Research progress of biomass conversion and utilization technology

2.2.2 Preparation of ethanol or methanol by enzyme technology

Various green plants (such as corncobs, fruits, beets, sweet sorghum, straw, straw, wood chips, grasses, and many cellulose-rich raw materials) can be used as raw materials for ethanol extraction. Ethanol, also known as alcohol, is often called "green oil" as a fuel. There are many ways to produce ethanol, mainly: ① the use of sugar-containing raw materials directly fermentation; ② Indirect use of carbohydrate or starch fermentation; ③ Cellulose raw materials such as wood are hydrolyzed by acid or enzyme hydrolysis to ethanol.

2.3 Thermochemical conversion technology

Thermochemical conversion technology refers to the use of chemical means to convert biomass into high-grade, easy to store, easy to transport, high energy density and commercial value of solid, liquid and gaseous fuels, as well as heat, electric energy and other energy products, fuel material technology J. Thermochemical conversion is an effective method to produce biofuels from biomass, which mainly includes baking, liquefaction, pyrolysis and gasification technologies. Through these conversion technologies, solid, liquid and gaseous biofuels produced from biomass are used for heat and electricity generation. Liquid bio-oil can be further converted into chemicals, while syngas can be synthesized into liquid fuel.

Pyrolysis is one of the best processes to deal with solid waste, the temperature is generally 300 ~ 600℃, there are three ways of slow pyrolysis, fast pyrolysis and flash pyrolysis. The process can be divided into four stages: material drying, hemicellulose pyrolysis, cellulose and lignin pyrolysis. In the process of biomass pyrolysis, heat is transferred layer by layer from outside to inside. The first is the surface of the particle, and then from the surface to the interior of the particle, the heated part of the particle is rapidly cracked into charcoal and volatile components, and the products after cracking will continue to crack under the action of temperature. Most of the biomass pyrolysis processes used in practice are atmospheric or near-atmospheric reactions, and the pyrolysis products are mainly composed of bio-oil, gas and solid carbon.

Biomass gasification is also a kind of biomass thermochemical transformation, its basic principle is in the case of incomplete combustion, the raw material heating, so that the high molecular weight of the compound cracking into H2, CO, small molecular hydrocarbons and CO2 and other low molecular weight mixture process. Air or oxygen, water vapor, and a mixture of water vapor and oxygen are usually used as gasification agents. The product of gasification is syngas, which is further converted into liquid fuels such as methanol and ethanol through Fischer-Tropsch synthesis or biosynthesis, and can also be directly used as fuel for gas motors.

2.4 Solid waste treatment technology

For the treatment of solid waste, there are three traditional ways: landfill, incineration and biochemical treatment. Landfill and incineration methods result in a waste of resources and energy. At present, more in-depth research has been done on the reuse of biomass energy in waste at home and abroad, mainly using feed, fertilizer, biogas, fuel and other ways to make scientific and effective use of biomass. If it is processed into feed, make full use of its nutrients; Composting technology was used to treat yard waste, organic biological waste, organic residual sludge and agricultural waste. Biogas technology is used to treat all kinds of organic wastes in agriculture, industry and human life. In order to avoid secondary pollution while producing biogas, it is necessary to reuse biogas residue and biogas liquid, which can be directly used as fertilizer or made into commercial fertilizer by solid-liquid separation. Using the compression molding technology of biomass, the original loose, fine, amorphous biomass raw materials can be compressed into rod, granular, block and other forming fuels under certain conditions.

2.5 Biomass liquefaction technology

The liquefaction technology of biomass energy refers to the technology of converting biomass into liquid fuel by hydrolysis, pyrolysis or catalysis. By chemical processing of biomass, liquid fuels such as fuel ethanol, methanol, bio-oil, etc. Under certain conditions, biological fermentation or acid hydrolysis technology can be used to convert biomass into ethanol for automotive or other industrial use. The use of biomass liquefaction technology can not only improve the utilization efficiency of biomass, but also expand its application range. Making liquid fuel from biomass liquefaction will be a frontier technology with development potential.

2.6 Supercritical transformation technology of biomass

Supercritical fluid (SCF) is a kind of fluid which is above critical temperature and critical pressure and has good fluidity, transferability, diffusivity and solubility between gas and liquid. It has the dual properties and advantages of both gas and liquid. Near its critical point, small changes in pressure and temperature will cause large changes in fluid density, solubility, dielectric constant and other physical properties.