Victor R Vasquez

University of Nevada, Reno | UNR · Department of Chemical and Materials Engineering

Hypothesis Reverse micellar solutions are thermodynamically stable systems in which surfactant molecules surround water droplets within a continuous organic phase. Among their many applications, they can be used for the synthesis of nanoparticles of controlled agglomeration. Here, we consider the role specific ion effects play in reverse micelle si...

We describe the effects of ethanol on the phase behavior of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n-heptane. Using dynamic light scattering (DLS), molecular dynamics (MD) simulations, and nuclear magnetic resonance (1H-NMR) spectroscopy, we investigate the aggregation behavior of AOT across a wide range of ethanol/AOT/n-heptane compositi...

Due to extraordinary ability in the production of hydrophobic surfaces, nanoparticles raise potential as an alternative to common chemical collectors. Meanwhile, graphene can be considered as one of the most promising candidates due to its hydrophobic nature. Based on this premise, adsorption of graphene nano-layers on silicon dioxide (glass) surfa...

We show results of basic energetics and interacting behavior of hydrogen with metal hexaboride surfaces using a combination of self-consistent density functional calculations and dynamics based on the Car-Parrinello method. Our results show that hydrogen is strongly attracted to localized exposed boron atoms and interactions with the terminal catio...

Metal hexaborides are ionic crystals having exceptional thermochemical stability and unique electrochemical behavior, including low work functions, making these materials ideal for electron emission applications. Here, the importance of specific interfacial properties for the development of efficient cathode devices is examined. In particular, the...

Nanoparticles have significant potential as new candidates for generating new types of flotation reagents with unique performance for wettability design and control. Hence, this study explores the wettability of a glass surface covered with polystyrene nanoparticles at various surface coverage percentage using molecular dynamics simulations. To inv...

In this work, we use and developed a phosphotungstic acid loaded KIT-5 (Korea Institute of Technology-5) catalyzing methanol process for biodiesel fuel production from used cooking oil and other non-edible feedstocks such as coffee oil and algae oil. Kinetics studies show that a simple catalytic mechanism describes the kinetics of the esterificatio...

The local structures of ternary alkaline-earth hexaborides ( MB6 , M = Ca 0.5 Sr 0.5 , Ca 0.5 Ba 0.5 and Sr 0.5 Ba 0.5 ) have been analysed using X-ray pair distribution function (PDF) analysis, Raman spectroscopy and transmission electron microscopy (TEM). The results show significant local deviations from the average cubic structure within the bo...

We present the effect of pulsed direct current on metal ion diffusion in CaB<sub>6M/sub>-SrB₆ diffusion couples, showing that the diffusivity of Ca²⁺ and Sr²⁺ across the diffusion couple interface is higher towards the positive electrode when subjected to a current flow of 2.2 kA at a temperature of 2007 K. We attri...

We present a modeling framework and discuss the energetics and structural features of the surface terminations of Ca, Ba, Sr and La hexaborides using density functional theory analysis in combination with X-ray photoelectron spectroscopy. There is significant uncertainty in the literature about the nature of the surface terminations in metal hexabo...

Increasing awareness of environmental issues surrounding power generation and transportation has increased interest in renewable energy sources such as geothermal. Renewable energy extraction is not without environmental cost, however; drilling operations and construction of the facilities required for utilization can be resource intensive. Complet...

We present the behavior of multiple solid solutions within ternary (BaxCa1-x)B6 and (BaxSr1-x)B6 compounds and demonstrate that nano-domain formation is preferred over uniform solid solutions under certain processing conditions. Instead of the expected single solid solution of M¹ and/or M² atoms within the MB6 phase, we note separation into nano-do...

As a non-food renewable energy resource, lignocellulosic biomass is essential in augmenting limited fossil fuels to produce liquid fuels and chemicals. Hydrothermal carbonization (HTC) is a process that pretreats lignocellulosic biomass to produce sugars in its aqueous product and a solid hydrochar of increased heating value. Biomass is reacted in...

Cohesive energy curves contain important information about energetics of atomic interactions in crystalline materials, and these are more often obtained using ab initio methods such as density functional theory. Decomposing these curves into the different interatomic contributions is of great value to evaluate and characterize the energetics of spe...

Alkaline earth hexaborides are thermoelectric materials with unique thermophysical properties that have a broad variety of applications with great potential for new uses in fields such as light-weight armor development, gas storage, and n-type thermoelectrics. In this work, we introduce a modeling framework to simulate the basic mechanical behavior...

Lanthanum hexaboride (LaB6) is a well-known refractory ceramic with unique mechanical and electrochemical behavior, leading to a diverse array of possible attractive applications. In this work, we present and discuss the development of interatomic potentials for LaB6 using a combination of density functional theory with molecular dynamics simulatio...

As a non-food, renewable energy resource, lignocellulosic biomass is can be used for reducing greenhouse gas emissions. Hydrothermal carbonization (HTC) is a process to prepare lignocellulosic biomass for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 °C and 275 °C and at pressures suffi...

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-c...

Rice is the fundamental food for about half the world's population and provides over 20% of calories consumed by humans. Since the rice hull or husk is 20% of the grain, vast quantities of rice hulls are produced worldwide, which are then disposed by either burning, generating pollution and CO2, or by disposal in landfills. As a secondary agricultu...

Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy dense solid fuel, called biochar, from underutilized lignocellulosic biomass. Compared to raw biomass, HTC biochar is both more hydrophobic for better storage and more friable for better processing. In this pretreatment method, the biomass i...

Pyrolysis of lignocellulosic biomass was performed in a thermogravimetric analyzer at temperature ranging 105 to 800°C at the heating rates of 5, 10, and 20°C min−1. Samples of raw loblolly pine and hydrothermally carbonized loblolly pine were used as feedstocks in pyrolysis study. Thermogravimetric experiments showed that more significant decompos...

We present a systematic investigation and analysis of the structure and stability of reverse micelle systems with the addition of NH(4)OH, ZrOCl(2), and Al(NO(3))(3) salts. We demonstrate that the reverse micelle size decreases with increasing salt additions until one reaches a critical concentration, which characterizes the onset of system destabi...

A process for increasing the energy density of a biomass, Which includes establishing a temperature and pressure Within a reaction chamber that includes Water and is at or above a desired reaction condition Wherein the desired reac tion condition is su?icient to increase the energy density of a reacted biomass; introducing a biomass into the reacti...

As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source. When pretreated by hydrothermal carbonization, the resulting biochar (or hydrochar) is hydrophobic and of higher energy density. Addition of ionic salts to this high pressure aqueous pretreatment reduces reaction pressure. Ca propionate, Ca acetate, M...

As a highly available waste product, rice hulls could be a starting block in replacing liquid fossil fuels. However, their silica covering can make further use difficult. This preliminary study investigates effects of dissolving rice hulls in the ionic liquids 1-ethyl-3-methylimidazolium acetate (EMIM Ac), 1-hexyl-3-methylimidazolium chloride, (HMI...

Biomass supply is complicated by diversity of feedstocks, seasonal availability, and widely distributed feedstock. The costs of biomass supply and logistics hinder commercialization for advanced fuel and power production. Hydrothermal carbonization (HTC, or wet torrefaction) is a pretreatment process for making a homogenized, carbon rich, and energ...

The equilibrium moisture content (EMC) of raw lignocellulosic biomass, along with four samples subjected to thermal pretreatment, was measured at relative humidities ranging from 11% to 97% at a constant temperature of 30 °C. Three samples were prepared by treatment in hot compressed water by a process known as wet torrefaction, at temperatures of...

Moisture content in foods affects many aspects of processing and storage, as well as quality and pathological activity. Understanding its behavior is very important in the food industry for designing effective long-term food management strategies, in particular transportation and storage. Most approaches found in the literature dealing with moistur...

We use molecular dynamics (MD) and dynamic light scattering (DLS) measurements to analyze the size of reverse micellar structures in the AOT-water-isooctane system at different water-to-surfactant ratios at ambient temperature and pressure. We find good qualitative agreement for the size and morphology behavior of the reverse micelle structures bet...

As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source or feedstock for further conversion. However, challenges exist with supply logistics of this geographically scattered and perishable resource. Hydrothermal carbonization treats any kind of biomass in 200 to 260°C compressed water under an inert atmosph...

As a renewable non-food resource, biomass has great potential as an energy source or feedstock for further conversion. However, potential problems exist with transportation and storage of this geographically widely scattered and perishable resource. As a precursor to further thermochemical conversion, wet torrefaction treats any kind of biomass in...

Logistical related costs and inferior fuel performance prevent the attractive commercialization of lignocellulosic biomass conversion into biofuels. Wet torrefaction, or hydrothermal carbonization, is a pretreatment process to help converting diverse feedstocks into a homogeneous energy-denser solid fuel. The pre-treatment product has more favorabl...

Confidence intervals (CIs) are common methods to characterize the uncertain output of experimental measurements, process design calculations and simulations. Usually, probability distributions (pdfs) such as Gaussian and t-Student are used to quantify them. There are situations where the pdfs have anomalous behavior such as heavy tails, which can a...

Solid handling of diverse lignocellulosic biomass feedstock is very challenging for thermochemical conversion to renewable fuels. Wet torrefaction is a pretreatment process to convert biomass to energy-dense solid fuel, with relatively uniform handling characteristics. The fuel value of the produced solid may be as much as 36% higher than that of t...

The second annual Nevada Renewable Energy Consortium meeting took place at UNLV on August 20. The meeting focused on the current three NVREC program areas: Solar, Biomass and Geothermal. Presentations were made by participating entities and a poster session followed.

Hydrothermal pretreatment is a process for treating lignocellulosic biomass to prepare for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 ˚C and 275 ˚C, and at pressures above the liquid vapor pressure for times less then 30 min. In this study, mass and energy balances of the hydrotherma...

Moisture content in foods and similar biomass substrates affects many aspects of their processing and handling. Among them, drying is required for quality, conditioning, and transportation among others. The heat of vaporization of water in these substrates depends strongly on the water chemical activity, which is affected by many aspects such as ad...

Disposal of wastewater sludge presents an expensive problem for nearly all wastewater treatment facilities. Due to its high moisture content, energy exploitation is often not considered viable. However, various sludges present useful characteristics, and invite further evaluation. We have characterized the fuel value in terms of proximate analysi...

Thermochemical conversion of lignocellulosic biomass is a promising technology for production of renewable power, fuels, and chemicals. Both pyrolysis and gasification of biomass have significant technical barriers that must be eliminated for successful widespread commercialization. Feedstock handling is complex due to the diverse nature of importa...

Thermochemical conversion of lignocellulosic biomass is a promising technology for production of renewable power, fuels, and chemicals. Both pyrolysis and gasification of biomass have significant technical barriers that must be eliminated for successful widespread commercialization. Feedstock handling is complex due to the diverse nature of importa...

Torrefaction is a process to convert diverse lignocellulosic biomass feedstocks into an energy dense homogeneous solid, a pretreatment for subsequent thermochemical conversion. Loblolly pine was treated by wet torrefaction (hot compressed water, 200–260°C) and dry torrefaction (nitrogen, 250–300°C), with mass yield of solid product ranging between...

Provided that moisture is well managed, biosolids, or digested wastewater sludge, can be converted from an expense to a resource of renewable energy. Toward this goal, the equilibrium moisture content (EMC) for biosolids was determined experimentally in the ranges of 10–84% relative humidity and 30–60°C. Several well-known models were used to fit t...

Equilibrium moisture content (EMC) plays a fundamental role on the properties of bioderived solids such as food, waste biomass, seeds, and many others. For foods, the moisture content affects flavor, texture, and the way the food is stored. In other applications, moisture affects drying conditions and energy requirements for biomass processing. Ade...

Equilibrium moisture content (EMC) plays a fundamental role on the properties of bio-derived products such as food, waste biomass, seeds, and many others. For foods, the moisture content affects flavor, texture, and storing conditions. In other applications, moisture affects drying conditions and energy requirements for food processing. Adequate mo...

Thermo chemical conversion of biosolids to syngas or to fuels often includes a thermal drying step as the moisture content of the biosolids must be around 30%. Equilibrium moisture content (EMC) data of biosolids are required for good design and control of the drying process. The EMC data for Municipal sludge were measured in the relative humidity...

Equilibrium moisture content (EMC) plays a fundamental role on the properties of bio-derived solids such as food, waste biomass, seeds, and many others. For foods, the moisture content affects flavor, texture, and the way the food is stored. In other applications, moisture affects drying conditions and energy requirements for biomass processing....

We present preliminary molecular dynamics results showing the effect of simulation time, initial configuration, and presence of model salts for the AOT/water/ isooctane system. Reverse micelles, in particular the ones formed by this system, are commonly used as nanoreactors for nanoparticle synthesis. We are interested in the synthesis of ZrO2 or s...

We present Monte Carlo simulation results for square-well homopolymers at a series of bond lengths. Although the model contains only isotropic pairwise interactions, under appropriate conditions this system shows spontaneous chiral symmetry breaking, where the chain exists in either a left- or a right-handed helical structure. We investigate how th...

The purpose of this work is to evaluate the potential of modeling the self-diffusion coefficient (SDC) of real fluids in all fluid states based on Lennard–Jones analytical relationships involving the SDC, the temperature, the density and the pressure. For that, we generated an equation of state (EOS) that interrelates the self-diffusion coefficient...

A Monte Carlo method is presented to study the effect of systematic and random errors on computer models mainly dealing with experimental data. It is a common assumption in this type of models (linear and nonlinear regression, and nonregression computer models) involving experimental measurements that the error sources are mainly random and indepen...

In this work, we propose a model for representing the viscosity of supercritical pure fluids over a wide range of conditions. A given pure real fluid is represented as a Lennard–Jones (LJ) fluid having effective values of the LJ intermolecular potential parameters. The LJ fluid is actually a corresponding states fluid where the dimensionless variab...

The effects of uncertainty in thermophysical properties on the evaluation of the environmental performance is demonstrated with a chemical process to recover toluene and ethyl acetate by absorption from a gaseous waste stream of a cellophane production plant. In this case study, the environmental performance is defined as the estimation of the vola...

We examine the behavior of binary surfactant mixtures using Monte Carlo simulations with a three-dimensional lattice model of a binary surfactant mixture, in which the surfactants are represented by a series of connected beads. The range of amphiphile concentrations used is around the critical micelle concentration. The quasichemical approximation,...

A method for fast calculation of viscosity from molecular dynamics simulation is revisited. The method consists of using a steady-state periodic perturbation. A methodology to choose the amplitude of the external perturbation, which is one of the major practical issues in the original technique of Gosling et al. [Mol. Phys. 26: 1475 (1973)] is prop...

In this work, we study the robustness of nonlinear regression methods under uncertainty for parameter estimation for chemical kinetics models. We used Monte Carlo simulation to study the influence of two main types of uncertainty, namely, random errors and incomplete experimental data sets. The regression methods analyzed were least-squares minimiz...

An exponential and heavy tail analysis method is presented to study the effect of systematic and random errors present in thermodynamic data on chemical process design and simulation. The true distribution tail characteristics (important for high levels of quality assurance) can be far from the estimates obtained with typical Gaussian distribution...

We have used Monte Carlo methods to study the sensitivity and uncertainty of heat exchanger designs to physical properties estimation. The determination of appropriate confidence intervals for the overall heat-transfer coefficient and total required heat-exchange area plays a very important role in heat-exchanger thermal designs. The physical prope...

Monte Carlo simulations of a lattice model for amphiphile/solvent systems are used to obtain data for the configurational energy of mixing. Based on the simulation results, the energy of mixing is correlated as a function of the interaction energy and volume fraction of the amphiphile using a Redklich–Kister correlation. The Helmholtz free energy o...

An inside-variance estimation method (IVEM) for regression of the kinetic parameters in kinetic models and binary interaction parameters in thermodynamic models is proposed. The new method substantially improves the model predictions when compared with traditional least squares regression methods.

An inside-variance estimation method (IVEM) for regression of the kinetic parameters in kinetic models and binary interaction parameters in thermodynamic models is proposed. This maximum likelihood method involves the re-computation of the variance for each iteration of the optimization procedure, automatically re-weighting the objective function....

An inside-variance estimation method (IVEM) for binary interaction parameter regression in thermodynamic models is proposed. This maximum likelihood method involves the re-computation of the variance for each iteration of the optimization procedure, automatically re-weighting the objective function. Most of the maximum likelihood approaches current...

A novel approach called equal probability sampling (EPS) is used for analyzing uncertainty and sensitivity in thermodynamic models. Uncertainty and sensitivity analysis for simulation and design of industrial processes are becoming increasingly important. The (EPS) method produces more realistic results in uncertainty analysis than methods based on...

A Monte Carlo method is presented to separate and study the effects of systematic and random errors present in thermodynamic data on chemical process design and simulation. From analysis of thermodynamic data found in the literature, there is clear evidence of the presence of systematic errors, in particular, for liquid−liquid equilibria data. For...

Thermodynamic models and experimental data exhibit the usual systematic and random errors. The severity of their errors depends on their use, such as for process calculations in a process simulator. Similarly, the value of better thermodynamic models andror data should be measured with reference to such use. We have developed techniques for quantif...

Parameters for the UNIQUAC (universal quasi-chemical) model were regressed from VLE and LLE data for the systems:  diisopropyl ether + acetic acid + water; 1,1,2-trichloroethane + acetone + water; and chloroform + acetone + water. The results show a very significant effect of the data type used in the regressions (binary versus ternary) on the unce...

A method is presented using Monte Carlo Simulation coupled with the Latin Hypercube Sampling technique and parameter correlations to determine the effect of different sets of experimental data on the uncertainties in model parameters and, thus, the uncertainties in predicted process performance. Specifically, the estimation of binary interaction pa...

In this work, we propose a model for representing both the viscosity and the self diffusion coefficient (SDC) of supercritical pure fluids in wide ranges of conditions. A given pure real fluid is represented as a Lennard-Jones (LJ) fluid having efective values of the LJ intermolecular potential parameters. The model is able to represent the pure co...

We present preliminary molecular dynamics results for the AOT/water/isooctane system. Reverse micelles, in particular the ones formed by this system, are commonly used as nanoreactors for nanoparticle synthesis. We are interested in the synthesis of ZrO2 or similar, and how these particles affect the dynamics and structure of the reverse micelles....