Article pubs.acs.org/IECR
Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Effect of Eco-Friendly Cyclodextrin on the Kinetics of Mixed Methane−Tetrahydrofuran Hydrate Formation Yanjie Lin, Hari Prakash Veluswamy,* and Praveen Linga* Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117585 S Supporting Information *
ABSTRACT: Use of environmentally friendly additives to promote methane hydrate formation is an active area of research for gas storage via solidified natural gas (SNG) technology. The key advantages of SNG technology include a high degree of safety and a compact mode of natural gas storage in comparison to conventional methods of NG storage. In this paper, we evaluate the effect of β-cyclodextrin as a kinetic promoter for mixed methane−tetrahydrofuran hydrate formation. β-Cyclodextrin is an eco-friendly cyclic oligosaccharide containing seven glucose monomers that form a ring structure. The concentration of β-cyclodextrin was varied under different hydrate forming conditions (temperature and pressure), and the formation kinetics along with the morphology of mixed hydrate formation were observed. It is found that β-cyclodextrin served as an effective kinetic promoter for mixed methane−tetrahydrofuran hydrate formation at moderate pressure and temperatures in a simple unstirred reactor configuration. Further, no foam formation was observed during the hydrate dissociation that envisages an enhanced gas recovery and suitability of SNG technology for methane storage.
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INTRODUCTION Several advantages exist for storing natural gas (methane) in the form of clathrate hydrates,1,2 termed as SNG (solidified natural gas) in comparison to available conventional methods of NG storage like compressed natural gas (CNG) and adsorbed natural gas (ANG). Key advantages of SNG technology include being the safest mode of natural gas storage as it is “nonexplosive” and a compact mode (unit volume of solid hydrate has the potential to encompass multifold volumes of gas) of natural gas storage with considerable storage capacity coupled with the feasibility to recover the stored methane in a controlled manner suited for long-term and large-scale gas storage applications.3 However, sluggish kinetics observed during hydrate formation is a major challenge that has deterred the commercialization of this technology. Different methods have been adopted to improve the kinetics of hydrate formation include the use of suitable kinetic promoter additives (predominantly surfactants),4 enhancing the gas/liquid contact area by innovation in the reactor design5 or by a combination of these two methods.6−9 Surfactants like sodium dodecyl sulfate have been studied exhaustively for improving the hydrate formation rates of different hydrate forming systems in different reactor configurations.7,10−13 Despite the significant promotion in kinetics offered by these conventional surfactants, there is a considerable environmental impact of these chemicals even when used at low concentrations.14 In addition, persistent foam formation15−17 occurring during the hydrate dissociation when employing such © XXXX American Chemical Society
surfactants has adverse effects on gas recovery and may not be suited for large scale applications. Thus, researchers have focused on studying the effect of eco-friendly additives like amino acids,3,15,18 biosurfactants,19 and starches20,21 on methane hydrate formation kinetics as these additives do not result in foam formation and do not deteriorate the environment. Cyclodextrins (CDs) are sugar molecules comprised of ring structures. The simplest of these cyclodextrins are α-cyclodextrin (Alpha-CD), β-cyclodextrin (Beta-CD), and γ-cyclodextrin (Gamma-CD) that are comprised of six, seven, and eight glucose monomer units respectively arranged in the form of a ring. Typically, CDs are produced from starch and find their application predominantly in the food22 and pharmaceutical23 industries. Mohammadi et al.24 reported an increase of 14.63% in dissolution of methane in water in the presence of 0.5 wt % β-cyclodextrin at 274.2 K and low pressures of 3 bar. Kuji et al.25 investigated the effect of α-cyclodextrin, βcyclodextrin, β-cyclodextrin polymers, and β-cyclodextrin modified with methyl and triacetyl groups on the kinetics of xenon and methane hydrate formation in a stirred tank reactor. 1.0 wt % of β-cyclodextrin polymer was found to be effective in Special Issue: PSE Advances in Natural Gas Value Chain Received: Revised: Accepted: Published: A
December 10, 2017 January 22, 2018 January 24, 2018 January 24, 2018 DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
to result in 32.4 mL of the solution. The calculated weight of Beta-CD measured using a Toledo AB 104-S analytical balance (uncertainty of 0.0001 g) was added to the prepared THF solution. Both THF and Beta-CD are completely soluble in water, resulting in a homogeneous solution that was loaded in the reactor and cooled to experimental temperature. After achieving the required temperature, the reactor was purged with methane to remove the initial air present and set to experimental pressure. Under these experimental conditions, hydrate forms and grows inside the reactor. The time of occurrence of the first hydrate crystal from the start of the experiment is referred to as the induction/nucleation time. This could be observed visually or be inferred from the temperature rise (the hydrate formation process is exothermic) in the reactor. Reactor pressure drops continuously during the hydrate formation and growth as methane gas occupies and stabilizes hydrate cages. The hydrate formation process is complete when no further pressure drop is observed in the reactor. All experiments performed were of the batch type, and the observed pressure drop is correlated to methane gas uptake in hydrates as detailed in our earlier studies.18,31 We report the normalized rate of hydrate formation during the first 30 min of hydrate formation (NR30) by a procedure detailed elsewhere.18,31 After the completion of hydrate formation, the reactor pressure was reduced to 1.0 MPa [this pressure was chosen so that hydrates will remain in a stable zone at experimental temperature (equilibrium pressure of 0.5 MPa at 283.2 K)]. After this, the temperature was increased to 301.7 K (ΔT = 28.5 K) so that all hydrates decomposed and the solution was regenerated. After the complete dissociation of hydrates, gas was vented off, and the reactor contents were kept undisturbed and cooled again immediately to the experimental temperature of 283.2 K for about 1 h for memory trials. To ensure repeatability, at least two cycles of hydrate formation/ dissociation (one fresh trial along with one or two memory trials) were performed for each experimental condition.
promoting methane hydrate formation at 274.2 K with a high rate constant. However, experimental pressure and driving force details for methane hydrate formation were not available in their work. Ji et al.26 recently performed molecular dynamic simulations on methane hydrate formation in the presence of βcyclodextrin and reported an improvement in kinetics and gas storage capacity. On the basis of simulations, they reported that the increase in gas−water interfacial curvature and the formation of water channel bridging hydrate and water were plausible reasons for accelerated kinetics of hydrate growth in the presence of Beta-CD. It has to be noted that β-cyclodextrin also has the potential to form clathrate by itself (ability to enclose guest molecules without the presence of water).27 Gorbatchuk et al.28 studied different methods of preparation of β-cyclodextrin clathrate for effective inclusion of volatile guests possessing moderate hydrophilicity. Recently, we reported a drastic methane hydrate formation in the presence of THF at 283.2 K and moderate pressures in a simple unstirred reactor configuration highlighting the potential to scale up this process.29 We also evaluated the temperature and pressure effect on the mixed methane hydrate formation kinetics and report faster hydrate formation close to ambient temperatures (293.2 K) and 7.2 MPa in the presence of low concentration (100 ppm) of sodium dodecyl sulfate surfactant.30 In the present work, for the first time, we evaluate in detail the macroscopic kinetics of mixed methane-tetrahydrofuran hydrate formation in the presence of varying concentrations of β-cyclodextrin at different temperatures and pressures in a quiescent unstirred reactor. Kinetic and morphology observations during the hydrate formation and dissociation are presented. Comparison of the kinetic performance in the presence of Beta-CD to that without any promoter (data reported in previous works29,30) has also been documented.
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EXPERIMENTAL SECTION Materials Used. A 99.9% pure methane compressed gas cylinder purchased from Air Liquide Pte Ltd., analytical reagent grade tetrahydrofuran (THF) of 99.7% purity obtained from Fisher Chemicals, and β-cyclodextrin (reagent grade, ≥97% purity) purchased from Sigma-Aldrich were used in experiments. Ultra-Pure Water obtained through reverse osmosis and cleansed by bactericidal UV lamp technologies in a conventional apparatus supplied by Elga was used for all experiments. Experimental Setup. The details on the experimental setup used for conduction of experiments are provided in the study by Veluswamy et al.18 A 142 cm3 stainless steel reactor customized with two viewing windows and a cooling jacket was used for experiments. A Polyscience chiller maintained the reactor contents at the experimental temperature. A Pressure Transmitter Rosemount 3051 and Copper- constantan T type thermocouple to record the pressure and temperature of the reactor were supplied by Emerson Process Management and Omega, respectively. Uncertainties in pressure and temperature measurement were 0.1% in the range of 0 to 20 MPa and 0.1 K, respectively. Temperature and pressure data of the reactor were recorded every 20 s through a data acquisition system supplied by National Instruments. Experimental Procedure. The experimental procedure adopted for hydrate formation and dissociation in the current study was the same as detailed by Veluswamy et al.30 The required concentration of THF solution was prepared by dissolving the calculated volume of the tetrahydrofuran in water
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RESULTS AND DISCUSSION Hydrate Formation Experiments with Beta-CD at 283.2 K and 5.0 MPa. Experiments to evaluate the effect of Beta-CD on kinetics of mixed methane hydrate formation were performed at 5 MPa and 283.2 K. These conditions were chosen considering the moderate pressures and temperature employed in our previous study wherein experiments were performed under the same conditions without any promoter. Thus, the data presented for these conditions (A1−A3*), in this study for experiments without the promoter, were from the earlier study by Veluswamy et al.30 The pressure driving force and temperature driving force of hydrate formation under these conditions are 4.5 MPa32 and 16.7 K,33 respectively. Betacyclodextrin (Beta-CD) promoter was added in varying concentrations of 100, 500, and 5000 ppm, and the effect of the promoter concentration on the formation kinetics was observed. Figure 1 presents methane gas uptake profiles during mixed methane−THF hydrate formation under the operating conditions of 283.2 K and 5 MPa with varying concentrations of Beta-CD. Time zero corresponds to the induction time (start of hydrate formation). Only the fresh trial experimental data for each of the Beta-CD concentrations is shown for easy understanding. The memory trial experimental data are included in the Supporting Information Figure S1. It can be B
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
From Table 1, it is observed that all the experimental trials with β-cyclodextrin exhibit improvement in methane uptake rate (NR30) and time required for 90% completion (t90). The 500 ppm β-cyclodextrin is found to be the optimal concentration recording a higher gas uptake of 68.75 (±0.05) mmol/mol water, a shorter t90 of 37.27 (±0.54) min, and a higher methane uptake rate of 4.31 (±0.09) kmol/m3/h. The methane uptake rate is 17% higher than the rate without any kinetic promoter. Figure 2 presents visual observations of methane−THF hydrate formation for the experimental trial C1 (500 ppm Beta-
Figure 1. Gas uptake curves during methane−THF hydrate formation with 5.6 mol % THF and different concentrations of beta-cyclodextrin under 283.2 K and 5 MPa within 1 h.
seen from Figures 1 and S1 that, at all concentrations of BetaCD, gas uptake profiles are steeper curves compared to trials without any kinetic promoter. Thus, there is considerable kinetic promotion observed for mixed methane hydrate formation in the presence of β-cyclodextrin. Table 1 provides the calculated and observed data with relevant process parameters for all experimental trials performed. The gas uptake does not vary significantly with lower dosages (100 and 500 ppm) of Beta-CD in comparison to that of the no promoter experiment. There is no significant difference among various concentrations of β-cyclodextrin during the first 25 min of formation. Nevertheless, a higher dosage of β-cyclodextrin (5000 ppm) decreases the final gas uptake by 16% despite the improvement in kinetics observed initially. Plausible reason for the decreased gas uptake at higher beta-CD concentrations could be the increased mass transfer resistance during the hydrate growth phase as observed for conventional kinetic promoters like SDS.30 However, the exact reason for the decrease in gas uptake cannot be ascertained from kinetic investigations performed and require detailed characterization studies like in situ Raman spectroscopy to shed additional information.
Figure 2. Morphology observations for the experimental trial C1 conducted with 500 ppm Beta-CD at 5 MPa and 283.2 K. IT refers to the induction time.
CD, fresh run) conducted at 5 MPa and 283.2 K. From the Figure 2, it can be seen that, there is gradual growth of hydrates from the interface into bulk solution until 10 min. Thereafter, hydrates grow in the upward direction above the gas/hydrate interface. At 10 min, the corresponding methane uptake recorded is only about 10 mmol gas/mol of water. The majority of gas uptake is achieved after this time when hydrate growth is predominantly above the gas/hydrate interface. There is no evident change in visual observations after 15 min, where there is an increase in the slope of kinetic curve observed. The same was highlighted in our previous study without any kinetic promoter29 and the postulation of a two-step hydrate growth mechanism that was verified and validated using differential calorimetric study.34 Visual observations for the trial D1 (5000 ppm Beta-CD, fresh run) are presented in the Supporting Information Figure S2. Morphologically, a similar hydrate
Table 1. Induction Time, t90, Methane Gas Uptake and Rate of Hydrate Formation for Experiments Conducted in Unstirred Tank Reactor Using Different Concentrations of Beta-CD at 283.2 K and Starting Pressure of 5 MPa
a
trial numbera
Beta-CD concentration (ppm)
induction time, IT (min)
time taken for 90% completion, t90 (min)
methane uptake at 1 h (mmol/mol water)
rate of methane uptake, NR30 (kmol/m3/h)
A1* A2* A3* average B1 B2 B3 average C1 C2 C3 average D1
0
26.67 4.33 3.67 11.56 (±15.11) 5.33 2 0 2.44 (±2.89) 0.33 11.33 0.33 4.00 (±7.33) 29
43 37 40.33 40.11 (±3.11) 35.33 38.67 40.67 38.22 (±2.89) 36.67 37.8 37.33 37.27 (±0.54) 36.67
69.84 70.36 68.53 69.58 (±1.05) 67.38 64.43 64.38 65.40 (±1.98) 68.77 68.76 68.70 68.75 (±0.05) 58.44
3.09 4.43 3.52 3.68 (±0.75) 4.64 3.67 3.3 3.87 (±0.77) 4.40 4.28 4.26 4.31 (±0.09) 4.39
100
500
5000
A1−A3* are data reported in our previous study;30 included here for better comparison. C
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research growth pattern was observed at higher concentrations of BetaCD (5000 ppm) as well as with no significant visual changes observed beyond 15 min from nucleation. Though the total gas uptake and t90 observed for experiments with Beta-CD are not significantly different in comparison to those of no promoter experiments, it has to be noted that at all times before the completion of the experiment, the gas uptake and rate of hydrate formation are significantly higher for experiments with Beta-CD. For example, at 30 min after nucleation, the gas uptake in the presence of 100/500 ppm Beta-CD was 50 mmol gas/mol of water in comparison to just 35 mmol gas/mol of water (30% higher) for the no promoter experiment. This difference could be still higher on a larger experimental scale, thus highlighting the potential of a biofriendly Beta-CD promoter for mixed methane−THF hydrate formation. Another important observation is that under similar experimental conditions, 100 ppm of SDS surfactant resulted in a significant drop (about 43%) in gas uptake as presented in Figure S4 of the Supporting Information. The reason for this is due to the drastic initial hydrate formation disrupting the channels during hydrate growth resulting in an increased mass transfer resistance as detailed in our earlier study.30 Thus, Beta-CD is a more effective kinetic promoter for mixed methane−THF hydrate formation than conventional anionic SDS surfactant at 283.2 K and 5 MPa. Hydrate Formation Experiments with Beta-CD at 288.2 K and 5.0 MPa. Experiments were then performed at 288.2 K and 5.0 MPa, in order to see the effect of Beta-CD at a lower driving force. The pressure driving force and temperature driving force of hydrate formation under these conditions are 3.8 MPa32 and 11.7 K,33 respectively. This attributes to a 0.7 MPa drop in pressure driving force and 5 K temperature driving force in comparison to a previous set of experiments. For these conditions, we had to perform the experiments without any promoter first followed by experiments with an optimized concentration of 500 ppm Beta-CD as determined in a previous set of experiments. One trial of higher concentration 2000 ppm Beta-CD was also performed to assess if the kinetic promotion improves at higher promoter concentrations at a lower driving force. Figure 3 presents the gas uptake curves of fresh trials of methane−THF hydrate formation with and without Beta-CD promoter under the operating conditions of 288.2 K and 5 MPa. All the relevant process parameters recorded and calculated are summarized in Table 2. Due to the decrease in driving force, the hydrate formation becomes sluggish, taking about 300 min for completion for the experiment without any kinetic promoter. Further, the hydrate formation exhibits multistage behavior, with very low gas uptake rates in the initial stages and increasing to a higher rate of 1.48 kmol/m3/h toward the completion. This multistage hydrate growth is similar to that observed in our previous study at lower driving forces.30 With the addition of 500 ppm of Beta-CD, hydrate growth was at a steady rate consistently higher than that observed for no promoter experiments with completion in about 240 min. In order to examine if the kinetics were better at higher concentrations of Beta-CD, one formation trial at 2000 ppm concentration was carried out. Despite a short initial sluggish hydrate growth phase until 50 min, hydrates form rapidly at a rate of 4.96 kmol/m3/h from 50 to 60 min with a significant gas uptake observed. However, the hydrate growth stabilized to 0.16 kmol/m3/h for the remaining time with a final
Figure 3. Kinetics of methane−THF hydrate formation with 5.6% mol THF and different concentrations of beta-cyclodextrin under 288.2 K and 5 MPa within 5 h (fresh runs).
uptake of only 52.18 mmol gas/mol of water (about 15−18% lower than experiments performed with 0 and 500 ppm BetaCD). This behavior was similar to that observed for 5000 ppm Beta-CD at 283.2 and 5.0 MPa. Morphology observations observed during this trial are provided in the Supporting Information Figure S3. Another interesting observation for experiments performed at 288.2 K is that all memory runs outperform the fresh runs with lesser time required for completion and improved hydrate formation rates as shown in Figure 4 and summarized in Table 2. Figure 4 shows that hydrate formation enters the rapid growth stage at about 45 min with 500 ppm β-cyclodextrin, while it takes more than 2 h without any kinetic promoter. The reason for this is postulated to be the growth of hydrates rapidly above the gas/hydrate interface as shown in morphology observations in Figure 5D−J. The hydrate growth rate during the rapid stage is much higher (4.14 kmol/m3/h) with 500 ppm β-cyclodextrin than the trials (1.52−1.99 kmol/ m3/h) without any kinetic promoter. Thus, despite the lower driving force available, Beta-CD serves as a kinetic promoter for mixed methane−THF hydrate formation with memory trials showing better performance than fresh trials. The reason for such a difference in morphology for memory trials cannot be ascertained from kinetic experiments performed and requires in depth characterization studies that probe the molecular level for understanding the mechanism of hydrate formation. Further, induction times for hydrate formation at 288.2 K and 5.0 MPa are much longer with an average of 8−12 h for both with and without promoter experimental trials. This is due to the lower driving force available under experimental conditions; the reduction in the nucleation time can be achieved by employing the combinatorial approach of stirring the solution for a short time (about 1 min), as reported in a study by Veluswamy et al.18 Hydrate Formation Experiments with Beta-CD at Varying THF Concentrations. Veluswamy et al.31 documented that the presence of THF was found to retard the kinetic promoting effect of surfactants during gas CH4/THF mixed hydrate formation investigated in a stirred tank reactor configuration at 278.2 K and 7.13 MPa. In our study, we observe that Beta-CD has a considerable promotion effect for the CH4/THF system under experimental conditions (milder than that in study by Veluswamy et al.31) in a simple unstirred D
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
Table 2. Induction Time, t90, Methane Gas Uptake and Rate of Hydrate Formation for Experiments Conducted in Unstirred Tank Reactor Using Different Concentrations of Histidine at 288.2 K and Starting Pressure of 5 MPa trial number E1 E2 E3 average F1 F2 average G1
Beta-CD concentration (ppm)
induction time, IT (min)
time taken for 90% completion, t90 (min)
methane uptake at 5 h (mmol/mol water)
0
133.33 765 821 573 (±440) 1178 0.5 589 (±589) 98
276.67 163.33 186.67 208.89 (±67.78) 204.5 125.8 165.15 (±39.35) 195.33
61.89 67.83 63.28 64.33 (±3.50) 60.55 63.25 61.90 (±1.35) 52.18
500
2000
rate of methane uptake, stage 1 (kmol/ m3/h)
rate of methane uptake, stage 2 (kmol/ m3/h)
rate of methane uptake, stage 3 (kmol/ m3/h)
0.94 0.69 0.6
0.29 1.99 1.52
1.48
0.62 0.76
1.15 4.14
0.49
4.96
0.16
Figure 4. Kinetics of methane−THF hydrate formation with 5.6% mol of THF and different concentrations of beta-cyclodextrin under 288.2 K and 5 MPa within 4 h (memory runs).
Figure 5. Morphology observations for the experimental trial F2 conducted with 500 ppm Beta-CD at 5 MPa and 288.2 K. IT refers to the induction time.
Figure 6. Gas uptake and rate of hydrate formation at varying concentrations of THF with and without Beta-CD under 283.2 K and 5 MPa.
reactor configuration. To examine if the presence of THF influenced the promotion effect of Beta-CD during mixed hydrate formation, two lower concentrations of THF − 4.5 mol % and 5 mol %, were tested in the presence of the optimized 500 ppm Beta-CD. Figure 6 shows the bar plots of gas uptake and the rate of hydrate formation with and without a Beta-CD promoter under the same experimental conditions of 5 MPa and 283.2 K. It has to be noted that slight variation in THF concentration does not significantly affect the thermodynamics of mixed methane− THF hydrate formation.35 Table 3 summarizes the kinetic data and process parameters associated with the experimental trials presented in Figure 6. From Figure 6b, it can be seen that for all concentrations of THF employed for the mixed hydrate
formation, there is an improvement in the kinetics in the presence of 500 ppm Beta-CD. Further, Figure 6a shows that the gas uptake achieved with the presence of Beta-CD is similar to that without a promoter. The gas uptake for experiments at lower THF concentrations (4.5 and 5 mol %) is lower than that at 5.6 mol % as the amount of THF available for mixed hydrate formation is lower. Thus, in comparison to conventional surfactants, the eco-friendly Beta-CD is the promising promoter for mixed methane−THF hydrate formation, even at varying concentrations of tetrahydrofuran under moderate conditions of temperature and pressure. E
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Table 3. Induction Time, t90, Methane Gas Uptake and Rate of Hydrate Formation for Experiments Conducted in Unstirred Tank Reactor Using Different Concentrations of Tetrahydrofuran with 500 ppm of Beta-CD at 283.2 K and Starting Pressure of 5 MPa trial number H1 H2 H3 average J1 J2 J3 average I1 I2 I3 average K1 K2 K3 average
Beta-CD concentration (ppm)
THF concentration (mol %)
0
4.5
500
0
500
5
induction time, IT (min)
time taken for 90% completion, t90 (min)
methane uptake at 1 h (mmol/mol water)
rate of methane uptake, NR30 (kmol/m3/h)
0.5 9.67 22.67 10.78 (±11.89) 0.5 1235 236 490 (±745) 134 3 6.33 47.78 (±86.22) 269.67 47.67 34.33 117.22 (±152.45)
40.5 39.4 40.67 40.19 (±0.78) 38.5 40.5 39.33 39.44 (±1.06) 35.67 38.94 37.5 37.37 (±1.70) 37.33 36.75 41.33 38.47 (±2.86)
54.47 58.72 55.88 56.36 (±2.36) 60.09 55.84 55.29 57.07 (±3.02) 63.13 62.82 61.75 62.57 (±0.82) 61.19 63.32 62.23 62.25 (±1.07)
3.19 3.84 3.43 3.49 (±0.35) 4.05 3.40 3.56 3.67 (±0.38) 4.39 3.76 3.94 4.03 (±0.27) 4.57 4.39 3.36 4.11 (±0.75)
Hydrate Dissociation in the Presence of Beta-CD. Figure 7 presents the morphology observations during the
hydrate formation for large-scale and long-term NG storage applications.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b05107. Figure S1 presents gas uptake profiles observed during memory trials of mixed methane−tetrahydrofuran hydrate formation experiments performed at 283.2 K and 5.0 MPa. Figures S2 and S3 present morphology observations for experimental trials D1 and G1 (higher beta-CD concentrations) at 283.2 and 288.2 K, respectively. Figure S4 shows the comparison of gas uptake profiles during mixed methane−THF hydrate formation in the presence of 100 ppm Beta-CD and SDS along with no kinetic promoter trial at 283.2 K and 5 MPa (PDF)
Figure 7. Morphology observations during the dissociation of the experimental trial K3 conducted with 500 ppm Beta-CD at 5 MPa and 283.2 K. Start refers to the start of the dissociation process.
dissociation of mixed methane−THF hydrate formation in the presence of 500 ppm Beta-CD. The dissociation process is gradual and complete in about 90 min. It can be seen that the regenerated solution (Figure 7J) does not have any foam, thus overcoming the disadvantage of the application of conventional surfactant. Further, we observed that almost complete recovery of gas is possible during the mixed hydrate dissociation.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Praveen Linga: 0000-0002-1466-038X
CONCLUSIONS
Notes
This paper reports in detail the macroscopic kinetic investigations on mixed methane−THF hydrate formation in presence of biofriendly cyclic oligosaccharide beta-cyclodextrin. All experiments were performed in a simple unstirred reactor configuration at moderate operating conditions of temperature and pressure. An optimal concentration of 500 ppm Beta-CD resulted in an effective promotion even at lower driving forces and lower concentrations of tetrahydrofuran. Further, no foaming during the dissociation or depressurization was observed while employing Beta-CD. This highlights the potential application of Beta-CD for mixed methane−THF
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work was funded in part under the Energy Innovation Research Programme (EIRP, Award No. NRF2015EWTEIRP002-002), administrated by the Energy Market Authority (EMA) of Singapore. The EIRP is a competitive grant call initiative driven by the Energy Innovation Programme Office and funded by the National Research Foundation (NRF). This invited contribution is part of PSE Advances in Natural Gas Value Chain. F
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research
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(23) Loftsson, T.; Brewster, M. E. Pharmaceutical applications of cyclodextrins: basic science and product development. J. Pharm. Pharmacol. 2010, 62 (11), 1607−1621. (24) Mohammadi, A.; Manteghian, M.; Mirzaei, M. Effect of βcyclodextrin on dissolution of methane in water. Chem. Eng. Res. Des. 2011, 89 (4), 421−427. (25) Kuji, Y.; Yamasaki, A.; Yanagisawa, Y. Effect of Cyclodextrins on Hydrate Formation Rates. Energy Fuels 2006, 20 (5), 2198−2201. (26) Ji, H.; Chen, D.; Wu, G. Molecular Mechanisms for Cyclodextrin-Promoted Methane Hydrate Formation in Water. J. Phys. Chem. C 2017, 121 (38), 20967−20975. (27) Szejtli, J. Introduction and General Overview of Cyclodextrin Chemistry. Chem. Rev. 1998, 98 (5), 1743−1754. (28) Gorbatchuk, V. V.; Gatiatulin, A. K.; Ziganshin, M. A.; Gubaidullin, A. T.; Yakimova, L. S. Unusually High Efficiency of βCyclodextrin Clathrate Preparation by Water-Free Solid-Phase Guest Exchange. J. Phys. Chem. B 2013, 117 (46), 14544−14556. (29) Veluswamy, H. P.; Wong, A. J. H.; Babu, P.; Kumar, R.; Kulprathipanja, S.; Rangsunvigit, P.; Linga, P. Rapid methane hydrate formation to develop a cost effective large scale energy storage system. Chem. Eng. J. 2016, 290, 161−173. (30) Veluswamy, H. P.; Kumar, S.; Kumar, R.; Rangsunvigit, P.; Linga, P. Enhanced clathrate hydrate formation kinetics at near ambient temperatures and moderate pressures: Application to natural gas storage. Fuel 2016, 182, 907−919. (31) Veluswamy, H. P.; Ang, W. J.; Zhao, D.; Linga, P. Influence of cationic and non-ionic surfactants on the kinetics of mixed hydrogen/ tetrahydrofuran hydrates. Chem. Eng. Sci. 2015, 132 (Supplement C), 186−199. (32) Zhang, Q.; Chen, G.-J.; Huang, Q.; Sun, C.-Y.; Guo, X.-Q.; Ma, Q.-L. Hydrate Formation Conditions of a Hydrogen + Methane Gas Mixture in Tetrahydrofuran + Water. J. Chem. Eng. Data 2005, 50 (1), 234−236. (33) Kumar, A.; Vedula, S. S.; Kumar, R.; Linga, P. Hydrate phase equilibrium data of mixed methane-tetrahydrofuran hydrates in saline water. J. Chem. Thermodyn. 2018, 117 (Supplement C), 2−8. (34) Kumar, A.; Daraboina, N.; Kumar, R.; Linga, P. Experimental Investigation To Elucidate Why Tetrahydrofuran Rapidly Promotes Methane Hydrate Formation Kinetics: Applicable to Energy Storage. J. Phys. Chem. C 2016, 120 (51), 29062−29068. (35) De Deugd, R.; Jager, M.; de Swaan Arons, J. Mixed hydrates of methane and water-soluble hydrocarbons modeling of empirical results. AIChE J. 2001, 47 (3), 693−704.
REFERENCES
(1) Gudmundsson, J. S.; Parlaktuna, M.; Khokhar, A. Storage of natural gas as frozen hydrate. SPE Prod. Facil. 1994, 9 (01), 69−73. (2) Gudmundsson, J. S. Method for production of gas hydrates for transportation and storage. U.S. Patent: US 5536893 A, 1996. (3) Veluswamy, H. P.; Lee, P. Y.; Premasinghe, K.; Linga, P. Effect of Biofriendly Amino Acids on the Kinetics of Methane Hydrate Formation and Dissociation. Ind. Eng. Chem. Res. 2017, 56 (21), 6145−6154. (4) Kumar, A.; Bhattacharjee, G.; Kulkarni, B. D.; Kumar, R. Role of Surfactants in Promoting Gas Hydrate Formation. Ind. Eng. Chem. Res. 2015, 54 (49), 12217−12232. (5) Linga, P.; Clarke, M. A. A Review of Reactor Designs and Materials Employed for Increasing the Rate of Gas Hydrate Formation. Energy Fuels 2017, 31, 1. (6) Ganji, H.; Manteghian, M.; Sadaghiani zadeh, K.; Omidkhah, M. R.; Rahimi Mofrad, H. Effect of different surfactants on methane hydrate formation rate, stability and storage capacity. Fuel 2007, 86 (3), 434−441. (7) Mandal, A.; Laik, S. Effect of the Promoter on Gas Hydrate Formation and Dissociation. Energy Fuels 2008, 22 (4), 2527−2532. (8) Kumar, A.; Kumar, R. Role of Metallic Packing and Kinetic Promoter in Designing a Hydrate-Based Gas Separation Process. Energy Fuels 2015, 29 (7), 4463−4471. (9) Yang, L.; Fan, S.; Wang, Y.; Lang, X.; Xie, D. Accelerated Formation of Methane Hydrate in Aluminum Foam. Ind. Eng. Chem. Res. 2011, 50 (20), 11563−11569. (10) Zhong, Y.; Rogers, R. E. Surfactant effects on gas hydrate formation. Chem. Eng. Sci. 2000, 55 (19), 4175−4187. (11) Zhang, J. S.; Lee, S.; Lee, J. W. Kinetics of Methane Hydrate Formation from SDS Solution. Ind. Eng. Chem. Res. 2007, 46 (19), 6353−6359. (12) Yoslim, J.; Linga, P.; Englezos, P. Enhanced growth of methanepropane clathrate hydrate crystals with sodium dodecyl sulfate, sodium tetradecyl sulfate, and sodium hexadecyl sulfate surfactants. J. Cryst. Growth 2010, 313 (1), 68−80. (13) Verrett, J.; Servio, P. Evaluating Surfactants and Their Effect on Methane Mole Fraction during Hydrate Growth. Ind. Eng. Chem. Res. 2012, 51 (40), 13144−13149. (14) Scott, M. J.; Jones, M. N. The biodegradation of surfactants in the environment. Biochim. Biophys. Acta, Biomembr. 2000, 1508 (1−2), 235−251. (15) Liu, Y.; Chen, B.; Chen, Y.; Zhang, S.; Guo, W.; Cai, Y.; Tan, B.; Wang, W. Methane Storage in a Hydrated Form as Promoted by Leucines for Possible Application to Natural Gas Transportation and Storage. Energy Technology 2015, 3 (8), 815−819. (16) Veluswamy, H. P.; Hong, Q. W.; Linga, P. Morphology Study of Methane Hydrate Formation and Dissociation in the Presence of Amino Acid. Cryst. Growth Des. 2016, 16 (10), 5932−5945. (17) Carter, B. O.; Wang, W.; Adams, D. J.; Cooper, A. I. Gas Storage in “Dry Water” and “Dry Gel” Clathrates. Langmuir 2010, 26 (5), 3186−3193. (18) Veluswamy, H. P.; Kumar, A.; Kumar, R.; Linga, P. An innovative approach to enhance methane hydrate formation kinetics with leucine for energy storage application. Appl. Energy 2017, 188, 190−199. (19) Rogers, R. E.; Kothapalli, C.; Lee, M. S.; Woolsey, J. R. Catalysis of Gas Hydrates by Biosurfactants in Seawater-Saturated Sand/Clay. Can. J. Chem. Eng. 2003, 81 (5), 973−980. (20) Fakharian, H.; Ganji, H.; Naderi Far, A.; Kameli, M. Potato starch as methane hydrate promoter. Fuel 2012, 94, 356−360. (21) Maghsoodloo Babakhani, S.; Alamdari, A. Effect of maize starch on methane hydrate formation/dissociation rates and stability. J. Nat. Gas Sci. Eng. 2015, 26, 1−5. (22) Astray, G.; Gonzalez-Barreiro, C.; Mejuto, J. C.; Rial-Otero, R.; Simal-Gándara, J. A review on the use of cyclodextrins in foods. Food Hydrocolloids 2009, 23 (7), 1631−1640. G
DOI: 10.1021/acs.iecr.7b05107 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
