Coal tar processing technology
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Coal tar is divided into high-temperature tar and medium-low temperature tar: High-temperature coal tar is a black, viscous liquid with a relative density greater than 1.0; it contains large amounts of pitch, while its other components are aromatic hydrocarbons and heterocyclic organic compounds. More than 400 compounds contained have been identified. In industry, the concentrated processing of coal tar facilitates the separation and extraction of compounds that are present in very small amounts. The processing begins with distillation to separate various fractions based on their boiling points, followed by further processing. The processing of each fraction using crystallization methods can yield products such as naphthalene and anthracene ； Nitrogen-containing basic heterocyclic compounds (known as tar bases) or acidic phenolic compounds (known as tar acids) can be obtained using acid or base extraction methods. Through further distillation and separation of taric acid and tar bases, phenol, cresol, dimethylphenol, as well as pyridine, methylpyridine, and quinoline can be obtained respectively. These compounds are important raw materials for dyes, pharmaceuticals, fragrances, and pesticides. The fraction oils obtained from coal tar distillation can also be used directly without separation; for example, the asphaltenes can be used to produce various important products such as electrode coke and carbon fibers, phenol oil can be used for wood preservation, washing oil serves as an absorbent for recovering crude benzene from gas, and light oil is processed together with crude benzene. Medium- and low-temperature coal tar is also a black, viscous liquid; it differs from high-temperature coal tar in that its relative density is usually less than 1.0, it contains less aromatic compounds and more alkanes, and its composition depends on the quality of the raw coal. Low-temperature carbonization tar is one of the important sources of synthetic oil, from which products such as gasoline and diesel are produced through high-pressure hydrogenation. Main uses: It can be used to distill various aromatic hydrocarbons, alkanes, phenols, etc., and it can also be used to produce asphalt shingles, fuel, and carbon black. Could everyone share their views on the technologies for utilizing coal tar and its future prospects? It would also be good to discuss the processing methods for high-temperature tar and those for medium- and low-temperature tar separately.
The technology for processing high-temperature coal tar is well-established; over the past few years I have been working on the processing of Chinese coal tar, following two different approaches. First, distill the oil roughly to use it as fuel oil. Second, take the fractions before 360, extract the phenols, then decolorize them; subsequently, these are combined to form kerosene diesel, and asphalt is further processed to produce fuel oil
A brief review of the above two approaches. First, distill the oil roughly to use it as fuel oil. A large amount of asphaltenes will be distilled out; if it is not possible to increase their value, it seems better not to process them at all and to sell coal tar directly. Second, the fractions obtained before 360 degrees are used to extract phenols, which are then decolorized and used to formulate coal diesel, while the asphaltenes are processed into fuel oil. With this extraction method, the yield of phenols is very low ； And it can’t be cleaned properly ； It can’t be purified properly; how could it then be turned into diesel? The term \"coal diesel\" is quite vague – it seems to be a term coined by someone, and it has nothing to do with diesel at all. This is for discussion only, as a reference. Last edited by stubstone on 2008-7-6 00:32
Decolorization: What should be used for decolorization? Can it be done effectively? How many days can the color be preserved? !
First, the asphaltene you mentioned is what we refer to as coal cokerefinery residue oil. In our process, we keep the Enneberg viscosity at 25, and this material can serve as a substitute for heavy oil as fuel for glass factories. The light component can be formulated into a cold spray oil. As for the profits, they’re of course not very high, but at least they’re better than those from selling coal tar. Second, the yield of phenols varies depending on the quality of coal tar, ranging approximately between 10 and 28 (for the initial fractions). Third, “coal diesel” is an informal term used in our region; the product catalog does not provide a definition for this substance. Fourth, as far as I know, there are no large enterprises in China that engage in the deep processing of medium-temperature coal tar at present. It is said that there is one company in Henan that carries out hydrogenation processes, while the other small enterprises follow the same approach. I would be very grateful if this expert could share any useful suggestions
The processing process in our factory generally involves the dehydration and deslagging of tar, followed by distillation to separate out the three-component mixture, light oil components, and asphalt. The asphalt can be sold after being modified, or it can also be sold directly without modification. The three-component mixture is washed to produce industrial naphthalene for sale; during this process, different compounds are formed, such as phenol oil, which is also sold directly. I would appreciate some guidance on which products offer a better return on investment if we were to invest in their further processing. This post was last edited by Jiang Yufei on 2008-7-6 08:39.]
The tar processing is basically the same now. All involve tar distillation (dehydration first, primary evaporator, secondary evaporator, fractionation column), as well as washing processes (phenol removal; pyridine is hardly removed), blowing, separation, and intermittent separation ； Industrial naphthalene distillation (primary tower, refined tower). Products: light oil, asphalt, anthracene oil, dephenolized phenol oil, crude phenol, industrial naphthalene, washing oil, etc.
The rapid commissioning of the Shenmu coal tar hydrogenation plant is likely underway; if it succeeds, it could have a significant impact on existing coal tar processing methods. However, this is possible only if high oil prices are maintained, otherwise profits won’t be substantial. In terms of the degree of resource utilization, coal tar hydrogenation discards (or at least partially discards) valuable chemical raw materials such as phenols, naphthenes, and anthracene derivatives; in particular, it eliminates those petroleum-based raw materials that cannot be synthesized economically. From this perspective, hydrogenation for oil production is not the best way to utilize these resources.
The coal tar hydrogenation plant in Shenmu has been put into operation; it employs multi-stage hydrogenation under high temperature and pressure, using the steam reforming process, and is currently achieving excellent results. However, as you said, many important components are discarded; from the perspective of long-term resource utilization, this does not represent advanced technology.
You mentioned that the yield of phenol is very high; I’m not sure if you’re referring to medium- or low-temperature coal tar. At the current stage, it seems that there is a lot of activity in the hydrogenation of medium- and low-temperature coal tar. I’m not sure how much you know about this; could you talk about the general situation? Also, could you talk about whether there are any companies specialized in separating fine components? Companies that engage in the advanced processing of coal tar, such as Lütgé in Germany and Shin Nihka in Japan?
There are many processes for converting it into diesel. At present, many small coal tar refining plants use this process; of course, the quality cannot be guaranteed, haha.