Method for preparing liquid oil and silicon carbide through microwave-assisted depolymerization of rice hulls
Technical Field
The invention belongs to the technical field of biomass energy and materials, and particularly relates to a method for preparing liquid oil and silicon carbide through microwave-assisted depolymerization of rice hulls.
Background
The rice hulls are one of the important components of biomass and are rich renewable energy sources on the earth. The rice husk is mainly from husked rice, and only China produces more than 5000 million tons of rice husk every year. At present, the rice hulls are mainly utilized by directly burning the rice hulls to supply heat, and the utilization added value is very low, so that a new way for high-value utilization of the rice hulls is urgently needed to be found.
In recent years, scholars at home and abroad have conducted a great deal of research on the pyrolysis mechanism and characteristics of rice hulls, the quality improvement of pyrolysis bio-oil and the like. The method for converting the rice hulls into the bio-oil or the chemical through the pyrolysis is one of the most potential methods for efficiently utilizing the rice hulls and is one of the current research hot directions related to the large-scale utilization of the rice hulls, but the problems of low utilization efficiency, low product conversion added value and the like still exist in the current rice hull utilization aspect due to the characteristics of high ash content and the like, and a high-valued utilization means needs to be found urgently.
Disclosure of Invention
The invention aims to provide a method for preparing liquid oil and silicon carbide by microwave-assisted depolymerization of rice hulls, which aims to overcome the technical problem that the ash content (silicon) of the rice hulls is high and cannot be effectively utilized and converted.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for preparing liquid oil and silicon carbide by rice hull microwave-assisted depolymerization comprises the following steps:
the method comprises the following steps: crushing rice hulls, uniformly mixing the crushed rice hulls with a microwave absorbent, and performing ball milling to obtain a rice hull and microwave absorbent composite material;
step two: carrying out microwave-assisted depolymerization on the rice hull and microwave absorbent composite material in an argon atmosphere;
step three: condensing pyrolysis gas generated in the microwave-assisted depolymerization process to obtain liquid oil, wherein solid matters generated in the microwave-assisted depolymerization process are silicon-carbon-oxygen mixtures;
step four: continuously carrying out microwave heating on the silicon-carbon-oxygen mixture in an argon atmosphere to obtain a solid substance which is a silicon carbide mixture;
step five: and calcining the obtained silicon carbide mixture in an air atmosphere, and obtaining a solid substance of silicon carbide after calcining and sintering.
Further, the grain diameter of the rice hulls in the step one is 0.1-0.5 mm, and the grain diameter of the microwave absorbent is 0.05-0.2 mm.
Further, the microwave absorbent in the step one is activated carbon, carbon black or graphene, and the mass ratio of the rice hull to the microwave absorbent is 1: (0.02-0.5).
Further, the ball milling time in the step one is 2-10 min.
Further, in the second step, microwave power used for microwave-assisted depolymerization is 1500-1700W, and reaction time is 20-60 seconds.
Further, the condensation temperature in the third step is-35 ℃ to 0 ℃.
Furthermore, in the fourth step, the microwave power used for microwave heating is 1800-2000W, and the reaction time is 60-100 seconds.
Furthermore, in the fifth step, the calcining temperature is 800-1000 ℃, and the calcining time is 1-3 hours.
Compared with the prior art, the invention has the following beneficial technical effects:
the method for preparing the liquid oil and the silicon carbide by microwave-assisted depolymerization of the rice hulls provided by the invention realizes high-efficiency depolymerization of the rice hulls, enables the rice hulls to be converted into the silicon carbide to reach theoretical yield, greatly improves the utilization rate and the utilization value of the rice hulls, and has the following specific advantages:
(1) based on the technical problem that the rice hull has high ash content (silicon) and cannot be effectively utilized, the liquid oil and the silicon carbide are obtained by the microwave-assisted depolymerization technology, and the high-value utilization of the rice hull is realized.
(2) Mixing rice hull and microwave absorbent, and ball milling (using ball mill tank rotation and wheel disc rotation opposite direction to give kinetic energy to milling ball)And (6) grinding. The microwave absorbent such as the activated carbon, the carbon black and the graphene is tightly embedded in the rice husk, so that uniform and rapid heat transfer and temperature rise between the rice husk and the microwave absorbent are facilitated, and more importantly, the carbon-based microwave absorbent is tightly embedded in the rice husk, so that carbon thermal reduction reaction under microwave excitation can be promoted, and SiO in the rice husk can be reduced2Can fully contact with the carbon-based microwave absorbent, and is beneficial to SiO2By forming the intermediate product SiO and then further converting the silicon carbide, oxygen is precipitated as CO.
(3) The invention provides a microwave-assisted depolymerization process for carrying out depolymerization twice, and firstly, the rice hull and microwave absorbent composite material is subjected to microwave-assisted depolymerization under an argon atmosphere, the microwave power is 1500-1700W, and the reaction time is 20-60 seconds. The temperature of the rice hull and microwave absorbent composite material is rapidly raised to 500-800 ℃ in a short time, volatile substances in cellulose, hemicellulose and lignin in the rice hull are converted into pyrolysis steam, participated solids are converted into a silicon-carbon-oxygen mixture, and the pyrolysis steam is condensed to obtain high-value liquid oil. And secondly, under the argon atmosphere, the microwave power is 1800-2000W, the reaction time is 60-100 seconds, the temperature is raised to 1400-2000 ℃, the silicon-carbon-oxygen mixture has high dielectric loss tangent and can quickly absorb the microwave and convert the microwave into heat, and under the condition, the silicon-carbon-oxygen mixture and carbon further undergo a carbothermic reduction reaction to generate silicon carbide.
(4) According to the invention, the silicon carbide mixture is calcined in an air atmosphere, and redundant carbon elements are removed through calcination, so that the purity of silicon carbide can be obviously improved; the stability of the silicon carbide crystal structure may also be improved by calcination.
Detailed Description
The invention is further described below.
A method for preparing liquid oil and silicon carbide by rice hull microwave-assisted depolymerization comprises the following steps:
the method comprises the following steps: crushing the rice hulls, uniformly mixing the crushed rice hulls with the microwave absorbent, and performing ball milling for 2-10 min to obtain the rice hulls and microwave absorbent composite material. The grain size of the rice husk is 0.1-0.5 mm, the grain size of the microwave absorbent is 0.05-0.2 mm, the microwave absorbent is activated carbon, carbon black and graphene, and the mass ratio of the rice husk to the microwave absorbent is 1: (0.02-0.5).
Step two: and (3) carrying out microwave-assisted depolymerization on the rice hull and microwave absorbent composite material under an argon atmosphere, wherein the microwave power is 1500-1700W, and the reaction time is 20-60 seconds.
Step three: and (3) condensing pyrolysis gas generated in the microwave-assisted depolymerization process under the condensation condition of-35-0 ℃ to obtain liquid oil, wherein the generated solid matter is a silicon-carbon-oxygen mixture.
Step four: and (3) continuously carrying out microwave heating on the silicon-carbon-oxygen mixture in an argon atmosphere, wherein the microwave power is 1800-2000W, the reaction time is 60-100 seconds, and the obtained solid matter is a silicon carbide mixture.
Step five: and calcining the obtained silicon carbide mixture in a muffle furnace, wherein the calcining atmosphere is air, the calcining temperature is 800-1000 ℃, the calcining time is 1-3 hours, and after calcining, the obtained solid substance is silicon carbide.
The present invention will be described in detail with reference to examples. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The following detailed description is illustrative of the embodiments and is intended to provide further details of the invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.
Example 1
Crushing 10g of rice hulls to obtain the rice hulls with the particle size of 0.1-0.3 mm, uniformly mixing the crushed rice hulls with 5g of activated carbon with the particle size of 0.05-0.1 mm, and performing ball milling for 2min to obtain the rice hulls and activated carbon composite material. And (2) carrying out microwave-assisted depolymerization on the rice hull and activated carbon composite material under the argon atmosphere, wherein the microwave power is 1700W, and the reaction time is 20 seconds. And (3) condensing pyrolysis gas generated in the microwave-assisted depolymerization process at the condensation condition of-35 ℃ to obtain liquid oil, wherein the generated solid matter is a silicon-carbon-oxygen mixture. And (3) continuously carrying out microwave heating on the silicon-carbon-oxygen mixture in an argon atmosphere, wherein the microwave power is 2000W, the reaction time is 60 seconds, and the obtained solid matter is a silicon carbide mixture. And calcining the obtained silicon carbide mixture in a muffle furnace in air at 1000 ℃ for 1 hour to obtain a solid substance of silicon carbide after calcining. The yield of the obtained liquid oil was 32.1%, the yield of the obtained silicon carbide was 45.8%, and the purity of the silicon carbide was 94.1%.
Example 2
Crushing 10g of rice hulls to obtain the rice hulls with the particle size of 0.4-0.5 mm, uniformly mixing the crushed rice hulls with 0.2g of carbon black with the particle size of 0.15-0.2 mm, and performing ball milling for 10min to obtain the rice hulls and carbon black composite material. And (2) carrying out microwave-assisted depolymerization on the rice hull and carbon black composite material under an argon atmosphere, wherein the microwave power is 1500W, and the reaction time is 60 seconds. And (3) condensing pyrolysis gas generated in the microwave-assisted depolymerization process at the condensation condition of 0 ℃ to obtain liquid oil, wherein the generated solid matter is a silicon-carbon-oxygen mixture. And (3) continuously carrying out microwave heating on the silicon-carbon-oxygen mixture in an argon atmosphere, wherein the microwave power is 1800W, the reaction time is 100 seconds, and the obtained solid matter is a silicon carbide mixture. And calcining the obtained silicon carbide mixture in a muffle furnace in air at 800 ℃ for 3 hours to obtain a solid substance of silicon carbide after calcining. The yield of liquid oil obtained was 35.6%, the yield of silicon carbide obtained was 43.4%, and the purity of silicon carbide was 93.7%.
Example 3
Crushing 10g of rice hulls to obtain the rice hulls with the particle size of 0.3-0.4 mm, uniformly mixing the crushed rice hulls with 2g of graphene with the particle size of 0.1-0.15 mm, and performing ball milling for 5min to obtain the rice hulls and graphene composite material. And (2) carrying out microwave-assisted depolymerization on the rice hull and graphene composite material under an argon atmosphere, wherein the microwave power is 1600W, and the reaction time is 40 seconds. And (3) condensing pyrolysis gas generated in the microwave-assisted depolymerization process at a condensation condition of-17 ℃ to obtain liquid oil, wherein the generated solid matter is a silicon-carbon-oxygen mixture. And (3) continuously carrying out microwave heating on the silicon-carbon-oxygen mixture in an argon atmosphere, wherein the microwave power is 1900W, the reaction time is 80 seconds, and the obtained solid matter is a silicon carbide mixture. And calcining the obtained silicon carbide mixture in a muffle furnace in air at 900 ℃ for 2 hours to obtain a solid substance of silicon carbide after calcining. The yield of the obtained liquid oil was 33.5%, the yield of the obtained silicon carbide was 44.6%, and the purity of the silicon carbide was 95.2%.
It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.