Investigation of CO2 separation from synthesis CO2/CH4 mixture utilizing tetra‐n‐butyl ammonium bromide semi‐hydrate

The separation of a gas mixture by hydrate technology is considered one of the most promising new separation technologies. Previous studies on biogas purified by hydrate separation had high energy consumption because of low separation efficiency. In this paper, we used 1,1-dichloro-1-fluoroethane (HCFC-141b) as an additive to capture CO2 from a mixture gas of 67.00 mol % CH4 and 33.00 mol % CO2, which not only reduced the hydrate formation pressure but also enhanced the difference of methane and carbon dioxide hydrate formation kinetics. The influence of HCFC-141b concentration, feed gas pressure, and initial gas/liquid volume ratio on separation efficiency and the kinetics of hydrate formation were investigated. The results showed that the CO2 captured ratio was 97.03% at 284.1 K @2MP and the separation factor was 61.38. The largest CO2 captured ratio was 97.89%. The concentration of CH4 in the residual gas phase increased from 67.00 to 98.01 mol %. The maximum gas hourly space velocity of the reactor reached 14.45 h–1, and the hydrate formation rate constant was 2.15 × 10–4 (mol2/(s·J)). Furthermore, the energy consumption was calculated by Aspen HYSYS software. The energy consumption of CH4 obtained from biogas at 284.1 K @2MP is 0.3530 kWh/kgCH4 . HCFC-141b acts as a kinetic and thermal promoter, which improved the energy efficiency of hydrate separation and reduced the energy consumption.

Section: Resultsmentioning

confidence: 69%

High Selectivity CO₂ Capture from Biogas by Hydration Separation Based on the Kinetic Difference in the Presence of 1,1-Dichloro-1-fluoroethane

Wang

Lü

et al. 2021

“…By considering the total amount of gas in the mixture gas consumed under different operating conditions, it was found that the best CO 2 separation and CH 4 recovery results were obtained with the largest CO 2 and CH 4 consumption proportions, respectively. Meanwhile, the gas consumption decreased significantly compared with that of binary gas mixture (CH 4 /CO 2 = 50/50) under same experiment conditions . The presence of N 2 increased the phase equilibrium pressures of the mixed gas hydrate under same temperatures, reduced the reaction driving force.…”

Section: Resultsmentioning

confidence: 88%

“…Therefore, the hydrate reaction process within 2 h and the kinetic characteristics of the resulting hydrate formation were studied in this work. Additionally, the amount of gas consumed in 2 h ( N 2h ) was calculated and compared to that consumed for the completed hydrate reaction ( N total ), using a previously reported method . The time required for the hydrate reaction to completely finish was defined as the time when the pressure decrease per minute was less than 0.01 MPa.…”

Section: Resultsmentioning

confidence: 99%

Experimental Study on Hydrate Formation with Synthesized CH₄/CO₂/N₂ Ternary Mixtures

Zang

Liang

2018

Self Cite

The variations in the equilibrium conditions of the hydrate phase between different gas components can be employed for gas separation. The use of hydrate-based gas separation technologies for CH4 recovery from biogas has gained prominence. In this study, the formation of a ternary mixture gas hydrate with CH4, CO2, and N2 was studied. The amount of gas consumed and the hydrate formation rate were calculated using pressure and temperature variations during the reaction. Gas composition changes, the CH4 recovery factor, and CO2 split ratio were the key parameters considered to evaluate the technical feasibility of HBGS. Results indicated that the formation of the mixture gas hydrate depends on the driving force between the hydrate equilibrium conditions and operating conditions. The process of hydrate formation can be divided into two stages: Most of the CO2 formed the hydrate in the first stage, and both CH4 and N2 may have entered the hydrate structure in the second stage. For a given gas, the CO2 separation and CH4 recovery could not be optimized for one specific P–T condition. The powder X-ray diffraction measurements indicated that the ternary mixture gas hydrate was an structure I. The experimental results herein can provide data and theoretical support for CH4 purification and CO2 separation from biogas.

“…The best result is experiment 4, under the condition of 2 MPa, subcooling of 6 K, and 5 wt % TBAB, and the separation factor is 37.05. Figure 15 shows the CO 2 separation factor in different reports, 41,69,70 and it is obvious from Figure 15 that the CO 2 separation factor obtained by the constant pressure operation at low pressure is significantly higher than that obtained by the nonconstant pressure operation at high pressure. Therefore, it is suggested that CO 2 capture from the lean-CH 4 /CO 2 mixture should be carried out in a 5 wt % Energy & Fuels…”

Section: Effects Of Tbab Concentration On Hbgs Undermentioning

confidence: 96%

Hydrate-Based Mild Separation of Lean-CH₄/CO₂ Binary Gas at Constant Pressure

Fan

Huang

et al. 2021

The product gas of natural gas hydrate production by CO2 replacement is the lean-CH4/CO2 binary gas which contains 85–95% CO2. In this work, the lean-CH4/CO2 (10 mol % CH4/90 mol % CO2) binary mixture was used to simulate the product gas of natural gas hydrate production via CO2 replacement, and a promising and mild (low pressure) hydrate-based gas separation (HBGS) technology was employed. This work innovatively proposes to inject the reaction liquid to maintain the constant pressure of the whole process, which makes hydrates form continuously to increase the gas consumption. First, the hydrate phase equilibrium of 10 mol % CH4/90 mol % CO2 + 5 wt % tetrabutylammonium bromide (TBAB, aq) was measured in the range of 280–287 K and 0.5–4 MPa. After that, hydrate-based mild separation of the lean-CH4/CO2 binary gas was conducted with the help of TBAB at a constant pressure in the range of 1–4 MPa. The results show that after HBGS in addition with 5 wt % TBAB(aq) at 1 MPa and 278 K, the CH4 concentration could be increased from 17.2 to 66.2 mol % under constant pressure operation, while it was just slightly increased to 17.2 mol % under nonconstant pressure operation. HBGS with 5 wt % TBAB under constant pressure had the best separation performance. Subcooling has a greater effect on the separation kinetics. HBGS of 10 mol % CH4/90 mol % CO2 under a constant pressure operation of 2 MPa, subcooling of 6 K, and 5 wt % TBAB has the highest separation factor above 37. It is suggested that hydrate-based lean-CH4/CO2 separation experiments are carried out at a mild pressure with low G/L and, more importantly, in a short time. This work proposed a mild HBGS of lean-CH4/CO2 separation, which could benefit the separation of gas produced by natural gas hydrate replacement exploitation. This work also simultaneously provides insights into other HBGS for other gas mixtures (flue gas, coalbed methane, biogas, and shift gas) to achieve low energy consumption, high gas consumption, and high efficiency.