Los Alamos NITRIC ACID VAPOR REMOVAL BY ACTIVATED, IMPREGNATED CARBONS. Gerry 0. Wood

Transcription

1 Title: NITRIC ACID VAPOR REMOVAL BY ACTIVATED, IMPREGNATED CARBONS Author(s): Gerry. Wood Submitted to U.S. Army Edgewood Reserch, Development nd Engineering (ERDEC) Scientific Conference Los Almos NATIONAL LABORATORY others to do so, for US. Government purposes. Los Almos Ntionl Lbortory requests tht the publisher identify this rticle s work performed under the uspices of the US. Deprtment of Energy. The Los Almos Ntionl Lbortory strongly supports cdemic freedom nd resercher's right to publish; s n institution, however, the Lbortory does not endorse the viewpoint of publiction or gurntee its technicl correctness. Form 836 (1/96)

2 F DISCLAIMER This report ws prepred s n ccount of work sponsored by n gency of the United Sttes Government. Neither the United Sttes Government nor ny gency thereof, nor ny of their employees, mke ny wrrnty, express or implied, or ssumes ny legl libility or responsibility for the cucy, completeness, or usefulness of ny informtion, pprtus, product, or process disclosed, or represents tht its use would not infringe privtely owned rights. Reference herein to ny specific commercil product, process, or service by trde nme, trdemrk, mnufcturer, or otherwise does not necessrily constitute or imply its endorsement, recommendtion, or fvoring by the United Sttes Government or ny gency thereof. The views nd opinions of uthors expressed herein do not necessrily stte or reflect those of the United Sttes Government or ny gency thereof.

3 Portions of this document my be illegible in electronic imge products. fmnces re produced from the best vhble originl d O ~ e I I t,

4 NITRIC ACID VAPOR REMOVAL BY ACTIVATED, IMPREGNATED CARBONS Gem -. Wood, Los Almos Ntionl Lbortory Mil Stop K-486, LOS Alos, NM Tel: (55) , Fx: (55) , E-mil: ABSTRACT Lbortory nd industril workers cn be exposed to vpors of nitric cid, especilly in ccidents, such s spills. Nitric cid cn lso be product of incinertion for energy production or wste (e.g., CW gent) disposl. Activted crbons contining impregnnts for enhncing vpor nd gs removl hve been tested for effectiveness in removing vpors of nitric cid from ir. The nitric cid vpor ws generted from concentrted cid solutions nd detected by trpping in wter bubbler for ph mesurements. Both low nd moderte reltive humidity conditions were used. All crbons were effective t vpor contct times representtive of ir-purifying respirtor use. One surprising observtion ws the desorption of low levels of mmoni from impregnted crbons. This ws pprently due to residul mmoni from the impregntion processes. INTRODUCTION The ASC Whetlerite crbon originlly developed for protection ginst chemicl gents hs lso been used in commercil industril ir-purifying respirtor crtridges. A recently-developed chromium-free militry crbon, ASZM-TEDA, lso hs the potentil for industril pplictions. Besides ir-purifying respirtor (gs msk) pplictions, such crbons hve potentil for ir cl&ming of effluents from demilitriztion nd industril chemicl destruction opertions. One of the potentil effluents from such opertions is nitric cid vpor. Therefore, we hve studied the effectiveness of these impregnted ctivted crbons for trpping vpors of nitric cid. W4rn@WJ T&3 i3xxctifi' 1s um$@fjl

5 EXPERIMENTAL The crbons discussed in this report were tken fiom C cnisters. The crbon we re clling ASC ws from Cnister, Chemicl-Biologicl, Msk, C ( ). The ASZM-TEDA crbon ws tken fiom Cnister, Chemicl-Biologicl, Msk, (ASZM- TEDA), CA1. Smples of the crbons fiom these cnisters were pcked into fluorocrbon tube of inner dimeter.1 cm. Totl ir flows of Llmin pssing through these beds consisted of min ir flow plus n cid genertor purge flow, ech clibrted with n electronic bubble flow meter. Crbon smple weights were scled to correspond t testing flow of L/min to the sme residence time s the full cnister bed weight t 5 L/min. Test beds of?4 these weights were lso tested to observe cid vpor brekthroughs in resonble test times. The nitric cid vpors were generted by pssing purge ir flow (45 ml/min) through chmber in which concentrted nitric cid ws being stirred. It ws found tht the cid needed to be ged severl hours before use in testing or else exceptionlly high removl efficiencies would be obtined, likely due to more wter nd less nitric cid being generted until n zeotropic mixture ws reched. The nitric cid output ws clibrted before ndor fter ech test by using n empty tube in plce of test bed. Nitric cid in bed effluent ir or chllenge ir (empty tube) ws mesured by continuously pssing prt of the effluent ir through bubbler contining ml of wter nd continuously monitoring the ph of the wter. The smpling flow verged 1.8 If:.3 L/min. Tests confirmed tht the collection efficiency of the bubbler ws 99.8% even fter 6 hours of smpling 5 ppm nitric cid vpors. A ph prob e immersed in the bubbler llowed continuous ph mesurements by meter tht sent the vlues to computer for dt cquisition t 1 minute intervls. The ph meter nd probe were clibrted periodiclly using stndrd buffer solutions. Min ir flow ws humidified for some tests by pssing it through chmber contining wter before mixing it with the cid genertor purge ir. Reltive humidity (RH) nd temperture (T) were monitored using dew point hygrometer upstrem of the mixing point. Thermocouple probes upstrem nd immeditely downstrem of the test bed llowed mesurements of temperture chnges in ir pssing through the bed. At selected times during test ph, RH, nd T were mnully recorded in notebook. DATA ANALYSIS The ph mesurements tken t 1-min intervls during test were put into spredsheet nd converted to cid concentrtions in the bubbler. For chllenge nd desorption concentrtion clcultion the verge slope of concentrtion vs. time over selected time intervl ws obtined by liner regression. It ws then converted to n verge cid vpor concentrtion using the.bubbler wter volume nd locl tmospheric conditions (1 molelmin = 6. x lo6 ppm). Evportion of the bubbler wter ws mesured to be liner with time nd dependent on reltive humidity. Corrections were mde for these losses in clculting chllenge nd brekthrough concentrtions.

6 ?, c RESULTS Full bed equivlent crbon weights (s defined bove, 4.5 g for the ASC nd 4.7 g for the ASZM-TEDA) were first tested for nitric cid vpor removl from ir. No cid ws observed in the effluent ir from the beds even fter 4 hours. Figure 1 shows two tests with ASC crbon, 4 ppm nitric cid vpor, nd 69% reltive humidity ir. -, u) E.5 W Z J. z5 O. -- u 5 7T g I - z CT) Brekthrough Time > 1476min Figure 1. Full equivlent bed ASC crbon tests t 69% reltive humidity with cid chllenge. Qurter bed equivlents were used for other tests to get mesurble brekthroughs. Figures nd 3 show brekthrough curves for ASC nd ASZM-TEDA, respectively. Smpler wter ws initilly slightly cidic (PH = 5-6), even though it hd been distilled nd boiled before use to remove crbon dioxide. Figures 1-3 show tht t the beginning of the cid brekthrough tests the cidity of the smpler wter ctully decresed. This occurred t both low (1-13%) nd moderte (6-7 %) reltive humidities, both with nd without cid vpor chllenge to the bed. However, using n unimpregnted crbon did not produce this effect..further tests wert: done to explore this effect. Figures 3-6 show exmples of the cid concentrtion decreses for humid nd dry ir nd both ctivted crbons. The results shown were obtined with full bed equivlents of crbons tken from freshly opened cnisters.

7 t. -8 \ E.5 * U 5. IZ.15 5 w Brekthrough Time > 4 rnin z.1 fy.5 n E! g Figure. ASC qurter bed equivlent brekthrough curves t 69% RH with cid chllenge. n r! -8 E.5 U z. G 4 W.15 Brekthrough Time > min 5.1 n G fy / 5 PPm.5 W. A 4 z Figure 3. ASZM-TEDA qurter bed equivlent brekthrough curves t 69% RH with cid chllenge. -

8 c. * - v -S z 6E-6 5W 5E-6 4E-6 t c Ammoni Relesed 5 3E-6 E-6 u! e 1E Figure 4. Full equivlent bed ASC crbon dry (1 1% RH) ir purge with no cid chllenge. 7E-6-5z 6E-6 5E-6 4E-6 W 5 3E-6 5: LLI -I Q 5 1E-6 Ammoni Relesed T I ti Figure-5. Full equivlent bed ASC crbon humid (67% RH) ir purge with no cid chllenge.

9 - 7E-6 E 6E-6 -z Ammoni Relesed i= 5E-6!w Z 4E-6 5 3E-6 E-6 z. - t I Figure 6. Full equivlent bed ASZM-TEDA crbon humid (66% RH) ir purge with no cid chllenge. DISCUSSION AND CONCLUSIONS Figures 1-3 show tht the ASC nd ASZM-TEDA crbons re highly effective in removing nitric cid vpors for long times. Similr experiments with n unimpregnted crbon hve lso shown such effectiveness, so tht some of the cpcity cn be ttributed to rections with the crbons nd/or their impurities. We sw no nitric cid desorption fter dsorption nd stopping the cid chllenge. We ttributed the observed decreses in smpler wter cidity mentioned bove to mmoni or some orgnic mine desorbing fiom the respirtor crtridge crbons. Ammoni slts re used in the ASC nd ASZM-TEDA formultions to enhnce the crbon rectivity. Recently, in response to Army requirements to eliminte chromium from militry cnister crbon n orgnic d e, triethylenedimine (TEDA), hs been used s one of the impregnets. A mss spectrometric study of the effluent fiom the crbons ws done to identify the bsic effluent. Becuse of bckground problems, it ws necessry to use helium, rther thn ir s the crrier gs. qso, short, heted inlet line ending immeditely downstrem of the test bed ws the only wy to void mmoni line losses. However, cler signls t mss peks 15, 16, nd 16, corresponding to the frctiontion pttern of mmoni, were observed. We sw no significnt mss peks corresponding to other compounds up to nd including mss 11 (TEDA). j

10 . I-" '. I Mximum concentrtions of mmoni in the effluents cn be clculted from the mximum rtes of cid decrese in the effluent smpler wter (negtive slopes in Figures 3-6). For full bed equivlents of these crbons t n ir flow corresponding to brething rte of 5 L/min, the mximum mmoni relese observed from these two crbons ws 1.3 ppm. This is well below the mmoni TLV of 5 ppm. The presence of mmonium slts on nd relese of mmoni from the two impregnted, ctivted crbons probbly enhnce their effectiveness in removing nitric cid from ir.