JPH0338314B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention is directed to aromatic products such as benzene, toluene, xylene, etc., which are refined from tar-based light oil obtained during coke production, that is, gas light oil derived from coke oven gas and tar light oil derived from coal tar. This invention relates to a method for refining light oil for producing family products. [Prior art] Gas light oil obtained from coke oven gas recovered during coke production and tar light oil obtained from coal tar contain large amounts of useful aromatic products such as benzene, toluene, and xylene. On the other hand, it also contains impurities such as dienes, olefins, sulfur compounds, and tar bases, and when producing aromatic products from these tar-based raw gas oils, it is necessary to separate and remove the impurities in the raw gas oil. Purification treatment is required. The method for refining this raw material gas oil is to first pre-distill the raw material gas oil to remove dissolved gases such as oxygen, moisture, etc.
The components are adjusted by removing heavy components such as low-boiling components such as C ₅ and high-boiling components such as C ₉ or higher, and then reacted with hydrogen gas to remove the various impurities contained in the raw gas oil. Hydrogenation and hydrogenolysis are performed, followed by purification and distillation. However, in conventional refining methods, useful tar bases such as pyridine and α-picoline are not only subjected to hydrogenation or hydrogenolysis in the hydrogenation process of raw material light oil, but also an increase in hydrogen consumption occurs. [Object of the Invention] The present invention was devised in view of the above-mentioned viewpoints, and its purpose is to obtain a highly pure aromatic hydrocarbon product, to consume less hydrogen,
The object of the present invention is to provide a distillation method that consumes less acid, alkali, etc., and to provide a light oil refining method that allows useful tar bases to be recovered easily and efficiently. [Structure of the Invention] That is, the present invention charges tar-based raw material light oil into a pre-distillation column and separates it into a low boiling point fraction, a heavy oil fraction, and a light oil fraction with a boiling point of 100 to 145°C. The resulting light oil fraction is debased by pickling and extraction, then neutralized with an alkali to remove residual acidic content, and then the residual alkaline content is separated and removed to obtain a refined light oil. This is a light oil refining method in which a distillate and the above-mentioned low-boiling fraction are combined and charged into a hydrogenation reaction step, and after hydrogenation, purification distillation is performed. In the present invention, the boiling point of raw gas oil is reduced by preliminary distillation.
It is separated into a low-boiling fraction with a boiling point lower than 100°C, a heavy oil fraction with a boiling point higher than 145°C, and a light oil fraction with a boiling point of 100-145°C. Low-boiling fractions and boiling points below 100℃
In the heavy oil fraction with a temperature higher than 145°C, tar bases such as pyridine and α-pyricone, which are targets of recovery, are hardly present, and other tar bases are also hardly present. Furthermore, when the amount of heavy oil with a temperature higher than 145°C increases, sludge is likely to be generated when it comes into contact with an aqueous acid solution, and the consumption of acids and alkalis also increases. Pre-distillation of feedstock gas oil may be carried out using multiple distillation columns, but if the light oil fraction containing useful tar bases such as pyridine and α-pyricone comes into contact with oxygen in the air for a long time, it will become acidic. The amount of sludge generated during the debasing treatment process by washing and extraction increases. Therefore, preferably, a low-boiling fraction with a boiling point lower than 100°C is extracted from the top of the column, and a low-boiling fraction with a boiling point lower than 100°C is extracted from the bottom of the column.
It is preferable to use a distillation column which extracts a heavy oil fraction having a temperature higher than 145°C and also extracts a light oil fraction having a boiling point of 100 to 145°C from its side cut as a side cut fraction. In addition, the proportions of low boiling point fractions, light oil fractions, and heavy oil fractions in the preliminary distillation of feedstock gas oil vary depending on the composition of the feedstock gas oil, but the ratio of low boiling point fractions, light oil fractions, and heavy oil fractions to 100 parts of feedstock gas oil varies depending on the composition of the feedstock gas oil. It is preferable that the fraction is 20 to 30 parts, the light oil fraction is 55 to 72 parts, and the heavy oil fraction is 8 to 15 parts. The above-mentioned debasing treatment by pickling and extraction of the light oil fraction can be carried out by a conventionally known method, but it suppresses the generation of sludge, increases the recovery rate of useful tar bases, and also improves the efficiency of the equipment. In order to prevent corrosion problems, it is preferable to recirculate a portion of the extract extracted from the lower layer of the separation tower to the debasing treatment process and add the required amount of acidic liquid to the recycled extract. The free acid concentration of the extract is maintained at about 5-10% by replenishing the extract. The light oil fraction and the extraction liquid may be mixed together by using a pipe mixer, for example, in the piping line that charges the light oil fraction into the separation column.
It is preferable to use a line mixer such as an orifice mixer or a static mixer. Furthermore, the light oil fraction and the extract are mixed and separated into layers in a stationary separation tower, and the abasic oil is extracted from the upper layer and the basic extract is extracted from the lower layer, and A small amount of generated sludge is extracted from the middle part. In addition, in this debasing treatment process, in order to reduce the chance of contact with oxygen in the air as much as possible and suppress the generation of sludge,
Preferably, the separation column is operated under an inert gas atmosphere such as nitrogen gas, or operated with full liquid to prevent contact with oxygen and provide a head for the next process, thereby saving energy. can. The upper layer of debasic oil is neutralized to remove residual acid content. Neutralization treatment is performed by contacting with a caustic alkali such as NaOH or KOH or an alkaline aqueous solution such as ammonia. The concentration of this alkaline aqueous solution is
Although not particularly limited, if acidic content remains in the light oil fraction after debasing treatment, it may cause problems such as corrosion and reduced catalyst activity in the hydrogenation process, so preferably The alkaline content should be approximately equal to or slightly in excess of the residual acidic content. The light oil fraction after the neutralization treatment is then charged to a step for separating and removing the alkaline content remaining in the light oil fraction. This residual alkali content can be separated and removed by washing with water or adsorption.
If alkaline content remains in the hydrogenation process, it will cause a decrease in catalyst activity and corrosion of equipment in this hydrogenation process, so it is necessary to completely separate and remove this residual alkali content, preferably using a light oil sump using an evaporator. It is preferable to carry out this method by evaporating the alkaline components and separating and removing the residual oil containing the residual alkaline components. When the light oil fraction is evaporated using the above evaporator to separate and remove the residual alkali, the operation of the evaporator is as follows:
As will be explained later, in order to save energy, it is best to carry out the operation under a pressure that allows the steam of the pre-distillation column to be used as a heating source.For example, if the pre-distillation column is operated at normal pressure, the evaporator should be operated at a pressure of 300 mmHg. Operated under reduced pressure: Furthermore, as for the reboiler of the evaporator, although there are no particular restrictions, since contamination tends to cause a decrease in heat transfer, it is preferable to use a reboiler that has a high heat transfer coefficient and is not likely to cause a decrease in heat transfer due to contamination. A film type one is best. In this evaporation process, it is recovered from the bottom of the evaporator,
Although the residual oil containing residual alkaline content may be used as fuel oil, it is preferably charged to a water washing process in order to recover useful components such as benzene, toluene, xylene, etc. contained in this residual oil. After washing with water, it is returned to the pre-distillation tower. The water washing step performed for this purpose is not particularly limited either, as long as it includes a mixing means for mixing the residual oil and washing water, and an oil-water separation means for separating oil and water. In this water washing step, preferably, the water separated by the oil-water separation means is regenerated in a water evaporator, and the regenerated water is used again as washing water to suppress the amount of water discharged outside the system. As a heat source, we use a heavy oil fraction with a boiling point of 145℃ or higher extracted from the bottom of the pre-distillation tower, and we also use a reboiler that has a high heat transfer coefficient and a fall that does not easily reduce heat transfer due to dirt. Use a film type. The refined light oil fraction after passing through the process of separating and removing the residual alkali content is combined with the low-boiling fraction extracted from the top of the pre-distillation column, and charged into the hydrogenation reaction process, using the usual method. Impurities are hydrogenated or hydrogenolyzed. At this time, it may be charged to the hydrogenation process together with other light oil fractions, such as aromatic-rich cracked gasoline or reformed gasoline. After hydrogenation and purification, the product is distilled in a distillation process to obtain purified benzene, toluene, xylene, and other aromatic products. Next, the method of the present invention will be specifically explained according to a flow sheet according to an example of implementation. In FIG. 1, raw gas oil is charged into a pre-distillation tower 2 from a line 1, and a low-boiling fraction with a boiling point of 100°C or less is extracted from the top of the pre-distillation tower 2.
The heavy oil fraction with a boiling point of 145℃ or higher is extracted from the bottom of the tower, and the boiling point is extracted from the side cut.
It is separated into a light oil fraction with a temperature of 100-145℃. The light oil fraction is charged through line 3 to a separation column 4 for debasing it and recovering useful tar bases. In this debasing treatment step, an extract with a free acid concentration of 5 to 10% used for the debasing treatment is extracted from the bottom of the separation column 4 through a line 5, and a portion of this extract is added through a line 6. Together with the acidic liquid to be replenished, it is supplied to the line 3 via the extract circulation line 7, mixed with a light oil fraction by a line mixer 8 provided in the line 3, and charged into the separation column 4. The remainder of the extract extracted from the bottom of the separation column 4 is introduced through line 9 to a tar base recovery step (not shown), where useful tar bases are recovered. Moreover, in the separation column 4,
The sludge generated between the upper layer of the debasic light oil fraction and the lower layer of the extract is continuously extracted from a sludge extraction line 10 provided at the interface between the upper and lower layers. Note that the separation column 4 in this debasing treatment step is operated under a nitrogen gas atmosphere or under pressure with full liquid. The light oil fraction subjected to the debasing treatment in the above debasing treatment step is extracted from the top of the separation column 4, charged into the neutralization column 12 through line 11, and added to the alkaline aqueous solution charged through line 13. It is then neutralized. In this neutralization step, the light oil fraction and the alkaline aqueous solution are mixed in the line mixer 14 installed in the line 11, and the alkaline aqueous solution extracted from the bottom of the neutralization tower 12 is partially alkali. The aqueous solution circulation line 15 is circulated to the line 11, and the sludge generated in the neutralization tower 12 is continuously or intermittently removed from the sludge withdrawal line 16 provided in the neutralization tower 12. It's starting to get picked out. The light oil fraction after the neutralization treatment is sent to the neutralization tower 12.
is extracted from the top of the column and introduced into the distillation process through line 17. In this evaporation process, the light oil fraction introduced from line 17 is first charged into a falling film type reboiler 18 and heated, and then charged into an evaporator 19. This evaporator 19 is operated under a reduced pressure lower than the operating pressure of the pre-distillation column, and heat is supplied to the reboiler 18 from the top of the pre-distillation column 2 through a line 2.
This is done by circulating a part of the low boiling point fraction with a boiling point of 100° C. or lower which is withdrawn via the low boiling point fraction circulation line 21 to the reboiler 18.
Also in this evaporation process, a part of the residual oil extracted from the line 22 at the bottom of the evaporator 19 is circulated through the residual oil circulation line 23 to the reboiler 18,
The evaporation efficiency of light oil fractions is increased. The refined light oil fraction evaporated in this evaporation step is extracted from the top of the evaporator 19 through a line 24,
It merges with the low boiling point fraction flowing through line 20, is charged to a hydrogenation reaction process (not shown), undergoes hydrogenation or hydrogenolysis, and is purified in a purification distillation process to produce aromatic products such as benzene, toluene, and xylene. becomes. Further, in this flow sheet, the residual oil extracted from the line 22 at the bottom of the evaporator 19 is introduced into the water washing process, mixed with washing water in the line mixer 25, and then charged into the oil-water separation tank 26. The oil is returned to the pre-distillation column 2 through line 27, and the water is extracted through line 28 and a portion thereof is circulated through line 29 to line mixer 25, and the remainder is sent through line 30 to the reboiler. 31, and the water regenerated in the water evaporator 32 is circulated again to the line mixer 25 together with additional water charged from the line 34 to be used as cleaning water. I have to. Furthermore, for the reboiler 31, a falling film type is used which has a high heat transfer coefficient and does not easily deteriorate heat transfer due to dirt. boiling point 145
The heavy oil fraction at a temperature of 0.degree. C. or above is circulated through line 33 for use. [Example] Gas light oil was used as tar-based light oil, and this gas light oil was purified according to the above flow sheet. The respective proportions of the low boiling point fraction, side cut fraction and heavy oil fraction obtained in the pre-distillation tower 2 are as follows:
They were 27%, 62% and 11%. Further, Table 1 shows the composition of the gaseous light oil, the composition of the side cut fraction, and the composition of the refined light oil fraction introduced into the hydrogenation reaction step (not shown). Further, the amount of impurities after purification distillation was as shown in Table 2. As a comparative example, a case where the product was distilled as it was without abasing treatment is shown. The recovery rates of viridine and α-pyricone were 95% and 100%, respectively.
It was %.

【table】

〔Effect of the invention〕

According to the present invention, tar-based light oil is purified to efficiently obtain aromatic products such as high-purity benzene, toluene, and xylene, and at the same time, useful tar bases such as pyridine and α-pyricone are produced from this light oil. can be easily and efficiently recovered.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a light oil refining method according to an example of the implementation of the present invention.

Claims (1)

[Claims] 1. Tar-based raw material gas oil is charged into a pre-distillation column,
It is separated into a low boiling point fraction, a heavy oil fraction, and a light oil fraction with a boiling point of 100 to 145°C, and the obtained light oil fraction is subjected to debasing treatment by pickling extraction and then neutralization treatment with alkali. The refined light oil fraction obtained by separating and removing the residual alkaline fraction and the above-mentioned low boiling point fraction are combined and charged into a hydrogenation reaction process, and after hydrogenation. A light oil refining method characterized by performing refined distillation. 2. Light oil fractions are extracted from the top of the column as low-boiling fractions with a boiling point lower than 100℃, and at the bottom of the column are extracted with a boiling point lower than 100℃.
The method for refining light oil according to claim 1, wherein the heavy oil fraction having a temperature higher than 145° C. is extracted from a side cut fraction of a distillation tower. 3. The method for refining light oil according to claim 1 or 2, wherein the residual alkali content is separated and removed by water washing or adsorption. 4. The method for refining light oil according to claim 1 or 2, in which the residual alkali content is separated and removed by evaporation in an evaporator to separate and remove the residual oil containing the residual alkali content. 5. The light oil refining method according to claim 4, wherein the side cut fraction is continuously processed from its debasing treatment step to its neutralization treatment step and evaporation step using an evaporator. 6. Light oil according to claim 5, in which the flow rate control when charging the light oil fraction after neutralization treatment to the evaporation process is performed by liquid level control in the reflux tank at the top of the evaporator and cascade control. Purification method. 7. The light oil refining method according to any one of claims 4 to 6, wherein the evaporator is operated using distilled steam from the preliminary distillation column as a heat source. 8. The light oil refining method according to any one of claims 4 to 7, wherein the evaporator heating method uses a falling film or thin film evaporator.