/O/Ca/Al/Na;

(5) Chemical chain reforming: A Fe/Co/Cu/Si-based composite oxygen carrier is constructed by chemical precipitation method, and then calcined at 800-900°C for 3 hours, and then crushed and sieved to prepare oxygen carrier particles with a particle size range of 40-60 mesh; the gaseous product produced by pyrolysis and gasification is sprayed and purified with an alkali solution containing Na ^+, and then chemically reformed with the oxygen carrier. The gaseous product and the oxygen carrier are in contact at high temperature, and the oxygen carrier is in a fixed state or a bubbling fluidized state. The active components in the gaseous product react with the lattice oxygen of the oxygen carrier, and the oxygen carrier is reduced to a low-valent oxide. The reaction temperature of the chemical chain reforming is 850°C, and the reaction time is 30 minutes. The tail gas after reforming can be burned to provide heat for the system;

(6) Hydrogen production process: reacting the oxygen carrier after the reaction in step (5) with high-temperature water vapor at 800° C. for 25 min to obtain high-purity hydrogen;

(7) Regeneration of oxygen carriers: The oxygen carriers after the reaction in step (6) are regenerated in a high temperature air atmosphere at 900°C for 60 minutes; the reaction heat obtained during the regeneration process is circulated through the oxygen carrier to provide heat for the chemical loop reforming and hydrogen production processes.

Implementation results: By gas chromatography (GC) test, the relative composition of the olefin product in step (4) is: the content of _C2 -C4 _olefins is 32.39%, the content of _C2 - _C4 alkanes is 8.35%, the content of C5 ₊ products is 2.11%, and the content of other gases such as _H2 /CO/ _CO2 / _CH4 is 56.17%; the fuel conversion efficiency is 61.17%. In step (6), during the chemical chain hydrogen production process, the hydrogen yield is 0.85L/g and the _H2 concentration is 89.11%.

Embodiments 2 to 9

The differences between Examples 2 to 9 and Example 1 are shown in Table 1 below.

Comparative Example 1

The differences between Comparative Example 1 and Example 1 are shown in Table 1 below.

Table 1

The test data of Examples 1 to 5 and Comparative Example 1 are shown in Table 2 below.

Table 2

It can be seen from the above-mentioned Examples 1 to 5 that the present invention uses waste plastics coupled with alkali lignin for pyrolysis and gasification, and utilizes alkali metals such as Na and Al in alkali lignin to produce catalytic synergy for the pyrolysis and gasification of waste plastics. The yield of the low-carbon olefins finally prepared is between 32% and 66%; the fuel conversion efficiency is between 61% and 96%, and the yield and fuel conversion efficiency of the low-carbon olefins in Examples 6 to 10 are also within this range. Furthermore, under the preparation conditions of Examples 2 to 5, the yield of the low-carbon olefins finally prepared is between 55% and 66%; the fuel conversion efficiency is higher than 90%. It can be seen that the present invention can cleanly and efficiently convert waste plastics and alkali lignin directly into low-carbon olefins and high-purity hydrogen, and can also co-produce carbon black for combustion and heating. The present invention has the advantages of simple process, low cost and high added value of products.

The foregoing examples are merely illustrative and are used to explain some features of the method of the present invention. The appended claims are intended to require the widest possible range that can be imagined, and the embodiments presented herein are demonstrated by the applicant's actual test results. Therefore, the applicant's intention is that the appended claims are not limited by the selection of examples that illustrate the features of the present invention. Some numerical ranges used in the claims also include sub-ranges therein, and changes in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims (5)

1. The method for preparing the low-carbon olefin and co-producing the high-purity hydrogen by coupling the waste plastics with the alkali lignin is characterized by comprising the following steps of:

s1, pyrolysis gasification: mixing the pretreated waste plastic with alkali lignin, and carrying out pyrolysis gasification at 550-750 ℃ to generate a gas-phase product, a liquid-phase product and a solid-phase product; the mass ratio range of the alkali lignin to the pretreated waste plastic is (0.62-0.99): 1, a step of;

In the step S1, a gasifying agent is also added, wherein the gasifying agent is water vapor and/or air;

in the step S1, an inhibitor is also added, wherein the inhibitor is a Ca-based inhibitor;

in the step S1, the reaction time of pyrolysis and gasification is 0.5-10 h;

S2, olefin preparation: adding a catalyst into the liquid-phase product in the step S1 to perform catalytic conversion at 500-600 ℃ to obtain an olefin product; the catalyst active component comprises: si/O/Ca/Al/Na or Si/O/Ca/Al/K;

S3, chemical chain reforming: in the step S1, the gas phase product and the oxygen carrier are subjected to chemical chain reforming at 800-1000 ℃; the oxygen carrier is a Fe/Co/Cu/Si-based composite oxygen carrier, a Fe/Co/Ni/Al-based composite oxygen carrier, a Fe/Cu/Ni/Si-based composite oxygen carrier or a Cu/Mn/Ni/Al-based composite oxygen carrier; in the step S3, the reaction time of the chemical chain reforming is 10-40 min;

S4, preparing hydrogen: reacting the oxygen carrier subjected to chemical chain reforming in the step S3 with steam at 700-1000 ℃ to obtain hydrogen;

S5, oxygen carrier regeneration: calcining the oxygen carrier reacted in the step S4 in air atmosphere, and enabling the calcined oxygen carrier to enter a step S3 for cyclic reaction;

the olefin product is olefin with 2-4 carbon atoms.

2. The method of claim 1, wherein the alkali lignin has a particle size in the range of 40 to 200 mesh.

3. The method of claim 1, wherein the oxygen carrier has a particle size in the range of 20 to 80 mesh.

4. The method according to claim 1, wherein in the step S2, the liquid-phase product is further subjected to a refining process treatment including a dehazer refining process, a dechlorination refining process and a desilication refining process before being added to the catalyst; in the step S3, the gas phase product is subjected to chemical chain reforming with the oxygen carrier after being sprayed and purified by alkali liquor.

5. The method according to claim 1, wherein the pretreatment comprises a pulverization treatment and/or a magnetic separation treatment; the crushing treatment is to crush the waste plastics to obtain waste plastic particles with the particle size range of 5-50 mm; the magnetic separation treatment is to remove metal foreign matters in the waste plastics.