1. Sorbents preparation:

Size: px

Start display at page:

Download "1. Sorbents preparation:"

Francis Russell
5 years ago
Views:

1 1. Sorbents preparaton: (1) Preparaton of pure slca aerogel (PSA) PSA was prepared by sol-gel method, usngteos (tetraethylorthoslcate, Snopharm Chemcal Reagent Co., Ltd., AR), H O, C H 5 (Snopharm Chemcal Reagent Co., Ltd., mn. 95%) and HCl wth molar ratos of 1.0:3.0:15.6: The reagents were mxed to hydrolyze TEOS by magnetc strrng n a beaker for 1.5 hours at 50 o C. APTES (3-amnopropyltrethoxyslane) (Nanjng Xangfe Chemstry Research Insttute, mn. 97%) and C H 5 mxture soluton(volume rato: 1:50) was added to adjust ph value to 8.0 for the gelaton. TEOS/C H 5 (volume rato: 1:.5) mxture was added tll 6.0 hours after gelatn pont and then aged for 6.0 days at 50 o C. The wet gel was washed by C H 5 soluton four tmes a day. Fnally, ethanol supercrtcal dryng was used to dry the wet gel. The dryng condtons were set as follows: mmerse the wet gel nto ethanol soluton n a kettle and pre-pressurze to 6.0Mpa. Rase the temperature gradually up to 65 o C and keep the pressure between 10.0~11.0Mpa. Keep the temperature 65 o C and the pressure 10.0Mpa for 1.5 hours. Release the gas from the kettle gradually and keep the temperature 65 o C tll the pressure n the kettle equals to the room pressure. Stop heatng and clean the sample by pure N gas. () Preparaton of amne modfed slca aerogel (AMSA) The frst several steps of AMSA were the same as PSA tll agng. Here, agng was named as modfcaton. 6.0 hours after gelaton pont, APTES dluted wth C H 5 was added for the modfcaton of wet gel for 6.0 days at 50 o C; the molar rato of APTES to the source materal of TEOS was 1:. C H 5 soluton was added after modfcaton to replace APTES that remaned n the gel network. AMSA was also dred by ethanol supercrtcal dryng lke the PSA dryng condtons. The preparaton steps are llustrated n Fg. 1: Fg. 1 Preparaton of pure and amne-modfed slca aerogels 1

2 S- and S-OC H 5 on gel surface prepared by TEOS are actve to react wth APTES or the APTES hydrolyzed producton. The modfcaton processes are shown as follows: OC H 5 OC H 5 S + C H 5 O S CH CH CH NH S O S CH CH CH NH + C H 5 OC H 5 OC H 5 (1) S + HO S CH CH CH NH S O S CH CH CH NH + H O () S OC H 5 + HO S CH CH CH NH S O S CH CH CH NH + C H 5 (3). Characterzaton of sorbents (1) Photo of the AMSA wthout cracks Fg. A cake of AMSA prepared by ethanol supercrtcal dryng () TG-IR combnaton Thermogravmetrc(TG) measurement was carred out at a heatng speed of 10 o C/mn from room temperature to 1000 o C n a N flow of 35ml/mn. The organc groups that desorbed from AMSA were dstrbuted n N flow, and they were measured by FTIR to assst the determnaton of successful modfcaton. The same as n FTIR, the background data should also be measured for the next deducton.

3 Fg. 3 TG/DTA results of AMSA from room temperature to 1000 o C, where T1=10 o C, T=350 o C, T3=500 o C, T4=650 o C, T5=750 o C, T6=950 o C. TG experment combned wth FTIR detectng the groups desorbed from AMSA was also appled to dentfyng the APTES modfcaton. Fg. 3 shows the TG-DTA result of AMSA. The 4.9% mass loss before 1 o C s the escape of ethanol, water or gases absorbed n the ar. A bg 1.% mass loss between 1 o C and 899 o C s the decomposton of -(CH ) 3 NH and -OC H 5. The FTIR results, whch stand for the characterstcs of organc groups desorbed or decomposed from AMSA mxed n N gas flow, were arranged from Fg.4(a) to Fg.4(f). The dsturbance of CO peaks n Fg.4(b)~Fg.4(f) are resulted from the deducton of the CO background n the apparatus before the experment. The dfferences between Fg.4(a) and Fg.4(b)~Fg.4(f) mply that AMSA absorbed CO n the ar n the room condton. Fg. 4(a): T1=10 o C. Wavenumbers of 1511cm -1 and 1541cm -1 whch appears n the followng fgures are assgned to the background n detecton. Fg. 4(b): T=350 o C. CO dsturbance whch appears n the next followng fgures s due to the background deducton before the analyss, ndcatng the adsorpton of CO n Fg. 4(a). 3

4 Fg. 4(c): T3=500 o C. The breakng of C-N was determned by 375cm -1, 3334cm -1, 166cm -1, 1674cm -1 ; the C-C breakng could be dentfed by 1391cm -1, 3011cm -1 for -CH 3, and 1449cm -1, 967cm -1 for -CH - as well. Fg. 4(d): T4=650 o C. The unsaturated carbon bonds appeared due to the wave numbers of 107cm -1, 181cm -1, whch could be attrbuted to the long chan breakng of -CH -CH -CH -. Fg. 4(e): T5=750 o C. The smlar results to Fg. 4(d) except the producton of -NH x, where x=1 or. Fg. 4(f): T6=950 o C, an end of the organc decomposton from AMSA. Fg.4 FTIR characterzaton of groups released from the AMSA n TG experment; the results ndcated the components on AMSA surface Fg.4(a) s the desorpton of free ethanol accordng to the wavenumber of 1058cm -1 and 976 cm -1, and the CO desorpton assgned to 300cm -1 ~500cm -1. Fg.4(b) has a stronger adsorpton and t should be the mnute amount of -OC H 5 decomposton from AMSA. Fg.4(c) shows a thermal bond breakng of C-N determned by the wavenumbers of 165cm -1, 1674cm -1, 375cm -1, and 3334 cm -1 ; unsaturated bond of -NH shfts the adsorpton peaks to hgher wavenumbers. Adsorpton wavenumbers at 107cm -1, 181cm -1 and 3014cm -1 n Fg.4(d) at 4

5 650 o C s the characterstcs of unsaturated bonds whch can be assgned to -CH -CH -CH - cleavage; -C C- s probably produced. In Fg.4(e) -NH s entrely decomposed from AMSA whle the chan scsson of -CH -CH -CH - s stll n progress. When temperature reaches 950 o C, the mass loss and decomposton stop. The results show a successful modfcaton and a stable property for AMSA n N below 300 o C. (3) SEM wth EDS Samples surface observaton (only AMSA) was obtaned by SEM wth an acceleratng voltage of 15KV wth a scale of 1:30,000. A small cake was cut from the prepared sample to have a fresh surface wth undamaged structure. Elements analyss except for hydrogen by EDS was used to estmate the content of ntrogen whch s related to -NH. Detaled nformaton s gven n table 1. Table 1 Elements analyss of AMSA by EDS, an approxmate atom percentage was gven. Element k-rato (calc.) ZAF Atom (%) Element (Wt%) C O S N Though ntrogen composes only 3.91% of all characterzed atoms, ts rato to slcon s about 1:7. Carbon, whch bulds up the organc groups of -(CH ) 3 -NH and -OC H 5 n APTES and TEOS, s the most of all. Oxygen s consdered a man content of the SO aerogel, ncludng the remanng -OC H 5 on the aerogel surface. The molar rato of APTES to the source of TEOS was 1: n the preparaton; that s a molar rato of 1:3 for N and S f APTES entrely grafted to the gel n the modfcaton. The results ndcate that some APTES remaned n modfcaton and escaped n dryng process owng to the ncomplete reacton and hgh dryng temperature. (4) Characterzaton of surface area, pore volume, pore wdth. Ntrogen adsorpton-desorpton sotherms both for PSA and AMSA were obtaned on a Mcromertcs ASAP-000 sorptometer at N lqud temperature. The samples were frst dred at 10 o C n pure N flow for 1.5 hours. The surface area of the sample was calculated by BET method, and the pore sze and dstrbuton were obtaned by BJH method. N adsorpton-desorpton sotherm results for PSA and AMSA are shown n Fg.5. The 5

6 adsorpton between N and the surface of SO aerogel s the mult-molecules adsorpton n the begnnng. When the pressure s close to the saturated vapor pressure, the adsorpton curve s almost parallel to the Y axs; t s a classc performance of agglomeraton between N and sold partcles. The adsorpton and desorpton curves breaks up at the mddle relatve pressure, showng that the pores n PSA and AMSA are open end to end. Fg.5 N adsorpton-desorpton sotherms for PSA and AMSA The surface area, pore volume, and mean pore wdth are lsted n Table. Compared wth PSA, the surface area and pore volume of AMSA decrease, whch can be related to APTES modfcaton; however, the mean pore wdths are both about 0nm. Table Surface area, pore volume, and mean pore wdth of PSA and AMSA Surface area (m /g) Pore volume (cm 3 /g) Mean pore wdth (nm) PSA AMSA Cumulatve pore volumes of AMSA and PSA are shown n Fg.6. PSA has more pore volume whose pore wdth s less than 0nm than that of AMSA; t ndcates that PSA should have more theoretcal physcal adsorpton for gases. The results show that the maxmal capacty of N absorbed n AMSA s less than that of PSA; t s well accordant to the physcal adsorpton theory. 6

7 Fg. 6 Cumulatve pore volume of PSA and AMSA: the at the end of the arrows s a symbol where the pore wdth s 0nm. (5) FTIR: The nfrared spectra of the sorbents were recorded by FTIR spectrophotometer wth dry KBr as the reference. Sorbents before and after adsorpton were especally measured to make comparsons for the successful modfcaton. Before the characterzaton, the background of the apparatus should be measured for the deducton. Fg. 7 FTIR analyss of PSA and AMSA, (a) and (b) descrbed the PSA before and after CO adsorpton, respectvely; (c) and (d) descrbed the AMSA before and after CO adsorpton, respectvely. FTIR characterzatons for PSA and AMSA before and after adsorpton are shown n Fg.7. Wavenumbers at 1084 cm -1, 799 cm -1 and 469 cm -1 are the Characters of S-O-S and O-S-O bonds. Adsorpton peak at 980 cm -1 s the -CH 3 stretchng vbraton, and 1381 cm -1 s the -CH 3 bendng vbraton, ndcatng the exstence of -OCH CH 3 on PSA surface. Wavenumber at 7

8 968cm -1 s the S- on PSA surface. After modfcaton -CH - vbratons at 938cm -1 and 1474cm -1 appear whle -CH 3 adsorpton peaks are weakened n the AMSA curves. In addton, accordng to the wavenumber at 695cm -1 for S-C, the dsappearance of S- n AMSA, and the N-H vbraton at 1563cm -1, the successful modfcaton of APTES s obvous. 4. CO adsorpton measurement The CO adsorpton measurements especally for AMSA were tested on the self-manufactured equpment whch contans gas source, water steam generator, sample holder, and CO concentraton detector. The drawng s llustrated n Fg. 8. The gas sources for experments were 10.0% volume CO and certan water vapor concentratons mxed n N flow, wth a flow rate of 0.3ml/mn and 0.1g/mn; the calculaton s shown n the followng calculaton steps. The samples were frst dred at 10 o C n N flow for at least 1.0 hour, and the desorpton of CO was undertaken at 85 o C for at least 10 mn. CO adsorpton capactes of AMSA were especally measured at 5 o C and 50 o C, respectvely. Each experment was repeated for 15 cycles to get an average. Fg. 8 Drawng of self-manufactured CO adsorpton measurement equpment. The detaled apparatuses and the effects are shown as below: a. Gas source: 90%vol pure N wth 10%vol CO are premxed before the experment. b. Flow meter: flow meter s fxed to detect the flow rate from the source gas. c. Water vapor generator: water vapor volume concentraton n mxed N /CO gas can be controlled by heatng water at certan temperature. 8

9 d. Thermal nsulaton: thermal nsulaton materals are used to keep the temperature of the mxed gases from generator. e. Heater: F1135 tube furnace (Barnstead Internatonal, Dubuque, IA), sample holder s fxed n and the temperature of adsorpton can be easly controlled. f. Sample holder: a quartz tubular reactor wth quartz wool as the bed holder nsde s fxed to the heater; samples are placed on the quartz wool. g. Gas dryng equpment: the dryng medum for the adsorpton of water n CO can be anhydrous Calcum chlorde or anhydrous magnesum sulfate; h. CO detector: ZRE Infrared Gas Analyzer (Fuj Electrc system Co. Ltd., Tokyo, Japan), and the data s collected by Data-Chart 3000 (Monarch Instrument Inc., Amherst, NH) The detal procedure of the measurement s as follows: Specal gas source wth a certan rato CO and N (10 vol% CO and 90 vol% N n our experment) s premxed. A gas flow meter s fxed between the Gas source and Water vapor generator to measure the outlet gas flow. CO adsorpton measurement: a quartz tubular reactor wth quartz wool (ttled 1) as the bed holder s fxed n the heater. Preheat the heater to the desred temperature tll t s stable. As s shown n fgure 8, the ends of A and B are frstly connected to the dashed reactor (ttled ) to get the saturated adsorpton for the apparatus. When the concentraton detected by the CO detecton s equal to that of source gas, connect A and B to the reactor 1 mmedately and then start to record the CO concentraton. The blank adsorpton s also recorded for the deducton of adsorpton capactes. Calculaton steps: We dvde adsorpton tme t nto Δ t on average, and suppose that t=n Δ t when we calculate the remanng content of CO. The dvson and calculaton are demonstrated as follows: 9

10 Fg. 9 Dvson of the orgnal recorded data when calculaton Suppose the gases from the source gas are deal gases, then CO n the mxed gases s PV m = nrt = t M CO RT = Pv CO 10% (1) P : gas pressure from the source gases. V : volume of CO n : molar of CO -1 R : kpa L mol -1 K T : expermental temperature(k) M CO : molar mass of CO v : flow rate of the gas fed by the source gas, 0.3L/mn n our experment m CO : mass of outlet CO from the source gases n a perod of t and t can be controlled by changng T, P, and v. In our experment, we controlled t as 0.1g CO per mnute. 10%: volume concentraton of CO n mxture gases before adsorpton Thus we got a constant n our experment 10

11 P v M RT mco 0.1 / mn = = t 10% 10% CO g () Equaton () shows the CO before passng through the gas flow meter, and the product of P v n the experment keeps a constant f the detected gas temperature equals to that of gas source. Suppose that P ' and v ' are the outlet gas pressure and flow rate from the gas flow meter, as the concentraton of CO n mxed gases retans the constant, thus P' v' M CO m 0.1g / mn CO = = RT t 10% 10% (3) Suppose that dv and dmco are the volume and mass of the remanng CO n a perod of dt at the exact tme t, and x % and v are the volume concentraton and gas speed, respectvely. Because the detectng pressure s controlled the same as the pressure from the flow meter, dmco P' dv = P' x % v dt = dn R T = R T (4) M CO dm CO P' x % v M CO = RT dt (5) because v = v, dm CO P' x % v M CO dt x % dt = = 0.1( g / mn) (6) RT 10% we can also dentfy the remanng CO at t durng the perod of Δ t P' x% v M CO Δt x % t Δ Δ m = = 0.1( g / mn) (7) CO RT 10% Thus, the CO adsorpton capacty at t n Δ t can be wrtten as: m a CO = 0.01 (10 x ) Δt (8) and the total adsorpton capacty of CO at t s 11

12 m a CO = (10 x ) Δt (9) m n equaton (9) ncludes the adsorpton by sorbent and bed holder(blank adsorpton), so a CO we should subtract the blank adsorpton to get the real capacty of the sorbent. Regeneraton of AMSA wth 10% volume water vapor and 10% CO n pure N flow. Fg.10 Adsorpton propertes of 15 cycles for AMSA wth the mxed gases of 10.0%vol water vapor n 10%vol CO and 90% N gases 1

modeling of equilibrium and dynamic multi-component adsorption in a two-layered fixed bed for purification of hydrogen from methane reforming products

modeling of equilibrium and dynamic multi-component adsorption in a two-layered fixed bed for purification of hydrogen from methane reforming products modelng of equlbrum and dynamc mult-component adsorpton n a two-layered fxed bed for purfcaton of hydrogen from methane reformng products Mohammad A. Ebrahm, Mahmood R. G. Arsalan, Shohreh Fatem * Laboratory