Coal - Sekitan (English spelling)

Japanese: 石炭 - せきたん（英語表記）coal

It is a flammable rock-like organic material, mainly composed of carbonaceous matter, that was formed when ancient plants were buried deep underground and were subjected to the influence of the geological environment (geothermal heat and pressure) for a long period of time. Along with petroleum and natural gas, it is a typical fossil fuel (resource), and research and development is being conducted on its use not only as an energy source, but also as a source of various hydrocarbons useful in the chemical industry.

Coal is classified into three types depending on its use: "coking coal," "steam coal," and "anthracite." Coking coal is a type of bituminous coal with caking properties, also known as coking coal, and is mainly used as a "raw material" for steelmaking (for coke). Coking coal is further divided into coal for blast furnaces, for coke, for gas, etc.

General coal includes thermal coal for combustion, steam coal for boilers, and steaming coal, and is mainly divided into those for power generation and those for general industrial use. Generally, non-caking bituminous coal and sub-bituminous coal are included. Anthracite is also used for blending with special coke and for producing briquettes and charcoal briquettes.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

History of coal use

There are ancient records of coal being used as fuel, and in 315 BC, a passage appears in "On Stones" by Theophrastus, a student of the great Greek philosopher Aristotle, stating that "coal mined in the Liguria region of northern Italy and Elis in Greece was used as fuel for blacksmiths." At the time, this was called anthrax, which is said to be the origin of the word anthracite (anthracite) used today.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Japan

In Japan, the "Nihon Shoki" records that in 668 (the 7th year of Emperor Tenchi's reign), burning earth and water were presented from the province of Echigo. The "burning earth" probably refers to coal, and the "burning water" to oil. It was variously called "moeishi," "iwaki," "ushi," and "ishizumi," but it was only after the Meiji period that it came into general use as "sekitan." Incidentally, the word "coal" first appeared in "Unkonshi," a natural history book on stones written by Kiuchi Sekitei (1724-1808) in the mid-Edo period.

All discoveries of coal remain the stuff of legend. For example, in 1469 (Bunmei 1), a farmer named Denji Saemon from Touka Village, Miike County, Chikugo Province (Omuta City, Fukuoka Prefecture) is said to have discovered coal when he made a bonfire on Mount Touka and saw the fire spread to nearby black stones (this is said to be the origin of the Miike Coal Mine). Although records are not very reliable, it seems that the Takashima Coal Mine (Nagasaki Prefecture) and the Chikuho Coalfields (Fukuoka Prefecture) were discovered in the 18th century. It is believed that they began to be used almost immediately after their discovery.

Records of coal use appear after the Genroku period (1688-1704). In Kaibara Ekiken's Chikuzen no Kuni Zoku Fudoki (1703) and Yamato Honzo (1709), it is written that coal was used instead of firewood, under the term "moeseki." The background to this was the rapid shortage of firewood and charcoal. For example, in the Fukuoka domain, timber was cut down indiscriminately to repay the domain's bonds, which led to a shortage of firewood and charcoal, so coal was used as a substitute fuel (Fukuoka Domain Minsei Shiryaku). At that time, coal was mixed with firewood and was not used much because it produced a bad odor, and was only used by medium-sized or smaller houses that could not afford to buy a lot of firewood. However, after it was empirically learned that coal turns into a crude coke-like lump when it is burned and then quickly put out, it gradually became more widely used as a household fuel. In other words, it was steamed (distilled) to produce "charcoal" or "coke."

Coal began to be used in earnest when it began to be used as fuel for salt production. Salt production requires a much larger amount of fuel than household use, so the shortage of firewood and charcoal was even more serious. During the Meiwa era (1764-1772), village headman Wada Sahei of Chikuzen Wakamatsu (Kitakyushu City) improved a salt-grilling kiln, and in 1778 (An'ei 7) it was introduced to Mitajirihama in Suo Province (Hofu City, Yamaguchi Prefecture). This led to the expansion of coal sales to the salt fields of 10 provinces along the Seto Inland Sea coast (coal was called "firewood stone" because it was burned as raw coal).

As coal became more marketable and tradeable, feudal domains, which were struggling financially, established a domain-run monopoly on coal produced within their territories as a way to restore their finances. The Fukuoka domain implemented the domestic monopoly method and established a firestone trading post in 1816 (Bunka 13), while the Saga domain took control of the Takashima coal mine around 1817 and monopolized its rights. Under such domain control, it was impossible to hope for the free development of coal mines. In 1869 (Meiji 2), the new Meiji government, which had its sights on coal as an energy source for modern industry, lifted the domains' control over mines and minerals and issued the "Mine Lift Order" which opened mines to the public for opening and mining, which led to the rise of the coal industry.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

world

Commercial coal mining appears to have begun in England around the 5th century, but in the 12th and 13th centuries, fuel shortages for industries such as ironmaking, blacksmithing, limestone burning, brewing, dyeing, pottery, glass, and brick making became serious, and full-scale coal mining began. It is said that 24 cubic feet of wood were needed to make one ton of iron, and even the great forests of Europe became bald. Coal production in England began in earnest around 1600. In 1735, A. Darby succeeded in making iron using coke for the first time, and from this point on coal production increased dramatically. In 1765, J. Watt's improvements to the steam engine brought about the Industrial Revolution in England, greatly expanding the role of coal as a power source.

Meanwhile, carbonization gas (coke oven gas), a by-product of coke production, was used as fuel for gas lamps, creating a romantic atmosphere in large cities at the time. Eventually, coal gas was converted into producer gas and water gas, which became the source of city gas in the first half of the 20th century.

Tar (coal tar), another by-product of coke production, was initially treated as a nuisance, but as analysis of it progressed, it led to groundbreaking developments in organic chemistry, such as the discovery of important organic compounds called aromatic compounds and the proposal of the benzene structural formula by German chemist F. A. Kekulé in 1865. Even more noteworthy was the synthesis of dyes, which led to major developments in organic synthetic chemistry, where organic compounds that had previously only been obtained from natural sources were synthesized.

As internal combustion engines developed, the demand for gasoline and other fuels increased, but at the time oil resources were thought to be limited, and Germany in particular had no domestic production. As well as this, the coal liquefaction industry developed due to the need for national defense with the rise of Hitler, with an annual production of 4 million tons by the end of World War II. In addition, an industry was also developing that first gasified coal to produce carbon monoxide and hydrogen, then synthesized these using the Fischer-Tropsch process to produce hydrocarbon oil (so-called synthetic oil). At that time, electricity was mostly supplied by hydroelectric and coal-fired power. In other words, up until this time coal was the main source of energy, and the organic chemical industry could almost be called a coal chemical industry.

The situation changed dramatically after World War II. With the discovery of large oil fields in the Middle East, convenient petroleum became available at low prices, and coal, which contains ash and is inconvenient to handle, was quickly replaced by petroleum. The period up until 1973 was dominated by petroleum. However, the first oil crisis of 1973, brought about by the unity of Arab countries, once again called for a rethinking of energy sources. In the 1980s, countries tried to switch back to coal, which had become relatively cheap.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

What is coal?

Coal has been used since ancient times, but it was only through research results from the mid-20th century onwards that its origins and physicochemical structure were revealed.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Reserves

Coal is produced worldwide, but the largest reserves are found in North America, Russia, China, Australia, and Indonesia.

The world's geological reserves are estimated at about 3.4 trillion tons, but the recoverable reserves that are technically and economically possible to mine are estimated at about 826 billion tons, with 411.3 billion tons of bituminous coal and anthracite, and 414.7 billion tons of subbituminous coal and lignite. Meanwhile, the world's coal production (including lignite) is estimated at 6,903 million tons, and according to the 2010 statistics of BP, the recoverable years (recoverable reserves/annual production) is 119 years, which is longer than other fossil resources.

Of these, most of the coal produced in North America, Eurasia, and Australia was deposited in the Paleozoic and Mesozoic eras, and is mostly highly carbonized bituminous coal. Eurasia and Australia also have huge reserves of brown coal and lignite that were deposited in the Tertiary Period. Coal in Japan was mainly deposited in the Tertiary Period, but because the ground temperature is high due to the influence of volcanic areas, much of the coal produced is highly carbonized to the bituminous level.

Japan's total reserves are estimated at about 20 billion tons, with recoverable reserves at around 1 billion tons. Japan's domestic coal production peaked at 55.41 million tons in 1961, but has been declining ever since due to the shift to petroleum and, since the 1980s, the impact of cheap imported coal. Since 2002, the rapid decline has been halted due to the rise in international crude oil prices, and in 2010, 1.15 million tons were produced, most of which was consumed for power generation. Imports of foreign coal exceeded domestic coal production in 1970, surpassed 100 million tons in 1988, and reached 186.64 million tons in 2010.

Japan's main coalfields used to be located throughout the country, mainly in northern Kyushu and Hokkaido, but today the only large coalfield remaining is in the Kushiro region of Hokkaido.

[Toshihiro Aramaki]

Cause

When coal is viewed under a microscope, plant cell tissue, pollen, spores, etc. can be seen, and sometimes ancient plant fossils are discovered, so there is no doubt that it was formed from plants. However, its original plants differ depending on the era. In the Devonian Period of the Paleozoic Era (416 million to 367 million years ago), Carboniferous Period (from the Devonian Period to 289 million years ago), Permian Period (from the Carboniferous Period to 247 million years ago), Triassic Period (from the Permian Period to 212 million years ago), Jurassic Period (from the Triassic Period to 143 million years ago), and Cretaceous Period (from the Jurassic Period to 65 million years ago), flowering plants did not appear, and instead cryptogams such as reed trees (Horsetails), scale trees (Rimboku), and seal trees (Lycopods), redwoods, and horsetails dominated. These plants grew well in the environment that was ideal for plant growth at the time, which was hotter, more humid and had higher concentrations of carbon dioxide than today. Based on fossils, it is believed that they grew into large trees with trunks over 1 meter in diameter and heights of 20 to 30 meters, forming large forests.

In the Paleogene period of the Cenozoic Era (from the Cretaceous Period of the Mesozoic Era to 24 million years ago), the cryptogams mentioned above gradually declined, and coniferous and broadleaf flowering plants such as the conifers (sequoia, metasequoia, holly, and bald cedar) and angiosperms (poplar, sycamore, elm, zelkova, walnut, cucurbit, and maple) that can be seen today began to flourish, and these became the source of coal. In addition to these, coal (candle charcoal), which is thought to have originated from underwater algae, is produced in very exceptional cases.

Of these large forests, those that grew in wetlands accumulated in the water even after falling trees, and accumulated without being biochemically decomposed by microorganisms (in situ deposition). On the other hand, those that were washed away by floods and accumulated in the water of lakes and coasts are called alluvial deposition. The plants that accumulated in this way are initially acted upon by microorganisms. In the air, aerobic bacteria are highly active, causing oxidative decomposition, and the plants are almost completely decomposed in a relatively short time, but in the water, anaerobic bacteria are active, and their activity is weak and reductive, so a large part of the plant remains. The accumulated plant layer gradually sinks, and eventually soil and sand are deposited on top of it, and the plant layer is gradually buried deeper underground. It is generally said that the temperature rises in the ground by 3 to 5 degrees Celsius per 100 meters, so the deeper the plant is buried, the more it is exposed to high temperatures, and the extremely slow pyrolysis reaction progresses. In the laboratory, pyrolysis is carried out at a fairly high temperature, so the reaction is completed in a short time, but in geological times, the reaction continues for an extremely long time even if the temperature is low. Another difference from laboratory pyrolysis is that in the laboratory, the low- and medium-boiling point decomposition products become gas and tar, which escape from the reaction system and no longer participate in the coalification reaction, but in the case of coalification, the temperature is low and there are rock layers above and below, so the product gases and medium-boiling point substances remain in the reaction system, and these continue to react with each other.

Compared to Carboniferous coal in Europe, Tertiary coal in Japan is often coalified to the same degree, despite the fact that the period of coalification is much shorter. This is presumably because in Japan, underground temperatures were higher than in Europe due to the presence of magma masses, etc.

This is how the carbonization process progressed, and various types of coal have been formed depending on the original plant species, initial biochemical changes, underground temperatures, and the elapsed time.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Classification

Coalification is basically a pyrolysis reaction, and because it is a carbon accumulation reaction, it ultimately leads to graphite. Therefore, the stage of coalification can be expressed simply by the carbon percentage, but the coal band plotted by the element ratios (hydrogen/carbon and oxygen/carbon) that make up coal is useful for understanding the maturation process of coal from the dehydration, demethanation, and decarbonation processes. It is also common to use the coal band to estimate and classify the coalification stage of unknown coal (newly developed coal).

Coal is classified according to its degree of coalification, such as anthracite, semi-anthracite, bituminous coal, sub-bituminous coal, brown coal, and lignite. It is also classified according to its use, such as coking coal (for blast furnace coke) and steam coal (for boilers and power generation). Coking coal is further classified according to its caking property, such as strong caking coal, caking coal, weak caking coal, slightly caking coal, and non-caking coal ( Table 1 ).

In addition to the above, there is also peat, which is formed when grass accumulates in wetlands in cold regions; cannel coal (coal that is oily, bright, and burns like a candle), which is thought to have been formed from algae; and fan coal, also known as natural coke, which is formed when magma from underground intrudes into a coal seam and is rapidly distilled underground.

The international classification system was created primarily out of the need for international trade ( Table 2 ). This is a method of classifying coal based on its volatile content, then classifying coals with a volatile content of 33% or more by their calorific value, and then further classifying each of these categories by their caking index, as shown in Table 3. Table 4 shows the international classification system and the Japanese coal quality classification system.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Tissue components

Coal often has a striped texture when viewed with the naked eye, and when polished coal is observed under a microscope, it is found to be a mixture of various fine texture components. Coal petrography (or petrology) is a classification of these following the example of petrology. Just as granite is composed of three crystals, namely quartz, feldspar, and mica, coal is also composed of fine texture components as shown in Table 5. These fine texture components are called macerals. Generally, minerals that make up rocks are crystalline inorganic compounds with a certain chemical composition, but coal macerals are non-crystalline organic compounds whose physical and chemical properties change depending on the coalification degree. Such macerals can be identified by their shape, brightness (reflectance), color, luster, and other properties observed under a microscope. Coal texture is observed under a microscope using reflected light through an oil immersion liquid.

Macerals are broadly divided into three maceral groups: vitrinite, ecdinite (or liptinite), and inertinite. Each group originates from a different proto-plant organ, and has different physical and chemical properties. For coals of the same rank, vitrinite contains more oxygen, ecdinite contains more hydrogen, and inertinite contains more carbon. Inertinite has the highest reflectance, while ecdinite has an extremely low reflectance. The inertinite group has a high reflectance and appears white to grayish white, the ecdinite group has a low reflectance and appears dark black, and vitrinite has a reflectance between inertinite and ecdinite and appears gray.

There are large differences in the properties of the microstructural components within a single coal, with exignite having the highest volatile content, being the most soluble in solvents, producing a large amount of tar when heated, and being easily liquefied. Conversely, fugite, which is part of the inertinite group, has the lowest volatile content, is almost insoluble in solvents, and has extremely low other chemical reactivity. The word inertinite originally means inactive because of these characteristics.

The complex properties that coal exhibits as a whole are greatly influenced by the composition ratio of these microstructures. For example, if the inertinite content is high, the heat softening property and fluidity will be low, and even in the case of high-pressure hydrogen liquefaction, the inertinite will hardly liquefy, so the overall liquefaction rate will be low. Therefore, knowing the composition ratio of the microstructure components of coal is extremely important for the actual application of coal.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Coal Analysis

Coal is a very heterogeneous natural product, so in order to analyze the properties of coal, the first problem is how to obtain an average sample that represents the whole. The Japanese Industrial Standards (JIS) stipulate the amount of sample to be taken randomly based on viscosity. The sample thus taken must then be further divided into portions for actual analysis. This is done using various tools and methods, such as a two-parter or a rotary divider, in order to obtain samples as uniformly as possible. An example is shown in Figure A.

When a homogeneous sample weighing about 180 grams is obtained in this way, the entire amount is crushed to 250 micrometers or less, mixed thoroughly, and used as an air-dried sample (a sample that has reached equilibrium when left in air at room temperature). A sample that has been left in a humidity chamber containing a saturated salt solution until it reaches a constant weight is called a constant-humidity sample. Coal analysis is broadly divided into proximate analysis and elemental analysis.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Industrial Analysis

The specific moisture, ash content, volatile matter (VM), and fixed carbon (FC) obtained from proximate analysis are not only necessary information for commercial trading of coal, but are also essential data regardless of the industrial use field.

The moisture content of coal is divided into surface moisture (adherent moisture) that adheres to the surface of coal particles and adsorbed moisture that exists in the micropores (internal surface) that have developed inside the particles, the sum of which is the total moisture. Adsorbed moisture is mostly determined by the rank of coalification (the higher the rank of coalification, the lower the inherent moisture content), so it is also called inherent moisture. On the other hand, surface moisture increases or decreases depending on the weather and coal storage conditions, which often becomes an issue in commercial transactions due to differences in the positions of buyers and sellers. It is important to clarify the definition of moisture and the conditions for measurement.

The inherent moisture, ash content, volatile matter, fixed carbon, etc. not only vary depending on the coal's place of origin, but also vary depending on the extent and depth of the strata even within the same coal-producing area, so when trading, industrial analysis is required for each lot.

Industrial analysis includes the following items:

(1) Inherent moisture: The percentage of weight loss when approximately 1 gram of a constant humidity sample is dried in an electric furnace at 107±2°C for 1 hour.

(2) Volatile content: Approximately 1 gram of a constant humidity sample is placed in a platinum crucible with a lid and rapidly heated in an electric furnace at 900±20°C for 7 minutes. The volatile content is the percentage weight loss minus the inherent moisture content.

(3) Ash content: The percentage of residue when approximately 1 gram of a constant humidity sample is heated to 815°C in air and incinerated.

(4) 100% fixed carbon minus the percent specific moisture, ash, and volatile matter.

[Toshihiro Aramaki]

Elemental analysis

Elemental analysis is the same as that of general organic matter, but because coal is extremely heterogeneous, microanalysis is not suitable. Usually, it is carried out on a macro or semi-micro scale, quantifying carbon, hydrogen, nitrogen, and sulfur, and calculating oxygen as a difference from 100%, but direct oxygen quantification is also possible. Carbon and hydrogen are determined by heating and burning the sample in an oxygen stream, and the resulting carbon dioxide and water vapor are absorbed in an absorbent, respectively, and the increase in their amounts is measured and expressed as a mass percentage relative to the anhydrous sample. Nitrogen is determined by the Kjeldahl method, semi-micro Kjeldahl method, etc. Sulfur is determined by measuring the total sulfur in the sample and the sulfur in the ash, and calculating the combustible sulfur as the difference. Carbon, hydrogen, and nitrogen are often determined by instrumental analysis (CHN coder).

In addition to the above, phosphorus analysis is also performed because phosphorus contained in coke during steelmaking can affect the quality of the pig iron.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Heat generation

Approximately 1 gram of a constant humidity sample is burned in a calorimeter, and the amount of heat generated is called the gross calorific value or high calorific value. This value is high because it includes the moisture content and the heat of condensation of the moisture produced when the hydrogen in the coal is burned. The actual amount of heat generated during combustion is the net calorific value or low calorific value minus the heat of condensation of the moisture, and is calculated using the following formula.

Here, h is the hydrogen percentage and W is the water percentage.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Ash composition analysis (X-ray fluorescence method)

A coal sample (1 gram, 149 micrometers or less) is calcined at 1000°C until it reaches a constant weight, and the weight loss (igross) is calculated. Next, the calcined sample (0.7 grams) is placed on a platinum dish, lithium tetraborate (4.5 grams) and lithium fluoride (0.5 grams) are added, and the sample is heated at 1000°C for 10 minutes to obtain a glass tablet (0.7 mm in diameter x 5 mm). The glass tablet is irradiated with X-rays (primary X-rays), and the secondary X-rays (fluorescent X-rays) generated by the excitation are detected to qualitatively and quantitatively identify the elements. Usually, the _elements are quantified as alumina _Al2O3 , silicon dioxide _SiO2 , calcium oxide CaO, magnesium oxide MgO, etc., using a calibration curve prepared in advance.

This is an ashed sample, so it does not show the actual form of the minerals contained in the coal. To investigate the minerals contained in the coal, oxygen plasma is used at around 200°C to remove organic matter, and the residue (low-temperature ashed material) is subjected to X-ray analysis. Many of the inorganic components obtained in this way are clay minerals. Some coals contain large amounts of pyrite.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Testing methods for coal and coke

Many of the test methods are related to coke making.

(1) Hard Glove Crushability Test 50 grams of a sample that has been sized, crushed, and sieved as specified is placed in a testing machine, 8 balls are added, and after 60 rotations, the sample is sieved through a 74 micrometer sieve. The index is calculated from the weight W of the sample under the sieve using the following formula.

Hard Globe Index = 13 + 6.93 W
The hardgrove grindability index (HGI) is an index that indicates grindability, and the higher the HGI, the better the grindability. For ordinary bituminous coal, the HGI is 50 to 60.

(2) Crucible expansion test: 1 gram of air-dried sample is placed in a quartz crucible, covered, and heated in an electric furnace under certain conditions, and the shape of the resulting charcoal is compared with a standard outline to obtain an index (button index). The button index expresses the degree of free expansion due to heating, and does not directly indicate the strength of the coke.

(3) Gieseler fluidity test: 200 grams of a sample crushed to 420 micrometers or less is placed in a test crucible, and a special torqued stirring rod is embedded in it. When heated at a constant temperature increase rate in a metal bath, the rotation speed of the stirring rod is recorded and expressed in ddpm (dial divisions per minute). The point at which the stirring rod starts to rotate and reaches 1 DDPM is called the softening start temperature, the fluidity at which it reaches its maximum is called the maximum fluidity, and the temperature at which it stops moving again is called the solidification temperature. This indicates the softening and melting properties of coal and is widely applied to coke coal (caking coals), but cannot be applied to non- or slightly caking coals.

(4) Ash melting point test Coal is incinerated, mixed with water or a 10% solution of dextrin, and molded into a triangular pyramid. It is then heated at a constant temperature in an electric furnace. The melting point of the ash is determined by the temperature at which the pyramid becomes hemispherical. Ash generated during pulverized coal combustion is collected as fly ash, but it may adhere to the walls of the furnace, reducing combustion efficiency or causing blockages, which can interfere with operation. In addition, during coal gasification, etc., ash can be extracted as solid powder at low temperatures, and as molten ash (slag) in gasification methods with extremely high temperatures. However, at temperatures between these two, the ash sinters and becomes a hard lump (clinker) in the furnace, or adheres to the furnace walls, causing the phenomenon of hanging, which can interfere with operation. The melting point of ash can be said to be one of the important physical properties, because it can determine what type of combustion furnace or gasification furnace to select, or what combustion or gasification conditions to choose.

[President Ouchi, Masaru Ueda, and Toshihiro Aramaki]

Coal structure

になったんです。 English: The first thing you can do is to find the best one to do ^. Anthracite is not solubilized by any reaction, so the average structure cannot be determined using such a method, but the number of aromatic rings estimated from X-ray diffraction, magnetic coefficient measurement, specific gravity measurement, etc. is very large, with a very large number of aromatic rings, at 10 or more. In other words, the coalization reaction is a condensation reaction of aromatic rings, which coincides with the fact that the coalization reaction mentioned in "genicity" is a kind of carbonization reaction. In other words, in the carcinogenic reaction, the aromatic rings are condensed with each other, gradually becoming aromatic rings with a large number of rings, and the stacking of these rings progresses, and finally, a graphite-like structure spreads in two-dimensional and three-dimensionally. ¹³ With the advent of C-NMR, it has become possible to find the average structure of coal in a solid state.

Lignet and lignite contain a large amount of hydroxy groups, carboxy groups (carboxyl groups), carbonyl groups, ether-type oxygen, etc., but these active groups gradually decrease with the degree of carbonization. The carboxy groups decrease the fastest, and are thought to decompose into carbon dioxide, and almost disappear at around 77% carbon content. Hydroxy groups, ether-type oxygen, etc. are thought to disappear as water.

It is said that lignin has propylbenzene as its backbone structure, and hydroxy and methoxy groups are bound heterogeneously to this, and these backbone structures are bound to each other in various ways to create a polymer structure. In lignin, lignin is likely to undergo some oxidation during the initial biochemical process, and dehydroxyl groups and demethoxylation have progressed from the slow pyrolysis process in the ground. However, these changes remain in the early stages, and the aromatic ring remains monocyclic. Even when oxidation products are analyzed, the majority are monocyclic compounds. Furthermore, its molecular weight is considered to be a considerable high molecular weight, and it is not likely that the pyrolysis of lignin has progressed much.

になったんです。 English: The first thing you can do is to find the best one to do.

Even coal with low degree of coalization does not soften and melt when heated. This is because, in addition to being originally a polymer, it also has many functional groups such as hydroxy, carboxy and carbonyl groups, which leave at relatively low temperatures, resulting in random bonds of radicals (free active groups) resulting in dense network structures.

As mentioned above, coal that becomes coke is a special range of coke that has heat softening properties, and coal that is even more powerful is limited to coal with a narrower carbon content of around 90%.