I currently have four active research interests:
1. Waste to Energy Conversion- Worldwide, there are many opportunities to convert wastes, including agricultural waste, wastewater sludge, municipal solid waste, construction waste, and forest debris, into useful fuels. We are developing expertise in thermal conversion processes, and have recently focused on drying studies.
2. Wastewater sludge- we are developing a process to convert wastewater sludge into renewable power. Our process tightly manages heat, to allow for an economical conversion process.
3. Cellulosic biomass- we are developing processes for homogenizing and densifying diverse biomass feedstocks for subsequent thermochemical conversion. The process uses hot compressed water, and produces a product that is similar to a biochar.
4. Particle Mixing in fluidization- For several years, we have been interested in looking at the rate of particle mixing and particle segregation in fluidization. We have looked at circulating fluidized beds and bubbling fluidized beds. Currently, our interest lies in using computational fluid dynamics tools to predict these phenomena in bubbling fluidized beds.
At the University of Nevada, Reno, ventures into the realm of alternative forms of renewable energy are being extensively researched. Under the direction of Dr. Charles Coronella and Dr. Víctor Vásquez, undergraduate and graduate students in the chemical engineering department are experimenting with lignocellulosic biomass, algae, and wastewater sludge. These three alternative sources are quite distinct in more ways than one, such as in physical properties, smell, and production; however, they all share the common trait that they have great potential for providing energy and a solution to the current energy crisis, ensuring a future for generations to come.
Dr. Wei Yan, a post doctorate from the University of Missouri, Columbia, is working closely with chemical engineering students on a project that deals primarily with the energy densification of lignocellulosic biomass and the corresponding changes in its properties. Yan is exploring two types of biomass pretreatment: wet and dry torrefaction.
Dr. Wei Yan, a post doctorate, adjusts the settings on the top portion of a mini-reactor he uses for wet and dry torrefaction experiments.Yan assembles the mini-reactor, which can be used for lignocellulosic biomass as well as for wastewater sludge..
“Lignocellulosic biomass is an abundant renewable resource so when the oil reserves are scarce, we can use this as a source of energy. Considering the first generation biofuels such as bioethanol and biodiesel which are produced from food feedstock, the second generation of biofuels can be made from lignocellulosic biomass,” says Yan. He oversees and is involved in a variety of experimentations, including proximate, ultimate, and fiber analysis for both types of lignocellulosic pretreated biomass.
Hydrothermal pretreatment, also known as wet torrefaction, is a relatively new method that can be used to enhance the energy density of lignocellulosic biomass. Samples are exposed to water under extreme temperatures and pressure in a mini-reactor and then dried for analysis. The fluid remaining in the reactor can also be used for analysis of sugar content. This reactor can also be used for dry torrefaction as well.
Dry torrefaction is a similar method; however, the samples are not heated in water but rather in an inert environment, such as in nitrogen. A thermogravimetric analyzer (TGA) is often used to measure changes in sample mass with change in temperature.
Both forms of torrefaction allow one to determine various components of the biomass. Jason Hastings, a second year graduate student in the chemical engineering Master’s program, is determining the higher heating value of loblolly pine and performing proximate and ultimate analysis and mass balances. The focus of his project is to determine not only these quantitative characteristics of loblolly pine but also to observe the overall effects of wet and dry torrefaction on this specific biomass.
“Hydrothermally pretreated loblolly actually smells really good,” says Hastings.
Jason Hastings, a graduate student, prepares for dry torrefaction of loblolly pine using the mini-reactor.Hastings prepares raw loblolly pine by first blending and then sieving the sample for particles small enough to fit in the TGA sample trays.
There are various other aspects to analyzing the effect of wet and dry torrefaction on lignocellulosic biomass. Tapas Chandra Acharjee, a second year graduate student in chemical engineering, is working to define the fiber content of the raw and pretreated samples, as well as determine mass and energy balances for each reaction taking place during wet and dry torrefaction. Fiber analysis shows the amount of hemicellulose, cellulose, lignin and aqueous solubles a given biomass has. These values help classify the various types of sample, which in this case is loblolly pine, and rank the energy content depending on the amount of each component available. Acharjee is also determining the equilibrium moisture content of loblolly pine using a desiccator and monitoring the change in moisture in a given sample.
Tapas Chandra Acharjee, a graduate student, dries samples of loblolly pine in a oven before pretreatment.Acharjee determines heat capacities of the raw and pretreated loblolly pint using a differential scanning calorimeter (DSC).
Various types of algae have been recently utilized for biodiesel production studies. Algae produce lipids that are essential to the production of biodiesel. Assessing the lipid content is important in determining the efficiency of a given sample of algae. The common method for extracting the lipids from the algae is the Bligh and Dyer method, which was originally used to extract lipids from fish.
Samantha Kerston, a fourth year undergraduate chemical engineering student, is working to improve on this method in hopes to quantify the lipid content of algae obtained from man-made ponds. This project is fully funded by an NSF-EPSCoR grant Kerston received for summer research. Her first task is to collect the algae and concentrating samples in distilled water. Using either a centrifuge or a three-gallon gravity filter, Kerston collects the algae, which she then uses for further analysis. A mixture of methanol, chloroform, and distilled water is used to separate the organic lipids from the aqueous remains of the pond water. The lipid-chloroform mixture is then placed in a water bath to remove the chloroform and isolate the lipids from the algae. Kerston then takes these lipids and prepares them for gas chromatography/mass spectroscopy (GC/MS) by acid esterifying and base transesterifying the samples. The GC/MS analysis will help determine the types of fatty acids present in the sample.
Samantha Kerston, a fourth year undergraduate student, assembles a three-gallon gravity filter to collect algae from pondwater.Kerston centrifuges and lightly boils her samples to isolate the algae and remove any excess water.
Wastewater sludge is a promising biomass stock but is currently being stored in landfills after highly economically inefficient processing. A more efficient way to handle this substance can be developed simply by utilizing its potential energy in the form of biodiesel. At the University of Nevada, Reno, wastewater sludge is being thoroughly studied in order to gain a greater understanding of this relatively uncommon feedstock as a source of renewable energy.
Soxhlet extraction was a method designed to extract lipids from solids; however, this method can also be also be applied to any solution in which the desired compound has a given solubility in the solvent and the impurities are insoluble in the solvent. This method, therefore, can be used to extract lipids from wastewater sludge, given that the appropriate solvents are used. The Soxhlet extractor consists of a reflux apparatus with a sample holder, in which the wastewater sludge is placed. The holder is gradually filled with warm solvent, the desired compound is dissolved, and then refluxed back into solution into the distillation flask.
For Mayur Doshi, a visiting third year chemical engineering student from IIT Kharipur, the desired compounds are fatty acids, that upon removal by Soxhlet extraction, undergo acid and base esterification. Esterification is a reaction in which an alcohol, which in this case is methanol, and an acid catalyst react to form a fatty acid methylester and water. This esterified fatty acid then undergoes transesterification with a base catalyst, potassium hydroxide. Once this process is complete, Doshi assesses the yield of fatty acid in the samples of wastewater sludge.
Mayur Doshi, a visiting student from ITT Kharipur, acid esterfies fatty acids collected from wastewater sludge post-Soxhlet extraction.
Chemical extractions are often used to separate unwanted particles from sludge in order to reduce the amount of waste that needs to be treated. Various solvents are available to provide different degrees of extraction. Solvent extraction is a common way to chemically extract that utilizes organic solvents to pull fatty acids from that the waste water sludge.
Cody Wagner, a second year graduate in the Master’s chemical engineering program, experiments with different solvents to determine the affects on the amount of fatty acids that can be extracted on a larger scale. His focus is to find the most efficient polar-nonpolar combination, such as heptane-ethylacetate, in order to extract as many fatty acids from the sludge as possible and then distilling the solvent away to leave a thick oily residue. Another method of extraction Wagner is experimenting with is in situ extraction, in which sulfuric acid is used along with heptane and methanol to extract the fatty acids and esterify into fatty acid methylesters, all in one process.
Cody Wagner, a graduate student, prepares the mini-reactor for wastewater sludge extraction experiments. These samples come into full contact with solvent, which is then distilled out later.Wagner sets up the distillation apparatus after obtaining the sludge-solvent mixture from the reactor.
Kevin Schmidt, a second year graduate student in the Master’s chemical engineering program, works primarily with the extracted lipid samples obtained after distillation and prepares them for GC/MS analysis. However, before he can perform this analysis, the lipid samples must undergo acid esterification and base transesterification, for which Schmidt uses methanoic-HCl and sodium methoxide respectively. Once he has formed fatty acid methylesters, Schmidt prepares the samples for GC/MS analysis by dissolving the esterified fatty acids in hexane. This form of analysis helps characterize each sample quantitatively and qualitatively.
As with lignocellulosic biomass there are a various types of analysis, these same analyses can be done with wastewater sludge.
Kevin Schmidt, a graduate student, prepares samples of extractions from sludge for GC/MS analysis by dissolving the fatty acids in excess hexane.
Schmidt also prepares a standard solution to run on GC/MS to ensure that readings are accurate.
Schinthia Islam, a fifth year undergraduate chemical engineering student, is currently conducting experiments to determine the proximate analysis of dried samples of sludge, for which the thermogravimetric analyzer is also used. Determining how much moisture content, volatile matter, fixed carbon and inert ash the sludge samples have help define its potential energy.
“When I’m running trials with the sludge in the TGA, everyone in the lab can tell because of its distinct odor. We definitely keep an air freshener handy,” says Islam.
Islam also focuses on maintenance of the TGA, making sure that it is periodically calibrated to ensure consistently accurate readings.