A robust Th-azole framework for highly efficient purification of C2H4 from a C2H4/C2H2/C2H6 mixture

Separation of C2H4 from C2H4/C2H2/C2H6 mixture with high working capacity is still a challenging task. Herein, we deliberately design a Th-metal-organic framework (MOF) for highly efficient separation of C2H4 from a binary C2H6/C2H4 and ternary C2H4/C2H2/C2H6 mixture. The synthesized MOF Azole-Th-1 shows a UiO-66-type structure with fcu topology built on a Th6 secondary building unit and a tetrazole-based linker. Such noticeable structure, is connected by a N,O-donor ligand with high chemical stability. At 100 kPa and 298 K Azole-Th-1 performs excellent separation of C2H4 (purity > 99.9%) from not only a binary C2H6/C2H4 (1:9, v/v) mixture but also a ternary mixture of C2H6/C2H2/C2H4 (9:1:90, v/v/v), and the corresponding working capacity can reach up to 1.13 and 1.34 mmol g−1, respectively. The separation mechanism, as unveiled by the density functional theory calculation, is due to a stronger van der Waals interaction between ethane and the MOF skeleton.

within the pores), and the surface area accessible to a N2 probe using the coordinated found by X-ray crystallography. The Accelrys Materials Studio (MS) 8.0 software package 3,4,5 was used to visualize the MOF structure and pore topology.

Supplementary Methods 4. Calculation of isosteric heat of adsorption
The binding energy is reflected in the isosteric heat of adsorption, Qst, is calculated from the Clausius-Clapeyron equation, as shown in Supplementary Equation 1, where p is the pressure, T is the temperature, R is the gas constant (8.314 J mol -1 K -1 ). By drawing the ln p vs 1/T plot of gas at various loadings, Qst = -slope×R. To extract the coverage-dependent isosteric heat of adsorption, the data were modeled with a virial-type expression 6,7 composed of parameters ai and bi that are independent of temperature: where N is the amount adsorbed (or uptake), m and n determine the number of terms required to adequately describe the isotherm. The isosteric heat of adsorption is calculated according to Supplementary Equation 3.
The coverage dependencies of Qst calculated from fitting the 273 and 298 K data are presented graphically in Fig. 4d, and the virial equation fit for C2H6, C2H4, and C2H2 adsorption isotherms of Azole-Th-1 are shown in Supplementary Fig. 7.

Supplementary Methods 5. Calculation of selectivity via ideal adsorption solution theory (IAST)
The with T-dependent parameters b, where the single-site Langmuir parameters for C2H6, C2H4, and C2H2 are provided in Supplementary Tab. 4.

Supplementary
where, Ecomplex, Egas, and EMOF (model) are the total energies of complex of gas with model, single C2H6/C2H4 gas, and MOF model at the optimized geometries, respectively.

Grand Canonical Monte Carlo (GCMC) Simulations:
The GCMC simulations, which were performed by Sorption code 4, 11 in MS software 3, 4, 5 , were carried out to investigate on the adsorbed capacity of Azole-Th-1 for C2H6/C2H4 at 298 K from 0.001 to 100 kPa. A simulation box of 1×1×1 crystallographic unit cell was used. During the simulations, 4×10 6 steps were performed to guarantee the equilibration and to sample the desired properties, respectively. Rigid framework assumption was used in all simulations. The Dreiding forcefield parameter 12 was used to describe the interactions, the van der Waals interaction with a cutoff of 15.5 Å were depicted by Lenard-Jones 12-6 potential.

Supplementary Methods 7. Thermogravimetric analysis
Thermogravimetric analysis (TG) was performed by a TGA Q600 thermal analysis system. All TG experiments were performed under a N2 atmosphere from room temperature to 800 °C at a rate of 2 °C /min.

Supplementary Methods 8. Breakthrough curve simulations
The performance of industrial fixed bed adsorbers is dictated by a combination of adsorption selectivity and uptake capacity. Transient breakthrough simulations were carried out for 50/50, 90/10, and 15/1 binary C2H4(1)/C2H6(2) mixtures and 9/1/90 ternary C2H6/C2H2/C2H4 mixture in Azole-Th-1 operating at a total pressure of 100 kPa and 298 K, using the methodology described in earlier publications. 13,14,15,16 The   Supplementary Figure 5. The TG analysis. The as-synthesized Azole-Th-1 samples, and the samples soaked in methanol for three days and one day under N2 atmosphere by 2℃ per min of ramp rate. The loss of major trapped solvent DMF from Azole-Th-1 sample is before 75℃, the plateau region is descending slightly due to the incomplete loss of DMF molecules. And then, the plateau region is still not obvious for sample soaked in methanol one day, which indicates that the solvent exchange is still incomplete. After the sample soaked in methanol three days, the clear plateau region appears, the solvent exchange is complete. Source data are provided as a Source Data file.