气驱油油气混相过程的界面传质特性及其分子机制

油气混相过程的界面传质特性对气驱提高原油采收率技术非常重要。本文针对吉林某油田的实际油组分,采用分子动力学模拟研究了气驱油过程,分析了不同气体和驱替压力下油气两相的状态变化以及界面特性,获得不同驱替气体的最小混相压力(MMP)。结果表明,随着驱替气体压力的升高,气相的密度逐渐增大,油相膨胀密度降低,气相与油相的混合程度增强,油气两相界面厚度增加,界面张力随之减小。同时发现,驱替相中二氧化碳浓度越高,在同等气体压力下,油气界面更厚,油气混合程度更高。纯CO₂驱油得到的MMP远远小于纯N₂驱油,当这两种气体摩尔比为1 : 1混合时MMP介于两种纯气体之间,说明要达到同样的驱油效果二氧化碳需要的压力更小。最后,本文从分子微观作用力角度解释了驱替气体不同时影响油气混相程度的机制,通过分子平均作用势曲线发现油相分子对CO₂的吸引力要大于N₂分子,因此CO₂分子更容易与油相混合,驱替效果更明显。     

添加助熔剂后朱集西煤灰熔融特性规律研究

以高灰熔点朱集西洗煤为对象,研究了助熔剂CaCO₃、Fe₂O₃、CaCO₃/Fe₂O₃复合助熔剂以及CaMg(CO₃)₂对其煤灰熔融特性的影响。结果表明,各助熔剂均可降低煤灰熔融温度,但助熔效果与助熔剂种类和添加量有关,采用CaCO₃/Fe₂O₃复合助熔剂以及CaMg(CO₃)₂在添加量较小时,助熔效果明显;利用FactSage热力学软件,分析了添加助熔剂对煤灰中矿物高温熔融行为的影响,为进一步掌握助熔剂的助熔机理提供理论帮助。     

超临界二氧化碳二元体系相平衡性质的研究

采用固定体积可视观察法测定了CO₂+甲苯、CO₂+环己烷、CO₂+正丁醛、CO₂+异丁醛、CO₂+甲醇及CO₂+乙醇二元体系的临界点性质,为超临界萃取和化学反应提供基础数据.在对二元体系相行为与单组分超临界相行为进行比较的基础上,对不同化学物质及不同配比的二元体系临界点与二氧化碳临界点之间的关系进行了讨论.     

羟基氧化铟团簇与二氧化碳和甲烷作用的密度泛函理论研究

二氧化碳(CO₂)和化石能源气体燃料甲烷(CH₄)均是化学稳定、 温室效应较大的分子, 因而对其活化、 转化和利用的研究具有显著的理论和实际意义. 本文采用密度泛函理论方法, 计算研究了羟基氧化铟团簇与CO₂, CH₄和(CO₂+CH₄)的作用. 结果表明, 氧化铟团簇通过其活性位点—In—O(桥氧)—对CO₂和CH₄分子进行[2+2]加成活化, 而羟基的引入调变了氧化铟团簇活性位点上的局部电荷, 显著降低了其与CO₂和CH₄分子作用的活化自由能垒, 使得CO₂和CH₄分子的活化变得容易进行. 活性位点—In—O(桥氧)—中的In, O上的局部电荷差值(q_In－q_O)越大, 其对CO₂和CH₄分子作用的活化自由能垒越低. 羟基氧化铟与CO₂和CH₄分子作用时, 电子由羟基氧化铟流向CO₂和CH₄分子(亲核活化); 而羟基引入前的氧化铟与CO₂和CH₄分子作用时, 电子则由CO₂和CH₄分子流向氧化铟(亲电活化).     

丙烯酰胺多面体低聚倍半硅氧烷在超临界CO2中的RAFT聚合

以超临界CO₂为聚合介质, 硫代苯甲酰基特丁基硫酯(TTBT)为链转移剂, 通过可逆加成-断裂链转移(RAFT)聚合制备了聚丙烯酰胺多面体低聚倍半硅氧烷(PAMPOSS)均聚物及其与甲基丙烯酸甲酯(PMMA)的嵌段共聚物(PAMPOSS-b-PMMA). 对产物结构组成和分子量及其分布进行表征. 结果表明, 在TTBT的控制下, POSS的均聚物和嵌段共聚物具有高分子量及窄分子量分布. 含POSS单体在超临界CO₂中为均相聚合, POSS聚合物的结晶性在一定程度上影响其在超临界CO₂中溶解性.     

二氧化碳转化为氨基甲酸酯的研究进展

二氧化碳(CO₂)是大气中主要的温室气体,同时也是一种丰富、无毒和可再生的碳一资源。因此,将CO₂转化为有价值的化学品对实现可持续发展具有重要意义。然而,由于CO₂的热力学稳定性和动力学惰性,其活化转化非常具有挑战性。氨基甲酸酯是一类具有生物活性的重要化合物,广泛存在于天然产物、农用化学品和医药相关分子中,同时也是重要的有机合成中间体。近年来,利用CO₂作为光气的替代品用于合成氨基甲酸酯吸引了广泛的关注。本文主要综述了CO₂和胺在不同的催化体系下合成氨基甲酸酯的最新研究进展,主要分为无过渡金属催化、过渡金属催化、电催化、光催化四种反应体系来归纳总结,并对CO₂转化为氨基甲酸酯的未来研究方向进行了展望。     

超临界二氧化碳偶合超声预处理强化玉米秸秆酶水解(英)

提出了一个木质纤维素生物质预处理的全绿色加工过程.以玉米秸秆和玉米芯为原料,以超临界CO₂和超声偶合法对木质纤维素进行预处理.超临界CO₂预处理条件为:压力15-25 MPa,温度120₁70℃,含水量50%,反应时间0.5₄ h.超声场功率600W,温度80℃,作用时间2-8 h.用纤维素酶水解反应获得的还原糖总量来评价预处理效果.结果表明,单纯超临界CO₂和超临界CO₂偶合超声预处理都能够提高生物质水解反应还原糖产量.对于玉米芯,超临界CO₂预处理（170℃,20 MPa,3 0min）后,还原糖产率为62%（未预处理的为12%）.对于玉米秸秆（170℃,20 MPa,2.5 h）,还原糖产率为46.4%.对于玉米芯,超临界CO₂偶合超声预处理（600 W,80℃下超声处理6 h,然后用170℃,20 MPa超临界CO₂预处理30 min）后,还原糖产率为87%.对于玉米秸秆,超临界CO₂偶合超声预处理（600 W,80℃下超声处理8 h,然后用170℃,20 MPa超临界CO₂预处理1 h）后,还原糖产率为25.5%.与未处理生物质相比,X射线衍射结果表明玉米秸秆和玉米芯在超临界CO₂和超声预处理后其结晶度没有明显变化.扫描电镜分析则发现木质纤维素的表面积显著增加.     

TM@Ti2CTx电催化还原CO2:官能团诱导电子轨道重构与电荷转移(英文)

单原子催化还原二氧化碳制备可再生燃料和化工原料是一种有前途二氧化碳资源化技术.受MXene纳米片及其表面官能团调节的启发,本文利用不同的官能团(T=-O和-S)构建了Ti₂C基单原子电催化剂(TM@Ti₂CT_x,TM=V,Cr,Mn,Fe,Co,Ni),采用从头算量子化学方法,通过调控MXene表面官能团引起电子轨道重构和电荷转移,从而调控MXene基电催化剂的二氧化碳电催化性能.本文研究发现,氧官能团表面锚定的单原子催化剂(TM@Ti₂CO₂)能够显著活化CO₂.当CO₂分子吸附在TM@Ti₂CO₂表面上时,CO₂分子的轨道发生了重构,CO₂分子2π^*_u反键轨道劈裂,部分轨道与单原子的3d轨道结合沉入费米能级之下,导致CO₂分子发生形变.当CO₂分子吸附在TM...     

亲二氧化碳碳氢聚合物及其应用*

超临界二氧化碳（scCO₂）作为一种新型“绿色溶剂”,具有无毒、不可燃、易于分离以及来源丰富等特点,有望替代传统的挥发性有机溶剂。但scCO₂是很弱的溶剂,大部分极性分子和高分子量聚合物在其中的溶解度都很低,限制了其工业应用。目前,应用scCO₂遇到的一个挑战就是寻找有效的适用于scCO₂的表面活性剂、配合物、相转移剂等。本文综述了亲二氧化碳聚合物的研究进展,从链段柔顺性和自由体积、溶质/溶质相互作用、溶质/CO₂相互作用三个方面介绍了亲二氧化碳碳氢化合物的设计原则,并介绍了亲二氧化碳聚合物在制备表面活性剂、增溶染料和催化剂等方面的相关应用。     

一维g-C3N4/二维Ti3C2Tx界面调制促进光催化CO2还原活性与选择性(英文)

碳中和是实现绿色可持续发展重要途径之一,以半导体光催化CO₂还原.反应(CO₂RR)为核心的人工光合成技术极具发展前景.石墨相氮化碳(g-C₃N₄)作为一种二维层状光催化剂,化学性质稳定,且满足CO₂RR的热力学要求,但传统的g-C₃N₄光催化活性和选择性较低,这主要归因于高的电荷复合几率和低的光电子利用效率.采用二维碳化钛(Ti₃C₂T_x)等碳基助催化剂作为电子受体,促进光生载流子的快速分离与转移,成为提高g-C₃N₄光催化CO₂RR效率的有效手段.然而,g-C₃N₄光催化剂与Ti₃C₂T_x助催化剂多数以2D/2D构型界面耦合,受限于二者界面弱的范德华相互作用、高的界面静电势垒和缓慢的界面电荷转...     

基于多酯头基的“油-二氧化碳两亲分子”设计及其助混规律

Miscibility between oil and supercritical carbon dioxide (scCO₂) phases has attracted significant attention in the field of oil recovery because it can be utilized in miscible gas displacement of oil, achieving nearly 100% recovery efficiency. The high recovery efficiency of miscible CO₂ flooding originates from the valuable heavy components of oil and CO₂ gas phase forming a homogenous phase with high mobility in the oil-scCO₂ miscible system. However, the high pressure required for oil-scCO₂ miscibility is a nontrivial obstacle for practical applications of scCO₂ flooding recovery. Therefore, it is important to develop assist-miscible agents to lower the necessary miscibility pressure. In oil and water systems, well-developed amphiphiles (such as surfactants) have shown great promise for reducing the interfacial tension and maintaining the stability of the emulsion system. Therefore, "oil-CO₂ amphiphiles" that can assist the miscibility between oil and scCO₂ have been proposed. Among potential oil-scCO₂ amphiphiles, a series of polyester-based oil-CO₂ amphiphiles with esters as the CO₂-philic groups and long carbon chains as the oil-philic groups were prepared. The polyester-based oil-CO₂ amphiphiles, acting as assist-miscible agents, showed great ability to lower the needed miscibility pressure. A visualized miscible method was used to examine the efficiency of the assist-miscible agents with white oil and kerosene as the oil phase. The height of the oil phase inside the chamber was measured through a glass window to monitor the miscibility with increasing CO₂ pressure. When the height of the oil reached the top of chamber, the oil filled the entire space, indicating miscibility. Using this method, the following conclusions could be drawn: First, amphiphiles with more ester groups exhibited stronger CO₂-philicity, providing stronger ability to dissolve carbon dioxide. Second, amphiphiles with hydrocarbon chain lengths of 16 carbons exhibited the optimal assist-miscible efficiency. Third, greater differences between the oil and scCO₂ phase showed more obvious differentiation among amphiphiles, showing the leveling and differentiating effect of oil. The temperature range of 50–80 ℃ did not influence the assist-miscible efficiency of the polyester-based amphiphiles. The best miscibility-assisting performance was obtained with CAA8-X, which contains eight ester groups and a palmitic acid chain. CAA8-X at a concentration of 1% (w, mass fraction) lowered the miscibility pressure in the white oil-scCO₂ system by 16.04%. Amphiphiles with polyether (PEO) groups also showed excellent assist-miscible efficiency. The findings presented herein extend the concept of "amphiphilicity" from oil-water phases to oil-scCO₂ phases and have the potential to guide future studies regarding scCO₂ flooding in actual CO₂ flooding oil recovery. Moreover, for other two-phase systems, according to the general amphipathic law and particular system parameters, it should be possible to design the optimal "amphiphiles".     

Research for reducing minimum miscible pressure of crude oil and carbon dioxide and miscible flooding experiment by injecting citric acid isopentyl ester

The minimum miscible pressure is one of the key factors to realize miscible flooding. As the minimum miscible pressure in the research area is higher than the formation fracture pressure, miscible flooding cannot be formed. To address this problem, it is necessary to find a way to reduce the minimum miscible pressure. Citric acid isopentyl ester can not only be dissolved in crude oil, but also be dissolved in carbon dioxide. Therefore, citric acid isopentyl ester was chosen to reduce the minimum miscible pressure in this research. The effect of citric acid isopentyl ester on reducing the minimum miscible pressure was measured by the method of long slim tube displacement experiment. The minimum miscible pressure in the research area was 29.6 MPa. The experimental results show that the minimum miscible pressure could decrease significantly with increasing the injected slug size of citric acid isopentyl ester, but the decrease became smaller and smaller. The optimum injected slug size of the chemical reagent is 0.003 PV. Under the condition of the slug size, the minimum miscible pressure was 24.1 MPa. The reduction was 5.5 MPa. The reduction rate was 18.58%. The research results have important guiding significance for enhancing oil recovery in the research area.     

A new strategy for supercritical fluid extraction of copper ions

Complexation combined with supercritical fluid extraction was used to extract Cu²⁺. The effects of pressure, temperature, and total volume of CO₂ on the efficiency of extraction were systematically investigated. The extraction recovery was low (57.32%) only by pure supercritical CO₂. Addition of a suitable amount of methanol (v/v=5%) to supercritical CO₂ could enhance the extraction of Cu²⁺ (72.69%, relative standard deviation (R.S.D.)=2.12%, n=3), and the recovery increased largely (90.52%, R.S.D.=2.20%, n=3) in the presence of nonionic surfactant Triton X-100. Reverse micelle formation is presented as a new strategy of improving the extraction of metal ions with supercritical CO₂ in this paper.     

Supercritical fluid extraction and gas chromatography analysis of arsenic species from solid matrices

A method in combination with derivatization-supercritical fluid extraction(SFE) and gas chromatography(GC) for the speciation and quantitative determination of dimethylarsinate(DMA), monomethylarsonate(MMA) and inorganic arsenic in solid matrices was investigated. Thioglycolic acid methyl ester(TGM) and thioglycolic acid ethyl ester(TGE) were evaluated as derivatization reagents. The effects of pressure, temperature, flow rate of supercritical CO_2, extraction time, modifier and microemulsion on the efficiency of extraction were systematically investigated. The procedure was applied to the analysis of real soil and sediment samples. Results showed that TGE was more effective for arsenic speciation as a derivatization reagent. Modifying supercritical CO_2 with methanol can greatly improve the extraction efficiency. Further, the addition of microemulsion containing surfactant Triton X-100 can further enhance recoveries of arsenic species. The optimum extraction conditions were 100 ℃, 30 MPa, 10 min static and 25 min dynamic extraction with 5%(v/v) methanol, and surfactant modified supercritical CO_2. Detection limits in solid matrices were 0.15, 0.3 and 1.2 mg/kg for DMA, MMA and inorganic arsenic,respectively. The method was validated by the recovery data. The resulting method was fast, easy to perform and selective in the extraction and detection of various arsenic species in solid matrices.     

Determination of Minimum Miscibility Pressure of CO2–Oil System: A Molecular Dynamics Study

CO₂ enhanced oil recovery (CO₂-EOR) has become significantly crucial to the petroleum industry, in particular, CO₂ miscible flooding can greatly improve the efficiency of EOR. Minimum miscibility pressure (MMP) is a vital factor affecting CO₂ flooding, which determines the yield and economic benefit of oil recovery. Therefore, it is important to predict this property for a successful field development plan. In this study, a novel model based on molecular dynamics to determine MMP was developed. The model characterized a miscible state by calculating the ratio of CO₂ and crude oil atoms that pass through the initial interface. The whole process was not affected by other external objective factors. We compared our model with several famous empirical correlations, and obtained satisfactory results—the relative errors were 8.53% and 13.71% for the two equations derived from our model. Furthermore, we found the MMPs predicted by different reference materials (i.e., CO₂/crude oil) were approximately linear (R² = 0.955). We also confirmed the linear relationship between MMP and reservoir temperature (T_R). The correlation coefficient was about 0.15 MPa/K in the present study.     

Gas permeation through PSF-PI miscible blend membranes

The permeation rates of He, H₂, CO₂, N₂ and O₂, are reported for a series of miscible polysulfone-polyimide (PSF-PI) blend membranes synthesized in our laboratory. For gases which do not interact with the polymer matrix (such as He, H₂, N₂ and O₂), gas permeabilities in the miscible blends vary monotonically between those of the pure polymers and can be described by simple mixture equations. In the case of CO₂, which interacts with PI, blend permeabilities decrease somewhat, compared to pure PSF and PI. This, however, is accompanied by a two-fold improvement in the critical pressures of plasticization vs. polyimide. Permselectivities of CO₂/N₂ and H₂/CO₂ in the blends deviate from mixing theory predictions, in contrast to selectivities of gas pairs which do not interact with PI. Differential scanning calorimetry measurements of pure and PSF/PI blend membranes show one unique glass transition temperature, supporting the miscible character of the PSF/PI mixture. Optical micrographs of the blend membranes clearly indicate perfect homogenization and no phase separation. Frequency shifts and absorption intensity changes in the FTIR spectra of the blends, as compared with those of the pure polymers, indicate mixing at the molecular level. This compatibility in mixing PSF and PI, results essentially in a new blend polymer material, suitable for the preparation of gas separation membranes. Such membranes combine satisfactory gas permeation properties, reduced cost, advanced resistance to harsh chemical and temperature environments, and improved tolerance to plasticizing gases.     

Monitoring of technical oils in supercritical CO(2) under continuous flow conditions by NIR spectroscopy and multivariate calibration

Metal parts and residues from machining processes are usually polluted with cutting or grinding oil and have to be cleaned before further use. Supercritical carbon dioxide can be used for extraction processes and precision cleaning of metal parts, as developed at Forschungszentrum Karlsruhe. For optimizing and efficiently conducting the extraction process, in-line analysis of oil concentration is desirable. Therefore, a monitoring method using fiber-optic NIR spectroscopy in combination with PLS calibration has been developed. In an earlier paper we have described the instrumental set-up and a calibration model using the model compound squalane in the spectral range of the CH combination bands from 4900 to 4200 cm⁻¹. With this model only poor prediction results were obtained if applied to technical oil samples in supercritical CO₂. In this paper we describe a new calibration model, which was set up for the squalane/carbon dioxide system covering the 323–353 K temperature and the 16–35.6 MPa pressure range. Here, calibration data in the spectral range from 6100 to 5030 cm⁻¹ have been used. This range includes the 5100 cm⁻¹ CO₂ band of the Fermi triad as well as the hydrocarbon 1st overtone CH stretching bands, where spectral features of oil compounds and squalane are more similar to each other.

The root mean-squared error of prediction obtained with this model is 4 mg cm⁻³ for carbon dioxide and 0.4 mg cm⁻³ for squalane, respectively. The utilizability of the newly developed PLS calibration model for predicting the oil concentration and CO₂ density of solutions of technical oils in supercritical carbon dioxide has been tested. Three types of “real world” cutting and grinding oil formulations were used in these experiments. The calibration proved to be suitable for determining the technical oil concentration with an error of 1.1 mg cm⁻³ and the CO₂ density with an error of 6 mg cm⁻³. Therefore, it seems possible to apply this in-line analytical approach on the basis of a cost-effective and time-saving model compound calibration for the surveillance of real world de-oiling and other extraction process based on supercritical carbon dioxide, and furthermore to establish an automated process termination criterion based on this technique.     

PSRK: A Group Contribution Equation of State Based on UNIFAC

A group contribution equation of state called PSRK (Predictive Soave-Redlich-Kwong) which is based on the Soave-Redlich-Kwong equation (Soave, 1972) has been developed. It uses the UNIFAC method to calculate the mixture parameter a and includes all already existing UNIFAC parameters. This concept makes use of recent developments by Michelsen (1990b) and has the main advantage, that vapor-uquid-equilibria (VLB) can be predicted for a large number of systems without introducing new model parameters that must be fitted to experimental VLB-data. The PSRK equation of state can be used for VLB-predictions over a much larger temperature and pressure range than the UNIFAC γ--approach and is easily extended to mixtures containing supercritical compounds. Additional PSRK parameters, which allow the calculation of gas/gas and gas/alkane phase equilibria, are given in this paper. In addition to those mixtures covered by UNIFAC, phase equilibrium calculations may also include gases like CH₄ C₂H₆, C₃H₆, c₄H₁₀, CO₂, N₂, H₂ and CO.