基于CPA状态方程的高压含硫天然气压缩因子计算方法研究

对于压力高于70 MPa的含H_2S天然气,其分子之间间距缩小,极性H_2S分子之间缔合作用增强,传统SRK、PR状态方程计算高压含硫天然气的压缩因子准确性有待进一步改进。基于压力3.72～97.58 MPa、H_2S体积分数0%～70.03%的154组压缩因子修正CPA(Cubic-Plus-Association)状态方程中H_2S与CH_4、CO_2分子间二元交互作用系数,综合评价SRK、PR、CPA状态方程对压缩因子的计算精度。结果表明,对于中低压含硫天然气(p35 MPa),采用PR方程精度最高,平均相对偏差为1.12%;对于高压及超高压含硫天然气(p35 MPa),CPA方程精度最高,平均相对偏差为-1.46%。进一步采用法国ST抗硫高压PVT仪测试了4种含硫天然气在70～131 MPa条件下的138组压缩因子实测值,验证了采用CPA状态方程对于高压含硫天然气压缩因子的计算精度。     

The CPA EoS application to model CO2 and H2S simultaneous solubility in ionic liquid [C2mim][PF6]

The CPA EoS was utilized for solubility modeling of pure CO₂ and H₂S and their mixture in [C₂MIM][PF₆]. The model is comprised of SRK EoS in addition to Wertheim's association term. Up to now, several associating models such as SAFT variants have been successfully applied to such systems. Considering the complexity and time consuming nature of SAFT EoSs, CPA can be a good alternative due to its accuracy and simplicity with respect to the SAFT.

The AAD % for binary systems including H₂S+ IL and CO₂+ IL are 11.78, 10.40 respectively. Moreover, the ternary system show AAD% equal to 16.51.     

The solubility of acid gases in the ionic liquid [C8mim][PF6]

Mixtures containing associating compounds, represent highly non-ideal phase behavior, due to the presence of powerful hydrogen bonding interactions. Up to now, several associating models such as SAFT variants have been applied to such systems. The CPA EoS was introduced by Kontogeorgis and his coworkers in order to combine a cubic EoS, and the SAFT theory. At the present survey, acid gas mixtures solubilities in IL [C₈mim][PF₆] has been thermodynamically modeled using CPA EoS. The AAD % for binary systems, including H₂S+ IL and CO₂+ IL are 8.74, 2.14 respectively. Moreover, for ternary systems AAD % is equal to 17.43.     

Application of reaction equilibrium thermodynamic model for correlation of H2S solubility in ionic liquids [emim][Ace] and [hmim][Ace] using CPA equation of state

Correlation of H₂S solubility in ionic liquids [emim][Ace] and [hmim][Ace] was performed using CPA EoS. For taking into account the effect of possible chemical reactions, the Reaction Equilibrium Thermodynamic Model (RETM) was used. This model assumes that an AB₂ type reaction mechanism between two IL molecules and one H₂S molecule is taken place. Both of H₂S and ILs was considered as association components following 4C and 2B association schemes, respectively. First, pure components parameters achieved using CPA EoS. Consequently, the binary systems were investigated applying RETM. The results show AAD% equal to 4.75 and 12.44 for [emim][Ace] and [hmim][Ace] respectively.     

Thermodynamic modeling of ternary systems containing imidazolium-based ionic liquids and acid gases using SRK,Peng-Robinson,CPA and PC-SAFT equations of state

Abstract

In this study, the cubic and the associative equations of state are applied to model the VLE data of ternary systems containing ionic liquids. In the first section, the simultaneous solubility of CO₂ and H₂S in the ionic liquids [omim][Tf₂N], [omim][PF₆] and [bmim][PF₆] is modeled and the selective absorption of CO₂/H₂S is investigated at the temperatures T/K = (303.15 and 343.15) and the pressures P/MPa = (0.1 and 1). According to the obtained results, the percent deviations in pressure were varying between 6.0 and 10.8 for the SRK EoS, 6.0 and 10.6 for the PR EoS, 2.6 and 9.6 for the CPA EoS and 3.4 and 6.1 for the PC-SAFT EoS. Also, percent deviations in vapor phase composition were varying between 3.1 and 4.9 for the SRK EoS, 3.3 and 4.9 for the PR EoS, 3.1 and 7.0 for the CPA EoS and 3.8 and 4.9 for the PC-SAFT EoS. In the selectivity calculations, at high ionic liquid concentrations, the cubic models predict the selectivity drop; while the associative models present increasing trend. In the second section, the CO₂ solubility in ethanol and [emim][Tf₂N] as well as the mixture of ethanol and [emim][Tf₂N] is modeled and the experimental points were tested for thermodynamic consistency. According to the obtained results, the percent deviation in pressure of the ternary systems was 3.9 for the SRK EoS, 3.9 for the PR EoS, 3.8 and 4.0 for the CPA EoS and 3.1 and 3.2 for the PC-SAFT EoS. In the same temperature and pressure, the CO₂ solubility decrease when the concentration of ethanol increases, and the proposed models can describe this phase behavior.     

Determination of asphaltene precipitation using a CPA equation of state

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. Therefore, predicting asphaltene phase behavior through thermodynamic modeling may help to control its precipitation and reduce the associated problems. In this work, a new modified CPA equation of state (EoS) was used to model asphaltene precipitation. This equation is based on a combination of a new physical part and the Wertheim association term.

The results of the new model were compared with the experimental data of five oil samples. The results showed that this modified CPA EoS can predict asphaltene precipitation with good accuracy.     

Modeling of acid gases solubility in ionic liquid [BMIM][MeSO4] using CPA EoS

This work follows the thermodynamically modeling procedure to correlate the solubility of pure CO₂ and H₂S in [BMIM][MeSO₄]. Moreover, solubility of acid gases mixture was predicted. The bubble point pressure calculation method was applied in which CPA EoS is responsible for fugacity coefficients calculation of the components. The CPA EoS combines SRK and Wertheim's association term to handle non-ideal behavior of the polar and associating components.

The AADs% of H₂S+IL and CO₂+IL binary subsystems were calculated as 18.4 and 17.36 respectively. Moreover, AADs% equal to 27.26 and 6.74 were obtained for predicted partial pressures of CO₂ and H₂S, respectively.     

Prediction of thermodynamic properties of natural gas mixtures using 10 equations of state including a new cubic two-constant equation of state

In this contribution, 10 equations of state (EoSs) are used to predict the thermo-physical properties of natural gas mixtures. One of the EoSs is proposed in this work. This EoS is obtained by matching the critical fugacity coefficient of the EoS to the critical fugacity coefficient of methane. Special attention is given to the supercritical behavior of methane as it is the major component of natural gas mixtures and almost always supercritical at reservoir and surface conditions. As a result, the proposed EoS accurately predicts the supercritical fugacity of methane for wide ranges of temperature and pressure. Using the van der Waals mixing rules with zero binary interaction parameters, the proposed EoS predicts the compressibility factors and speeds of sound data of natural gas mixtures with best accuracy among the other EoSs. The average absolute error was found to be 0.47% for predicting the compressibility factors and 0.70% for the speeds of sound data. The proposed EoS was also used to predict thermal and equilibrium properties. For predicting isobaric heat capacity, Joule–Thomson coefficient, dew points and flash yields of natural gas mixtures, the predictive accuracy of the EoS is comparable to the predictive accuracy of the Redlich–Kwong–Soave (RKS) EoS or one of its variants. For predicting saturated liquid density of LNG mixtures, however, the accuracy of predictions is between the RKS and Peng–Robinson (PR) EoSs.     

Implementation of CPA EoS for simultaneous solubility modeling of CO2 and H2S in ionic liquid [OMIM][Tf2N]

In this study, solubility of pure CO₂ and H₂S and their mixture in [OMIM][Tf₂N] modeled applying CPA EoS. CPA combines the SRK equation with an advanced association term, which is similar to that of SAFT. From a practical point of view, the target in the CPA project was to develop a thermodynamic model capable of describing complex equilibria of mixtures containing polar/associating chemicals through a simple procedure with respect to the SAFT.

The AAD% for binary systems, including H₂S+ IL and CO₂+ IL are 6.81, 5.21 respectively. Moreover, AAD% equal to 13.89 was achieved for the ternary system.     

Pseudo-component Delumping for Multiphase Equilibrium in Hydrocarbon-Water Mixtures

Abstract

An analytical and consistent delumping procedure is implemented for fluids of petroleum interest containing water, non-hydrocarbon gases (such as N₂, CO₂, and H₂S) and hydrocarbon (HC) compounds. Two sorts of difficulties are associated with these fluids: they often exhibit three or more equilibrium phases, and their thermodynamics cannot be described by conventional cubic equations of state (EoS). In this work, the Søreide-Whitson modification of the Peng-Robinson EoS, in which different binary interaction parameters are used in the aqueous and non-aqueous phases, is used. The method is successfully tested on two cases in the two- and three-phase regions: one synthetic HC/N₂/CO₂/H₂O fluid and a “real” water/reservoir fluid.     

Wash water disinfection of a full-scale leafy vegetables washing process with hydrogen peroxide and the use of a commercial metal ion mixture to improve disinfection efficiency

Hydrogen peroxide (H₂O₂) was used to maintain the microbial wash water quality of a full-scale leafy vegetables (radicchio, sugar loaf, curled endive, lollo, lollo rosso) wash water process. Despite addition of 300 L/h of 1.8% H₂O₂ to a 450 L washing bath (333 ± 50 kg/h fresh-cut produce introduction speed), the H₂O₂ quickly decreased and a lower wash water contamination of aerobic psychrotrophic plate count (APC) and enterococci than without addition of H₂O₂ could not be maintained. There was no significant difference between the APC on fresh-cut leafy vegetables washed with H₂O₂ and those washed with water.In a second part, lab-scale experiments were performed to assess the impact of a commercial metal ion formulation (Bacsan^®, containing a. o. Cu²⁺, Zn²⁺, Ag⁺) on the stability of H₂O₂ in artificial wash water, made from iceberg lettuce and tap water. Bacsan improved the stability of H₂O₂ in artificial lettuce wash water and fresh-cut leafy vegetables wash water from a processing company and synergistically increased the disinfection efficiency of APC and Escherichia coli (E. coli) compared to H₂O₂ or Bacsan. Increasing chemical oxygen demand (COD) had detrimental effect on the H₂O₂ stability and disinfection efficiency. Addition of Ag⁺ to Bacsan further synergistically enhanced the H₂O₂ stability.H₂O₂ is not suited as an in situ wash water disinfectant to avoid cross-contamination in fresh-cut leafy vegetables washing processes due to the slow water disinfection kinetics and the rapid H₂O₂ consumption. However, H₂O₂/Bacsan shows potential for use in off-line processes.     

Determination of asphaltene precipitation using a new CPA-based equation of state

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. Therefore, predicting asphaltene phase behavior through thermodynamic modeling may help to control its precipitation and reduce the associated problems. In this work, a new modified cubic-plus-association (CPA) equation of state (EoS) was used to model asphaltene precipitation. This equation is based on a combination of a new physical part and an association term.

The new physical part has an evolved cubic equation of state with a new attractive term in this work. The results of the new modification of CPA EoS were compared with the experimental data of two oil samples (oil samples 1 and 2) that belonged to Moradi et al. The results showed that this modified CPA EoS can predict asphaltene precipitation with good accuracy.     

Determination of acetylene solubility in dispersed water by computer simulation

The interaction of acetylene molecules with the (H₂O)₂₀ cluster was studied by molecular dynamics simulation. The behavior of the derivative of the chemical potential (?μ/?i)_V,T (i is the number of acetylene molecules) shows that the cluster stability is retained when no more than two C₂H₂ molecules add to the cluster. The system composed of (C₂H₂)_i(H₂O)₂₀ clusters has higher values of dielectric permittivity (both real and imaginary terms) than the (H₂O)_{20 + n} cluster system. The medium formed by water clusters with C₂H₂ molecules both absorbs and reflects IR radiation with a higher intensity as compared to a system of this type with pure water. The addition of C₂H₂ molecules to water clusters is also accompanied by an increase in the number of bands in an IR reflection spectrum. Adsorbed C₂H₂ molecules are aligned with the tangent to the water core of the cluster, thus impeding their penetration into the aggregate and, hence, decreasing the solubility of acetylene.     

Aflatoxin and fumonisin contamination of yam flour from markets in Nigeria

The natural occurrence of aflatoxins (AFs) and fumonisins (FBs) in yam flour samples (n = 100) obtained in south-western Nigeria was evaluated. AFs were determined by HPLC with fluorescence detection and FBs by HPLC coupled with mass spectrometry. Aflatoxin B₁ (AFB₁) and aflatoxin G₁ (AFG₁) were found in 57% and 21% of flours from white yam with concentrations ranging from <0.02 (limit of detection, LOD) to 3.2 μg kg⁻¹ (mean = 0.4 μg kg⁻¹) and from <0.05 to 3.5 μg kg⁻¹, respectively. AFB₁ was the only aflatoxin detected in samples from water yam, contaminating 32% of the samples with values ranging from <LOD to 0.6 μg kg⁻¹ (mean = 0.1 μg kg⁻¹). Fumonisin B₁ was found in 32% of the white yam samples (<0.5 (LOD) to 91 μg kg⁻¹; mean = 5 μg kg⁻¹) and in 5% of water yam samples (<LOD to 2 μg kg⁻¹). AFs and FBs were significantly higher (P < 0.05) in white yam flours compared to water yam flours. Preparation of amala from naturally-contaminated yam flour resulted in reduction of AFB₁ and AFG₁ by 44% and 51% respectively. From this study, only 7% of the samples contained AFs above the European standard limits for cereals intended for direct human consumption, while all the FBs-positive samples were well below the limits. The occurrence of ochratoxin A, zearalenone and deoxynivalenol was also evaluated in 20 samples; these mycotoxins were never detected.     

A New Approach for Accurate Prediction of the Phase Behavior of the Complex Mixtures of Acid Gases,Hydrocarbons, Water,and Methanol in the Petroleum Industry

In this work a new approach for accurate prediction of the vapor-liquid equilibrium of the complex mixtures of water, methanol, acid gases (H₂S, CO₂), and hydrocarbons considering the hydrogen bonding association, hydrolytic dissociation, and acid gas solvation effects is presented. The overall average absolute deviation between the predicted and measured compositions regarding 330 sour gas mixtures is about 3.22%. The proposed CPA/electrolyte model is quite reliable over wide ranges of temperatures and sour gas concentrations and can be employed for accurate design of sour natural treatment and flow assurance systems in oil and gas industries.     

Effect of combination of ultraviolet light and hydrogen peroxide on inactivation of Escherichia coli O157:H7, native microbial loads,and quality of button mushrooms

Mushrooms are prone to microbial spoilage and browning during growing and processing. Ultraviolet light (254 nm, UV-C) has been used as an alternative technology to chemical sanitizersfor food products. Hydrogen peroxide (H₂O₂) is classified as generally recognized as safe for use in foods as a bleaching and antimicrobial agent, and could control the bacterial blotch and browning of mushrooms. This study investigated the effects of water wash (control), 3% H₂O₂ wash, 0.45 kJ m⁻² UV-C, and combination of H₂O₂ and UV-C (H₂O₂ + UV) on microbial loads and product quality of mushrooms during storage for 14 days at 4 °C. Additionally, the inactivation of Escherichia coli O157:H7 inoculated on mushrooms was determined. Results showed that water wash, H₂O₂, UV-C and H₂O₂ + UV resulted in 0.44, 0.77, 0.85, and 0.87 logs CFU g⁻¹ reduction of E. coli O157:H7, respectively. Hydrogen peroxide, UV-C and the combination reduced total aerobic plate counts on the surface of mushrooms by 0.2–1.4 logs CFU g⁻¹ compared to the control, while there was no significant difference among the three treatments during storage. After storage, UV-C treated mushrooms had similar L* and a* values as the control while H₂O₂ and H₂O₂ + UV-C treated mushrooms had higher L* (lighter) and lower a* (less brown) values than the control. Compared to water wash, all the treatments inhibited lesion development on the mushroom surface on day 14. The combination of H₂O₂ and UV achieved the best overall dual control of lesion and browning. There was no significant difference in ascorbic acid and total phenolic content among the treatments. Overall our results suggested that H₂O₂ + UV reduced microbial loads, and extended storage life by reducing lesion development without causing deterioration in nutritional quality of button mushrooms. Therefore, when properly utilized, H₂O₂ + UV could potentially be used for maintaining postharvest quality while marginally reducing populations of E. coli O157:H7 and background microflora.     

Modeling of sporicidal effect of hydrogen peroxide in the sterilization of low density polyethylene film inoculated with Bacillus subtilis spores

The sporicidal effect of hydrogen peroxide (H₂O₂) in the sterilization of low density polyethylene film (LDPE) was evaluated using a Central Composite Design (CCD). The effects of contact time (5-19s), bath temperature (23–70 °C) and concentration of H₂O₂ (0–35%) in an immersion bath were investigated. A 16 cm² film surface was evenly inoculated with 100 μL of the test microorganism Bacillus subtilis var. globigii ATCC9372 spores. The effective H₂O₂ sporicidal activity was demonstrated at concentrations from 18 to 35% and in a temperature range from 46 to 70 °C, resulting in 2–7 decimal reductions of B. subtilis spores. A quadratic mathematical model representative of the action of H₂O₂ on the B. subtilis spores was developed as a function of concentration, time and temperature. Test specimens sanitized with 28% H₂O₂ at 60 °C for 8 s showed 4 decimal reductions. In the same sterilization procedure, but extending the time to 16 s, this value increased to 7 decimal reductions, demonstrating the efficiency of H₂O₂ as a function of contact time. The sterilization system tested showed satisfactory performance in the sterilization of LDPE films, being capable of reaching up to 7 decimal reductions of the bacterial spore population.     

Estimation of growth parameters of Listeria monocytogenes after sublethal heat and slightly acidic electrolyzed water (SAEW) treatment

Time to detection experiments (TTD) based on turbidometry using an automatic Bioscreen C is a useful and straightforward method for estimating microbial growth parameters (lag time (λ), growth rate (μ) and “work to be done” (h₀)) at constant temperature. This study investigated the effects of slightly acidic electrolyzed water (SAEW) and heat treatment on Listeria monocytogenes growth at different recovery temperatures (10 °C, 15 °C, 25 °C, and 30 °C). Similar surviving and sublethally injured L. monocytogenes populations were obtained by heat treatment (55 °C for 10 min) and SAEW treatment (available chlorine concentration of 30 mg/l and ratio of bacteria against SAEW of 8:2 for 30 s). In these experimental conditions, stresses had greater impact on the λ and h₀ parameter in comparison with recovery temperature while there was no great change in growth rate under isothermal conditions. Larger λ values and h₀ parameters were observed in sublethal-heat injured L. monocytogenes (the maximum λ and h₀ parameters are 30.199 h and 1.6492) as compared to SAEW groups (the maximum λ and h₀ parameters are 22.634 h and 1.4396). The sensitivity analysis of SAEW and heat treatments on h₀ parameter indicated that SAEW treatment showed a higher influence. The collinearity diagnostics of independent variables [recovery temperature (T), μ, λ] for dependent variable (h₀ parameter) demonstrated that T, μ and λ had strong collinearity. In addition, the established secondary models in this study have good performances on predicting the effect of recovery temperature on bacterial growth parameters.     

气体在N-甲酰吗啉溶液中溶解度模型的研究

估算了N-甲酰吗啉(NFM)的临界参数Tc,Pc和偏心因子ω,结合计算出的临界参数,运用状态方程,对文献中CO2,H2S,C2H6和CH4在N-甲酰吗啉溶液中的溶解度进行了考核,并通过相平衡实验数据优化得到了组分间的交互作用参数Kij。考核结果表明,对于以上气体在NFM中的溶解度计算,应用PR状态方程结合vdW混合规则是较好的选择。     

Efficacy of electrolyzed oxidizing water as a pretreatment method for reducing Listeria monocytogenes contamination in cold-smoked Atlantic salmon (Salmo salar)

Listeria monocytogenes contamination in ready-to-eat (RTE) fish products, in particular in cold-smoked salmon is an important food safety concern. This study evaluated the antimicrobial activity of electrolyzed oxidizing (EO) water as a pretreatment method during the process of cold-smoked salmon to inactivate L. monocytogenes. In addition, the effect of EO water treatment on the sensory and textural quality of the final product was also evaluated. Raw Atlantic salmon (Salmo salar) fillets were inoculated with L. monocytogenes (with an approximately cell number of 6 × 10⁵ CFU/g L. monocytogenes ATCC 19114) and treated with EO water at three different temperatures (20, 30, and 40 °C) and at three different exposure time of 2, 6, and 10 min before the cold-smoking process. A combination of EO water and a mild temperature (40 °C) had reduced L. monocytogenes populations by 2.85 log₁₀ CFU/g. The sensory as evaluated by a consumer panel (N = 71) and texture, which was measured by texture analysis showed no significant changes between EO and mild temperature treated samples and the control.