Introduction:
Wood is the oldest building material and a renewable resource that can meet human needs in producing fire. It is worth mentioning that according to global food and agriculture statistics, half of the wood is used as fuel, and in 2015, it had a growth rate of 7%. It has even been introduced as the only fuel. However, due to the high price of oil and the inability to access it permanently, there is a need for renewable resources. Due to the increasing demand in the market, traditional methods of using coal are not effective for several reasons:
- Environmental pollution (due to the release of a large amount of smoke into the surrounding air).
- Commercialization
- Use of modern methods: In modern methods of coal production, wood is heated in an environment away from air and the gases emitted from the wood are also condensed and poured into a special container. This by-product of the process is called wood vinegar or liquid smoke. It is called pyrolysis acid in scientific articles.
Characteristics:
Reddish-brown liquid,
Composed of several different substances,
It has a distinct odor due to the presence of various acids,
The specific gravity of 1.500 to 1.016 grams per milliliter,
Insoluble tar content ranges from 23% to 89% by weight, and
its Brix degree ranges from 1.7 to 6.6.
The Japan Pyrolysis Association has provided seven parameters for better quality. In Japan, wood vinegar is produced from a wide range of species such as oak, Japanese oak, and cherry blossom trees. From every 1000 kilograms of dry wood, 314 kilograms of wood vinegar are obtained which contains about 200 chemical compounds such as alcohols, acids, neutral substances, phenols, and alkaline substances.
Collecting wood vinegar:
Various compounds are produced during the pyrolysis of wood due to the different components inside the wood. For example, organic acids such as acetic acid and various alcohols are obtained from the pyrolysis of cellulose and hemicellulose, while phenolic substances are produced from lignin pyrolysis. The amount of collected wood vinegar during carbonization depends on the volume of water in the wood and the collection method.
Purification of wood vinegar:
The container is kept stationary for three months, forming three layers consisting of clear oil on top, wood in the middle, and tar at the bottom. It is better to purify it with charcoal powder. However, industrial filtration methods are also used for purification.
Chemical composition of wood vinegar:
Wood vinegar is a complex mixture of polar and non-polar chemical substances that contains more than 200 different compounds in total, depending on the raw materials and pyrolysis conditions. However, the most important substances include acetic acid, acetone, methyl acetate, methanol, dissolved creosote, 75% water, phenols and monophenols from lignin decomposition, and furfural from cellulose. The final heat treatment during carbonization plays an important role in the quality and quantity of charcoal and wood vinegar production. Wood vinegar contains two types of carcinogenic substances that can be partially prevented by controlling carbonization temperature below 425 degrees Celsius.
Uses of wood vinegar:
1- Medical use: In countries such as Japan (where it is called Mokusaku and is believed to balance the body and promote health), Korea, China, and the United States, wood vinegar is used to reduce the absorption of carcinogenic alkaline substances, increase the absorption of calcium and magnesium, and improve blood circulation.
2- Agricultural use: Wood vinegar can be used as a natural alternative to chemical fertilizers to repel pests, promote the germination and flowering of plants, and improve soil quality. The necessary ratios for using wood vinegar in agriculture (It should be diluted with water at different ratios) are:
– For killing pests: 1:20
– For killing weeds: 1:50
– To prevent stem and root rot: 1:100
– To prevent pests and mold for rapid plant growth: 1:200
– To prevent plant lice: 1:400
– To increase fruit growth: 1:500
Wood vinegar can also be used as a natural food preservative to improve the quality and growth rate of agricultural products.
3- Livestock use: Wood vinegar can be used as a dietary supplement to reduce bacteria in the intestines.
4- Pest control use: The presence of acetic acid along with phenolic compounds gives wood vinegar its antifungal properties. It can be used for rubber production, wood preservation, agricultural pest control (to protect plants from insects and pests), etc.
Conclusion:
Today, wood vinegar cannot be considered just an alternative product. Given its wide range of uses, researchers are using various lignocellulosic materials such as sawdust or agricultural waste to produce it. The temperature and time of pyrolysis have a significant effect on the quality and composition of wood vinegar. Using high pyrolysis temperatures can increase the concentration of hazardous phenolic compounds that are carcinogenic. It is recommended that researchers, especially those in the field of agriculture, pay more attention to using wood vinegar for pest control or soil fertility.
