Publications

Moving horizon closed-loop production scheduling using dynamic process models

by Pattison, RC; Touretzky, CR; Harjunkoski, I; Baldea, M

AICHE JOURNAL; Volume: 63; Issue: 2; Pages: 639-651; DOI: 10.1002/aic.15408; Published: FEB 2017

The economic circumstances that define the operation of chemical processes (e.g., product demand, feedstock and energy prices) are increasingly variable. To maximize profit, changes in production rate and product grade must be scheduled with increased frequency. To do so, process dynamics must be considered in production scheduling calculations, and schedules should be recomputed when updated economic information becomes available. In this article, this need is addressed by introducing a novel moving horizon closed-loop scheduling approach. Process dynamics are represented explicitly in the scheduling calculation via low-order models of the closed-loop dynamics of scheduling-relevant variables, and a feedback connection is built based on these variables using an observer structure to update model states. The feedback rescheduling mechanism consists of, (a) periodic schedule updates that reflect updated price and demand forecasts, and, (b) event-driven updates that account for process and market disturbances. The theoretical developments are demonstrated on the model of an industrial-scale air separation unit. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 639-651, 2017

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Using Mercury Isotopes To Understand Mercury Accumulation in the Montane Forest Floor of the Eastern Tibetan Plateau

by Wang, X; Luo, J; Yin, RS; Yuan, W; Lin, CJ; Sommar, J; Feng, XB; Wang, HM; Lin, C

ENVIRONMENTAL SCIENCE & TECHNOLOGY; Volume: 51; Issue: 2; Pages: 801-809; DOI: 10.1021/acs.est.6b03806; Published: JAN 17 2017

Mercury accumulation in montane forested areas plays an important role in global Hg cycling. In this study, we measured stable Hg isotopes in soil and litter samples to understand Hg accumulation on the forest floor along the eastern fringe of the Tibetan Plateau (TP). The low atmospheric Hg inputs lead to the small Hg pool size (23 +/- 9 mg m(-2) in 0-60 cm soil horizon), up to 1 order of magnitude lower than to -0.05 parts per thousand) in the litter at low elevations (3100 to 3600 m) suggests an influence of local anthropogenic emissions, whereas the more significant negative Delta Hg-199 (-0.38 to -0.15 parts per thousand) at high elevations (3700 to 4300 m) indicates impact from long-range transport. Hg input from litter is more important than wet deposition to Hg accumulation on the forest floor, as evidenced by the negative Delta Hg-199 found in the surface soil samples. Correlation analyses of Delta Hg-199 versus total carbon and leaf area index suggest that litter biomass production is a predominant factor in atmospheric Hg inputs to the forest floor. Precipitation and temperature show indirect effects on Hg accumulation by influencing litter biomass production in the eastern TP.

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An Elastic, Conductive, Electroactive Nanocomposite Binder for Flexible Sulfur Cathodes in Lithium-Sulfur Batteries

by Milroy, C; Manthiram, A

ADVANCED MATERIALS; Volume: 28; Issue: 44; Pages: 9744-+; DOI: 10.1002/adma.201601665; Published: NOV 23 2016

A conductive, elastic, electroactive binder composed of polypyrrole and poly urethane is adopted for flexible, high-loading lithium-sulfur cathodes. The conductivity of the polypyrrole helps mitigate the negative effects of insulating sulfur, and the elastomeric matrix accommodates sulfur volume expansion. The binder is used with a simple carbon/sulfur composite to produce high-performance, flexible electrodes without excessive carbon, interlayers, or special additives.

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Development and Characterization of Stimuli Responsive Hydrogel Microcarriers for Oral Protein Delivery.

by O'Connor, C; Steichen, S; Peppas, NA

J Biomed Mater Res A. 2017 Feb 8. doi: 10.1002/jbm.a.36030.

A family of pH-responsive terpolymers composed of methacrylic acid (MAA), N-vinyl pyrrolidone (NVP), and poly(ethylene glycol) monomethylether monomethacrylate (PEGMMA) have been developed and evaluated for their pH-responsive swelling behavior, protein loading capabilities, and cytocompatibility. These terpolymer hydrogels, designated as P((MAA-co-NVP)-g-EG), were synthesized with varying PEG chain lengths and monomer feed ratios. The incorporation of MAA into the terpolymer structure was quantified with potentiometric titration. Equilibrium and dynamic swelling studies confirmed the pH-responsive behavior of the hydrogel, with the system remaining collapsed/complexed in acidic pH conditions and swollen/decomplexed in neutral pH conditions. The ability of the hydrogels to partition protein into the swollen network was assessed for two model proteins of varying molecular weight: insulin and porcine growth hormone. Finally, the cytocompatibility of the hydrogels in the presence of two model intestinal cell lines was investigated and confirmed minimal cytotoxicity at and below 2.5 mg/mL. The developed P((MAA-co-NVP)-g-EG) hydrogels exhibit unique properties that could potentially be utilized for drug delivery and separation applications. This article is protected by copyright. All rights reserved.

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Characterization of protein interactions with molecularly imprinted hydrogels that possess engineered affinity for high isoelectric point biomarkers.

by Clegg, JR; Zhong, JX; Irani, AS; Gu, J; Spencer, DS; Peppas, NA

J Biomed Mater Res A. 2017 Feb 8. doi: 10.1002/jbm.a.36029

Molecularly imprinted polymers (MIPs) with selective affinity for protein biomarkers could find extensive utility as environmentally robust, cost-efficient biomaterials for diagnostic and therapeutic applications. In order to develop recognitive, synthetic biomaterials for prohibitively expensive protein biomarkers, we have developed a molecular imprinting technique that utilizes structurally similar, analogue proteins. Hydrogel microparticles synthesized by molecular imprinting with trypsin, lysozyme, and cytochrome c possessed an increased affinity for alternate high isoelectric point biomarkers both in isolation and plasma-mimicking adsorption conditions. Imprinted and non-imprinted P(MAA-co-Aam-co-DEAEMA) microgels containing PMAO-PEGMA functionalized polycaprolactone nanoparticles were net-anionic, polydisperse, and irregularly shaped. MIPs and control non-imprinted polymers (NIPs) exhibited regions of Freundlich and BET isotherm adsorption behavior in a range of non-competitive protein solutions, where MIPs exhibited enhanced adsorption capacity in the Freundlich isotherm regions. In a competitive condition, imprinting with analogue templates (trypsin, lysozyme) increased the adsorption capacity of microgels for cytochrome c by 162% and 219% respectively, as compared to a 122% increase provided by traditional bulk imprinting with cytochrome c. Our results suggest that molecular imprinting with analogue protein templates is a viable synthetic strategy for enhancing hydrogel-biomarker affinity and promoting specific protein adsorption behavior in biological fluids. This article is protected by copyright. All rights reserved.

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Analyte-Responsive Hydrogels: Intelligent Materials for Biosensing and Drug Delivery.

by Culver, HR; Clegg, JR; Peppas, NA

Acc Chem Res. 2017 Feb 21;50(2):170-178. doi: 10.1021/acs.accounts.6b00533. Epub 2017 Feb 7.

Nature has mastered the art of molecular recognition. For example, using synergistic non-covalent interactions, proteins can distinguish between molecules and bind a partner with incredible affinity and specificity. Scientists have developed, and continue to develop, techniques to investigate and better understand molecular recognition. As a consequence, analyte-responsive hydrogels that mimic these recognitive processes have emerged as a class of intelligent materials. These materials are unique not only in the type of analyte to which they respond but also in how molecular recognition is achieved and how the hydrogel responds to the analyte. Traditional intelligent hydrogels can respond to environmental cues such as pH, temperature, and ionic strength. The functional monomers used to make these hydrogels can be varied to achieve responsive behavior. For analyte-responsive hydrogels, molecular recognition can also be achieved by incorporating biomolecules with inherent molecular recognition properties (e.g., nucleic acids, peptides, enzymes, etc.) into the polymer network. Furthermore, in addition to typical swelling/syneresis responses, these materials exhibit unique responsive behaviors, such as gel assembly or disassembly, upon interaction with the target analyte. With the diverse tools available for molecular recognition and the ability to generate unique responsive behaviors, analyte-responsive hydrogels have found great utility in a wide range of applications. In this Account, we discuss strategies for making four different classes of analyte-responsive hydrogels, specifically, non-imprinted, molecularly imprinted, biomolecule-containing, and enzymatically responsive hydrogels. Then we explore how these materials have been incorporated into sensors and drug delivery systems, highlighting examples that demonstrate the versatility of these materials. For example, in addition to the molecular recognition properties of analyte-responsive hydrogels, the physicochemical changes that are induced upon analyte binding can be exploited to generate a detectable signal for sensing applications. As research in this area has grown, a number of creative approaches for improving the selectivity and sensitivity (i.e., detection limit) of these sensors have emerged. For applications in drug delivery systems, therapeutic release can be triggered by competitive molecular interactions or physicochemical changes in the network. Additionally, including degradable units within the network can enable sustained and responsive therapeutic release. Several exciting examples exploiting the analyte-responsive behavior of hydrogels for the treatment of cancer, diabetes, and irritable bowel syndrome are discussed in detail. We expect that creative and combinatorial approaches used in the design of analyte-responsive hydrogels will continue to yield materials with great potential in the fields of sensing and drug delivery.

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Thermodynamic and Mass-Transfer Modeling of Carbon Dioxide Absorption into Aqueous 2-Amino-2-Methyl-1-Propanol

by Sherman, BJ; Rochelle, GT

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH; Volume: 56; Issue: 1; Pages: 319-330; DOI: 10.1021/acs.iecr.6b03009; Published: JAN 11 2017

Explanations for the mass-transfer behavior of 2-amino-2-methyl-1-propanol (AMP) are conflicting, despite extensive study of the amine for CO2 capture. At equilibrium, aqueous AMP reacts with CO2 to give bicarbonate in a 1:1 ratio. Although this is the same stoichiometry as a tertiary airline, the reaction rate of AMP is 100 times faster. This work aims to explain the mass-transfer behavior of AMP, specifically the stoichiometry and kinetics. An eNRTL thermodynamic model was: used to regress wetted-wall column mass-transfer data with two activity-based reactions: formation of carbamate and formation of bicarbonate. Data spanned 40-100 degrees C and 0.15-0.60 mol CO2/mol alk. The fitted carbamate rate Constant is 3 orders of magnitude greater than the bicarbonate rate constant. Rapid carbamate formation explains the kinetics, while the stoichiometry is explained by the carbamate reverting in the bulk liquid to allow CO2 to form bicarbonate. Understanding the role of carbamate formation and diffusion in hindered amines enables optimization of the solvent amine concentration by balancing viscosity and free amine concentration. This improves absorber design for CO2 capture.

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Contrasting the Influence of Cationic Amino Acids on the Viscosity and Stability of a Highly Concentrated Monoclonal Antibody

by Dear, B; Hung, JJ; Truskett, TM; Johnston, KP

PHARMACEUTICAL RESEARCH; Volume: 34; Issue: 1; Pages: 193-207; DOI: 10.1007/s11095-016-2055-5; Published: JAN 2017

To explain the effects of cationic amino acids and other co-solutes on the viscosity, stability and protein-protein interactions (PPI) of highly concentrated (>= 200 mg/ml) monoclonal antibody (mAb) solutions to advance subcutaneous injection.

The viscosities of >= 200 mg/ml mAb1 solutions with various co-solutes and pH were measured by capillary rheometry in some cases up to 70,000 s(-1). The viscosities are analyzed in terms of dilute PPI characterized by diffusion interaction parameters (k(D)) from dynamic light scattering (DLS). MAb stability was measured by turbidity and size exclusion chromatography (SEC) after 4 weeks of 40 degrees C storage.

Viscosity reductions were achieved by reducing the pH, or adding histidine, arginine, imidazole or camphorsulfonic acid, each of which contains a hydrophobic moiety. The addition of inorganic electrolytes or neutral osmolytes only weakly affected viscosity. Systems with reduced viscosities also tended to be Newtonian, while more viscous systems were shear thinning.

Viscosity reduction down to 20 cP at 220 mg/ml mAb1 was achieved with co-solutes that are both charged and contain a hydrophobic interaction domain for sufficient binding to the protein surface. These reductions are related to the DLS diffusion interaction parameter, k(D), only after normalization to remove the effect of charge screening. Shear rate profiles demonstrate that select co-solutes reduce protein network formation.

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Central metabolic nodes for diverse biochemical production

by Cordova, LT; Alper, HS

CURRENT OPINION IN CHEMICAL BIOLOGY; Volume: 35; Pages: 37-42; DOI: 10.1016/j.cbpa.2016.08.025; Published: DEC 2016

Central carbon metabolism is conserved among all organisms for cellular function and energy generation. The connectivity of this metabolic map gives rises to key metabolite nodes. Five of these nodes in particular, pyruvate, citric acid, tyrosine and aspartate, acetyl-CoA, serve as critical starting points for the generation of a broad class of relevant chemical molecules with ranging applications from fuels, pharmaceuticals and polymer precursors. This review highlights recent progress in converting these metabolite nodes into valuable products. In particular, acetyl-CoA, the most well-connected node, serves as the building block for several classes of molecules including fatty acids and terpenes. Systematic metabolic engineering efforts focused on these metabolic building blocks has enabled the production of industrially-relevant, biobased compounds.

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