JP2007197472A - Method for reutilizing hydrocarbons - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover and reutilize high-purity hydrocarbons and to suppress the concentration of hydrocarbons released to the atmosphere by packing an adsorbent having a low specific surface area and a large particle diameter into an introduction part of one adsorption and desorption column, packing an adsorbent having a high specific surface area and a small particle diameter into a discharge part of the adsorption and desorption column, carrying out an adsorption step of the hydrocarbons, then a replacement step of the hydrocarbons and subsequently performing a desorption step of the hydrocarbons. <P>SOLUTION: A method for reutilizing the hydrocarbons is carried out as follows. Vapors of the hydrocarbons are efficiently adsorbed and collected with the adsorbents having different particle diameters and specific surface areas and packed into the one adsorption and desorption column. In the replacement step, the purity of the hydrocarbons is raised to recover the high-purity liquid hydrocarbons by desorption, cooling and condensation and suppress the release to the atmosphere. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for recovering and reusing hydrocarbons from exhaust gas containing gaseous hydrocarbons, and in particular, discharge of halogenated hydrocarbons that are one of the causes of atmospheric environmental pollution and ozone layer destruction. The present invention relates to a technique for recovering and reusing recovered halogenated hydrocarbons with relatively high purity while suppressing gas concentration to a low concentration.

In recent years, the number of complaints regarding bad odors has increased, and the source of bad odors has been in various fields such as the cleaning industry, the plating industry, and the automobile parts manufacturing industry. In particular, there are many small and medium-sized businesses that are privately managed in the cleaning industry and the plating industry, and are often located in residential areas. Organic solvents are used in the cleaning process in the cleaning industry, plating industry, automobile parts manufacturing industry, etc. Among them, halogenated hydrocarbons such as tetrachloroethylene and trichlorethylene, which are called parklen and trichlene, which have excellent detergency, are frequently used. Tend to be. These hydrocarbons are not only odorous when discharged into the atmosphere, but are also unfavorable for health, and have problems that lead to deterioration of the air environment and destruction of the ozone layer. As a means for solving this problem, an adsorption apparatus having a plurality of adsorption towers has been proposed (Patent Document 1).

JP-A-11-71584

However, while the conventional technology is complicated and large in size, it is considered suitable for exhaust gas countermeasures in large-scale plants, but for small and medium-sized businesses such as private management, there are points such as space, operation management, and operation costs. It is difficult to introduce from. Furthermore, batch cleaning is mainly used in small- and medium-sized cleaning industries, plating industry, and automobile parts manufacturing industries. For example, in the small and medium-sized cleaning industry, there are many cases in which discharge peaks of relatively high concentrations of hydrocarbons are observed for several minutes for each washing batch.

However, the technology so far has been focused on reducing hydrocarbon emissions into the atmosphere through continuous treatment, and the relatively high concentration of vapor as seen in the small businesses mentioned above. If this occurs, the technology developed with the continuous processing up to now has problems such as complicated operations. Furthermore, it cannot be said that the quality of the recovered hydrocarbons is considered in the prior art, and the reuse of hydrocarbons is currently difficult. As described above, halogenated hydrocarbons are superior in detergency, but the unit price is higher than ordinary hydrocarbons, so it is difficult to reduce costs with conventional technologies that make it difficult to reuse hydrocarbons. It is extremely difficult to adapt to small and medium businesses.

Most of the methods disclosed so far are provided with a plurality of adsorption towers as exemplified in Patent Document 1, for example, the pressure of the adsorption tower is alternately and continuously varied, and the adsorption process is performed in one of the adsorption towers. Meanwhile, the desorption step (regeneration of the adsorbent) is performed in the other adsorption tower. When the pressure is varied, the adsorption process is at normal pressure or under pressure, while the desorption process is often placed under reduced pressure. In an apparatus having a plurality of adsorption towers, the number of valves is large, and complicated valve control is required. (Sequence) may be required. In addition, the use of a plurality of adsorption towers tends to increase the size of the apparatus or increase the weight. Therefore, it is difficult for small and medium-sized businesses to introduce, and furthermore, when the quality of the recovered hydrocarbons is low, the industrial waste treatment is forced to make the introduction more difficult. Furthermore, in the small and medium-sized cleaning industry, etc., mainly batch-type washing is performed, and there are many cases where discharge peaks of relatively high concentrations of hydrocarbons are observed for several minutes per batch, and this is based on continuous operation. There is inconvenience in the apparatus up to.

However, hydrocarbons emitted from these small and medium businesses cannot be ignored from the viewpoint of air environment conservation. To solve this problem, the recovered hydrocarbons can be reused and treated with industrial waste. Development of a small, simple, and high-quality technology for recovered hydrocarbons that can reduce costs and minimize new purchases of hydrocarbons is awaited. The development of this technology has promoted the spread of halogen-containing hydrocarbon recovery-type environmental purification equipment to small and medium-sized businesses, which combined with the reduction of the use of hydrocarbons and the reduction of atmospheric emissions, Improvement is expected.

It is an object of the present invention to reduce and recover gaseous hydrocarbons in exhaust gas containing gaseous hydrocarbons in a small and simple manner, substantially reducing the recovered hydrocarbons to a reusable level. It is to provide a method related to this.

Therefore, as a result of earnest research and development of a method for recovering and reusing hydrocarbons that are small, light, and low in running cost, the present inventor has obtained an adsorption / desorption tower having one adsorbent that alternately performs adsorption and desorption. After the exhaust gas containing gaseous hydrocarbons is passed through the adsorption / desorption device using a desorption device, and then the gaseous hydrocarbons are adsorbed by the adsorbent in the adsorption / desorption tower (adsorption step) After the purified gas is released into the atmosphere, the gas containing the main components of the gaseous hydrocarbons is once vented (substitution process), then the inside of the adsorption / desorption tower is depressurized with a vacuum pump (desorption process), and desorbed. The gaseous hydrocarbons can be recovered and reused as liquid hydrocarbons having such a purity that they can be cooled and condensed and reused. Furthermore, the particle size of the adsorbent packed in the adsorption / desorption tower is large on the exhaust gas introduction part side (hereinafter referred to as adsorption / desorption tower introduction part) containing gaseous hydrocarbons in the adsorption / desorption tower, and purification in the adsorption / desorption tower. A method for recovering and reusing hydrocarbons in a liquid form from the exhaust gas containing the above-mentioned gaseous hydrocarbons, characterized in that it is small on the gas exhaust side (hereinafter abbreviated as the adsorption / desorption tower discharge unit), The adsorbent filled in the adsorption / desorption tower introduction part of the desorption tower is an adsorbent having a low specific surface area, and the hydrocarbons are recovered in liquid form from the exhaust gas containing the gaseous hydrocarbons and reused. The present inventors have found a method capable of effectively suppressing the release of hydrocarbons to the atmosphere and recovering the hydrocarbons while keeping the purity of the hydrocarbons high by the method, and completed the present invention.

That is, the technical solution means of the present invention uses (1) an adsorption / desorption apparatus having one adsorption / desorption tower filled with an adsorbent that alternately performs adsorption and desorption, and the adsorption / desorption apparatus contains exhaust gas containing gaseous hydrocarbons. And the purified gas after the step of adsorbing the gaseous hydrocarbons to the adsorbent in the adsorption / desorption apparatus is released into the atmosphere, and then the gas containing the main components of the gaseous hydrocarbons is temporarily removed. This is a method of recovering and reusing the desorbed gaseous hydrocarbons through the step of venting and the step of desorbing the inside of the adsorption / desorption tower with a vacuum pump, and the step of cooling the desorbed gaseous hydrocarbons. (2) The specific surface area of the adsorbent packed in the adsorption / desorption tower introduction part is 5 m ² / g or more and less than 140 m ² / g, and carbonized from the exhaust gas containing gaseous hydrocarbons as described in (1) This is a method in which hydrogens are recovered in liquid form and reused. (3) The particle size of the adsorbent packed in the adsorption / desorption tower is an average of 3 mm or more and an average of 8 mm or less at the introduction / desorption tower introduction part, and an average of 1.5 mm or more and an average of 3.5 mm or less at the adsorption / desorption tower discharge part ( 1) A method in which hydrocarbons are recovered in liquid form from exhaust gas containing gaseous hydrocarbons described in 1) and reused.

As described above, according to the present invention, halogenated hydrocarbons such as tetrachloroethylene, trichloroethylene, dichloroethylene, and monochloroethylene used in the cleaning industry, the plating industry, the machine component manufacturing industry, etc. are recovered with high purity and reused. In addition to preventing contamination, it also reduces running costs.

Hereinafter, the details of the present invention will be described in detail by way of examples. However, the present invention is intended to specifically describe the technical contents of the present invention and does not limit the scope of the present invention.

(Exhaust gas to be collected)
The hydrocarbons contained in the exhaust gas to be recovered (hereinafter abbreviated as vapor) are the halogenated alkenes such as tetrachloroethylene, trichloroethylene, dichloroethylene, monochloroethylene, hexachloroethane, pentachloroethane, trichloroethane, dichloroethane, monochloroethane, etc. Halogenated alkanes, halogenated aromatic hydrocarbons such as chlorobenzene, alkanes such as pentane, hexane, heptane, octane, alkenes such as pentene, hexene, heptene, octene, alicyclic hydrocarbons such as cyclopentane, and the like These volatile compounds such as halides can be preferably handled. These can be used preferably even if they contain a single or a plurality of hydrocarbons.

For example, a mixed vapor of tetrachloroethylene and trichlorethylene can be preferably handled. Of these, preferred hydrocarbons are halogenated hydrocarbons, more preferred hydrocarbons are chlorinated hydrocarbons, and more preferred hydrocarbons are halogenated alkenes such as tetrachloroethylene, trichloroethylene, dichloroethylene, and monochloroethylene, And halogenated alkanes such as hexachloroethane, pentachloroethane, trichloroethane, dichloroethane, and monochloroethane, most preferably tetrachloroethylene and trichloroethylene.

In the case of a single component concentration or a mixture of these vapors, the total concentration of the components is preferably 700 vol.ppm or more and 80000 vol.ppm or less, more preferably 1000 vol.ppm or more and 50000 vol.ppm or less, and 2500 vol.ppm or more and 25000 vol. More preferably, it is not more than ppm, and is most preferably not less than 4000 vol.ppm and not more than 10,000 vol.ppm.

If this range is exceeded, there is a possibility that it can be handled by existing technologies such as cooling and condensation, and the superiority of this technology will be diminished. Below this range, the amount of adsorbent will increase and blower and decompression This is not preferable because a rotating machine such as a pump is increased in size, and there is a possibility that a technical advantage in applications for small and medium-sized businesses may be diluted.

(Adsorbent)
As the adsorbent, at least two kinds of adsorbents having different particle sizes are used. As the adsorbent filled in the adsorption / desorption tower introduction section, a relatively large particle adsorbent is preferable. The average particle size of the adsorbent packed in the adsorption / desorption tower introduction part is preferably 3 mm or more and 10 mm or less on average, more preferably 3 mm or more and 8 mm or less on average, and most preferably 3.5 mm or more and 6 mm or less on average.

If it is less than this range, it is likely that the effect of reducing the pressure loss is reduced because a gas with a relatively high concentration that is relatively easy to adsorb and remove while suppressing heat generation and setting the linear velocity at the adsorption / desorption tower introduction part, Exceeding this range is not preferable because the gap between the adsorbent and the gap between the adsorbent and the adsorption / desorption tower wall becomes too large.

The material of the adsorbent is not particularly limited, and known materials such as activated carbon, natural zeolite, synthetic zeolite, hydrophobized silica gel, and high silica zeolite can be preferably used. However, a high surface area adsorbent generates heat during adsorption. It is excessive and not preferable in handling.

The preferred specific surface area is preferably 5 m ² / g or more and less than 140 m ² / g, more preferably 7 m ² / g or more and less than 130 m ² / g, more preferably 8 m ² / g or more and less than 100 m ² / g, most preferably 9 m. ² / g or more and less than 60 m ² / g. If it is less than this range, the capacity of the adsorbent tends to be insufficient, and the amount of adsorbent used increases, which is not preferable. Exceeding this range is not preferable because, as described above, heat generation during adsorption becomes significant, and the adsorption ability may be hindered due to temperature rise.

As for the activated carbon, a known carbon material made of coconut shell or the like can be preferably used, and a carbon material obtained by baking sludge obtained at a sewage treatment plant or the like can be preferably used. The activated carbon obtained sludge was obtained by firing at sewage treatment process, many things specific surface area within the range of a few m ² / g to hundred m ² / g, is preferably used as the cost inexpensive material it can.

The adsorbent filled in the adsorption / desorption tower discharge section is preferably an adsorbent having a small pore diameter and a high surface area so that the exhaust gas from which the vapor has been roughly removed in the adsorption / desorption introduction section does not overflow to the downstream side. In addition, in the adsorption / desorption tower discharge part, it is desirable that the particle size of the adsorbent is relatively small from the viewpoint of almost completely adsorbing vapor.

Preferably at least 150 meters ² / g with respect to the specific surface area, more preferably at least 200 meters ² / g, more preferably more than 250 meters ² / g, most preferably at least 300m ² / g. Below this, hydrocarbon vapors may overflow from the outlet located downstream of the adsorption / desorption tower. The upper limit is not particularly limited, but the upper limit of a general adsorbent obtained industrially is from about 400 m ² / g to about 1000 m ² / g, and therefore, the substantial upper limit is considered to be similar thereto.

The size of the adsorbent packed in the lower part of the adsorption / desorption tower is preferably 1.5 mm or more and 3.5 mm or less on average, preferably 1.5 mm or more and 3.0 mm or less on average, and most preferably 1.8 mm or more and 2.8 mm or less on average. If it is less than this range, there is a tendency to limit the exhaust gas treatment amount, which is not preferable. Conversely, when this range is exceeded, the gap between adsorbent particles increases, and vapor tends to overflow to the downstream side, which is not preferable.

The material of the adsorbent is not particularly limited, but known materials such as silica gel, high silica zeolite, activated carbon, alumina, and natural zeolite can be preferably used. The shape of the adsorbent filled in the adsorption / desorption tower of the present invention can be preferably selected from spherical, cylindrical, prismatic, hollow, fiber, spindle, four-leaf, three-leaf, honeycomb, mesh, and the like. These adsorbents having different shapes can also be mixed and used.

(Adsorption / desorption tower)
With respect to the shape of the adsorption / desorption tower filled with the above-mentioned adsorbent, a prismatic shape, a cylindrical shape, a spherical shape and the like can be preferably adopted, and among them, the cylindrical shape is particularly preferable. For example, a cylindrical adsorption / desorption tower having a radius (R) and a height (H) as shown in FIG. 1 can be preferably used. Moreover, it is not hindered to install a baffle plate in order to efficiently bring the gas to be collected into contact with the adsorbent. Further, it does not prevent the baffle plate from being provided with a hole, processed into a corrugated shape, or made into a porous body such as punching metal. As the shape of the hole, a circle, a polygon, a four-leaf type or the like can be preferably used.

(Adsorption / desorption system)
The adsorption / desorption device of the present invention has a schematic configuration shown in FIG. The adsorption process, the replacement process, and the desorption process are operated in this order to recover hydrocarbons and purify the exhaust gas. First, in the adsorption step (solid arrow), high-concentration exhaust gas is introduced from the hydrocarbon vapor introduction path 1 by the blower 2 and enters the adsorption / desorption tower 3. In the adsorption / desorption tower, high concentration vapor is removed by the adsorbent 4 having a large particle size and a small specific surface area. The vapor whose concentration is reduced continues to be almost completely removed by the adsorbent 5 having a small particle size and a large specific surface area, and the purified gas is discharged from the discharge port 6 to the atmosphere. After a certain period of time, the adsorption process is terminated and the process proceeds to a replacement process. In the replacement step, a part of the regeneration solvent is introduced from the atmosphere and the pipe 9 through the atmosphere introduction path 7 by the decompression pump 8 and is introduced into the adsorption / desorption tower 3 while being vaporized. This step has the effect of lowering the partial pressure of components other than the solvent component and replacing the solvent component to increase the purity of the recovered hydrocarbons. After a certain period of time, the replacement process is terminated, and the process moves to the final desorption process (dotted arrow). The vapor, which has been concentrated and increased in purity by the introduction of the atmosphere from the atmosphere introduction path 7 by the decompression pump 8, is liquefied by the chiller 10 and the purified gas is discharged from the discharge port 11. The liquid hydrocarbons (recovered hydrocarbons) thus obtained are stored in the reservoir 13 through the pipe 12 and taken out from the recycled product take-out port 14. A part of the regeneration solvent is returned to the atmosphere introduction path 7 through the pipe 9 in the replacement step. By repeating the adsorption step, the substitution step, and the desorption step in this manner, a high purity solvent component is recovered, and the vapor concentration of hydrocarbons when released into the atmosphere can be reduced. In addition, the layer height (filling amount) of the adsorbent 4 and the adsorbent 5 can be arbitrarily set depending on the type and concentration of hydrocarbon, the processing amount of the apparatus, and the like.

The present invention is used in workplaces that handle hydrocarbons such as cleaning industry, plating industry, automobile parts manufacturing industry, etc., thereby suppressing the release of hydrocarbons into the atmosphere and reusing them to ensure the atmospheric environment. Contamination can be eliminated.

It is a figure for demonstrating the concept of the adsorption / desorption tower in connection with the Example of this invention. It is a block diagram of the adsorption / desorption apparatus concerning the Example of this invention.

Explanation of symbols

R radius
H Tower height

DESCRIPTION OF SYMBOLS 1 Hydrocarbon vapor introduction path 2 Blower 3 Adsorption / desorption tower 4 Adsorbent with a large particle size and a small specific surface area 5 Adsorbent with a small particle diameter and a large specific surface area 6 Outlet 7 Atmospheric introduction path 8 Decompression pump 9 Piping 10 Chiller 11 Discharge port 12 Piping 13 Reservoir 14 Recycled product outlet

Claims (3)

Using an adsorption / desorption apparatus having one adsorption / desorption tower filled with an adsorbent for alternately performing adsorption and desorption, exhaust gas containing gaseous hydrocarbons is passed through the adsorption / desorption apparatus, and the adsorbent in the adsorption / desorption apparatus After the purified gas after the process of adsorbing the gaseous hydrocarbons to the atmosphere is released to the atmosphere, the process of once venting the gas containing the main components of the gaseous hydrocarbons and the inside of the adsorption / desorption tower with a vacuum pump Through a desorption step of depressurizing and recovering and reusing the desorbed gaseous hydrocarbons through a step of cooling ^{2. The} hydrocarbons from the exhaust gas containing gaseous hydrocarbons according to claim 1, wherein the adsorbent filled in the adsorption / desorption tower introduction part has a specific surface area of 5 m ² / g or more and less than 140 m ² / g. How to recover and reuse in liquid form 2. The particle size of the adsorbent packed in the adsorption / desorption tower is an average of 3 mm or more and an average of 8 mm or less at the adsorption / desorption tower introduction part, and an average of 1.5 mm or more and an average of 3.5 mm or less at the adsorption / desorption tower discharge part. For recovering and reusing hydrocarbons in liquid form from exhaust gas containing various gaseous hydrocarbons

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