JP3400100B2 - Drying method of hydrous activated carbon - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying activated carbon. More specifically, when the activated carbon is filled in an adsorption tower such as a solvent recovery apparatus, when water is added to the activated carbon to form a slurry, or when water is injected into the activated carbon tower for a temporary stop, a solvent recovery apparatus or the like is used. This is a method of removing water contained in activated carbon applied at the start of operation, that is, a method of drying activated carbon. 2. Description of the Related Art Activated carbon has a high adsorptivity and therefore requires a large amount of heat and a long time to dry activated carbon containing water. When the activated tank is filled with activated carbon in a solvent recovery device or the like, water is usually added to the activated carbon for the sake of filling the activated carbon to form a slurry, and then the activated carbon is used after removing water, ie, drying. At this time, it is often necessary to pass superheated steam for several hours to two days in order to dry the activated carbon. However, even if such a powerful drying method is applied, the water in the activated carbon cannot be sufficiently removed, and in a device such as a solvent recovery device in which the performance is reduced due to the presence of water in the system, the activated carbon is normally used. It may take 1 to 2 days after the start of operation and several days if it is long before the adsorption capacity is exhibited. [0003] Accordingly, not only does the recovery efficiency decrease during that time, but also air pollution by the solvent released into the atmosphere has become a problem. Although a method for drying activated carbon containing water using various desiccants is also disclosed, there is a problem that a separate apparatus is required for regeneration or recovery of the desiccant. [0004] When activated carbon is used as an adsorbent in a solvent recovery device or the like, it is necessary to dry the activated carbon containing water. Since water is adsorbed on the micropores of activated carbon and has a large latent heat of evaporation of water, the method of directly blowing and drying overheated steam has low thermal efficiency and cannot be dried sufficiently. Therefore, the aim is to improve the drying method of hydrated activated carbon to develop a method that has high thermal efficiency and can be dried almost completely in a short time. [0005] The present inventors have found that the surface of carbonaceous materials such as graphite has a certain degree of hydrophobicity, but that hydrocarbons, esters, ketones and alcohols are converted from water to carbonaceous materials. We paid attention to the high affinity of For this reason, it has been found that when activated carbon adsorbing water is immersed in these organic solvents, the water contained in the activated carbon is replaced by the solvent, and the property of discharging water is also large. Based on this, considering that the latent heat of vaporization of these organic solvents is significantly smaller than the latent heat of vaporization of water, the present inventors also studied a method for drying the water-containing activated carbon after replacement with these organic solvents and reached the present invention. did. That is, the water-containing activated carbon is selected from the group consisting of hydrocarbons, esters, ketones and alcohols.
This is a method for drying hydrated activated carbon, which comprises immersing and draining in a kind or two or more kinds of organic solvents, and then desorbing the organic solvent and water contained in the activated carbon by superheated steam. Hereinafter, the present invention will be described in detail. [0008] The drying method of the present invention is applied to activated carbon containing water. The activated carbon used as the base material here has a large surface area of usually several hundred m ² or more per gram, and can be used in a wide range as long as it is a carbon material exhibiting high adsorptivity. As the raw material of the activated carbon, a carbide such as coconut shell or wood or coal is usually used, but any material may be used. The activation method may be one obtained by steam or carbon dioxide at a high temperature or by any of zinc chloride, phosphoric acid, concentrated sulfuric acid treatment and the like. Although the effect can be recognized with any of crushed coal, granulated coal or granulated coal, a sheet-like adsorption layer to which granulated coal or activated carbon is attached is convenient for handling such as pressure loss and replacement. Granulated coal is 30 to 60 per 100 parts of carbon material according to the usual method.
The mixture is adjusted by adding a portion of petroleum pitch or coal tar as a binder and activating after mixing and molding. [0010] Activated carbon is a unique substance having extremely excellent adsorptivity as a non-polar adsorbent, and is known to exhibit high adsorptivity to almost all gaseous or liquid substances. Further, it has various other unique properties and is used for many purposes. Activated carbon is often used for the adsorption and recovery of organic solvent gas contained in the gas phase, but is characterized in that it exhibits a high recovery even when the content of the organic solvent gas in the gas phase is low. Therefore, it is widely used in this field. Although the water content of the activated carbon used in the present invention is not limited, the drying method of the present invention is particularly effective when the water content is high. In the present invention, it is necessary to use one or more organic solvents selected from the group consisting of hydrocarbons, esters, ketones, and alcohols as the organic solvent used as a water replacement agent contained in the activated carbon. is there. This is because these organic solvents have higher affinity for activated carbon than water, and there is no risk of causing a chemical reaction even if the organic solvent is retained in a state of being adsorbed in the pores of activated carbon for a long time. As hydrocarbons, unsaturated hydrocarbons can be used in addition to saturated hydrocarbons. However, chain-like unsaturated hydrocarbons may react with other organic solvents and the like. Therefore, a saturated hydrocarbon is more preferable, and there may be a side chain. Further, alicyclic hydrocarbons are also included in the hydrocarbons of the present invention. In addition, aromatic hydrocarbons are preferable like chain-like saturated hydrocarbons because of their high stability. Esters are not particularly limited, but esters obtained from saturated fatty acids and saturated alcohols are preferred for the same reasons as hydrocarbons. Ketones and alcohols are water-soluble or partially water-soluble, and as the molecular weight increases, mutual solubility decreases and the compound becomes insoluble, but any ketone and alcohol can be used. Ketones and alcohols having a high molecular weight have a boiling point higher than that of water, but are insoluble in water and have a property of azeotropic distillation with water, so that they can be used in the present invention. These organic solvents include, for example, n-hexane, isopentane, benzene, toluene, ethyl acetate,
For example, isopropyl acetate or acetone. These organic solvents can be used alone or in combination of two or more. When used in an organic solvent recovery device,
It is preferable to use the same solvent as the organic solvent to be recovered as the immersion agent for drying the activated carbon. This is because the immersion agent remaining after drying the activated carbon does not become an impurity even when mixed into the recovery solvent, and has an advantage that it can be used as it is. When an organic solvent soluble in water is used, a solvent containing water can be used as it is as an immersion agent, and the use of an aqueous solution of ketone and alcohol is also included in the present invention. In this case, it is natural that the higher the solvent concentration is, the more preferable it is. However, if the solvent concentration is about 30% or more, a considerably large effect of replacing with water is recognized. When an organic solvent is added to the water-containing activated carbon to replace the water contained in the activated carbon, the amount of the organic solvent added is sufficient to soak the activated carbon. The time for immersing and contacting the activated carbon in the organic solvent is preferably 10 minutes or more. After immersing the water-containing activated carbon in an organic solvent, it is necessary to drain the liquid to separate the water discharged outside the activated carbon and the organic solvent remaining around the activated carbon. For example, in the case of an activated carbon filling tank, the drainage is performed by opening a valve at the bottom of the tank and allowing the immersion liquid to flow naturally. Since the separated immersion liquid contains an organic solvent and water, it is separated by decanter or distillation depending on its mutual solubility, and the solvent is recovered and reused. The activated carbon that has been drained after immersion still contains an organic solvent and moisture. The residual organic solvent and moisture must be desorbed by superheated steam. The reason for using the superheated steam is to supply the heat of evaporation of the organic solvent and water remaining inside the activated carbon to sufficiently desorb the remaining components and dry the inside of the pores of the activated carbon. Although the amount of superheated steam used for desorption is usually 30 to 50% by weight based on the amount of activated carbon, there is a considerable effect.
More than twice the amount is preferred. The degree of overheating of the steam is appropriately set in consideration of the required amount of heat. Desorption gas is cooled
Condensed. Since the condensed desorbing liquid contains an organic solvent and water, it is separated by decanter or distillation depending on its mutual solubility, and the solvent is recovered and reused. Function Even if steam is directly blown to dry the water-containing activated carbon, a large amount of heat and time are required, and it is difficult to sufficiently remove the water in the pores of the activated carbon. Hydrocarbons, esters, ketones or alcohols have a much higher affinity for activated carbon than moisture. Utilizing this property, the water-containing activated carbon is once immersed in these organic solvents to replace the water contained in the activated carbon with the organic solvent by utilizing the difference in affinity, and after further draining, the excess By blowing superheated steam having an appropriate amount of heat, the water contained in the activated carbon can be easily evaporated and removed. Further, when the method of the present invention is applied to a solvent recovery apparatus or the like, by selecting the same solvent as the organic solvent to be recovered from these specific organic solvents, the solvent remaining after drying the activated carbon can be reduced. Even if mixed into the recovered solvent, it does not become an impurity and can be used as it is. Further, there is an advantage that the recovery rate and the exhaust gas concentration become almost in a steady state immediately after the start of the operation of the solvent recovery apparatus, so that loss of the solvent and adverse effects on the environment can be prevented. The present invention will be described more specifically below with reference to examples. (Example 1, Comparative Example 1) FIG. 1 shows a solvent recovery test apparatus used in Examples and Comparative Examples of the present invention. A plate 10 was provided at the bottom of the adsorption tank 1, and the upper portion thereof was filled with 400 g of previously dried activated carbon 11 for solvent recovery ("Kuraray Coal 4GS" manufactured by Kuraray Chemical Co., Ltd.). The adsorption tank 1 is covered with a heat insulating agent 9 to prevent heat loss. The valves 2, 3 and 5 were closed, the valve 4 was opened, water was poured into the adsorption tank 1, and the activated carbon 11 was left completely immersed for 1 hour to absorb water sufficiently. After standing, the valves 4 and 5 were opened to drain water from the adsorption tank, and the adsorption tank was weighed. Since the weight of the adsorption tank 1 is weighed in advance, the water content of the activated carbon is calculated from this. The water content of the activated carbon, that is, the water absorption is always almost constant at 103 to 107% by weight (hereinafter referred to as WT%) based on the dry weight of the activated carbon. Next, the valve 4 was opened, and toluene (reagent grade 1) measured in advance was injected into the adsorption tank 1, and the activated carbon was completely immersed and left for 1 hour. At this time, although the immersion time is about 10 minutes, a sufficient effect is obtained, but the immersion is performed for 1 hour with a margin. During this time, the toluene is replaced by the water contained in the activated carbon. After immersion, the valves 4 and 5 were opened and the liquid in the adsorption tank was taken out. Since the upper layer solution was separated into toluene as the upper layer solution and water as the lower layer solution, it was separated by a separating funnel, and the volume of toluene in the upper layer solution was measured. Next, the valves 4 and 5 are closed, the valves 1 and 3 are opened, and steam heated at 120 ° C. is introduced into the adsorption tank from the valve 4 and passed through the tank in a downward flow to desorb toluene adsorbed on the activated carbon for 40 minutes. (First time steam desorption). The desorbed gas was taken out of the valve 5 and led to the cooler 6 to collect toluene. Since this collected liquid was also separated into toluene as the upper layer liquid and water as the lower layer liquid, it was separated by a separating funnel, and the amount of toluene in the upper layer liquid was measured. After the desorption, the adsorption tank was removed, weighed in the same manner as above, and the difference between the weight of the adsorption tank in a state in which only the activated carbon which had been weighed in advance and filled with the dried activated carbon before water injection, was left in the activated carbon. The weight of the solution was calculated. Furthermore, the amount of toluene injected into the adsorption layer at the time of immersion in toluene, the amount of toluene contained in the liquid taken out of the adsorption layer after the immersion of toluene, and the desorbed gas at the time of the first steam desorption were collected and guided by a cooler. From the difference from the sum of the amounts of toluene contained therein, the content of toluene contained in the residual liquid in the activated carbon (indicated by WT% relative to the activated carbon dry weight) was calculated.
When a water-soluble organic solvent was used instead of toluene, the solvent content after removal from the adsorption tank after the solvent immersion and the condenser collected during the first steam desorption were not separated into solvent and water. It was quantified by gas chromatography. Next, the valves 4 and 5 are closed, and the valves 1 and 3 are closed.
Was opened, and a gas having a toluene content of 4500 ppm was passed through the adsorption tank at a flow rate of 20 cm / sec from the valve 2 to adsorb toluene on the activated carbon. The gas that has passed through the activated carbon tank passes through the valve 3 and is discharged outside through the exhaust discharge port 7. At that time, the concentration of toluene in the released gas is measured by the analyzer 8. When the amount of toluene adsorbed reached 10 WT% with respect to the dry weight of the activated carbon, the gas was stopped (referred to as first adsorption). After toluene adsorption, valves 2 and 3 were closed, valves 4 and 5 were opened, and superheated steam at 120 ° C. was introduced into the adsorption tank from valve 4 and passed through the tank in a downward flow for 20 minutes to adsorb the activated carbon. The toluene was desorbed. The desorbed gas was taken out from the valve 5 and led to the cooler 6 to recover toluene. Thereafter, the adsorption / desorption cycle was repeated, and the number of repeated adsorption / desorption cycles until the steady state was reached, in which the concentration of the released gas at the time of adsorption in the previous and subsequent cycles became equal (Example 1). For the sake of comparison, after the activated carbon filled in the adsorption tank was immersed and drained in water, and then treated under the same conditions as in Example 1 except that the step of immersing in activated carbon was removed, Analyzes the amount of liquid remaining in the activated carbon and the toluene concentration of the released gas when adsorbing toluene-containing gas, and repeats the adsorption / desorption cycle until reaching the steady state where the released gas concentration during adsorption in the previous and subsequent cycles is equal The number was determined (Comparative Example 1). Table 1 shows these test conditions, and Table 2 shows the results of measuring the concentration of toluene in the released gas at the time of the first adsorption and the number of cycles to reach a steady state. [Table 1] [Table 2] From this result, when the hydrated activated carbon is dried,
Once immersed in toluene, a remarkable effect of replacing the water inside the activated carbon with toluene is recognized, and it can be seen that the drying of the activated carbon is greatly promoted by desorption with superheated steam. Furthermore, it is recognized that the toluene adsorption effect in the toluene recovery step is significantly improved. (Examples 2 and 3, Comparative Examples 2 and 3) Example 1
And Comparative Example 1, when treated under the same conditions except that n-hexane was used instead of toluene (Example 2,
Comparative Example 2) and treated under the same conditions except that ethyl acetate was used instead of toluene (Example 3, Comparative Example 3).
. Table 1 shows the test conditions in that case. In addition, after the first steam desorption, the amount of liquid remaining in the activated carbon, the content of n-hexane or ethyl acetate in the liquid, and the emission gas concentration at the time of adsorption are analyzed. The number of adsorption / desorption cycles until the steady state was reached was measured. Table 2 shows the results. From these results, it can be seen that when n-hexane or ethyl acetate is used instead of toluene, the same effect of replacing these organic solvents as toluene and the effect of promoting the drying of hydrated activated carbon are obtained. Example 4 and Comparative Example 4 In Example 1 and Comparative Example 1, acetone was used instead of toluene as the immersion solvent, and the acetone concentration in the gas supplied to the adsorption tank was 18,000 ppm. The treatment was carried out under the same conditions except that the time for desorption of the superheated steam after the first time was set to 10 minutes. Table 1 shows the test conditions in that case. After the first steam desorption, the amount of liquid remaining in the activated carbon, the acetone content in the liquid, and the concentration of gas released during adsorption are analyzed. The number of adsorption / desorption cycles until reaching was measured. Table 2 shows the results. (Examples 5 to 7) In Example 4, instead of acetone, a 60 WT% acetone aqueous solution (Example 5), a 40 WT% acetone aqueous solution (Example 6), and a 30 WT% acetone aqueous solution were used in place of acetone. Processing was carried out under the same conditions except that (Example 7) was used. Table 1 shows the test conditions.
Shown in After the first steam desorption, the amount of liquid remaining in the activated carbon, the acetone content in the liquid, and the concentration of gas released during adsorption are analyzed. The number of adsorption / desorption cycles until reaching was measured. Table 2 shows the results. Comparing the results with those of Example 4 and Comparative Example 4, when immersion of hydrated activated carbon in an acetone aqueous solution,
Although the effect is reduced as compared with the case of immersing only in acetone containing no water, a considerably large effect is recognized as compared with the case where the immersion step is omitted, and it is possible to use an acetone aqueous solution instead of acetone in the present invention. It turns out that it is. (Examples 8 to 10) In Example 4, the initial steam desorption time was 80 minutes (Example 8) and 20 minutes, respectively.
(Example 9) and 10 minutes (Example 10), except that the treatment was carried out under the same conditions. Table 1 shows the test conditions. After the first steam desorption, the amount of liquid remaining in the activated carbon, the acetone content in the liquid, and the concentration of gas released during adsorption are analyzed. The number of adsorption / desorption cycles until reaching was measured. Table 2 shows the results. When the time for the first steam desorption is shortened, it is recognized that the adsorption performance at the time of the first adsorption of activated carbon tends to decrease. (Comparative Examples 5 and 6) In Comparative Example 4, the initial steam desorption time was 600 minutes (Comparative Example 5) and 14 minutes, respectively.
Except for 40 minutes (Comparative Example 6), the treatment was carried out under the same conditions. Table 1 shows the test conditions in these cases. In addition, after the first steam desorption, the amount of liquid remaining in the activated carbon and the released gas concentration at the time of adsorption are analyzed, and the adsorption / desorption cycle until the steady state is reached, where the released gas concentrations of the preceding and following adsorption / desorption cycles are equal. The number was measured. Table 2 shows the results. When this result is compared with Comparative Example 1, it can be seen that the degree of reduction of the residual water inside the activated carbon is small and the initial adsorption performance is poor, although the initial steam desorption time is greatly extended. The present invention provides a method for drying activated carbon by immersing the activated carbon in a specific organic solvent to replace the water in the activated carbon with the solvent, followed by drying with superheated steam. It is possible to remove the moisture inside. Furthermore, when the present invention is applied to a solvent recovery apparatus, the same solvent as the organic solvent to be recovered is selected as a desiccant, so that the solvent remaining after drying of the activated carbon is mixed with the recovered solvent and can be used as it is. In addition, there is an advantage that the recovery rate and the exhaust gas concentration can be almost in a steady state immediately after the operation of the solvent recovery apparatus is started.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a flow sheet of a solvent recovery test device used in the present invention. [Description of Signs] 1 Adsorption tank 2, 3, 4, 5 Valve 6 Cooler 7 Exhaust outlet 8 Analyzer 9 Insulation material 10 Plate 11 Activated carbon

Claims (1)

(57) [Claims] [Claim 1] Immersion and draining of hydrous activated carbon in one or more organic solvents selected from the group consisting of hydrocarbons, esters, ketones and alcohols, followed by heating A method for drying hydrated activated carbon, comprising desorbing an organic solvent and water contained in activated carbon by steam.