JPS6357413B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for removing impurities from tar acids (phenols, cresols, xylenols). Prior Art Sodium carbonate (hereinafter referred to as phenolate) obtained by extracting the carbolic acids in tar-based distillate oil with caustic soda contains impurities such as trace amounts of tar base and neutral oil. These impurities must be removed because they will eventually transfer to the tar acid product(s) and cause quality deterioration. In order to facilitate the removal of bases, the purification and removal stage is performed at the stage where tar acid is combined with caustic soda to form a phenolate, that is, the stage before the process of decomposition with carbon dioxide gas to produce crude tar acid. It is common practice to do so. Conventional refining methods for this purpose include the ``steam stripping method'' using steaming and the light oil cleaning method (see pages 181 and 182 of the Tar Industry Handbook), and one or both methods can be incorporated into the equipment. ing. When removing impurities using the steam stripping method alone, it is difficult to remove high-boiling bases and high-boiling neutral oils, which increases steam consumption and reduces efficiency (efficiency decrease due to foaming in the column). It was extremely uneconomical to operate from the point of view of problems and energy saving. Furthermore, when conventional light oil cleaning is used in combination, a spray tower or a packed tower has been used as the light oil cleaning device. The reason why it is necessary to remove trace amounts of impurities such as tar bases and neutral oils in the phenolate is to suppress the coloring of various tar acid products obtained in the final process and to pass the neutral oil test. The purpose of this method is to remove base components that are the main cause of coloration, especially high-boiling base components that are difficult to remove in the next step, steam stripping, such as aniline, toluidine, and quinoline. The main purpose is to remove fractional distillation products such as phenol, ortho-cresol, meta-para-cresol,
The aim is to obtain high quality products in xylenol and high boiling point tar acid. Conventional spray towers and irregularly packed towers have the following drawbacks. a) Due to the large amount of hold-up in the system, phenolate replacement is slow and the response to changes in operating conditions such as changes in extraction ratio is slow. b When the operating load of extractant and extractant is reduced (loaddown), the extractant (phenolate) which is the dispersed phase
is not uniformly dispersed, so the contact effect tends to deteriorate. c The equipment occupies a large area and is not compact. Purpose An object of the present invention is to provide a method for removing impurities from tar acids, which overcomes the drawbacks of the conventional methods described above, has excellent removal efficiency, and consumes less energy. Configuration As a result of intensive research to achieve the above object, the present inventor has developed a perforated plate reciprocating type countercurrent extraction column in which the perforated plate is vibrated up and down when removing impurities from tar acids using an extractant. It has been found that the above object can be achieved by providing a method for removing impurities from tar acids, which is characterized by using a method for removing impurities from tar acids. Carbolic acids are mainly recovered from coal tar. Carbol oil and naphthalene oil obtained by distilling tar are extracted and separated with an aqueous solution of caustic soda and extracted as phenolate. The extracted phenolate contains impurities such as tar base and neutral oil. The present invention is an impurity removal method that attempts to extract and remove these impurities with high efficiency (improved performance) using a small amount of extractant (energy saving). The phenolate is then neutralized and decomposed with carbon dioxide gas, sulfuric acid, etc. to obtain crude tar acid. As the extractant in the present invention, in addition to conventionally known crude benzol, hydrogenated oil (unifinate), pure benzol, tar light oil generated during tar distillation can be used as the extractant. Tar diesel oil has a boiling point of 170℃
The yield of the following fractions is less than 1% of tar, which is a very small amount, and the benzene and triol content is lower than normal crude benzole, so they are collected by mixing them with crude benzole, improving the recovery rate. It was considered to be unsuitable as an extractant for cleaning light oil. However, by using a "perforated plate reciprocating type countercurrent extraction tower" (a type of perforated plate with a porosity of 50 to 60%, such as the Sumitomo/Karl column extractor, that vibrates vertically), which has high contact efficiency even at a low oil/agent ratio. It has become possible to remove impurities with high efficiency even from tar gas oil, which has a limited usage amount. Especially for high-boiling neutral oils, the characteristics of this machine are clearly demonstrated due to the large partition coefficient (balanced concentration in the extraction phase/balanced concentration in the raffinate phase). . In general, when the extractant ratio is set to a small value, the number of theoretical plates required for extraction to ensure a given removal rate tends to increase, and the plate efficiency (contact efficiency) tends to decrease, which is a dual problem. However, this machine can be considered to cover the latter and maintain a high removal rate. The details of the present invention will be explained below with reference to FIGS. 1 and 2, which show an extraction column used to carry out the method of the present invention and an apparatus system combining two of the extraction columns. The phenolic acids in the tar distillate are extracted with caustic soda, and the resulting crude phenolate is passed through pipe 1.
is introduced from the top of the first extraction column 7, and after extracting impurities as a dispersed phase, it is introduced into the second extraction column from the bottom via pipe 2.
The pipe 3 is introduced into the extraction tower 8 from the top, as in the first extraction tower, from the bottom after impurities are extracted as a dispersed phase.
It is extracted as purified phenolate and sent to the next step, the crude tar acid step, for treatment. The extractant is introduced into the lower part of the second extraction tower 8 through the pipe 4, and the impurities in the phenolate are extracted as a continuous phase (the extractant is charged into both extraction towers 7 and 8 before the start of operation). The phenolate is extracted as an overflow through a pipe 6 and introduced into the bottom of the first extraction column 7, where impurities in the phenolate are extracted in the same manner as in the second extraction column, and then extracted as an overflow through a pipe 6 and recovered. In this case, the interface between the phenolate and the extractant appears at 10 at the bottom of the extraction tower 7 and 8, and the phenolate is extracted from the bottom through pipes 2 and 3 under control by an interfacial meter without breaking this interface. The perforated plate 1 is attached to the shaft 12 by adjusting the number of vertical strokes of the driving machine 11 according to the impurity removal rate, the type of extractant, and the extractant ratio.
It is used at the optimal position of 3 vertical vibrations. Furthermore, the optimal column height (number of columns) for single-stage or multi-stage extraction towers can be selected depending on the desired removal rate. Next, the present invention will be explained with reference to the following examples and comparative examples using conventional methods. Example Phenolate: 2000/hour Tar light oil: 150/hour Extractant ratio: 0.075 (S/F) Neutral oil and base content in phenolate (unit: ppm)

[Table] The above implementation data is based on the actual operating data of the deoxidizing equipment in the tar distillation equipment. Normally, in order to obtain the above value, in conventional methods, the extractant ratio is
Must be in the range 0.5 to 4.0. Comparative values of a conventional apparatus system for obtaining impurity removal efficiency equivalent to that of the embodiment of the present invention are shown below.

【table】

[Table] * Filling: Raschig Ring Comparative Example Actual data on light oil cleaning with tar light oil in one line of mixer-settler type deoxidizing equipment (mixer: static mixing type, settler: independent static tank type).

[Table] When treated with the method of the present invention using the same extractant ratio as above: Removal rate (1) Aniline 1360ppm→480ppm 65% (2) Toluidine 460→50 89 (3) Quinoline 2330→400 83. Although this example describes the case where tar light oil is used as the extractant, the removal rate of impurities can be further increased if pure benzol, etc., which contains almost no impurities to be removed, is used as the extractant. It goes without saying that it can be done. Effects As mentioned above, by using a highly efficient perforated plate reciprocating type countercurrent extraction tower, the extractant ratio (extractant/
This makes it possible to significantly reduce the amount of extractant (phenolate), and to reduce the amount of energy required to regenerate used extractor, resulting in significant energy savings. On the other hand, in the case of reducing the extractant ratio, the targets for extraction and removal are narrowed down to the aforementioned impurities with large partition coefficients, which is very convenient since these impurities are high-boiling neutral oils and high-boiling bases. be. In other words, impurities can be easily removed in the next step of deoiling in a steaming tower, and the amount of steam used in this step is also reduced, resulting in energy savings.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an extraction column used in the present invention, and FIG. 2 is a system diagram of an apparatus system for carrying out the method of the present invention, which combines two of the extraction columns. 1, 2, 3, 4, 5, 6... Pipe, 7, 8... Extraction column, 9... Overflow liquid level, 10... Interface (extraction agent/phenolate), 11... Drive machine, 12... Shaft, 13... Porous plate .

Claims (1)

[Claims] 1. When removing impurities from tar acids recovered in a tar distillation process using an extractant, a perforated plate reciprocating type countercurrent extraction column in which the perforated plate is vibrated up and down is used. How to remove impurities.