HUE034207T2 - Eljárás primer amin foszfogenálásával gázfázisban elõállított izocianát elválasztására a foszfogenálás gáz halmazállapotú nyerstermékétõl - Google Patents

Description

IOÄÄSf RIMER A MI A FOSZFOGENäLÄsAväL GÁZFAAISBÁA ELfMLLlYOTT IZOOaNÂI' :;j^yJtosarAsÁRA. AFos«eÄIÄs«äz a pnKöss'i&r.^piMHB^ 'fæçpied l>y>.m%c-öb8 oi® wîtin str excess: of phosgeste :i» the gas phase loam the gasePhS crude tuodtrei obtained ay tse reaction, wherein (í) the gaseous crude product is partially liquefied by contacting with a quenching hquid, (») the gas phase obtained is step (i) is partial iy condensed, (iîiÿ it© condesisate «Étained is step ¢11} is used as the quenehing liquid to step fs), (h the portions of the gasphase that were notsoniettsed iS step |ii) are at least partially dqueHed* 5^1 the llquidphase obtained in step (iv) i« ||^^Ä:ös«d as! the qjn#«fel»& liquid In step (S), and the Itquid pltuse ehtainad lb step Ci) is wofledldp to the pare Isocyanate without previously Irelnghsed asquenehmg ingái,

Ils? preparation of isocyanates, itt particular diisocsanates, in tlte::ip§:;;|i|t^e lids :i|^:#esërib«d: in#«, prior art ire: a relatively long time and is used industrially, in particular tor the production or tosuyleoc dhsocyanate, Bhfteamethylene dbsocyanare, isopltoroae diisocyauare amd dtisopphatodieyelohexylmethsoe, In alt processes thorp is formed a gaseous crade product which ootnprises at least l^^MUtey^drpg^iSölöÄ': and onreacted phosgene (phosgene is always used in excess) and Which ottixt he woflcct obtain the desired Aocy&amp;nsne sn pure form, lech a process: is desmbed, tbr csspple, itt: EP Ô IP MO HI, The dnssreyanates formed in a. tubular reactor are trot therntslliy: stable: at the: reaction tetpperetures of up to SÖüfHq. Rapid eobbhg of the reaction gases atcr tffo phösgetsatídh redetlbn ta tespperatotes helöw 1:50¾ is éftfefö* order to avoid the: testation of undesirable: sseesrdary products by the thermal decomposition of dhsocyaháié: or by a: Anther reaction. In fi 749 95A ®f, the gaseous mixture continuously leaving the reaction <dteih©r. which comprises mree o/to dtisocyanate, phosgene and hydrogen chloride, is to that cod passed into an Inert solvent,: for example dichlorobenxene, A disadsÁíttage oi this process ts that the Slow speed with which tne gas mixture is passed through she solvent baits must be chosen to oe raiatsvety low oeeause sotvent and the compounds dissolved therein ί» foö'iüp, 'lie bipod compounds would have tele separated from the gas In a subsequent step. A further disadvantage A that, owing to the low Sow speed and a lose heat transfer, I^:Solv^'<Âaliiir«Â&amp;ê:im8 lu Order to achieve ooeilug.

Also known are processes which use heat exchangers for coolmg the reaction gases anal-or relax tue gttses m vmm (DE föl: JS 160 Al). The disadvantage of heat exchangers is that, because of the poor beta treoslyr, large exchange duriirees, ássd thus .large 'heat exchangers», are required lor cl tech vu coolmg. in addision, deposits of solids on the comparatively cold aurfocss of the heat exchangers can occur owing to secomlary reaetioos of the gas mixture, such as, tor example, debompostitonj polymerssaObh orpreerplîSiion,

In the process according to EP I 761 *M 8Í, If Is attempted to shorten the dwell time betväre&amp; ire end of the réaction and tire cooling rőtre by prowdmg a region of Reduced' How cross· sects©» txtwecn the reset-on gone and; the gone in which termination of the reaction is effected.

ptodnetng isocyanqfes flu the g«« phase). describes a ípmehing rxm.iti wMqh cooled rapidly byinjection ot* a quenching liquid. ïn &amp;H qtieaeSlög-jspftie» fee reaction mlxturei which consists substantially ofHte jso«fasnste^,.jphô%ôas *f$ llydrqjSpeas chloride, is mixed intensively wish the injected iiquid. Mixing is. carried oat in such a warmer thai the femneratote of the reaction mi stare, starting from TOO to a/OWf, ts feworeo to 100 to '2U0VL and die ssocsamne comprised in the reaction mixture ss trunsfetrcd wholly or partially into the injected hquio droplets ny condensation; white the phosgene and the hydrogen chloride regain substantially who it y tn täte gas pnu»s. Solvents, ssoey&amp;nate mixtures and soiventrisocyanaie mixtum arc mentioned as possible quenching liquids. Mere ion is made ot the injection of a qecnchiec iiquid to coni the reaction mixture and selective!;. dissolve the diisneyanate that has formed itt the solvent. a ftrst separation into tt liquid phase and gas phase comprising predominantiy phosgene and hydrogen chloride as constituents being carried out. The two phases are subsequenti> fed to a corresponding working, up. Possible ways of optimising this method step are not discussed; Wíi) 2i)l i./öi33d32 ä! also discloses ë method $jtr Tâpi<% Opqlittg. $$$. ;p£«dus: Tsa«#ö» fe&amp;te hy Ispctitig: a questehtng liquid im« the gas: mixture ffewlng eodfitiuously Sóm iMimmïm- 'mm--ím&amp; te. downstream penohing mm.

The inicction of quettéhíug liquid by means of at feast twwxpray rnetfeies* which: are arrangediaf fee entry to thepenehing .zoaogis disclosed: irt EP 1 403 248 ST. Stutabie tpenchittg ftqulds here are:organic solvents ur a mixture ofdifferent orgamc solvents which do nofmet with ihe idilsoeyatiateitltatihiss farmed. A solutlmt of tire tfüsocysîvafe thist has tereit hr .¾ suif able organic ;sol verst «an also be; used, which reduces the amount of solvent used. The diameter of the quenching: aorte can fee: larger m sttraiier than the diatneter ofethe reaction same, Queuehmg of the reach on gases emt take place in one stage or irt a plareliiy of stages.

This system iS::qplimM«t»dl^;:iS':tef^ring of ÉP 1 MS 87511 Id thag in order to ferminme the reaction, the reacfitm tdixmm Is guided from the reaetiot? .«taste: 'Sketch Into which liquids are injected in two zones, so that direct cooiirsg in the cooling stretch takes place in one stage (i.e. yielding ottiy one condensation mixture) in two or more cooling zones connected one behind the other. At lests! in the second mm* a cooling iiquid is used feat comprises the preparedisocyanate in eonslhmifele amounts fsse patent claim I, last paragraph^ jfee dfisecyanate produced Is feerefey obtained in a common condensation: mixfefe. litis: mixture is preferably coliected in a liquid collecting vessed arranged bsnsath the ctwHng stretch. This condensation mixture can be discharged in order to separate off the isocyanate that has been j^odneed or, preferably aifer cooling has taken place, can partially be fed back to one or -note cooling zones of the cooling stretch. A possibic disadvantage of this use of the liquid crude product mixture from the gas-phase phosgénation is the occurrence of contamination of the described cooler before entry into tin; qncnd'.cr. Causes of this can be undesirable secondary products or polymer compounds from the pbospuation reaction, it addition to the condensation mixture in fee collecting vessel, there Is obtained downsfeeast of the crmlmg stretch, a gas stream comprising at least hydrogeo chloride, phosgene, optionally solvent, and the iMevanatc that has: bean producab. T ins gas stream Is removed from the colledtog vessel and fed to a washhtgmoifeon, where if is largely Iked of its isocyanate components. This washing preferably fakes place eonnter-cttrrentiy -with solvent. The wash phase so ofetafeed, consisting: of dslsoeyanate attd predominantly sdlvestt, is used: in a preferred emlmdimeur as ihe quenching liquid of the first cooling sone of the cooling: stretch. The residual gas iront the washing column

consists. substantially of phosgene, hydrogen chloride «nd solvent These vapour* lesve the column to the lops whereby. :1¾..:¾ prefötyed ehtfrodkttsitt, b? pestis of pntist| pnilensstidb., :lvó sólpspí: eppïppsîP: ss largely reteloed öy wav of ;wo cnodeixsers having dl-To ent coolant tefttpenoxotis aoc h ted book îo the column a» pnttiîu condensate. The rcsidiud g&amp;s obtained thereafter which eoosùa.x subsianthuly <0 phosgene. hyurogeo ch bride: and sc-heot residues, is than treated íunher in a npqoef knoon por so, as described, id? example, in EF I S4P 76? B :. the use oi ΙίίΡϊχοο venueis- wunciutte Pysid o«fe\m^ is ftkewne mentioned m Lb ! O' 8b AS lldfçrsnee is also îsqde tfteretiy to the two a|r^y«s?cldl5g:|ft|fild ofim washing hqosd from the gas wsshpg ox 1¾¾ vapoarsigpvktg the eondeosate collecting vessel Pier be quencher. EP 2 I Pô 455 Ai also refers to a plurality of cooling acmes in Use quenching stage. lyfettttost is. made here lor the first time of the ithegnuod çs>mhix«ttion of the cooling. -meet of a plurality oi tcacosrs Mth a qaencluns tinge. WO 2ÖtOdb?6ó6 .AS makes reterettcr ;« a possible problem of dm qnenehitsg variants known hitherto It at least &amp; portson cd the xpenelutig liquid A removed from the collecting vessel alter the qnenenef. inat ts 1« say flic Has i id orotic product mi cinre, mere is the possibility shat scdxds mas be pieseot, widen con block ibe quenching növelés. Vxwous tcciinkpies, such as, tot e>:nnq>ie, centrifugation, removal by d>si illat ion s<t the liquid coinpnnesk p?o\ t*wd bt the queue hug. or filtrtniots, are described, lo order to adjust the tetnpennnt« cd tU 's-,« o tots ow \ttoan v ke ttxve o'>vd v neont „\ be s'oSv >>t heated, by means til a heal exchanger, Tins specification discloses Ip ti:, I d to b p. Is. second paragraph) vámos sedfretb i?r tM qucixching medium: a part-3«f«am 15 htattcheel írom the phase sepaeatot 9 provided dovstwlrcnto or tue tpOPeher ? (which necessarily also comprises isocyanate iiqnefed in the: quencher), fresh solvent 19, a ponton of lac liquid phase 13 obtainud in rise phase separator. and a part-stream oi the two-phase product stream /, Ina speotfioatkin docs not disclose an embodiment in which the quenching medium ss obiamed from the gas phase II obtained ht the phase separator If and recycling of iscicyanate .iiqaefred m the quencher' ht diapsnsed with completely. 1st WO 20id 1 - '«nig Kg s «vc;ne w of dw oocftehef n disclosed, Is sxtu" io owe«'! wf wquun raci lots? of the sv.knost g&amp;s sa or docvtv«;ctm of the quenching stagu* the onrnrhmg U\W.;'s .uses ;.v <\p< n % ' s Ia » \ iji\ *'u 't ge«c N 'trp\>v vv\Hn«' of if e watg in mo qoetichiog ixegoto t,ikos place, dite enflro resedcsn mixture is iherefey included. I hete are psciposed as quenching, liquids solvents at tveri ptvxtiires with iscscvanate «r crude, mialura front the phosgettutioa reaetiottj opnotta::y afres part lew ictiiovus IIP 2 4h3 275 ΛI discloses a prove;;;; verbot for isocyanate eoncsmraffrnts of greatet ;bap ?o by mass in Ilse liquid bobom product leaving the quenching aune. 1 he stream leaving the qaeatehutg ao.ae m gas form jS passed directly mi« a i&amp;cket-cuoicd umdetwett without passing tbrongh a washing, eolumn. The gas streunt that, tesnaisss is fed direuh to phosgene recovery. Despite the high; temperature and high K-eymcne conceittration itt the l>quid bottofo product of the qiteacltiog, .eoae, ncs ndormalino ts givvo rcgatxnng revinoai ;sncyanetc eonw'ote at the gss sfreatti that remains. The eondensms streant ts cotnh.ated wipt: the epttdcnaatc ot the sapoto atxesan « nirt f h\ ! 'h'Xoi . - o ), ’ ot d be ' o fs >d \ he th-. 'ovttclt t,x o to .nta o hd b s.K '' gteral < t 1 tSv-

The specifications hitherto were concerned, a; the quettüter reg am öl the gas'phese pnosgenaticn or-diamines, sPhstantudiy nch >p«otnvng «he actual curneho sxa;e«n.. \®a«> '«« -« cw'vpr„«ts the •teriphcral systems associated wllit the qtiettcher were disregarded. Inc esccy·;io'.r· are, lot ex<'.snp:v\ tneniiöoed above, the use of condensation mistere iroxn che liquid Collecting vessel ôi the psnchsr et of lits fiwémm* ôf Ée: espoirs siïeuïti % flash yagbdsröön:..of the condensation: pMm, or the «se m the quenching liquid of the washing liquid from the gas waslursg of the vapours leaving the condexisam colieetxng vessel; ate iie qeeeshe?. By using ÏU )|^#wtlecfe£ vessel ,of the qsisneher, Ihq amoust el solvers; required fur cooling -he meet ion ω? « seduced h> replacing externally sealed quenching Ijqeti te diisocyaxsste produced in the gas-phase pte|#«ti# pi-pIvurttatodyMinprisedmite^ddett^t^, Likewise, the total amount of quenching liquid can bo reduced by using some of the washing; liquid torn th®m washing of the vapours leaving the eoodensate collecting vessel alter the quencher, Boil) proecdorns lead to a reduction of she solves:) circulating In the process as a whole and accordingly. when used: successfully, contribute towards reducing thmenergy consumption astdesm optimally conmibuse towards reducing costs in terms of apparatus. A typical process of the prior art wit bo explained by way of example hy means of She first figure (Fig. 1):

The gaseous erode product (MIT: consisting pedbmmtmdy of ifeecyanafe* hyÄgen chloride abb phosgene used 1st a snpersiöichissneirie^ snmout. its cooled quickly m the quencher (Ai I): hf isqeetidU of queuehiog iquilpOT and 116) kt order to avoid astdeslrabie subsequent reactions. The stream ((82): that: leaves dm qsseneher is the Ikpud slate and composes especially isocyanate and quenching liquid is passed for (he smaller patt: to product poriieatioo sätd fe the: larger part: rot the quench cooler (Wit) to shd quencher as )1:Ι^μΐα.. :SH«íi*ü:::t©--:itíí@i=ï«r^e bauuiatlsg strean);, uprnnp (Pl 1) of an appropriately hugbsM foustilsc Installed, nodi thermal stress of the pmduct by repeated eonitmtiog: with the hot ps stremn::tent: Hid: reaction timst: he tp&amp;sn hxto aiïcômd. which leads tolssses of yield and an increased outlay in tenus of worlhlg tsp> Solids and high boilers formed io or introdneed toto the reaction: or quenching rone pass with the liquid: qneodh prod«# Mb the quexsclr cooler (Wl I) ami the quenching nossdes and: can oauae eontummalibn them 2)¾ substtmee sneâî« flöh) that leaves the quencher in gas form and comprises especMly vaporised quemdhng liquid, hydrogen chloride nod phoapne is passed to the washing column (Aî2h ht order to retnbvh residual contents of isocyanate iront the vapour stream as contpietefy es possible, The higher the conicnf 6Í isocyanates iu dte anbstançe stream (106) that is supplied, the greaser the washing liquid streaos isolveni) passed to tile top: of the washing column, and the greater the nsmhee.Äups^tsr'a^sa^ulo^iforMUdydxrettmBott, The washing liquid stream is compoaed of ino eondensate i Î13) of the condenser· (AVIS) and additional solvcxn Π 10), which may comprise low boilers such as phosgene hot is virtually isocyaxsme-hce. The vutually Isocyanate-free vapour stream (114) comprises especially phosgene and hydrogen chloride. The liquid bottom run-off (115) comprises especially solvent and is advantageously led ;o the quencher as quenching liquid.

The temperature of the substance streams at the outlet of the quenching siep must he adjusted while halaneinf opntmry aims, inter din. on the one hand, between IPW^emsi'itroÄdl: wmssl bwMlmWmä. isocyanate content m the vapour stream to he purified and recycled (im tmpmtlme is positive) msd, on the other hand, iow^ carhumic acid chloride ibrnmtionqnddow energy requlfststent:In the product scorknsg-up:thigh u-mpemuie is posun'e}. The temperatures of the substancesttestms at the outlet: of the quenchiiig Ashe is determined, with a given gas stream ftppyheireag'döö'igöne, %itgtamö8ßi* te«tpet»0«OV.8nd' emwposidon ofthe quenching liquid streams.

On the baste of this prior art, there was δ need id? :¾ f-uthei optimisation of the quenching ·:>Γ a gaseous lifocyhnsie crude product. lin pardonisc, the process sections öf (a) transfer o$$6 liquid ettssin ittqäuctghi^iqis® ttom the quencho into the further working-up stages, φ* treatment of the gas phage (vapours) obtainedIp; tltn qttencher, including gas tvásMug* ám! κ) supply of the queachiog stage against the background of low oppsting sud apparatus costa with bip availability aslsimpte, reliable controllability were so bé Cpinitesä bitte

Taking account of this need, the; posera invention provides a process for separating an isocyanate prepared by reaction pf a primary amine- β an excess of phosgene in the gas phase ter the gaseous crude product obtained in the reaction, wherein (-:} tlegasuu , t V í pr<x.i it s,'dn -, uw w-ί eu > woes i i Kdr v c lionn <ii unreacted phosgene, is converted by contacting with, preferably by injection ot, at least one quenching nquie into a liquid phase (.:.02) comprising a- least quenching honid and isocyanate and into a gas phase (206) comprising at least hydrogen chloride and phosgene iso-called '‘quenching" of the gaseous erssbc product), (11) the gus phase , Mny obtained it- sU " pi is p -r tlh o. ich nst d. pit); #e condensate (208) obtained in step (ii) is used as the quenching liqtiM in stop (i), (iv): the portions (207) of the gas pha*e <2061 that wem oof condensed: in step (ii) are at least :priislly liquefied ίο obtain a liquid phase i 2 i s); ív) the liquid phase (215) obtained in step (iv) is likewise used as the queuchiue liquid m step (ii. and ; vi.) the iíqttúi phase v )0-) s'otnund n . p n't 's " 'rkcv. up ο Λ * j\ n “»nw-iu-f. without prov.tousi.y being

Mbdas quenching Honid, within the context of the present invention, the word V’ ih connection with coantable items is to be un ion KH«d .is besng u numerái only when this is stated expressly (c g by the expression "c.roeny one"), It, lot example. va condenser" is mentioned in the following, the word “a” is to be intorpreted tnerciy as an indefinite .unde and not as a numeral; at cordate this alun includes an embodiment in wirich two or more condensers arc connected ist scries.

Ibelroitatiö» "without previously being ».serf as quewking liquid* m step (vi) of the process aceord% to the invention moans that isocyanate liquefied in step (i) is not a constituent of the quenching liquides) used in step Ο), that: Is to say, unlike in the prior art, there is -no ptÂb:?eoypUng-ôf:-Éjë:jiipéâodr isocyanate nito the "quenching" of the gaseous crude product <201i).

Etubtxiimenis o? the process according to the invention are described in greater detail below. Different embodiments can fee combined with one another as desired, unless the comrary is .clearly apparent to the person -skilled hi thcart from the context. Reference numerals with à "2” as the rind digit refer to the socotid r|guro f Ftp 2 ), in which a prefen ed fortes nfthe process according to the invention is shown schematically,:

The reaction of o primary amine with an cxccps of phosgene in Üíé gas phase itt orderte oblate the gaseous crude product (201} comprising the corresponding Isocyanate can in principle be carried out according to stny process of gas-phase phosgénation known bom the- prim' art. Examples of suitable gas-phase phosgénation processes are described in £P 0 570 799 Al, BP i 55§-258AI> EP I 526 129 A! and DE 10-1 61 384 Ai, as sveil ss in particular for aliphatic isocyanates ln EP 0 289 840 8·! and EP i 754 698 Bl,

Suitable prinmrv mttnm are in particular the isomers of tofoyicnediamlOe (TDA herettibefosy); the Isomers of diphenylmethasedlamine (MDA hereinbelow), i .ödiexmnetbyienediataine (H.DA hereinbelowj, the isoniidirs --öl:-hö)iihom»tókm|;jíto flfe&amp;A herembeiowj und the t$m«ws dtamtnódtcyelöhexyh?>etóíane (Híd-MPA herdmbaloW). l-ÚA irpmieoiariy preferred, me precise imxm compinstmn pesest m hót being important fW the process seconding to Use ínyenttö«. tBA wnicp is prerembry w®á-coraprises from U % bymfm 'é: 82 % by ms;« 2,4-TDA am* tőm B%W « to 22 % ^ιβ’ΜΜ, Used «η the total mass of the 2,4- and 2,6- I'D A isomers. Based «*»«» total ,8t*ss of the TIM, the 2,4- sod 2,b~ llIA ^mm ρΐΦΦΐΫ- mmM: !» total to? mm. m-M Ψά w to 100 % ftp mass, jmtfcuferiy' PoféraMy from 98.Ö % by mass to 1ÖÖ % by mass.

The primary anmte is reacted with phsspne. Both eonlinunas .and batchwiss operation ate possible, phosgénation with continuous opera-ion is preferred. The resets#» preferably Takes pmee at » temperature or iVoto 3<30':'C m hOir'C. preferably from 300*0 to 500c€, and; so absolute pressure of (font ISO tuber to Ï Û bar, preferably from 1.0 bar to 3.11 bar. The mobs· excess offhnsgetW Is preferably from 2(1% lo 400% ot theory.

Step (1) of the process according so fee invention, the rapid cooling and partial ilqqefeetmri (“qisertchihg") of fee gaseous craie priUtOdt (201} of fee flő^fiöa by contacting with, preferably by injection ok a quenching liquid, cap (abb place in any desired apparalM (All) known from the prior art. Suitable tea are sfescfebed, fer sample, k BP 1 4P t4$ At, seu in prtfeuliU the thawings wilt the associated explanations in paragraphs BKH ?] m [081¾. and BF I 83S Pô Ai, see in particular paragraphs fOOiSJ to 10022] ar-d [00:0] to [004¾ but il muta be ensured within the context of the present invention that isocyanate te stream 202 liqtieffed in step ft) is not a cons; irnettt of (he quenching liquid (see step (vs.) of the presen· invention).

In ndditinh to (fee qnendipng liquids ions step pi;} and step tv) (see below tor furiher dotalis), s fresh stream of an organic sete esd afetltionaily P Osod as (he ««#« Squid (Ml shown in Fig, % Preferred solvents are chlorinated ammstse hydrocarhoM, such Its, fee example, chintfebeodene, o-dichlpmbeaaene, p-d!ehioroixo5.xene, triehktrobmeeoes, the corresponding eblorotolnenes or chioroxykmes, chloroethylbenaone, tnonochlorndiphenyl, <x~ and P-naphthyl ehloride;, benaoic acid ethyl ester, phthaho acid diafeyl esters, dilsodiefeyi pbthalaie. toluene and xylenes. Particularly pretested solvants arc cblorolsesaene and the Isnmers of dichlombeoaeoe, with o-dichiorobemone being extraordinarily particularly preferred, This : additional stream of fresh organic solvent preferably has: a temperatnre Of pom 40*C to 15o°C. I koveyep even only pdrilal reeyeiiug of (he liquid phase 202 as qnenehing liquid is excluded according to the Invention (see step (vi)nf the presfeu mmúm% 'This .has the sibet that the quenching liquid(s): used comprise at inosi insignificant amounts of Isocyanate ffeom small amoanis of isocyanate not: liquefied in step fi}, ivaicit lease the qnöi?eiie.r A2Í With the gas stream 206).

In ibis manner there are obtained:!!® step fi) s liquid:phase (2ö2)TOmpnShig st least qhcnchihgliqhid and Isocyanate and a gas phase (206) comprising at least hydrogen ddoride Md phosgene.

Step pi) of the process according to the invention, the partial condensation Of the gas phase (206) obtained In step fi), can be carried out in may desired condenser (W23) known froth (he prior art. The condenser (W.23) can be in nsuiti-stag« fönn, tor esampic in order in ose varions coolhtg media and/or in Order to obtain &amp; plurality of process condcttsate igtabties, whiclt eat; opionaliy be fed back in at different points in 0w process. The condenser (1(23 ) is preferably in (be form of an ihdirevi cooier with trlokiing; ÜqÄ A pssibfe fetM la, fer cuainple, a trieMe-rhim condenser in which a portion of the condensate *s fOii back to the same condenser as trickling liquid, As well as comprising hydrogert chloride: and phosgene, the gss: phase f206j genofally Ä eomprterpätip* amömís·«« ipcpmtte and animehmg liqxqfo because the separation thereof from phosgene and hydmgeo chloride in step ft); geuendlv does not take place completely. In the condenser used tu Step ( h>, Ük-majority of the fmnohiug bquki thai remained ln the gas phase <2Ö§} and of foe isoeytmsteiscootlemed. Tins >* Äeted by pooling the gagpfonte CÄ% which 1 prelerahiy; passed into the condenser wlitl s itnxtpemtufs: Of tom 120*€ m 250°C, to a temperature of preferably Írom 4Öfo: to iPt^Cpilap pfis p^fte&amp;îy «sod to obtain: Stisamvprefontbly low-pressure steam Mê ban

Tfe condensate (20¾} obtained ootnpmes especially solvent (from the quenching iiqul$|-aad igtiterefbm particularly:· suitable for recycling «Sr quenching hquid (209). Because it is the coixlens&amp;fe· font a sitoarfi: in: vsqotir forth, the proportion oHtigh boilers and tire risk of solids contents is very much tower than in tits liquid crude product mixture (202). The tendency tor cooiandoation in the heat excltaxtger (W23), pump (P2s>, the quenching noxzies tor stream (2Ö9) andassociated piping is tous substatxdally lower flmua possible; tendency tor cootamimhiem in she comparable plant pans earning liquid crxfde product mixture in the prior art (pomp Pis, heat exchanger Wl I» qpendung noaxies tor stream 105. associated fopittg).

In addtiou to Ute gas phase (206) obtained In step si), :·# a portion (219) of the condensate (2011} obtained in step p) or (fo a solvent stre&amp;m (220) or ¢0) stream la) (219) and streune (h; (220) cast aisé be passed into the condenser (W23). The condensation of the vapours (20b) ts itoersby toetSdated, Mnt haPStof surfaces are we·tod uniformly, adhesions are avötápd pr rinsed off äSÜrffi. absorption: actibu? is: achieveto fhe-Ädenser (W22) is operatod or top process si# pjÄÄdy ftqteö«®n% twfcfc vapour sættti :ïàpëi phase, in order (<s pertuit high vapohr(speeds and small appudtos dtoiensiqas. Swever, it can also be confuted coimter-eusreotiy, in particular in order to achieve more item one theoretical sep&amp;ralor stage, in order to tnmlmise (he proportion ofisocyanate in the antergtog vapour stream (20?).

The condensate (208) obtained to step (iv) is removed horn the: cemdenssq if mqutmd convoyed by means ofa puuip |b23), and used id stop fii) amibe quenching liquid (2159) to toe quenching stage (stopfi)), Whit a sultafell^a^hÄ.^tt^Ctellqtiid mfc&amp;iï Is ensured), thepqmpesn be omitted; If required, foestrestu: (2(58) can be cooled further by means of an additional coolxog medium before it is used as quenching liquid (2(59), fixe quenching dquid (209) is brought into contact with, pre&amp;iss&amp;ly;' mjecisd :M%: -&amp;». .gpestös- crude prndtmt'ati®^:(20V)-f^r#iy::dt a temperatxsre of from 3(PC to i?0°C. The use of the condensate (208) as the quenching liquid replaces the quenching liquid flOSfl'O® Ibe prior art. In other words, It is not necessary uftM: process aecoahng to tire invention to use costsiderabls p urilofts of dm crude product Hquefied in the quenching rone (A3!) as toe quenching liquid. The sssomtefodssisdvantages of foe prior aíf wbieb;bsye:beéa described above, are therefore avoided, hi particular*(the: quench cooler xviih a ppteMisl tendency tof contamination, and the associated ctoeidatiag pump (P115 arc unnecessary. By completely dispensing with recycling into the quencher of foe crude product ml store liquefied in the quenching zone sA2h or of the condensai® of the vapour (with a significant isocyanate eontent) formed by tis#:yapqfisati^##fIftMii|rti# product mixture, the tendency to tenu deposit hoiki-ups in pipelines sod It) the quenching rone itself and also product decomposition, are reduced.

Step (ív) oi' the procès* accordingto the invention, tiw al feast psctl&amp;l hquefaerion of the perilous (30?) of the gas phase {2oos shat were cot awakened In step (it), is preferably carried out in a washing eohmm (Λ22) with ai leas! one stfeusator 'stage, at feast one solvent stream being led to tbs washing eohsmn (A22)as washing liquid. Particularly preferably, the gaseous top stream (21?) of the washing cmluinn (A32) is coikfensed Id à condenser (W22h and the condensate t. I.<! so obtained is ted bask into die washing column (A22> as addiinual washing liquid Suitable washing columns K\22) for step uv) are described, for example, m PerïÿsChemical Engineers' Handbook. 7th Edition. Mc«fo tu-Hife ihapier 14. “Gas .Absorption and Gas-Liquid System Design“. Preferred suiveurs for step ftv) are çitlonnafoçi aromatic hydritesrbtms,; such .äs* for example, duorobsnaene, odfehlorobemteae, p-dlehlorobenjfeiääipöi^lorobenzbOöS. 4h» .eötrespoöámg-'hfeÍoífötotertes or etdorosyleness pidoroethnbesaepe, moooebfonxüphenyl, «·· and fe-»8phfeyl. chloride, bewfofe acid ethyl ester, pMialic aeid disikyf estem, dlisôdiethyl phthalate, toluene and xylenes,:pPättleüiarly preferred solvents are èhiorohengsdç: :aíki the iadidhfscpfidiçhlprobenKene, with ofeichlpriibenxene being exfesordinäfdy particularly preferred. life at feast ope solvent stream can consist of fee# solvent, it is, however, also possible to use reeve led : #iygskvOdmprisin|:direams In ôte process, in one embodiment, exactly one solvent stream (different from (213)) is fed to -.he washing column (A22). in a further emhtxhment, a solveffoftfotnp (2ÍÖ) is ;.áboV«:'iä&amp;e separator siago. where a plurality of separator stages are present above (be uppermost separator stage, if a recycled solvent-comprising stream is to be used m the solvent stream (210) instead of Ifesb solvent, if rnnsf be ensure ihat u comprises the isocyanate thai is to fes ss(»4ed off in an «fess--of '10§- based on she total mass of the solvent stream (210),. k order fo avoid the ibrmífeiöö Of decomposition products.

Alternatively to or itr combinai«)« with this erob«dfo:fe«t, a solveni gfeeafo (211 ) -cm be fed id (be washing column (A22) below the sqferafor slap, where a plurality of separator stages ate présent below fee lowermost separator stage. If a recyckfe .solvent-comprising stream Is to be used as the solvent Stream (211) instead of flesh solvent the requirements regarding the maximum ism yanafe: content are less fenol ihan k the ease of stream (210), Owing to the diifect contribution of stream (210) to the s^gwfellpJÉ fpSÉrti»» with the top prodtsef siream, in the vapour state, of the washing- column, which most be largely isocyanateriree. fee-Isoeyanate eomonts that eats be permitted: In stream (210! are mtkfe lower fean in stream (211). Solvent stream (211) <m dikpfe bp· f®':#0 %:#" mass isocyanate, bused cut the total mass of the solvent: stream (211),

The use of the condenser in the process accordktg fo the invention in step (it) has the effect, in contrast to the prim art. Utat the volume stream fed to the washing column (Â22) is comparatively small (namely only frotn 20% to 80% of the corresponding gax stream without step (ii)b eopferises considerably fess isocyanate {tsamely preferably ionil) % by mass to 5 % by mass, pätdetdärly preferably feypr 10 ppm fo 0,5 % by mass, ip each case based on the fotsf mass of stream 206), anti a lower femperattnc (namely preferabiy feom 4b*Cie 170^0). fedte condensation temperature in the condemet Wgl is suitably chosen (e.g. 60*C), wife the aid of W23 fee volonté of the vapour stream to the washing column is redoced by about 55% as compared with the prior art shown in Fig, 1 (207 confected with löd) and: foducedf hy a factor Of about: )00(} fo wm®? i|#äkä0Mfef wocyanale present. ''CmsoqmMM* possÉls- íö vvöík &amp;,ν^δ1«;5$ cotes« uí small dimtfeter tmdwhh s ssasdl osmbor ö|Vs«mrg|ör sjgp;s is step (iv) according to the invention. ïbersoueeu semtgíratoró nod the nshthisted lower mmmt of quenohmgliquid Id iss a tlipswirfe eoïîbeuam of the washing column. Th« smaller apparatus dimensions mentioned above laepase the Oimporpy of dm process, The cooling capacity displaced than the condenser (%22> ot ids Wwisng eohmmfothe condenser <:W23> of nép fii) can be used to obiadist®prsto^ owing to thë higher eottdessailon tempemture level, id KOínpáílsöO mitiidhs priof sei,less washing liquid has to nc used in the massing epumm ($22>;beeaus» the vapour stream (207} fed thereto already comprises less isocyanate, According to the poor art, dm totality of the; washing liquid is oottveyed into the quenching zone via the bottom of the wsxnipg column and too® determines the solvent content of the llqucied crude product mixture removed at the bottom of dm quenenlng: rone, A snmller amount of washing liquid its tie process according; to die invention thus permits a lower so; vent: content in; the liqold cmde ptsdudf terms of working up in step (vs), without the purification action (that is to say the reduction of the isocyasnn.e content of the gas strenm) id' step (vi) being reduced compared with the prior art, As a result of the process according to tie Invention, m Mmmi of circulating soi vent and the required efectrieu; ptmtpingcapacity are rémmé, which is expressed as an energy saving.

Ip addition to the liquid phase (215), a gaseous stream p£4) also toons In step (iv). This; gaseous stream PbPSlpfe sobst&amp;oiiaHy of hydrogen chloride gas, stoichtometiditiiy excess phosgene, htsther gases, such as, for exampfei nitrogen and carbon monoxide, and small amqupts of solvent; This gaseous product stream is preferably· fed to farther working op, where solvent, excess phosgette ood resulting hydrogen chloride gas are generally separated from one another. Solvent and excess phosgene (separately from one another) are preferably fed to the resetlot; again for reasons of economy, the hydrogen chloride eon be fed to vsrtous possible; uses, speis as, fer examplfe an oxychlorhtation of ethylene to ethylene dichksnde or o recycling process. which feeds chlorine bach into the isocyanate process again. Such recycling processes include the cnfalytic oxidation, of to tip Deacon; poems, the electrolysis of gaseons hydrogen chloride, and the electrolysis of an aqaeotts sohition of hydrogen chloride (hydrochloric acid).

The liquid phase f2 IS) obtained in stop (iv) is, if required, conveyed by means of a pump (F22) and IP step (v) likewise used ^Ât^qénsÉàt^"^|Âpl#l» step (I). Whit a suitable ajtpamtns seDnp pee liquid runoff is ensured), the pomp cm; be omitted. If required, the stream (215) can be cooled further by means of so ädd&amp;fÄ:'^öÄg. irtî»· bMÄ'lhk u^)^;,<fp6Ä| ΙίρΜ·$ 1% The queuemog liquid plb) is brought Into contact with, ptPfefabiy rejected ipfo, the gaseous crude produet strssnfpô 1 ) preferably hi a Temperature Of hour 3ÖW1 to ibd^C. Aecordingly, in one etuhodintent, the quenching ilduliot step tin) and the quenching liquid of step (v) are, introduced, preferably hpsiod,.'Mb: the gaseous crude product oi the phosgénation (20)) Separately tfom otto; another (209( 210) In step ii). Preferably, the quenching liquid (216) is thereby introduced, ptoferably hpeted, into the gaseous erode product stream |201); above is«; qeenehSog liquid horn step: (ill) (Idd). Tins is because, owing tu rise feet that, in the process acembfog to die invention, a largo part of the isocyanate comprised in the vapours (206) Is afeidy sepanned ofe; ;in; the oopdepser <W21)y thp feocygnsie content of fhe liquid phase (215) obtained in step (iv), which is used; as quenching liquid (211), tails, as described above. Because isocyanate in the qncnchmg liquid, in particular at the high temperatures in the 'Uff^aöSÍ part of the q«e«chmg ?onv. teals fe Increased formation of u{Kb$kabb-|^C««dá||f·

MyfefetgOfefe u> feed sbrçam (216) into du* qaemfemg »«* separately am), relativemdt« iss« Sb««, upstream oifeeahffSP}. Agcomjsared wife fee ρτ»οτ an (feg I). the reduced isocyauate coûtent of(2ii;MF if he process ôôio^Égï b the SKvesfipîU as compared wife (1)6). pcrmhu a« mlvanfagyous low««· (mtMÎm of seeondasy products, However, jfeis also possible in principle loos show» la f lg, 2) to tmmbme streams (!()#)· q«si$15band bring them inf:» contact with, preferably inject there into, she gaseous erode produd: stream (20;) together as a quenching liquid stream. This Is preferably elfeded by passing the eoi?de«safe stream (208) into fee bottom of :fef:^hfeg^ól««:#2^ iu which fee liquid phase (215} is located. A combined quenbhmg liquid stream is then removed from the washing column and sssed in step (i). The pump (F23i can be omitted so this embodiment.

Step (vi) offne process according ίο the invention, the working up of the liquid phase (202) obtained In step^emiibe..caÂà.omli5?:-»8ÿ process biw fi-out the prierait PsdM reeve ling of the stream (2Ö2) tothe questeblng 2one (A2() ikoot: necessary in the process ácsoméig:to the invention;;: fee ciretdafihg pump (PH) and the quench cooler (Wldfe which Is potentially susceptible to eontaminatmn, cun accordingly ibe: orellfed. Because thé product passes through fee- quencher only once, it Is subjected to thermal stress fer a shoberfime, which reduces the fereustfen of secondary products. Because the quencher bottom in Fig. 1 si fee same time: thbfptßstp·: feèbi»' ihr fee large chcniutlngpustptifFil), the hold-up of fee : quencher bottom in the process according::iu Fig. 2i without a chetfeifesg pump or with a stfesfenbsliy ssnnlfet:product discharge pump-can he made smaller, which ferfeer reduces the dwell time of the quencher bottom preduct (2(52) and: accordingly the fbrmaboit of secondary preducts. The liqtud crude product mixture stream :(202) comprise»: sifestantialiy Isoeyanate, sol vent (from the queachmg liquid) and a small amount of unreaefed phosgene. This •liquid crude product mixture stream is then fed to working up by distiihdion, generally la a plurality of stages, whereby dissolved jfeosgens and fee solvent are separated oif This working np by distillation of the crude isocyanate can be carried out by generally know« methods. Examples are described m EF-A-T 413 571. US 2093(8230475 M (TOly andiEF 0288 MO Bi («131, IDEI snd:Hi2ddM},

The process according to fee invention additionally also has the following advantages over fee prior art:

Unl ike the prior art (Fig. 1), an adduiosai degree of freedom is obtained id the process according fe the invention (Fig, 2): As mentioned above; In fee process according to the prior art it is necessary when choosing the tetrqseraiuie of the substance streams at the outlet of fee quenching none to htdaoce, on fee one hand, low thermal product stress and low solvent land isocyanate content in fee vapour stream to he purified and recycled (few temgmeHm· ispaeMm) and, on fee other hand, low carbamic acid chloride formation and low energy requirement m working up of the product (High iempermirs fe piwfeve), fit fee process according to the invention, on the other hand, the quencher bottom temperature and the washing column inlet temperature can he chosen independently of one another. Tbs carhsmie add ebferide formation is th us reduced and energy Is saved In the: working up of few product (preheating of the distillation column feed), while at: the same: time: thefeermal stress on the product Is reduced Id forms of time because It: passes thtmigb (he queneifetg Koste: only once, and the hlgber solventland isoeyanme content in feevaponrstreamdoesmA lead fe tt larger, more:emttplex washfeg cohmsre

At fee same quencher bottom temperehtrfe the reduced condensation .oapdiy of the condenses (W22; gccordih| to F)g, 2 is "only” Misplaced" is|m fhq :iiew: cno:deuset (W23X however, owing to the higher process- Ä le th ne rature level in (W2Ï), the apparatus ccm be coestrucwd smaller and «a» better be used for a heel-intogfáive connection of process streams. Owing to the higher proecss-mde temperalore level the cooling capacity can also partndi> be used for low-pressure steam generation. The same h: true for the quencher cooler: The cooling capacity -of the quencher -cooler which »s onntteu. is onty" uisp*aced into tnc new oottdonser <W23), but, became of the higher heat transfer owing to process-side condensation and the higher tompersrure change in (W23) on the process side, the apparatus can likewise he made smaller ^ti can better be sited tor a heai-totsgradve eottoeefloitof process streatos,

Intoe process igdctirdlhg id Fig, i , toe amohtii oi wsshtogdiqotd td 18) determmes1 the solvent content ot hi® Hqthd erttoe: posdnet tRiXtare in the eneneher bottoni (181:). A lower soivsth:con«enhsitonreduces the outlay required dor wotting up the product and is: dereidre adsatniagenns ht terms of energy and apparatus. However, the amotmi of solvent mpfed to »hieve stifőeiest isocyanate washing in the washing column (AS) downwardly limits the desirable mduetism of the solvent content I« the iiqpnl: ptodncl tslxtore (103). Tins lismtathm takes efreet in particular at low solvent contents m the liquid product mixture (102). In the process aecordtog to the invention according to Fig, 2, iar lower solvent contents in the liquid crude product mixture are poss teguse the isocyanate content at the ink to the washing column is thready substantlaliy : lower totd; less wsshfnh iiOhld is therefore required for retaining the isocyanate than according to the priortut (Fig. 1). totoder to keep ite qitoneher bottom tginperstuto dotwatol according to too prior art (Fig^il, the miet: temperature of toe liquid etude prOdttet Intxture led back ifdto the quencher hototos to the quencher is cottvemionaiiy actively couttohed, tihdesiotbie vártafions th the quencher boltost temperature occur in particular in the case of load changes of toe reaction aorte, In the proccdnrc according to ton invention according to Fig. 2, toe vapour steam : .removed from the quencher in vapour form increases as the quencher bottom tetoperature increases aeeosding to the vapeutoliquld equilibrium, Aecortongiy; when toe condensation temperature in (W23) is unchanged, there is ito ttutomatic inbrease in the amourtt of condensate discharged in liquid term, which is fed hack as quenching liquid and counteracts toe increase in toe quencher bottom: fetopsratsné Witoduf active control. Accordingly, toe process according to the invention exhibits an

IM«M ïhe processes according to Fig, 1 (comparison · - Example l) and Fig. 2 (according to the invention -Example 2) were reproduced by means of process simulation, la both cases, si She entry of the reaction stone (not shown In the figures) upstream of (AI i) or (Â21), the only outiét stream of which is the gaseous crude product stream (MS! -or <2(31), Shore was used a gaseous st&amp;Mof material: mixture havmg toe following composition of the major constituents (subordinate amounts of secondary products have been disregarded):

Tie volume of toe vapour siremw to thw^ Mf« smaller tn lxasnplc j than in

Example I f Mh), and the washing column, In ilsampie 2 (Atoto could bo copfigured: with a 3811¾ssmller diameter than in Example I (All),