JPH0478417A - Method and device for recovering solvent - Google Patents

Abstract

PURPOSE:To separate and remove high-boiling-point material by storing the drain condensed in an adsorption vessel until desorption is finished and discharging the drain and the gaseous component outside the vessel from another outlet after desorption is finished. CONSTITUTION:A desorbed gas is discharged from its outlet 8, passed through a condenser 12, cooled, condensed and accumulated in a separation vessel 13, and the recovered solvent (s) and water (w) are separated therein by gravity. Steam (v) is blown into an absorption vessel 1 to heat it, hence the desorbed solvent is mostly vaporized, and the solvent in the drain (d) is simultaneously vaporized, discharged from the outlet 8 and recovered through the condenser 12 and separation vessel 13. Since the b.p. of most of the high-boiling-point material is higher than the steam temp., the material is accumulated at the lower part of the adsorption vessel 1 as drain (d). When the recovery of solvent is finished, a steam valve 3 and a desorbed gas discharge valve 9 are closed, a drain valve 11 is opened, and the drain (d) at the bottom of the adsorption vessel 1 is discharged into a waste liq. tank 14.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a method for preventing the coloring of recovered solvents, which is an obstacle when recovering and reusing solvents used in manufacturing, processing, etc. Regarding equipment.

[Conventional technology]

In general, in industries such as printing, rubber manufacturing, and adhesive tape manufacturing, volatile solvents used in manufacturing and processing processes are recovered from the waste air at the place where the solvent is used and reused. There is.

The types of solvents used in such manufacturing and processing steps include hydrocarbon solvents such as liquid propane, benzene, and toluene, alcohol solvents such as methanol, ethanol, and ethylene glycol, and ketone solvents.
Examples include ether-based and ester-based solvents.

Methods for recovering these solvents include condensation methods, absorption methods, adsorption methods, etc., but adsorption methods are widely used because of their superior recovery efficiency and recovery of low concentration gases.

Solvent recovery using the adsorption method involves guiding waste air containing such solvents to an adsorption tank, allowing the solvent in the waste air to be adsorbed by the adsorbent while passing through an adsorbent layer in the adsorption tank, and then using a low-pressure The adsorbed solvent is desorbed from the adsorbent by blowing steam into the adsorption tank, and the vapor is passed through a condenser outside the adsorption tank to be cooled and condensed.The condensed liquid is separated into the solvent by gravity separation in the separation tank. The solvent is recovered by separating it from water. Activated carbon is generally used as the adsorbent in this case.

[Problem to be solved by the invention]

However, in the manufacturing and processing process, there are some substances that have a boiling point higher than that of the solvent, such as plasticizers in tape base materials, oils and fats added for the purpose of thickening adhesives, and their altered products. Contamination with high boiling point substances (hereinafter referred to as high boiling substances) will cause the recovered solvent to turn yellow, and if such colored recovered solvent is reused, it will turn the product yellow and reduce the quality of its appearance. let

Such high boiling substances cannot be removed by solvent recovery using conventional adsorption methods for the reasons described below.

That is, in the desorption process, not only high-boiling substances but also solvents and vapors condense in the adsorption tank and become drain and accumulate at the bottom of the adsorption tank. The above-mentioned drain containing a large amount of steam, vaporized solvent, and high-boiling substances is always discharged in a mixed state from the same discharge port provided in the adsorption tank.

The mixture of steam, gaseous solvent, and condensate discharged from the adsorption tank in this way is then cooled in a condenser to condense the gas content, discharged from the condenser, and stored in a separation tank, making use of the difference in specific gravity. separated.

However, in this case, the high-boiling substances exist in a dissolved state in the solvent, so the solvent in which the high-boiling substances are dissolved and water can be separated by the difference in specific gravity. Separation from the solvent is extremely difficult in conventional solvent recovery using adsorption methods, and as a result, the recovered solvent is colored yellow by high-boiling substances.

The present invention was made to solve these problems, and provides a means for simply and almost completely preventing coloring of recovered solvent without requiring large-scale capital investment or complicated operations. It provides:

[Means for Solving the Problems] In order to achieve the above object, the method for preventing coloration of solvent in solvent recovery of the present invention is such that waste air containing a solvent is adsorbed by an adsorbent in an adsorption tank, and then the adsorbed gas is adsorbed by an adsorbent in an adsorption tank. During solvent recovery, the solvent is desorbed from the adsorbent by blowing steam into the adsorption tank, cooled and condensed in the condenser, and separated and recovered in the separation tank.Drain condensed in the adsorption tank is adsorbed until the desorption is completed. The gist is to separate and remove high boiling point substances by storing them in a tank and discharging them out of the adsorption tank from a separate outlet from the gas component after desorption is complete.

As used herein, condensate refers to condensates of steam, high boilers, and solvents. Moreover, the completion of desorption refers to the fact that the extraction of the solvent adsorbed on the adsorbent is almost completed and the supply of steam is stopped.

The temperature of the steam used for desorption is effectively higher than the boiling point of the solvent (and lower than the boiling point of the high-boiling substance), and is preferably set at, for example, 100°C to 110°C.

The cutting recovery device of the present invention usually has a plurality of adsorption tanks (usually two).
), 1 condenser, 1 separation tank to separate solvent and water
The main equipment is one waste liquid tank for storing drainage containing high-boiling substances, and activated carbon, activated alumina, silica gel, activated bauxite, etc. are used as adsorbents.

Each adsorption tank has an inlet for waste air containing solvent, an inlet for desorption steam, a desorption gas outlet for discharging the desorbed gaseous solvent and steam, a drain outlet for discharging condensate, and an inlet for desorption steam. A clean air outlet for discharging clean air after the adsorbent has adsorbed solvents, high-boiling substances, etc. in the air, and valves for opening and closing these are provided. The gas outlet is connected to the separation tank via the condenser, and the drain outlet is directly connected to the waste liquid tank.

Note that the opening and closing operations of the above valves may be performed manually, but
It is preferable that remote and automatic operation is possible using the power of an air cylinder, hydraulic cylinder, electric motor, magnetic coil, or the like.

(Function) The desorption process in the present invention is shown in FIG. 1.

In other words, the temperature inside the adsorption tank before the start of desorption after adsorbing the solvent is close to room temperature, so even if steam at about 110°C is started to be blown into the adsorption tank, some of the solvent will remain at a high temperature for the first time. It condenses together with boiling matter and steam and is stored as drain at the bottom of the adsorption tank (stage 0 in Figure 1). As steam is further blown into the tank, the temperature inside the tank rises as shown in the curve shown in FIG. 1, and almost all of the solvent desorbed from the adsorbent becomes gas. In addition, the solvent mixed in the condensate that has condensed and accumulated at the bottom is vaporized again (■'v4 in FIG. 1). The solvent thus desorbed and turned into a gas is discharged together with steam from the gas outlet, cooled and condensed in a condenser, separated from water in a separation tank, and recovered. On the other hand, since the boiling point of high-boiling substances is higher than the temperature of steam, even if desorption progresses and the temperature inside the tank rises, the high-boiling substances continue to be converted into drains in the adsorption tank without being vaporized. The substances remain as they are at the bottom of the adsorption tank (period ■ in Figure 1), and after the desorption is completed, they are discharged into the waste liquid tank from a drain outlet separate from the solvent (period 0 in Figure 1).

As described above, most of the high-boiling substances that cause the coloration of the solvent are separated and removed from the recovered solvent, thereby preventing the coloration of the solvent.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a process flow chart showing one embodiment of the present invention.

In this embodiment, two adsorption tanks 1, 1 are provided so that continuous operation is possible. These two adsorption tanks are operated to perform adsorption and desorption alternately. The upper adsorption tank 1 in the figure will be explained below, but the lower adsorption tank 1
The same applies to

In FIG. 2, a is the activated carbon layer of the adsorbent loaded in the adsorption tank 1. In FIG. On the tank wall above the activated carbon layer a of the adsorption tank 1, there is a desorption steam population 2, a steam valve 3 that opens and closes the desorption steam population 2, and an activated carbon layer that removes solvents and high boiling substances in the produced air e during the adsorption process. A clean air discharge port 4 for discharging the clean air C after being adsorbed by a, and a clean air discharge valve 5 for opening and closing the clean air discharge port 4 are provided. In addition, on the tank wall below the activated carbon layer a of the adsorption tank 1, there is an inlet 6 for inlet air e sent into the adsorption tank l by a recovery blower (not shown), and an inlet 6 for opening and closing the inlet 6. An inlet valve 7, a desorption gas outlet 8 for discharging the desorption gas g which is a mixture of the desorbed gaseous solvent and steam, and a desorption gas exhaust valve 9 for opening and closing the desorption gas outlet 8 are provided. . Further, at the bottom of the tank wall, a drain outlet lO and a drain valve 11 for opening and closing the drain outlet 10 are provided.
Further, the drain outlet 10 is directly connected to a waste liquid tank 14.

In the apparatus configured as described above, the desorption process will be described in detail below, assuming that the activated carbon layer a has already adsorbed the solvent in the produced air e and has completed the adsorption process.

When attaching and detaching, first, the clean air discharge valve 5, the produced air introduction valve 7, and the drain valve 11 are closed.

Next, when the steam valve 3 is opened and the low-pressure steam V for desorption at about 110°C is blown into the adsorption Ml and passed through the activated carbon layer a, the solvent adsorbed on the activated carbon layer a is desorbed. In the initial stage, since the temperature in the activated carbon layer a and the adsorption tank 1 is low, close to room temperature, most of the high-boiling substances, steam, and solvent are condensed and collected at the bottom of the adsorption tank 1 as a drain d. On the other hand, the desorption gas is discharged from the desorption gas outlet 8, cooled and condensed while passing through the condenser 12, and collected in the separation tank 13, where it is separated into the recovered solvent S and water W due to the difference in specific gravity.

When the temperature inside the adsorption tank 1 is further increased by blowing in steam (2), most of the desorbed solvent becomes gas, and at the same time, the solvent in the drain (d) is re-vaporized and discharged from the desorption gas outlet 8, and the condenser 12, Although it is recovered through the separation tank 13, since the boiling point of most of the high-boiling substances is higher than the steam temperature, it continues to become drain d and accumulate at the bottom of the adsorption tank 1.

When the recovery of the solvent is completed, the fume valve 3 and the desorption gas discharge valve 9 are closed, and the drain valve 11 is opened instead to discharge the drain d accumulated at the bottom of the adsorption tank 1 to the waste liquid [14].

As described above, high-boiling substances that cause solvent coloring can be almost completely removed in the desorption step, thereby preventing coloring of the recovered solvent S.

Next, an example will be described in which the solvent in the degassed e generated from the adhesive is recovered in the vinyl adhesive tape manufacturing process using the apparatus and method of the above embodiment.

In the degassing e containing solvent generated from the adhesive, in addition to aromatic organic solvents such as cyclohexane and aliphatic organic solvents such as hexane, motor oil added as a thickener, vinyl eluted into the solvent, etc. Plasticizers, etc. in the base material are included as high boiling substances. The solvent concentration in this degassed e is approximately 2,000
0 ppm, and the above-mentioned high-boiling substances contained in the solvent are 0.2 to 0.3% by weight.

The solvent in the above degassed e was recovered by the method described in the above example, and using a colorimeter (CT210 manufactured by Minolta), it was measured at L"a"b'" specified by CIE (Commission Internationale de l'Eclairage).
The Ll-all 5m value of the color system was measured. In addition, the same method can be applied to the solvent recovered using the conventional technology.
The "b" value was measured. The results were as shown in Table 1.

Further, as a result of visual comparison, the solvent recovered by the method of this example was almost colorless and transparent, whereas the solvent recovered by the method of the prior art had a yellow color, and a significant color difference was observed.

〔Effect of the invention〕

As is clear from the above description, by using the solvent recovery method and device of the present invention, high boiling substances that cause coloration of the solvent can be almost completely removed from the recovered solvent in the desorption process of recovering exhaust gas containing solvent. Because it can be separated and removed,
Coloring of the recovered solvent can be prevented.

[Brief explanation of drawings]

FIG. 1 is a graph showing the progress of the desorption process in the present invention, and FIG. 2 is a process flow diagram showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Adsorption tank, 2... Steam inlet for desorption, 8... Desorption gas outlet, 10... Drain outlet, 12... Condenser, 13... Separation tank, 14... Waste liquid tank, a
...activated carbon layer, d...drain, g...desorption gas,
S...Recovered solvent. Figure 1 Procedural amendment (formality) Case description 1990 Patent Application No. 191704 2゜Name of invention Address ■530 2-4-4 Nishitenma, Kita-ku, Inusaka-shi In the specification [
1. “Name of invention” column. 5゜Amendment: ``Solvent recovery method and its equipment'' should be corrected to ``Solvent recovery method and its equipment.''that's all

Claims (2)

[Claims] (1) Solvent recovery in which the waste air containing the solvent is adsorbed on the adsorbent in the adsorption tank, then the solvent is desorbed from the adsorbent by blowing steam, cooled and condensed in the condenser, and the solvent is separated and recovered in the separation tank. A solvent recovery method characterized in that condensate condensed in the adsorption tank is stored in the adsorption tank until desorption is completed, and after the desorption is completed, the drain is discharged from the adsorption tank through a separate outlet from the gas component. (2) It has an adsorbent layer inside, and a steam inlet for desorption and a clean air outlet are provided on the tank wall above the adsorbent layer,
In addition, the adsorption tank is equipped with an inlet for waste air containing solvent and an outlet for desorbed gas on the tank wall below the adsorbent layer, and a drain outlet at the bottom of the tank wall. Characteristic solvent recovery equipment.