Mahbod Shafei, an expert on biomass conversion from Iran, wrote an article about the applications of bio-oil from biomass in different sectors like agriculture, water filtration, the fine chemicals industry, biofuels.
High-value Bio-oil from biomass and its applications in agriculture, water filtration, fine chemicals industry, and biofuels
In recent years, many articles have been written on renewable energies in scientific papers. Certainly, one of the best-known renewable energy is biomass. It is common knowledge that using biomass as a renewable source of energy has opened its place in the global renewable energy share charts instead of fossil fuels, and governments use biomass in various energy applications in the industry. Interestingly, biomass is not only used as an energy source in the market, but also many industrial products are biomass-based, such as agricultural products, chemical resins, adhesives, fine chemicals, water, air filters, soil amendments, and cosmetics.
Scientists have done several experiments to improve the quality and performance of biomass products since 2010. They have obtained remarkable results that promise good biomass usability in agriculture and the chemical industry in particular instead of fossil-based materials, which motivated the governments to invest more in this field.
This article tries to demonstrate thermo-chemical conversion technologies technically, especially recent innovative ones called pyrolysis. Pyrolisis produces Bio-oil and Bio-char applicable in the chemical and agricultural fields. Also, some of its benefits are the reduction of environmental risks, transportation costs, and an increase in economical efficiency. This method draws scientists and industry attention in recent years for various end products. They believe in the necessity of research and development in this unique area of biomass conversion. Finally, the most unique and more applicable area of Bio-oil and Bio-char from pyrolysis described.
Pyrolysis is the thermal decomposition of organic materials in the absence of or nearly without the oxygen, also known as “dry distillation” and is the main process for Bio-oil production from the waste. Pyrolysis is an effort to maximize the liquid product yield from solid biomass. It is a potential candidate for Bio-oil production, which is carbon-based liquid.
Pyrolysis is the second stage of gasification after drying and followed by gasification. Pyrolysis of biomass depended on many different variables of biomass nature. The moisture content of biomass has a strong effect on pyrolysis. Many references have noticed that moisture content of biomass should be around 10% and particle size should be small enough around 2 mm to 20 mm to have sufficient reactions in the reactor.
Pyrolysis of biomass divided into four different groups contains flash, fast, mild, and slow pyrolysis. Under these conditions, biomass does not combust although the main components like cellulose, hemicelluloses, and lignin decompose to solid-phase known as Bio-char, a liquid phase known as tar or Bio-oil and gaseous products. Bio-char is usually determined as porous carbon that remains after hydrogen and oxygen fractions. Bio-char has other components like mineral fractions, alkaline, and hydrocarbons. That’s why it is used as fuel, soil amendment, fertilizer, or filtration of water or air.
Bio-char is the main product of slow and mild pyrolysis, with the low oven temperature and high-residence time used in many countries as the traditional way of making charcoal. According to analyzing experiments, Bio-char produced by pyrolysis has a very low O/C and H/C ratio, around 0.1 to 0.3 respectively. Bio-char distribution in pyrolysis generally varies between 12% to 35%, depending on the conditions and type of pyrolysis.
After pyrolysis, the tar (vapor phase) species have the largest mass fractions of products formed. Elemental analysis shows that the composition of Bio-oil is quite similar to that of fuels. But Bio-oil is acidic, and it requires specific changes in the machinery for its use. For example, storage and machinery need to be stainless steel or fiberglass. Bio-oil distribution in pyrolysis generally varies between 30% to 75%, depending on the conditions and type of pyrolysis.
The proportion of the products depends on several factors, such as the composition and size of biomass, and the process conditions, such as the rate of heat transfer, oven temperature, and residence time. By increasing the oven temperature, the heat transfer rate could rise, and in short residence time, the dominant product is Bio-oil, which is vapor in pyrolysis temperature and liquid at room temperature. However, a higher heating rate and reactor temperature accelerate the Bio-oil formation.
At around 150 °C and 190 °C, pyrolysis decomposition involves a reduction in molecular weight, elimination of water, and formation of carbon monoxide and carbon dioxide, and finally Bio-char from lignin. At a temperature lower than 300 °C, the product varies with residence time, which is torrefaction with the main product of char about 82%, and it has a higher heating value in comparison with biomass. Pyrolysis of cellulose at a temperature higher than 300 °C, and consequently higher heat transfer rate, with residence time mainly shorter than a minute (few seconds), contains various complex reactions to a large amount of Bio-oil.
Fast pyrolysis operates at a temperature range between 600 °C to 1,000 °C with a very high heating rate of more than 1,000 °C/second but the short residence time is less than 0.5 seconds. Flash pyrolysis operates at around 500 °C with a heating rate of more than 1 °C/second at a residence time of under 2 seconds. They have the same product distribution, but due to the short residence time of fast pyrolysis, the high-quality rich condensable vapors produced could be used for the production of alcohol or gasoline.
Bio-oil is the main product of flash and fast pyrolysis with 50 % to 70 % weight of the biomass. The ideal reaction conditions for gaining a high amount of liquids are at the temperature of app. 900°C using a heating rate of 1000 °C/s, under exclusion of oxygen in flash or fast pyrolysis, with short residence time. Under this condition, the main product is Bio-oil.
Temperature, residence time, heat transfer rates
|Product distribution (wt %)|
|Fast pyrolysis||800 °C to 1000 °C, < 0.5 second, >1000 °C/sec||65 %||24 %||10 %|
|Flash pyrolysis||500 °C to 600 °C, ~ < 2 second, >1 °C/sec||75 %||12 %||13 %|
|Mild pyrolysis||300 °C to 450 °C, 10 to 20 seconds|
0.1 to 1 °C/sec (controlled heating rate to control tar formation)(mercury release)
|50 %||25 %||25 %|
|200 °C to 300 °C, Short residence time (up to 30 minutes), 0.1 to 0.5 °C/sec, limited oxygen||–||82 %||18 %|
|250 °C to 300 °C, long residence time (hours to a day), 0.1 to 0.5 °C/sec||30 %||35 %||35 %|
Table 1) pyrolysis modes have been categorized by temperature, residence time, and heat transfer rate [1, 2, 3, and 4]
Applications for pyrolysis products
As I previously mentioned, biomass conversion products can be used as an energy source. This article aims to show other recent innovative applications of biomass-based products that reduce environmental risks and benefit the economy of a region. Various oxygen and hydrogen organisms exist in Bio-oil cause instability and a high tendency toward polymerization. But there is an extensive amount of chemicals with oxygen groups producing from fossil-based sources that Bio-oil can be utilized in an economical way to produce value-added chemicals.
Several experiments show that Bio-oil contains many valuable components such as phenols, aldehyde, and furan that have the potential to be used for chemical products such as Resorcinol Formaldehyde (RF) resin in particular. RF resin is an adhesive in wood structural materials that can be set at ambient temperature. A study shows that the RF adhesive resin from Bio-oil exhibited the best flexural and tensile strength. Studies show adhesive properties of Bio-oil derived from woodchips and waste paper could bond two aluminum plates with high tensile strength generally. Moreover, an investigation shows Bio-oil itself has adhesive properties and maximum tensile strength of bonding between two aluminum plates from approximately 2520 N (Bio-oil from spruce wood chips) to 2300 N (Bio-oil from waste paper) .
Studies show Bio-oil from fast pyrolysis can be used for soil conditioning. The innovation here is the fact that Bio-oil reacts readily with ammonia, urea, and related compounds to form organic nitrogen. These compounds polymerize and solidify with heating to produce stable products. These compounds called slow-release fertilizers. These high-quality organic fertilizers produced from waste biomass, enhancing fast pyrolysis economic justification. The new fertilizers avoid groundwater pollution and containing the –NH2 group. So its effect could be very positive if its use and production extended to the agricultural field .
Providing clean water to communities is a crucial issue for many countries. Contamination including pesticides, pharmaceuticals, and a fuel compound is a growing problem, as these chemicals can cause cancer. Char filters work with the process of adsorption. For water, treatment contaminants diffuse into char pores binding to char surfaces. Large porosity and high surface area of bio-chars provide reactive ground for dissolved compounds as well as hazardous contaminants. Moreover, to avoid clog of char pores the sand pool removes a large portion of organic matter from the water.
Bio-char filters do differently from activated carbon. Most commercial activated filters are made from nonrenewable whereas Bio-char is made from biomass. Bio-char filters are not activated and they may not have the same capacity as commercial ones, that’s why their filter design may use a great amount of Bio-char.
Recent studies show Betulin extracted from fast pyrolysis of birch bark with lower cost and toxicity. These studies tried to produce activated carbon from biomass-based materials. They achieved good results by using Bio-char, a byproduct of Betulin from birch bark, which used steam or carbon dioxide as the activation agent .
4. Soil amendments
Biochar is a carbon enriched material that can be used as soil amendments to sequester carbon and increase the physical quality of the soil such as soil structure or porosity. It also enhances water retention as well as microbial quality. Therefore, using sustainable Bio-char is an innovative and favorable practice for sustainable agriculture. Agriculture currently encountered two considerable constraints, including low-nutrient content and accelerated mineralization of soil organic matter. Field experiments show that Bio-char is much more effective than other organic matter to make nutrients available for plants and is a more stable nutrient source than manure. Also, its pore structure is hospitable to the bacteria that plants need to absorb from the soil.
Several investigations show the effect of Bio-char on crop yields. Most studies showed that Bio-char addition increases crop yields. Therefore, Bio-char application has increased year by year since 2010, with no weak results reported.
Moreover, several experiments have been done on the evacuation of organic compounds by Bio-char. Sorption of ammonium and phosphate ions (NH4+ and PO43-) by Bio-char have been done by using the batch equilibrium method. The results show that woodchips and wood pellets start pyrolysis at 450 ̊ C to 750 ̊ C respectively, and both remove NH4+ and PO43-. Also, the Bio-char capacity for PO43- was higher than the activated carbon’s .
In the end, it is convincing that biomass is applicable not only in the energy sector but in the agriculture or chemical industry because it is feasible and more environmentally friendly than other fossil-based materials. Therefore, the universities, institutes, and companies should open more areas into the practical study for research and development in this field.
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