Amine-immobilized HY zeolite for CO2 capture from hot flue gas

Wanqiao Liang,Jihuan Huang,Penny Xiao,Ranjeet Singh,Jining Guo,Leila Dehdari,Gang Kevin Li

Department of Chemical Engineering,The University of Melbourne,Parkville,Victoria 3010,Australia

Keywords:Zeolite HY Amine-immobilization CO2 capture Monoethanolamine (MEA)Ethylenediamine (ED)Adsorption

ABSTRACT Solid amine-based adsorbents were widely studied as an alternative to liquid amine for post-combustion CO2 capture (PCC).However,most of the amine adsorbents suffer from low thermal stability and poor cyclic regenerability at the temperature of hot flue gases.Here we present an amine loaded proton type Y zeolite (HY) where the amines namely monoethanolamine (MEA) and ethylenediamine (ED) are chemical immobilized via ionic bond to the zeolite framework to overcome the amine degradation problem.The MEA and ED of 5%,10%and 20%(mass)concentration–immobilized zeolites were characterized by X-ray diffraction,Fourier-transform infrared spectroscopy,and N2-196°C adsorption to confirm the structure integrity,amine functionalization,and surface area,respectively.The determination of the amine loading was given by C,H,N elemental analysis showing that ED has successfully grafted almost twice as many amino groups as MEA within the same solvent concentration.CO2 adsorption capacity and thermal stability of these samples were measured using thermogravimetric analyser.The adsorption performance was tested at the adsorption temperature of 30,60 and 90°C,respectively using pure CO2 while the desorption was carried out with pure N2 purge at the same temperature and then followed by elevated temperature at 150 °C.It was found that all the amine@HY have a substantial high selectivity of CO2 over N2.The sample 20% ED@HY has the highest CO2 adsorption capacity of 1.76 mmol∙g-1 at 90 °C higher than the capacity on parent NaY zeolite (1.45 mmol∙g-1 only).The amine@HY samples presented superior performance in cyclic thermal stability in the condition of the adsorption temperature of 90 °C and the desorption temperature of 150 °C.These findings will foster the design of better adsorbents for CO2 capture from flue gas in post-combustion power plants.

1.Introduction

As the main cause to global warming,greenhouse gas,especially carbon dioxide (CO2) needs to be captured and sequestered to mitigate the emissions.Four common technologies such as absorption,adsorption,cryogenic distillation and membrane purification [1] are widely studied for CO2capture from flue gas in coal-fired power plant which is the major source of anthropogenic energy-related CO2emissions [2].Among these technologies,absorption using aqueous alkanolamine solutions is the most mature one [3].However,it still has several drawbacks such as energy-intensive regeneration,corrosion of equipment due to high pH solvents and solvent degradation problems [4].To avoid the above limitations,adsorption technology has been widely studied as a promising alternative with low energy consumption.

In the adsorption process,adsorbent selectively adsorbs target adsorbates by either weak intermolecular forces or ionic bonding,that is physisorption and chemisorption respectively [4].The adsorbent is a key element in the adsorption process,determining the performance of the process.There are a number of adsorbents available such as activated carbons [5–7],zeolites [8,9],aminefunctionalized porous material [10,11] alkaline metal oxides [12],metal–organic frameworks (MOFs) [13] and microporous organic polymers (MOPs) [14].CO2working capacity on adsorbent mainly depends on the characteristics of the adsorbent,but also CO2partial pressure,working temperature and the composition of the feedstock.For physisorption,zeolite 13X is considered to be one of the most efficient adsorbents at ambient temperature and low pressure[10].However,the emitted flue gas from coal-fired power plants is typically around 50–90 °C after various cleansing processes with a low CO2concentration (12%–15%) [15].At the moderate temperature,the low CO2concentration will limit CO2working capacity,and the presence of water vapour in the flue gas will also negatively affect CO2adsorption capacity [16].To overcome these limitations above,adsorbent with unique amine groups have been developed,where amino function groups within amines can react with CO2.People studied the modification of zeolites 13X by amino-functionalized groups using polyethyleneimine(PEI) [17],monoethanolamine (MEA) [10] and ethylenediamine(ED) [18].The amine-modified zeolites have high CO2working capacity in a moderate temperature and high selectivity in the presence of water vapour,so it will be the most promising and cost-efficient adsorbent for CO2capture from flue gas [19].However,in the physical impregnation method,the amine loaded within zeolite degraded gradually,especially at a high temperature[20].

Kim et al.[20]firstly investigated the H form Y zeolite modified with ED by chemical grafting method in temperature swing adsorption(TSA)process.In their experiment,the thermal stability under 40 °C adsorption and 150 °C desorption was significantly increased because of the ionic bonding between amines and HY zeolite compared with those physically impregnated zeolites.However,40°C is still too low for post combustion flue gas.Performance of the amine functionalized materials need to be tested at higher temperature relevant to real carbon capture working conditions.

In this study,we immobilized two amines namely alkanolamines MEA and ED on HY zeolite and tested their cyclic thermal stability and CO2adsorption/desorption capacity at 30,60 and 90 °C respectively with a desorption temperature of 150 °C.The synthesized samples have been characterized to confirm and determine the amine loadings and to investigate the property change.In consideration of the potential vacuum pressure swing adsorption technology (VPSA application) for CO2capture from flue gas in power plants directly [21],our cyclic process test at the temperature of 90°C is particularly important for guiding the flue gas carbon capture in a more economical way [22].

2.Experimental

2.1.Preparation of samples

The parent material zeolite HY was synthesized from commercially available binderless NaY zeolite beads (from Chemiewerk Bad Koestritz,Germany).Firstly,zeolite NaY beads were placed into 1 mol∙L-1ammonium chloride (NH4Cl >99.99%,from Sigma Aldrich)solution with a solid–liquid ratio of 1:25[23].The solution was changed six times until the NaY was fully ion-exchanged.The NH4Y beads (above) were placed in an oven at 120 °C for one day,and then the sample was calcinated within dry air at 500 °C for 1 day [24].NH4+was decomposed to NH3and H+,and then HY was formed.

For amine-immobilized zeolites preparation,two amine solvents were used in this experiment (monoethanolamine(MEA) >99.5% solution from Chem-Supply and ethylenediamine(ED) >99% solution from Sigma-Aldrich).The chemical grafting of amines onto zeolite is slow,thus the immobilization was done by a reflux method at 60 °C for 2 h in a solid–liquid ratio of 1:2[11].In the solution,5%,10% and 20% (mass) of selected amines,respectively were dissolved into 30 ml methanol.After the reflux,the samples were dried at room temperature overnight.

2.2.Characterization and analysis

In this study,the crystalline structure of the samples was obtained by X-ray powder diffraction (XRD,D8 Advance Powder Diffractometer,Bruker,Germany),and the estimated actual amines immobilization was given by C,H,N elemental analysis conducted via Thermo Scientific Flash Smart(Thermo Fisher,USA).The actual amine loading was calculated based on nitrogen mass percentage in amine immobilized sample because all the nitrogen come from amines:

BET surface area was obtained from N2adsorption isotherm tested at -196 °C by 3-Flex (Micromeritics,USA).CO2and N2adsorption isotherms were measured with ASAP 2010(Micromeritics).Amine function groups immobilized within zeolite HY can be determined by Fourier transform infrared spectroscopy (FTIR) using Bruker model TENSOR II Spectrometer with an A225/Q Platinum ATR according to different adsorption abilities of light at a specific wavelength.Samples were analysed for 64 scans per sample with a resolution of 4 cm-1.

Adsorption/desorption performance at different temperatures(Sections 3.2 and 3.3)was tested with a thermogravimetric analyser TGA-2(Mettler Toledo,Switzerland),where about 175 mg sample was used for each analysis.Pure CO2and N2were used for adsorption and desorption,respectively at the flow rate of 30 ml∙min-1with a 10 °C∙min-1heating rate starting from room temperature to the target temperature.The boiling point of MEA and ED is 170 and 116 °C respectively,but ED@HY zeolite can be thermally stable up to 180 °C [20].Thus,the amine-immobilized zeolites were degassed at 150 °C for 2 h before all the adsorption tests and the desorption temperature in the TGA process was also set to be 150°C to avoid the possible deactivation[10].For adsorption isotherm measurements (Section 3.3.1),NaY and HY were degassed firstly at 350 °C for 6 h but they were degassed at 150°C for 2 h in TGA adsorption tests(Sections 3.2 and 3.3)to keep uniform with other amine-immobilized zeolites.

For the TGA adsorption experiment,there were four steps:(1)degassing at 150 °C for 2 h;(2) adsorption with pure CO2at 30,60 or 90°C,respectively for 2 h;(3)desorption using pure N2purge at corresponded 30,60 or 90°C,respectively for 2 h;(4)desorption with pure N2purge at 150 °C for 2 h.The data was collected after degassing,so the starting point was the sample initial mass after degassing and then the sample mass changed with CO2adsorption amount.The adsorption capacity was calculated based on CO2adsorption amount (mg)/sample mass after degassing (g).Based on the same starting point,the curves of adsorption capacity vs.experiment time were obtained.

In TGA cyclic experiments at different temperatures,there were three steps:(1)degassing at 150°C for 90 min;(2)adsorption with pure CO2at 30,60 or 90°C,respectively for 120 min;(3)desorption with pure N2purge at 150 °C for 90 min;then repeating steps (2)and (3).At the temperature of 30 °C,amines are less likely to escape,so only the highest amine loaded samples 20% ED@HY and 20% MEA@HY were tested.From our initial result,20%MEA@HY escaped much less than 20% ED@HY,so all the samples 5%,10%,20%ED@HY and 20%MEA@HY were tested at 60 and 90°C.

For TGA cyclic experiments at the same temperature in adsorption and desorption processes,there were three steps:(1)degassing at 90 °C for 90 min;(2) adsorption with pure CO2at 90 °C for 120 min;(3) desorption with pure N2purge at 90 °C for 90 min;then repeating steps (2) and (3).

3.Results and Discussion

3.1.Characterization of amine immobilized zeolite and measurement of amine immobilization amount

The X-ray powder diffraction of raw material NaY and the highest immobilized zeolite beads namely 20% MEA@HY and 20%ED@HY are presented in Fig.1.This XRD pattern indicates that there is no significant change even after the heaviest immobilization,thus the amine immobilization doesn’t destroy the crystalline structure of NaY.

Fig.1.XRD patterns of NaY,20% MEA@HY and 20% ED@HY.

The BET surface area of the parent HY sample and the selected immobilized samples were given by N2isotherm adsorption test at-196°C as shown in Fig.2 and Table 1.The reduction of micropore surface area and volume indicates that the loaded amines partially occupy the pores in HY zeolite.Also,the pore blockage of MEA@HY samples is less than that of ED@HY,which is related to the amine type such as molecule size and structure.Besides,both ED@HY and MEA@HY samples remain partial microporosity to allow CO2molecular diffusion,and thus CO2molecules can react with the amine function groups within the structure of samples.

Table 1 BET surface area for the parent and amines@HY zeolites

From FTIR in Fig.3,the presence of peaks in the range from 1200 to 1700 cm-1relates to amine immobilization,indicating that MEA and ED have been successfully grafted within HY zeolite even with the lowest amine concentration in solvent.The peak at 1635 cm-1,which is related to NH2wag of H—O—H band,can attributed to the incorporation of protonated amine group.Thus,it can infer that the amines are connected to the Brønsted acid site in the form of —NH2+O—Si— [10,25].

Fig.2.N2 adsorption–desorption isotherms of the parent and amines@HY zeolites at-196°C:(1)NaY;(2)HY;(3)10%MEA@HY;(4)10%ED@HY.(Solid symbol with line is adsorption,hollow symbol with line is desorption).

Fig.3.IR spectra of parent material and amines@HY samples showing protonated amine groups at 1635 cm-1.

The mass percentage of carbon,hydrogen and nitrogen element grafted was obtained by Thermo Scientific Flash Smart.The corresponded amines and amino group loading based on the nitrogen content are listed in Table 2.The temperature at the reflux immobilization was 60°C which is far below the decomposition temperature of amines,so all the elements C and N in the samples were attributed to amines.The presences of C and N further reveal that the immobilization of amines within zeolite HY is successful and the loading increases as the amine concentration in the solution increases [17].With the same amine concentration solution,the actual amine loading of ED is slightly less than that of MEA,indicating MEA is easier to be grafted in HY zeolite.Because ED molecule contains two amino groups while MEA just has one,ED can be immobilized almost twice as many amino groups as MEA in the same concentration of the solution.

Table 2 Elemental analysis (weight percentage) for amines@HY zeolite beads

3.2.Effect of temperature on CO2 adsorption and desorption

Adsorption capacity profiles for the amine immobilized HY zeolites at 30,60 and 90 °C are shown in Fig.4.NaY zeolite as a raw adsorbent and synthesized HY as a parent material are also measured.

The adsorption step (step 2) involves both physisorption and chemisorption,and the physisorption normally weakens but the chemisorption enhances as temperature increases [26,27].Thus,as shown in Fig.4,there is the highest CO2adsorption amount on zeolite NaY and HY at 30°C(physisorption),and the adsorption capacities decrease as temperature increases.ED@HY samples also present the highest CO2adsorption amount with the combined physisorption and chemisorption at 30 °C,showing the chemisorption at a low temperature has significantly enhancedCO2adsorption.As mentioned before,ED samples have been immobilized almost two times of amino groups than MEA@HY samples,thus two amine groups in ED participate in the CO2capture while only one in MEA takes part in the reaction.It can be implied that the amine group of MEA and one of two amine groups of ED were chemically bonded with the Brønsted acid sites of HY zeolite through hydrogen bonding.The chemisorption of CO2reaction with amino function group in ED and MEA can be described as reaction (1) [10,11,20]:

Fig.4.The adsorption profiles for the parent and amines@HY zeolites at (a) 30 °C,(b) 60 °C and (c) 90 °C.

In the presence of water vapour,both reactions will further have the following reaction (2),which is the same reaction mechanism with solvent absorption between liquid amine and CO2gas[11,19]:

Compared with MEA,ED has double amino groups,so that the chemisorption for ED@HY material should be much stronger than that for MEA@HY.The reaction is enhanced with elevated temperature and loaded amine amount,therefore,it is observed that the gap of CO2adsorption amounts among 20% ED@HY,10% ED@HY and 5% ED@HY increases as adsorption temperature increases.Since the CO2adsorption combines physisorption and chemisorption (mentioned above),the total adsorption amount of CO2still decreases as temperature increases.The MEA modified adsorbent presents a similar trend but CO2adsorption capacity is much less,especially the adsorption amount is lower than its parent adsorbent HY at 30 °C where the physisorption is the predominant mechanism and it is weakened due to partial blockage of its porous structure.

Fig.4 also shows that the ED@HY and MEA@HY samples have much steeper curves than NaY and HY in step 2,indicating the chemisorption enhances CO2adsorption at very low CO2partial pressure and the reaction kinetic is much faster while for the only physisorption happened within zeolite NaY and HY,CO2adsorption capacity is low at a low CO2partial pressure [28].

Fig.5.TGA cyclic tests at the adsorption temperature of (a) &(d) 30 °C,(b) &(e) 60 °C,and (c) &(f) 90 °C and the desorption temperature of 150 °C.

In the following step,mainly physical desorption occurs using N2purge at the same temperature of adsorption,CO2adsorbed in amine-immobilized samples desorbs more slowly than that in NaY and HY at a low temperature,while the desorption amount of CO2within amine-immobilize samples increases as temperature increases.During the desorption process,two driving forces are involved:thermal driving force and partial pressure driving force[29].For chemisorption,the adsorbates are connected to adsorbents by chemical interaction,thus a high temperature is needed to break the bonding energy while pressure difference can only break the weak electrostatic interaction in physisorption [17].As a result,amine-immobilized zeolites release less CO2amount than NaY and HY,especially at low working temperature due to the less physically adsorbed CO2amount,indicating the chemically adsorbed CO2amount remains within the amine-immobilized zeolites.It is also observed that three MEA@HY samples and 5%ED@HY sample can fast release CO2so that such developed amine immobilized zeolite may be used in the pressure swing adsorption(PSA)process.Thus,it is necessary to test their adsorption–desorption behaviours at a lower desorption temperature in Section 3.3.2.Also,all ED@HY and MEA@HY samples show high adsorption selectivity of CO2over N2.In the isothermal desorption process,the amine modified samples almost do not adsorb nitrogen when the temperature is higher than 60 °C.Thus,they would be ideal adsorbents for CO2capture from flue gas which typically contains CO2concentration(12%–15%)and the small amount of other components balanced with N2[15,30].

In the final step,the adsorbed CO2within all the samples can be completely desorbed at 150°C with N2purge.Amine-immobilized zeolites desorb faster than NaY and HY because the high desorption temperature provided a strong thermal driving force to break the chemical bonding while NaY and HY still mainly depend on the partial pressure driving force by N2purge.The heating rate is 10°-C∙min-1,thus,there is a slop at the beginning of the 150°C desorption process.

The result of adsorption capacity at 90 °C is summarized in Table 3,indicating all ED@HY and MEA@HY samples perform better than HY,and 20%ED@HY even has a higher adsorption capacity than the raw material NaY.Although CO2adsorption capacities on MEA@HY samples are slightly low,their adsorption–desorption kinetics are much faster than other samples.

Among all the figures presented in Fig.4,5% ED@HY has the best overall performance because it has high CO2adsorption capacity,the high selectivity of CO2over N2and fast kinetic during isothermal desorption at 90 °C.

3.3.Stability of amine-immobilized samples during adsorption and desorption cycles

3.3.1.Performance at different adsorption temperatures

The thermal stability of amine-immobilized zeolite is very important to determine if such material can be commercially used in industrial applications.Most of the current studies only focus on the improvement of CO2uptake,however,the regeneration ability is also a key element to implement a newly developed adsorbent on a large scale.This section is to test the thermal stability of amine-immobilized zeolite samples within cyclic adsorption and desorption experiments.The adsorption temperature is set to be 30,60 and 90 °C,respectively and the desorption temperature to be 150 °C.

Fig.5 shows the profiles of adsorption and desorption for 8 cycles at the temperature of (a) 30 °C,(b) 60 °C or (c) 90 °C for CO2adsorption and the temperature of 150 °C for CO2desorption with N2purge.The losses of overall adsorption capacities after 8 cycles are summarized in Table 4.

It is observed that 20% ED@HY presents the highest CO2capacity loss at all the temperatures while the rest samples have a relatively good performance.Compared to 20% MEA@HY,20% ED@HY has more than triple times adsorption loss.This initial loss includes amine chemical loss and CO2adsorption capacity loss resulted from escaping of less secured amines in the first several cycles and this loss become minimal gradually as the rest of the amines are securely immobilized.Because amine escaping is related to temperature,the most loss may happen at a high temperature during N2purge.

From Table 4,the loss of CO2capacity on amine immobilized adsorbents decreases as the amine immobilization percentage decreases,showing that the thermal stability for low amineimmobilized zeolites 5%ED@HY and 20%MEA@HY performs better with 4% and 3.3% (mass) capacity loss,respectively at adsorption temperature of 90 °C.5% ED@HY has a higher average adsorption capacity of 1.09 mmol∙g-1at 90 °C while 20% MEA@HY is0.87 mmol∙g-1,and both 5%ED@HY and 20%MEA@HY have similar excellent performance at 90 °C.Also,the capacity loss at 60 and 90 °C for the same sample is similar except 5% ED@HY,which can infer that high amine-immobilized samples are able to be used at a temperature of 90 °C.

Table 3 Adsorption capacities on parent andamines-immobilized adsorbents

Table 4 Loss of adsorption capacities for amine@HY adsorbents after 8 cycles (at the desorption temperature of 150°C)

Fig.6.Isotherms of CO2 on different ED@HY samples and 20% MEA@HY sample at 60°C(solid symbol with line is adsorption,hollow symbol with line is desorption).

The isotherms of CO2on ED@HY zeolites at 60°C are presented in Fig.6 to confirm the adsorption capacity in TGA experiment.From the isotherms,CO2adsorption capacity at 1×105Pa for samples 5% ED@HY,10% ED@HY,20% ED@HY and 20% MEA@HY are 1.99,2.14,2.21 and 1.23 mmol∙g-1respectively,which matches with the adsorption data in the first cycle (Fig.5(e)).The desorption pathway in the isotherms almost follows the same line with adsorption,indicating the reversible chemisorption at 60 °C.The small gap between adsorption and desorption means that there is an irreversible reaction between the amine functional group and CO2,however,this chemical sorbent–sorbate interaction can be broken by a higher temperature [17].

Fig.7.Isotherms of N2 on different samples at 60 °C:(1) NaY;(2) HY;(3) 5%ED@HY;(4)10%ED@HY;(5)20%MEA@HY;(6)20%ED@HY.(Solid symbol with line is adsorption,hollow symbol with line is desorption).

The isotherms of N2for different samples are shown in Fig.7 and the adsorption capacities are summarized in Table 5,proving that the amines@HY samples have a higher selectivity of CO2over N2than NaY and HY zeolites,which is corresponding to the result of step 2 in Fig.4(b).As shown in Fig.7 and Table 5,with increasing ED concentration,the N2adsorption capacity of ED@HY decreases significantly.Both samples—20%ED@HY and 20%MEA@HY show a similar low N2adsorption capacity of 0.027 mmol∙g-1.The adsorption kinetics of N2only involves physisorption due to the interaction between the quadrupole moment of N2and the adsorbents,while the quadrupole CO2molecules have a stronger electrostatic interaction with the adsorbents,implying that the ammine immobilization can weaken the interaction of N2and the adsorbents at high temperature [31,32].The blockage of accessible micropores by amines immobilization can also reduce N2adsorption capacity[33].As a result,the selectivity of CO2over N2is highly improved by amines immobilization on HY zeolite due to the enhanced CO2adsorption and weakened N2adsorption.

Table 5 Adsorption capacities of N2 for different samples at 60°C

3.3.2.Cyclic experiment at the same adsorption/desorption temperature of 90 °C

As discussed previously,amine escaping most likely happened at a high temperature during CO2desorption process.In this part,we investigate cyclic performance at the same adsorption/desorption temperature of 90 °C,which is also equivalent to adsorption and desorption by reducing CO2partial pressure in the PSA process.In consideration of typical flue gas temperature and PSA feature,the temperatures for both the adsorption and desorption were set to 90 °C.

The adsorption amount in Fig.8(a)is based on the mass change of samples.It is observed that the lowest point of each cycle remains at the same level indicating the amine immobilized within zeolite does not have an obvious change,compared with the results in Section 3.3.1.The loss of CO2adsorption capacity after eight cyclic experiments can also be ignored.The data of adsorption capacity and capacity loss for each cycle are shown in Table 6.

Table 6 Loss of adsorption capacitiesfor amines-immobilized adsorbents after 8 cycles at the same temperature of 90°C

From the experiment,the best performing sample 5% ED@HY presents the highest cyclic CO2adsorption capacity of 0.77 mmol∙g-1.Since all three samples have very good thermal stabilities,they have the potential to be used in the PSA process for CO2capture from the power plant.

4.Conclusions

In this study,MEA and ED have been successfully immobilized within HY zeolite beads using a reflux method,and the modified zeolite presents improved CO2adsorption capacity and selectivity.XRD test shows that the same crystalline structure remains after the amine immobilization on the zeolite,while BET surface area decreases since the amine molecules partially block micropores within the zeolites.Since ED has double amino groups as MEA,ED@HY has a strong reaction of the ionic bond between amino groups and the Brønsted acid site in HY.Based on C,H,N analysis,at the same concentration solution,ED has been immobilized slightly more than MEA onto the HY zeolite,and the actual amino group immobilization of ED is twice as many as MEA.There are improved CO2adsorption capacities on all ED and MEA immobilized samples when the adsorption temperature is higher than 60°C.At 90°C,20%ED@HY shows the highest adsorption capacity of 1.76 mmol∙g-1,higher than other solid amines known in literature,while commercial zeolite NaY has the capacity of 1.45 mmol∙g-1.Furthermore,from the 8 cyclic adsorption–desorption experiments,5%ED@HY and 20%MEA@HY performed the best thermal stability with 4% and 3.3% (mass) capacity loss at the adsorption temperature of 90 °C and the desorption of 150 °C,while at desorption temperature of 90 °C,samples 5% ED@HY,10% MEA@HY and 20% MEA@HY present excellent thermal stabilities.Overall,this novel amine immobilized zeolite has enhanced cyclic CO2adsorption capacity at a moderate temperature of 60 and 90°C,and the unique chemisorption presents very high selectivity of CO2over N2.The thermal stability of the developed samples also reveals that the amine immobilized zeolite is a potential candidate to be used in the PSA process for CO2capture from hot post-combustion flue gases.

Fig.8.TGA cyclic performance of adsorption and desorption at 90 °C.** Because of the time limitation in TGA setting,only a four-cyclic experiment can be done each time.Fig.5 combines two four-cyclic experiments,and the gap between the two experiments was 30 min.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.