Hydrofluorocarbon Refrigerants Research Articles

Benefits and challenges in deployment of low global warming potential R290 refrigerant for room air conditioning equipment in California

High global warming potential gases (“high GWP”) are the fastest growing sector of greenhouse gas emissions in the world and in California and are primarily used as refrigerant gases in refrigeration and cooling equipment. Hydrofluorocarbons (HFCs) refrigerants are the dominant type of high GWP gases with GWP values thousands of times larger than CO2 on a 100-year timescale. Refrigerant-grade propane (“R290”) has a very low GWP (GWP = 3.3) with good thermodynamic properties and good cooling equipment performance but the flammability of any leaked refrigerant makes equipment design, handling, and maintenance critical factors to manage. This paper focuses on the potential climate benefits and costs of transitioning to R290 refrigerant in small room air conditioning (AC) units, specifically window AC, packaged terminal AC/heat pumps (PTAC/PTHP), and mini-split heat pumps. Overall climate impact for a transition to all three types of air conditioning units in the 2022–2051 timeframe is found to be from 15 to 64 million metric tons of greenhouse gas (GHG) savings in California with a cost of saved CO2eq that ranges from $14.50 per ton of CO2eq saved to −$50.30 per ton of CO2eq saved (net savings) depending on whether the baseline refrigerant is R32 or R410A and depending on the relative energy efficiency for R290 units compared to baseline units.

Ionic liquid fluoropolymer membranes for the separation of R-410A: Understanding the effect of ionic liquid on membrane characteristics and separation performance

Environmental legislation such as the American Innovation and Manufacturing Act will phase out today's generation of high-global warming hydrofluorocarbon refrigerants over the next two decades. Energy-efficient technologies are needed to separate these often azeotropic and complex mixtures. Membrane technology and extractive distillation with ionic liquids as entrainers have been individually developed for the separation of azeotropic refrigerant mixtures. This study provides details for the separation of R-410A through combining the benefits of glassy, amorphous polymers with ionic liquids to form ionic liquid polymer membranes. Two different classes of ionic liquid polymer membranes are considered: polyvinyl acetate composite membranes with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, and 1-hexyl-3-methylimidazolium chloride, and Hyflon AD 60 with 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide. The membranes are characterized with FTIR, helium pycnometry, differential scanning calorimetry, and a high-pressure view-cell to characterize the effect of ionic liquid on polymer properties. The Hyflon AD 60 composite membranes were evaluated for the separation of R-410A through pure-gas permeability, selectivity, solubility, and diffusivity measurements, which show exceptional selectivity for separation of R-410A. Results provide insights on the effect of ionic liquid on the separation of R-410A and indicate that improved separation performance of glassy polymers can be achieved with the addition of ionic liquid.

On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases.

The enforcement of a global hydrofluorocarbon (HFC) refrigerant phase down led to the introduction of hydrofluoroolefins (HFOs) as a low Global Warming Potential (GWP) substitute, given their low atmospheric lifetime. However, to this date it is not fully clear the long-term atmospheric fate of HFOs primary degradation products: trifluoro acetaldehyde (TFE), trifluoro acetyl fluoride (TFF), and trifluoroacetic acid (TFA). It particularly concerns the possibility of forming HFC-23, a potent global warming agent. Although the atmospheric reaction networks of TFE, TFF, and TFA have a fair level of complexity, the relevant atmospheric chemical pathways are well characterized in the literature, enabling a comprehensive hazard assessment of HFC-23 formation as a secondary HFO breakdown product in diverse scenarios. A lower bound of the HFOs effective GWP in a baseline scenario is found above regulatory thresholds. While further research is crucial to refine climate risk assessments, the existing evidence suggests a non-negligible climate hazard associated with HFOs.

ReaxFF reactive molecular dynamic and density functional theory study on the co-pyrolysis mechanism of waste 1,1,1,2-tetrafluoroethane and waste plastics to produce high value-added chemicals and fuels

Pyrolysis is one of the potential way for the degradation of hydrofluorocarbons, but it is difficult to make effective use of the complex pyrolysis products. The addition of plastics can provide sufficient hydrogen source for the degradation of hydrofluorocarbons to generate the high value-added chemicals and fuels. Density functional theory calculation and reactive molecular dynamic simulation are employed to investigate the co-pyrolysis mechanism of 1,1,1,2-tetrafluoroethane and low-density polyethylene in this work. The results show that the H atoms provided by low-density polyethylene promote the defluorination reactions of 1,1,1,2-tetrafluoroethane to generate HF and short chain hydrocarbons, and the number of F atoms in HF molecules accounted for nearly 80 % of the whole reaction system, achieving a better defluorination effect. The defluorination rate of 1,1,1,2-tetrafluoroethane and plastics co-pyrolysis is more than 5 times that of pure 1,1,1,2-tetrafluoroethane pyrolysis. The main co-pyrolysis products of 1,1,1,2-tetrafluoroethane and low-density polyethylene are H2, HF and short chain hydrocarbons, the purpose of hydrofluorocarbons degradation into high value-added chemicals and fuels is realized in this study. This work provides a green, effective way for the conversion waste hydrofluorocarbons and waste plastics into high value-added chemicals and fuels, and achieves the conversion of waste hydrofluorocarbon refrigerants to more economical products.

The comprehensive research on the transcritical CO2 thermal management system used in thermostatic transport vehicles

Natural fluid CO2 has become the preferred target of refrigerant alternative in the electrified transportation field in recent years to replace positive temperature coefficient (PTC) heaters, reduce energy consumption, and respect the international ban on Hydrofluorocarbons (HFCs) refrigerants. Thermostatic transport vehicles (TTVs) are well suited to exploit the benefits of CO2 due to their working conditions with a broad range of ambient temperatures, extensive transit distances, and substantial heating capacity requirements in cold climates. In this paper, a transcritical CO2 heat pump air-conditioning system used in TTV was constructed initially with proper control logic. Then following the assessment of the system’s steady-state performance, the dynamic operation process under high thermal inertia was thoroughly examined and analyzed in detail. Ultimately, the optimization of the dynamic response process was realized under varying heat flow boundary conditions. The primary results demonstrated that the rationally designed CO2 thermal management system performed admirably in various operating conditions, particularly in the heating mode where the coefficient of performance (COP) exceeded 3.2. Addressing the high-frequency fluctuation caused by the cargo thermal inertia, the temperature could be maintained with only two starts and stops within 3×105 seconds when the system control logic was refined. The optimized thermal management system of TTV efficiently allowed cargo to achieve the proper temperature as quickly as possible and sustain stability. This study provides an effective theoretical basis for the promotion of the transcritical CO2 thermal management system in the field of TTVs.

Investigation of environmentally friendly new generation refrigerant R471A instead of R404A in low and medium temperature commercial refrigeration system

Hydrofluorocarbon (HFC) refrigerants (such as R134a and R404A), which are widely used in commercial refrigeration systems, contribute greatly to global warming. Because the global warming potential (GWP) values of HFC refrigerants are high. With increasing concerns about the environment (global warming, climate change, etc.) various legal regulations have been made to limit or phase out the use of refrigerants with high GWP values. To use the R471A refrigerant developed by Honeywell in 2022 as an environmentally friendly new-generation refrigerant in the commercial refrigeration system, the performance of the R471A refrigerant should be comprehensively evaluated. In this study, energy, exergy, and environmental analyses of using R471A refrigerant instead of R404A in low and medium-temperature commercial refrigeration systems were carried out and presented. Evaporator temperatures of − 30 °C, − 25 °C, − 20 °C, − 15 °C and − 10 °C and condenser temperatures of 30 °C, 40 °C, and 50 °C were selected to represent low and medium cooling temperatures and hot and cold country seasons. It was seen that R471A presents a lower mass flow rate (between 67 and 71%) and cooling capacity (between 61 and 68%) than R404A however has higher COP (between 6% and 14%) and R404A has exergy efficiency value of 6–14% lower than R471A. Also, from an environmental point of view, R471A has better environmental results than R404A.

Study on the combustion characteristics of NH3 and the inhibition characteristics of R134a on NH3

NH3 has been considered as an alternative to hydrofluorocarbon (HFC) refrigerants due to its environmentally friendly properties, while it is flammable. Therefore, it is necessary to investigate the flammability of NH3 (R717) and find its matching flame retardant to broaden its application. In this paper, the combustion behaviors of R717 and the inhibition characteristics of flame retardant R134a on R717 were studied experimentally and theoretically. Firstly, the flame propagation pattern, flammability limit, laminar burning velocity, and Markstein length of pure R717 were measured by a constant volume combustion bomb from 300 K to 400 K. Then the flammability characteristics of R134a/R717 mixture were further tested. The results indicated that R134a had a distinct flame retardancy on the flammability limits of R717. Further, the flame retarding mechanism of R134a on R717 was analyzed by density functional theory (DFT) on the 6–311++G(d,p) level. The flame retarding effects of R134a were classified to physical and chemical mechanisms. The physical force mainly depended on the dilution effect of additional R134a. The chemical mechanism was contributed to the newly flame retarding reactions introduced by R134a, which reflected in the dehydrogenation of R717 and the consumption of OH and H active radicals by fluorine-contained radicals (CF3, CF2, and F).

Scenario analysis of hydrofluorocarbons consumption and emission reduction in China's mobile air-conditioning sector

The automobile air conditioning industry is an important consumption area of hydrofluorocarbons (HFCs), and the analysis of the use and emission reduction of HFCs in this industry is of great significance for environmental protection. This study aims to measure and analyze the HFC consumption and emission reduction in China's MAC industry and the cost of emission reduction in automobile enterprises through an in-depth analysis, to provide a scientific basis for the formulation of relevant policies and to support the country in achieving HFC emission reduction targets in the field of environmental protection. In this study, the Gompertz model combined with the vehicle survival rate Weibull was used to predict the vehicle ownership and sales in China, and then the HFC consumption and emission reduction in China's MAC industry and the cost of emission reduction in automobile enterprises were measured and analyzed with reference to the experience of relevant domestic and foreign measurement models. The results show that under the four scenarios of R27-X29, R29-X29, R29-X29, and R29-X35, the cumulative use of HFCs will be reduced by 61.44%−73.19%, and the cumulative emission will be reduced by 51.85%−64.55% in the period of 2023–2060, while the cumulative abatement cost of the automobile enterprises in the period of 2023–2060 will be RMB 419.31–481.02 billion. 481.02 billion yuan. The adoption of a policy banning HFCs refrigerants in M1 and N1 vehicles has a significant effect on reducing HFCs consumption and emissions, and the abatement cost will decrease with the expiration of new refrigerant patents, increased demand, and technological advancements.

The emission reduction potential and cost-effectiveness of low-GWP refrigerants in electric vehicle air conditionings

Electric vehicles play a crucial role in the carbon neutrality transformation of urban transportation, provided that they are powered by electricity generated from renewable (rather than fossil-based) generation sources. However, the substantial indirect emissions from electric vehicle air conditioning energy consumption and the significant direct emissions from HFCs (hydrofluorocarbons) refrigerants pose considerable challenges. In order to identify low-GWP (global warming potential) refrigerants -such as R1234yf, R744, and R290 - that can effectively minimize carbon emissions while maintaining certain cost-effectiveness, this paper establishes the relevant life-cycle analysis and life-cycle cost analysis models for electric vehicle air conditioning. The results obtained show that, in 2022, the total carbon emissions of China’s automotive air conditioning fleet were approximately 162 million tons CO2-eq. The nationwide average carbon emissions ranking of various refrigerant heat pumps is R290 < R1234yf < R744 < R134a. The Net Present Value (NPV) of the life cycle cost for R134a electric vehicle heat pump is estimated to be around 11,500 yuan. Among the three low-GWP refrigerants, the life cycle cost of R290 is significantly lower than that of R134a under nationwide average conditions, while R744 exhibits the best life cycle performance in certain cold cities/regions.

Vapor-liquid equilibrium measurements of ionic liquid [DEME][TFSI] with different hydrofluorocarbon refrigerants R152a, R32, and R143a

To overcome the shortages of traditional working pairs (LiBr/H2O and NH3/H2O) for absorption-refrigeration systems (ARSs), novel working pairs consisting of low global warming potential (GWP) hydrofluorocarbons difluoroethane (R152a) and difluoromethane (R32) plus low-viscosity ionic liquid N,N‑diethyl-2‑methoxy-N-methylethan-1-aminium bis((trifluoromethyl)sulfonyl)amide ([DEME][TFSI]) are studied. Firstly, solubilities of R152a and R32 in [DEME][TFSI] are measured by the isochoric saturation method in the temperature range of 293 K ∼ 343 K and pressure range of 0.14 MPa ∼ 1.664 MPa with the relative expanded uncertainty of 0.03. A high-GWP hydrofluorocarbon 1,1,1-trifluoroethane (R143a) is involved in the experiment for further comparison. The non-random two-liquid model is used to correlate the vapor-liquid equilibrium data with average absolute relative errors of 0.55 % (R152a), 0.58 % (R32), and 0.94 % (R143a), respectively. [DEME][TFSI] shows its low viscosity and good solubility of hydrofluorocarbons by contrast with conventional ionic liquids. A refrigerant solubility rank order in [DEME][TFSI]: R152a > trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) > R32 > 2,3,3,3-tetrafluoro-1-propene (R1234yf) > R143a is obtained from the comparison. This work provides the possibility to apply low-GWP working pairs R152a/[DEME][TFSI] and R32/[DEME][TFSI] in ARSs.

Machine learning‐assisted analysis and prediction for the thermal effect of various working fluids in a vortex tube

AbstractWith the widespread application of vortex tube in various fields, it becomes essential to quantitatively explore the separation effect of different fluids (natural fluids, hydrocarbons, etc.) within the vortex tube and to promote its utilization. A new approach has been developed in this study to establish quantitative models for predicting the thermal effects of different fluids in a vortex tube. These models are based on both the macro properties of the working fluid and micro molecular descriptor through a molecular scale. A dataset of 11 numerical simulation results of hydrocarbons and hydrofluorocarbons refrigerants is employed. Three operating conditions, 10 property parameters, and 115 molecular descriptors are screened and identified using random forest feature analysis. Two types of models (micro and macro) have been developed by employing artificial neural network (ANN) modeling techniques. In the result, four key influencing fluid property parameters (the specific heat ratio γ, the multiplication of heat capacity and the molar weight cp·M, the kinematic viscosity ν, and the thermal conductivity λ) and nine molecular descriptors in affecting the thermal effect are identified and respectively chosen as the input in the macro and the micro ANN model establishment. Both types of developed models show a high correlation coefficient (R > .999) and a comparatively low mean square error (MSE). When R600 is employed in the validation, most of the relative error is less than 10%, suggesting both types of models can work effectively in predicting the thermal effect for other fluid. The findings contribute to a deeper understanding of the thermodynamic effect of vortex tubes and provide a valuable tool for selecting and optimizing working fluids in various applications.

A Comparative Study of R134a and Propane (R290) as Refrigerants in Heat Pump Water Heaters

In the context of decarbonization efforts, heat pump water heaters (HPWHs) offer an attractive solution over conventional electric resistance type hot water systems due to their 2-3 times higher efficiency. However, the high manufacturing costs and taxes associated with using hydrofluorocarbon (HFC) refrigerant make HPWHs expensive. As a means to tackle this issue, this paper explores the use of propane (R290) as a refrigerant in HPWHs. The study involves an experimental comparison of R290 and R134a, with refrigerant charges optimized for the unit at different ambient temperatures. This current work demonstrates that R290 achieves a 10% improvement in coefficient of performance (COP) at ambient temperatures beyond 20°C. However, at 10°C ambient temperature, the study shows that R290 offers no advantage over R134a, and the COP is lower. These results indicate that the compressor is the largest source of inefficiency, and this aligns well with experimental results on system performance. Additionally, simulation tests using compressors designed for R290 did not predict better COP values than the test unit. Overall, the study suggests that R290 is a viable refrigerant option for HPWHs, but further research is necessary to optimize it’s use.

Machine Learning-Enabled Development of Accurate Force Fields for Refrigerants.

Hydrofluorocarbon (HFC) refrigerants with zero ozone-depleting potential have replaced chlorofluorocarbons and are now ubiquitous. However, some HFCs have high global warming potential, which has led to calls by governments to phase out these HFCs. Technologies to recycle and repurpose these HFCs need to be developed. Therefore, thermophysical properties of HFCs are needed over a wide range of conditions. Molecular simulations can help understand and predict the thermophysical properties of HFCs. The prediction capability of a molecular simulation is directly tied to the accuracy of the force field. In this work, we applied and refined a machine learning-based workflow to optimize the Lennard-Jones parameters of classical HFC force fields for HFC-143a (CF3CH3), HFC-134a (CH2FCF3), R-50 (CH4), R-170 (C2H6), and R-14 (CF4). Our workflow involves liquid density iterations with molecular dynamics simulations and vapor-liquid equilibrium (VLE) iterations with Gibbs ensemble Monte Carlo simulations. Support vector machine classifiers and Gaussian process surrogate models save months of simulation time and can efficiently select optimal parameters from half a million distinct parameter sets. Excellent agreement as evidenced by low mean absolute percent errors (MAPEs) of simulated liquid density (ranging from 0.3% to 3.4%), vapor density (ranging from 1.4% to 2.6%), vapor pressure (ranging from 1.3% to 2.8%), and enthalpy of vaporization (ranging from 0.5% to 2.7%) relative to experiments was obtained for the recommended parameter set of each refrigerant. The performance of each new parameter set was superior or similar to the best force field in the literature.

Evaluating Eco-Friendly Refrigerant Alternatives for Cascade Refrigeration Systems: A Thermoeconomic Analysis

A simple vapor-compression refrigeration system becomes ineffective and inefficient as it consumes a huge energy supply when operating between large temperature differences. Moreover, the recent Kigali amendment has raised a concern about phasing out some hydrofluorocarbon refrigerants due to their impact on the environment. In this paper, a numerical investigation is carried out to compare the performance of a cascade refrigeration system with two environmentally friendly refrigerant combinations, namely, R170–R404A and R41–R404A. Refrigerant R170, from the hydrocarbon category, and refrigerant R41, from the hydrofluorocarbon category, are separately chosen for the low-temperature circuit due to their similar thermophysical properties. On the other hand, refrigerant R404A is selected for the high-temperature circuit. An attempt is made to replace refrigerant R41 with refrigerant R170 as a possible alternative. The condenser temperature is kept constant at 40 °C, and the evaporator temperature is varied from −60 °C to −30 °C. The mathematical model developed for the cascade refrigeration system is solved using Engineering Equation Solver (EES). The effect of evaporator temperature on different performance parameters such as the COP, exergetic efficiency, and total plant cost rate is evaluated. The predicted results show that the thermoeconomic performance of the R170–R404A-based system is marginally lower compared to that of the R41–R404A-based system. The system using refrigerant pair R170–R404A has achieved only a 2.4% lower exergetic efficiency compared to the system using R41–R404A, with an increase in the annual plant cost rate of only USD 200. As the global warming potential (GWP) of R170 is less than that of R41, and R170 belongs to the hydrocarbon category, the use of the R170–R404A combination in a cascade refrigeration system can be recommended as an alternative to R41–R404A.

Numerical simulation of condensation from isobutane vapour – air mixture

Hydrocarbon condensation has been a topic of interest in recent years due to its applications in refrigeration, chemical processing and air conditioning. The condensation of friendly fluids reduces the Global Warming Potential and Ozone Depletion Potential, which can be used as an alternative to many hydrofluorocarbon (HFC) refrigerants. The main objective of this study is to investigate the combined heat and mass transfer of laminar film condensation from isobutane vapour in the presence of a small percentage of non-condensable gas (air) inside a vertical tube. The external tube wall is subjected to a constant temperature. To achieve our goal, a mathematical model based on mass conservation, momentum, and energy in both gas and liquid phases is established. The discretization of equations in each region with the boundary conditions is realised using an implicit finite difference scheme. The validity of the numerical model developed is verified in comparison with the results of the literature. The obtained results show that the condensation process is enhanced by increasing the inlet velocity and the inlet-to-wall temperature difference. Moreover, the results indicate that the presence of non-condensable gas reduces the efficiency of heat and mass exchanges.

Density and isochoric heat capacity of {x trans-1,3,3,3-Tetrafluoropropene + (1-x) Propane} at temperatures from (285.45 to 349.71) K and pressures up to 10.384 MPa

The increasingly serious global warming problem has accelerated the elimination of traditional hydrofluorocarbon (HFC) refrigerants. R1234ze(E) + R290 binary mixture as a potential alternative refrigerant are expected to overcome the deficiencies of R1234ze(E) (low volumetric refrigeration capacity) and R290 (flammability and explosiveness). In this paper, the 38 density and 119 isochoric specific heat capacity data of R1234ze(E)+R290 mixtures were measured at temperatures from (285.45 to 349.71) K using an adiabatic batch calorimeter with intermittent heating. Uncertainties of temperature, pressure, density and isochoric heat capacity were estimated to be less than 12 mK, 5 kPa, 0.30% and 1.0%. The density data were correlated using the Tait equation, and good regression results were obtained, with the AARD of 0.19% and MARD of 0.83%. A comparison was conducted between the Tait equation and REFPROP 10 and Peng-Robinson equation of state (PR EoS), the Tait equation gives the best prediction performance. In addition, the isochoric specific heat capacity data were compared with the values calculated by four models (PR model, Zhong model, Sheng model and REFPROP 10). Among them, the three models, the Zhong model, Sheng model and REFPROP 10, give the same prediction performance, with AARD of 2.88%, 2.47% and 2.51%, respectively. But for the PR model, the density data has a significant impact on the result, especially for the low-temperature region. When the density data were calculated by the Tait equation, the PR model presents the best prediction performance for the heat capacity of R1234ze(E) + R290 mixtures with the AARD of 2.00%, nevertheless, when the density data were calculated from the PR EoS, the PR model showed a large deviation in the prediction of isochoric heat capacity with the AARD and MARD of 3.74% and 11.11%. An empirical equation was correlated to represent the experimental heat capacity data with the MARD of 3.07% and the AARD of 1.15%.

Experimental study on the pull‐down performance of a −80°C cascade refrigeration freezer

AbstractTo cope with global climate change, chlorofluorocarbons and hydrofluorocarbons refrigerants have been or will be abandoned by different countries worldwide. Natural refrigerants seem to be promising substitutes in the near future. In this study, eco‐friendly refrigerants R290 and R170 are adopted as high‐temperature and low‐temperature fluid in a cascade refrigeration freezer to generate −80°C. The experimental measurements are carried out to investigate the pull‐down performance of the freezer. The inlet and outlet pressure of two compressors are monitored and tested. Temperatures of different state monitors in high‐temperature cycle and low‐temperature cycle are measured to analysis the operation performance of the cascade refrigeration system. Different temperature test points are set to research the temperature drop and temperature distribution in the freezer. Some new findings are obtained. Due to the lack of ultralow temperature experimental data on cascade refrigeration system, this study can enrich and deepen the understanding on operation mechanism of ultralow temperature cascade refrigeration freezer.

What Data Are Most Valuable to Screen Ionic Liquid Entrainers for Hydrofluorocarbon Refrigerant Reuse and Recycling?

What Data Are Most Valuable to Screen Ionic Liquid Entrainers for Hydrofluorocarbon Refrigerant Reuse and Recycling?

Coordinating to promote refrigerant transition and energy efficiency improvement of room air conditioners in China: Mitigation potential and costs

Implementing the Kigali Amendment to the Montreal Protocol has imposed certain restrictions on the production and consumption of hydrofluorocarbons (HFCs). Taking this opportunity to promote the alternatives of high global warming potential (GWP) HFC refrigerants in the room air conditioner (RAC) sector as well as improve the energy efficiency can bring double benefits. With the RAC sector as an example, a demand-emissions-cost model is developed to assess the potential and costs of emission reductions in different regions of China under different scenarios. The model includes three scenarios: a business as usual (BAU) scenario, a Kigali energy efficiency (KAE) scenario with simultaneous energy efficiency improvements following the Kigali amendment, and an accelerated transition energy efficiency (ATE) scenario with accelerated HFCs reduction and energy efficiency improvements. The results show that under the KAE and ATE scenario, the GHG emissions of the RAC sector will peak in 2025 at 389.8–393.9 Mt CO2-eq and 378.8–382.8 Mt CO2-eq in China. The main contribution to this result is the alternative of low GWP refrigerants. From 2021 to 2060, the cumulative direct emission reductions are about 6.4–7.4 Gt CO2-eq and 8.5–9.5 Gt CO2-eq in KAE and ATE, and the cumulative indirect emission reductions for both scenarios are 1.6–1.8 Gt CO2-eq. The cumulative abatement costs are $286–321 billion and $288–322 billion (prices in 2020). Under the ATE scenario, direct emissions from refrigerants in the RAC sector are near zero in 2060, and indirect emissions depend on the power system structure. The RAC sector's average abatement cost varies significantly in diverse climatic environments. Given the variation in average abatement cost, it is critical to tailor mitigation policies to local conditions to ensure maximum benefits.

Decomposition mechanism of hydrofluorocarbon (HFC-245fa) in supercritical water: A ReaxFF-MD and DFT study

In this work, the concept of using supercritical water to treat Hydrofluorocarbons (HFCs) refrigerants waste is proposed. Taking 1,1,1,3,3-Pentafluoropropane (HFC-245fa) as the research object, based on the ReaxFF reactive force field molecular dynamics method and density function theory, the decomposition mechanism of HFC-245fa in supercritical water, the effects of temperature, HFC-245fa mass concentration and oxygen addition on the decomposition of HFC-245fa in supercritical water and decomposition mechanism were studied. The results show that the main stable products of HFC-245fa decomposition in supercritical water are HF, CO2, CO and H2. In supercritical water, ·F radicals can easily combine with H2O molecules and then rapidly decompose to generate HF molecules and ·OH radicals. The hydrogen extraction reaction of ·H radicals with H atoms in HFC-245fa molecules and H2O molecules has relatively low energy barrier. ·OH radicals can also participate in the dehydrogenation reaction, promoting the further dehydrogenation of HFC-245fa molecules and their molecular fragments. Moreover, it can combine with carbon-containing molecular fragments to promote the conversion of C element to CO and CO2. The lower concentration of HFC-245fa promotes the conversion of C element and generation of H2. The addition of oxygen facilitates the generation of ·OH radicals and promotes the conversion of C element to CO2, but reduces the generation of CO and H2. Under the condition of HFC-245fa mass concentration of 13.0%, the calculated formation apparent activation energies of HF, CO and CO2, H2 are 196.3, 368.5 and 249.0 kJ·mol−1, respectively.