The characteristic curvature (Cc) definition and its use in assessing Cc for single ionic surfactants

The hydrophilic–lipophilic-difference (HLD) is a set of empirical equations that correlate the formulation conditions at phase inversion (HLD = 0). Based on partition studies for nonionic surfactants, the HLD can be interpreted as a normalized chemical potential difference between the surfactant dissolved in water and oil. The net-average curvature (NAC) model extrapolates this interpretation into a curvature form that has been used to fit and predict the phase behavior of surfactant-oil–water (SOW) systems. The curvature interpretation led to renaming the HLD surfactant parameter, sigma (σ), as the characteristic curvature (Cc). This work tests the validity of the curvature interpretation of the HLD, and the Cc concept, for single ionic surfactants and the use of this concept as a method to assess the Cc without the use of reference surfactants or alcohols. To this end, the net curvature of six anionic and two cationic surfactants was evaluated from solubilization data at the characteristic condition of 25°C, no added cosolvent, in the presence of an oil mixture with equivalent alkane carbon number (EACN) of zero, and as a function of salinity. These studies showed that the original HLD equation for ionic surfactant could not be interpreted as chemical potential or curvature because a salinity prefactor (coefficient) “bi” was missing. The revised equation, HLD_bi = bi∙ln(S)-k_bi∙EACN+Cc_bi -a_Tbi∙(T-25°C), could now be interpreted as a curvature expression, and it was demonstrated that Cc could be obtained from curvature using the expression Cc = Cc_bi/bi. This single surfactant method produces uncertainties that, for most surfactants, ranged from 0.2 to 1 Cc units, similar to the uncertainty obtained with the conventional method of Cc determination using mixtures of test and reference surfactants.     

The HLD Study of Surfactant Partitioning for Oilfield Corrosion Inhibitors

The partitioning of corrosion inhibitor (CI) products is a measure of their potential to protect oilfield pipelines. In this paper the hydrophilic–lipophilic deviation (HLD) model is first used to quantify their partitioning in terms of the characteristic curvature (C _c,act) of a series of anionic (alkoxylated phosphate esters) and cationic (alkoxylated amines, aromatic amines, imidazoline acetates and quaternary amines) actives. This parameter is expressed over a range of pHs within which pipeline corrosion occurs. The HLD model is next used to predict the partitioning of each active from water into toluene at increased salinities. Linear mixing rules are lastly used to predict the characteristic curvature of Product A (C _c,mix) as a function of the C _c,act of a subset of actives.     

New Interfacial Rheology Characteristics Measured using a Spinning‐Drop Rheometer at the Optimum Formulation of a Simple Surfactant–Oil–Water System

A new spinning‐drop tensiometer with an oscillating rotation velocity was used to measure the interfacial rheological properties of systems with very low interfacial tensions in the zone close to the so‐called optimum formulation of surfactant–oil–water systems. 2 simple formulation scans were selected: One with an extended anionic surfactant using a salinity variation in the water phase, and another with a mixture of 2 nonionic surfactants in a scan produced by changing their proportion. With both systems it was corroborated that at optimum formulation (i.e., at hydrophilic–lipophilic deviation (HLD) = 0), both the interfacial tension and the emulsion stability exhibit a deep minimum. A clear relationship was also found between the phase behavior and the interfacial rheological properties (dilational elasticity and viscosity). For the very first time and in both kinds of scans (salinity or average ethylene oxide number), it was found that the interfacial elastic modulus E and the interfacial viscosity, as well as the phase angle also exhibit a minimum at optimum formulation. These groundbreaking findings could be applied to emulsion instability at optimum formulation and to its applications in emulsion breaking.     

Robust Flash Calculation Algorithm for Microemulsion Phase Behavior

The HLD-NAC model was recently modified to match and predict microemulsion phase behavior experimental data for Winsor type III regions. Until now, the HLD-NAC model could not generate realistic phase behavior for type II? and type II+ two-phase regions, leading to significant saturation and composition discontinuities when catastrophe theory is applied. These discontinuities lead to significant failures in modeling surfactant applications. We modify the HLD-NAC equations to ensure consistency over the entire composition space including type II? and II+ regions. A robust and efficient algorithm is developed that always converges and provides continuous estimates with any formation variable of tie lines and triangles for all Winsor types. Discontinuities are eliminated and limiting tie lines near critical points are determined analytically. The tuning procedure is demonstrated using several sets of experimental data. Excellent predictability of tie lines and tie triangles, and solubilization ratios are shown.     

Correlation between Detergency of Different Oily and Solid Non-Particulate Soils and Hydrophilic–Lipophilic Deviation

This research examined the correlation between the detergency of soils with varying equivalent alkane carbon numbers (EACN) and hydrophilic–lipophilic deviation (HLD) values. The detergency of oily soils with EACN ranging from 5.2 to 16.6 was evaluated using C₁₀-4PO-SO₄Na as a primary surfactant system and a 1:1 binary mixture of C₁₀-4PO-SO₄Na and AOT as a confirmatory surfactant system (with 65/35 polyester/cotton at 25°C). These surfactant systems were characterized using HLD concepts which showed that C₁₀-4PO-SO₄Na was more hydrophilic (had a higher negative Cc value) than that of the mixed surfactant system. Detergency of the selected soils was evaluated at different salinities corresponding to HLD ranging from negative to positive values. The results showed that detergency of all soils increased with increasing salinity (starting with an HLD = −3.0 (Winsor Type I microemulsion)), reached the maximum at widely different optimum salinity (S*) but at an identical HLD value of zero (optimum Type III), and then decreased with further increasing salt levels corresponding to positive HLD values (Type II). The preferred HLD range from −3.0 to 0.0 showed detergency levels exceeding 80% removal with interfacial tension values (IFT) below 1 mN m⁻¹ for all oily soils studied. Detergency of octadecane (EACN = 18, solid at 25°C) was further conducted and demonstrated that performing detergency at HLD = −3.0 to 0.0 likewise revealed superior soil removal (over 80%) versus systems with HLD values outside this range. Thus, this work highlighted the utility of using the HLD approach in designing surfactant formulations for detergency of soils with widely varying EACN.     

Planting rates and delays during the establishment of willow biomass crops

Biomass for bioproducts and bioenergy can be sourced from multiple sources. There is little information on commercial planting operations for willow biomass crops in North America. The objectives of this study were to evaluate the field capacities of two commercial machines (Step and Egedal Energy Planter) planting willow crops in northern New York State, determine the amount and distribution of delays. A study was conducted to evaluate planter activities. The two machines had similar mean field capacities (C_f) ranging from 0.89 to 1.14 ha h⁻¹. Above-average rainfall in the later part of the planting season decreased C_f by over 20% for the Step planter from 1.14 to 0.91 ha h⁻¹; largely due to delays in the headlands. Approximately 70% of the total delay time associated with the Step planter consisted of long-duration delays (>5 min) compared to 35% for the Egedal. Quality of planting stock was an issue for operations; undersized stems resulted in feeding issues. Several potential factors were identified for improved planting operations: loading stems and clearing feeding mechanisms at each turn, improved planting stock and quality control, improving machine design for wet conditions, and improved preparation for in-field repairs. In-field delays should be minimized to reduce demand on the crew and ensure a more uniform crop is established in the field.     

Application of the Hydrophilic–Lipophilic Deviation Concept to Surfactant Characterization and Surfactant Selection for Enhanced Oil Recovery

The hydrophilic–lipophilic deviation (HLD) concept has been demonstrated to be useful in determining characteristic curvature (Cc) of a surfactant. Cc is a surfactant parameter that reflects the hydrophobicity/hydrophilicity or the tendency of the surfactant to form microemulsions in an oil–water system. In order for the Cc value to be calculated, the formation of the optimum Winsor III microemulsion of oil and water systems under specific salinity and temperature conditions is required. Surfactant Cc values have been widely used to quantitatively screen and select a suitable surfactant in formulations for different application areas, especially enhanced oil recovery (EOR). The HLD concept is an effective tool for designing new surfactant molecules to meet the target Cc value for a specific formulation condition. The HLD equation indicates the dependence of a microemulsion system on the changes of various system parameters. This article demonstrates how the HLD equation can be derived in different ways depending on the characteristics of the surfactant to identify the proper experimental approach so that the Cc values of different types of surfactants can be determined. Three types of surfactants were studied, including nonionic alcohol ethoxylates, anionic alkyl propoxy ethoxy sulfates, and carboxylates. The application of the HLD concept to surfactant selection for EOR application was also demonstrated.     

Synthesis and Characterization of Novel Surfactants based on 2-Hydroxy-4-(Methylthio)Butanoic Acid Part 3: Microemulsions from Nonionic Sulfoxide Ester Surfactants

In this work, ester sulfoxide (ESO) surfactants based on 2-hydroxy-4-(methylthio) butyric acid are shown to have temperature-sensitive microemulsion phase behaviors. Both C10 (C₁₀ESO) and C12 (C₁₂ESO) surfactants studied contained one sulfoxide unit in the structure. Phase inversion temperatures (PIT) and interfacial tensions (IFT) between water-rich and oil-rich phases have been measured for ternary systems of water, oil, and sulfoxide surfactants. Hydrophilic–lipophilic deviation (HLD) parameters of these surfactants were obtained by fitting the experimental data to a semiempirical HLD equation. The characteristic surfactant parameter and temperature sensitivity of C₁₀ESO and C₁₂ESO surfactants were obtained and compared with similar ethoxylated alcohol surfactants. By comparing the characteristic parameters of these surfactants with those of ethoxylated alcohol surfactants, it was shown that one sulfoxide ester moiety is equally hydrophilic as approximately 5 ethylene oxide groups. The temperature sensitivity of the ESO was roughly a factor of four less than ethoxylated surfactants based on the temperature coefficient of the HLD equation.     

Effect of Ethylene Oxide Group in the Anionic–Nonionic Mixed Surfactant System on Microemulsion Phase Behavior

The phase behavior of microemulsions stabilized by a binary anionic–nonionic surfactant mixture of sodium dihexyl sulfosuccinate (SDHS) and C12-14 alcohol ethoxylate (C_{12 − 14}E_j) that contains an ethylene oxide (E_j) group number, j, of either 1, 5, or 9 was investigated for oil remediation. The oil–water interfacial tension (IFT) and optimal salinity of the microemulsion systems with different equivalent alkane carbon numbers (EACN) were examined. The anionic–nonionic surfactant ratio was found to play a pivotal role in the phase transition, IFT, and optimal salinity. The minimum IFT of mixed SDHS − C_{12 − 14}E_j systems were about three times lower than those of neat SDHS systems. A hydrophilic–lipophilic deviation (HLD) empirical model for the mixed anionic–nonionic surfactant system with the characteristic parameter was proposed, as represented in the excess free energy term . The results suggested that the mixed system of SDHS − C_{12 − 14}E₁ was more lipophilic, while SDHS − C_{12 − 14}E₉ was more hydrophilic than the ideal mixture (no excess free energy during the microemulsion formation), and the SDHS − C_{12 − 14}E₅ system was close to the ideal mixture. The findings from this work provide an understanding of how to formulate mixed anionic–nonionic microemulsion systems using the HLD model for oils that possess a wide range of EACN.     

Heat exchanger network design of large-scale industrial site with layout inspired constraints

This paper presents a systematic approach for the synthesis of the heat recovery network in total site using a Mixed Integer Linear Programming model. This model returns a near-to-optimal network configuration with minimum utility cost while allows to select geographically closest matches. The Heat Load Distribution is the subproblem of the network design and has been reported to be quite expensive to solve for large-scale problems. The computational complexity of HLD resides in the number of streams and the feasible networks. An additional challenge, raising particularly in industrial problems, has been the intermediate heat transfer network which aggravates the combinatorial complexity. The presented methodology deals with those difficulties by priority consideration based on the location of process units. It helps significantly reducing the computational time and also comes with a realistic network sketch with respect to the plant layout. Several examples are discussed along with a real industrial case study.