JPS6236481Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to preventing deposits from adhering to the inner wall surface of a multi-effect can for concentrating an aqueous lactam solution containing an oligomer in multiple stages.

For example, a product obtained by polymerizing ε-caprolactam contains several to ten-odd percent of unpolymerized substances (ε-caprolactam and oligomers thereof) in addition to polycaprolactam. Since these unpolymerized substances deteriorate the original excellent properties of polycaprolactam, they are removed by a method such as hot water extraction. A few percent contained in the large amount of extracted water generated here.
In order to recover unpolymerized products, the extracted water is concentrated to the desired concentration. Multi-effect cans are commonly used for this concentration.

Conventionally, an apparatus as shown in FIG. 1 has been used as a multi-effect canister used for concentrating extracted water, that is, an aqueous solution containing unpolymerized substances. Figure 1 shows a concentrator, a reboiler installed outside the concentrator, and two tubes 1 installed between the concentrator and the reboiler to circulate an aqueous solution to be concentrated.
This is a multi-effect can consisting of a plurality (n) stages of concentrating systems each having at least a set of circulation pipes, and shows the final n-th stage and (n-1) stage concentrating systems B and A. . FIG. 1 is a schematic vertical cross-sectional view of a conventional multi-effect can. The unpolymerized material-containing aqueous solution to be concentrated is supplied to the concentration system A through the aqueous solution supply pipe 2A, partially concentrated in the concentration system A, and then supplied to the next concentration system B. The aqueous solution supplied by the aqueous solution supply pipe 2B is supplied to the gas phase portion 8B or the submerged portion of the concentrator 3B. Since the reboiler 1B is heated by the steam generated by the pre-concentrator 3A that is transferred through the steam pipe 9, the aqueous solution that has entered the concentrator 3B is passed through the circulation pipe between the concentrator 3B and the reboiler 1B. 4B, it self-circulates and becomes concentrated due to the density difference. This naturally circulating amount has a positive correlation with the heating efficiency in the reboiler 1B, and the better the heating efficiency is, the larger it is. If the amount of circulation is large and the concentration of the aqueous solution is low, precipitation and accumulation of oligomers on the inner walls of the apparatus will hardly be a problem.

However, in a multi-effect canister in which concentrating systems are connected in series, as the concentration progresses sequentially, oligomers are more likely to precipitate in the later concentrating systems. Thermal efficiency decreases due to adhesion and accumulation of oligomers. As the thermal efficiency decreases, the amount of aqueous solution circulated decreases, leading to a vicious cycle in which more oligomers adhere to the solution, resulting in a sharp decrease in concentration efficiency. For this reason, it has been necessary to periodically dismantle and clean the apparatus and clean the inside of the apparatus to remove oligomer deposits.

Therefore, the main purpose of the present invention is to provide a multi-effect can that can concentrate without having to be dismantled and cleaned for a long period of time by preventing the adhesion and accumulation of oligomers mentioned above, and has improved thermal efficiency of the reboiler. It was designed for the purpose of circulating an aqueous solution to be concentrated between a concentrating can, a reboiler installed outside the concentrating can, and the concentrating can and the reboiler. In a multi-effect can comprising a plurality (n) stages of concentrating systems each having at least one set of two circulation pipes arranged in a row, the liquid to be concentrated is supplied from at least the (n-1)th stage concentrating system. The above objective is achieved by connecting the can to the bottom of the reboiler of the n-th stage concentration system to form a multi-effect can for concentrating an aqueous lactam solution containing oligomers. That is, in the present invention, the aqueous solution to be supplied to at least the final n-stage concentration system is supplied to the bottom of the reboiler instead of being supplied to the concentrator (gas phase or liquid phase part). increases the amount of circulation and precipitates oligomers,
Its main feature is to prevent deposition.

The apparatus according to the present invention will be described below with reference to FIG. 2, which is a schematic vertical sectional view showing one embodiment thereof.

The oligomer-containing lactam aqueous solution to be concentrated, supplied through the aqueous solution supply pipe 2A, is partially concentrated by the reboiler 1A and the concentrator 3A, as in the conventional device, and then by the aqueous solution supply pipe 2B. It is then fed to the concentrating system B, ie to the bottom 6B of the reboiler 1B. In multiple effect cans, concentrated system A,
Since concentration is carried out at progressively lower pressure and temperature for each B,..., when the aqueous solution is supplied from the aqueous solution supply pipe 2B to the bottom 6B of the reboiler 1B, flash paper is generated and the reboiler Aqueous solution circulation within 1B is promoted. Therefore, even if the concentration of the aqueous solution increases, the adhesion and accumulation of oligomers in the reboiler is greatly reduced, making it possible to continue concentration work without having to dismantle and clean the device for a long period of time.

Aqueous solution supply pipe 2B communicated with reboiler bottom 6B
Similarly to the conventional supply pipe, it is preferable to provide a valve 7 for controlling the concentration tank liquid level.

The above-mentioned aqueous solution supply pipe 2B is connected to the reboiler bottom 6B.
It is most effective to apply the concentrating system B, which is connected to It may be applied to the second stage and other stages from the final stage, that is, the (n-1)th stage concentration system.

Example A dilute aqueous solution containing ε-caprolactam and its oligomer was concentrated in a quadruple-effect can using the concentration system shown in Figure 1 or Figure 2 as the third and fourth stage concentration systems. . The amount of aqueous solution supplied to the first stage concentration system (not shown) is 5000 Kg/hr, and the amount of aqueous solution supplied to the final fourth stage concentration system is 1550 Kg/hr.
hr, the temperature inside the concentration canister 3A of the third stage concentration system is 90
℃, the concentration in the concentrator 3B of the fourth stage concentration system is 40℃
Concentration operation was performed.

In the case of the quadruple-effect can (Fig. 2) according to the present invention, 120 kg/hr of flash paper is generated at the bottom of the reboiler, compared to the case of the conventional quadruple-effect can (Fig. 1). The thermal efficiency of the equipment has been improved by approximately 20%, and the total number of days it can be operated before dismantling and cleaning is required has been extended from 70 to 100 days.

[Brief explanation of the drawing]

The drawing shows the final nth stage and (n-1) of the multi-effect can.
FIG. 1 is a schematic longitudinal section showing a concentration system in stages, and FIG. 1 shows a conventional multi-effect can, and FIG. 2 shows an embodiment of the multi-effect can according to the present invention. 1A, 1B...Reboiler, 2A, 2B...Aqueous solution supply pipe, 3A, 3B...Concentrator can, 4A, 4B...
Circulation pipe, A, B...concentration system, 6B...bottom of reboiler, 7B...valve.

Claims (1)

[Scope of utility model registration request] A concentrator, a reboiler provided outside the concentrator, and a set of two circulation pipes provided between the concentrator and the reboiler to circulate an aqueous solution to be concentrated. In a multi-effect can formed by connecting a plurality (n) stages of concentrating systems having at least A multi-effect canister connected to the bottom of the reboiler for concentrating an aqueous lactam solution containing oligomers.