Enhancement of hydrogen release kinetics from ethane 1,2 diamineborane (EDAB) by micronization using Supercritical Antisolvent (SAS) Precipitation

1 Enhancemen o hyd ogen elease kine ics om e hane 1,2 diaminebo ane (EDAB) by mic oniza ion using Supe c i ical An isol en (SAS) P ecipi a ion Mi iam Rueda1, Luis Miguel Sanz-Mo al1, José Juan Sego ia2, Ángel Ma ín1* 1Depa men o Chemical Enginee ing and En i onmen al Technology - Uni e si y o Valladolid c/ Doc o Me gelina s/n 47011 Valladolid (Spain) 2TERMOCAL Resea ch G oup – Uni e si y o Valladolid, c/ Paseo del Cauce 59 47011 Valladolid (Spain) Tel: +34 983423174, e-mail: [email p o ec ed] (Á. Ma ín) 2 Abs ac E hane 1, 2 diaminebo ane (EDAB) was mic onized om THF solu ions using Supe c i ical An isol en (SAS) p ocess. The in luence o empe a u e, solu e concen a ion and ca bon dioxide ac ion on he inal p ope ies o EDAB pa icles was s udied. By SAS mic oniza ion, he o iginal p isma ic EDAB pa icles o abou 400 µm wi h a c ys alli e size o 100 nm we e con e ed in o mic osphe es o less han 2 µm wi h a c ys alli e size o 50 nm. This educ ion in he pa icle and g ain sizes esul ed in an imp o emen in he mal p ope ies. The kine ics o elease o hyd ogen by he molysis a 100ºC was also signi ican ly enhanced due o he educ ion in he di usion leng h, educing he ime needed o he decomposi ion o he hyd ide by a ac o o six. Mo eo e , a supp ession o induc ion ime was ob ained by des abiliza ion o he hyd ide a e ea men . XRD and FTIR analyses showed ha no chemical decomposi ion and no a ia ion o he c ys alline s uc u e ook place by SAS p ocessing. Keywo ds: Hyd ogen s o age; E hane diaminebo ane; mic oniza ion; kine ics; supe c i ical ca bon dioxide; supe c i ical an i sol en 1. In oduc ion In ecen yea s, impo an e o s ha e been made in o de o ind enewable ene gy sou ces ha can sa is y he cu en necessi ies. This is p omo ed by he deple ion o ossil uels and he clima e change due o he elease o g eenhouse gases [1]. Howe e , an impo an limi a ion o he main enewable ene gy esou ces is he unp edic abili y o 3 luc ua ions in hei ou pu . In his con ex , hyd ogen could be a solu ion o hese p oblems using i as an ene gy ec o , in an app oach known as ‘hyd ogen economy’ o ‘hyd ogen socie y’ [2]. In he case o onboa d applica ions, he simples idea would be o use hyd ogen as gas o a liquid. Howe e , in he case o gas, high p essu es anks would be necessa y in o de o ha e he equi ed high densi y o hyd ogen and his would mean high olumes o anks and, he e o e, high cos s o ma e ial. Using hyd ogen a c yogenic condi ions, a conside able ene gy inpu (es ima ed a ound 30% o he o al ene gy s o ed in hyd ogen) would be equi ed in o de o main ain he desi ed empe a u e [3]. Fo hese easons, solid s a e hyd ogen s o age appea s as a compelling al e na i e. Di e en solid hyd ogen s o age ma e ials ha e been es ed, such as me al hyd ides, complex hyd ides [4], me al o ganic amewo ks (MOF) [5], adso ben s, polyme composi es o cla h a e hyd a es [6], among o he s [7,8]. Howe e , ill now, no ma e ial sa is ies all he la es a ge s se o onboa d applica ions by he US Depa men o Ene gy (DoE) o 2017 o a p ac ical au omo i e applica ion (5.5 w % hyd ogen con en , elease empe a u e a 85°C, 100% e e sibili y, good cyclabili y) [9]. Many ecen esea ch wo ks ha e been ocused in bo on-ni ogen-hyd ogen sys ems, especially in ammonia bo ane (AB). AB has been widely in es iga ed due o i s high con en o hyd ogen (19.6 w %) which is eleased a mode a e empe a u es. Mo eo e , i is non- oxic and s able a oom empe a u e. Howe e , he mos impo an limi a ions ela ed o his compound a e he egene a ion and cyclabili y o he compound and he emission o some ola ile byp oduc s as bo azine, dibo ane o ammonia du ing he elease o hyd ogen which could be poisonous o he uel cell [10]. 4 Ca bon de i a i es o AB, such as e hane 1,2 diaminebo ane (BH3NH2CH2)2, known as EDAB, a e p omising al e na i es. EDAB has a high con en in hyd ogen (10 w %), which is eleased below 473 K in a wo-s ep eac ion. Mo eo e , i is also e y s able unde ambien condi ions (pa icula ly, agains ambien oxygen and humidi y), e en mo e han AB, which acili a es he manipula ion o his ma e ial. Howe e , only a ew wo ks can be ound ela ed o his compound [11,12,13]. Among o he esul s, i has been obse ed ha he modi ica ion o AB o ob ain EDAB p oduces a chemical s uc u e wi h a s onge B-H bond and a mo e he mal s able B-N bond due o he exis ence o C-N and C-C bonds, esul ing in he p oduc ion o less non-desi able ola ile gases in he hyd ogen ou s eam [11]. Howe e , mo e in es iga ion is necessa y in o de o des abilize he compound du ing he mal decomposi ion p ocess a mode a e empe a u es, in o de o imp o e he kine ics o elease o hyd ogen. Nanoenginee ing could be a solu ion o educe he c ys alli e size and imp o e he decomposi ion a e by inc easing he di usion a e and he e o e, educe he hyd ogen elease empe a u e [7]. Di e en me hods can be used in o de o educe he size o he me al hyd ide such as lase abla ion, apo condensa ion, spu e ing o ball milling [14]. One o he mos used me hods is ball milling [4,15]. Wi h his me hod, hyd ogen elease kine ics a e enhanced due o he educ ion o he di usion leng hs wi hou any cos o a ca alys o a educ ion o s o age capaci y. Milling can also induce o he ma e ial changes, such as an inc ease in he numbe o de ec s [16], c ea e mo e diso de and s ain in o he ma e ial [17], and he e o e imp o e su ace p ope ies. The p oblem o his me hod is he inhomogenei y o he p oduc a e milling [18]. Because o his disad an age, Supe c i ical An isol en Solu ion is p oposed as a p omising al e na i e me hod in o de o mic onize he hyd ide con olling he educ ion o he pa icle size by changing he condi ions and he supe sa u a ion d i ing o ces. In 5 his way, he ad an ages o milling a e p esen in his me hod, while ob aining a much mo e homogeneous p oduc . This echnique has been used o mic onize a wide ange o compounds such as polyme s, pha maceu ical compounds [19] o ca alys s. Fo i s applica ion, he only equi emen is ha he compound which is going o be mic onized needs o be soluble in an o ganic sol en and s able in CO2 a mosphe e [20]. In his wo k, he mic oniza ion o EDAB om THF solu ions using Supe c i ical An isol en (SAS) p ocess is epo ed. The in luence o he concen a ion o he solu ion, he empe a u e and he ca bon dioxide mola ac ion on he p ope ies o he mic onized p oduc has been s udied. Scanning elec on mic oscopy, FT-IR spec oscopy, X- ay di ac ion, DSC analyses and he measu emen o hyd ogen elease kine ics by he mal decomposi ion a 100 ºC ha e been done in o de o cha ac e ize and compa e he inal p oduc s ob ained a di e en condi ions in con as o he bulk EDAB. 2. Expe imen al me hods 2.1 Ma e ials E hane 1,2 diaminebo ane (EDAB, pu i y: 96 w %) was supplied by Sigma-Ald ich. As shown in he SEM mic og aph p esen ed in Figu e 1, he ma e ial was cons i u ed by p isma ic pa icles o a ound 400 µm. D y e ahyd o u an (wi h maximum wa e o 0.0075w %) was pu chased om Pan eac (Spain). Ca bon dioxide (pu i y: 99.95w %) was supplied om Ca bu os Me álicos S.A. (Spain). (FIGURE 1) 2.2 Mic oniza ion o EDAB by Supe c i ical An i Sol en (SAS) p ocess 6 Supe c i ical An isol en echnique is he p ocess used o mic onize EDAB in his wo k. I akes place in he same semi con inuous equipmen epo ed in a p e ious wo k [18], and schema ically ep esen ed in Figu e 2. A cylind ical essel o 1.5 L was used as p ecipi a o . Fi s , p ehea ed ca bon dioxide was pumped a a low a e o 2 kg/h wi h a diaph agm pump (Dosap o Mil on Roy, Spain) un il s able condi ions o empe a u e and p essu e we e eached. The p essu e was main ained in all he expe imen s a 100 ba in o de o ha e a single phase in he sys em [21]. P essu e was con olled wi h a back p essu e al e (model BP66, GO, USA). Then, pu e THF was lowed o he p ecipi a o in o de o ob ain s eady composi ion condi ions o he luid phase. A e his, 0.5 g o EDAB dissol ed in di e en olumes (0.02-0.15 L) o THF, depending on he concen a ion s udied in each expe imen , we e pumped o he p ecipi a o using a HPLC pump Jasco model PU-2080, maximum low a e: 10 mL/min ( low a e con ol wi h an accu acy o 1%). Bo h solu ions we e pumped con inuously h ough a coaxial nozzle which was loca ed in he uppe zone o he essel in which he solu ion lowed h ough he inne ube, wi h an inne diame e o 100 m, and CO2 lowed h ough he coaxial annulus. A his poin o he essel, he mix u e p oduces he supe sa u a ion o he dispe sed phase and he pa icles a e o med [22]. The pa icles hus o med we e collec ed in a s ainless s eel i co e ed wi h a polyme ic memb ane il e (po e size o 0.1 µm) which was loca ed a he bo om o he p ecipi a o . Once he solu ion was pumped, CO2 was lowed o 1 h o assu e he o al elimina ion o he sol en and a e his ime, he sys em was dep essu ized ill ambien condi ions. The in luence o he concen a ion o EDAB in THF in he ange 3-25 g/L, which is wi hin he solubili y limi o EDAB in THF (46-47 g/L a 25 °C) [23], he empe a u e 7 (308-318K) and he mola ac ion o CO2 in he CO2-THF luid mix u e (0.96-0.98) we e s udied. (FIGURE 2) 2.3 P oduc cha ac e iza ion Pa icle mo phology was obse ed by Scanning Elec on Mic oscopy (SEM) using Jeol JSM 820 equipmen . A gold spu e was used o co e he samples wi h a hin laye o gold o allow he elec on e lec ion o pa icle e alua ion. To de e mine pa icle size om SEM mic og aphs, a ound 100 indi idual pa icles we e coun ed om SEM pho os using Image J so wa e. The mean pa icle size was calcula ed as numbe a e age diame e [24]. C ys allini y o he di e en samples ob ained a e mic oniza ion was examined using an X- ay powde di ac ome e (model B uke Disco e D8). The measu ing condi ions we e CuKα adia ion, λ=1.5418 Å, 2θ angle anging om 5º o 70º wi h a scan a e o 4 s/s ep and a s ep size o 0.020º. Also, Fou ie T ans o m In a ed Spec oscopy (FT-IR) assays we e pe o med using a BRUKER ALPHA spec ome e wi h a Pla inum-ATR single di ac ion sampling module. Rega ding he he mal cha ac e iza ion o p oduc s, di e en ial scanning calo ime y (DSC) analyses we e ca ied ou in a Me le Toledo model 822e wi h a ce amic senso o high sensi i i y. Ni ogen gas lowed a 60 mL/min, wi h a hea ing a e o 5ºC/min om 0 o 250ºC (273.15 o 523.15K) using less han 1 mg o sample in each analysis. Hyd ogen elease kine ics we e measu ed by a olume ic me hod employing a s ainless s eel cell o 4.7 mL. The cell was loaded wi h a ound 30 mg o EDAB, weighed using a balance wi h ±0.1 mg o unce ain y. Ai was hen emo ed om inside he cell wi h a acuum pump, down o an absolu e p essu e o less han 0.02 ba . A e ha , he sample was hea ed o 100ºC (373.15K), in oducing he cell in a ch oma og aphic o en. The 8 elease a e o hyd ogen om he sample was de e mined by measu ing he inc easing gas p essu e inside he cell, which was eco ded wi h a ce i ied p essu e ansduce model DPI-104 (GE D uck om Ge many) wi h an accu acy o 0.001 MPa, connec ed o a da a acquisi ion compu e ha eco ded he p essu e measu emen e e y 10 seconds. The amoun o hyd ogen eleased was calcula ed om p essu e eco dings assuming ha he gas phase o med was en i ely cons i u ed by hyd ogen acco ding o [12], using he Hyd ogen Re e ence Equa ion o S a e [25] implemen ed in he Re e ence Fluid The modynamic and T anspo P ope ies Da abase (REFPROP) so wa e de eloped by he Na ional Ins i u e o S anda ds and Technology (NIST) [26]. 3. Resul s and discussion Table 1 shows a summa y o he condi ions o he di e en SAS expe imen s pe o med, oge he wi h he pa icle size ob ained by image analysis o SEM mic og aphs. As p e iously desc ibed, di e en expe imen s we e ca ied ou a ying he concen a ion o EDAB in he solu ion ( uns 1-7), he empe a u e ( uns 7-9) and he mola ac ion o CO2 ( uns 7, 10 and 11). (TABLE 1) 3.1 S uc u al p ope ies o mic onized EDAB Rega ding he c ys allini y, Figu e 3 shows he di ac og am o unp ocessed EDAB which ag ees well wi h hose p e iously epo ed [27]. As i can be obse ed in Figu e 3, he di ac og am o mic onized samples co esponds o ha o unp ocessed ma e ial, indica ing ha he c ys alline s uc u e o he ma e ial was p ese ed. While Figu e 3 only p esen s he esul s co esponding o he mic onized sample ob ained in expe imen al un 9, simila spec a we e ob ained in all SAS expe imen s. (FIGURE 3) 9 The a e age c ys allize size was calcula ed using he Sche e equa ion [28] which is shown in equa ion 1. eq[1] Whe e K is a Sche e cons an (0.9 o sphe ical pa icles), λ is he wa eleng h o he inciden x- ays (1.5418Å), β is he ull wid h a hal maximum (FWHM) and θ is he B agg angle. The inal diame e is he mean o he diame e ob ained o he peaks a 2θ= 16.4°, 19.7°, 23.4°, 24.4° and 25.6°. Table 2 shows he c ys alli e size ob ained o unp ocessed EDAB and mic onized SAS in expe imen s 1, 7, 8 and 9. (TABLE 2) As able 2 shows, c ys alli e size was educed by SAS mic oniza ion, bu a big di e ence is no obse ed be ween he di e en expe imen s ca ied ou using SAS echnique. (FIGURE 4) Rega ding he esul s o FTIR analyses, he peaks iden i ied co espond wi h hose epo ed o EDAB in [11,29]. Figu e 4 shows no a ia ion in he FTIR spec a o EDAB a e SAS p ocess ( o all he condi ions es ed). This esul indica es ha no chemical decomposi ion ook place du ing ec ys alliza ion p ocess a supe c i ical condi ions. B-H s e ching and N-H bands appea ed a he same wa enumbe alue wi hou any shi ha could indica e a weakening in he bond. This is due o he s ong C-N and C-C bond ha makes his compound much mo e he mal s able compa ed o o he compounds om he amily o Ammine Bo anes [11]. 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[31] A.Ma ín, M.J.Coce o, Nume ical modeling o je hyd odynamics, mass ans e and c ys alliza ion kine ics in he supe c i ical an isol en (SAS) p ocess, J. Supe c i . Fluids 32 (2001) 203-219. 18 [32] Y.Song, N.Ma, X.Ma, F.Fang, X.Chen, Y.Guo, Syn ehsis o Ammonia Bo ane Nanopa icles and he Diammonia e o Dibo ane by di ec combina ion o Dibo ane and Ammonia, Chem. Eu . J. 22 (2016) 6228-6233. [33] Bé ubé V; Radked G; D esselhaus M; Chen G, Size e ec s on he hyd ogen s o age p ope ies o nanos uc u ed me al hyd ides: A e iew. In . J. Ene g. Res. 31 (2007) 637–663 [34] R.C.W.Moo e, S.S.Kelly. Ino ganic Syn heses. s.l.: Mc-G aw Hill Book Company, (1970) 109-115. [35] S.F ueh, R.Kelle , C.Malle y e al, Pi oly ic decomposi ion o ammonia bo ane o bo on ni ide, Ino g. Chem. 50 (2011) 783-792. 19 Figu e Cap ions Figu e 1. SEM image (magni ica ion a io: 25x/120x, size ba : 900 m/200 m) o unp ocessed EDAB. Figu e 2. Schema ic diag am o he Supe c i ical An i Sol en appa a us. Figu e 3. XRD spec a o unp ocessed and SAS EDAB samples. Cu es a e e ically displaced o cla i y. Figu e 4. FTIR spec a o unp ocessed and SAS-mic onized EDAB samples. Cu es a e e ically displaced o cla i y. Figu e 5. a) SEM o mic onized EDAB samples a di e en concen a ion o he solu ion. A) c=3.3g/L; B) c=8.1g/L; C) c=10.0g/L; D) c=12.5g/L; E) c=16.7g/L; F) c=25.0g/L (magni ica ion a io: 5000X; size ba : 5 µm). b) Pa icle size dis ibu ion o he samples ob ained om SEM mic og aphs. Figu e 6. a) SEM o mic onized EDAB samples a di e en empe a u e and c=25g/L. G) T=35 °C (308.15K); H) T= 40 °C (313.15K); I) T= 45 °C (318.15K) (Magni ica ion a io: 5000X; size ba : 5 µm). b) Pa icle size dis ibu ion o he samples ob ained om SEM mic og aphs. Figu e 7. a) SEM o mic onized EDAB samples a di e en mola ac ion o CO2 a 40 °C (313.15K) and c=25g/L. J) x=0.964; K) x=0.975; L) x=0.981 (Magni ica ion a io: 5000X; size ba : 5 µm). b) Pa icle size dis ibu ion o he samples ob ained om SEM mic og aphs. Figu e 8. DSC cu es o unp ocessed EDAB and mic onized SAS samples a di e en condi ions. A) In luence o he concen a ion o he inle solu ion B) In luence o he empe a u e o he SAS p ocess C) In luence o he mola ac ion o CO2. 20 Figu e 9. DSC cu es o mic onized SAS samples a di e en condi ions in he ange 170-200 ºC (443.15-473.15K). A) In luence o he concen a ion o he inle solu ion B) In luence o he empe a u e o he SAS p ocess C) In luence o he mola ac ion o CO2. Figu e 10. Iso he mal kine ics o hyd ogen elease om unp ocessed and SAS p ocessed EDAB samples a 100ºC. Figu e 11. FTIR spec a o EDAB be o e and a e he mal kine ic a 100 °C (373.15K). Cu es a e e ically displaced o cla i y. 21 Tables T c EDAB x CO2 Dp Run (°C) (g/L) (mol ac) (µm) 0 unp ocessed 400 1 40 3.3 0.964 2.3 2 40 6.1 0.964 2.3 3 40 8.1 0.964 2.2 4 40 10.0 0.964 2.7 5 40 12.5 0.964 1.7 6 40 16.7 0.964 2.1 7 40 25.0 0.964 2.3 8 35 25.0 0.959 2.0 9 45 25.0 0.971 2.2 10 40 25.2 0.975 2.3 11 40 24.8 0.981 2.0 Table 1. Expe imen al condi ions o di e en expe imen s ca ied ou o mic onize EDAB using Supe c i ical An isol en (SAS) p ocess. 22 Run C ys alli e size (nm) unp ocessed 93.1±10.7 SAS 1 59.6±4.1 SAS 7 52.6±3.1 SAS 8 57.4±6.0 SAS 9 52.6±3.0 Table 2. C ys alli e size ob ained by Sche e equa ion o unp ocessed and SAS mic onized EDAB samples.