Jinlong Li ,Xiaoqing Wang ,Puxu Liu ,Xiaohua Liu ,Libo Li,2,*,Jinping Li,2

1 College of Chemistry and Chemical Engineering,Shanxi Key Laboratory of Gas Energy Efficient and Clean Utilization,Taiyuan University of Technology,Taiyuan 030024,China

2 Key Laboratory of Coal Science and Technology,Ministry of Education and Shanxi Province,Taiyuan University of Technology,Taiyuan 030024,China

Keywords:Metal-organic frameworks Alginates Shaping Mechanical properties Adsorption Separation

ABSTRACT The separation of ethylene and ethane is a crucial,challenging and cost-intensive process in chemical engineering.Metal-organic frameworks (MOFs) are a class of novel porous adsorbents used for the separation of ethylene/ethane mixtures.However,MOFs are normally crystalline powders that cause multiple problems,such as dust,abrasion and heat/mass loss,as well as significant pressure drops on the adsorption bed resulting in a sudden stop in production.To solve these issues,we have prepared four different sphere-shaped adsorbents,including Mg-gallate,Co-gallate,MUV-10(Mn) and MIL-53(Al) using a calcium alginate method to achieve excellent ethylene/ethane separation performance.The performance of the sphere-shaped adsorbents has been validated using mechanical strength measurements,powder X-ray diffraction,scanning electron microscopy,thermogravimetric analysis,gas adsorption isotherms and dynamic breakthrough experiments.The excellent mechanical strength of these sphere-shaped adsorbents meets the criteria for industrial application in gas separation.Thus,the energy consumption and operating cost will be further reduced in the ethylene production process.We believe that this shaping method will open a prosperous route to the development of MOFs toward higher technology levels and their commercial application.

1.Introduction

Ethylene (C2H4) is a core feedstock obtained from the petrochemical industry with the world’s total production capacity increasing to 190 million tons and total demand reaching 170 million tons in 2018 [1].It is usually producedviasteam cracking of ethane(C2H6),in which a small amount of unreacted ethane exists as an impurity and needs to be removed by an additional separation step to obtain high purity ethylene [2].However,due to the similar volatility and molecular size of C2H4and C2H6(the difference in boiling point of C2H4and C2H6is 15 °C,with the boiling point of C2H4around 169.5°C and C2H6around 184.6°C and their molecular sizes are close,with the kinetic diameter of C2H4around 0.4163 nm and C2H6around 0.4443 nm),cryogenic distillation remains the most commonly applied separation process used in the chemical industry,which is operated under high pressure(700-2800 kPa) and low temperature (-90 to -15 °C) conditions using a high reflux-ratio (2.5-4) over 100 trays [3].Thereafter the energy consumption in this process is substantial,which accounts for～40% of all the energy used in the entire chemical industry [4].For the purpose of saving energy and reducing the cost,it is highly urgent to find an alternative separation method.

Recently,adsorption separation processes based on porous adsorbents such as activated carbon,zeolites [5-7] and metal-organic frameworks (MOFs) [8-10] have exhibited tremendous potential in the separation of ethylene and ethane and fulfil the requirements of an energy-efficient separation economy.Specifically,when compared with other adsorbents,MOFs are made up of metal ions or clusters with organic ligands,which play an important role in the choice of adsorbent used to address the problems mentioned beforehand by virtue of their large specific surface area,distinctive pore structures,tunable pore sizes,exceptional porosity,and facile functionalization [11-16],which also allow them to be widely applied in gas storage [17-20],catalysis [21-23],sensing[24-26],drug delivery[27-29]and many other fields.However,conventional methods used to prepare MOFs normally result in crystalline powders with lots of voids between the discrete microcrystals [30].Typically,crystalline MOFs powders are not industrially favorable due to the significant drop in pressure as gas flows through the adsorption bed,dust,unsatisfactory mechanical strength,abrasion,heat/mass loss,clogging and difficulties in handling [31-33].Therefore,it is imperative to develop methods for the production of sphere-shaped MOFs with enhanced mechanical strength,without sacrificing their intrinsic adsorption performance.As a novel class of promising adsorbents used for gas separation,shape engineering of MOFs will be a key aspect for the future industrialization of MOFs.

In this regard,lots of methods to shape MOFs have been developed,including pressing [34-37],granulation [38-41],extrusion[42-46]and sol-gel methods[47-49].The resulting MOFs are usually processed into thin films,granules,spheres,extrudates,foams,and monoliths,etc.However,these methods have been proven difficult to balance the adsorption performance and mechanical strength,and their harsh conditions do not suit the majority of MOFs.Alginate is a natural macromolecular polymer isolated from brown seaweed,which is composed of 1,4-linked β-D-mannuronic acid (M segments) and α-L-guluronic acid (G segments),among which only the G segments participate in gel formation and form tight linkages [50,51].Alginate is a hydrophilic,non-toxic and excellent formable polymer that can be used to prepare hydrogels with outstanding mechanical strength after drying upon ultra-fast cross-linking with divalent and trivalent metal cations under modest conditions[52-55].Therefore,the calcium alginate method is a green,simple and promising shaping process utilizing sodium alginate to prepare sphere-shaped MOFs[56].For this method,a slurry of the MOFs and sodium alginate was prepared and then added dropwise into a CaCl2solution acting as a gelling agent to form MOFs spheres,which are good options for adsorption beds due to the high density of MOFs packed in a small volume.Small MOFs spheres with high mechanical strength are preferred in order to decrease the void fraction in the bed and to prevent mass loss and crushing.However,this method has been rarely investigated.Grande [57] and others used this method to successfully shape UiO-66.By adjusting and optimizing many operating variables,the resulting sphere-shaped MOFs exhibited a mechanical strength up to 25 N with only a 10% reduction in surface area.

Herein,we report the shaping process of four different adsorbents,including Mg-gallate,Co-gallate,MUV-10(Mn) and MIL-53(Al).Mg-gallate and Co-gallate are ethylene-selective adsorbents exhibiting good separation performance for ethylene/ethane mixtures based on the molecular cross-section size sieving.MUV-10(Mn) and MIL-53(Al) are ethane-selective adsorptive materials,which can directly obtain high-purity ethylene product excluding low-concentrations of ethane as an impurity.The wellmaintained adsorptive performance of these MOFs materials before and after shaping were investigated using mechanical strength measurements,powder X-ray diffraction,scanning electron microscopy,gas adsorption isotherms and breakthrough curves studies.This exceptional separation performance shows the promising future of the calcium alginate method for shaping MOFs,which will greatly narrow the gap between their laboratory synthesis and scale-up for industrialization.

2.Experimental

2.1.Materials

Mg-gallate,Co-gallate,MUV-10(Mn) and MIL-53(Al) were synthesized as previously described in the literatures[58-60].Sodium alginate (AR) and calcium chloride (CaCl2,AR) were purchased from Beijing Innochem Co.Ltd.(China).Water was deionized.C2H4(99.99%),C2H6(99.99%),C2H4/C2H6mixtures (1/1,volume ratio) and C2H6/C2H4mixtures(1/9,volume ratio) were purchased from Beijing Special Gas Co.Ltd.(China).All the chemical reagents were commercially available and used without further purification.

2.2.Preparation of sphere-shaped MOFs

The shaping procedure used for the production of sphereshaped MOFs can be described as follows (Fig.1):18.0 g of MOFs powder (Mg-gallate,Co-gallate,MUV-10(Mn) or MIL-53(Al)) was added to 100.0 ml of deionized water.The solution was stirred for 10 min before 2.0 g of sodium alginate powder was added to the mixtures.The mixed slurry was stirred at room temperature for 30 min in order to form a homogeneous solution.The stirred solution was added dropwise to the different mass concentrations of CaCl2solution(10%,20%,30%,40%and 50%)using a 20.0 ml syringe,and the well-shaped spheres were allowed to soak for 15 min.Finally,the resulting～2 mm diameter spheres were washed at least five times using a 10-fold volume of deionized water for 10 min to remove the excess calcium and chloride ions.The washed spheres were finally dried overnight at 60 °C under vacuum.

2.3.Characterization

2.3.1.Mechanical strength test

The mechanical strength of the sphere-shaped MOFs was measured on a homemade set-up comprised of a high-precision pressure sensor (SBT674-100 N,Guangzhou Simbatouch Co.Ltd.,China) and high frequency pressure display instrument (SBT951-T,Guangzhou Simbatouch Co.Ltd.,China).In order to minimize the deviation in the mechanical strength results,we chose 25 spheres with similar shape and size for the parallel compression test.Each sphere was placed on the pressure sensor equipped with the pressure display instrument to precisely record the downward pressure loading on the sphere.The 25 measurements were conducted to determine the average mechanical strength of the sphere-shaped MOFs.

2.3.2.Powder X-ray diffraction (PXRD)

Prior to conducting the XRD measurements,The sphere-shaped MOFs were ground into powder using a mortar and pestle.The PXRD patterns were recorded on a D8 ADVANCE X-ray diffractometer (Bruker,Germany) equipped with Cu Kα radiation(λ=0.15418 nm) at room temperature and operated at 30 kV and 15 mA.The data were obtained over a 2θ range of 5°-40°.

2.3.3.Scanning electron microscopy (SEM)

The morphologies of the samples were acquired using scanning electron microscopy (SU8010,Hitachi,Japan).

2.3.4.Thermogravimetric analysis (TGA)

TGA data for the adsorbent materials were obtained on a thermal analyzer (STA 449F5,NETZSCH,Germany).The samples were heated to 800 °C at a heating rate of 10 °C·min-1under a nitrogen atmosphere.

2.3.5.Pure-component adsorption measurements and selectivity of MOFs spheres

CO2sorption at 0°C for Mg-gallate and Co-gallate and N2sorption measurements at -196 °C for MUV-10(Mn) and MIL-53(Al)were performed on a ASAP 2460 (Micromeritics,USA) adsorption analyzer.The specific surface area was estimated using the BET(Brumaire-Emmett-Teller) model.The adsorption isotherms for C2H4and C2H6on four MOFs adsorbents were obtained at 25 °C over a pressure range of 0-100 kPa on a ASAP 2020 plus(Micromeritics,USA) adsorption analyzer.Prior to analysis,the sample was activated (Mg-gallate and Co-gallate at 120 °C for 12 h,MUV-10(Mn) at 100 °C for 12 h and MIL-53(Al)at 150 °C for 8 h) under high vacuum (＜10-4kPa) to remove any residual solvent.Ideal adsorbed solution theory (IAST) calculations were performed to estimate the adsorption selectivity of C2H4/C2H6(1/1,volume ratio) for Mg-gallate spheres and Co-gallate spheres or C2H6/C2H4(1/9,volume ratio) for MUV-10(Mn) spheres and MIL-53(Al) spheres.

Fig.1.A schematic representation of the preparation of the sphere-shaped MOFs.

2.3.6.Breakthrough experiment and cycling performance

In dynamic breakthrough experiments,the MOFs spheres were divided into 40-60 mesh particles by grinding through a sieve.The preactivated sample was loaded into the column (Mg-gallate,5.15 g;Co-gallate,6.09 g;MUV-10(Mn),4.12 g;MIL-53(Al),4.14 g,for both powder and spheres samples).Breakthrough curves for the C2H4/C2H6(1/1,volume ratio) and C2H6/C2H4(1/9,volume ratio) mixtures were measured at a flow rate of 5 ml·min-1(3 ml·min-1for MUV-10(Mn))at 25°C and 100 kPa.For the cycling breakthrough experiment,the adsorption column regenerated by purging in situ with helium at a flow rate of 30 ml·min-1for 3 h at 25 °C before each experiment.

3.Results and Discussion

3.1.Material structure and characterization

Based on the hydrogel spheres produced when sodium alginate was cross-linked with CaCl2,four porous materials,including Mggallate,Co-gallate,MUV-10(Mn)and MIL-53(Al),were shaped into spheres with diameters of～2 mm (Fig.S1,Supplementary Material).Due to the regular morphology of the sphere-shaped MOFs,we purposely investigated the mechanical strength of these materials.Fig.S2 shows that we manually increased the pressure loading on the MOFs spheres to precisely record the maximum mechanical strength of four sphere-shaped MOFs.The average mechanical strength data of 25 measurements was summarized at Table S1.The mass concentration of CaCl2did not have obviously impact on the mechanical strength of Mg-gallate,MUV-10(Mn)and MIL-53(Al) spheres,and the average mechanical strength of the different sphere-shaped MOFs were maintained at about 29.96,28.71 and 23.23 N.But the mechanical strength of Cogallate spheres was significantly affected by the mass concentration of CaCl2:as the mass concentration exceeded 20%,the mechanical strength decreases significantly from 46.09 to 32.74 N.To further explore the different mechanical strength of the four shaped adsorbents prepared using the sodium alginate method,we compared the SEM images of the four original MOFs powder under the same magnification (Fig.2).It can be seen that the particle sizes of the crystals obtained for the four MOFs are different.The mechanical strength of the four shaped MOFs adsorbents followed the order:Co-gallate ＞ Mg-gallate ≥ MUV-10(Mn) ＞MIL-53(Al),which was in line with the order of the crystal particle size for each material.Moreover,Co-gallate was almost the smallest microcrystal powder(～200 nm).Therefore,with the more contact area,Co-gallate exhibited the highest mechanical strength of all materials studied.However,once the concentration is too high,it will lead to the excessive gelation of composite spheres,which could be attributed to the newly formed outer surface prevents the internal gelation.To further confirm the structure and phase purity of the sphere-shaped MOFs,the PXRD patterns of the original powder and shaped sphere were collected and shown in Fig.S3.The diffraction peaks indicate that the structure of the four materials remained unchanged and exhibited high crystallinity.

Fig.2.SEM images obtained for the different MOFs powders and spheres:(a) Mggallate powder;(b) Mg-gallatespheres;(c) Co-gallate powder;(d) Co-gallate spheres;(e) MUV-10(Mn) powder;(f) MUV-10(Mn) spheres;(g) MIL-53(Al)powder;(h) MIL-53(Al) spheres.

SEM was conducted to elucidate the mechanism for the formation of the sphere-shaped MOFs.The SEM images shown in Fig.2 were used to compare the sphere-shaped MOFs and the original powder.It can be seen that a layer of amorphous material was tightly attached to the smooth surface of the MOFs crystals,indicating that the calcium alginate method successfully bonded the discrete microcrystals together to form a strong sphere-shaped adsorbent.

The thermal stability of the different sphere-shaped MOFs was investigated using TGA under a N2atmosphere.Fig.S4 shows the disintegration curves obtained for the sphere-shaped MOFs were similar to the original curves.All of the sphere-shaped MOFs exhibited approximately 5%-10% lower additional losses than the original powder due to the hydrophilic nature of sodium alginate.In addition,the decomposition temperatures for the Mg-gallate,Cogallate,MUV-10(Mn) and MIL-53(Al) powder and spheres were 550,450,500 and 450°C,respectively,demonstrating the thermal stability of the sphere-shaped MOFs was unchanged.Based on the above characteristics,we have selected the sphere-shaped MOFs with the highest mechanical strength which have a higher service life in the actual industry as the key research object.

3.2.Pure-component adsorption measurements and selectivity of MOFs spheres

The porosity and specific surface area of Mg-gallate and Cogallate were characterized using CO2adsorption-desorption experiments performed at 0 °C.Figs.S5(a) and (b) show that the trend in the adsorption curves observed for the two materials before and after shaping remained the same.The specific surface area of Mg-gallate and Co-gallate powder were calculated to be 349 and 265 m2·g-1,respectively,and the specific surface areas for the shaped spheres were 238 and 153 m2·g-1,respectively.The reduction in the specific surface area of the two shaped MOFs was calculated to be 31.81% and 42.26%,respectively.It was roughly speculated that the significant reduction in the surface areas of the Mg-gallate and Co-gallate spheres was attributed to the exposed calcium or chloride ions affect the active sites of Mg-gallate and Co-gallate for CO2adsorption,and the shaped sphere is denser,resulting in slower CO2diffusion rate and lower adsorption capacity.N2sorption experiments performed at -196 °C were used to compare the effect of MUV-10(Mn) and MIL-53(Al).Interestingly,Fig.S5(c)shows the specific surface area of MUV-10(Mn)changes from 549 to 503 m2·g-1.The H4hysteresis loop shown in the N2adsorption curves obtained for MUV-10(Mn)over a relative pressure range of 0.4-0.9 indicate the formation of mesopores during the shaping process,which is also the reason why the BET surface area of MUV-10(Mn) did not significantly change after shaping.We further conduct the pore size distribution calculation (Fig.S5(c) inset),the results indicated some newly formed mesopores (2.8,5.8,6.5,8.8 nmet al.) was generated during the shaping process,which could ascribe to the intercrystal pore.For MIL-53(Al),the BET surface area changed from 842 to 514 m2·g-1,which is a decrease of～38.95% (Fig.S5(d)).This may be attributed to the calcium alginate limiting the ‘‘breathing” of the original MOFs powder.

To evaluate the adsorption performance of the shaped spheres,the gas adsorption isotherms of the four materials toward C2H4and C2H6before and after shaping were systematically studied at 25°C and 100 kPa (Table S2).Fig.3(a)and (b)show that Mg-gallate and Co-gallate take up larger amounts of C2H4than of C2H6.For the powder samples,the C2H4adsorption capacity of Mg-gallate and Co-gallate were 66.87 and 73.21 cm3·g-1,respectively.The C2H4uptake of the Mg-gallate and Co-gallate spheres were 57.93 and 70.80 cm3·g-1,respectively.The adsorption capacity of C2H4for shaped spheres was slightly lower compared to powder sample,which shows that no obvious pore blockage has been caused by calcium alginate.The reason could attribute to the slower diffusion rate in denser shaped spheres,and results in a decrease in adsorption capacity of C2H4.While,the adsorption amounts of C2H6is almost unchanged because the large size C2H6is almost excluded by the pores of Mg-gallate and Co-gallate.The IAST selectivity in the case of the C2H4/C2H6(1/1,volume ratio) mixtures on Mggallate and Co-gallate spheres were calculated as 13.4 and 27.9 at 25 °C and 100 kPa (Fig.3(c)).

MUV-10(Mn) and MIL-53(Al) take up larger amounts of C2H6than C2H4(Fig.3(d) and (e)).If C2H6is preferentially adsorbed,the desired C2H4product can be directly recovered in the adsorption cycle.For pure MUV-10(Mn) powder,the C2H6and C2H4adsorption capacities are 52.80 and 45.12 cm3·g-1,respectively.After shaping,there was an increasing trend in the C2H6and C2H4adsorption capacities(58.60 and 51.22 cm3·g-1,respectively).This may be attributed to the mesopores produced in the sphereshaped MOFs (Fig.S5(c) inset) made the diffusion rate of C2H6and C2H4faster.Unfortunately,the performance of the MIL-53(Al)spheres was not maintained.The adsorption capacity was significantly reduced when compared with the powder sample and the C2H6uptake of MIL-53(Al)decreased from 86.25 to 63.76 cm3-·g-1,and the C2H4uptake decreased from 84.63 to 60.17 cm3·g-1,respectively.This may be attributed to the calcium alginate destroying the unique ‘‘breathing” of MIL-53(Al),which inhibited any structural changes.For MUV-10(Mn) and MIL-53(Al) spheres,which are ethane-selective adsorbents,the IAST selectivity in the situation of the C2H6/C2H4(1/9,volume ratio) mixtures were 1.4 and 1.8 at 25 °C and 100 kPa (Fig.3(f)).In short,these adsorption results show that the sphere-shaped MOFs produced using the calcium alginate method maintain their excellent adsorption capacity,with the exception of MIL-53(Al).

3.3.Breakthrough experiment and cycling performance

To evaluate the separation performance of the sphere-shaped MOFs produced using the calcium alginate method under industrial conditions,a fixed-bed breakthrough experiment was performed using C2H4/C2H6mixtures (1/1,volume ratio) and C2H6/C2H4mixtures (1/9,volume ratio) at 25 °C and 100 kPa,and a mixed gas flow rate of 5 ml·min-1(3 ml·min-1for MUV-10(Mn)).The breakthrough separation experiments were performed on a homemade instrument (Fig.S6).In order to clearly compare the separation effect of MOFs powder and spheres,we have filled the adsorption column with the same quality powder and particles.When compared with their powder samples,the four sphereshaped MOFs shortened the co-adsorption time to different degrees.Fig.4(a) shows that the experimental breakthrough curves obtained using Mg-gallate powder and spheres for the separation of a C2H4/C2H6mixtures (1/1,volume ratio) at 25 °C and 100 kPa.During the Mg-gallate spheres separation test,C2H6was detected after～3 min with high purity,and C2H4remained in the packed column until 43 min later,while the retention times for C2H6and C2H4using Mg-gallate powder were 5 and 50 min,respectively.This was because the gaps between the stacked shaped particles allowed the gas to breakthrough faster.Because Mg-gallate and Co-gallate have the same separation mechanism,a similar situation was observed for the Co-gallate powder and spheres.Fig.4(b) shows the retention times for C2H6and C2H4using the pure powder was 7 and 59 min,respectively,while the retention times for C2H6and C2H4using the Co-gallate spheres were 6 and 56 min,respectively.

Fig.4(c) shows that the experimental breakthrough curves obtained for MUV-10(Mn) powder and spheres using a C2H6/C2H4mixtures (1/9,volume ratio) at 25 °C and 100 kPa.Due to the formation of additional mesopores and the increased diffusion rate of the MUV-10(Mn)spheres after shaping,the breakthrough time for C2H4using the MUV-10(Mn) powder was shortened by 34% from 67 to 44 min.However,the separation time for MUV-10(Mn)powder and spheres was the same,which was 6 min,during which pure ethylene can be obtained.This is very beneficial for practical industrial applications.(Fig.4(d)) shows the separation curve obtained for MIL-53(Al) powder and spheres.The decreased coadsorption time due to the calcium alginate affecting the unique‘‘breathing” of MIL-53(Al).Although the adsorption capacity of C2H6/C2H4has decreased,the separation time of spheres and powder is the same (7 min) in the actual separation process.

Fig.3.The single-component adsorption isotherms of C2H4 and C2H6 obtained for different MOFs adsorbents at 25 °C:(a) Mg-gallate powder and spheres;(b) Co-gallate powder and spheres;(d)MUV-10(Mn)powder and spheres;(e)MIL-53(Al)powder and spheres and IAST selectivity for four sphere-shaped MOFs at 25°C:(c)C2H4/C2H6=1/1,(volume ratio);(f) C2H6/C2H4=1/9,(volume ratio).

Fig.4.Experimental breakthrough curves obtained for different adsorbents at 25 °C and 100 kPa:(a) Mg-gallate and (b) Co-gallate for C2H4/C2H6 mixtures (1/1,volume ratio);(c) MUV-10(Mn) and (d) MIL-53(Al) for C2H6/C2H4 mixtures (1/9,volume ratio)).

In addition,we calculated and compared the gas separation efficiency of the four adsorbents before and after shaping (Table S3).The results show that the four different sphere-shaped adsorbents have different degrees of improvement compared with the powders,this is industrially favorable due to the shortened coadsorption time and maintained separation time.Based on the integral area of the dynamic breakthrough curve (Fig.S7),the dynamic adsorption capacity and selectivity for C2H4and C2H6on the breakthrough experiments at 25°C and 100 kPa has been summarized in the Table S4.It shows that the dynamic selectivity of Mg-gallate sphere,Co-gallate sphere,MUV-10(Mn) sphere and MIL-53(Al) sphere is 10.27,13.12,1.23 and 1.32,respectively.The above shows that the four sphere-shaped MOFs have excellent separation performance of C2H4/C2H6mixtures and well maintain the separation performance of the original MOFs powder.

The good structural stability and renewability of the pellets were investigated and shown in Fig.5.Twenty cycles of the dynamic breakthrough test using the sphere-shaped MOFs were conducted after regeneration under the same operating conditions.The results shows that the MOFs spheres produced using the calcium alginate method can maintain their original separation performance.In addition,the quality of different MOFs was recorded before and after the twenty cycles of the dynamic breakthrough test (Table S5).It was found that the mass loss of the four sphere-shaped MOFs was less than 0.5%,indicating that the shaped particles have good erosion resistance.Thus,this method has great potential as a useful shaping method for the realization of MOFs industrial applications.

Fig.5.Twenty cycling column breakthrough curves obtained for the sphere-shaped MOFs conducted under the same conditions:(a) Mg-gallate spheres;(b) Co-gallate spheres;(c) MUV-10(Mn) spheres;(d) MIL-53(Al) spheres.

4.Conclusions

In summary,given the issues of shaping MOFs for commercial and industrial applications,we have reported a series of sphereshaped MOFs with high mechanical strength and wellmaintained gas separation performance prepared using the calcium alginate method with sodium alginate and CaCl2solution.These four water-stable MOFs (Mg-gallate,Co-gallate,MUV-10(Mn) and MIL-53(Al)) can be shaped into～2 mm spheres containing 90%(mass)MOFs with excellent mechanical strength and good separation performance similar to their original powders.We believe that shaping of MOFs is a crucial step toward the development of such materials to higher technology levels and their commercial application.The shaping method is general and promising as long as the MOFs has sufficient water stability in order to withstand the residence time in the water-rich slurry used in the process.An additional advantage is that the preparation of MOFs with various morphologies can be easily implemented on large scale.This work not only provides four shaped MOFs adsorbents with excellent C2H4/C2H6separation performance,but also gives some insight into the manageable measures used to shape MOFs materials into variable forms for real applications.

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.

Acknowledgements

We acknowledge the financial support from the National Natural Science Foundation of China (Nos.21908153,21922810 and 21878205).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2021.08.010.