JP4810018B2 - Coal tar distillation method and distillation apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coal tar distillation method and a distillation apparatus, and more particularly to a technique for suppressing the corrosion of a distillation tower by chlorine contained in the coal tar and extending the life of the coal tar during distillation.
[0002]
[Prior art]
Generally, when coke is produced by dry distillation of coal, generated exhaust gas is cooled, and volatile components in the exhaust gas are condensed and recovered as coal tar. This coal tar is a mixture of various aromatic hydrocarbons, but when further distilled, as shown in FIG. 2 (a), various tar oils (carbol oil, naphthalene oil, washing oil, anthracene are used as distillate oil. Oil) is recovered, and the distillation residue is thermally modified to become binder pitch (hereinafter referred to as pitch). This distillate oil is used as a chemical industrial raw material, and pitch is used as various carbon materials (for example, an electrode raw material for electrolytic refining of aluminum).
[0003]
By the way, since coal tar contains several hundred ppm of chlorine, when distilled as it is, a specific temperature region in the distillation column (the hatched portion in the figure has a boiling point of 200 to 230 ° C. at normal pressure). (Near the outlet of naphthalene oil). And if the chlorine concentration there exceeds 500 ppm, it is known that the wall of the distillation tower (material is carbon steel) is significantly corroded. Therefore, normally, as shown in FIG. 2 (b), sodium carbonate as an anticorrosive is added to the raw coal tar, and chlorine is immobilized as sodium chloride. Thereafter, the sodium chloride is extracted from the distillation tower as a distillation residue along with the pitch (see, for example, the aromatic and tar industrial handbook, edited by the Japan Aromatic Industry Association, first published in December 1978).
[0004]
However, in the conventional technique in which the sodium carbonate described above is added to the distillation column, a large amount of sodium chloride is contained in the pitch that is the distillation residue. This causes another problem that the use of the pitch is limited. In order to solve this problem, it is necessary to separately clean the pitch with hot water or the like, and this conventional technique is economically undesirable.
[0005]
[Problems to be solved by the invention]
In view of such circumstances, an object of the present invention is to provide a method for distillation of coal tar that not only prevents the inner wall of the distillation tower from being anticorrosive but also does not require reprocessing of the distillation residue.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the inventor conducted intensive studies on a method for preventing the formation of a chlorine-enriched region in a distillation column, and the results were embodied in the present invention.
[0007]
That is, the present invention relates to a method for distillation of coal tar in which a column tower type distillation column hecoal tar provided with a distillation outlet according to the type of distillate to be distilled is continuously supplied and naphthalene oil is distilled from one distillation outlet. And adding an aqueous alkaline solution to the distilled naphthalene oil to separate the produced sodium tarate, and separating a portion of the sodium naphthalate and purifying a portion of the purified naphthalene oil from the naphthalene oil in the distillation column. The coal tar distillation method is characterized in that the coal tar is returned to a stage corresponding to the above-described distillation outlet or a higher stage.
[0008]
In addition, the present invention provides a column tower distillation column provided with a distillation outlet according to the type of distillate to be distilled, supplied with coal tar, and a distillate piping for naphthalene oil from the distillation column. A supply means of an alkaline aqueous solution to be added to and mixed with naphthalene oil passing through the outlet pipe, an oil / water separator for separating the mixed solution into a water phase and an oil phase, and a naphthalene oil separated by the oil / water separator Is a coal tar distillation apparatus characterized in that a part of the coal tar is returned to a stage corresponding to a naphthalene oil distillation outlet in the distillation column or a pipe higher than that.
[0009]
In these methods and apparatuses, the alkali is preferably sodium hydroxide.
[0010]
In the present invention, chlorine concentrated in the vicinity of the outlet of naphthalene oil in a plate column distillation column (hereinafter referred to as a distillation column) is circulated through a portion of naphthalene oil obtained by separating and refining sodium tartrate, Since the chlorine concentrated in the vicinity of the distillate outlet of naphthalene oil is washed and distilled, the chlorine in the distillated naphthalene oil is transferred to sodium tartrate by the addition of an alkaline aqueous solution, so the naphthalene oil in the distillation column It becomes possible to suppress the concentration of chlorine in the vicinity of the distillate outlet. As a result, not only can the inner wall of the distillation column be protected from corrosion, but there is no chloride such as sodium chloride in the distillation residue, so that reprocessing of the distillation residue becomes unnecessary. The plate column type distillation column is provided with a plurality of step beds such as bubble bell trays, valve trays and perforated plate trays in the distillation column.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below based on the circumstances leading to the invention.
[0012]
First, the inventor decided not to add sodium carbonate to coal tar supplied to the distillation column in order to avoid a large amount of chloride (such as sodium chloride) from being transferred to pitch, which is a distillation residue. Accordingly, chlorine concentration naturally occurs near the specific temperature range in the distillation column, that is, near the stage corresponding to the naphthalene oil distillation outlet (hereinafter referred to as the distillation stage). Is required.
[0013]
Therefore, the inventor added, “In the tar industry, as shown in FIG. 2 (b), an aqueous sodium hydroxide solution was added to the naphthalene oil in order to recover sodium tarate from the naphthalene oil distilled from the distillation column. (For example, refer to the aromatic and tar industrial handbook, edited by the Japan Aromatic Industry Association, published in the first edition of December 1978). This is because, from the viewpoint of a normal acid-base reaction, if chlorine, which is an acidic element, is present in naphthalene oil, the chlorine is extracted into sodium tartrate (aqueous phase) produced by the addition of an aqueous sodium hydroxide solution.
[0014]
In order to confirm this, the inventor conducted an experiment in which a sodium hydroxide aqueous solution was added to and mixed with naphthalene oil added with ammonium chloride as a chlorine source using a beaker. As a result, it was confirmed that chlorine was transferred to the aqueous phase along with sodium tartrate. At the same time, it was confirmed that the reaction between chlorine and sodium hydroxide proceeds by an acid-base equivalent reaction, and that the reaction shifts very easily if the aqueous phase is alkaline. This means that even if sodium carbonate is not added to coal tar in the distillation tower and chlorine is removed, if an aqueous alkali solution is added to the distilled naphthalene oil, it will accompany the soda tartrate (water phase) produced. This suggests that chlorine can be removed from the system. The chlorine can be easily removed by a purification process such as dehydration of sodium tartrate.
[0015]
However, even if the chlorine of naphthalene oil is removed at the stage of being extracted from the distillation column, the chlorine enters the distillation column along with the newly supplied coal tar, which is concentrated in the specific temperature range. There is no change. Therefore, the inventor decided to wash and distill chlorine in this specific temperature range. As the substance for washing and distilling, naphthalene oil containing no chlorine is preferable. The naphthalene oil may be introduced separately from the outside of the distillation column, but it is most preferable from an economic standpoint if the product separated and purified by recovery of sodium tartrate can be returned to the distillation column and used again. Therefore, a pipe for separating sodium tarate and returning a part of the refined naphthalene oil to the distillation tower was additionally installed in the existing equipment, and the present invention was completed.
[0016]
Furthermore, in the present invention, among distillate oils obtained by distilling coal tar, a sodium hydroxide aqueous solution is added to naphthalene oil. The temperature of naphthalene oil at that time is 60 ° C. or higher and below the distillation temperature. It is preferable. More preferably, it is 80-100 degreeC. If this temperature is 100 ° C or higher, a separate pressurizing operation is necessary for the convenience of contact with the aqueous phase, and if it is higher than the distillate oil temperature, the vapor pressure of naphthalene oil increases, and equipment with pressure resistance specifications is required This is because the equipment cost becomes high. Moreover, at 60 degrees C or less, naphthalene oil coagulates and it becomes impossible to operate. Note that the production of sodium tartrate and the extraction of chlorine into the aqueous phase by contact of naphthalene oil and aqueous sodium hydroxide proceed almost instantaneously. Therefore, in the practice of the present invention, a line mixer such as a static mixer may be used as the contact means.
[0017]
In addition, in the present invention, the addition amount of the aqueous sodium hydroxide solution is adjusted so that the pH of the hydrous sodium tartrate as the separation aqueous solution is 5 or more, preferably 12 or more. This is because an existing apparatus for extracting sodium tarate can be used. Further, when the pH of the hydrous sodium tartrate is 5 or less, the extraction of chlorine is insufficient.
[0018]
In addition, in the present invention, the amount of naphthalene oil to be returned to the distillation column is preferably returned while maintaining the relationship shown in FIG. In FIG. 1, (X) is the amount of naphthalene oil extracted from the distillation column, (a) is the amount of sodium tarate produced, and (Y) is the amount of purified naphthalene oil as a product. The value of (XYA) is preferably 50% by mass or more, and more preferably 50 to 170% by mass with respect to coal tar 2. By setting it to 50% by mass or more, removal of chlorine is ensured. Moreover, it is because the excessive temperature fall of a distillation tower can be prevented by setting it as 170 mass% or less. When the amount of heat in the distillation column is insufficient, the distillation column may be supplemented with heat, such as heating the returned naphthalene oil.
[0019]
Moreover, in this invention, it is good to return the position which returns said dechlorinated naphthalene oil to the distillation stage same as or higher than the distillation stage of naphthalene oil. This is because returning to a lower stage does not result in cleaning or distilling chlorine. Moreover, as long as it is the same or higher stage, it may be returned to any place, but it is preferably returned to about one theoretical stage, that is, for example, in the case of a plate tower, it is returned to the second to the third stage. This is because, in the same stage, the heat / material exchange efficiency of the gas / liquid in the tower is not sufficient, so that the operation of the distillation tower is possible, but the balance is easily lost and the state becomes unstable. Moreover, if it returns to a stage higher than necessary, the rectifying effect of the distillation column will decrease.
[0020]
Hereinafter, specific contents of the coal tar distillation method according to the present invention will be described with reference to FIG.
[0021]
First, as shown in FIG. 3, the naphthalene oil 4 distilled from the distillation column 1 is cooled to 100 ° C. or less by a cooler 1. After bringing this into contact with the sodium hydroxide aqueous solution 14 by the line mixer 10, the hydrous sodium tartrate 6 as an aqueous phase is left and separated in the oil / water separation tank 5. Then, a part of the dechlorinated naphthalene oil (refined naphthalene oil 13) is returned to the distillation column 1 to produce the remaining purified naphthalene oil as the product 15. Here, if a steam boiler is adopted as the cooler 3, heat can be recovered, so that the energy cost is advantageous. In the oil / water separation tank 5, an interface meter 7 is preferably installed to adjust the production amount of the hydrous sodium tartrate 6. The extraction of naphthalene oil 4 from the distillation column 1 is performed at a constant flow rate while monitoring a flow meter, and the amount returned to the distillation column 1 is adjusted based on the temperature in the column. The oil / water separation tank 5 that divides the water phase and the oil phase may be any device that separates by the difference in specific gravity between the two liquids, for example, a centrifuge. In the example of FIG. 3, the dechlorinated naphthalene oil is returned to three stages above the distillate stage of naphthalene oil.
[0022]
【Example】
(Example 1)
The distillation apparatus shown in FIG. 3 was applied, and coal tar 2 was distilled at normal pressure.
[0023]
Naphthalene oil 4, which is a distillate having a boiling point of 200 to 230 ° C. at normal pressure, was extracted from distillation column 1 in an amount corresponding to 80% by mass of the coal tar supply amount, and cooled to 90 ° C. with cooler 3. This was mixed with a 15% by mass sodium hydroxide aqueous solution 14 with a line mixer 10 and then supplied to the oil / water separation tank 5. The liquid temperature in the oil / water separation tank 5 at this time is 70 ° C., and the pH of the aqueous phase is 12.1. Next, a part of the naphthalene oil separated and purified in the oil / water separation tank 5 was returned to the distillation column. The naphthalene oil returned to the distillation column 1 is 63 to 65% by mass of the amount of coal tar supplied to the distillation column 1. The return position is three stages above the naphthalene oil distillation stage.
[0024]
This operation was carried out continuously for 7 days, and naphthalene oil was periodically sampled from the vicinity of the naphthalene oil distillation outlet of the distillation column to measure the amount of chlorine. As a result, it was confirmed that the chlorine concentration during the operation was constant at about 310 ppm, and no concentration of chlorine occurred.
(Example 2)
Example 1 except that the amount of naphthalene oil withdrawn from the distillation column was 120% by mass (based on the raw material coal tar) and the amount of return of the purified naphthalene oil was 100% by mass (based on the raw material coal tar). Then, coal tar was distilled continuously for 7 days.
[0025]
As a result, it was confirmed that the chlorine concentration in the vicinity of the naphthalene oil distillation outlet during operation was constant at about 130 ppm, and no chlorine concentration occurred.
[0026]
Moreover, it turns out that the amount of chlorine can be restrained low by increasing return amount.
(Comparative example)
7 days in the same manner as in Example 1 except that the amount of naphthalene oil extracted from the distillation column was 20% by mass (relative to the raw coal tar) and the purified naphthalene oil was not returned. Coal tar was distilled.
[0027]
As a result, the chlorine concentration near the naphthalene oil distillation outlet at the start of operation was 320 ppm, but increased to 400 ppm after 7 days. If it is not returned, it can be seen that chlorine concentration has occurred.
(Reference example)
Refined by using 20% by weight sodium bicarbonate aqueous solution of 0.3% by weight coal tar as the raw material for distillation, and extracting 20% by weight of naphthalene oil from the distillation column (relative to the raw coal tar). The coal tar was continuously distilled for 7 days in the same manner as in Example 1 except that the naphthalene oil was not returned.
[0028]
As a result, the chlorine concentration in the vicinity of the naphthalene oil distillation outlet at the start of the operation was 140 ppm, but after 7 days it was 145 ppm, and there was a tendency to increase slightly.
[0029]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress the concentration of chlorine near the outlet of naphthalene oil in the distillation column. As a result, not only can the inner wall of the distillation column be protected from corrosion, but there is no chloride such as sodium chloride in the distillation residue, so that reprocessing is not necessary.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram for explaining the relationship between the amount of naphthalene oil extracted from a distillation column and the amount of return in the practice of the present invention.
FIG. 2 is a diagram showing a conventional coal tar distillation method, in which (a) shows no addition of Na ₂ CO ₃ to coal tar, and (b) shows distillation by adding Na ₂ CO ₃ to coal tar. In this case, NaOH is added to the naphthalene oil.
FIG. 3 is a diagram illustrating a coal tar distillation apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Distillation column 2 Coal tar 3 Cooler 4 Naphthalene oil 5 Oil-water separation tank 6 Hydrous soda 7 Interface meter 8 Carbolu oil 9 Washing oil 10 Line mixer 11 Anthracene oil 12 Pitch 13 Purified naphthalene oil 14 Sodium hydroxide aqueous solution 15 Product

Claims (2)

In the method for distillation of coal tar, which continuously feeds a coal tower hecoal tar provided with a distillation outlet according to the type of distillate to be distilled, and distills naphthalene oil from one distillation outlet,
An aqueous alkali solution is added to the distilled naphthalene oil to separate the produced sodium tartrate, and a part of the naphthalene oil purified by separating the sodium tarate is separated from the naphthalene oil in the distillation column. A method for distilling coal tar, characterized in that the coal tar is returned to the stage corresponding to the distillation outlet or higher. Coal tar is supplied and passes through the distillation pipe to a column-type distillation column provided with a distillation outlet corresponding to the type of the distillate to be distilled, and a naphthalene oil distillation pipe from the distillation tower. A supply means of an alkaline aqueous solution to be added to and mixed with naphthalene oil, an oil / water separator for separating the mixture into a water phase and an oil phase, and a part of naphthalene oil separated by the oil / water separator, A coal tar distillation apparatus, comprising: a pipe corresponding to a stage corresponding to a distillation outlet of naphthalene oil in a distillation tower or a pipe returning to a higher stage.

Images