Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2025 Dec 18;11(1):1236–1244. doi: 10.1021/acsomega.5c08532

Mechanochemical Synthesis of Cu(I)-MOF-74 for Improved Ethylene/Ethane Separation

Reza Pirdadeh Beiranvand 1, Saeed Ovaysi 1,*
PMCID: PMC12809307  PMID: 41552451

Abstract

A new metal–organic framework (MOF), i.e., Cu­(I)-MOF-74, is developed to selectively adsorb ethylene in ethylene-ethane gas mixtures. This new MOF is synthesized through the mechanochemical reaction between 2,5-dihydroxyterephthalic acid (DHTA) and cuprous oxide. The mechanochemical reactions between Cu2O and DHTA at various ratios are investigated to determine the exact stoichiometry of the reaction. Using the XRD patterns of the synthesized MOF, we identified a 2:1 molar ratio of Cu2O/DHTA as the correct reaction stoichiometry. The synthesized Cu­(I)-MOF-74 is stable up to 163 °C as evidenced by its thermogravimetric analysis, and has a 1371 m2/g BET surface area. Also, the adsorption isotherms of ethylene and ethane on this MOF are measured at 278, 298, 313, and 353 K. Finally, the isosteric heats of adsorption of ethylene and ethane on Cu­(I)-MOF-74 are calculated, and using the ideal adsorption solution theory (IAST), adsorption selectivities at the four above-mentioned temperatures are calculated.

graphic file with name ao5c08532_0013.jpg

graphic file with name ao5c08532_0011.jpg

Introduction

Recovery of ethylene from the off-gas stream in polyethylene manufacturing plants is imperative to avert waste. This off-gas stream is mainly composed of ethylene, ethane, butene, hexane, H2, N2, and TEA. However, ethylene and ethane are the primary components and constitute more than 80% of the off-gas stream. The investigation of ethylene recovery from its mixtures with ethane is also relevant due to its other industrial applications, the challenges associated with the similar properties of ethylene and ethane, and the potential for enhanced selectivity using advanced materials. Ethylene-ethane separation typically necessitates energy-intensive techniques such as distillation and cryogenic extraction, with the aim of yielding a polymer-grade output. When it comes to distillation, a substantial number of trays and elevated reflux rates are indispensable, and the process must be performed at exceedingly low temperatures and high pressures. Using a distillation column with over 100 trays that operates at −25 °C and 25 bar pressure is necessary to separate ethylene-ethane mixtures. Additionally, for small-scale and on-site operations, cryogenic distillation is not an economic option. Among the two alternative methods of adsorption and absorption, physical adsorption-based separation using microporous materials is widely recognized as a promising choice, mainly due to low energy consumption and high-purity gas separations under mild conditions. Metal–organic frameworks (MOFs) are an attractive class of porous materials characterized by design versatility, tunable pore size, remarkable thermal and chemical stability, and high surface area. MOFs are selectively employed as promising agents for drug delivery, − catalysis, , and gas separation and storage. −

So far, several types of MOFs have been synthesized using solvothermal methods. However, due to their lack of scalability and negative environmental impacts, solvothermal methods are not the preferred method for MOF production on an industrial scale. In contrast, MOFs can be produced on an industrial scale, using mechanochemical methods. , This approach involves conducting a chemical reaction through ball milling, either with or without a small quantity of solvent. , Furthermore, the challenges associated with conventional methods, such as low space-time yield, prolonged reaction time, and the requirement for substantial amounts of costly solvents, are effectively addressed by employing this technique. Consequently, this method is recognized as a scalable and environmentally friendly alternative to more common solvothermal methods. It is worth noting that ball milling enables the quantitative production of high-quality MOFs with specific surfaces comparable to those prepared through conventional means. , The mechanochemical synthesis of various MOFs, including ZIFs, MOF-5, MIL-100, MOF-74, , HKUST-1, and UiO-66, is previously documented. Among them, MOF-74 is prepared in the presence of various solvents, such as DMF, water, THF, and methanol. ,, However, owing to its distinctive properties and advantages over other solvents, which yields an MOF-74 with the highest achievable BET surface area, DMF is the preferred solvent in the mechanochemical synthesis of MOF-74.

So far, MOF-74 has been synthesized utilizing various metal sites, including Co, Mg, Fe, Ni, and Cu (II). Also, it is understood that Co-MOF-74 and Zn-MOF-74 have the maximum and minimum adsorption capacities, respectively. − However, when it comes to the choice of metal site for MOF-74, the relevant adsorption mechanism plays a significant role. Among the various mechanisms of adsorption, π complexation promises more efficient ethylene-ethane separations. Copper­(I) and Ag (I) ions can form π complexes with the carbon–carbon double bonds of olefin molecules. Moreover, the lower desorption energy for the copper­(I) π complex with the ethylene molecule (79.9 kJ/mol), compared to that for silver in silver zeolite A (95 kJ/mol) and PAF-1-SO3Ag (106 kJ/mol), highlights a less severe temperature or pressure swing desorption if a copper­(I) π complex is utilized. Therefore, using copper­(I) metal in MOF-74 is desirable to effectively recover and purify ethylene from ethylene-ethane mixtures. Thus far, the synthesis of this type of MOF, i.e., Cu­(I)-MOF-74, has not been reported in the literature.

This study focuses on the mechanochemical synthesis of Cu-MOF-74 using copper­(I) oxide, looking into key parameters, such as milling time, ball-to-powder ratio, milling speed, and the presence or absence of an assistant liquid. XRD and TGA analyses are conducted to ensure the accuracy of the synthesis and to determine the thermal stability of the synthesized framework. Also, BET analysis is utilized to calculate the specific surface area and pore volume. Additionally, the synthesized samples are subjected to ethylene and ethane adsorption isotherm measurements at 278, 298, 313, and 353 K using the volumetric method. This helps one better understand the adsorption selectivity of Cu­(I)-MOF-74 synthesized in this study for ethylene and ethane gases.

Experimental Section

Materials

Anhydrous copper­(I) oxide (Cu2O, ≥99.99%) and anhydrous N,N-dimethylformamide (DMF, 99.8%) were provided by Sigma-Aldrich and used without further purification. Anhydrous 2,5-dihydroxyterephthalic acid (DHTA, >83%) was synthesized using the procedure published in our previous study.

Synthesis of Cu­(I)-MOF-74

The mechanochemical synthesis of Cu­(I)-MOF-74 was carried out using a ball-mill apparatus assembled in the petroleum research laboratory. It is important to note that the milling was performed by using stainless steel balls in a glass container. A TZS 8808 electromotor made by the Aqualife brand provides the power, enabling the reaction chamber to rotate at a constant speed of 6.6 Hz (396 rpm). This rotation speed is maintained throughout the synthesis of all samples. The rotation speed and the weight and number of the balls utilized are the key parameters impacting the reaction speed in mechanochemical processes.

Table reports the reaction conditions for the mechanochemical synthesis of Cu­(I)-MOF-74 under four different scenarios in this study. A fixed ball-to-powder weight ratio of 10:1 is used throughout all the runs to ensure optimal activation energy, grinding efficiency, and uniformity. Three different Cu2O/ligand ratios of 1:1, 2:1, and 4:1 are used to investigate the actual stoichiometry of the reaction. The parameter η (solvent-to-reactants ratio in μL/mg) is kept between 0 and 1 in all but one run. Liquid DMF is chosen as the solvent in this study to enhance the efficiency and quality of the grinding process as well as to minimize heat loss during the mechanochemical synthesis. , Also, using this solvent facilitates the industrial-scale production of the MOF synthesized in the present study.

1. Materials and Reaction Conditions for the Synthesis of Cu­(I)-MOF-74.

run no. Cu2O/ligand ratio DHTA g (mmol) Cu2O g (mmol) DMF μL η μL/mg weight of balls g no. of balls reaction time h
1 1:1 0.5117 (2.5826) 0.3708 (2.5914) 610 0.6912 8.78 20 8
2 2:1 0.5083 (2.5655) 0.7211 (5.0395) 760 0.6182 12.25 28 4.5
3 4:1 0.2216 (1.1185) 0.6355 (4.4413) 550 0.6417 8.75 20 8
4 2:1 0.5032 (2.5397) 0.7269 (5.08) 0 0 12.27 28 8
Open in a new tab

Characterization Methods

The synthesized Cu­(I)-MOF-74 is characterized using both X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The XRD analysis is conducted at room temperature using a monochromatized Cu–Kα1 (λ = 1.54056 Å) STOE STADIP MODEL apparatus at a 40 kV voltage and 30 mA current. The spectra of the analyzed samples are measured in the range of 0° to 120° with a step size of 0.02. The TGA is carried out using a 2-star Mettler Toledo instrument to investigate the degradation process of the synthesized sample at 25–600 °C. The N2 adsorption isotherm (up to P/P 0 = 1 and 77 K) is measured with a BELSORP mini II device after activation employing the BELPREP VAC II instrument at 120 °C and 10–3 bar for 2 h. The Brunauer–Emmett–Teller (BET) and t-plot surface area and micropore volume of the samples are calculated based on the N2 adsorption isotherm.

Ethylene/Ethane Adsorption Isotherm Measurements

Before conducting the isotherm measurements, the adsorbent samples are subjected to degassing at 120 °C for 6 h under vacuum in a separate column. Also, each experiment starts by measuring the equilibrium adsorption of ethylene and ethane via highly accurate Brooks mass flow controllers (MFCs) using the adsorption setup shown in Figure , without loading any adsorbent into the adsorption cell. Once these baseline measurements are established, 100 mg of the Cu­(I)-MOF-74 is introduced into the vessel, and subsequent measurements of the gas quantities, as described below, are conducted. The differences between these two sets of values clearly indicate the adsorption capacities. The adsorption process is started by first closing valves V-1 and V-3, opening valve V-2, and activating the vacuum pump to remove residual gases within the adsorption cell. Following this, based on the test gas used, either MFC-1 or MFC-2 is opened to allow gas injection into the adsorption cell via valve V-1 while keeping valves V-2 and V-3 closed. The above-mentioned MFCs regulate the gas injection rate until a preset equilibrium pressure is achieved in the adsorption cell. The MFC-reported cumulative masses of the injected gases are used to calculate the equilibrium amount of ethylene and ethane adsorbed per unit mass of adsorbent (q e in mmol/g). This process is repeated at various pressures within 1 × 10–3-1.013 bar for each of the four 278, 298, 313, and 353 K temperatures. It has to be mentioned that the isothermal conditions of the adsorption cell are maintained by circulating an ethylene glycol solution. Furthermore, the precision of the pressure and temperature measurements is 0.001 bar and 0.1 K, respectively.

1.

1

Open in a new tab

Volumetric adsorption laboratory setup.

Results and Discussion

Characteristics and X-ray Diffraction (XRD) Analysis of Cu­(I)-MOF-74

Figure shows the colors and the XRD spectra of the various synthesized samples according to runs 1–4 in Table . Comparing the XRD spectra of the simulated Cu­(I)-MOF-74 with those of other samples, it becomes evident that run number 2, with a Cu2O/DHTA ratio of 2:1, follows the correct reaction stoichiometry. Judging by the XRD spectra of Cu2O and DHTA shown in this figure, it is concluded that runs 1 and 3 end up with an excess of DHTA and Cu2O, respectively, in the reaction products. Furthermore, it is concluded that neat grinding in the absence of the DMF solvent in run 4 does not yield any MOF at all. To ensure this, the ball milling was allowed to continue up to 8 h in run 4. However, as evidenced in the XRD spectrum of the reaction products from run 4, in the absence of a solvent, no chemical reaction takes place. It has to be stressed that the mechanochemical synthesis of Cu­(I)-MOF-74 during run 2 completed in 4.5 h, as noticed by the color change of the reaction products from red to light green. For the other three runs, almost no color change was observed. Therefore, the ball milling was allowed to continue up to 8 h.

2.

2

Open in a new tab

Color and X-ray diffraction measurements of the Cu­(I)-MOF-74 samples.

Since the reaction conditions of run 2 followed the correct stoichiometry as well as the appropriate amount of DMF solvent, those conditions were repeated during several more runs to synthesize enough Cu­(I)-MOF-74 for the additional tests elaborated in the following sections. The light-green Cu­(I)-MOF-74 powder is obtained after drying at 160 °C and atmospheric pressure for 3 h.

It has to be noted that Cu2O is moderately sensitive to air under normal conditions and gradually converts to CuO in the presence of O2 or H2O. The conversion rate depends on temperature, partial pressure of oxygen, and particle size. Since CuO is not sensitive to atmospheric oxygen and moisture, water is commonly used as a solvent to assist the milling process in the mechanochemical synthesis of Cu­(II)-MOF-74, which uses CuO as a reactant. However, in this study, atmospheric oxygen and moisture can contaminate the end product by converting Cu2O to CuO. To prevent this conversion, we performed the mechanochemical synthesis in a sealed jar. Additionally, DMF was employed as the solvent to coat the reactants and limit the availability of atmospheric oxygen and moisture trapped in the jar.

Furthermore, an XRD test would help determine the presence of impurities caused by Cu2O to CuO conversion. As shown in Figure , small amounts of CuO are seen at 35.5°, 39°, and 49°. However, the quantity of CuO in the final product is negligible and does not cause any significant change in the structure of the synthesized Cu­(I)-MOF-74.

Thermal Properties

To investigate the degradation process of the synthesized framework, 14.3941 mg of the Cu­(I)-MOF-74 sample synthesized in this study is heated under a nitrogen atmosphere at a rate of 5 °C/min by the ramp method. Conferring Figure , the first weight loss of ∼12.7473% occurs between 70 to 130 °C. This weight loss can be attributed to the evaporation of any moisture or the assisted liquid (DMF) that is trapped in the framework. The sample maintains its stability against temperatures up to 163 °C and then starts to lose 58.4435% of its weight from 163 to 380 °C. This weight loss is caused by the decomposition of the framework. No more weight losses are observed from 380 to 600 °C. Therefore, any process employing Cu­(I)-MOF-74 should not exceed 163 °C.

3.

3

Open in a new tab

Thermogravimetric analysis of the 2:1 sample.

BET Surface Area and Pore Volume

Figure shows the nitrogen adsorption at 77 K of the synthesized Cu­(I)-MOF-74. As shown, the adsorption process starts rapidly to reach near equilibrium at P/P 0 = 0.15. By increasing the relative pressure to 0.65, the rate of nitrogen adsorption rises gradually. Furthermore, a quick rise in nitrogen adsorption takes place at higher pressures close to the nitrogen saturation point. Looking at the desorption pattern, it is evident that no hysteresis takes place, highlighting the uniform pore structure of the synthesized MOF. The BET and t-plot methods calculate 1371.83 and 1368.9 m2/g for the specific surface area of the synthesized Cu­(I)-MOF-74, respectively. Furthermore, the calculated micropore volume is 0.4898 cm3/g.

4.

4

Open in a new tab

N2 adsorption at 77 K in Cu­(I)-MOF-74.

Figure displays a comparison of the BET surface areas of some recently synthesized MOFs. As shown, using cuprous oxide to synthesize Cu­(I)-MOF-74 in this study yields a high specific surface area, i.e., 1370 m2/g. In contrast, the Cu­(II)-MOF-74 synthesized in previous studies via solvothermal methods using cupric oxide achieves a lower specific surface area, i.e., approximately 1100 m2/g.

5.

5

Open in a new tab

BET surface area comparison of recently synthesized MOFs. References: NUS-36 and UiO-66-ADC, Na-ETS-10, Cu@UiO-66-(COOH)2, UTSA-280, M-gallate (M = Ni, Co, Mg), Zeolite 5A, PAF-1-SO3Ag, M-MOF-74 (M = Co, Ni, Cu, Mg, Zn), ZnAtzPO4 h and 1.6AgM-DS and Fe-MOF-74 and HKUST-1 and NOTT-300 and (Cr)-MIL-101-SO3Ag.

Ethylene and Ethane Adsorption Isotherms

The adsorption isotherms of ethylene and ethane on the synthesized Cu­(I)-MOF-74 at temperatures of 278, 298, 313, and 353 K are illustrated in Figure . As shown, the adsorption capacities increase/decrease by increasing pressure/temperature. Thus, the maximum adsorption capacities occur at 278 K and 101,325 Pa. For ethylene and ethane, these maximum adsorption capacities stand at 7.34 and 5.26 mmol/g, respectively. Clearly, these numbers decrease by increasing temperature and decreasing pressure. However, compared to ethane, ethylene tends to adsorb more easily on Cu­(I)-MOF-74.

6.

6

Open in a new tab

Single-component adsorption isotherms of ethylene and ethane at temperatures of 278, 298, 313, and 353 K on Cu­(I)-MOF-74. The reference pressure in the horizontal axis is the atmospheric pressure, i.e., P 0 = 101.325 KPa.

Isotherms Fittings Comparison

The experimentally obtained adsorption isotherms in this study were used to estimate the parameters of three adsorption models, i.e., the Langmuir, Sips, and Toth modes, which are represented by eqs through , respectively.

n=abP1+bP 1
n=a(bP)1/t1+(bP)1/t 2
n=abP[1+(bP)t]1/t 3

where n is the adsorbed amount (loading), and a, b, and t denote the maximum uptake capacity (mmol/g), the model’s constant, and the heterogeneity parameter, respectively. The closer the heterogeneity parameter is to unity, the more homogeneous the pore size distribution within the adsorbent.

The regression results are listed in Table . As shown by the correlation coefficients, all the three models fit the experimental data well. In other words, the Sips and Toth models perform only slightly better than the Langmuir model. Thus, it is fair to state that the adsorption of either ethylene or ethane on Cu­(I)-MOF-74 follows a monolayer pattern, as suggested by Langmuir.

2. Sips, Toth, and Langmuir Isotherm Parameters of Ethylene/Ethane Adsorption on Cu­(I)-MOF-74.

    Sips parameters
 Toth parameters
 Langmuir parameters
gas temperature (K) a b t R 2 a b t R 2 a b R 2
ethylene 278 9.3340 0.0427 1.1571 0.9998 10.0188 0.06473 0.7234 0.9999 8.3828 0.0564 0.9985
298 9.2549 0.0191 1.0259 0.9998 9.2767 0.0203 0.9556 0.9998 8.9656 0.0205 0.9998
313 8.7134 0.0124 1.0092 0.9996 8.1586 0.0132 1.0560 0.9996 8.5745 0.0128 0.9996
353 6.2654 0.0048 1.0810 0.9999 9.3185 0.0046 0.6617 0.9999 4.8709 0.0076 0.9997
ethane 278 6.6864 0.0427 1.1571 0.9998 7.1770 0.0647 0.7234 0.9999 6.0050 0.0564 0.9985
298 5.2596 0.0191 1.0259 0.9998 5.2724 0.0203 0.9555 0.9998 5.0952 0.0205 0.9998
313 4.3380 0.0124 1.0091 0.9996 4.0623 0.0132 1.0558 0.9996 4.2689 0.0128 0.9996
353 3.6804 0.0051 1.0219 0.9999 4.0638 0.0050 0.8895 0.9999 3.4073 0.0058 0.9999
Open in a new tab

Isosteric Heat of Adsorption and Selectivity

The amount of heat released when the adsorbate molecules bind to the solid surface of the adsorbent is known as the isosteric heat of adsorption. In this study, the Clausius–Clapeyron approach is used to calculate the isosteric heats of adsorption of ethylene and ethane on the synthesized Cu­(I)-MOF-74. Using this approach, the adsorption pressures on two different isotherms for the same loadings are inserted in eq to calculate the isosteric heat of adsorption, denoted by ΔH ads.

ΔHads(n)=−Rln(p2p1)T1·T2(T2−T1) 4

where R is the universal gas constant.

The Sips model with the parameters reported in Table was used to calculate adsorption pressures p 1 and p 2 on two different isotherms for the same amount of loading. Generally, the isosteric heat of adsorption decreases by increasing the loading, reaching the latent heat of vaporization of the adsorbate at the limit of infinite loading. Therefore, the ratio of the isosteric heat of adsorption to the latent heat of vaporization for any specific adsorbate scales its affinity with the adsorbent. Figure illustrates the variation of the above-mentioned ratio with loading for the adsorption of ethylene and ethane on synthesized Cu­(I)-MOF-74. Using the thermophysical data from NIST and Watson’s equation, the heats of vaporization for ethylene and ethane at 278 K were estimated to be 3.978 and 8.345 KJ/g mol, respectively. It has to be mentioned that the isosteric heats of adsorption in this figure are calculated using the adsorption isotherms at 278 and 298 K. This makes the figure valid only within the 278–298 K range.

7.

7

Open in a new tab

Variation of the isosteric heat of adsorption to the latent heat of vaporization at a 278 K ratio for ethylene and ethane adsorption on the synthesized Cu­(I)-MOF-74.

As shown in Figure , during the initial stages of adsorption, ethylene and ethane molecules preferentially bind to the most active and high-energy adsorption sites on the MOF surface. These sites, characterized by strong interaction energies, result in a higher release of adsorption heat. As these primary sites become occupied, molecules begin to adsorb onto weaker sites with lower interaction energies, leading to a decrease in the isosteric heat of adsorption. As discussed in the previous section, the Langmuir isotherm provides an adequate fit to the adsorption data. Therefore, as loading increases, more and more active sites of the MOF get occupied by either ethylene or ethane molecules in a monolayer pattern.

Comparing the ratios of isosteric heat of adsorption to heat of vaporization for ethylene and ethane, it is concluded that the Cu­(I)-MOF-74 developed in this study has a higher affinity for ethylene than for ethane. This could be related to the π-complexes formed between the delocalized π-electrons of ethylene and Cu­(I) atoms. To better understand this and to better measure this affinity, the ideal adsorption solution theory (IAST) was used to compute the selectivity of Cu­(I)-MOF-74 to preferentially adsorb ethylene in a 50–50 mol % as well as a 10–90 mol % gas mixture of ethylene and ethane (c.f. Figures and ). The selectivities are defined by eq

S=xC2=xC2yC2=yC2 5

where x and y represent the mole fractions in the adsorbed solid phase and gas phase, respectively.

8.

8

Open in a new tab

Variation of the Cu­(I)-MOF-74 selectivity with temperature and pressure to preferentially adsorb ethylene in a 50–50 mol % gas mixture of ethylene and ethane.

9.

9

Open in a new tab

Variation of the Cu­(I)-MOF-74 selectivity with temperature and pressure to preferentially adsorb ethylene in a 10–90 mol % gas mixture of ethylene and ethane.

As shown in Figure , for a 50–50 mol % gas mixture of ethylene and ethane, at very low pressures, the selectivities increase with temperature to reach a peak of 2.01 at 313 K. This means that the amount of ethylene adsorbed at 313 K is more than twice that of ethane. Beyond this temperature, selectivities drop by increasing temperature, although this drop in selectivity is sharper at higher pressures.

Figure illustrates the variation of Cu­(I)-MOF-74 selectivity for a 10–90 mol % ethylene-ethane gas mixture at various temperatures and pressures. Compared to 50–50 mol %, the impact of pressure on selectivity is much more pronounced for a 10–90 mol % mixture. Additionally, at pressures equal to and greater than 50 kPa, selectivities tend to decrease rather sharply by increasing temperature. While at pressures lower than 5 kPa, selectivities start at a low value around 2 and by increasing temperature, after reaching a minimum, tend to increase. This increase in selectivity is sharper at very low pressures, i.e., 0.1 kPa. Overall, Cu­(I)-MOF-74 performs much better to separate ethylene-ethane gas mixtures at lower ethylene concentrations, as evidenced by the higher selectivities in a 10–90 mol % mixture compared to those for a 50–50 mol % mixture, i.e., Figures and . It has to be stressed that higher pressures have a very positive impact on selectivities for low-concentration ethylene-ethane mixtures.

Comparison of Cu­(I)-MOF-74 with Other Adsorbents

The Cu­(I)-MOF-74 adsorbent can be stored and utilized indefinitely under a nitrogen atmosphere without experiencing decomposition, side reactions, or oxidation. However, when stored under ambient conditions, it remains stable for up to 1 week. Additionally, the storage temperature should not exceed 163 °C, as this is the onset temperature for degradation. According to Figure , the ethylene adsorption capacity of Cu­(I)-MOF-74 is significantly higher than that of Cu­(II)-MOF-74. This may be due to the presence of more accessible copper sites for ethylene adsorption via π-complexation, which improves the formation of coordination bonds between copper and ethylene sites for improved adsorption. Furthermore, π-complexation plays a major role in the favorable selectivities achieved for ethylene adsorption. However, further investigation and analyses are needed to confirm this.

10.

10

Open in a new tab

Comparison of the ethylene and ethane uptake in this study with those in previous studies. References: AgNO3, Na-ETS-10, Zeolite 5A and 13X, M-MOF-74 (M = Co, Ni, Cu, Mg, Zn), CuBTC and zeolite 13X, UTSA-280, Co-gallate, Cu­(I)-MFU-4l. The missing ethane adsorption data for certain adsorbents are due to unavailable data.

Conclusions

In this study, a new adsorbent, i.e., Cu­(I)-MOF-74, was synthesized using a mechanochemical process. The synthesized Cu­(I)-MOF-74 was then analyzed using TGA to determine the onset temperature of its decomposition at 163 °C which is far above the desired temperature for industrial ethylene purification processes using adsorption. Comparing the XRD analysis of the synthesized MOF with that of the simulated Cu­(I)-MOF-74 confirmed the correct reaction stoichiometry and synthesis process. Also, the synthesized MOF has a BET surface area equal to 1371 m2/g, which is a relatively high number. Additionally, the ethylene and ethane adsorption isotherms at 278, 298, 313, and 353 K were measured by using an experimental setup explained earlier. These isotherms were then fitted to the Langmuir, Sips, and Toth models to obtain their parameters. A good fit of the experimental adsorption data to the Langmuir model suggests a monolayer adsorption mechanism for both ethylene and ethane under the conditions studied in this research. The Sips model was then used to calculate the isosteric heats of adsorption for both ethylene and ethane. Comparing the ratio of isosteric heats of adsorption to the latent heats of vaporization suggests that ethylene has more affinity for Cu­(I)-MOF-74. Further confirmation of this is achieved through the calculation of ethylene versus ethane adsorption selectivities using the idealized adsorption solution theory. This theory is utilized to calculate the aforementioned selectivities when either a 50–50 or a 10–90 mol % gas mixture of ethylene and ethane is exposed to the Cu­(I)-MOF-74.

In summary, the synthesized Cu­(I)-MOF-74 proves to be a reliable adsorbent to selectively adsorb ethylene in gas mixtures, especially for the waste gas streams of HDPE plants utilizing slurry reactors, thus minimizing flaring and at the same time improving the economics of HDPE production. Additionally, given its mechanochemical means of synthesis, industrial production of Cu­(I)-MOF-74 is both straightforward and eco-friendly.

Acknowledgments

Kermanshah Polymer Company provided the laboratory and equipment support for this research. Their support is gratefully acknowledged.

The authors confirm that the data supporting the findings of this research are available throughout the article.

The authors declare no competing financial interest.

References

  1. Wang C., Yan J., Ma Z., Wang Z.. Highly efficient separation of ethylene/ethane in microenvironment-modulated microporous polymers. Sep. Purif. Technol. 2022;287:120580. doi: 10.1016/j.seppur.2022.120580. [DOI] [Google Scholar]
  2. Jin F., Lin E., Wang T., Geng S., Wang T., Liu W., Xiong F., Wang Z., Chen Y., Cheng P., Zhang Z.. Bottom-Up Synthesis of 8-Connected Three-Dimensional Covalent Organic Frameworks for Highly Efficient Ethylene/Ethane Separation. J. Am. Chem. Soc. 2022;114(12):5643–5652. doi: 10.1021/jacs.2c01058. [DOI] [PubMed] [Google Scholar]
  3. Anwar F., Khaleel M., Wang K., Karanikolos G. N. K.. Selectivity Tuning of Adsorbents for Ethane/Ethylene Separation: A Review. Ind. Eng. Chem. Res. 2022;61(34):12269–12293. doi: 10.1021/acs.iecr.2c02438. [DOI] [Google Scholar]
  4. Zhang L., Li L., Hu E., Yang L., Shao K., Yao L., Jiang K., Cui Y., Yang Y., Li B., Chen B., Qian G.. Boosting Ethylene/Ethane Separation within Copper­(I)-Chelated Metal–Organic Frameworks through Tailor-Made Aperture and Specific π-Complexation. Adv. Sci. 2020;7(2):1901918. doi: 10.1002/advs.201901918. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Xie W., Yang L., Zhang J., Zhao X.. The Adsorptive Separation of Ethylene from C2 Hydrocarbons by Metal-Organic Frameworks. Chem.Eur. J. 2023;29(30):e202300158. doi: 10.1002/chem.202300158. [DOI] [PubMed] [Google Scholar]
  6. Yang R. T., Kikkinides E. S.. New sorbents for olefin/paraffin separations by adsorption via π -complexation. AIChE J. 1995;41(3):509–517. doi: 10.1002/aic.690410309. [DOI] [Google Scholar]
  7. Kerry, F. G. Industrial Gas Handbook: Gas Separation and Purification, 1st ed.; Taylor & Francis Group: Boca Raton, 2007; Vol. 1. [Google Scholar]
  8. Wang Y., Peh S. B., Zhao D.. Alternatives to Cryogenic Distillation: Advanced Porous Materials in Adsorptive Light Olefin/Paraffin Separations. Small. 2019;15(25):1900058. doi: 10.1002/smll.201900058. [DOI] [PubMed] [Google Scholar]
  9. Abd A. A., Naji S. Z., Hashim A. S., Othman M. R.. Carbon dioxide removal through physical adsorption using carbonaceous and non-carbonaceous adsorbents: A review. Journal of Environmental Chemical Engineering. 2020;8(5):104142. doi: 10.1016/j.jece.2020.104142. [DOI] [Google Scholar]
  10. Bloch E. D., Queen W. L., Krishna R., Zadrozny J. M., Brown C. M., Long J. R.. Hydrocarbon Separations in a Metal-Organic Framework with Open Iron­(II) Coordination Sites. Science. 2012;335(6076):1606–1610. doi: 10.1126/science.1217544. [DOI] [PubMed] [Google Scholar]
  11. Baamran K., Newport K., Rownaghi A. A., Rezaei F.. Development and assessment of magnetic Fe2O3@MOF-74 composite sorbents for ethylene/ethane separation. Chem. Eng. J. 2023;451:139006. doi: 10.1016/j.cej.2022.139006. [DOI] [Google Scholar]
  12. Jiang H., Su W., Liu J., Sun Y.. Guest-Induced Mutation of a Local Coordinative Structure in M-Gallate Metal–Organic Frameworks for Selective Adsorption of Ethylene from Ethane. ACS Applied Nano Materials. 2023;6(11):9639–9648. doi: 10.1021/acsanm.3c01331. [DOI] [Google Scholar]
  13. Jeyaseelan C., Jain P., Soin D., Gupta D.. Metal organic frameworks: an effective application in drug delivery systems. Inorg. Nano-Met. Chem. 2022;52(12):1463–1475. doi: 10.1080/24701556.2021.1956966. [DOI] [Google Scholar]
  14. Yang J., Yang Y.-W.. Metal–Organic Frameworks for Biomedical Applications. Small. 2020;16(10):1906846. doi: 10.1002/smll.201906846. [DOI] [PubMed] [Google Scholar]
  15. Lee J., Farha O. K., Roberts J., Scheidt K. A., Nguyen S. T., Hupp J. T.. Metal–organic framework materials as catalysts. Chem. Soc. Rev. 2009;38(5):1450–1459. doi: 10.1039/b807080f. [DOI] [PubMed] [Google Scholar]
  16. Liu J., Chen L., Cui H., Zhang J., Zhang L., Su C.-Y.. Applications of metal–organic frameworks in heterogeneous supramolecular catalysis. Chem. Soc. Rev. 2014;43(16):6011–6061. doi: 10.1039/C4CS00094C. [DOI] [PubMed] [Google Scholar]
  17. Herm Z. R., Bloch E. D., Long J. R.. Hydrocarbon Separations in Metal–Organic Frameworks. Chem. Mater. 2014;26(1):323–338. doi: 10.1021/cm402897c. [DOI] [Google Scholar]
  18. Cui W.-G., Hu T.-L., Bu X.-H.. Metal–Organic Framework Materials for the Separation and Purification of Light Hydrocarbons. Adv. Mater. 2020;32(3):1806445. doi: 10.1002/adma.201806445. [DOI] [PubMed] [Google Scholar]
  19. Li J.-R., Kuppler R. J., Zhou H.-C.. Selective gas adsorption and separation in metal–organic frameworks. Chem. Soc. Rev. 2009;38(5):1477–1504. doi: 10.1039/b802426j. [DOI] [PubMed] [Google Scholar]
  20. Beamish-Cook J., Shankland K., Murray C. A., Vaqueiro P.. Insights into the Mechanochemical Synthesis of MOF-74. Cryst. Growth Des. 2021;21(5):3047–3055. doi: 10.1021/acs.cgd.1c00213. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Rubio-Martinez M., Avci-Camur C., Thornton A. W., Imaz I., Maspoch D., Hill M. R.. New synthetic routes towards MOF production at scale. Chem. Soc. Rev. 2017;46(11):3453–3480. doi: 10.1039/C7CS00109F. [DOI] [PubMed] [Google Scholar]
  22. Do J.-L., Friščić T.. Mechanochemistry: A Force of Synthesis. ACS Central Science. 2017;3(1):13–19. doi: 10.1021/acscentsci.6b00277. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Das A. K., Vemuri R. S., Kutnyakov I., McGrail B. P., Motkuri R. K.. An Efficient Synthesis Strategy for Metal-Organic Frameworks: Dry-Gel Synthesis of MOF-74 Framework with High Yield and Improved Performance. Sci. Rep. 2016;6(1):28050. doi: 10.1038/srep28050. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Czaja, A. ; Leung, E. ; Trukhan, N. ; Müller, U. . Metal-Organic Frameworks. In Industrial MOF Synthesis; Wiley Online Books, 2011; pp 337–352. [Google Scholar]
  25. Chen D., Zhao J., Zhang P., Dai S.. Mechanochemical synthesis of metal–organic frameworks. Polyhedron. 2019;162:59–64. doi: 10.1016/j.poly.2019.01.024. [DOI] [Google Scholar]
  26. Klimakow M., Klobes P., Thünemann A. F., Rademann K., Emmerling F.. Mechanochemical Synthesis of Metal–Organic Frameworks: A Fast and Facile Approach toward Quantitative Yields and High Specific Surface Areas. Chem. Mater. 2010;22(18):5216–5221. doi: 10.1021/cm1012119. [DOI] [Google Scholar]
  27. Užarević K., Wang T. C., Moon S.-Y., Fidelli A. M., Hupp J. T., Farha O. K., Friščić T.. Mechanochemical and solvent-free assembly of zirconium-based metal–organic frameworks. Chem. Commun. 2016;52(10):2133–2136. doi: 10.1039/C5CC08972G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Lee Y.-R., Jang M.-S., Cho H.-Y., Kwon H.-J., Kim S., Ahn W.-S.. ZIF-8: A comparison of synthesis methods. Chemical Engineering Journal. 2015;271:276–280. doi: 10.1016/j.cej.2015.02.094. [DOI] [Google Scholar]
  29. Szczęśniak B., Borysiuk S., Choma J., Jaroniec M.. Mechanochemical synthesis of highly porous materials. Materials Horizons. 2020;7(6):1457–1473. doi: 10.1039/D0MH00081G. [DOI] [Google Scholar]
  30. Wang Z., Li Z., Ng M., Milner P. J.. Rapid mechanochemical synthesis of metal–organic frameworks using exogenous organic base. Dalton Transactions. 2020;49(45):16238–16244. doi: 10.1039/D0DT01240H. [DOI] [PubMed] [Google Scholar]
  31. Liu P., Zhao T., Cai K., Chen P., Liu F., Tao D.-J.. Rapid mechanochemical construction of HKUST-1 with enhancing water stability by hybrid ligands assembly strategy for efficient adsorption of SF6. Chemical Engineering Journal. 2022;437:135364. doi: 10.1016/j.cej.2022.135364. [DOI] [Google Scholar]
  32. Germann L. S., Katsenis A. D., Huskić I., Julien P. A., Užarević K., Etter M. O. K., Friščić T., Dinnebier R. E.. Real-Time in Situ Monitoring of Particle and Structure Evolution in the Mechanochemical Synthesis of UiO-66 Metal–Organic Frameworks. Cryst. Growth Des. 2020;20(1):49–54. doi: 10.1021/acs.cgd.9b01477. [DOI] [Google Scholar]
  33. Głowniak S., Szczęśniak B., Choma J., Jaroniec M.. Mechanochemistry: Toward green synthesis of metal–organic frameworks. Mater. Today. 2021;46:109–124. doi: 10.1016/j.mattod.2021.01.008. [DOI] [Google Scholar]
  34. Vornholt S. M., Henkelis S. E., Morris R. E.. Low temperature synthesis study of metal–organic framework CPO-27: investigating metal, solvent and base effects down to – 78 °C. Dalton Transactions. 2017;46(25):8298–8303. doi: 10.1039/C7DT01223C. [DOI] [PubMed] [Google Scholar]
  35. Flores J. G., Sánchez-González E., Gutiérrez-Alejandre A., Aguilar-Pliego J., Martínez A., Jurado-Vázquez T., Lima E., González-Zamora E., Díaz-García M., Sánchez-Sánchez M., Ibarra I. A.. Greener synthesis of Cu-MOF-74 and its catalytic use for the generation of vanillin. Dalton Transactions. 2018;47(13):4639–4645. doi: 10.1039/C7DT04701K. [DOI] [PubMed] [Google Scholar]
  36. Julien P. A., Užarević K., Katsenis A. D., Kimber S. A. J., Wang T., Farha O. K., Zhang Y., Casaban J., Germann L. S., Etter M., Dinnebier R. E., James S. L., Halasz I., Friščić T.. In Situ Monitoring and Mechanism of the Mechanochemical Formation of a Microporous MOF-74 Framework. J. Am. Chem. Soc. 2016;138(9):2929–2932. doi: 10.1021/jacs.5b13038. [DOI] [PubMed] [Google Scholar]
  37. Liao Y., Zhang L., Weston M. H., Morris W., Hupp J. T., Farha O. K.. Tuning ethylene gas adsorption via metal node modulation: Cu-MOF-74 for a high ethylene deliverable capacity. Chem. Commun. 2017;53(67):9376–9379. doi: 10.1039/C7CC04160H. [DOI] [PubMed] [Google Scholar]
  38. Zhao X., Wang Y., Li D.-S., Bu X., Feng P.. Metal–Organic Frameworks for Separation. Adv. Mater. 2018;30(37):1705189. doi: 10.1002/adma.201705189. [DOI] [PubMed] [Google Scholar]
  39. Wang H., Luo D., Velasco E., Yu L., Li J.. Separation of alkane and alkene mixtures by metal–organic frameworks. Journal of Materials Chemistry A. 2021;9(37):20874–20896. doi: 10.1039/D1TA04096K. [DOI] [Google Scholar]
  40. Cho S., Han S., Kim J., Park J., Rhee H.. Adsorptive ethylene recovery from LDPE off-gas. Korean Journal of Chemical Engineering. 2002;19(5):821–826. doi: 10.1007/BF02706975. [DOI] [Google Scholar]
  41. Li B., Zhang Y., Krishna R., Yao K., Han Y., Wu Z., Ma D., Shi Z., Pham T., Space B., Liu J., Thallapally P. K., Liu J., Chrzanowski M., Ma S.. Introduction of π-Complexation into Porous Aromatic Framework for Highly Selective Adsorption of Ethylene over Ethane. J. Am. Chem. Soc. 2014;136(24):8654–8660. doi: 10.1021/ja502119z. [DOI] [PubMed] [Google Scholar]
  42. Mohamed M. H., Yang Y., Li L., Zhang S., Ruffley J. P., Jarvi A. G., Saxena S., Veser G., Johnson J. K., Rosi N. L.. Designing Open Metal Sites in Metal–Organic Frameworks for Paraffin/Olefin Separations. J. Am. Chem. Soc. 2019;141(33):13003–13007. doi: 10.1021/jacs.9b06582. [DOI] [PubMed] [Google Scholar]
  43. Beiranvand R. P., Ovaysi S.. Synthesis and Optimization of 2,5-Dihydroxyterephthalic Acid in a Slurry Reactor. J. Chem. 2024;2024:5944449. doi: 10.1155/2024/5944449. [DOI] [Google Scholar]
  44. Mason J. R., Weyrich J. N., Yang H.. Mechanistic Study of Porosity Formation in Liquid-Assisted Mechanochemical Synthesis of Metal-Organic Framework Cu3­(BTC)­2 for Adsorption-Based Applications. Sustainability. 2022;14(15):9150. doi: 10.3390/su14159150. [DOI] [Google Scholar]
  45. Julien P. A., Friščić T.. Methods for Monitoring Milling Reactions and Mechanistic Studies of Mechanochemistry: A Primer. Cryst. Growth Des. 2022;22(9):5726–5754. doi: 10.1021/acs.cgd.2c00587. [DOI] [Google Scholar]
  46. Su M., Cao J., Tian X., Zhang Y., Zhao H.. Mechanism and kinetics of Cu2O oxidation in chemical looping with oxygen uncoupling. Proceedings of the Combustion Institute. 2019;37(4):4371–4378. doi: 10.1016/j.proci.2018.06.162. [DOI] [Google Scholar]
  47. Wang Y., Yuan S., Hu Z., Kundu T., Zhang J., Peh S. B., Cheng Y., Dong J., Yuan D., Zhou H.-C., Zhao D.. Pore Size Reduction in Zirconium Metal–Organic Frameworks for Ethylene/Ethane Separation. ACS Sustainable Chem. Eng. 2019;7(7):7118–7126. doi: 10.1021/acssuschemeng.9b00062. [DOI] [Google Scholar]
  48. Anson A., Wang Y., Lin C. C. H., Kuznicki T. M., Kuznicki S. M.. Adsorption of ethane and ethylene on modified ETS-10, Chem. Eng. Sci. 2008;63(16):4171–4175. doi: 10.1016/j.ces.2008.05.038. [DOI] [Google Scholar]
  49. Zhao J., Wang W., Tang H., Ramella D., Luan Y.. Modification of Cu2+ into Zr-based metal–organic framework (MOF) with carboxylic units as an efficient heterogeneous catalyst for aerobic epoxidation of olefins, Molecular Catalysis. 2018;456:57–64. doi: 10.1016/j.mcat.2018.06.023. [DOI] [Google Scholar]
  50. Gong Y., Cai X., You W., Jiang X., Liu W., Lively R., Walton K. S., Sholl D. S.. Selective Uptake of Ethane/Ethylene Mixtures by UTSA-280 is Driven by Reversibly Coordinated Water Defects, Chem. Mater. 2023;35(7):2956–2966. doi: 10.1021/acs.chemmater.3c00065. [DOI] [Google Scholar]
  51. Henao-Sierra W., Romero-Sáez M., Gracia F., Cacua K., Buitrago-Sierra R.. Water vapor adsorption performance of Ag and Ni modified 5A zeolite, Microporous Mesoporous Mater. 2018;265:250–257. doi: 10.1016/j.micromeso.2018.02.036. [DOI] [Google Scholar]
  52. Gao Z., Liu Y., Wu S., Tang J., Yuan K., Pan C., Yu G.. Metal-Decorated Porous Organic Polymers: Bridged the Gap between Organic and Inorganic Scaffolds, Chin. J. Chem. 2024;42(22):2902–2934. doi: 10.1002/cjoc.202400386. [DOI] [Google Scholar]
  53. Mukherjee S., Sensharma D., Chen K.-J., Zaworotko M. J.. Crystal engineering of porous coordination networks to enable separation of C2 hydrocarbons, Chem. Commun. 2020;56(72):10419–10441. doi: 10.1039/D0CC04645K. [DOI] [PubMed] [Google Scholar]
  54. Pourhakkak, P. ; Taghizadeh, A. ; Taghizadeh, M. ; Ghaedi, M. ; Haghdoust, S. . Chapter 1 - Fundamentals of adsorption technology. In Interface Science and Technology; Elsevier, 2021; pp 1–70. [Google Scholar]
  55. Nuhnen A., Janiak C.. A practical guide to calculate the isosteric heat/enthalpy of adsorption via adsorption isotherms in metal–organic frameworks, MOFs, Dalton Transactions. 2020;49:10295–10307. doi: 10.1039/D0DT01784A. [DOI] [PubMed] [Google Scholar]
  56. Myers A. L., Prausnitz J. M.. Thermodynamics of Mixed-Gas Adsorption. AIChE J. 1965;11(1):121–127. doi: 10.1002/aic.690110125. [DOI] [Google Scholar]
  57. Teramoto M., Takeuchi N., Maki T., Matsuyama H.. Ethylene/ethane separation by facilitated transport membrane accompanied by permeation of aqueous silver nitrate solution. Sep. Purif. Technol. 2002;28(2):117–124. doi: 10.1016/S1383-5866(02)00045-X. [DOI] [Google Scholar]
  58. Shi M., Lin C. C. H., Kuznicki T. M., Hashisho Z., Kuznicki S. M.. Separation of a binary mixture of ethylene and ethane by adsorption on Na-ETS-10. Chem. Eng. Sci. 2010;65(11):3494–3498. doi: 10.1016/j.ces.2010.02.048. [DOI] [Google Scholar]
  59. Golipour H., Mokhtarani B., Mafi M., Moradi A., Godini H. R.. Experimental Measurement for Adsorption of Ethylene and Ethane Gases on Copper-Exchanged Zeolites 13X and 5A. Journal of Chemical & Engineering Data. 2020;65(8):3920–3932. doi: 10.1021/acs.jced.0c00251. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The authors confirm that the data supporting the findings of this research are available throughout the article.

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES