CA1050730A - Process for the preparation of nitric acid - Google Patents
Process for the preparation of nitric acidInfo
- Publication number
- CA1050730A CA1050730A CA223,744A CA223744A CA1050730A CA 1050730 A CA1050730 A CA 1050730A CA 223744 A CA223744 A CA 223744A CA 1050730 A CA1050730 A CA 1050730A
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- Canada
- Prior art keywords
- stream
- zone
- nitric acid
- stripper
- reactor
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
- C01B21/24—Nitric oxide (NO)
- C01B21/26—Preparation by catalytic or non-catalytic oxidation of ammonia
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Treating Waste Gases (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
ABSTRACT OF THE INVENTION
A process for the preparation of nitric acid from nitrogen oxides, oxygen and water utilizes utilizes an aqueous stripping liquid having a nitric acid content within a specified range which passes through a reaction. By controlling the process parameters within specified ranges three zones are provided within the reaction zone.
A process for the preparation of nitric acid from nitrogen oxides, oxygen and water utilizes utilizes an aqueous stripping liquid having a nitric acid content within a specified range which passes through a reaction. By controlling the process parameters within specified ranges three zones are provided within the reaction zone.
Description
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_Cl;CI~OIJNI) Ol~' Tlll~ .N'I`ION
Tllis invcnt;oll relatc.s to a process for the prcpar.ltion of nitrie aci(l and, more particularly to an atmospllcric prcssllrc process for the conversion of nitrogell oxides to nitric aeid in a relatively small reaCtiOIl ~.one as eompared to those employed in existing atmospheric pressule processes .
Most commercially available nitric acid is produeed by the first step of oxidizing ammonia to form nitrogen oxides, followed by absorption of the nitrogen oxides into water to form nitric acid. In the first step, the ammonia is initially converted to nitric oxide by oxidizing the ammonia in the presence of excess oxygen over a suitable catalyst .such as a platinum gau7e catalyst. The ammonia oxidation is exothermic, with water being a by-produet. In balanced form, the equation for this reaction is:
~ ri3 -~ 1 . 2 J O2 - NO . 1 . 5H2 0 The nitric oxide formed in reaction (l)is then oxidized to form nitrogen dioxide.
'I'he reaetion is relatively slow and homogeneous and proceeds according to the equation:
_Cl;CI~OIJNI) Ol~' Tlll~ .N'I`ION
Tllis invcnt;oll relatc.s to a process for the prcpar.ltion of nitrie aci(l and, more particularly to an atmospllcric prcssllrc process for the conversion of nitrogell oxides to nitric aeid in a relatively small reaCtiOIl ~.one as eompared to those employed in existing atmospheric pressule processes .
Most commercially available nitric acid is produeed by the first step of oxidizing ammonia to form nitrogen oxides, followed by absorption of the nitrogen oxides into water to form nitric acid. In the first step, the ammonia is initially converted to nitric oxide by oxidizing the ammonia in the presence of excess oxygen over a suitable catalyst .such as a platinum gau7e catalyst. The ammonia oxidation is exothermic, with water being a by-produet. In balanced form, the equation for this reaction is:
~ ri3 -~ 1 . 2 J O2 - NO . 1 . 5H2 0 The nitric oxide formed in reaction (l)is then oxidized to form nitrogen dioxide.
'I'he reaetion is relatively slow and homogeneous and proceeds according to the equation:
(2) 2~0(g) + 2(g) = 2N2 Below 150C, the equilibrium constant strongly favors the formation of 20 nitrogen dioxide (and its dimer, nitrogen tetroxide) so that almost all nitric oxide v/ill combine with any oxygen present to form nitrogen dioxide (and its dimer nitrogen tetroxide).
In the latter step, nitrogen dioxide (or its dimer nitrogen tetro~cide) is abfiorl)etl in water to produce the nitric acid. Thc cquation for this rc~ction is:
In the latter step, nitrogen dioxide (or its dimer nitrogen tetro~cide) is abfiorl)etl in water to produce the nitric acid. Thc cquation for this rc~ction is:
(3) 3~,TO2(~ 2o(liq.) = 2 1~N3(aq) ~ NO(g) As can be seen, additional nitric oxide is prodllced in this reaction.
The nitric oxi~le prodnced in this reactioll then combines with any oxyE~en present . .
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to form rlitro~en clioxide tnntl its cl;mer nitrogL~Il tetro:cide) aeeortlill¢
to rc!action (2). 'l'he nitro~,rell dioxide th-l'; formctl absolbs in any water present alld atklition,ll nitric o.~;icle is releasecl. For every three moles of nitrogen dioYide that is converted to nitric acid in reaction (3), one mole of nitric o.Yide is released. As the concentration of nitric oxide gets smaller and ~smaller, reaction (2) goes more and more slowly; and, in fact~
never of itself goes to completion. Irou ever, in any commercial process the last traee~s of nitric oxide should be removed from the exhaust ~ases so that these gases will be within the standards set by the Environmental 10 Pro-tection Agency for pollutants and also to minimize the economic penalty paicl when the nitric oxide, a reaetant, is lost to the atmosphere. Heretofore, removal of the last nitric oxide has been accomplished by the use oE
inereased operation pressures and/or the use of large reae-tor volumes.
The reaetion between nitrie o.~:ide ancl oxygen is a tllird orcler rea~:tion alld its reaction rate wi ll increase as the square of the pressure. The residenee time for a given quantity o~ gas (by weight) in passing through ca reaetor of given volume increases in direct proportion to the pressure. It follow~s that the volume of the oxidation space to accomplish a given degree of oxidation of nitrie oxide would be inverse!y proportional to the eube of the 20 pressure. For a pressure of 8 atm, the reactor volame required would be only 1/512 of that neeessary at atmospheric pressure. Of course, the pressure equipment required is e~pensive to con9truet and maintain.
One proeess utili~ing elevated operating pressures is that developed by DuPont. ~ good summary of this proeess and its development is given in T. H. Chilton, Chem. Enr. Prog. Mon ~rraph ~eries-No~ 3, Vol. 5~, ~m. Inst. Chem. Eng., N.Y. (1960).
In a plant employing the "DuPont Proces.s", air is eompressed to abc>ut between 50 and 125 psig, preheated to about 250C, ancl mi.Yed with . . .
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amn1-)nia v;3por. 1hc ~ ;turc, containing al~out 10~/o ;IllllnOIIi;l by vohlmc, Ilows down throllgll a pack of Ilat gall,~.cs proclucing nitric oxide at an efficiency of about 95% at a tcmperatllrc of abo-lt 900 C. The hot gas leaving the gauzc is cooled by cxchangc with the feed air and in a tail-gas reheater before flowing to a cooler condenser. Wealc acid produced in the condenser is pumped to an intermediate tray of the al~sorption tower wllile the uncondensed process gas Ilows in the bottom. The absorption to~,ver consists of a series of bubble cap trays provided with cooling coils for removing the heat of reaction. As the gas flows up the tower countercurrent 10 to the acid flow, nitrogen dio~ide dissolves in water forming nitric acid and releasing nitric oxide, which is reoxidized in the space between the trays by the excess oxygen present. Steam condensate is added to the top o the tower as the absorbent; dissolved nitrogen oxides are removed from the procillct acid hy contact with sccolldary air in a "bleaching" tower. The tail ~as lcaving the absorption tower is reheated to about 250C by exchange with the process gas and then expanded through a gas engine which provides up to about ~0% of the power required for driving the reciprs~cating air compressors.
Typically such a plant wlll produce 250 tons a day of 100% nitric acid at a volumetric efficiency of about 85 to 90 pou~:~ds of 100% nitric acid per day per 20 cubic foot of reactor.
The alternative to the use of elevated pressure to minimize the amollnt of nitric oxide in the exhaust gases is to use a series of reactors to oxidize the nitric oxide to nitrogen dioxide. In this process, the exhaust gas containing the regenerated nitric oxide is fed into a second reactor where it is contacted with additional oxygen and water to form nitric acid and, of course, additional regenerated nitric o~ide, which is in turn fed into a third rcactor; al)d the process is repeated until the nitric o~;ide level in the exhaust is practically eliminated.
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5~39~ -As can be apprcciatccl cach of these tcchlli(lues has its drawbaclis. Thc use Or large rcactor machincs rcquires not only considerable capital investment but also increases thc retention time of gns in the reactor. Increasing the operating prcssure also increases the gas retention time and furtller necessitates the use Or pressure eq~lipment wllich is co~tly to install and maintain.
It is therefore an object of this invention to provide a process foP the preparation of nitric acide from nitrogen o~icles which virtually eliminates regenerated nitrogen o~;ides in the process exhaust 10 gases.
Another object of this invention provides a process of the type described herein which can be operated at essentially atmospheric pressure with relatively srnall reactor volumes.
It is yet another object Or thi.s invcnL;on to provide such a process that operates in a single gas-liquid contacting reaction zone.
Still another object of this invention lies in the provision of a process as described herein which is capable of achieving yields of 85% and greater of 100% nitric acid.
A further object of this invention is to provide such a process 20 characterized by its ability to effectively react dilue concentrations of nitrogen oxides.
~ et another object provides an integral process as described hercin for efriciently and economically converting ammonia to nitric acid.
BRIEF VESCRIPTION OF TIIE Dl~l~WINGS
-Other objccts and advantagcs of the process will become apparent in thc following dcscription and acCompanyin~J drawings in which:
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~5C1 73[1 I~lIGIJI~E 1 clepicts a cross sectional side vicw of onc embodiment for carryillg out tllc hcre;ll descril~ed inYelltion;
FIG. 2 dcpicts a cross scctional side vicw of a furtller embodimcnt for carryinG out the hCreill described invention;
l~IG. 3 depicts a cross sectional sidc view of an apparatus having ports throu~h which gas samples can be removed for analysis; and FIG. 4 is a graph with thc concentration of nitrogen oxides measured in the gas phase being its ordinate and the reactor volume being its abscissa.
BRIEF DESCRIPTION OF T~IE IN~rENTION
To avoid the problem of the ever decreasing concentration and resulting decrease in the reaction rate of the conversion of regenerated nitric oxide to nitrogen dioxide, the process of the present invention, in general, utili~es an aque~us striljpiil~ liquid having a nitric acid content within a ,, specific range which p~sscs througll a reaction Y.one. P.y appropr;ately mailltaill-ing the tt~mperature of the stripping liquid and by coordinating it with the other process parameters, a stripper zone and a desorbin~ zone are provided which concentrate the nitrogen oxides into a concentration ~one wherein the conversion of nitric oxide to nitrogen dioxide or its dimer is relatively fast. This stripping 20 liquid, serving as a first stream, provides a sufficient liquid level in the reaction zone to at least give a gas seal. A second stream is continuously removed from the desorbing zone and is separated to form a recycle stream and an eventual product strcam.
The overall conversion of nitrogen oxides to nitrogen dioxide or its dimer by means of concentrating the nitro~en oxides is fast and efficient and eliminates thc need for somc of the cquipment associated with the present - commercial processes such as expensive large volume reactors and hi~h prcssurc cquipment. ~urtller, tllc concentration of thc nitrogen oxides in thc rractor also speeds thc convcr~;ion Or thc nitr Ogt?n dioxidc or its dimer ::. . `.: :' .. . . : . .
~(~5~)73a3 nitric acid.
While thc in~ntion is susceptil~le to various modifications and altcrn;ltive forms, a preEcrrcd embotlimellt tht?I eof has been sholvn in the drawings and will bc described in dctail hereinaftcr. In this cml)odiment, a single, vertical towcr serves as the reaction zone and carries out various functions including gas~ id contacting for stripping and the like. It should be understood, however, by those sl;illed in the art that it is not intended to ~ -limit the invention to the particular form disclosed, blit, to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. For example, it should be appreciated that a horizontal-oriented, gas-liquid contact apparatus, as is known, may be employed in Ihe place of the vertical apparatus of the preferred embodiment herein disclosed withollt departing from the scope of thc pres~rt lnvc;;tio;l. L1 addition, while the embo;liment illustrated sets fortll a pI'OCCSS wher~ tlle nitrogen o ;ide reactant is formed as the first step of an integral process by oxidi~.ing ammonia, this advantageous step need not be incorporated. ~ny source of nitrogen oxides may certainly be utilizcd DET~ILED D~SCRIl'TION OF THE DIRAWINGS
Turning now to FIGUR E 1 of the drawings, there is shown an 20 integral process for converting ammonia to nitric acid. To provide the nitrogen oxide reactant source, ammonia is first oxidized to nitrogen oxides as i6 weII l;no~n. Thu9, as is shown, ammonia and a primary source of rnolecular oxygen, such as air, are combined, heated and admixed in a conventional gas mixer 11. A slight excess of molecular oxygen over that which is theoretically required to convert the ammonia to nitrogen oxidcs is employed.
The mixed molccular oxygen-ammonia gas is then reacted to form a mixturc of nitrogcll oYides by passing thc oxy~en-arnmonia mixture . ~ .
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, a convelltiollal b~lrner reactor 12 WhiC~ n~; leen proviclc!d with a conventiol-al hcnted platinum ~auze catalyst 13. 'rhe oxygell-ammonia ~,ras mixture is passed over the heatt!d pl;ltinllm ~auze catalyst to convert the ammonia to nitrogen oxides~ principally nitric oxidc ancl nitrol;fen dioxic3e.
'rO convert the ammonia oxiclation products to nitro6ren dio.~;ide or its dimer, thesc gaseous products are continuously introduced into the concentration ~.one of the reaction zone. Thus, as is shown in FIGU~E 1, the nitrogen o.Yide products exiting from the burner reactor 12 are continuouslyintroduced into a reaction zone comprising reactor 14 at the concentration f ~one 16 via inlet 25. The limits defining the concentration ~cne and the overall gathering or concentrating of the nitrogen oxides into this zone will bedescribed hereinafter as the description proceeds. .In accordance with a preferred embodiment, these products are combined with a supplemental source of oxygen such ac air, and c:hov:n ag secondary 2.ir in FIGURE 1, to insure thal a(leqllate oxy~ten ~ill be prescnt for conversion Or the product~ to nitrogen dioxide or its dimer. The secontlary air is preferably mixed with the products prior to entry into the reactor, as is shown. Reactor 1~ is desirably a conventional vertical and generally cylindrical stripper-reactor.
The temperature of the incoming products gases, with or without 20 the secondary air, is not particularly critical. It has been found suitable to employ temperatures such that the temperature of the gases in the concentration zone are typically below about 300F. This temperature is dependent upon several factors includin~ the temperature of the aqueous nitrie acid in the stripper zone 17, the temperature of the aqueous nitric acid in the desorber zone 15, the amount of nitrogen o~:ides and oxy,~en introduced into the reaetor (since the reactions tl3at convert nitro~,en oxides to nitric acid are exothermic) and the tcmperature of the incoming nitroFen o.;ides-oxygcn mixture. Suitable reslllt~; have becn achicved w~en the telmperatllre of the incomin~ nitro~en oxide-o.~:yF~ l mi.~;tllrc is in the rar~ e of from al.out 100 to abollt 200F.
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In accord.lnc e ~r;th OllC? aisl~ct of the presellt invell~ion, at least a pOltiOll of tl-e conccllttation zOlle is complet~ly devoid of any p.lclcillg or the like. I'his allows oi)timum m;xillg of the ~aSCS ch~rillg conversion to nitrogen clioxicle or its climer. ~rhus, in accordance \vith the preferred embocli-m nt, the incoming ~ases are introdllced into free space l0 via inlet 25.
To provide a carrier for the nitric acid that is ultimatel3~ produced i~ the reaction zone and to allo~Y for the concentrating of the nitrogen oxides into the eoncentration zone, a further and important aspect of this invention provides a stripping liquid ~vhich is continuously introducecl into the reaction 10 zone. Thus, in aecordance with this invention, the stripping liquid, termed herein the first stream, consists of aqueous nitric acid having a nitrie acid content of from aibout 10 to about 40%, preferabl~ about 20 to about 30%.
By suitable maintenance of the temperature of the first stream as i~ pa~;ses througll the reaction zone, and in accordance with a still further and importatlt aspect of the present invention, a stripper zone, a concentration ~one and a desorbing zone are achievecl with the nitrogen oxides being conlinuously directed to the coneentration zone from the stripper and desorbing zones .
To this end, as seen in FIGUR:E: 1, the first stream is introduced 20 into the stripper zone 17 that is Eormed via inlet 26. The temperature of the first stream in this zone is maintained in the range of from about 40 to about 105F. If the temperature of this zone is too high, the nitrogen oxides moving out of the eoneentration zone will move upward in the reaetor and extend past the inlet 26 through which aqueous nitrie acid is introduced into the reactor.
If this oeeurs, some of the nitrogen oxides ~ill not be dissolved by the aqueous nitrie aeid but will instead be lost in the exhaust gases. It has been found that little or no unreacted nitro~en ox-ides are k)st in the exhaast ga:~es if the temperature of the ~as ancl liquicl in the stripper zone are mailltair~d below '~ ! U
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al)ollt 105~F. lt shollld be appreciatcd ~hat the l(~n~th of the stripper %one shoul(l be SUC]l that the gases in tllis %one c;u~ m;lintaitle(l below about 1 05~
Wllile this temperaturc rallge may of course be achieved by introducing the first strcam which is suitably cooled, it has been found dcsirablc to provide a cooling means positioncd in the stripper zone 17.
Any suitable means may be used; alld, as shown, a coollng coil 23 may desil ably serve this purpose ~
To achieve optimum results, it is desirable to introduce the 10 first stream into the stripper zone in such a fashion that optimum gas-liquid contact is provided between the first stream and the gases containing unreacted ritrogen o.~ides which reach the stripper zone. Thus, and to this end, the first stream is introduced in the form of a spray or as small droplets; and optimum ~as-liquid cGntact is aecon~,clislle~d by sicuating in e strlpper zone, a packing or the like providing a relatively large surface arca. ~ny incrt packing providing a relatively large surface area and having a high void content may be utilized, as for example, conventional bubble plates, glass Raschi~ rings, Berl saddles or stainless steel shavings.
Preferably, stainless steel shavings are employed since the highest yields 20 of nitric acid were obtained therewith. In FIGUI~E 1, the packing is designated as 18.
The gases, freed of substantially all of the unreacted nitro~en oxides by contact with the first stream, are allowed to vent to the atmosphere as exhallst gases via outlet 2~ fromlhe stripper zone 17.
In accordance with yet another aspcct of the process of this invention, and as has beenbriefly referred to herein, a desorber zone is formcd which includes a ~as seal for the reaction zone and which serYes to liberate at least a major amount of the dissolvcd ~raseous products including ' . , ' '' :'' : , . ~ ' .. . .
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m~logcll o.~;idcs prior to rcmov~l l`rolll thc reactioll zonc of any nit~ic acid stream. To this etld, the first strcam is hltroducctl into tllc stril)pcr zone at a ratc sufficicllt to allo-v mailltenance of a prcdctermined lcvel of the first stream of liquid in the dcsorber zolle s~lfficicnt to hold the temperature thereof in thc range of to at least about 130 and prefcrably at least about 1~0F. In the preferred form this predetermined liquid level shollld be sufficient to allow dcsorption of ~ascs in the desorber zone. The temperature oE this liquid may be as hi~,h as and can reach its boiling point.
In1his fashion, most or all of the gases such as the unreacted nitrogen oxicles can be directed towards the concentration zone. ~s shown in F`IGURE 1, a desorber zone 15 is provided: and the liquid retained is heated by any con-ventional means, such as by the illustrative heating coil 19.
In accordance with a preferred aspect of the present invention, the desorber zone includes paeking or the like to prevent the estab]ishment of convection currents which might Elllo~v dissolved nitrogen oxides in significantamounts to be removed from the rcaction zone. Thus, packing 18 is provided for this purpose. Any of the conventior~lly known means for preventing eddy currents in Iiquids may be used, such as, for example, perforated plates.
To delineate the interface between the stripper and concentration zones on the one hand, and the concentration and desorber zones on the other, it should be appreciatecl that this is principally defined by the temperature ~radients existing within the reaction zone. Thus, in relation to the interface between the stripper and concentration zones, the concentration zone be~ins in the area where the first stream Or liquid passi ng through the stripper zone has reached a temperature of at least about 110F, preferabiy 120F.
I~e~arding the concentration and desorher zones, the interface is defined as the area whcre the liq-lid is at a temperature of ahout 130F, preferably about 150l?.
l'he conversion of the nitro~en idoYi(le or its dimer forrned to nitric acid is, of course, achi-!ved by re~ction with tht~ ter pres--nt in the -.
~OS~73~) f ~ ~t stream pcassill~ thro~llth tile reaction :~.one as well as by thc ~vater formccl in the reactions occurrin~r in tlle rcactioll zone. Thus, principi?c]ly in tlle conccntration %ont~, thc nitrogell oxidcs and o.~;ygell rea(:t in the prcsencc of the watcr to produce ~aseous reaction products including nitrogtn dio.~;idt- and liquid reaction products, principally nitric acid. Tho nitric acid produced ~vill combine ~ith the first stream o aqueous nitric acid to enrich the nitric acid content thereof while the gaseous reaction products ~rill tend to tlisappear in three distinct ways.
First, any nitrogeb dioxide produced will genterally and subsequently react with the water present in the first stream of aqueous nitric acid to form additional nitric acid. As with the nitric acid in the liquid reaction products, this nitric acid will combine ~vith the first stream of aqueous nitrie acid to enrich the nitric acid content thereof.
S~condly, som~ of tl~e gaseous r~actiorl ~roduc-Ls ~Yill dissolve in, b~lt not react with, the firfit strt am. These dissolvcd and wnreacted gases are prevented from being carried Oltt of the reaction zone by tht~ operation o~ the desorber zone 15 which liberates these gases and Eorces the dissolved and unreacted gaseous reaction products out of the ~iquid as gases and directs them back upward into the concentration zone. To facilitate desorption of the 20 gases in this zone a heating means 19, as for example a steam coil, may be ctnployed to heat the liquid in this zone.
Third, some gaseous reaction products will pass up the reaction zone to the stripper zone and exit as exhaust gast s through outlt t 2~c. The stripper ziol1e functions to absorb these gases and thereby nninimize the amount of un-reacted nitrogen o~iides in the e.Yhaust gases to an acceptable level.
The combined effect of the introduction of the first stream of cold aqueous nitric acid~ the cooling in the stripper zone 17 and the htating of the l;quitl in thc desorbcr zone 15 is to concentrate the nitrogt!n oxides, pnrt~culllrly nitrol~roll dioxi(lt! und nitric o:;idc, and the oxygcrl in and .about the conccJltrlltion %one 16 of tllc rcactor .so that thc nitrogen clioxido can react ... ...
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form nitric acicl ancl thc~ nitric o.~;icle ean rc act to iOr m nitl ogen clio.~;ide.
13y conthlllo~lsly concelltrating the nitrogen oxicles in tllis lashion, it has bc?en found that the problems cliscussecl herein c~used by tlle re-gcncration of nitric o.~;ide in the r eaction of nitrogen c3io~;icle with water to form nitric acid llave been overcome. I`hus, since the nitro~,rell ohides including the rcgeneratecl nitric o~:ide are continuously beillg coneentrated, the o.Yidation of nitric o.~;ide to forrn nitrogen dio.~;ide is not hindered by low eoneentrations. ~Ioreover, sinee the regenerated nitrie oxide is effeetively stripped from the exhaust gases and is 10 eontinuously being recc-ncentrated in the reaction zone, the proeess reaehes a state of dynamie equilibrium in which the nitrie oxide eontinuously reacts with o~ygen to form nitrogen dioxide which i:
turn reaets with water to form nitrie aeid.
This is aecompl~shed without tne use of e1evated operating pre,S~ reS 0.1` Q sucecss;ve series of reactors as is eharaeteristie of present proce.qses.
To obtain product nitrie acid, the seeond stream is removed from tlle liquid of the first stream in the desorber ~one in an amount and at a rate that is eoordinated with that of the first stream being introduced into the 20 stripper zone Eo that the requisite amoun~ of liquid is retained in the desorber zone. This seeond stream may be eonventionally eoneentrated to provide nitrie aeid of the desired eoncentration.
In aeeordanee with a prirne aspeet of the present invention, the seeond stream is separated into a produet stream that may be eoneentrated, if desired, and a reeyele stream, whieh serves as the source for the first stream. As some water is withdrawn with the produet stream, water in an amount and at a rate eq~lal to or greater than the amount and rate of the water withdrawn in the produet stream must be adc3ec3 to this reeyele stream to maintain the liquid level in the reaetion zone as wc ll as to maintain thr nitrie acid eoneentration thereof inUle rangc- o~ from al~ollt 10 to ~10% hy wei~11t.
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1ll this faS]liOIl, lllC COtliiUllO-IS l'C'aCtiOII iS m~itltain~d without thc ne(~d for l(k~ g an~ frcsll clilute aqucous nitric ~cid cxccpt dllring pL'OCC~;S St;l~`t-Up, ~t anothcr aspect of thc prcferrccl cn~bocliment of this invention utilizes the water extractc(l il1 the concclltratin-t of the products stream to servc as thc cliluent for thc nitric acid cnriched recycle stream to minimize thc Elmount of nc~v lvater that m-lst be addcd to maintain the desired nitric acid conccntration in the first stream.
To this end, as is shown in FIGURE 1 a second stream ~0 is withdrawn from the reaction zone via outlet 20 and is directed by pump 22 to valve 41 where the second stream is separated into a product stream ~3 and a recycle stream 42. Yalve 4l directs the recycle stream to the stripper zone 17 to serve as the first stream andlhe product stream to concentrator 44. The water removed from concentrtor 44 is first cooled in a heat e~changer 5Q and then pumped to recycle stream 42 by pump 45, via line ~6. Water frorn an additional source, not shown, may be added to recycle stream 42, via line ~7.
13efore bein~t retllrned to the 5tripper zone 17 of reactor 1~ as the first stream, the recycle stream ~" may be cooled by any conventional cooling means, as for example a heat exchanger, which is sho~vn in FIG. 1 at 48.
Whilc the desorber zone is preferably an integral part of the reactor employed, a desorber unit, separate and spatially removed from reactor 14, may ~Iso be utilized. An embodiment of this type is shown in FIG. 2. Inasmuch as most of the elements remain the same, the identical numerals have been used.
The oper ation of the embodiment illustrated in FIG. 2 is the same as thc FIGU~E 1 embodiment, except for thc function of the desorber unit 15.
In this embodiment, part or all of the function of thc desorber zonc 15 may be carried out by the tower 30. Thus, in one mode of operation, the dcsorber zonc 15 nced not be hcate(l, and the amount of liquid therein nced only be adcqllate to providc a gr~$ scal. In this modc, tllc liberatin~ of thc unrcacted .
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rogen o~;i(les is achicvecl in lhe scparatc to~ver 30.
l~ltcrnatively, if desired, thc dcsonbirltr function may be partially carric(l out in dcsorber ~one 15 and thc rcmaillder accomplished in tower 30. In this modc of operation, as in the operation of tl-e ]?IGUl~E 1 embocliment, the desorber zone 15 is heated and more than the minimum amount of liquid is maintained therein. This mode is particularly desirable wllere the capacity of the desorber zone 15 is inadequate to accomplish complete desorbtion.
I'urning now to FIG. 2, the second stream is removed from reactor 14 via outlet 20 :?nd directed by pump 22 to inlet 32 in tower 30.
Tower 30 may suitably comprise a generally cylindrical, vertical tower having packin& 31, similar to that employed in the stripper zone 1~. l'he aqueous n;trie aeid passes down the tower by force of the gravity and through the paeking 31. The aqueous nitric acid in tha tower is maintained at a temperature of at least about 130Ii`, preferably about 130F by suitable heating means such as the steam coil jacket 37.
As the aqueous nitric acid passes down through the heated tower, any unreacted gases dissolved in the liquid are liberated or desorbed. These libcrated gases mix with the air introduced into the tower through inlet 36 and pass upward through the packed tower~ and out through outlet 33 as sccondary feecl gases. These secondary feed gases are then returned to the reaetor 14 ~or conver sion to nitric acid by means of inlet 3~ in reactor 14.
A stream of aqueous nitric acid, after the unreacted ~ases have been desorbed, is withdrawn from the tower through outlet 35. The withdrawn stream passes to pump 22a and then to valve 41 where it is separated into a produet stream and a reeyele stream. The product stream may be then coneentrated in the manner described above with respect to the FIGURE 1 embodiment.
. .
~S(1~73~
` . In both ~hc l;`lGV~: 1 und FIG. 2 cmbodiments, it is de~ able to witlldraw tll~ prod~ t strealll (c:~p ressecl as 100% nitric aeid) at a rate equ.ll to the amount of nitric acià (also e~;pressed as 100% nitric acid) that is produced in thc process~ Further, to efriciently extract the gaseous reaction proclllcts from the gases rising in the column, the amount of nitric acid recycled to the reactor, and forming the first strea~n, must be controlled. For example, in the reactor shown in the embodiments disclosed, a ratio of 20 to 1 by volume of gases rising in the column to acid (22%
concentration) has been found to strip at least 96% of the gaseous reaction products from the exhaust gases.
As discussed herein, the continuous concentration of the nitrogen oxides contributes to the hi~her reaction rates and yields obtained with the present process. That a concentration of the nitrogen oxides is effected by the prec ent proeess is shown by FIGU~tES 3 an(l 4 and by the data given below in :~i,x.lmplc ~.
The feed gases from the catalytic ammonia oxidation reactor in Example 4 were analyzed and were found to contain 9. 86% NOx. The apparatus u,sed in Example 4 is shown in FIG. 3. Additional air was introduced at the base of the reactor through inlet 49 and admixed with the nitrogen oxides-oxygen feed gas mixture entering the reactor 14 through inlet 25. As shown in ~IG. 3, the reactor was provided with ports through which ~as samples could be withdrawn from the reactor and analyzed, these ports being i(lentified as points, A, B, C and D.
The ~as port at point A was between the inlet 25, through whieh the nitrogen oxides-oxygen feed gas mixture entered the reactor 14, and the liquid lcvel in the desorber zone 15 of the reaetor. The gas port at point B was jl~St below (appro.Y. 2. 5 inehes) the packine 18 in the stripper zone 17 oï
t~le reaetor. 'rhe ~as port at point C was in thepacking 18 in the stripper .. . .: ' ' . , :: . ' ' '' :' . . .,:
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7 ? 17 just below ~approx. 6 inches) thc point at which two ,~ortions of thc reclCtOr were joined. This ~as port was adj;3ccnt to the cooling coil 23 in the stripper ~one 17. Tlle gas port at point V was at a point just above where the two portions cf the reactor we re joined.
- Analysis of the gas sample taken from gas port 13 showed that the concentrations of NOx in the reactor at this point was 9. 92%. As can be calculated by the dilution of the inflowing gas, wherein 86% of gas containing 9. 86% NOX is admixed ~nth 1~% additional air, the admixed gases at this point in the reactor should contain 8. 46% NOx. Actual analysis shows that the admixed ~ases contain 9. ~12% NOX. Thus, it can be seen that the process of the invention concentrates the nitrogen oxides despite the competin~
process of conversion of NOx to HN03.
The process of the present invention herein described may be further illustrated by means of the following examples, which are intcndt?tl to be illustrative of, but not in limitation of, the scope of the invcntion. The yield of nitric acid, in the following examples, was based upon the ammonia fed lnto the amrnonia o.~idation burner, calculating the amount of nitric acid which should be formed in accordance with the following equations:
NH3 + 1. 2502 = NO ~ 1. 5 H20 2N0 ~ 2 = 2N2 3N02 + H20 = 2HN03 -i- NO
This theoretical amount was then compared with the amount of nitric acid achlcllly formed to determine a percentage yield.
l~xample 1 .
Ammonia at a rate of 110. 9 grams per hour and air which had been dried, and with the carbon dio~;ide removed, at a rate of 1323 grams per hour werc fed into a convcntional ~as mixer and then into a catalytic - l G -:.
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re;tctor fittccl with a platinum gau~e catal~ st . The pl ttinum ~au~e cat.llyst was a circular disc 3 h~ches in diameter, and was forme(l from, I)y wei~ht, a 90% platinunl-10% rhoclium wire, having a diameter of 0.003 inches, and had a mesh size of 80 x 80. The platinum gauze catalyst was maintainecl at a temperatllre of about 1630F. The reaction of the ammonia and ox~en from the air was initiatcd by heating a small spot in the platinum wire catalyst with a small electric arc. After initiation, the reaction spread slowly over the rest of the wire gauze. This took bet~Yeen one and two minutes.
The composition of the off-gases from the catalytic burner was measured lû by conventional gas phase chromatography techniques and was found to be as followæ:
Percent by W ~ht_ Oxygen & .Ar~on 1. 00 Nit rogen 81 . 0 0 Ni t r o~en Oxides 17 . 50 [reported as NO2) Nitrous Oxide 0. 61 The reaction products containin~ nitrogen oxides from the catalytic reactor was then admixed with additional air, added at a rate of 272 grams per hour, The temperature of the resultant gas stream was about 20 150F. This gas stream was then fed into a generally cyIindrical ~ ertical countercurrent tower reactor. This reactor was made from stainless steel and was approximately 193 inches in hei~ht. The lower 49 inch portion of this reactor was approximately four inches in diameter with the upper 144 inch portion was appro~imately three inches in diameter. The volume of this reactor was about 1787 cubic inches.
The interior of the tower was provided with a section containing stainless steel shavings as a packin~ that was spaccd ei~hteen inches from thc bottom of thc tower and was supported by means of a stainles.s ~au~e - , ~ . : .
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Y~ 1 extenclecI across the insicle of thc tower. '~`his packecl scction c,~;tcntle(l to thc top Or thc tower. 1`he volume o~ this packcd portion of the counter-current towcr reactor was about 1540 cubic inches. The unpackcd ei~lltccn inch lower section of the tower below the packed section contained liquid to a level of 6 inches. The base of the tower was provided with an outlct that was appro.~imately one half inch in diameter so that the effluent liquid could be withdrawn from the tower. In the wall of the tower in the unpacked lower portion of the tower just below thc packed section was located the inlet through which the ~as stream from the ammonia-o.Yygen burner, with added air, was admitted to the tower.
An inlet approximately one quarter inch in di ameter was located < in the wa ll of the tower about two inches from the top of the tower 'hrough which an aqueous nitric acid solution was admitted to the tower. A8 the reaction proceeded the aqueous nitric acid solution was continuously fcd into thc countercurrent towe~ rcactor through this inlet at a rate of about 14, OGO
grams per hour. At~the top of the tower an outlet approximatcly one quarter inch in diameter was provided through which the e.~;haust gases passed out of the tower. The liquid in the lower section of the tower was maintained at about 135F.
The temperature of the packed section of the tower reactor just above the wire ~auze supporting the packed sect;on of the tower wa3 determined by thermocouple to be about 101F. while the temperature of this packed sectlon at the top of the tower near the nitric acid inlet was detcrmined by thermocouple to be about 50F.
After the gaseous products from the ammonia oxidation with added air had been admitted to the tower and the reaction had proceeded for a while the tcmperaturc in the unpacked portion just beneath the packed section ~vas dctcrmined to be about 146F.
73~
~s the reaction proceedecl an aqueollsrlitric acicl solutioll was continuously recycled to the unit by collecting the effluerlt from the reaetor which passed out of the tower through the outlet in tlle base of the unit.
Before the reaction was initiated 1324 ~rams(100/0 ~INO3) of nitric acid was charged to the countercurrent tower reactor. This acid was added as a 24. 3% aqueous solution. As previously maintained the r ecycle rate of this aqueous solution of nitric acid was about 1a~, 060 grams per hour. The effluent from the reactor may contain some dissolved nitrogen o.~;ides. These unreacted nitrogen oxides may be stripped from the effluent and returned to the tower reactor. To aceomplish this the effluent from the tower reactor was passed into a second stainless steel tower which was approximately ~6 inches in height and two inches in diameter and had a volume of approximately 261 cubic inches. The second tower was packed with the same stainless steel shavings as employed in the paclced seclions of the tower reaetor. The effluent was introdllced into the top of this second pac]ced tower by means of an inlet three quarters of an inch in diameter and located in the wall of the tower about three inches from the top of the tower and allowed to pass down through the packed tower by means of ~ravity. The second tower was fitted with a steam jaeket so that the temperature of lhe tower could be maintained at least about 150F so that any nitrogen oxides dissolved in the effluent would be desorbed as a gas. The desorbed gases passed up the tower and out of it through an outlet in the top of the tower which was approximately one quarter ineh in diameter. These desorbed gases were returned to the reactor for eonversion to nitrie aeid by means of an inlet in the reaetor about one quarter ineh in diameter and located in the l,vall of the reaetor just above the ~iquid in the bottom of the tower reactor which was about six inches above the bottom of the reactor. A stream of aqueous nitrie aeid was withdrawn from this second tower through an outlet, approximately one . . , . ' :
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~ ter incl~ in diameter, wh~ch was located in the bottom of the second to~ver. This withdrawn stream of aqueous nitr;c acid was cooled to about ambient temperature and recycled by means of a conventional pllmp to maintain the countercurrent Elow of aqueous nitric acid in the reactor. After four hours of reaction time the amollnt of acid removed from the unit was 2787 grams (100% HNO3) and the concentration of the acid recovered was 27. 4% the acid produced was 1463 grams (100% HNO3) and represented a yield of 85. 9%. It was found that the exhausl: gases from the tower reactor were about 1700 grams per hour with 0. 20% of this eshaust gas being nitrogen oxides. The temperature of the exhallst gases was about 73F.
The volumetric efficiency of the reaction in this example was 16. 3 pounds of nitric acid per cubic foot per day~
Example 2 _ Exa~nple 1 was repeated except that the temperature of the %onc between the lower llquitl scction and the packing in the upper portion of the reactor tower was maintalned at about 121~. The amount of acid initially charged to the unit was about 1602 grams (100% HNO3) added as a 25. 2% aqueous solution. After four hours of reaction time the amount of acid removed from the unit was 2936 grams (10~% HNO3) and the concentration of the acid recovered was 28.1%. The acid produced was 1334 grams (100% HNO3) and represented a yield of 80. 3%. The exhaust from the tower reactor was 1700 grams per hour of which 0. 38% represented nitrogen oxides. The volumetric efficiency of the reactor in this example was 1~. ~ pounds of nitric acid per cubic foot per day.
Example 3 Example 1 was repeated e.Ycept that the temperature of the zone betwcen thc liquid in the lower zone and the packing in the upper zone of the r eactor was maintained at about 159E. The amount of acidinitially .
1~5~3l:D
ch- -~ed to the unit was 1325 gIams(lOOOIINO~) adde(l as a 2~.3%
aqueous solution. Aftcr four hours of reaction time the amount of acid removed from the unit \vas 2708 ~r;lms (lOO~lo IINO3) and lhe concentration of the acid recovered was 30. 3%. The acid produccd WilS 1383 grams (100%
MNO3) and r epresented a yield of 84. 2%. The cxi1aust from the tower reactor ~Yas about 1500 grams pCI hour of which 0. 71% represented nitrogen o.~;ides.
`The volumetric efficiency of the reactor in this example was 15. 4 pounds of nitric acid per cubic foot per day.
~:xample 4 This example was run using a reactor similar to the one shown in FIG. 3. This reactor differed slightly in its dimensions frorn the reactor employed above in Examples 1, 2 and 3 and was provided vith gas sample ports at points A, B, C and D as shown in FIG. 3.
~ mmonia at a rate of 101. 0 grams per hour and air which had bcen dried, at a ratc Or 1315 grams per hour were fed into a conventional gas mixer and then into a catalytic reactor fitted with a platinum galIze catalyst. The platinum gauze catalyst was a 3 layer circular disc 3 inches in diameter, and was formed from, by weight, a 90% platinum-10% rhodium wire, having a diameter of 0. 003 inches, and had a mesh size of 80 x 80.
20 The platinum gauze catalyst was maintained at a temperature of about 1700F. The reaction of the ammonia and oxygen from the air was initiated by heating a small spot in the platinum wire catalyst with a small electric arc.
l~fter initiation, the reaction spread slowly over the rest of the wire ~au~e.
This took between one and two minutes. The composition of the off-~afies from the catalytic burner was measured by conventional gas phase chromatography techniques and was found to be as follo~s:
~ ' .;
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Pcrcent by Wei~ht Oxygen 6. 20 Nitrogen 83. 60 Nitrogen O.~;ide 9. 86 (rcporte(l as N02) Nitrous Oxide 0. 3~
The temperature of the air-nitrogen o~iide mi.~ture was cooled to about ~8F. This gas stream was then fed into a vertical tower reactor similar to the one shown in FIG. 3. This reactor was generally cylindrical and was made from stainless steel and was appro~imately loO inches in height. The lower 60 inch portion of this reactor was approxin~ tely four - inches in diameter with the upper 120 inch portion was approximately threc inches in diameter. The top one foot portion of the to-ver diameter was four i nchei, in diameter. The volume of this tower reactor was about 1823 cuhic inches.
'11~e liquid level in the lower- portion was about 19 inches deep. The base of the reE~ctor was provided with an ou-tlet that was approximately one half inch in diameter so that liquid could be withdrawn from the reactor. In the wall of the reactor between the upper packed portion and the liquid lev~l was located the inlet through ~,vhich the gas stream from the ammonia-oxy~en 20 burner, v/ith added air, was admitted to the reactor.
An inlet approximately one quarter inch in diameter was located about six inches from the top of the reactor through which an aqueous nitric acid solution was admitted to the reactor. As the rcaction proceeded the aqueous nitric acîd solution was continuously fed into the reactor t':lrough this inlct at a rate of about 1~, 060 grams per hour. At the top of the reactor an cutlet approximately one quarter inch in diameter was provided throu~h which the e~;haust gases passed out of the reactor. The liquid in the lower portion of the reactor was maintained at about 200F. Thc temperature of the pacl;ed ur)per portion of the reactor lO inches abov e thc wire gau~e supportin~ the 1~5~73~ `
~ king was determlnecl by thermocouple to be abollt G0Ii'. whilc the tcmperaturc OI the nitric acid at the inlet was determined by thermocollple to be about 40F.
As shown in FIG. 3, the reactor was provided with ports through whicll gas samples could be withdrawll from the reactor and analy~ed, these ports being shown at points A, 13, C and D. The gas port at point A
was between the inlet 25, thn~ ugh which the nitrogen oxides-oxygen feed gas mixture entered the reactor 14, and the liquid level in the desorber ~one 15 of the reactor. The gas port at point B was just below ~approx.
10 2. 5 inches) the packing 18 in the stripper %one 17 of the reactor. The gas port at point C wa s in the packing 1~ in the stripper zone 17 just below (approx. 6 inches) the point at which two portions of the reactor were joined.
This gas port was adjacent the cooling coil 23 inthe stripper zone 17. The gas port at point D was at a point just abo~e where the two portions of the rcactor wcrc joined.
After the gaseous products from the ammonia oxidation, with added air, had been admitted to the reactor and the reaction had proceeded for a while the temperature in the portion of the reactor between the upper i packed portion and the liquid level in the lower portion ~vas determined to 20 about 130F.
As the reaction proceeded an aqueoùs nitric acid solution was continuously recycled to the tower reactor by collecting the stream of nitric acid withdrawn from the reactor through the outlet in the base of the unit.
Before the reaction was initiated 1159 grarns (100% HNO3) of nitric acid was charged to the reactor. This acid was added as a 21. 8% aqueous solution. As previously mentioned the recycle rate of this aqueous solution oî nitric acid was about 14, 000 grams per hour. Thc liquid from tlle reactor may contain some dissolved nitrogen oxides. Thefie unreactcd nitrogcn oxides are prcfcrably eliminated ~rom the cffluent by heatin~ the bottom of the tower ! -23-'' ' . ' . "' .' ' ' , . ' ~ :.'', .
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r ` ctor. Tu accomplish tllis a heatillg coil ~,vas ~)laccd in ~he bottom one foot of the reactor. The coil is heatcd wi~ll hot water so that the tcmperature at the bottom of the tower can be maintained at least about 150F. .so that any gases dissolved in the liquid in the bottom of the rcactor wo~lld be desorbed.
These desorbecl gases passed up the tower r eactor to be convertecl to nitric acid. Liqu;d withdrawn from the reactor was cooled and recycled to the reactor to maintain the st ream of aqueous nitric acid into the tower reactor.
~ fter four hours of reaction time the amolmt of acid removed from the unit ~,vas 2435 grams (100% HNO3) and the concentration of the acid recovered was 26. l'~o. The acid produced was 1276 grams (100% HNO3) and represented a yield of 85. 3%. It was found that the exhaust gases from the tower reactor were about 17S0 grams per hour with 0. 80% of tbis exhaust gas being nitrogen o~cides. The temperature of the exhaust gas was about 75~.
~ s the reaction proceecled, s~mp1es were taken from the reactor through gas ports A, B, C and D and alla4~ed by means of conventional gas chromatrographic procedures. The results of these analysis were 2 N2 NOX(as NO2~ N2o A 7.2% 83.3% 9.16% 0.32%
B 7. 3% 82. 6% 9. 92% 0. 30%
G 7. 7% 90. 0% 2. 07% 0.. 32%
D 7.8% 91.1% 0.80% 0.33%
The results of these analysis are shown graphically in FIG. 4. The concentration of reactive nitrogen oxides at point B was 9. 92U/o by weight and the concentration of nitrogen cr~ides at point C was 2. 07% by weight.
Based upon the ammonia feed, the theoretical amount of nitric acid produced by the process was 18. 7 lbs. per day per cubic foot of reactor space. It was lollnd that the efficicncy of the ammonia oxidation burner was 89. 3%. Correcting to lOO~o ammonia oxidation burner efficiency -2~-~ ,, .: .- , ' ':
.
.
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~a 'elcl oî ~35. G% was ol)tclinecl with the process whicll represe~-lts a volllmetrie yield of 17. 0 lbs. of nitric acid per day per c~ll)ic foot of re;lctor s~ ce. The actual conversion }~ate was 15. ~3 lbs. of nitrie acid per day per cubie foot of reactor space bast!d on actual recovered nitric acid~
Thus, as has been shown the speed and cfficiency of the conversion of nitrogen oxides to nitric acid in the process of the present invention with its continuous concentration o~' nitrogen oxides can be attributed to at least three factors. First, the process provides an efficient system for extracting nitrogen oxides (principally nitric oxide) even in low concentrations from the reactor off-10 gases and returning these nitrogen oxides toanitrogen oxic'e rich reaction ~one for conversion to nitric acid. Second, the proces,s provides a high {' concentration of reactive nitrogen oxides which is in continuous contact with a liquid so that nitrogen oxides are readily converted to nitrie acid. Third, the process prnvides an efficient system for extraeLir!~ dissolved nitrogon oxides fromthe liquid u~hich is empl~yetl in the pl'OCCSS and eoneentrates these nitrogen oxides to that they can readily be converted to nitrie aeid.
.
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The nitric oxi~le prodnced in this reactioll then combines with any oxyE~en present . .
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to form rlitro~en clioxide tnntl its cl;mer nitrogL~Il tetro:cide) aeeortlill¢
to rc!action (2). 'l'he nitro~,rell dioxide th-l'; formctl absolbs in any water present alld atklition,ll nitric o.~;icle is releasecl. For every three moles of nitrogen dioYide that is converted to nitric acid in reaction (3), one mole of nitric o.Yide is released. As the concentration of nitric oxide gets smaller and ~smaller, reaction (2) goes more and more slowly; and, in fact~
never of itself goes to completion. Irou ever, in any commercial process the last traee~s of nitric oxide should be removed from the exhaust ~ases so that these gases will be within the standards set by the Environmental 10 Pro-tection Agency for pollutants and also to minimize the economic penalty paicl when the nitric oxide, a reaetant, is lost to the atmosphere. Heretofore, removal of the last nitric oxide has been accomplished by the use oE
inereased operation pressures and/or the use of large reae-tor volumes.
The reaetion between nitrie o.~:ide ancl oxygen is a tllird orcler rea~:tion alld its reaction rate wi ll increase as the square of the pressure. The residenee time for a given quantity o~ gas (by weight) in passing through ca reaetor of given volume increases in direct proportion to the pressure. It follow~s that the volume of the oxidation space to accomplish a given degree of oxidation of nitrie oxide would be inverse!y proportional to the eube of the 20 pressure. For a pressure of 8 atm, the reactor volame required would be only 1/512 of that neeessary at atmospheric pressure. Of course, the pressure equipment required is e~pensive to con9truet and maintain.
One proeess utili~ing elevated operating pressures is that developed by DuPont. ~ good summary of this proeess and its development is given in T. H. Chilton, Chem. Enr. Prog. Mon ~rraph ~eries-No~ 3, Vol. 5~, ~m. Inst. Chem. Eng., N.Y. (1960).
In a plant employing the "DuPont Proces.s", air is eompressed to abc>ut between 50 and 125 psig, preheated to about 250C, ancl mi.Yed with . . .
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amn1-)nia v;3por. 1hc ~ ;turc, containing al~out 10~/o ;IllllnOIIi;l by vohlmc, Ilows down throllgll a pack of Ilat gall,~.cs proclucing nitric oxide at an efficiency of about 95% at a tcmperatllrc of abo-lt 900 C. The hot gas leaving the gauzc is cooled by cxchangc with the feed air and in a tail-gas reheater before flowing to a cooler condenser. Wealc acid produced in the condenser is pumped to an intermediate tray of the al~sorption tower wllile the uncondensed process gas Ilows in the bottom. The absorption to~,ver consists of a series of bubble cap trays provided with cooling coils for removing the heat of reaction. As the gas flows up the tower countercurrent 10 to the acid flow, nitrogen dio~ide dissolves in water forming nitric acid and releasing nitric oxide, which is reoxidized in the space between the trays by the excess oxygen present. Steam condensate is added to the top o the tower as the absorbent; dissolved nitrogen oxides are removed from the procillct acid hy contact with sccolldary air in a "bleaching" tower. The tail ~as lcaving the absorption tower is reheated to about 250C by exchange with the process gas and then expanded through a gas engine which provides up to about ~0% of the power required for driving the reciprs~cating air compressors.
Typically such a plant wlll produce 250 tons a day of 100% nitric acid at a volumetric efficiency of about 85 to 90 pou~:~ds of 100% nitric acid per day per 20 cubic foot of reactor.
The alternative to the use of elevated pressure to minimize the amollnt of nitric oxide in the exhaust gases is to use a series of reactors to oxidize the nitric oxide to nitrogen dioxide. In this process, the exhaust gas containing the regenerated nitric oxide is fed into a second reactor where it is contacted with additional oxygen and water to form nitric acid and, of course, additional regenerated nitric o~ide, which is in turn fed into a third rcactor; al)d the process is repeated until the nitric o~;ide level in the exhaust is practically eliminated.
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5~39~ -As can be apprcciatccl cach of these tcchlli(lues has its drawbaclis. Thc use Or large rcactor machincs rcquires not only considerable capital investment but also increases thc retention time of gns in the reactor. Increasing the operating prcssure also increases the gas retention time and furtller necessitates the use Or pressure eq~lipment wllich is co~tly to install and maintain.
It is therefore an object of this invention to provide a process foP the preparation of nitric acide from nitrogen o~icles which virtually eliminates regenerated nitrogen o~;ides in the process exhaust 10 gases.
Another object of this invention provides a process of the type described herein which can be operated at essentially atmospheric pressure with relatively srnall reactor volumes.
It is yet another object Or thi.s invcnL;on to provide such a process that operates in a single gas-liquid contacting reaction zone.
Still another object of this invention lies in the provision of a process as described herein which is capable of achieving yields of 85% and greater of 100% nitric acid.
A further object of this invention is to provide such a process 20 characterized by its ability to effectively react dilue concentrations of nitrogen oxides.
~ et another object provides an integral process as described hercin for efriciently and economically converting ammonia to nitric acid.
BRIEF VESCRIPTION OF TIIE Dl~l~WINGS
-Other objccts and advantagcs of the process will become apparent in thc following dcscription and acCompanyin~J drawings in which:
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~5C1 73[1 I~lIGIJI~E 1 clepicts a cross sectional side vicw of onc embodiment for carryillg out tllc hcre;ll descril~ed inYelltion;
FIG. 2 dcpicts a cross scctional side vicw of a furtller embodimcnt for carryinG out the hCreill described invention;
l~IG. 3 depicts a cross sectional sidc view of an apparatus having ports throu~h which gas samples can be removed for analysis; and FIG. 4 is a graph with thc concentration of nitrogen oxides measured in the gas phase being its ordinate and the reactor volume being its abscissa.
BRIEF DESCRIPTION OF T~IE IN~rENTION
To avoid the problem of the ever decreasing concentration and resulting decrease in the reaction rate of the conversion of regenerated nitric oxide to nitrogen dioxide, the process of the present invention, in general, utili~es an aque~us striljpiil~ liquid having a nitric acid content within a ,, specific range which p~sscs througll a reaction Y.one. P.y appropr;ately mailltaill-ing the tt~mperature of the stripping liquid and by coordinating it with the other process parameters, a stripper zone and a desorbin~ zone are provided which concentrate the nitrogen oxides into a concentration ~one wherein the conversion of nitric oxide to nitrogen dioxide or its dimer is relatively fast. This stripping 20 liquid, serving as a first stream, provides a sufficient liquid level in the reaction zone to at least give a gas seal. A second stream is continuously removed from the desorbing zone and is separated to form a recycle stream and an eventual product strcam.
The overall conversion of nitrogen oxides to nitrogen dioxide or its dimer by means of concentrating the nitro~en oxides is fast and efficient and eliminates thc need for somc of the cquipment associated with the present - commercial processes such as expensive large volume reactors and hi~h prcssurc cquipment. ~urtller, tllc concentration of thc nitrogen oxides in thc rractor also speeds thc convcr~;ion Or thc nitr Ogt?n dioxidc or its dimer ::. . `.: :' .. . . : . .
~(~5~)73a3 nitric acid.
While thc in~ntion is susceptil~le to various modifications and altcrn;ltive forms, a preEcrrcd embotlimellt tht?I eof has been sholvn in the drawings and will bc described in dctail hereinaftcr. In this cml)odiment, a single, vertical towcr serves as the reaction zone and carries out various functions including gas~ id contacting for stripping and the like. It should be understood, however, by those sl;illed in the art that it is not intended to ~ -limit the invention to the particular form disclosed, blit, to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. For example, it should be appreciated that a horizontal-oriented, gas-liquid contact apparatus, as is known, may be employed in Ihe place of the vertical apparatus of the preferred embodiment herein disclosed withollt departing from the scope of thc pres~rt lnvc;;tio;l. L1 addition, while the embo;liment illustrated sets fortll a pI'OCCSS wher~ tlle nitrogen o ;ide reactant is formed as the first step of an integral process by oxidi~.ing ammonia, this advantageous step need not be incorporated. ~ny source of nitrogen oxides may certainly be utilizcd DET~ILED D~SCRIl'TION OF THE DIRAWINGS
Turning now to FIGUR E 1 of the drawings, there is shown an 20 integral process for converting ammonia to nitric acid. To provide the nitrogen oxide reactant source, ammonia is first oxidized to nitrogen oxides as i6 weII l;no~n. Thu9, as is shown, ammonia and a primary source of rnolecular oxygen, such as air, are combined, heated and admixed in a conventional gas mixer 11. A slight excess of molecular oxygen over that which is theoretically required to convert the ammonia to nitrogen oxidcs is employed.
The mixed molccular oxygen-ammonia gas is then reacted to form a mixturc of nitrogcll oYides by passing thc oxy~en-arnmonia mixture . ~ .
, ' . ~ ' :
~L~5073~
, a convelltiollal b~lrner reactor 12 WhiC~ n~; leen proviclc!d with a conventiol-al hcnted platinum ~auze catalyst 13. 'rhe oxygell-ammonia ~,ras mixture is passed over the heatt!d pl;ltinllm ~auze catalyst to convert the ammonia to nitrogen oxides~ principally nitric oxidc ancl nitrol;fen dioxic3e.
'rO convert the ammonia oxiclation products to nitro6ren dio.~;ide or its dimer, thesc gaseous products are continuously introduced into the concentration ~.one of the reaction zone. Thus, as is shown in FIGU~E 1, the nitrogen o.Yide products exiting from the burner reactor 12 are continuouslyintroduced into a reaction zone comprising reactor 14 at the concentration f ~one 16 via inlet 25. The limits defining the concentration ~cne and the overall gathering or concentrating of the nitrogen oxides into this zone will bedescribed hereinafter as the description proceeds. .In accordance with a preferred embodiment, these products are combined with a supplemental source of oxygen such ac air, and c:hov:n ag secondary 2.ir in FIGURE 1, to insure thal a(leqllate oxy~ten ~ill be prescnt for conversion Or the product~ to nitrogen dioxide or its dimer. The secontlary air is preferably mixed with the products prior to entry into the reactor, as is shown. Reactor 1~ is desirably a conventional vertical and generally cylindrical stripper-reactor.
The temperature of the incoming products gases, with or without 20 the secondary air, is not particularly critical. It has been found suitable to employ temperatures such that the temperature of the gases in the concentration zone are typically below about 300F. This temperature is dependent upon several factors includin~ the temperature of the aqueous nitrie acid in the stripper zone 17, the temperature of the aqueous nitric acid in the desorber zone 15, the amount of nitrogen o~:ides and oxy,~en introduced into the reaetor (since the reactions tl3at convert nitro~,en oxides to nitric acid are exothermic) and the tcmperature of the incoming nitroFen o.;ides-oxygcn mixture. Suitable reslllt~; have becn achicved w~en the telmperatllre of the incomin~ nitro~en oxide-o.~:yF~ l mi.~;tllrc is in the rar~ e of from al.out 100 to abollt 200F.
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In accord.lnc e ~r;th OllC? aisl~ct of the presellt invell~ion, at least a pOltiOll of tl-e conccllttation zOlle is complet~ly devoid of any p.lclcillg or the like. I'his allows oi)timum m;xillg of the ~aSCS ch~rillg conversion to nitrogen clioxicle or its climer. ~rhus, in accordance \vith the preferred embocli-m nt, the incoming ~ases are introdllced into free space l0 via inlet 25.
To provide a carrier for the nitric acid that is ultimatel3~ produced i~ the reaction zone and to allo~Y for the concentrating of the nitrogen oxides into the eoncentration zone, a further and important aspect of this invention provides a stripping liquid ~vhich is continuously introducecl into the reaction 10 zone. Thus, in aecordance with this invention, the stripping liquid, termed herein the first stream, consists of aqueous nitric acid having a nitrie acid content of from aibout 10 to about 40%, preferabl~ about 20 to about 30%.
By suitable maintenance of the temperature of the first stream as i~ pa~;ses througll the reaction zone, and in accordance with a still further and importatlt aspect of the present invention, a stripper zone, a concentration ~one and a desorbing zone are achievecl with the nitrogen oxides being conlinuously directed to the coneentration zone from the stripper and desorbing zones .
To this end, as seen in FIGUR:E: 1, the first stream is introduced 20 into the stripper zone 17 that is Eormed via inlet 26. The temperature of the first stream in this zone is maintained in the range of from about 40 to about 105F. If the temperature of this zone is too high, the nitrogen oxides moving out of the eoneentration zone will move upward in the reaetor and extend past the inlet 26 through which aqueous nitrie acid is introduced into the reactor.
If this oeeurs, some of the nitrogen oxides ~ill not be dissolved by the aqueous nitrie aeid but will instead be lost in the exhaust gases. It has been found that little or no unreacted nitro~en ox-ides are k)st in the exhaast ga:~es if the temperature of the ~as ancl liquicl in the stripper zone are mailltair~d below '~ ! U
, "`;'' ' '' " ' ' ' ' ' ' . ' ~a3S1~73~
al)ollt 105~F. lt shollld be appreciatcd ~hat the l(~n~th of the stripper %one shoul(l be SUC]l that the gases in tllis %one c;u~ m;lintaitle(l below about 1 05~
Wllile this temperaturc rallge may of course be achieved by introducing the first strcam which is suitably cooled, it has been found dcsirablc to provide a cooling means positioncd in the stripper zone 17.
Any suitable means may be used; alld, as shown, a coollng coil 23 may desil ably serve this purpose ~
To achieve optimum results, it is desirable to introduce the 10 first stream into the stripper zone in such a fashion that optimum gas-liquid contact is provided between the first stream and the gases containing unreacted ritrogen o.~ides which reach the stripper zone. Thus, and to this end, the first stream is introduced in the form of a spray or as small droplets; and optimum ~as-liquid cGntact is aecon~,clislle~d by sicuating in e strlpper zone, a packing or the like providing a relatively large surface arca. ~ny incrt packing providing a relatively large surface area and having a high void content may be utilized, as for example, conventional bubble plates, glass Raschi~ rings, Berl saddles or stainless steel shavings.
Preferably, stainless steel shavings are employed since the highest yields 20 of nitric acid were obtained therewith. In FIGUI~E 1, the packing is designated as 18.
The gases, freed of substantially all of the unreacted nitro~en oxides by contact with the first stream, are allowed to vent to the atmosphere as exhallst gases via outlet 2~ fromlhe stripper zone 17.
In accordance with yet another aspcct of the process of this invention, and as has beenbriefly referred to herein, a desorber zone is formcd which includes a ~as seal for the reaction zone and which serYes to liberate at least a major amount of the dissolvcd ~raseous products including ' . , ' '' :'' : , . ~ ' .. . .
.
~(~S~73~
m~logcll o.~;idcs prior to rcmov~l l`rolll thc reactioll zonc of any nit~ic acid stream. To this etld, the first strcam is hltroducctl into tllc stril)pcr zone at a ratc sufficicllt to allo-v mailltenance of a prcdctermined lcvel of the first stream of liquid in the dcsorber zolle s~lfficicnt to hold the temperature thereof in thc range of to at least about 130 and prefcrably at least about 1~0F. In the preferred form this predetermined liquid level shollld be sufficient to allow dcsorption of ~ascs in the desorber zone. The temperature oE this liquid may be as hi~,h as and can reach its boiling point.
In1his fashion, most or all of the gases such as the unreacted nitrogen oxicles can be directed towards the concentration zone. ~s shown in F`IGURE 1, a desorber zone 15 is provided: and the liquid retained is heated by any con-ventional means, such as by the illustrative heating coil 19.
In accordance with a preferred aspect of the present invention, the desorber zone includes paeking or the like to prevent the estab]ishment of convection currents which might Elllo~v dissolved nitrogen oxides in significantamounts to be removed from the rcaction zone. Thus, packing 18 is provided for this purpose. Any of the conventior~lly known means for preventing eddy currents in Iiquids may be used, such as, for example, perforated plates.
To delineate the interface between the stripper and concentration zones on the one hand, and the concentration and desorber zones on the other, it should be appreciatecl that this is principally defined by the temperature ~radients existing within the reaction zone. Thus, in relation to the interface between the stripper and concentration zones, the concentration zone be~ins in the area where the first stream Or liquid passi ng through the stripper zone has reached a temperature of at least about 110F, preferabiy 120F.
I~e~arding the concentration and desorher zones, the interface is defined as the area whcre the liq-lid is at a temperature of ahout 130F, preferably about 150l?.
l'he conversion of the nitro~en idoYi(le or its dimer forrned to nitric acid is, of course, achi-!ved by re~ction with tht~ ter pres--nt in the -.
~OS~73~) f ~ ~t stream pcassill~ thro~llth tile reaction :~.one as well as by thc ~vater formccl in the reactions occurrin~r in tlle rcactioll zone. Thus, principi?c]ly in tlle conccntration %ont~, thc nitrogell oxidcs and o.~;ygell rea(:t in the prcsencc of the watcr to produce ~aseous reaction products including nitrogtn dio.~;idt- and liquid reaction products, principally nitric acid. Tho nitric acid produced ~vill combine ~ith the first stream o aqueous nitric acid to enrich the nitric acid content thereof while the gaseous reaction products ~rill tend to tlisappear in three distinct ways.
First, any nitrogeb dioxide produced will genterally and subsequently react with the water present in the first stream of aqueous nitric acid to form additional nitric acid. As with the nitric acid in the liquid reaction products, this nitric acid will combine ~vith the first stream of aqueous nitrie acid to enrich the nitric acid content thereof.
S~condly, som~ of tl~e gaseous r~actiorl ~roduc-Ls ~Yill dissolve in, b~lt not react with, the firfit strt am. These dissolvcd and wnreacted gases are prevented from being carried Oltt of the reaction zone by tht~ operation o~ the desorber zone 15 which liberates these gases and Eorces the dissolved and unreacted gaseous reaction products out of the ~iquid as gases and directs them back upward into the concentration zone. To facilitate desorption of the 20 gases in this zone a heating means 19, as for example a steam coil, may be ctnployed to heat the liquid in this zone.
Third, some gaseous reaction products will pass up the reaction zone to the stripper zone and exit as exhaust gast s through outlt t 2~c. The stripper ziol1e functions to absorb these gases and thereby nninimize the amount of un-reacted nitrogen o~iides in the e.Yhaust gases to an acceptable level.
The combined effect of the introduction of the first stream of cold aqueous nitric acid~ the cooling in the stripper zone 17 and the htating of the l;quitl in thc desorbcr zone 15 is to concentrate the nitrogt!n oxides, pnrt~culllrly nitrol~roll dioxi(lt! und nitric o:;idc, and the oxygcrl in and .about the conccJltrlltion %one 16 of tllc rcactor .so that thc nitrogen clioxido can react ... ...
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form nitric acicl ancl thc~ nitric o.~;icle ean rc act to iOr m nitl ogen clio.~;ide.
13y conthlllo~lsly concelltrating the nitrogen oxicles in tllis lashion, it has bc?en found that the problems cliscussecl herein c~used by tlle re-gcncration of nitric o.~;ide in the r eaction of nitrogen c3io~;icle with water to form nitric acid llave been overcome. I`hus, since the nitro~,rell ohides including the rcgeneratecl nitric o~:ide are continuously beillg coneentrated, the o.Yidation of nitric o.~;ide to forrn nitrogen dio.~;ide is not hindered by low eoneentrations. ~Ioreover, sinee the regenerated nitrie oxide is effeetively stripped from the exhaust gases and is 10 eontinuously being recc-ncentrated in the reaction zone, the proeess reaehes a state of dynamie equilibrium in which the nitrie oxide eontinuously reacts with o~ygen to form nitrogen dioxide which i:
turn reaets with water to form nitrie aeid.
This is aecompl~shed without tne use of e1evated operating pre,S~ reS 0.1` Q sucecss;ve series of reactors as is eharaeteristie of present proce.qses.
To obtain product nitrie acid, the seeond stream is removed from tlle liquid of the first stream in the desorber ~one in an amount and at a rate that is eoordinated with that of the first stream being introduced into the 20 stripper zone Eo that the requisite amoun~ of liquid is retained in the desorber zone. This seeond stream may be eonventionally eoneentrated to provide nitrie aeid of the desired eoncentration.
In aeeordanee with a prirne aspeet of the present invention, the seeond stream is separated into a produet stream that may be eoneentrated, if desired, and a reeyele stream, whieh serves as the source for the first stream. As some water is withdrawn with the produet stream, water in an amount and at a rate eq~lal to or greater than the amount and rate of the water withdrawn in the produet stream must be adc3ec3 to this reeyele stream to maintain the liquid level in the reaetion zone as wc ll as to maintain thr nitrie acid eoneentration thereof inUle rangc- o~ from al~ollt 10 to ~10% hy wei~11t.
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1ll this faS]liOIl, lllC COtliiUllO-IS l'C'aCtiOII iS m~itltain~d without thc ne(~d for l(k~ g an~ frcsll clilute aqucous nitric ~cid cxccpt dllring pL'OCC~;S St;l~`t-Up, ~t anothcr aspect of thc prcferrccl cn~bocliment of this invention utilizes the water extractc(l il1 the concclltratin-t of the products stream to servc as thc cliluent for thc nitric acid cnriched recycle stream to minimize thc Elmount of nc~v lvater that m-lst be addcd to maintain the desired nitric acid conccntration in the first stream.
To this end, as is shown in FIGURE 1 a second stream ~0 is withdrawn from the reaction zone via outlet 20 and is directed by pump 22 to valve 41 where the second stream is separated into a product stream ~3 and a recycle stream 42. Yalve 4l directs the recycle stream to the stripper zone 17 to serve as the first stream andlhe product stream to concentrator 44. The water removed from concentrtor 44 is first cooled in a heat e~changer 5Q and then pumped to recycle stream 42 by pump 45, via line ~6. Water frorn an additional source, not shown, may be added to recycle stream 42, via line ~7.
13efore bein~t retllrned to the 5tripper zone 17 of reactor 1~ as the first stream, the recycle stream ~" may be cooled by any conventional cooling means, as for example a heat exchanger, which is sho~vn in FIG. 1 at 48.
Whilc the desorber zone is preferably an integral part of the reactor employed, a desorber unit, separate and spatially removed from reactor 14, may ~Iso be utilized. An embodiment of this type is shown in FIG. 2. Inasmuch as most of the elements remain the same, the identical numerals have been used.
The oper ation of the embodiment illustrated in FIG. 2 is the same as thc FIGU~E 1 embodiment, except for thc function of the desorber unit 15.
In this embodiment, part or all of the function of thc desorber zonc 15 may be carried out by the tower 30. Thus, in one mode of operation, the dcsorber zonc 15 nced not be hcate(l, and the amount of liquid therein nced only be adcqllate to providc a gr~$ scal. In this modc, tllc liberatin~ of thc unrcacted .
Q~3G~
rogen o~;i(les is achicvecl in lhe scparatc to~ver 30.
l~ltcrnatively, if desired, thc dcsonbirltr function may be partially carric(l out in dcsorber ~one 15 and thc rcmaillder accomplished in tower 30. In this modc of operation, as in the operation of tl-e ]?IGUl~E 1 embocliment, the desorber zone 15 is heated and more than the minimum amount of liquid is maintained therein. This mode is particularly desirable wllere the capacity of the desorber zone 15 is inadequate to accomplish complete desorbtion.
I'urning now to FIG. 2, the second stream is removed from reactor 14 via outlet 20 :?nd directed by pump 22 to inlet 32 in tower 30.
Tower 30 may suitably comprise a generally cylindrical, vertical tower having packin& 31, similar to that employed in the stripper zone 1~. l'he aqueous n;trie aeid passes down the tower by force of the gravity and through the paeking 31. The aqueous nitric acid in tha tower is maintained at a temperature of at least about 130Ii`, preferably about 130F by suitable heating means such as the steam coil jacket 37.
As the aqueous nitric acid passes down through the heated tower, any unreacted gases dissolved in the liquid are liberated or desorbed. These libcrated gases mix with the air introduced into the tower through inlet 36 and pass upward through the packed tower~ and out through outlet 33 as sccondary feecl gases. These secondary feed gases are then returned to the reaetor 14 ~or conver sion to nitric acid by means of inlet 3~ in reactor 14.
A stream of aqueous nitric acid, after the unreacted ~ases have been desorbed, is withdrawn from the tower through outlet 35. The withdrawn stream passes to pump 22a and then to valve 41 where it is separated into a produet stream and a reeyele stream. The product stream may be then coneentrated in the manner described above with respect to the FIGURE 1 embodiment.
. .
~S(1~73~
` . In both ~hc l;`lGV~: 1 und FIG. 2 cmbodiments, it is de~ able to witlldraw tll~ prod~ t strealll (c:~p ressecl as 100% nitric aeid) at a rate equ.ll to the amount of nitric acià (also e~;pressed as 100% nitric acid) that is produced in thc process~ Further, to efriciently extract the gaseous reaction proclllcts from the gases rising in the column, the amount of nitric acid recycled to the reactor, and forming the first strea~n, must be controlled. For example, in the reactor shown in the embodiments disclosed, a ratio of 20 to 1 by volume of gases rising in the column to acid (22%
concentration) has been found to strip at least 96% of the gaseous reaction products from the exhaust gases.
As discussed herein, the continuous concentration of the nitrogen oxides contributes to the hi~her reaction rates and yields obtained with the present process. That a concentration of the nitrogen oxides is effected by the prec ent proeess is shown by FIGU~tES 3 an(l 4 and by the data given below in :~i,x.lmplc ~.
The feed gases from the catalytic ammonia oxidation reactor in Example 4 were analyzed and were found to contain 9. 86% NOx. The apparatus u,sed in Example 4 is shown in FIG. 3. Additional air was introduced at the base of the reactor through inlet 49 and admixed with the nitrogen oxides-oxygen feed gas mixture entering the reactor 14 through inlet 25. As shown in ~IG. 3, the reactor was provided with ports through which ~as samples could be withdrawn from the reactor and analyzed, these ports being i(lentified as points, A, B, C and D.
The ~as port at point A was between the inlet 25, through whieh the nitrogen oxides-oxygen feed gas mixture entered the reactor 14, and the liquid lcvel in the desorber zone 15 of the reaetor. The gas port at point B was jl~St below (appro.Y. 2. 5 inehes) the packine 18 in the stripper zone 17 oï
t~le reaetor. 'rhe ~as port at point C was in thepacking 18 in the stripper .. . .: ' ' . , :: . ' ' '' :' . . .,:
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7 ? 17 just below ~approx. 6 inches) thc point at which two ,~ortions of thc reclCtOr were joined. This ~as port was adj;3ccnt to the cooling coil 23 in the stripper ~one 17. Tlle gas port at point V was at a point just above where the two portions cf the reactor we re joined.
- Analysis of the gas sample taken from gas port 13 showed that the concentrations of NOx in the reactor at this point was 9. 92%. As can be calculated by the dilution of the inflowing gas, wherein 86% of gas containing 9. 86% NOX is admixed ~nth 1~% additional air, the admixed gases at this point in the reactor should contain 8. 46% NOx. Actual analysis shows that the admixed ~ases contain 9. ~12% NOX. Thus, it can be seen that the process of the invention concentrates the nitrogen oxides despite the competin~
process of conversion of NOx to HN03.
The process of the present invention herein described may be further illustrated by means of the following examples, which are intcndt?tl to be illustrative of, but not in limitation of, the scope of the invcntion. The yield of nitric acid, in the following examples, was based upon the ammonia fed lnto the amrnonia o.~idation burner, calculating the amount of nitric acid which should be formed in accordance with the following equations:
NH3 + 1. 2502 = NO ~ 1. 5 H20 2N0 ~ 2 = 2N2 3N02 + H20 = 2HN03 -i- NO
This theoretical amount was then compared with the amount of nitric acid achlcllly formed to determine a percentage yield.
l~xample 1 .
Ammonia at a rate of 110. 9 grams per hour and air which had been dried, and with the carbon dio~;ide removed, at a rate of 1323 grams per hour werc fed into a convcntional ~as mixer and then into a catalytic - l G -:.
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re;tctor fittccl with a platinum gau~e catal~ st . The pl ttinum ~au~e cat.llyst was a circular disc 3 h~ches in diameter, and was forme(l from, I)y wei~ht, a 90% platinunl-10% rhoclium wire, having a diameter of 0.003 inches, and had a mesh size of 80 x 80. The platinum gauze catalyst was maintainecl at a temperatllre of about 1630F. The reaction of the ammonia and ox~en from the air was initiatcd by heating a small spot in the platinum wire catalyst with a small electric arc. After initiation, the reaction spread slowly over the rest of the wire gauze. This took bet~Yeen one and two minutes.
The composition of the off-gases from the catalytic burner was measured lû by conventional gas phase chromatography techniques and was found to be as followæ:
Percent by W ~ht_ Oxygen & .Ar~on 1. 00 Nit rogen 81 . 0 0 Ni t r o~en Oxides 17 . 50 [reported as NO2) Nitrous Oxide 0. 61 The reaction products containin~ nitrogen oxides from the catalytic reactor was then admixed with additional air, added at a rate of 272 grams per hour, The temperature of the resultant gas stream was about 20 150F. This gas stream was then fed into a generally cyIindrical ~ ertical countercurrent tower reactor. This reactor was made from stainless steel and was approximately 193 inches in hei~ht. The lower 49 inch portion of this reactor was approximately four inches in diameter with the upper 144 inch portion was appro~imately three inches in diameter. The volume of this reactor was about 1787 cubic inches.
The interior of the tower was provided with a section containing stainless steel shavings as a packin~ that was spaccd ei~hteen inches from thc bottom of thc tower and was supported by means of a stainles.s ~au~e - , ~ . : .
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Y~ 1 extenclecI across the insicle of thc tower. '~`his packecl scction c,~;tcntle(l to thc top Or thc tower. 1`he volume o~ this packcd portion of the counter-current towcr reactor was about 1540 cubic inches. The unpackcd ei~lltccn inch lower section of the tower below the packed section contained liquid to a level of 6 inches. The base of the tower was provided with an outlct that was appro.~imately one half inch in diameter so that the effluent liquid could be withdrawn from the tower. In the wall of the tower in the unpacked lower portion of the tower just below thc packed section was located the inlet through which the ~as stream from the ammonia-o.Yygen burner, with added air, was admitted to the tower.
An inlet approximately one quarter inch in di ameter was located < in the wa ll of the tower about two inches from the top of the tower 'hrough which an aqueous nitric acid solution was admitted to the tower. A8 the reaction proceeded the aqueous nitric acid solution was continuously fcd into thc countercurrent towe~ rcactor through this inlet at a rate of about 14, OGO
grams per hour. At~the top of the tower an outlet approximatcly one quarter inch in diameter was provided through which the e.~;haust gases passed out of the tower. The liquid in the lower section of the tower was maintained at about 135F.
The temperature of the packed section of the tower reactor just above the wire ~auze supporting the packed sect;on of the tower wa3 determined by thermocouple to be about 101F. while the temperature of this packed sectlon at the top of the tower near the nitric acid inlet was detcrmined by thermocouple to be about 50F.
After the gaseous products from the ammonia oxidation with added air had been admitted to the tower and the reaction had proceeded for a while the tcmperaturc in the unpacked portion just beneath the packed section ~vas dctcrmined to be about 146F.
73~
~s the reaction proceedecl an aqueollsrlitric acicl solutioll was continuously recycled to the unit by collecting the effluerlt from the reaetor which passed out of the tower through the outlet in tlle base of the unit.
Before the reaction was initiated 1324 ~rams(100/0 ~INO3) of nitric acid was charged to the countercurrent tower reactor. This acid was added as a 24. 3% aqueous solution. As previously maintained the r ecycle rate of this aqueous solution of nitric acid was about 1a~, 060 grams per hour. The effluent from the reactor may contain some dissolved nitrogen o.~;ides. These unreacted nitrogen oxides may be stripped from the effluent and returned to the tower reactor. To aceomplish this the effluent from the tower reactor was passed into a second stainless steel tower which was approximately ~6 inches in height and two inches in diameter and had a volume of approximately 261 cubic inches. The second tower was packed with the same stainless steel shavings as employed in the paclced seclions of the tower reaetor. The effluent was introdllced into the top of this second pac]ced tower by means of an inlet three quarters of an inch in diameter and located in the wall of the tower about three inches from the top of the tower and allowed to pass down through the packed tower by means of ~ravity. The second tower was fitted with a steam jaeket so that the temperature of lhe tower could be maintained at least about 150F so that any nitrogen oxides dissolved in the effluent would be desorbed as a gas. The desorbed gases passed up the tower and out of it through an outlet in the top of the tower which was approximately one quarter ineh in diameter. These desorbed gases were returned to the reactor for eonversion to nitrie aeid by means of an inlet in the reaetor about one quarter ineh in diameter and located in the l,vall of the reaetor just above the ~iquid in the bottom of the tower reactor which was about six inches above the bottom of the reactor. A stream of aqueous nitrie aeid was withdrawn from this second tower through an outlet, approximately one . . , . ' :
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~ ter incl~ in diameter, wh~ch was located in the bottom of the second to~ver. This withdrawn stream of aqueous nitr;c acid was cooled to about ambient temperature and recycled by means of a conventional pllmp to maintain the countercurrent Elow of aqueous nitric acid in the reactor. After four hours of reaction time the amollnt of acid removed from the unit was 2787 grams (100% HNO3) and the concentration of the acid recovered was 27. 4% the acid produced was 1463 grams (100% HNO3) and represented a yield of 85. 9%. It was found that the exhausl: gases from the tower reactor were about 1700 grams per hour with 0. 20% of this eshaust gas being nitrogen oxides. The temperature of the exhallst gases was about 73F.
The volumetric efficiency of the reaction in this example was 16. 3 pounds of nitric acid per cubic foot per day~
Example 2 _ Exa~nple 1 was repeated except that the temperature of the %onc between the lower llquitl scction and the packing in the upper portion of the reactor tower was maintalned at about 121~. The amount of acid initially charged to the unit was about 1602 grams (100% HNO3) added as a 25. 2% aqueous solution. After four hours of reaction time the amount of acid removed from the unit was 2936 grams (10~% HNO3) and the concentration of the acid recovered was 28.1%. The acid produced was 1334 grams (100% HNO3) and represented a yield of 80. 3%. The exhaust from the tower reactor was 1700 grams per hour of which 0. 38% represented nitrogen oxides. The volumetric efficiency of the reactor in this example was 1~. ~ pounds of nitric acid per cubic foot per day.
Example 3 Example 1 was repeated e.Ycept that the temperature of the zone betwcen thc liquid in the lower zone and the packing in the upper zone of the r eactor was maintained at about 159E. The amount of acidinitially .
1~5~3l:D
ch- -~ed to the unit was 1325 gIams(lOOOIINO~) adde(l as a 2~.3%
aqueous solution. Aftcr four hours of reaction time the amount of acid removed from the unit \vas 2708 ~r;lms (lOO~lo IINO3) and lhe concentration of the acid recovered was 30. 3%. The acid produccd WilS 1383 grams (100%
MNO3) and r epresented a yield of 84. 2%. The cxi1aust from the tower reactor ~Yas about 1500 grams pCI hour of which 0. 71% represented nitrogen o.~;ides.
`The volumetric efficiency of the reactor in this example was 15. 4 pounds of nitric acid per cubic foot per day.
~:xample 4 This example was run using a reactor similar to the one shown in FIG. 3. This reactor differed slightly in its dimensions frorn the reactor employed above in Examples 1, 2 and 3 and was provided vith gas sample ports at points A, B, C and D as shown in FIG. 3.
~ mmonia at a rate of 101. 0 grams per hour and air which had bcen dried, at a ratc Or 1315 grams per hour were fed into a conventional gas mixer and then into a catalytic reactor fitted with a platinum galIze catalyst. The platinum gauze catalyst was a 3 layer circular disc 3 inches in diameter, and was formed from, by weight, a 90% platinum-10% rhodium wire, having a diameter of 0. 003 inches, and had a mesh size of 80 x 80.
20 The platinum gauze catalyst was maintained at a temperature of about 1700F. The reaction of the ammonia and oxygen from the air was initiated by heating a small spot in the platinum wire catalyst with a small electric arc.
l~fter initiation, the reaction spread slowly over the rest of the wire ~au~e.
This took between one and two minutes. The composition of the off-~afies from the catalytic burner was measured by conventional gas phase chromatography techniques and was found to be as follo~s:
~ ' .;
. ` .
: :, 73~
Pcrcent by Wei~ht Oxygen 6. 20 Nitrogen 83. 60 Nitrogen O.~;ide 9. 86 (rcporte(l as N02) Nitrous Oxide 0. 3~
The temperature of the air-nitrogen o~iide mi.~ture was cooled to about ~8F. This gas stream was then fed into a vertical tower reactor similar to the one shown in FIG. 3. This reactor was generally cylindrical and was made from stainless steel and was appro~imately loO inches in height. The lower 60 inch portion of this reactor was approxin~ tely four - inches in diameter with the upper 120 inch portion was approximately threc inches in diameter. The top one foot portion of the to-ver diameter was four i nchei, in diameter. The volume of this tower reactor was about 1823 cuhic inches.
'11~e liquid level in the lower- portion was about 19 inches deep. The base of the reE~ctor was provided with an ou-tlet that was approximately one half inch in diameter so that liquid could be withdrawn from the reactor. In the wall of the reactor between the upper packed portion and the liquid lev~l was located the inlet through ~,vhich the gas stream from the ammonia-oxy~en 20 burner, v/ith added air, was admitted to the reactor.
An inlet approximately one quarter inch in diameter was located about six inches from the top of the reactor through which an aqueous nitric acid solution was admitted to the reactor. As the rcaction proceeded the aqueous nitric acîd solution was continuously fed into the reactor t':lrough this inlct at a rate of about 1~, 060 grams per hour. At the top of the reactor an cutlet approximately one quarter inch in diameter was provided throu~h which the e~;haust gases passed out of the reactor. The liquid in the lower portion of the reactor was maintained at about 200F. Thc temperature of the pacl;ed ur)per portion of the reactor lO inches abov e thc wire gau~e supportin~ the 1~5~73~ `
~ king was determlnecl by thermocouple to be abollt G0Ii'. whilc the tcmperaturc OI the nitric acid at the inlet was determined by thermocollple to be about 40F.
As shown in FIG. 3, the reactor was provided with ports through whicll gas samples could be withdrawll from the reactor and analy~ed, these ports being shown at points A, 13, C and D. The gas port at point A
was between the inlet 25, thn~ ugh which the nitrogen oxides-oxygen feed gas mixture entered the reactor 14, and the liquid level in the desorber ~one 15 of the reactor. The gas port at point B was just below ~approx.
10 2. 5 inches) the packing 18 in the stripper %one 17 of the reactor. The gas port at point C wa s in the packing 1~ in the stripper zone 17 just below (approx. 6 inches) the point at which two portions of the reactor were joined.
This gas port was adjacent the cooling coil 23 inthe stripper zone 17. The gas port at point D was at a point just abo~e where the two portions of the rcactor wcrc joined.
After the gaseous products from the ammonia oxidation, with added air, had been admitted to the reactor and the reaction had proceeded for a while the temperature in the portion of the reactor between the upper i packed portion and the liquid level in the lower portion ~vas determined to 20 about 130F.
As the reaction proceeded an aqueoùs nitric acid solution was continuously recycled to the tower reactor by collecting the stream of nitric acid withdrawn from the reactor through the outlet in the base of the unit.
Before the reaction was initiated 1159 grarns (100% HNO3) of nitric acid was charged to the reactor. This acid was added as a 21. 8% aqueous solution. As previously mentioned the recycle rate of this aqueous solution oî nitric acid was about 14, 000 grams per hour. Thc liquid from tlle reactor may contain some dissolved nitrogen oxides. Thefie unreactcd nitrogcn oxides are prcfcrably eliminated ~rom the cffluent by heatin~ the bottom of the tower ! -23-'' ' . ' . "' .' ' ' , . ' ~ :.'', .
- : , , .
73~
r ` ctor. Tu accomplish tllis a heatillg coil ~,vas ~)laccd in ~he bottom one foot of the reactor. The coil is heatcd wi~ll hot water so that the tcmperature at the bottom of the tower can be maintained at least about 150F. .so that any gases dissolved in the liquid in the bottom of the rcactor wo~lld be desorbed.
These desorbecl gases passed up the tower r eactor to be convertecl to nitric acid. Liqu;d withdrawn from the reactor was cooled and recycled to the reactor to maintain the st ream of aqueous nitric acid into the tower reactor.
~ fter four hours of reaction time the amolmt of acid removed from the unit ~,vas 2435 grams (100% HNO3) and the concentration of the acid recovered was 26. l'~o. The acid produced was 1276 grams (100% HNO3) and represented a yield of 85. 3%. It was found that the exhaust gases from the tower reactor were about 17S0 grams per hour with 0. 80% of tbis exhaust gas being nitrogen o~cides. The temperature of the exhaust gas was about 75~.
~ s the reaction proceecled, s~mp1es were taken from the reactor through gas ports A, B, C and D and alla4~ed by means of conventional gas chromatrographic procedures. The results of these analysis were 2 N2 NOX(as NO2~ N2o A 7.2% 83.3% 9.16% 0.32%
B 7. 3% 82. 6% 9. 92% 0. 30%
G 7. 7% 90. 0% 2. 07% 0.. 32%
D 7.8% 91.1% 0.80% 0.33%
The results of these analysis are shown graphically in FIG. 4. The concentration of reactive nitrogen oxides at point B was 9. 92U/o by weight and the concentration of nitrogen cr~ides at point C was 2. 07% by weight.
Based upon the ammonia feed, the theoretical amount of nitric acid produced by the process was 18. 7 lbs. per day per cubic foot of reactor space. It was lollnd that the efficicncy of the ammonia oxidation burner was 89. 3%. Correcting to lOO~o ammonia oxidation burner efficiency -2~-~ ,, .: .- , ' ':
.
.
'' ' ' '.' . ' '' ' '' ' . . ' ~ ' :. . . ~',. , ' ' : ' . ' ~5~73~
~a 'elcl oî ~35. G% was ol)tclinecl with the process whicll represe~-lts a volllmetrie yield of 17. 0 lbs. of nitric acid per day per c~ll)ic foot of re;lctor s~ ce. The actual conversion }~ate was 15. ~3 lbs. of nitrie acid per day per cubie foot of reactor space bast!d on actual recovered nitric acid~
Thus, as has been shown the speed and cfficiency of the conversion of nitrogen oxides to nitric acid in the process of the present invention with its continuous concentration o~' nitrogen oxides can be attributed to at least three factors. First, the process provides an efficient system for extracting nitrogen oxides (principally nitric oxide) even in low concentrations from the reactor off-10 gases and returning these nitrogen oxides toanitrogen oxic'e rich reaction ~one for conversion to nitric acid. Second, the proces,s provides a high {' concentration of reactive nitrogen oxides which is in continuous contact with a liquid so that nitrogen oxides are readily converted to nitrie acid. Third, the process prnvides an efficient system for extraeLir!~ dissolved nitrogon oxides fromthe liquid u~hich is empl~yetl in the pl'OCCSS and eoneentrates these nitrogen oxides to that they can readily be converted to nitrie aeid.
.
: ~ . ': : .: . . : : , ;' , ., , :
..
Claims (15)
1. A continuous process for the preparation of nitric acid comprising:
(a) providing a reaction zone having a stripper zone, a concentration zone, and a desorber zone;
(b) continuously introducing a first stream of aqueous nitric acid containing from about 10 to about 40% nitric acid into said stripper zone at a rate sufficient to allow maintenance of a predetermined level of aqueous nitric acid in said desorber zone;
(c) continuously introducing gaseous ammonia oxidation products and a gaseous oxidizing agent including molecular oxygen into said concentration zone;
(d) reacting the ammonia oxidation products and the oxidizing agent in the presence of said first stream to produce gaseous reaction products including nitrogen dioxide and liquid reaction products incl uding nitric acid which combine with said first stream to enrich the nitric acid content thereof;
(e) maintaining the temperature of said first stream as it passes through the stripper zone in the range of from about 40°F. to about 100°F. to dissolve at least a major amount of the gaseous reaction products entering the stripper zone into said first stream;
(f) maintaining the temperature of the aqueous nitric acid in the desorber zone at a temperature of at least 130°F. to liberate at least a major amount of the dissolved gaseous reaction products therein;
(g) withdrawing a second stream having the enriched nitric acid content from the liquid in the desorber zone at a rate allowing maintenance of said predetermined liquid level;
(h) separating said second stream into a product stream and a recycle stream;
(i) continuously introducing said recycle stream into stripper zone to provide said first stream; and (j) adding H2O to said stripper zone, the amount and rate of H2O added, and product stream being separated, being coordinated to provide said first stream having a HNO3 concentration in the range of from about 10 to about 40% by weight.
(a) providing a reaction zone having a stripper zone, a concentration zone, and a desorber zone;
(b) continuously introducing a first stream of aqueous nitric acid containing from about 10 to about 40% nitric acid into said stripper zone at a rate sufficient to allow maintenance of a predetermined level of aqueous nitric acid in said desorber zone;
(c) continuously introducing gaseous ammonia oxidation products and a gaseous oxidizing agent including molecular oxygen into said concentration zone;
(d) reacting the ammonia oxidation products and the oxidizing agent in the presence of said first stream to produce gaseous reaction products including nitrogen dioxide and liquid reaction products incl uding nitric acid which combine with said first stream to enrich the nitric acid content thereof;
(e) maintaining the temperature of said first stream as it passes through the stripper zone in the range of from about 40°F. to about 100°F. to dissolve at least a major amount of the gaseous reaction products entering the stripper zone into said first stream;
(f) maintaining the temperature of the aqueous nitric acid in the desorber zone at a temperature of at least 130°F. to liberate at least a major amount of the dissolved gaseous reaction products therein;
(g) withdrawing a second stream having the enriched nitric acid content from the liquid in the desorber zone at a rate allowing maintenance of said predetermined liquid level;
(h) separating said second stream into a product stream and a recycle stream;
(i) continuously introducing said recycle stream into stripper zone to provide said first stream; and (j) adding H2O to said stripper zone, the amount and rate of H2O added, and product stream being separated, being coordinated to provide said first stream having a HNO3 concentration in the range of from about 10 to about 40% by weight.
2. The process of claim 1 wherein the reaction zone is vertical and said vertical zone has an upper zone, lower zone and an intermediate zone.
3. The process of claim 1 wherein said first stream of aqueous nitric acid contains from about 20 to about 30% nitric acid.
4. The process of claim 1 wherein said gaseous oxidizing agent including molecular oxygen is present in an amount sufficient to increase conversion of nitric oxide to nitrogen dioxide.
5. The process of claim 1 wherein the temperature of said ammonia oxidation products and said oxidizing agent is between about 100°F
to about 200°F.
to about 200°F.
6. The process of claim 1 wherein the temperature of the aqueous nitric acid in the desorber zone is maintained at a temperature of at least about 150°F.
7. The process of claim 1 wherein said product stream is separated at a rate and an amount such that the amount of nitric acid removed is equal to the nitric acid produced in the process.
8. The process of claim 1 wherein the product stream is concentrated to provide a stream of water and a stream of concentrated nitric acid, said stream of water being added to said recycle stream to provide said first stream of aqueous nitric acid.
9. A continuous process for the preparation of nitric acid comprising:
(a) providing a reaction zone having a stripper zone, a concentration zone, and a desorber zone;
(b) continuously introducing a first stream of aqueous nitric acid containing from about 10 to about 40% nitric acid into said stripper zone at a rate sufficient to allow maintenance of a predetermined level of aqueous nitric acid in said desorber zone;
(c) continuously introducing nitrogen oxides and a gaseous oxidizing agent including molecular oxygen into said concentration zone;
(d) reacting the nitrogen oxides and the oxidizing agent in the presence of said first stream to produce gaseous reaction products including nitrogen dioxide and liquid reaction products including nitric acid which combine with said first stream to enrich the nitric acid content thereof;
(e) maintaining the temperature of said first stream as it passes through the stripper zone in the range of from about 40°F. to about 105°F. to dissolve at least a major amount of the gaseous reaction products entering the stripper zone into said first stream;
(f) maintaining the temperature of the aqueous nitric acid in the desorber zone at a temperature of at least 130°F. to liberate at least a major amount of the dissolved gaseous reaction products therein;
(g) withdrawing a second stream having the enriched nitric acid content from the liquid in the desorber zone at a rate allowing maintenance of said predetermined liquid level;
(h) separating said second stream into a product stream and a recycle stream;
(i) continuously introducing said recycle stream into stripper zone to provide said first stream; and (j) adding H2O to said stripper zone, the amount and rate of H2O added, and product stream being separated, being coordinated to provide said first stream having a HNO3 concentration in the range of from about 10 to about 40% by weight.
(a) providing a reaction zone having a stripper zone, a concentration zone, and a desorber zone;
(b) continuously introducing a first stream of aqueous nitric acid containing from about 10 to about 40% nitric acid into said stripper zone at a rate sufficient to allow maintenance of a predetermined level of aqueous nitric acid in said desorber zone;
(c) continuously introducing nitrogen oxides and a gaseous oxidizing agent including molecular oxygen into said concentration zone;
(d) reacting the nitrogen oxides and the oxidizing agent in the presence of said first stream to produce gaseous reaction products including nitrogen dioxide and liquid reaction products including nitric acid which combine with said first stream to enrich the nitric acid content thereof;
(e) maintaining the temperature of said first stream as it passes through the stripper zone in the range of from about 40°F. to about 105°F. to dissolve at least a major amount of the gaseous reaction products entering the stripper zone into said first stream;
(f) maintaining the temperature of the aqueous nitric acid in the desorber zone at a temperature of at least 130°F. to liberate at least a major amount of the dissolved gaseous reaction products therein;
(g) withdrawing a second stream having the enriched nitric acid content from the liquid in the desorber zone at a rate allowing maintenance of said predetermined liquid level;
(h) separating said second stream into a product stream and a recycle stream;
(i) continuously introducing said recycle stream into stripper zone to provide said first stream; and (j) adding H2O to said stripper zone, the amount and rate of H2O added, and product stream being separated, being coordinated to provide said first stream having a HNO3 concentration in the range of from about 10 to about 40% by weight.
10. The process of claim 9 wherein the reaction zone is vertical and said vertical zone has an upper zone, lower zone and an inter-mediate zone.
11. The process of claim 9 wherein said first stream of aqueous nitric acid contains from about 20 to about 30% nitric acid.
12. The process of claim 9 wherein said gaseous oxidizing agent including molecular oxygen is present in an amount sufficient to increase conversion of nitric oxide to nitrogen dioxide.
13. The process of claim 9 wherein the temperature of said ammonia oxidation products and said oxidizing agent is between about 100°F
to about 200°F.
to about 200°F.
14. The process of claim 9 wherein the products stream is concentrated to provide a stream of water and a stream of concentrated nitric acid, said stream of water being added to said recycle stream to provide said first stream of aqueous nitric acid.
15. The process of claim 9 wherein said product stream is separated at a rate and an amount such that the amount of nitric acid removed is equal to the nitric acid produced in the process.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US45817374A | 1974-04-05 | 1974-04-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1050730A true CA1050730A (en) | 1979-03-20 |
Family
ID=23819675
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA223,744A Expired CA1050730A (en) | 1974-04-05 | 1975-04-03 | Process for the preparation of nitric acid |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS514095A (en) |
| CA (1) | CA1050730A (en) |
| DE (1) | DE2514839A1 (en) |
| FR (1) | FR2274557A1 (en) |
| NL (1) | NL7504061A (en) |
| NO (1) | NO751143L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117839568A (en) * | 2024-03-08 | 2024-04-09 | 交城县三喜化工有限公司 | Negative pressure lifting device for producing nitric acid |
-
1975
- 1975-04-03 NO NO751143A patent/NO751143L/no unknown
- 1975-04-03 CA CA223,744A patent/CA1050730A/en not_active Expired
- 1975-04-04 NL NL7504061A patent/NL7504061A/en not_active Application Discontinuation
- 1975-04-04 FR FR7510674A patent/FR2274557A1/en active Granted
- 1975-04-04 DE DE19752514839 patent/DE2514839A1/en not_active Withdrawn
- 1975-04-05 JP JP50040835A patent/JPS514095A/ja active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117839568A (en) * | 2024-03-08 | 2024-04-09 | 交城县三喜化工有限公司 | Negative pressure lifting device for producing nitric acid |
| CN117839568B (en) * | 2024-03-08 | 2024-05-07 | 交城县三喜化工有限公司 | Negative pressure lifting device for producing nitric acid |
Also Published As
| Publication number | Publication date |
|---|---|
| NO751143L (en) | 1975-10-07 |
| DE2514839A1 (en) | 1975-10-23 |
| FR2274557A1 (en) | 1976-01-09 |
| JPS514095A (en) | 1976-01-13 |
| NL7504061A (en) | 1975-10-07 |
| FR2274557B1 (en) | 1979-02-09 |
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