Aqueous extraction of propionitrile from chloropicrin

Abstract

A method for extracting propionitrile from liquid chloropicrin includes the step of supplying a feed solution composed of liquid chloropicrin and a propionitrile solute dissolved therein. A liquid aqueous solvent that is immiscible with the feed solution is also supplied. The solvent absorbs at least a portion of the propionitrile solute from the feed solution, and the feed solution and the solvent are mixed to extract. Thereafter, the feed solution is separated from the solvent and the extracted propionitrile solute to produce a liquid extract and a liquid raffinate. The liquid extract contains the aqueous solvent and the propionitrile solute absorbed by the solvent, and the raffinate contains the feed solution from which the propionitrile solute has been extracted.

Description

Technical Field

[0001] The present invention relates to a method for extracting propionitrile, an impurity, from chloropicrin, which is a fumigant. More specifically, the present invention provides a method for efficiently and effectively reducing propionitrile from chloropicrin by aqueous extraction.

Background Art

[0002] Chloropicrin is a commonly and widely used soil fumigant, especially in agricultural applications. Chloropicrin is generally produced from nitromethane, which contains propionitrile, an environmentally undesirable impurity. In a normal manufacturing process, propionitrile usually remains in the final chloropicrin product. The maximum allowable level of propionitrile in chloropicrin, as determined by many world government agencies and regulatory bodies, varies depending on where and how chloropicrin can be used. Reduction of the concentration of propionitrile in chloropicrin reduces potential environmental risks and significantly improves the marketability of the fumigant.

[0003] So far, conventional efforts to economically and practically reduce the level of propionitrile in nitromethane used to produce chloropicrin have not been successful. Specifically, fractional distillation has been employed, but this method cannot economically reach the desired low level of propionitrile. To obtain very high-quality and more marketable chloropicrin, a very large amount of reduction is required to sufficiently reduce propionitrile. Alternative methods for removing propionitrile from nitromethane, the raw material, including the use of various absorbents and extraction solvents, have been investigated, but so far, no method has been shown to be commercially practical. Similarly, no commercially successful technique for removing propionitrile from the final chloropicrin product itself is known.

Summary of the Invention

Problems to be Solved by the Invention

[0004] (Summary of the Invention) Accordingly, an object of the present invention is to provide a method for effectively, efficiently and economically reducing the level of propionitrile in a chloropicrin fumigant by an aqueous extraction method.

[0005] A further object of the present invention is to provide a method for extracting propionitrile from chloropicrin, which shows a significant improvement over conventional methods such as fractional distillation or the use of selective absorbents.

[0006] A further object of the present invention is to provide a method for directly extracting propionitrile from manufactured chloropicrin rather than from the nitromethane raw material of chloropicrin.

[0007] A further object of the present invention is to provide an aqueous extraction method for removing propionitrile from chloropicrin by using any of various liquid-liquid extraction methods including batch processes, multi-stage processes, continuous co-current processes and counter-current processes.

[0008] A further object of the present invention is to provide an aqueous extraction method for removing propionitrile from chloropicrin by using any of various known operating devices suitable for liquid-liquid extraction, such as Scheibel columns, Kuhni columns, Treybal columns, Karr reciprocating columns, rotating disk columns, pulsed columns, and many other implementation purposes.

[0009] A further object of the present invention is to provide a method for producing a high-quality chloropicrin fumigant with a reduced propionitrile level, a reduced potential for adverse environmental impacts, and a low manufacturing cost, which has an expanded commercial marketability.

Means for Solving the Problems

[0010] The present invention results from the realization that propionitrile can be removed more effectively and efficiently from a chloropicrin fumigant produced by aqueous liquid-liquid extraction. The above extraction can be carried out by using an aqueous solvent which may be either pure water or an aqueous solution in order to extract propionitrile from the finally produced chloropicrin fumigant. The above extraction can be carried out using various types of liquid-liquid extraction devices and process techniques including batch processes, multi-stage processes, continuous processes of co-current and / or counter-current, or multi-stage batch processes.

[0011] The present invention is characterized by a method for extracting propionitrile from liquid chloropicrin. The method includes a step of supplying a feed solution containing liquid chloropicrin and a propionitrile solute dissolved therein. A liquid aqueous solvent immiscible with the feed solution is also supplied. The feed solution and the solvent are mixed such that the solvent absorbs at least a part of the propionitrile solute from the feed solution and extracts it. Thereafter, the feed solution is separated from the solvent and the extracted propionitrile to produce a liquid extract and a liquid raffinate. The liquid extract contains the aqueous solvent and the propionitrile solute absorbed by the solvent. The raffinate contains the feed solution from which the propionitrile solute has been extracted.

[0012] The liquid solvent and the feed solution may be mixed in a single batch process or in a multi-stage batch process. The liquid solvent and the solution may be mixed in a counter-current multi-stage batch process. The liquid solvent and the solution may be mixed in a co-current continuous process or a counter-current continuous process.

[0013] In a preferred embodiment, the liquid solvent consists of water or alternatively contains an aqueous solution. The aqueous solvent stream and the chloropicrin feed stream can be fed to opposite ends of a mixing unit or a series of multiple mixing units where the streams flow in a countercurrent direction consistent with the normal technique of continuous countercurrent liquid-liquid extraction, such that the flows are in continuous contact with each other. The above-described continuous countercurrent arrangement enables increasing the concentration of the propionitrile solute in the final extract so that the targeted level of reduced propionitrile in the final chloropicrin raffinate product can be achieved with a minimal use of solvent. The product with less PN can then be dehydrated to prevent it from decomposing into corrosive compounds. The spent extract can be regenerated by distillation to remove the PN solute so that it can be reused as fresh solvent.

[0014] Other objects, features, and advantages may result from the following description of the preferred embodiment and the accompanying drawings.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0016] FIG. 1 shows a schematic diagram depicting a highly cost - effective and efficient method for extracting propionitrile (PN) from the fumigant chloropicrin (CP). It should be understood that the method of the present invention can be implemented using various known types of liquid extraction devices. The specific apparatus and hardware for implementing the extraction method are understood by those skilled in the art and do not constitute a limitation of the present invention.

[0017] FIG. 1, by itself, discloses Method 10 using a single - batch extraction method. First, chloropicrin is produced by a conventional method that reacts the raw material nitromethane with other chemical components. This produced chloropicrin (CP) contains propionitrile (PN) impurities that need to be reduced. A liquid CP feed solution 12 containing the PN solute is prepared as a feed solution and supplied to a container 14. The container can include a drum, bottle, flask, test tube, or any substantially sealed container suitable for containing CP. A liquid aqueous solvent 16 is also added to the container 14. The solvent must be immiscible with the feed solution 12. The solvent 16 may consist of pure water or, alternatively, an aqueous solution containing but not limited to NaCl, bleach, or NaOH. Since the aqueous solvent 16 and the CP feed solution 12 are immiscible, the denser feed solution 12 containing propionitrile PN sinks to the bottom of the container 14, and the relatively lighter aqueous solvent 16 floats on top of the feed solution along the interface 20.

[0018] Container 14 is vigorously agitated as indicated by the double arrows 18. This mixes the solvent 16 and the CP feed solution 12. As schematically shown in the subsequent right - hand depiction of container 14, this mixing causes the aqueous solvent 16 to absorb at least some of the propionitrile solute 22 from solution 12 and effect extraction. The agitation of container 14 is stopped and the immiscible phases 12 and 16 are separated. The denser phase containing the raffinate liquid 12a composed of the chloropicrin feed solution and the residual propionitrile solute 22 sinks to the bottom of the container, and the extract liquid 16a composed of the aqueous solvent and the extracted PN solute 22 floats on top of the raffinate liquid. The phases are again separated along the interface 20. Thereby, the solvent 16 is effectively extracted and the PN solute 22 is obtained from the CP feed solution 12. The PN solute is redistributed between the two liquid phases 12 and 16 based on the relative solubility of propionitrile in each of the chloropicrin phase and the aqueous solvent phase.

[0019] After the aforementioned liquid - liquid extraction occurs, the aqueous extract liquid and the raffinate liquid are removed from container 14. The aqueous solvent and its extracted PN solute 22 can be decanted from container 14 as the extract liquid 16a. The CP feed solution and its residual PN solute 22 contained in the raffinate 12a are withdrawn from container 14 as indicated by arrow 25 and introduced into the collection container 26. Chloropicrin containing moisture is in contact with water and, if left untreated, can cause hydrolysis and corrosion within the fumigation storage container and the application machinery. The long - term presence of water also tends to degrade chloropicrin. Thus, chloropicrin containing moisture may be passed through a dehydrator 28 to remove all residual water from the collected chloropicrin raffinate.

[0020] As further shown in FIG. 2, additional batch liquid-liquid extraction can be carried out on the picric acid raffinate 12a before it is discharged from the vessel 14. Following removal of the extract 16a from the vessel 14 by decantation (FIG. 1), additional fresh solvent 16x (FIG. 2) can be added to the raffinate 12a within the vessel 14. A second extraction similar to the aforementioned extraction can then be carried out between the fresh solvent 16(x) and the raffinate 12a within the vessel 14. In particular, after the vessel 14 is stirred strongly again, it can be left to stand so that the immiscible phases separate as shown in the right hand representation of the vessel 14 in FIG. 2. This results in a new extract liquid 16b with less solute 22 than the solution 16a, and also a new raffinate 12b with less residual solute 22 than the raffinate 12a. This process can be repeated as many times as necessary until the residual PN22 in the picric acid reaches the desired level, gradually reducing the solute PN content in the raffinate picric acid 12a, 12b…12n (where n represents the number of similar batch extraction steps carried out). When the content of the residual PN solute 22 has been sufficiently reduced, the remaining picric acid raffinate can be withdrawn from the vessel 14 as indicated by the arrow 25x and collected and dehydrated as described above. This latter variation is known as multi-stage batch liquid-liquid extraction.

[0021] Single batch liquid-liquid extraction or multi-stage batch liquid-liquid extraction is relatively simple to set up and perform on a small scale, but is not the most advantageous and efficient for commercial purposes. The process of reducing the propionitrile content is a more efficient multi-stage countercurrent batch extraction process as shown in Figure 3, in which the aqueous solvent 116 and the CP feed solution 112 are each supplied to opposite ends and move continuously and stepwise in opposite directions through a series of extractor vessels or cells C1, C2, C3…Cn that are communicatively connected. The last symbol Cn represents the last cell of the train and reflects that any number of cells can be used. In particular, the aqueous solvent 116 (which may also contain either pure water or an aqueous solution) passes continuously from left to right through cells C1, C2, C3, Cn in the forward direction as indicated by flows E1, E2…En, and the feed solution 112 is supplied continuously from right to left in the opposite or reverse direction through cells Cn to C1 as indicated by flows Rn…R2, R1. The terms “first,” “forward,” “reverse,” “backward,” “right,” and “left” are understood to refer only to the directions relevant to the figure. In each cell, the flow is stopped and the batch extraction is carried out between the extract or solvent from the preceding cell and the raffinate or feed from the subsequent cell. For example, cell C2 is charged with extract E1 from cell C1 and raffinate R3 from cell C3. The contents of cell C2 are then mixed and separated by batch extraction, with extract E2 being discharged to cell C3 while raffinate R2 is discharged to C1. Similar behavior as described in the foregoing example for cell C2 occurs in each of the other cells in which various respective flows from the preceding and subsequent cells are involved. The independent batch extractions occurring in each of the cells increase the propionitrile content of the aqueous solvent and drastically reduce the propionitrile in the feed chloropicrin solution. The levels of the PN solute in the chloropicrin raffinates Rn, R3, R2, and R1 decrease continuously upon each respective extraction in cells Cn, C3, C2, C1.Extracts E1, E2, E3, En each contain a rich amount of PN solute in respective cells C1, C2, C3, Cn. As a result, the last extract En contains the solute very richly and requires a minimum amount of solvent for the PN content in the last chloropicrin raffinate R1 to reach the desired level.

[0022] Figures 4 and 5 schematically depict a Scheibel continuous countercurrent liquid-liquid extraction column designed and manufactured by Koch Modular Process Systems. In principle, it operates like a multi-stage countercurrent batch extraction process, but the solvent and feed solution always flow into and out of any given cell without any interruption in the flow. Column 210 uses a container 214 with an internal chamber. A shaft rotation shaft 215 supporting a plurality of turbine impellers 219 extends vertically through the chamber of the container 214. Each impeller is mounted on the shaft so that as the shaft rotates, the impeller rotates between a pair of spaced horizontal inner baffles 221, 222. The inner baffles themselves are supported between respective horizontal pairs of an upper baffle 223 and a lower baffle 225. The baffles around each impeller having an impeller generally comprise a representative stage or cell of this multi-stage countercurrent liquid-liquid extraction device. The design of a liquid-liquid extraction device such as a Scheibel column efficiently provides a very large number of physical extraction stages or cells in a very small space. A Scheibel column may have more than 30 physical stages in a single container with a height of only 10 feet or less. It should be understood, although repeated, that column 210 is commercially available and does not constitute a feature of the present invention. Nevertheless, the illustrated liquid-liquid extraction device can be advantageously used to implement the method of the present invention as follows.

[0023] The aforementioned CP feed solution 212 is introduced into the internal chamber of column 210 through an inlet port 280 attached near the upper end of container 214. At the same time, an aqueous solvent 216 is introduced into the chamber of container 214 through a lower inlet port 282. Feed solutions and solvents of various selected volumes can be used. The relatively heavy CP feed solution sinks through the chamber of column 210, and the relatively light solvent floats. At the same time, the rotary drive 217 operates to rotate the shaft 215 and the impeller 219. This thoroughly mixes the solution 212 and the solvent 216 as they pass through a continuous vertical extraction stage or cell defined by baffles 221, 222, 223, and 225 around the respective impeller blades 219. When the solution and the solvent are mixed, the aqueous solvent extracts the PN solute out of the chloropicrin solution. The two phases are immiscible, and the denser and relatively heavy CP solution continues to sink downward through column 210, while the relatively light solvent continues to float. Since each phase passes through the upper and lower parts within the individual vertical stages of the column, the extraction of the PN solute from the CP solution into the solvent is carried out in a manner similar to the multi-stage countercurrent batch liquid-liquid extraction process shown and described in relation to Figure 3.

[0024] In operation, the relatively light saturated extract solution containing the solute PN is collected at the top of the column above the feed port 280 and discharged from the container 214 through port 290. The relatively heavy raffinate solution with a significantly reduced PN solute is collected at the bottom of the column below the solvent port 282 and discharged from the bottom of the column at port 286. The discharged raffinate R is transferred to a dehydration system, as described above, to quickly dehydrate the chloropicrin.

[0025] It should be understood that various other liquid-liquid extraction mechanisms and apparatuses can be used to implement the method of the present invention. These include Kuhni agitation columns, Karr models or other types of reciprocating plate columns, pulsed flow columns, rotating disk columns, centrifugal sedimenters, perforated plate columns, simple packed columns, and even empty pipes through which two liquid streams flow in opposite directions. The present invention can also be implemented using a co-current continuous liquid-liquid extraction device. The construction and operation of the above devices can be understood by those skilled in the art.

[0026] In each embodiment of the present disclosure, the consumed extract liquids 16a, 16b, En, 216y can be distilled to remove the PN solute and regenerate the aqueous solvent. The solvent can then be efficiently reused to perform additional liquid-liquid extraction of the PN solute from the chloropicrin feed solution.

Examples

[0027] The following examples reflect the results achieved using the method of the present invention.

[0028] [Example 1] 50 grams of chloropicrin containing 2245 ppm of PN solute was placed in a 250 ml separatory funnel together with a solvent containing 150 grams of deionized water. The liquid was shaken vigorously for 60 seconds and the mixture was allowed to stand. The extracted chloropicrin solution was removed from the bottom of the funnel. The propionitrile content in the obtained chloropicrin was measured to be 889 ppm.

[0029] [Example 2] 50 grams of chloropicrin containing 2018 ppm of PN was placed in a 250 ml separatory funnel together with 150 grams of deionized water and shaken for 60 seconds. After allowing the mixture to stand, the phases were separated and the extracted chloropicrin solution was returned to the funnel together with a second 150 gram portion of deionized water solvent. The funnel was shaken again for 60 seconds and the phases were separated again. The process was repeated a total of 5 times, using 150 g of fresh deionized water solvent for extraction each time. After the 5th extraction, the level of PN solute remaining in the final chloropicrin raffinate decreased to less than 10 ppm.

[0030] [Example 3] A 30 - stage pilot Scheibel column, described in FIGS. 3 and 4 and having dimensions of 6 inches in height and 80 mm in diameter, was assembled and operated. Feed chloropicrin containing 2938 ppm of propionitrile was continuously fed at a rate of 0.17 pounds per minute to the top inlet of the column while deionized water was injected at a rate of 0.56 pounds per minute to the bottom inlet of the column. After operating the column for 4 hours to reach steady - state conditions, a sample of the chloropicrin raffinate discharged from the bottom of the column was taken and the propionitrile content in the discharged chloropicrin was measured at 154 ppm. Thus, approximately 95% of the PN solute was removed during the process.

[0031] The aqueous extraction method disclosed herein presents highly unpredictable advantages associated with the production of high-quality chloropicrin. Conventionally, chloropicrin produced from more economical and commercially available sources of nitromethane can have PN solute levels of 2000 ppm or more even after known methods for reducing solutes have been used. Using pure water or an aqueous solution for liquid-liquid extraction with a chloropicrin solution is an economically efficient and practical approach that advantageously reduces the level of propionitrile to less than 200 ppm. Water has not been used at all for performing the above liquid-liquid extraction with chloropicrin, and in the past, such use was considered counterintuitive and highly impractical. Conventionally, the use of water in and around chloropicrin has been avoided because water tends to cause undesirable hydrolysis of chloropicrin. This can significantly degrade the quality of the fumigant and corrode CP storage containers and application devices. In the method of the present disclosure, those problems are avoided due to the rapid and sufficient dehydration of the final raffinate from which an advantageous amount of propionitrile has been removed.

[0032] Chloropicrin produced using the method of the present invention exhibits greatly improved quality. Due to the substantial reduction in the propionitrile level, the fumigant exhibits less toxicity and is much safer to apply. In certain markets and for certain applications, chloropicrin with relatively high PN levels cannot be used. The method of the present invention presents the ability to manufacture CP for sale in those markets and those applications that use nitromethane, which may have a high PN content but is less costly and more readily available. For example, all nitromethane produced in the United States has a high PN content. Nitromethane with a low PN content is produced only in China using environmentally unfriendly processes. Therefore, its continued availability is not certain. The method of the present invention makes it possible to produce chloropicrin with a desired low PN content by efficiently and cost-effectively using nitromethane with a high PN content that is available in the United States.

[0033] Accordingly, the present invention discloses an aqueous extraction method for effectively and inexpensively reducing the propionitrile level in chloropicrin. Certain features of the present invention are shown in several drawings, and this is for convenience only since, although other points are not shown, each feature can be combined with any and all other features according to the present invention.

Claims

1. A method for extracting propionitrile from liquid chloropicrin, comprising: supplying a feed solution containing liquid chloropicrin and propionitrile solute dissolved therein; supplying an aqueous solvent in liquid form that is immiscible with the feed solution; mixing the feed solution and the solvent so that the solvent absorbs at least a portion of the propionitrile solute from the feed solution for extraction; and separating the feed solution from the solvent and the extracted propionitrile solute to produce a liquid extract and a liquid raffinate, wherein the liquid extract contains the aqueous solvent and the propionitrile solute absorbed by the solvent, and the raffinate contains the feed solution from which the propionitrile solute has been extracted. A method comprising the above steps.

2. The method according to claim 1, wherein the liquid solvent consists of water.

3. The method according to claim 1, wherein the liquid solvent contains an aqueous solution.

4. The method according to claim 1, wherein the liquid solvent and the feed solution are mixed in a single-stage batch process.

5. The method according to claim 1, wherein the feed solution is mixed with the liquid solvent multiple times in a multi-stage batch process.

6. The method according to claim 1, wherein the liquid solvent and the feed solution are mixed in a multi-stage countercurrent batch process.

7. The method according to claim 1, wherein the liquid solvent and the feed solution are mixed in a continuous process.

8. The method according to claim 1, wherein the liquid solvent and the feed solution are mixed in a continuous countercurrent process.

9. A method for reducing the propionitrile solute in a chloropicrin solution, comprising: supplying a continuous series of continuously connected continuous mixing cells; continuously feeding a liquid feed solution containing chloropicrin containing the propionitrile solute through the continuous mixing cells in a first direction; simultaneously, continuously feeding an aqueous solvent that is immiscible with the liquid feed solution through the continuous mixing cells in the opposite direction; and A step of mixing the feed solution and the solvent in each mixing cell such that the solvent extracts and absorbs the propionitrile solute from the feed solution, generating an extract having a gradually increasing propionitrile level in each successive cell in the first direction, and further generating a raffinate having a gradually decreasing propionitrile level in each successive cell in the reverse direction A method comprising this step

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