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Predictive reverse osmosis (RO) models have been well-developed for many systems. However, the applications to dilute organic−water systems require the modification of transport models and the understanding of solute−polymer interactions. Studies with various substituted, nonionized phenolic compounds showed that these could cause substantial membrane water flux drop, even in dilute solutions with negligible osmotic pressure. Further, the organics could significantly adsorb on the cross-linked aromatic polyamide active layer. In some cases, even concentrations as low as 0.2 mM, 2,4-dinitrophenol (solution in particle-free, double-distilled water) can cause as much as a 70% flux drop with an aromatic polyamide membrane. Two models are presented in this paper:  a modified steady-state solution diffusion model and an unsteady-state diffusion adsorption model which are able to predict flux and permeate concentrations from a single RO experiment. Further, the development of these models allows for the understanding of the mechanisms of organic−membrane interactions. For instance, it has been proposed that increased adsorption inherently leads to an increase in flux drop. However, we have found, on one hand, that due to specific interactions with membrane water transport groups, chloro- and nitro-substituted phenols cause significant flux drops. On the other hand, benzene had a high physical adsorption but caused negligible flux drop. The results were further extended to nanofiltration experiments with an aromatic pollutant containing two types of charge groups. The adsorption and separation results are explained according to an ionization model.

This study ascertained the technical potential of producing biofuel from a naturally occurring macroalgae. The algae examined grow in Jamaica Bay, New York City, on water containing nitrates, phosphates, and carbon dioxide that comes from the atmosphere. The process consisted of manual and mechanical harvesting, drying, grinding, and subjecting the algal matter to acid hydrolysis to extract carbohydrates to form an algal sugar solution. Fermentation of that solution to butanol was performed with butanol ultimately removed by distillation. An average of 15.2 g/L of reducing sugars was extracted in the hydrolysate showing that macroalgae (Ulva lactuca) have significant usable carbohydrates after hydrolysis. It was found necessary to remove the excess solids from the hydrolysate prior to fermentation, as the productivity fell by 75% if this was not done. With the bacterial strains (Clostridium beijerinckii and C. saccharoperbutylacetonicum) and the algal sugar solutions used, an acetone butanol ethanol (ABE) fermentation was used to make butanol. The butanol concentration in the fermentation broth reached about 4 g/L, which is close to the theoretical value for the sugar concentration obtained, and compares well (when adjusted for sugar concentration in the media) with values reported in the literature for other systems. The recovery of reducing sugars in the media during the pilot study was 0.29 g butanol/g sugar. © 2011 American Institute of Chemical Engineers Environ Prog, 2012

In this work, plasmonically heated solid-state gold nanoparticle (AuNP) arrays are investigated under novel conditions that include large (>35°C) steady-state (SS) temperature increases (∆T) dominated by conduction in open environments that allow vapor-liquid phase change. Evaporative cooling from the open system decreases SS ∆T of the system by as much as (11.6 ( 0.33)°C (45%), consistent with predictions from an energy balance model expanded in this work to account for evaporative cooling and associated decreasing thermal mass. Comparing dynamic and steady temperature profiles from water evaporating from a AuNPcoated Si cell at 50 mW laser irradiation with the model yielded an average accumulated residual sum of squares of 2.95°C 2 over 200 s. Temperature increases that distribute nonuniformly across sample cell surfaces due to high laser power (e150 mW) and conductive heat transfer are accurately and uniformly (<0.7% difference) represented by an infinite fin model at laser powers from 50 to 150 mW, resulting in R 2 values near unity. Overall heat transfer coefficients for air cells estimated from both dynamic and steady-state models agree within 2.05 to 11.45%. This model independence allows predicting temporal evolution or steady-state distribution of temperatures from just two measured values. The improved models and increased understanding of these systems will play an important role in implementing plasmonically heated structures in sustainable energy applications, biomedical applications and many others.

Dynamic and equilibrium thermal behavior of plasmon-heated gold/silica capillary nanocomposite during evaporative cooling by water or butanol is accurately described at centimeter length scales by continuum optoplasmonic thermodynamics for continuous-wave laser irradiation of 15-50 mW. Gold nanoparticles randomly distributed on the capillary via electroless plating exhibited a composite extinction cross section of 66.74 ± 0.72% of the area of the laser spot, more than 2-fold larger than the physical cross-section of the AuNPs. The extinction cross-section of the AuNPs capillary was invariant for incident laser powers of 15-150 mW and was reduced slightly in the presence of butanol and water due to absorption peak-shifting to lower energies. Introducing composite thermal parameters into the optoplasmonic thermodynamic relation extended its ability to predict heat transfer to laser powers of 100 and 150 mW for water and butanol, respectively. Nonlinear behaviors such as exponential thermal profiles caused by limited thermal conductivity and film boiling are identified at higher laser powers and prevent further extension of the relation. Mathematical reduction of temperature and time variables of the mathematical description shows it accounts for all measured thermodynamic effects when the aforementioned nonlinear behaviors are not present. This confirms that extraordinary thermal transport observed in some nanocomposites are absent for AuNP/silica systems in the given ranges, which allows a macroscale, continuum approach to describe thermal transport.

Passive membranes have been used for separations ranging from seawater desalination via reverse osmosis to the separation of particles with microfiltration membranes. However, active membranes, achieved by immobilization of macromolecules containing multiple functional sites to microfiltration membranes, allow for more selective separations. We have designed a novel membrane system consisting of cellulose-based microfiltration membranes functionalized with poly(amino acid)s (2500-10 000 MW). Because of the high carboxyl content of the poly(amino acid)s, these membranes have been shown to be extremely useful in the separation of heavy metals from aqueous solutions. The advantages of the membrane system, including high capacity and rapid sorption, have been demonstrated in this paper. A model has also been presented relating the effect of the pore size, poly(amino acid) attachment density, pH, and metal type to the initial metal sorption rate. It should be noted that, in contrast to homogeneous systems, the molar sorption capacities of the functional carboxyl sites are significantly enhanced in the membrane pores because of counterion condensation that results partly from the extremely high charge densities in the membrane pores. This phenomenon must also be incorporated in a kinetic model for the prediction of sorption behavior.

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Abstract:In making alternative fuels from biomass feedstocks, the production of butyric acid is a key intermediate in the two-step production of butanol. The fermentation of glucose via Clostridium tyrobutyricum to butyric acid produces undesirable byproducts, including lactic acid and acetic acid, which significantly affect the butyric acid yield and productivity. This paper focuses on the production of butyric acid using Clostridium tyrobutyricum in a partial cell recycle mode to improve fermenter yield and productivity. Experiments with fermentation in batch, continuous culture and continuous culture with partial cell recycle by ultrafiltration were conducted. The results show that a continuous fermentation can be sustained for more than 120 days, which is the first reported long-term production of butyric acid in a continuous operation. Further, the results also show that partial cell recycle via membrane ultrafiltration has a great influence on the selectivity and productivity of butyric acid, with an increase in selectivity from ≈9% to 95% butyric acid with productivities as high as 1.13 g/Lh. Continuous fermentation with low dilution rate and high cell recycle ratio has been found to be desirable for optimum productivity and selectivity toward butyric acid and a comprehensive model explaining this phenomenon is given. OPEN ACCESSEnergies 2012, 5 2836