Chinese herbs: treasure troves for the discovery of environmentally friendly promoters for methane hydrate formation

Abstract

Chinese herbs are rich resources for the discovery of new environmentally friendly promoters for methane hydrate formation. We demonstrated that 20 out of 300 kinds of Chinese herbs were highly...

A Highly Effective Inorganic Composite Promoter: Synergistic Effect of Boric Acid and Calcium Hydroxide in Promoting Methane Hydrate Formation under Static Conditions

“…The organic anionic surfactant SDS has long been regarded as the benchmark promoter because of its excellent promoting performance on MH formation. ,− As shown in Figure , at a concentration of 0.20 wt %, SDS can greatly promote MH formation to reach a gravimetric capacity of 132.2 mg g –1 in 1000 min with a t 90 of around 13 min. Under the same conditions, the best promoting performance (131.8 mg g –1 with a t 90 of around 18 min) of the inorganic composite promoter on MH formation is still slightly lower than that of SDS. ,, However, MH formed by using SDS promoter produced copious and persistent foam after dissociation (right inset in Figure ) which would be a troublesome engineering problem on larger scales. , By contrast, MH that formed from the inorganic composite promoter solution dissociated without foaming under the same conditions (left inset in Figure ). It has been observed that an unusual growth of gas hydrate can occur in the presence of some kinetic inhibitors under high driving force .…”

“…Under the same conditions, the best promoting performance (131.8 mg g −1 with a t 90 of around 18 min) of the inorganic composite promoter on MH formation is still slightly lower than that of SDS. 15,38,43 However, MH formed by using SDS promoter produced copious and persistent foam after dissociation (right inset in Figure 2) which would be a troublesome engineering problem on larger scales. 41,43 By contrast, MH that formed from the inorganic composite promoter solution dissociated without foaming under the same conditions (left inset in Figure 2).…”

“…Pressure–temperature dependence measurement ( P – T plot) under the isochoric condition is a powerful approach to determine the effectiveness of a promoter in enhancing gas hydrate formation. ,,,, Figure b shows the P – T plots for the system with the inorganic composite promoter (0.20 wt % B­(OH) 3 plus 0.02 wt % Ca­(OH) 2 ) and the system with 0.02 wt % Ca­(OH) 2 .…”

“…Methane hydrate (MH) is an ice-like, nonstoichiometric crystalline inclusion compound composed of a hydrogen-bonded water lattice that encages the methane molecules within polyhedral cages with an ideal gravimetric capacity of 154.9 mg g –1 according to the theoretical formula of CH 4 ·5.75H 2 O, which offers an economically feasible and safe solution to transport methane (natural gas) in hydrate form. ,− However, MH formation is a sluggish gas–liquid interfacial reaction under static conditions, which is the major barrier to its practical applications. ,,, A number of approaches have been employed to address such an issue, including the use of mechanical mixing, , spraying, crushed ice particles, , dry water, , supports, , bioclathrates, , and the addition of surfactants. − Compared with other approaches, the use of surfactants as promoters to enhance the MH formation kinetics under static conditions has attracted the most attention. , To date, anionic, cationic, nonionic, and zwitterionic surfactants have all been proven to be effective in promoting MH formation. In particular, the anionic surfactant sodium dodecyl sulfate (SDS) is highly effective, and it was usually used as the benchmark promoter. − However, even at a low concentration, the use of surfactant SDS will create copious quantities of foam which would be a troublesome engineering problem on practical scales. ,, Moreover, most of the surfactant promoters are derived from petroleum-based feedstocks that are not sustainable and may cause serious environmental problems. , The environmentally benign promoters such as natural products can significantly accelerate the kinetics of MH formation; ,− however, high cost could be a potential obstacle in their practical applications on large scales.…”

Humic Acids as a New Type of Methane Hydrate Formation Promoter and a Possible Mechanism for the Hydrate Growth Enhancement

“…Due to this, the hydrate film generally remains impermeable to the liquid. An argument favoring these assumptions is the large number of recently published studies in which the acceleration of hydrate formation and an increase in the degree of water-to-hydrate transformation have been observed in the solutions of various substances, from boric acid, amino acids, and kinetic hydrate inhibitors to brewed tea and components of tea and other herbs. , In all these cases, the solutions used for hydrate formation contained polar or ionic substances that can adsorb on the surface of hydrate particles and inhibit hydrate formation in the case of high concentrations in solutions. Thus, the promoting effect may not be related to additive chemical features but caused by the same impact both on the formation of hydrate film and properties of this film.…”