JPS6340445B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an apparatus for removing low molecular weight compounds from polyamide chips containing monomers and oligomers (hereinafter referred to as low molecular weight compounds). Prior Art When polyamide chips contain a large amount of low molecular weight compounds, various problems such as thread breakage occur when they are melt-spun or melt-molded as they are. Therefore, if the polyamide chips obtained in the polymerization process contain a large amount of low-molecular compounds, such as polyε-caprolactam chips (nylon-6), they may cause problems in the subsequent process before being supplied to the spinning or molding process. Low-molecular-weight compounds are removed in advance through a cleaning process to the extent that they do not cause any damage. Many methods and devices have been proposed to obtain polyamide chips with a low content of low molecular weight compounds.
None of them were satisfactory in terms of economy or performance. When cleaning is performed under industrial conditions using an extractant that does not contain monomers (for example, pure water) or an extractant with a low monomer concentration, the residual low molecular weight compounds in polyamide chips are reduced to only about 1.0wt%. do not. The reason for this is thought to be that 80 to 90% of the 1.0 wt% of low molecular weight compounds remaining in the chips are oligomers, and oligomers are difficult to dissolve in water. Even when washing with a hot water extractant, oligomer removal is not sufficient, and in a continuous washing device, the extract is extracted at a position of 30 to 60% from the start of column washing, and the monomer concentration at the top of the column is reduced to 5 to 10%. A method has been proposed (Japanese Patent Laid-Open No. 101898/1989) that improves the oligomer removal effect by removing the extractant from the middle of the column, but the monomer concentration of the extractant at the top of the column increases and the extraction The concentration of oligomers contained in the agent may also increase, and the ability to continuously and steadily remove oligomers from the chips may decrease. On the other hand, conventional methods for effectively removing oligomers include a multi-column continuous system using two or more towers or a batch system.
The problem is that running costs and equipment costs are extremely high compared to tower-type cleaning. TECHNICAL BACKGROUND OF THE INVENTION The present inventors first investigated the monomer concentration distribution and retention time of low-molecular-weight compounds in polyamide chips in a single-column continuous washing system for polyamide chips in a batch type or continuous two-column type. The content was determined, and the optimum extract monomer concentration distribution in a one-column type washing tower was simulated and studied. It has been said in the past that by increasing the monomer concentration at the top of the tower, the oligomer content in the chips retained in the top region can be effectively removed, and the highly water-soluble monomer components in the bottom region can be reduced to a lower monomer concentration. This is a continuous cleaning method in which the extract is removed using a low-temperature extractant (pure water at the extractant column inlet). Here, Japanese Patent Application Publication No. 54-101898
In the method described in the publication, which aims to improve the removal efficiency of oligomer components by increasing the monomer concentration at the top of the column by withdrawing the extract from the middle of the column, the oligomer concentration in the extract at the top of the column also increases. In order to
In particular, by providing a nozzle at an intermediate position and injecting the monomer through the nozzle, the monomer concentration in the column top region was improved and the removal efficiency of oligomer components was improved. In this method, a certain amount of extract liquid is always injected and at the same time, a certain amount of extract liquid overflows and flows out of the tower, so the oligomer concentration at the top of the tower will never rise above a certain value even during continuous use. The oligomer removal effect can always be efficiently obtained. Next, the countercurrent relative velocity difference between the chip and the extract is
The inventors have repeatedly investigated a number of methods for uniformly injecting monomer liquid in an amount of about 1/10 of the extraction liquid into a flow rate of less than cm/min. As a result, in the lactam-only injection method, the upward flow rate of the extract was slow;
Due to the countercurrent flow of the tip and the small amount of liquid injected, it is difficult to achieve completely uniform mixing by blowing out. Therefore, the extract liquid is forcibly drawn out of the column from the middle of the column, and the monomer is injected into the extracted liquid. They discovered that it is extremely effective to achieve the required uniform monomer concentration by blowing the monomer into the column together with the extract, leading to the present invention. Structure of the Present Invention The present invention involves moving polyamide chips containing monomers and oligomers from the top of the washing tower downward, and moving an extractant upward from the bottom, bringing the chips and the extractant into countercurrent contact, thereby removing the monomers and oligomers from the polyamide chips. In a polyamide chip cleaning device that performs continuous extraction and removal, a cleaning liquid dispersion nozzle and a suction nozzle corresponding to the dispersion nozzle are arranged at approximately the same level in the middle of a cleaning tower, and the suction nozzle and dispersion nozzle are connected to the outside of the tower. 1. A continuous cleaning device for polyamide chips, characterized in that a liquid circulation circuit is formed by connecting a pipe line having a circulation pump installed in the liquid circulation circuit, and a supply nozzle for injecting monomer in a fixed amount is connected to the liquid circulation circuit. . The present invention will be explained below based on the drawings. FIG. 1 is a schematic explanatory diagram showing a specific example of the present invention. In the figure, reference numeral 1 denotes the main body of the washing tower, and a chip introduction nozzle 2 and a chip extraction nozzle 3 are provided at the top and bottom of the tower, respectively. In addition, an extraction liquid supply nozzle 4 is attached to the bottom of the column, and a discharge nozzle 5 is attached to the top of the column. It is designed to be derived by overflowing from . 6 is a liquid circulation line, and as shown in FIG. 2, an annular supply pipe 7 is disposed horizontally and coaxially with the cylindrical column body 1 between the nozzles 4 and 5 in the middle of the column body 1.
and a dispersion nozzle 9 having a plurality of radially oriented dispersion holes 8 on the inner and outer circumferential surfaces of the supply pipe 7, and a suction nozzle having a filter 11 located approximately at the same position as or slightly below the center of the annular supply pipe 7. 10
(The supply pipe 7, suction nozzle 10, etc. are preferably provided at 1/2 to 2/3 of the height of the tower body 1 from the tower bottom), the nozzles 12 and 13 attached to the tower body 1 and the supply pipe 7,
It is constructed by connecting connecting pipes 14, 15 that connect the suction nozzle 10, and connecting pipes 16, 17 that connect the nozzles 12, 13 and a circulation pump 18 arranged outside the column.
Further, a monomer supply line 19 that communicates with a pump 20 that supplies a fixed amount of monomer is connected to the connecting pipe 16 of the liquid circulation line 6 via a nozzle 21.
A predetermined amount of monomer is continuously supplied to the connecting pipe 16. The monomer feed pressure to the connecting pipe 16 is maintained at a higher pressure side than the liquid circulation line pressure by a non-illustrated check valve or the like, and a heat-retaining trace is provided. Incidentally, the monomer supply line 19 may be connected to other continuous pipes 14, 15, 17, etc., or a mixer may be provided in these connecting pipes 14-17. The installation position of the dispersion nozzle 9 is appropriately determined depending on the chip residence time, the required amount of residual low molecular weight compounds in the chips, etc.
It is best to install it at 2/3 of the height. Dispersion nozzle 9
It is preferable that the structure is formed into a similar annular shape corresponding to the cross-sectional shape of the tower body so that the liquid can be spewed out horizontally from the inner and outer peripheral surfaces of the tower body, but the structure is not limited to this. 8 is the flow velocity distribution of the extract in the column, and since the velocity on the wall side becomes low, it is preferable to increase the flow rate on the outer circumferential side than on the inner circumferential side. Effects In the apparatus having such a configuration, chips A are slid down by their own weight from the introduction nozzle 2 at the top of the tower, and extract B is supplied from nozzle 4 at the bottom of the tower, and chips A and extract B are Due to the alternating current contact, the extract overflows from the nozzle 5, and the chips are continuously discharged from the nozzle 3, respectively. In this case, in the liquid circulation line, the suction nozzle 1
The extract flowing from 0 passes through the communication pipes 15 and 17 to the circulation pump 18, and from there it flows into the communication pipe 1.
6 and 14, and is sent to the dispersion nozzle 9, but since a fixed amount of monomer is continuously supplied to the connecting pipe 16 by the pump 20, the extract containing a fixed amount of monomer is sent to the dispersion nozzle 9. flows out radially from the dispersion holes 8 on the inner and outer circumferential surfaces. Here, the suction nozzle 10 is provided at almost the same level as the dispersion nozzle 9, especially the dispersion hole 8 (the level position with respect to the dispersion hole is preferably about 0 to -100 m/m), so the air is emitted from the dispersion hole 8. The discharged extract having a high monomer concentration is diffused very well, and backflow toward the bottom of the column is prevented.
Therefore, the high concentration of monomer above the dispersion nozzle 9 is extremely uniform, and the removal of oligomer components in the chips that come into countercurrent contact with the extract in this region (top region) is very effective. be exposed.
The chips are then transported to the region below the dispersion nozzle 9 (tower bottom region), where mainly the monomer components are removed by the extraction liquid supplied from the bottom of the tower, and the chips are taken out from the nozzle 3 at the bottom of the tower to remove the remaining High quality chips with low molecular compounds can be stably obtained. The amount of liquid circulated in the liquid circulation line is 5 to 15 times the amount of extract liquid supplied from the bottom of the column, especially 10
Preferably, the amount is about twice as large.If the amount is too large, the flow of the extract in the tower will be disturbed due to the backflow of the blown circulating liquid, and if it is too small, significant variations in the monomer concentration distribution within the tower will likely occur. As explained above, in the present invention, (1) the monomer is extracted during the circulation of the extract to improve the monomer concentration, so that even a small amount of monomer can be uniformly mixed in the middle of the line. (2) Since a liquid blowing nozzle system using an extract circulation line is adopted, the diffusion energy of the extract and chips in the tower is high, and the monomer concentration in the extract near the spouting hole is made uniform, and the monomer concentration in the extract is uniform in the tower top area. Removal of oligomers is very effective. (3) The dispersion nozzle and suction nozzle are located at almost the same level, which helps the dispersion of the circulating liquid and prevents backflow of high-concentration monomer circulating liquid to the bottom of the tower, resulting in uniformity. It allows us to improve further. Example Using a continuous washing tower with a diameter of 0.7 m and a length of 9 m as shown in Fig. 1, polyε with a low molecular weight compound content of 10.5% was
-Caprolactam chip (diameter 2.3φm/m, length
2.5m/m) was continuously washed. supply of chips,
The discharge amount is 160Kg/hr, and the extraction liquid (pure water)
was supplied to the column at a rate of 210 l/hr at 115°C. The extraction liquid circulation rate is 2.5m ³ /hr, and the amount of extracted monomer is
The flow rate was 16 l/hr, and the monomer concentration of the extract overflowing from the top of the column was controlled to be 13.5%. The residence time of the chips in the column was 13 hours, and monomer dispersion nozzles were installed at positions such that the residence time of the chips was 4 hours in the high concentration monomer layer (tower top region) and 9 hours in the low concentration monomer layer (tower bottom region). In addition, there is a conventional pure water cleaning method that does not include a dispersion nozzle (liquid circulation line 6), that is, pure water is supplied from the supply nozzle 4 at the bottom of the column, and is brought into countercurrent contact with the chips moving downward, while being brought into contact with the discharge nozzle 5 at the top of the column. (conventional example), and in FIG. 1, 100% concentration monomer is supplied to the dispersion nozzle 9 via the monomer supply line 19, communication pipe 14, etc., and the monomer is discharged from the dispersion nozzle 9. For comparison, a method using a simple monomer injection device (comparative example) that only disperses the monomer and does not perform liquid circulation is shown. Table 1 summarizes the conditions and results of these examples, conventional examples, and comparative examples.

[Table] As is clear from Table 1, according to the present invention, the effect of removing oligomer components is remarkable compared to conventional pure water cleaning, and the injected monomer is made more uniform (improved cleaning effect) compared to simple monomer injection cleaning. ) is found to be very good.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing a specific example of the present invention, and FIG. 2 is an enlarged view for explaining the dispersion nozzle section of FIG. 1. DESCRIPTION OF SYMBOLS 1... Tower body, 4... Supply nozzle, 5... Discharge nozzle, 6... Liquid circulation line, 9... Dispersion nozzle, 10...
Suction nozzle, 18... Circulation pump, 19... Monomer supply line, 20... Pump.

Claims (1)

[Claims] 1. The polyamide chips containing monomers and oligomers are moved downward from the top of the washing tower, and the extractant is moved upward from the bottom, and the chips and the extractant are brought into countercurrent contact to continuously extract and remove the monomers and oligomers from the polyamide chips. In the cleaning equipment for polyamide chips, a cleaning liquid dispersion nozzle and a suction nozzle corresponding to the dispersion nozzle are arranged at almost the same level in the middle of the cleaning tower, and a circulation pump is provided with the suction nozzle and the dispersion nozzle outside the tower. 1. A continuous cleaning device for polyamide chips, characterized in that a supply nozzle for injecting a monomer in a fixed amount is connected to the liquid circulation circuit to form a liquid circulation circuit.