CO₂Enclathration in Hydrates of Peralkyl-(Ammonium/Phosphonium) Salts: Stability Conditions and Dissociation Enthalpies

Abstract

The present work investigates equilibrium conditions and dissociation enthalpies of semiclathrate hydrates formed from CO 2 + tetra-n-butylammonium chloride (TBACl) + water, CO 2 + tetra-n-butylammonium nitrate (TBANO 3 ) + water, and CO 2 + tetra-n-butylphosphonium bromide (TBPB) + water mixtures. Differential scanning calorimetry (DSC) was used for the determination of hydrate-liquid-vapor (H-L-V) equilibrium conditions in the presence of TBACl, TBANO 3 , and TBPB solutions at ammonium salt mass fractions of 0.3618, 0.3941, and 0.3707, respectively, and at CO 2 pressure in the range of (0.5 to 2.0) MPa. Results reveal that semiclathrate hydrates of TBACl, TBANO 3 , and TBPB are able to incorporate carbon dioxide in their structure and that the resulting mixed hydrates have significantly lower formation pressures than those of pure CO 2 hydrate. The dissociation enthalpies of semiclathrate hydrates of TBACl, TBANO 3 , and TBPB with CO 2 were determined by both DSC and the Clausius-Clapeyron equation. The DSC experiments demonstrate that mixed hydrates of TBANO 3 , TBACl, and TBPB with CO 2 have higher melting enthalpies than single hydrates. From our measurements, it appears that mixed TBPB + CO 2 hydrate has appropriate stability conditions (p, T) and latent heat content for secondary refrigeration applications. DSC measurements combined with the Clausius-Clapeyron equation show that mixed TBPB + CO 2 hydrate can store large amounts of CO 2 and thus could be attractive for gas capture and storage applications.

Semiclathrate-based CO2 capture from flue gas mixtures: An experimental approach with thermodynamic and Raman spectroscopic analyses

“…However, these conventional thermodynamic promoters, such as THF and CP, have several disadvantages to their use in actual processes. They are highly volatile and toxic, indicating that an additional process for further purification of the gas phase and complete recovery from the liquid phase is required after use [26,54]. A significant loss after repeated use can also be expected because of their high volatility.…”

“…To avoid and overcome this concern, gas hydrate formation needs to be performed at much milder pressure and temperature conditions. Thus, extensive efforts have been undertaken to reduce hydrate equilibrium pressures or to enhance hydrate equilibrium temperatures by adding thermodynamic promoters to the system [10,12,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Semiclathrates, which share many physical and chemical properties with gas hydrates, could be an attractive alternative to gas hydrates because in general, they can maintain their thermodynamic stability under atmospheric pressure conditions [19,[31][32][33][34][35][36][37][38][39]. In gas hydrates, the guest molecules are not physically bonded to host water lattices, whereas in semiclathrates, guest molecules can both take part in building the host water frameworks and occupy cages after breaking part of the cage structure.…”

“…In QAS semiclathrates, anions such as Br À , Cl À , and F À are involved in forming cage structures with the host water molecules, and tetra-n-butyl ammonium (TBA) cations are incorporated into the large cages. In addition, the QAS semiclathrates have small 5 12 cages which are left vacant and thus, can be used for capturing small-sized gas molecules [19,22,23,[25][26][27][28][31][32][33][34][35][36][37][38][39][40][41]. Due to their significant thermodynamic stability and guest gas enclathrating ability, QAS semiclathrates have been investigated as an alternative to gas hydrates for gas storage and separation [23,27,31,[42][43][44][45][46][47][48].…”

An experimental study on the formation behavior of single and binary hydrates of TBAB, TBAF and TBPB for cold storage air conditioning applications

“…Besides, more phase equilibrium data of TBA + and TBP + hydrates has been provided as a function of the salt mass fraction [21][22][23][24][25][26].…”

Effects of Promoter on the Formation of Gas Hydrate from Blast Furnace Gas

“…완벽한 clathrate를 이루지 않고 semi-clathrate를 형성하는 TBAB (Tetra-n-butyl ammonium bromide), TBAC(Tetra-n-butyl ammonium chloride), TBAF(Tetra-n-butyl ammonium fluoride) 등을 통칭하는 TBAX와 TBPB(tetra-n-butyl phosphonium bromide) 등이 있다 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] 3. 결과 및 고찰 Table 2에 Gas hydrate dissociation pressure for , N 2 + water system [44]; , BFG model gas + water system; and , CO 2 + water system [45].…”