Water extraction of propionitrile from nitrochloroform

Abstract

A method of extracting propionitrile from liquid nitrochloroform includes providing a feed solution including liquid nitrochloroform and a propionitrile solute dissolved therein. A liquid water-based solvent that is immiscible with the feed solution is also provided. The feed solution and the solvent are mixed such that the solvent absorbs and extracts at least a portion of the propionitrile solute from the feed solution. The feed solution is then separated from the solvent and the extracted propionitrile solute to produce a liquid extract comprising the water-based solvent and the propionitrile solute absorbed by the solvent and a liquid raffinate comprising the feed solution from which the propionitrile solute has been extracted.

Description

Field of the Invention

[0001] The present invention relates to a method for extracting impurity propionitrile from the fumigant chloropicrin. More particularly, the present invention provides a method for efficiently and effectively reducing propionitrile in chloropicrin by water extraction. Background Art

[0002] Chloropicrin is a common and widely used soil fumigant, particularly in agricultural applications. Chloropicrin is typically produced from nitromethane, which contains propionitrile, an environmentally harmful impurity. During normal manufacturing processes, propionitrile often finds its way into the final chloropicrin product. The maximum permissible levels of propionitrile in chloropicrin set by many global governments and regulatory agencies vary depending on where and how the chloropicrin will be used. Reducing the concentration of propionitrile in chloropicrin reduces potential environmental risks and significantly increases the marketability of the fumigant.

[0003] Conventional efforts to economically and practically reduce the level of propionitrile in the nitromethane used to produce chloropicrin have thus far been unsuccessful. In particular, fractional distillation has been employed, but achieving the desired low levels of propionitrile by this method is not economically feasible. A more substantial reduction in propionitrile is required to achieve a sufficiently high level of propionitrile to produce a significantly higher quality and more marketable chloropicrin. Alternative methods of removing propionitrile from the raw nitromethane have been investigated, including the use of various absorbents and extraction solvents; however, to date, no method has proven to be commercially practical. Likewise, there is no known commercially successful method for removing propionitrile from the final chloropicrin product itself. Summary of the invention

[0004] It is therefore an object of the present invention to provide a method for effectively, efficiently and economically reducing the level of propionitrile in chloropicrin fumigants by means of water extraction.

[0005] Another object of the present invention is to provide a method for extracting propionitrile from chloropicrin which is significantly improved over conventional methods such as distillation or the use of selective absorbents.

[0006] Another object of the present invention is to provide a method for extracting propionitrile directly from manufactured chloropicrin, rather than extracting propionitrile from the nitromethane component of chloropicrin.

[0007] Another object of the present invention is to provide a water extraction technique for removing propionitrile from chloropicrin by using any of various liquid-liquid extraction techniques including batch, multi-stage, continuous co-current and counter-current processes.

[0008] Another object of the present invention is to provide a water extraction technique for removing propionitrile from chloropicrin by using any of various known operating equipment suitable for liquid-liquid extraction purpose such as Scheibel column, Kuhni column, Treybal column, Karr reciprocating column, rotating disk column, pulse column, etc.

[0009] Another object of the present invention is to provide a method for producing high quality chloropicrin fumigants having reduced levels of propionitrile, reduced potential for adverse environmental impacts, reduced manufacturing costs and expanded commercial marketability.

[0010] The present invention arises from the recognition that propionitrile can be more effectively and efficiently removed from manufactured chloropicrin fumigants by means of aqueous liquid-liquid extraction. Such extraction can be performed by using a water-based solvent (which can be pure water or an aqueous solution) to extract propionitrile from the final manufactured chloropicrin fumigant. Such extraction can be performed using various types of liquid-liquid extraction equipment and process technologies, including batch, multi-stage, co-current and / or countercurrent continuous or multi-stage batch processing.

[0011] The present invention provides a method for extracting propionitrile from liquid chloropicrin. The method includes providing a feed solution including liquid chloropicrin and propionitrile solute dissolved therein. A liquid water-based (aqueous) solvent immiscible with the feed solution is also provided. 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. The feed solution is then separated from the solvent and the extracted propionitrile to produce a liquid extract and a liquid raffinate. The liquid extract includes a water-based solvent and the propionitrile solute absorbed by the solvent. The raffinate includes the feed solution from which the propionitrile solute has been extracted.

[0012] The liquid solvent and feed solution can be mixed in a single batch process or a multi-stage batch process. The liquid solvent and solution can be mixed in a countercurrent multi-stage batch process. The liquid solvent and solution can be mixed in a cocurrent or countercurrent continuous process.

[0013] In a preferred embodiment, the liquid solvent is composed of water, or alternatively comprises an aqueous solution. The aqueous solvent stream and the chloropicrin feed stream can be fed at opposite ends of a mixing unit or a series of multiple mixing units, wherein these streams are in continuous contact with each other but flow in a countercurrent direction, which is consistent with the conventional technology of continuous countercurrent liquid-liquid extraction. This continuous countercurrent arrangement allows a high concentration of propionitrile solute in the final extract, so that the target level of propionitrile in the final chloropicrin raffinate product can be reduced when using minimal solvent. The low PN product can then be dried to prevent decomposition into corrosive compounds. The spent extract can be regenerated by distillation to remove the PN solute so that it can be reused as a fresh solvent subsequently. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Other objects, features and advantages will be apparent from the following description of preferred embodiments and the accompanying drawings, in which:

[0015] Figure 1 is a schematic diagram showing a single batch water extraction process for reducing the level of propionitrile in chloropicrin according to the present invention;

[0016] Figure 2 is a schematic diagram of an alternative water extraction method, in which Figure 1 The initial stage extraction shown is followed by an optional secondary batch extraction of propionitrile from chloropicrin;

[0017] Figure 3 is a schematic diagram of a water extraction method using a continuous multi-stage countercurrent extraction system;

[0018] Figure 4 is a simplified schematic diagram of the method of the present invention carried out in a continuous process using a commercially available liquid-liquid extraction column; and

[0019] Figure 5 yes Figure 4 Schematic diagram of a representative section of the extraction column shown in . DETAILED DESCRIPTION

[0020] exist Figure 1 A schematic diagram depicting a method for extracting propionitrile (PN) from the fumigant chloropicrin (CP) in an extremely cost-effective and efficient manner is shown in FIG. It should be understood that the method of the present invention can be implemented using various known types of liquid extraction equipment. Those skilled in the art will understand the specific equipment and hardware used to implement the extraction technology and do not constitute a limitation of the present invention.

[0021] Figure 1 A method 10 using a single batch extraction technique is disclosed per se. Initially, chloropicrin is produced in a conventional manner by reacting raw nitromethane with other chemical components. This manufactured chloropicrin (CP) includes a propionitrile (PN) impurity that requires reduction. A liquid CP feed solution 12 including a PN solute is prepared as a feed solution and provided to a container 14. The container may include a bucket, a bottle, a flask, a test tube, or almost any closed container suitable for containing CP. A liquid water-based (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 may be an aqueous solution including, but not limited to, NaCl, bleach, or NaOH. Since the water-based 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 lighter water-based solvent 16 floats above the feed solution along the interface 20.

[0022] The vessel 14 is stirred vigorously, as indicated by the double arrow 18. This mixes the solvent 16 and the CP feed solution 12. As shown in the subsequent right-hand diagram of the vessel 14, this mixing causes the water-based solvent 16 to absorb and extract at least a portion of the propionitrile solute 22 from the solution 12. The stirring of the vessel 14 is stopped and the immiscible phases 12 and 16 are separated. The dense phase includes a raffinate solution 12a composed of the chloropicrin feed solution and the residual propionitrile solute 22, which sinks to the bottom of the vessel, while the extract solution 16a is composed of the water-based solvent and the extracted PN solute 22, which rises and floats on the raffinate solution. The phases are separated again along the interface 20. The solvent 16 is thus effectively extracted and captured by the PN solute 22 from the CP feed solution 12. The PN solute is redistributed between the two liquid phases 12 and 16 according to the relative solubility of propionitrile in each of the chloropicrin and water-based solvent phases.

[0023] After the above-described liquid-liquid extraction occurs, the aqueous extract solution and the raffinate solution are removed from the vessel 14. The aqueous solvent and its extracted PN solutes 22 may be decanted from the vessel 14 as an extract solution 16a. The raffinate 12a comprising the CP feed solution and its residual PN solutes 22 is withdrawn from the vessel 14 as indicated by arrow 25 and deposited in a collection vessel 26. The wet chloropicrin has been in contact with water, which, if not treated, may cause hydrolysis and corrosion in the fumigation storage container and application machinery. The long-term presence of water also tends to degrade the chloropicrin. Therefore, the wet chloropicrin may be passed through a dryer 28 to remove any residual water from the collected chloropicrin raffinate.

[0024] like Figure 2 As further shown, the chloropicrin raffinate 12a may be subjected to an additional batch liquid-to-liquid extraction before being discharged from the vessel 14. The extract 16a ( Figure 1 ) after which additional fresh solvent 16x ( Figure 2 ) is added to the raffinate 12a in vessel 14. A second extraction similar to that described above can then be performed between the fresh solvent 16(x) and the raffinate 12a in vessel 14. In particular, vessel 14 is again vigorously stirred and then allowed to settle so that the immiscible phases separate, as shown in FIG. Figure 225a. This produces a new extract solution 16b which is lower in solute 22 than solution 16a, and a new raffinate 12b which is also lower in residual solute 22 than raffinate 12a. This process can be repeated as many times as desired to gradually reduce the solute PN content in the raffinate chloropicrin 12a, 12b...12n (where n represents the number of stages selected for the batch-like extraction) until the desired residual PN 22 level in the chloropicrin is reached. When the residual PN solute 22 content is sufficiently reduced, the remaining chloropicrin raffinate can be withdrawn from the vessel 14, as shown by arrow 25x, and collected and dried as described above. The latter variation is referred to as multi-stage batch liquid-liquid extraction.

[0025] Single or multistage batch liquid-liquid extraction is relatively easy to set up and perform on a small scale, but is not optimal for commercial purposes. Figure 3 The more efficient multi-stage countercurrent batch extraction process shown, the process of reducing the content of propionitrile has been significantly improved, wherein the water-based solvent 116 and the CP feed solution 112 are fed separately at opposite ends and gradually pass through a series of interconnected extraction containers or units C1, C2, C3...Cn in opposite directions. The latter name Cn represents the last unit in the series and reflects that any selected number of units can be used. In particular, the water-based solvent 116 (which can also include pure water or an aqueous solution) passes through units C1, C2, C3, Cn in a forward direction from left to right, as shown in streams E1, E2...En, and the feed solution 112 passes through units Cn-C1 in a counter or reverse direction from right to left, as shown in streams Rn...R2, R1. It should be understood that the terms "first", "positive", "reverse", "backward", "right" and "left" refer only to the relative directions in the figure. In each unit, the flow is stopped and a batch extraction is performed between the extract or solvent from the previous unit and the raffinate or feed from the next unit. For example, unit C2 is filled with extract E1 from unit C1 and raffinate R3 from unit C3. Then, the contents of unit C2 are mixed and separated by batch extraction, and the extract E2 is discharged to unit C3, while the raffinate R2 is discharged to unit C1. Similar actions also occur in other units involving various corresponding streams from the previous unit and the next unit, in a manner similar to the aforementioned example described with respect to unit C2. A separate batch extraction occurs in each unit, in which the propionitrile content in the water-based solvent is increased, while the propionitrile in the feed chloropicrin solution is depleted. The PN solute levels in the chloropicrin raffinates Rn, R3, R2 and R1 are sequentially reduced during extraction in each unit Cn, C3, C2, C1. In each unit C1, C2, C3, Cn, the extracts E1, E2, E3, En are enriched in PN solutes. Therefore, the final extract En is very rich in solutes and a minimum amount of solvent is required to achieve the desired PN content level in the final chloropicrin raffinate R1.

[0026] Figure 4 and Figure 5 A Scheibel continuous countercurrent liquid-liquid extraction column designed and manufactured by Koch Modular Process Systems is schematically depicted. In principle, it functions similarly to a multistage countercurrent batch extraction process; however, the flow never stops, so that solvent and feed solution are constantly flowing into and out of any given unit. Column 210 employs a vessel 214 having an internal chamber. An axially rotating shaft 215 supporting a plurality of turbine impellers 219 extends vertically through the chamber of vessel 214. Each impeller is mounted on the shaft so that when the shaft turns, the impeller rotates between spaced-apart horizontal pairs of inner baffles 221, 222. The inner baffles themselves are supported between corresponding horizontal pairs of upper and lower baffles 223 and 225. The baffles around each impeller, together with the impeller, constitute a representative stage or unit of the multistage countercurrent liquid-liquid extraction device. Liquid-liquid extraction device designs such as Scheibel columns effectively provide a very large number of physical extraction stages or units in a very small space. The Scheibel column may have 30 or more physical stages in a single vessel that is only 10 ft. or less in height. Again, it should be understood that column 210 is commercially available and does not constitute a feature of the present invention. Nevertheless, the illustrated liquid-liquid extraction apparatus may be advantageously used to practice the method of the present invention, as shown below.

[0027] As previously described, the CP feed solution 212 is introduced into the interior chamber of the column 210 through the inlet port 280 near the upper end of the container 214. At the same time, the aqueous solvent 216 is introduced into the chamber of the container 214 through the lower inlet port 282. Various selected volumes of feed solution and solvent can be used. The heavier CP feed solution sinks through the chamber of the column 210, and the lighter solvent rises. At the same time, the rotary drive 217 operates to rotate the shaft 215 and rotate the impeller 219. This thoroughly mixes the solution 212 and solvent 216 as they pass through successive vertical extraction stages or units defined by baffles 221, 222, 223 and 225 around each impeller blade 219. As the solution and solvent mix, the aqueous solvent draws the PN solutes out of the chloropicrin solution. The two phases are immiscible, and the denser and heavier CP solution continues to sink downward through the column 210, while the lighter solvent continues to rise. As the respective phases pass upward and downward through the various vertical stages of the column, extraction of the PN solute from the CP solution into the solvent occurs, similar to the Figure 3 A multistage countercurrent batch liquid-liquid extraction process is shown and described.

[0028] In operation, a lighter saturated extract solution containing solute PN is collected at the top of the column above feed port 280 and is discharged from vessel 214 through port 290. A heavier raffinate solution depleted of PN solute is collected at the bottom of the column below solvent port 282 and is discharged from the bottom of the column at port 286. The discharged raffinate R is sent to a drying system to rapidly dry the chloropicrin, as previously described.

[0029] It should be understood that various other liquid-liquid extraction mechanisms and equipment can be used to perform the method of the present invention. These include Kuhni stirred towers, Karr models or other types of reciprocating plate towers, pulsed flow columns, rotating disk columns, centrifugal settlers, perforated plate columns, simple packed columns, and even empty tubes with two liquid streams flowing in opposite directions. The present invention can also be practiced using a co-current continuous liquid-liquid extraction device. Those skilled in the art will understand the construction and operation of such devices.

[0030] In each of the embodiments disclosed herein, the spent extract solution 16a, 16b, En, 216y may be distilled to remove PN solutes and regenerate the aqueous solvent. The solvent may then be effectively reused to perform additional liquid-liquid extractions of PN solutes from the chloropicrin feed solution.

[0031] The following examples reflect the results obtained using the method of the present invention:

[0032] Example 1

[0033] Fifty grams of chloropicrin containing 2245 ppm PN solute were placed in a 250 ml separatory funnel with a solvent containing 150 g deionized water. The liquid was shaken vigorously for 60 seconds and the mixture was allowed to settle. The extracted chloropicrin solution was taken out from the bottom of the funnel. The propionitrile content in the recovered chloropicrin was measured to be 889 ppm.

[0034] Example 2

[0035] Fifty grams of chloropicrin containing 2018 ppm PN were placed in a 250 ml separatory funnel with 150 grams of deionized water and stirred for 60 seconds. After the mixture settled, the phases were separated and the extracted chloropicrin solution was returned to the funnel with a second 150 gram portion of deionized water solvent. The funnel was stirred again for 60 seconds and the phases were separated again. This process was repeated for a total of five times, using 150 grams of fresh deionized water solvent for each extraction. After the fifth extraction, the remaining PN solute level in the final chloropicrin raffinate was reduced to less than 10 ppm.

[0036] Example 3

[0037] Assemble and run as Figure 3 and Figure 4The 30-stage pilot Scheibel column shown has dimensions of 6' in height and 80 mm in diameter. Feed chloropicrin containing 2938 ppm of propionitrile is continuously fed into the top inlet of the column at a rate of 0.17 lbs. / min, while deionized water is pumped into the bottom inlet of the column at a rate of 0.56 lbs. / min. The column is run for a period of 4 hours to reach steady state conditions, after which time the chloropicrin raffinate discharged from the bottom of the column is sampled and the propionitrile content of the discharged chloropicrin is measured to be 154 ppm. Thus, almost 95% of the PN solutes are removed in the process.

[0038] The water extraction method disclosed herein provides significant unexpected benefits in producing high-quality chloropicrin. Traditionally, chloropicrin produced from more economical and commercially available nitromethane sources will have PN solute levels of 2000ppm or higher, even after adopting known solute reduction techniques. Liquid-liquid extraction of chloropicrin solutions using pure water or aqueous solutions enables propionitrile levels to be advantageously reduced to less than 200ppm in an economically effective and practical manner. This liquid-liquid extraction of chloropicrin has never been performed using water, and such use was previously considered counterintuitive and highly impractical. Traditionally, water is avoided in and around chloropicrin because it is prone to causing undesirable hydrolysis of chloropicrin. This can significantly reduce the quality of the fumigant and corrode CP storage containers and application equipment. These problems are avoided in the disclosed method because the final raffinate from which a favorable amount of propionitrile is removed is quickly and fully dried.

[0039] Chloropicrin produced using the method of the present invention exhibits greatly improved quality. Since the propionitrile level has been greatly reduced, the fumigant exhibits fewer harmful effects and is safer to use. In certain markets and for certain applications, chloropicrin with higher PN levels cannot be used. The method of the present invention provides the ability to use nitromethane with a higher PN content but which may have a lower cost and is more readily available to manufacture CP for sale to those markets and for those applications. For example, all nitromethane manufactured in the United States has a high PN content. Nitromethane with a low PN content is manufactured using a process that is not environmentally friendly. Therefore, its continued availability is uncertain. The method of the present invention enables the efficient and cost-effective use of high PN content nitromethane available in the United States to produce the desired low PN content chloropicrin.

[0040] Thus, the present invention discloses an aqueous extraction process for effectively and inexpensively reducing the level of propionitrile in chloropicrin. Although specific features of the invention are shown in some of the figures and not in others, this is for convenience only as each feature may be combined with any and all other features according to the invention.

Claims

1. A method for extracting propionitrile from liquid chloropicrin, the method comprising: providing a feed solution comprising liquid chloropicrin and a propionitrile solute dissolved therein; providing a liquid water-based solvent, the liquid water-based solvent being immiscible with the feed solution; mixing the feed solution and the solvent so that the solvent absorbs and extracts at least a portion of the propionitrile solute from the feed solution; as well as The feed solution is separated from the solvent and the extracted propionitrile solute to produce a liquid extract comprising a water-based solvent and the propionitrile solute absorbed by the solvent and a liquid raffinate comprising the feed solution from which the propionitrile solute has been extracted.

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 includes an aqueous solution.

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

5. The method according to claim 1, wherein: The feed solution and liquid solvent are mixed 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 propionitrile solute in a chloropicrin solution, the method comprising: Providing a series of sequentially interconnectable mixing units; conveying a liquid feed solution comprising chloropicrin containing propionitrile solute in a first direction through the successive mixing units in sequence; Simultaneously conveying a water-based solvent that is immiscible with the liquid feed solution in an opposite direction through the successive mixing units; The feed solution and solvent are mixed in each mixing unit so that the solvent extracts and absorbs the propionitrile solute from the feed solution, which produces an extract solution having a propionitrile level that gradually increases in each successive unit in a first direction, and also produces a raffinate solution having a propionitrile level that gradually decreases in each successive unit in an opposite direction.

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