JPH0367549B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a coal liquefaction method for converting coal into liquid substances such as light oil and heavy oil. Conventional technology and its problems The principle of coal liquefaction has been known for a long time.
Usually, the method used is to add hydrogen to coal and liquefy it under high temperature and pressure. In this coal liquefaction method, it is difficult to continuously introduce solid coal directly into the high-pressure system, so solid coal is finely pulverized and mixed with a solvent to form a slurry and then introduced into the high-pressure system. A method of pressure feeding is adopted. The solvent used in the above coal liquefaction method must have good affinity with the coal itself, do not cause solid-liquid two-phase separation, and have the ability to uniformly disperse and stabilize the liquefied product. It is usually obtained by liquefying coal because it is desirable to have high aromaticity from the viewpoint of solubility, etc., it has hydrogen donating ability to promote the liquefaction reaction, and it is also economical. Heavy oil components are used. When this medium-heavy oil component is used as a solvent for coal liquefaction, it can be recycled as is or it can be hydrotreated and recycled. It is necessary to remove aliphatic hydrocarbons, which degrade them. In other words, the main component of aliphatic hydrocarbons obtained by liquefying coal is n-paraffin, whose carbon number distribution ranges from about C ₁₀ to C ₃₀ , and these paraffins are the main components of coal liquefied oil. This paraffin has properties such as having a low affinity with certain aromatic components, being difficult to decompose even under coal liquefaction conditions at a reaction temperature of 400°C or higher, and being easy to coagulate and precipitate. When concentrated, the performance of the solvent deteriorates significantly, resulting in a decrease in liquefaction reaction efficiency.
Furthermore, as the degree of circulation of the solvent increases, the viscosity of the solvent increases, and the pressure loss of the entire coal liquefaction facility gradually increases. Furthermore, solid matter adheres to the piping system, often causing problems such as blockage.
In particular, the above-mentioned troubles occur frequently in the slurry supply system. This tendency appeared when coal with a low degree of coalification was liquefied, and when the reaction temperature was low, the entire solvent or slurry sometimes solidified. Purpose of the Invention The present invention was made to solve the above-mentioned conventional problems, and improves the solvent performance by removing n-paraffin from the circulating solvent, improves the efficiency of the coal liquefaction reaction, and also solves the problem of clogging the piping system. The purpose of the present invention is to propose a coal liquefaction method that prevents such troubles and makes it possible to recover n-paraffin, which is a useful resource. Composition of the Invention The method for liquefying coal according to the present invention includes cooling a part or the entire amount of the circulating solvent to 20°C or less when reusing medium-heavy oil components obtained by liquefying coal as a solvent for coal liquefaction. It is characterized in that it is used as a solvent for coal liquefaction after removing the precipitated solids. That is, this invention utilizes the property that n-paraffin easily dissolves in a circulating solvent at high temperatures, is difficult to dissolve at low temperatures, and easily precipitates, and cools this circulating solvent to a temperature of 20°C or less. This is a method in which n-paraffin is precipitated by a method, which is then removed and used as a circulating solvent. The solubility of n-paraffin in circulating solvent is
As seen in the relationship between the concentration and solubility of n-paraffin shown in Figure 2, the concentration is relatively small up to about 20°C, but increases rapidly above 20°C. Therefore, it is possible to easily precipitate n-paraffin by cooling the circulating solvent to below 20°C, but if the circulating solvent is cooled too much, other components will also precipitate at the same time, reducing the purity of n-paraffin in the precipitate. Therefore, the temperature is preferably 0°C or higher. In addition, the hydrogenation process partially hydrogenates the aromatic compounds in the circulating solvent, lowering the freezing point of these compounds and making it possible to selectively extract paraffin without precipitating it during paraffin precipitation. However, it has the characteristic that it can enhance the hydrogen donating property of the solvent. Here, the hydrogenation process refers to Ni-Mo and Co-
A process of hydrogenating a circulating solvent using a trickle-bed reactor filled with Mo-based catalyst, etc.
Generally reaction temperature 250~350℃, pressure 50~200Kg/ ^cm2
The reaction is carried out under conditions such as G and LHSV0.5 to 2. The tendency for n-paraffin to accumulate becomes more pronounced as the temperature in the liquefaction process is lower (within the temperature range that allows the liquefaction reaction) and as the reaction time is shorter. This is because secondary decomposition occurs, and the decomposition reaction depends on the reaction temperature and reaction time. Therefore, it is possible to keep the n-paraffin concentration in the circulating solvent low by increasing the temperature and reaction time of the liquefaction process, but this method also decomposes the liquefied oil and solvent, causing gas This method cannot be adopted because only the yield of liquefied oil increases and the liquefied oil yield decreases. Specific Example FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out the method of this invention. That is, the coal 7 and the circulating solvent 8 are stirred and mixed in the slurry forming step 1 to form a slurry. This slurry is sent to the liquefaction reaction step 2, and after the liquefaction reaction is completed, the product enters the distillation column 3, where it is separated into light oil component 9, medium oil component 10, and heavy oil component 11. Part or all of the oil component is used as a circulating solvent 8, either as it is, or after being hydrogenated in the hydrotreating step 6-1, sent to the cooling step 4, where it is cooled to a temperature of 20°C or less to convert it into n-paraffin. The precipitate is separated and removed in a separation step 5 to recover n-paraffin 12. The circulating solvent from which n-paraffin has been removed is used as it is or after being hydrogenated in the hydrogenation step 6-2 and sent to the slurry forming step 1 for circulation. In addition, as a means for cooling the circulating solvent, for example, a method of exchanging heat with cold water or cold air from the outside or inside (double pipe) of a transport pipe for the circulating solvent can be adopted. Further, as a means for separating and removing n-paraffin precipitated in the cooling step, for example, a filter can be used. Example 1 Coal crushed to 100 mesh or less and solvent (boiling point
A slurry made with a 1:5 weight ratio of 200-538°C fraction) was used to create a slurry with an internal volume of 10 (slurry holding capacity 2.5).
Using a coal liquefaction equipment equipped with two stirred reactors in series, the slurry flow rate was 5/hr, and the reaction temperature was
The mixture was liquefied under the conditions of 450° C., reaction pressure of 170 Kgf/cm ² G, and hydrogen gas/slurry flow rate ratio of 700. After that,
The liquid product was distilled to obtain a fraction with a boiling point of 200 to 538°C, which was cooled to 18°C in a cooling tank, the resulting precipitate was separated using a filter, and the resulting liquid was used as a circulating solvent. . Table 1 shows the results of repeating the above operation 10 times.
Table 1 shows the boiling points obtained by liquefying coal under the same conditions as above and distilling the liquefied product.
The results of using the 200-538°C fraction as a circulating solvent without cooling are also shown. From the results in Table 1, when the circulating solvent is cooled, the n-paraffin concentration is significantly lower than when it is used as a circulating solvent without cooling, and the liquefaction reaction efficiency is improved. are doing. In addition, in the case of the circulating solvent that had been cooled, there were no problems with clogging of the slurry supply line or other piping system, whereas in the case of the circulating solvent that had not been cooled, the slurry and liquefaction at room temperature started from around the 5th time. Problems began to occur in the supply of the product, and after 10 cycles it became completely solid at room temperature, making it unusable.

[Table] Example 2 The circulating solvent obtained under the same conditions as Example 1 was mixed with a sulfurized Ni-Mo catalyst (Ni15%, Mo3%/
Hydrogen gas pressure of 100 Kg/cm ² G in a trickle bed reactor with an inner diameter of 69 mm filled with 2 liters of Al ₂ O ₃ )
Hydrogenation was carried out at a reaction temperature of 290°C and LHSV1, and the resultant was used as a solvent for the next liquefaction. Perform the above operations 10
Table 2 shows the results of repeated tests. Table 2 shows the results of liquefying coal under the same conditions as above, hydrogenating the resulting solvent (boiling point 200-538°C fraction) without cooling, and using it as a liquefaction solvent. The results obtained are also shown as Comparative Example 2. From the results in Table 2, in this example, as in Example 1, when the circulating solvent was cooled, and when the circulating solvent was directly hydrogenated without cooling treatment (Comparative Example 2). Compared to this, the n-paraffin concentration was greatly reduced and the liquefaction reaction efficiency was improved. However, in this case, since the circulating solvent has been hydrogenated, the effect is smaller than when no hydrogenation treatment is performed, but as in Comparative Example 1, slurry and liquefaction formation at room temperature starts around the 7th cycle. Problems with the delivery of goods began to occur.

[Table] Effects of the Invention As is clear from the examples above, according to the method of this invention, it is possible to keep n-paraffin in the circulating solvent at a low level, which not only increases the efficiency of the coal liquefaction reaction. This prevents troubles such as blockages in the piping system and stabilizes operations. At the same time, since n-paraffin, which is a useful resource, can be recovered, it can also contribute to resource saving.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out the method of the present invention, and FIG. 2 is a chart showing the relationship between the temperature of the circulating solvent and the concentration and solubility of n-paraffin in the present invention. 1... Slurrying process, 2... Liquefaction reaction process,
3... Distillation column, 4... Cooling process, 5... Separation process, 7... Coal, 8... Circulating solvent.

Claims (1)

[Claims] 1. In a coal liquefaction method in which medium-heavy oil components obtained by liquefying coal are recycled as a solvent for coal liquefaction either as they are or after hydrogenation treatment, part or all of the circulating solvent is cooled to 20°C or less. A method for liquefying coal, characterized in that the precipitated solids are removed and then used as a solvent for coal liquefaction.