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

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[0003]

[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 the normal manufacturing process, propionitrile usually remains in the final chloropicrin product. The maximum allowable level of propionitrile in chloropicrin set 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 method 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) Therefore, the 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 aqueous extraction.

[0005] A further object of the present invention is to provide a method for extracting propionitrile from chloropicrin that shows 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 extracting propionitrile directly 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 the 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 liquid-liquid extraction, such as a Scheibel column, Kuhni column, Treybal column, Karr reciprocating column, rotating disk column, pulse column, and any of the many other known operating devices suitable for the intended purpose.

[0009] A further object of the present invention is to provide a method for producing a high-quality chloropicrin fumigant with reduced propionitrile levels, reduced potential for adverse environmental impacts, lower manufacturing costs, and increased commercial marketability. [Means for solving the problem]

[0010] The present invention relates to the realization that propionitrile can be removed more effectively and efficiently from chloropicrin fumigants produced by aqueous liquid-liquid extraction. The extraction can be carried out by using an aqueous solvent, which may be pure water or an aqueous solution, to extract propionitrile from the finally produced chloropicrin fumigant. The extraction can be carried out using various types of liquid-liquid extraction apparatus, as well as process technologies including batch processes, multi-stage processes, parallel and / or counter-flow continuous processes, or multi-stage batch processes.

[0011] The present invention is characterized by a method for extracting propionitrile from liquid chloropicrin. The method includes the step of supplying a feed solution containing liquid chloropicrin and propionitrile solute dissolved therein. A liquid aqueous solvent that is immiscible with the feed solution is also supplied. The feed solution and the solvent are mixed so that the solvent absorbs and extracts at least a portion of the propionitrile solute from the feed solution. Subsequently, 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 feed solution may be mixed in a single-batch process or in a multi-stage batch process. The liquid solvent and solution may be mixed in a counter-flow multi-stage batch process. The liquid solvent and solution may be mixed in a parallel flow continuous process or a counter-flow continuous process.

[0013] In preferred embodiments, the liquid solvent consists of water or, instead, an aqueous solution. The aqueous solvent stream and the chloropicrin feed stream can be supplied to opposing ends of a mixing unit or a series of multiple mixing units, where the flows are in continuous contact with each other but flow in a counterflow direction consistent with the conventional techniques of continuous counterflow liquid-liquid extraction. The above continuous counterflow arrangement allows for an increased concentration of propionitrile solute in the final extract so that the target level of reduced propionitrile in the final chloropicrin raffinate product can be achieved with minimal solvent use. The product, with its low PN content, can then be dehydrated to prevent decomposition into corrosive compounds. The consumed extract can then be regenerated by distillation to remove the PN solute so that it can be reused as a fresh solvent.

[0014] Other purposes, features, and advantages may arise from the following description of preferred embodiments and the accompanying drawings. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram illustrating a single-batch aqueous extraction method for reducing the level of propionitrile in chloropicrin according to the present invention. [Figure 2] Figure 1 shows a schematic diagram of an alternative aqueous extraction method in which an optional second-stage batch extraction of propionitrile from chloropicrin is performed, following the initial extraction stage shown in Figure 1. [Figure 3] This is a schematic diagram of an aqueous extraction method performed using a continuous multi-stage counterflow extraction system. [Figure 4] This is a simplified diagram of the method of the present invention, which is carried out in a continuous process using a commercially available liquid-liquid extraction column. [Figure 5] Figure 4 shows a diagram of typical segments of the extraction column. [Modes for carrying out the invention]

[0016] Figure 1 shows a schematic diagram illustrating 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 carried out using various known types of liquid extraction apparatus. Specific apparatus and hardware for carrying out the extraction method will be understood by those skilled in the art and do not constitute a limitation of the present invention.

[0017] Figure 1 discloses a method 10 that uses a single-batch extraction method. First, chloropicrin is produced by a conventional method of reacting 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 may include a drum, bottle, flask, test tube, or any substantially sealed container suitable for containing the 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 an aqueous solution containing, but not limited to, NaCl, bleach, or NaOH instead. Because 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, while the relatively lighter aqueous solvent 16 floats on the feed solution along the interface 20.

[0018] Container 14 is vigorously stirred as indicated by the double arrow 18. This mixes the solvent 16 with the CP feed solution 12. As schematically shown in the subsequent right-hand drawing of container 14, this mixing allows the aqueous solvent 16 to absorb and extract at least some propionitrile solute 22 from the solution 12. The stirring of container 14 is stopped and the immiscible phases 12 and 16 are separated. The denser phase containing the raffinate solution 12a, consisting of the chloropicrin feed solution and residual propionitrile solute 22, settles to the bottom of the container, while the extract solution 16a, consisting of the aqueous solvent and extracted PN solute 22, floats and rests on top of the raffinate solution. The phases are separated again along the interface 20. This effectively extracts the solvent 16, yielding the PN solute 22 from the CP feed solution 12. The PN solute is redistributed between two liquid phases, phase 12 and phase 16, based on the relative solubility of propionitrile in the chloropicrin phase and the aqueous solvent phase, respectively.

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

[0020] As further shown in Figure 2, an additional batch liquid-liquid extraction can be performed on the chloropicrin raffinate 12a before it is discharged from container 14. Following the removal of extract 16a from container 14 by decantation (Figure 1), additional fresh solvent 16x (Figure 2) can be added to the raffinate 12a in container 14. A second extraction, similar to the extraction described above, can then be performed between the fresh solvent 16(x) and the raffinate 12a in container 14. In particular, after vigorously agitating container 14 again, it can be allowed to stand to separate the immiscible phase as shown in the right-hand representation of container 14 in Figure 2. This yields a new extract liquid 16b with less solute 22 than solution 16a, and a new raffinate 12b with less residual solute 22 than raffinate 12a. This process can be repeated as many times as necessary to gradually reduce the solute PN content in the raffinate chloropicrin 12a, 12b…12n (where n represents the number of selected similar batch extraction steps performed) until the residual PN 22 in the chloropicrin reaches a desired level. When the content of residual PN solute 22 has been sufficiently reduced, the remaining chloropicrin raffinate can be withdrawn from the container 14 as indicated by arrow 25x, 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 are relatively easy to set up and implement on a small scale, but are not the most advantageously efficient for commercial purposes. The process for reducing propionitrile content is considerably improved by using a more efficient multi-stage counterflow batch extraction process, as shown in Figure 3, in which the aqueous solvent 116 and CP feed solution 112 are supplied to opposite ends and move sequentially in opposite directions through a series of connectably connected extraction vessels or cells C1, C2, C3…Cn. The last symbol Cn represents the last cell of the continuum and reflects that any number of cells of any choice can be used. In particular, the aqueous solvent 116 (which may also contain either pure water or an aqueous solution) passes sequentially through cells C1, C2, C3, Cn in the forward direction from left to right as indicated by flows E1, E2…En, and the feed solution 112 is supplied sequentially from cell Cn to C1 in the opposite or reverse direction from right to left as indicated by flows Rn…R2, R1. It should be understood that the terms “first,” “forward,” “reverse,” “backward,” “right,” and “left” refer to directions relevant only to the diagram. In each cell, the flow is stopped, and batch extraction is performed between the extract or solvent from the preceding cell and the raffinate or feed from the succeeding cell. For example, cell C2 is fed 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 and raffinate R2 being discharged to C1. Similar behavior occurs in each of the other cells involving various flows from the preceding and succeeding cells, similar to the example described above with respect to cell C2. The independent batch extractions occurring in each cell increase the propionitrile content of the aqueous solvent and drastically decrease the propionitrile content of the feed chloropicrin solution. The levels of PN solute in chloropicrin raffinate Rn, R3, R2, and R1 decrease continuously during extraction in cells Cn, C3, C2, and C1, respectively.Extracts E1, E2, E3, En each contain a rich amount of PN solute in their respective cells C1, C2, C3, Cn. As a result, the last extract En contains the solute very richly, and the minimum amount of solvent is required 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 that supports 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 each horizontal pair of an upper baffle 223 and a lower baffle 225. The baffles around each impeller having an impeller generally comprise a typical 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 that is only 10 feet or less in height. It should be understood that, although repeated, 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 in 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 greatly 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 carry out the method of the present invention. These include Kuhni stirring columns, Karr model or other types of reciprocating plate columns, pulse flow columns, rotating disk columns, centrifugal sedimentation units, perforated plate columns, simply packed columns, and empty pipes through which two liquid flows in opposite directions. The present invention can also be carried out using a parallel-flow continuous liquid-liquid extraction apparatus. The construction and operation of the above devices should be understood by those skilled in the art.

[0026] In each embodiment of this disclosure, the consumed extract solutions 16a, 16b, En, and 216y can be distilled to remove the PN solute and regenerate the aqueous solvent. The solvent can then be efficiently reused to carry out 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] Fifty grams of chloropicrin containing 2245 ppm of PN solute were placed in a 250 ml separatory funnel 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 at 889 ppm.

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

[0030] [Example 3] A 30-stage pilot Scheibel column, as depicted in Figures 3 and 4, with dimensions of 6 inches in height and 80 mm in diameter, was assembled and put into operation. Feed chloropicrin containing 2938 ppm propionitrile was continuously supplied to the top inlet of the column at a rate of 0.17 lbs / min, while deionized water was injected to the bottom inlet of the column at a rate of 0.56 lbs / min. After running the column for 4 hours to reach steady-state conditions, a sample of 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 offers highly unpredictable advantages related to 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 higher, even after known methods for reducing solute have been employed. Using pure water or aqueous solution to carry out liquid-liquid extraction with chloropicrin solution allows for a favorable reduction of propionitrile levels to less than 200 ppm in an economically efficient and practical manner. Water has never been used to carry out 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 equipment. In the method of this disclosure, these problems are avoided due to the rapid and sufficient dehydration of the final raffinate from which a favorable amount of propionitrile has been removed.

[0032] Chloropicrin produced using the method of the present invention exhibits significantly improved quality. Because the propionitrile level is substantially reduced, the fumigant exhibits less toxicity and is far 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 produce CP for sale to those markets and their applications using nitromethane, which has a high PN content but is lower in cost 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 uncertain. The method of the present invention makes it possible to produce desired low PN content chloropicrin by efficiently and cost-effectively using high PN content nitromethane available in the United States.

[0033] Accordingly, the present invention discloses an aqueous extraction method for effectively and inexpensively reducing propionitrile levels in chloropicrin. Certain features of the present invention are shown in some of the drawings, while others are not shown, but this is for convenience only, as each feature can be combined with any and all other features of the present invention.

Claims

1. A method for extracting propionitrile from liquid chloropicrin, A step of supplying a feed solution containing liquid chloropicrin and a propionitrile solute dissolved therein, A step of supplying an aqueous solvent that is incompatible with the feed solution, A step of mixing the feed solution and the solvent such that the solvent absorbs and extracts at least a portion of the propionitrile solute from the feed solution, and A step of 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 comprises the aqueous solvent and the propionitrile solute absorbed by the solvent, and the raffinate comprises the feed solution from which the propionitrile solute was extracted. Includes, A method comprising mixing the liquid solvent and the feed solution in a multi-stage counterflow batch process, a continuous process, or a continuous counterflow process.

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

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

4. A method for reducing propionitrile solute in a chloropicrin solution, A process of supplying a continuous series of interconnected continuous mixing cells, A step of continuously feeding a liquid feed solution containing chloropicrin with propionitrile solute through the continuous mixing cell in a first direction, Simultaneously, a step of continuously supplying an aqueous solvent that is incompatible with the liquid feed solution in the reverse direction through the continuous mixing cell, and A step of mixing the feed solution and the solvent in each mixed cell so that the solvent extracts and absorbs the propionitrile solute from the feed solution, wherein an extract solution having a gradually increasing propionitrile level in each continuous cell toward the first direction is produced, and a raffinate solution having a gradually decreasing propionitrile level in each continuous cell toward the reverse direction is produced. Methods that include...

5. A method for extracting propionitrile from liquid chloropicrin, A step of supplying a feed solution containing liquid chloropicrin and a propionitrile solute dissolved therein, A step of supplying an aqueous solvent that is incompatible with the feed solution, A step of mixing the feed solution and the solvent such that the solvent absorbs and extracts at least a portion of the propionitrile solute from the feed solution, and A step of 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 comprises the aqueous solvent and the propionitrile solute absorbed by the solvent, and the raffinate comprises the feed solution from which the propionitrile solute was extracted. Includes, A method wherein the liquid solvent includes an aqueous solution.

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