To improve the rate of formation of carbon dioxide hydrates, tetra- n -butylammonium bromide (TBAB) was compounded with different concentrations of sodium dodecyl sulfate (SDS) and nanographite, and the effects of these mixtures on carbon dioxide hydrate formation were studied. The addition of TBAB alone, as well as mixtures of TBAB and SDS or nanographite, shortened the induced nucleation time, and the induction times of the TBAB–2.5 g/L nanographite and TBAB–0.24 g/L SDS systems were the shortest and longest, respectively. Further, on mixing TBAB and SDS, the induced nucleation time first increased and then decreased with the increase in the SDS concentration. When TBAB and nanographite were mixed together, the induced nucleation time first decreased, then increased, and again decreased with the increase in the nanographite concentration. In addition, the hydrate formation rate and conversion were highest for the TBAB–0.48 g/L SDS system and lowest for the TBAB–0.06 g/L SDS system; in the first 35 min, from the end of gas charging, the TBAB–10 g/L nanographite and TBAB–5 g/L nanographite systems yielded the highest and lowest hydrate formation rates and conversions, respectively. For the composite systems, obvious effects were observed in the initial stages of reaction, but the effects varied over the course of the reaction. Overall, the use of different accelerators resulted in little differences in the total production, conversion, and formation rate of carbon dioxide hydrates over the course of the reaction.

Carbon dioxide hydrates have attracted considerable attention because of their high gas storage capacity and low-cost carbon capture, but their low formation rate limits their application. Currently, the formation rate of hydrates is mainly improved via physical and chemical methods. Chemical methods promote hydrate formation through the addition of accelerators, which entail low cost and energy. To improve the formation rate of CO2 hydrates, 0.244 g/L sodium dodecyl sulfate (SDS), 0.288 g/L tetra-n-butylammonium bromide (TBAB), and 0.33 g/L nanographite were used, and the effects of different accelerator systems on CO2 hydrate formation were observed. The results show that the single and combined use of promoters SDS, TBAB, and nanographite can shorten the induced CO2 hydrate nucleation time. The combinations of nanographite–TBAB and SDS–TBAB shortened the induced nucleation time better than the single SDS, TBAB, and nanographite systems, while the single SDS and nanographite systems showed better promoting effect compared to the SDS–nanographite system. Thus, the combined accelerators do not necessarily promote the formation of hydrates. Among all accelerator systems, SDS–TBAB showed the shortest induced nucleation time, followed by the other three combinations. Among the single acceleration systems, TBAB showed the largest formation amount, formation rate, and conversion rate in the first 35 min from inflation stoppage. Meanwhile, among the compound systems, SDS–TBAB exhibited the best promoting effect. A comparison of all experiments shows that the accelerator significantly affects the formation amount, conversion, and formation rate of hydrates 35 min before the start of inflation; furthermore, a different effect is observed in the subsequent period. The total production, conversion, and saturation of CO2 hydrates in different accelerator systems show a minimal difference. By providing reference for the rapid formation of CO2 hydrates in a short time, this study promotes the industrial application of hydrate technology.