Title:AqueousExtractionofPropionitrilefrom Chloropicrin

Inventors:R.KeithWarbington,JohnNorthup

FIELD OFTHE INVENTION

Thisinventionrelatestoamethodofextractingtheimpuritypropi onitrilefrom the fumigantchloropicrin.Moreparticularly,theinventionprovidesam ethodofefficientlyand effectivelyreducingpropionitrilefrom chloropicrinbyaqueousextraction.

BACKGROUND OFTHE INVENTION

Chloropicrinisacommonandwidelyusedsoilfumigant,particular lyinagricultural applications.Chloropicrin is commonly produced from nitromethane,which contains propionitrile, an environmentally undesirable impurity. In normal manufacturing processes,propionitrilegenerallycarriesthroughintothefinalch loropicrinproduct.The maximum permissible levelof propionitrile in chloropicrin set by many worldwide governmentalandregulatorybodiesvariesdependingonwhereandhow thechloropicrin willbe used.Reducing the concentration ofpropionitrile in chloropicrin lessens the potentialenvironmentalriskandsignificantlyimprovesthemarketa bilityofthefumigant.

To date,conventionaleffortsto economicallyand practically reducethe levelof propionitrile inthe nitromethane usedtoproduce chloropicrinhave been unsuccessful. Specifically,fractionaldistillationhasbeenemployed,butitisno teconomicallyfeasible toachievedesiredlow levelsofpropionitrilebythismethod.A muchgreaterreductionis neededforthepropionitriletobereducedsufficientlysothatasigni ficantlyhigherquality and more marketable chloropicrin is obtained. Alternative methods to remove propionitrilefrom the raw materialnitromethane havebeenstudied,includingtheuseof various absorbents and extraction solvents;but,to date,no method has proven commerciallypractical.Likewise,there isnoknowncommerciallysuccessfulmeansto removepropionitrilefrom thefinalchloropicrinproductitself.

SUMMARY OFTHE INVENTION

Itisthereforeanobjectofthepresentinventiontoprovideametho dforeffectively, efficientlyandeconomicallyreducingthelevelofpropionitrileinc hloropicrinfumigantby meansofaqueousextraction.

Itisafurtherobjectofthisinventiontoprovideamethodofextrac tingpropionitrile from chloropicrinthatrepresentsasignificantimprovementoverconvent ionalmethods suchafractionaldistillationortheuseofselectiveabsorbents.

Itisafurtherobjectofthisinventiontoprovideamethodofextrac tingpropionitrile from manufactured chloropicrindirectly ratherthanfrom the nitromethane ingredientof chloropicrin.

Itisafurtherobjectofthisinventiontoprovide an aqueousextractiontechnique thatremovespropionitrilefrom chloropicrinbyusinganyofvariousliquid-liquidextraction techniques including batch, multistage, continuous cocurrent and countercurrent processing.

Itisafurtherobjectofthisinventiontoprovideanaqueousextrac tiontechnique thatremoves propionitrile from chloropicrin by using any ofvarious known operating equipmentsuitedforthepurposeofperformingliquid-liquidextract ionsuchasScheibel columns, Kuhnicolumns,Treybaltowers,Karr reciprocating towers, rotating disc columns,pulsedcolumns,andmanyothers.

Itisa furtherobjectofthisinvention to provide a method forproducing a high qualitychloropicrinfumigantwithareducedpropionitrile level,a reduced potentialfor adverseenvironmentaleffect,alowercostofmanufacture,andexpand edcommercial marketability.

Thisinventionresultsfrom therealizationthatpropionitrilecanberemovedmore effectively and efficiently from a manufactured chloropicrin fumigant by means of aqueous liquid-liquid extraction.Such extraction can be made by employing a waterbased solvent,which may be eitherpure wateroran aqueoussolution,to extractthe propionitrilefrom thefinalmanufactured chloropicrinfumigant.Such extractioncanbe made using various types of liquid-liquid extraction equipment and processing techniques including batch,multistage,cocurrentand/orcountercurrentcontinuousor multistagebatchprocessing. Thisinventionfeaturesamethodofextractingpropionitrilefrom liquidchloropicrin. The method includes providing a feed solution thatincludes liquid chloropicrinwith a propionitrile solute dissolved therein.A liquid,water-based (aqueous)solventthatis immisciblewiththefeed solutionisalsoprovided.Thefeedsolutionandthesolventare intermixedsuchthatthesolventabsorbsandextractsatleastaportio nofthepropionitrile solutefrom the feed solution.Thefeed solutionisthenseparatedfrom thesolventand extractedpropionitriletoproducealiquidextractandaliquidraffi nate.The liquidextract includesthewater-basedsolventand propionitrilesolute absorbed bythesolvent.The raffinateincludesthefeedsolutionfrom whichthepropionitrilesolutehasbeenextracted.

The liquidsolventandfeedsolutionmaybe intermixed inasinglebatchprocess orinamultistagebatchprocess.The liquidsolventandsolutionmaybe intermixed ina countercurrent multistage batch process.The liquid solvent and solution may be intermixedinacocurrentorcountercurrentcontinuousprocess.

In a preferred embodiment,the liquid solventconsists ofwater,oralternatively includesanaqueoussolution.Anaqueoussolventstream andchloropicrinfeedstream may be fed atoppositeendsofa mixing unitorseriesofmultiple mixing unitsinwhich the streams are in continuous contactwith one anotherbutflow in countercurrent directions consistentwith the normalartof continuous countercurrent liquid-liquid extraction. Such a continuous countercurrent arrangement allows for a high concentrationofpropionitrilesoluteinthefinalextractsuchthatt hereducedtargetlevel ofpropionitrile inthefinalchloropicrinraffinate productcanbe achievedwitha minimal useofsolvent.Thatproduct,low inPN,maythenbedriedtopreventdecompositioninto corrosive compounds.Thespentextractmay be regenerated bydistillation to remove thePN solutesothatitmaybe reusedsubsequentlyasfreshsolvent.

BRIEF DESCRIPTION OFTHE DRAWINGS

Otherobjects,featuresand advantageswilloccurfrom thefollowingdescription ofapreferredembodimentandtheaccompanyingdrawings,inwhich:

FIGS.1isaschematicview illustratingasinglebatchaqueousextractionmethod forreducingthelevelofpropionitrileinchloropicrininaccordance withthisinvention;

FIG.2 isaschematicview ofanalternativeaqueousextraction methodwherein an optionalsecond stage batch extraction ofpropionitrile from the chloropicrin is performedfollowingtheinitialstageextractionshowninFIG.1;

FIG.3 isa schematicview ofthe aqueousextraction method being performed usingacontinuousmultistagecountercurrentextractionsystem;

FIG.4 is simplified diagrammatic view ofthe method ofthis invention being implemented in a continuous process using a commercially available liquid-liquid extractioncolumn;and

FIG.5 is a diagrammatic view ofa representative segmentofthe extraction columnshowninFIG.4.

DETAILED DESCRIPTION OFPREFERRED EMBODIMENTS

ThereisshowninFIG.1aschematicdiagram thatdepictsamethodofextracting propionitrile (PN)from thefumigantchloropicrin (CP)inanextremelycostefficientand effective manner.Itshould be understood thatthe method ofthis invention may be practiced using various known types ofliquid extraction equipment.The particular equipmentand hardware forpracticing the extraction technique willbe understood to personsskilled intheartanddonotconstitutealimitationofthisinvention.

FIG.1,by itself,discloses a method 10 thatemploysa single batchextraction technique.Initiallychloropicrinisproducedinaconventionalmann erbyreactingtheraw materialnitromethanewithotherchemicalcomponents.Thismanufact uredchloropicrin (CP)includesthe propionitrile (PN)impuritythatrequires reduction.A liquid CP feed solution 12whichincludes PN solute isprepared asa feed solution and providedtoa vessel14.Thevesselmaycompriseadrum,bottle,flask,testtubeorvi rtuallyanyclosed containersuitedforaccommodatingCP.A liquid,water-based (aqueous)solvent16is alsoaddedtovessel14.Thesolventmustbeimmisciblewithfeedsoluti on 12.Solvent 16 may consistofpure wateror,alternatively,an aqueous solution including butnot limited to NaCI,bleach orNaOH.Because the water-based solvent16 and CP feed solution 12are immiscible,thedenserfeedsolution12containingpropionitrile PN sinks tothebottom ofvessel14 andthe lighterwater-based solvent16floatsabovethefeed solutionalonginterface20.

Vessel14 isagitatedvigorouslyasindicated bydouble-headed arrows 18.This intermixes solvent16 and CP feed solution 12.As represented schematically in the subsequentrighthanddepictionofvessel14,thismixingcauseswater -basedsolvent16 to absorb and extractatleastsome ofthe propionitrile solute 22 from solution 12. Agitationofvessel14 isdiscontinuedandtheimmisciblephases12and 16areallowed to separate.The denserphase comprising a raffinate solution 12a,composed ofthe chloropicrinfeed solutionand residualpropionitrile solute22,sinkstothe bottom ofthe vesselandanextractsolution 16a composed ofthewater-basedsolventandextracted PN solute 22 rises above and floats on the raffinate solution.The phases are again separatedalonginterface20.Solvent16hastherebyeffectivelyextr actedandacquired PN solute22from CPfeedsolution12,ThePN soluteisreapportionedbetweenthetwo liquid phases 12and 16 baseduponthe relativesolubilityofthepropionitrile ineach of thechloropicrinandwater-basedsolventphases.

Afterthe foregoing liquid-liquid extraction has occurred,the aqueous extract solutionandraffinatesolutionareremovedfrom vessel14.Theaqueoussolventandits extractedPN solute22maybedecantedfrom vessel14asextractsolution16a.TheCP feed solution and its residualPN solute 22 comprising raffinate 12a are drawn from vessel14,as indicated byarrow 25,and deposited in a collection vessel26.The wet chloropicrin has been in contactwith water,which,ifleftunaddressed,could cause hydrolysis and corrosion in fumigation storage containers and application machinery. The prolonged presence ofwateralso tendsto degrade thechloropicrin. Accordingly, the wetchloropicrin may be passed througha dryer28 to eliminate allresidualwater from thecollectedchloropicrinraffinate.

As furthershown in FIG.2,additionalbatch liquid to liquid extractions may be performed on the chloropicrin raffinate 12a before itis discharged from vessel14. Followingthe removalofextract16a(FIG.1)from vessel14 bydecantation,additional fresh solvent16x (FIG.2)may be added to the raffinate 12a in vessel14.A second extractionanalogoustothatpreviouslydescribed,maythenbe performed invessel14 betweenfreshsolvent16(x)andraffinate 12a.Specificallyvessel14 isagainvigorously agitated andthenallowedtosettlesothattheimmiscible phasesseparateasshownin therighthandrepresentationofvessel14inFIG.2.Thisresultsinane w extractsolution 16bwhichislowerinsolute22thansolution16a,andanew raffinate 12bwhichisalso lowerin residualsolute 22 than raffinate 12a.Thisprocessmaybe repeated as many times as necessary to progressively reduce the solute PN contentin the raffinate chloropicrin 12a,12b..I2n (wherein n represents the selected numberofanalogous batch extraction stages performed)untilthe desired levelofresidualPN 22 in the chloropicrin is achieved.When the content of residualPN solute 22 is reduced sufficiently,the remaining chloropicrin raffinate may be withdrawn from vessel14 as indicated byarrow 25x,collectedanddriedaccordinglyasdescribedabove.Thislatter variationisknownasmultistagebatchliquid-liquidextraction.

Singleormultistagebatchliquid-liquidextractionisrelativel ysimpletosetupand perform ona smallscale,butitisnotoptimallyefficientforcommercialpurposes .The process of reducing propionitrile content is improved considerably by employing a more efficient multistage, countercurrent batch extraction process as shown in FIG. 3, wherein water-based solvent 116 and CP feed solution 112 are respectively fed at opposite ends and move step wise in opposite directions sequentially through a series of communicably connected extraction vessels or cells C1 , C2, C3....Cn. The latter designation Cn represents the final cell in the series and reflects that any selected number of cells may be utilized. In particular, water-based solvent 116 (which again may comprise either a pure water or an aqueous solution) is passed sequentially through cells C1, C2, C3, Cn in the forward direction from left to right as indicated by flows E1 , E2... En, and feed solution 112 is fed sequentially through cells Cn - 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”, “rearward", “right” and “left” refer to relative directions in the figure only. At each cell, flow is stopped and a batch extraction is performed between the extract or solvent from the previous cell and the raffinate or feed from the subsequent cell. For example, cell C2 is charged with extract E1 from cell C1 and with raffinate R3 from cell C3. The contents from cell C2 are then mixed and separated in a batch extraction and the extract E2 is discharged to cell C3 while the raffinate R2 is discharged to C1 . A similar action occurs in each of the other cells involving the various respective flows from preceding and subsequent cells in like manner to the foregoing example described concerning cell C2. A separate batch extraction occurs in each cell whereby the water-based solvent increases in propionitrile content and the feed chloropicrin solution is depleted in propionitrile. The level of PN solute in the chloropicrin raffinate Rn, R3, R2 and R1 decreases sequentially upon extraction in each cell Cn, C3, G2, C1 . The extract E1 , E2, E3, En is enriched in PN solute in each cell C1 , C2, C3, Cn. As a result, the final extract En is very rich in solute and a minimum amount of solvent is required to achieve the desired level of PN content in the final chloropicrin raffinate R1 .

FIGS. 4 and 5 schematically depicts a Scheibel continuous countercurrent liquidliquid extraction column designed and manufactured by Koch Modular Process Systems. In principle it acts like a multistage counter current batch extraction process; however flow is never stopped such that solvent and feed solution are constantly flowing in and out of any given cell. Column 210 employs a vessel 214 having an interior chamber. An axially rotatable shaft 215 supporting a plurality of turbine impellers 219 extends vertically through the chamber of the vessel 214. Each impeller is mounted to the shaft such that when the shaft turns the impeller rotates between a spaced apart pair of horizontal inner baffles 221, 222. The inner baffles are themselves supported between a respective horizontal pair of upper and lower baffles 223 and 225. Collectively the baffles around each impeller with the impeller comprise a representative stage or cell of this multistage countercurrent liquid-liquid extraction device. A liquid-liquid extraction apparatus design such as a Scheibel column efficiently provides for a very large number of physical extraction stages or cells in a very small space. A Scheibel column might have 30 or more physical stages in a single vessel with a height of only 10 ft. or less. Again, it should be understood that column 210 is commercially available and does not constitute a feature of this invention. Nonetheless, the illustrated liquid-liquid extraction device may be used advantageously to practice the method of this invention as follows.

The CP feed solution 212, as previously described, is introduced into the interior chamber of column 210 through an inlet port 280 attached proximate the upper end of the vessel 214. At the same time, a water-based solvent 216 is introduced into the chamber of vessel 214 through a lower inlet port 282. Various selected volumes of feed solution and solvent may be employed. The heavier CP feed solution sinks through the chamber of column 210 and the lighter solvent rises. At the same time, rotary drive 217 is operated to turn shaft 215 and rotate impellers 219. This thoroughly intermixes the solution 212 and solvent 216 as they pass through successive vertical extraction stages or cells defined by the baffles 221 , 222, 223 and 225 around each impeller blade 219. As the solution and solvent are mixed, the aqueous solvent draws the PN solute out of the chloropicrin solution. The two phases are immiscible, and the denser and heavier CP solution continues to sink downwardly through the column 210 while the lighter solvent continues to rise. As the respective phases pass upwardly and downwardly through the individual vertical stages of the column, extraction of the PN solute from the CP solution into the solvent takes place analogous to the process of multistage counter current batch liquid-liquid extraction shown in and described in connection with FIG. 3.

In operation, the lighter saturated extract solution containing the solute PN collects at the top of the column above the feed port 280 and is discharged from vessel 214 through port 290. The heavier raffinate solution, depleted of PN solute, collects at the bottom of the column below the solvent port 282 and is discharged from the bottom of the column atport 286.The discharged raffinate R isdeliveredtoa drying system for promptdryingofthe chloropicrinaspreviouslydescribed.

Itshouldbeunderstoodthatvariousotherliquid-liquidextracti onmechanismsand equipmentmightbeemployedtoperform themethodofthisinvention.Theseincludethe Kuhniagitatedtower,the Karrmodelorothertypesofreciprocating platetowers,pulse flow columns,rotatingdiskcolumns,centrifugalsettlers,perforatedpl atecolumns,simple pack columns and even an empty pipe with two liquid streams flowing in opposite directions.The inventionmayalso bepracticedusingcocurrentcontinuousliquid-liquid extractionequipment.Theconstructionandoperationofsuchdevices willbeunderstood topersonsskilledintheart.

Ineach embodimentdisclosed herein,the spentextractsolution 16a,16b,En, 216ymaybedistilledtoremovethePN soluteandregeneratetheaqueoussolvent.The solventmaythenbereusedefficientlytoperform additionalliquid-liquidextractionofPN solutefrom achloropicrinfeedsolution.

The following examples reflect results achieved using the method ofthis invention:

Example 1

Fiftygramsofchloropicrin containing 2245 ppm PN solutewas placed ina 250 ml separatoryfunnelwithasolventcomprising 150gdeionizedwater.The liquidswere shakenvigorouslyfor60secondsandthe mixturewasallowed tosettle.Theextracted chloropicrinsolutionwasremovedfrom thebottom ofthefunnel.Thepropionitrilecontent inthe retrievedchloropicrinwasmeasuredat889ppm.

Example2

Fifty grams ofchloropicrin containing 2018 ppm PN was placed in a 250 ml separatoryfunnelwith150gramsofdeionizedwaterandagitatedfor60 seconds.After the mixturesettled,the phaseswereseparated and theextracted chloropicrinsolution wasreturnedtothefunnelwithasecond 150gram allotmentofdeionizedwatersolvent. Thefunnelwas agitated againfor60 seconds and the phaseswere again separated. Theprocesswasrepeated and performed atotaloffivetimes,eachtime using 150gof freshdeionizedwatersolventfortheextraction.Afterthefifthextr action,thelevelofPN soluteremaininginthefinalchloropicrinraffinatewasreducedtobe low 10ppm.

Example3

A 30-stagepilotScheibelcolumnasdepictedinFIGS.3and4havingdimen sions of6 ¹ in heightand 80 mm indiameterwasassembledandoperated.Feedchloropicrin containing2938ppm propionitrilewasfedcontinuouslyintothetopinletofthecolumnat a rate of0.17 lbs./minwhile deionized waterwaspumped into the bottom inletofthe columnata rateof0.56 lbs./min.Thecolumnwasoperatedforaperiod of4 hoursto reachsteadystateconditions,afterwhichtimethechloropicrinraff inatedischargedfrom the bottom ofthe column wassampled andthe propionitrile contentin the discharged chloropicrinwasmeasuredat154 ppm.Accordingly,almost95% ofthe PN solutewas removedinprocessing.

Theaqueousextractionmethoddisclosedhereinprovidessignific antunexpected benefits in relation to the production of high quality chloropicrin.Conventionally, chloropicrinproducedfrom themoreeconomicalandcommerciallyavailablesourcesof nitromethane willhave PN solute levels of2000 ppm orgreater,even afterknown techniquesforreducing the solute have been employed.Employing pure wateroran aqueoussolutionto perform liquid-liquid extractiononthechloropicrinsolutionenables propionitrile levelstobeadvantageouslyreducedtobelow 200 ppm inaneconomically efficientand practicalmanner.Waterhasneverbeenusedtoperform such liquid-liquid extractiononchloropicrinand previouslysuchusewouldbeconsidered counterintuitive and highly impractical.Traditionally,the use ofwaterin and around chloropicrin is avoided becausewatertendsto causeundesirablehydrolysisofchloropicrin.Thiscan significantlydegradethequalityofthefumigantandcorrodeCP storagecontainersand application equipment.Those problems are avoided in the disclosed method due to promptand adequate drying ofthefinalraffinate from which anadvantageousamount ofpropionitrile hasbeenremoved.

The chloropicrin produced usingthe method ofthis invention exhibitsa greatly improved quality.Because the propionitrile levelhas been substantially reduced,the fumigantexhibitsfewerharmfuleffectsand is muchsaferto apply.In certain markets and forcertain applications chloropicrin with higherPN levels cannotbe used.The method ofthis invention provides forthe ability to manufacture CP forsale to those marketsandforthose applicationsusing nitromethanethatishigherin PN content,but which may have a lower cost and be more readily available. For example,all nitromethane thatis manufactured in the US is high in PN content.Low PN content nitromethane ismanufacturedonlyinChinausinga processthatisnotenvironmentally friendly.Accordingly,itsongoing availabilityisnotcertain.Themethodofthisinvention enablesthehighPN contentnitromethane,availableintheUS,tobeusedefficientlyand costeffectivelyto produceadesiredlow PN contentchloropicrin.

Accordingly,the presentinvention disclosesan aqueous extraction method for effectively and inexpensively reducing propionitrile levels in chloropicrin.Although specificfeaturesoftheinventionareshowninsomeofthedrawingsand notothers,this isforconvenienceonly,aseachfeature maybecombinedwithanyandalloftheother featuresinaccordancewiththisinvention.