Browsing by Author "Hou-min Chang, Committee Member"

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Factors Affecting Interactions of Polyelectrolytes During Charge Analysis.
(2004-07-18) Chen, Junhua; Martin A. Hubbe, Committee Chair; Hou-min Chang, Committee Member; Carl L. Bumgardner, Committee Member; John A. Heitmann, Committee Co-Chair
The streaming current method is commonly used for charge analysis in water treatment and the paper industry. The working mechanism of this method is understood to involve polyelectrolyte complex (PEC) formation. Since the formation of PECs is important for many applications, the factors that could affect this complexation have been widely investigated. Studies have found increasing deviations from 1:1 stoichiometry of complexation with increasing salt concentration. The colloidal charge of water recirculated within a paper mill can affect process efficiency and product quality. With increased conductivities due to water recirculation and reuse, the need for accurate and reliable charge measurements at high conductivities has become more important. This research focused on experiments that define the range of sample types and electrical conductivity where it is possible to achieve accurate and reliable results from streaming current titrations. Other studies related to the theories of polyelectrolyte complexation involved titrations carried out between solutions of a strong poly-acid and a strong poly-base over a range of salt concentrations. The results showed that deviations from 1:1 stoichiometry are consistent with earlier studies. In addition, it was found that the stoichiometry of PEC complexation depended on the direction of the titration. An excess over the stoichiometric amount was required to achieve a streaming current reading of zero. Theoretical models based on non-equilibrium complexation are proposed to explain the current results. Other tests, such as turbidity and electrophoretic mobility also have been used to evaluate the theoretical models. The results are consistent with those from the streaming current analysis. Factors that can influence the polyelectrolyte adsorption and PEC formation were studied also. It is thought that the charge density of anionic polyelectrolytes may affect the titration stoichiometry to some extent at high conductivities; however, no clear trend was found in this study with crboxylmethylcelluloses. It was also found that the shape of the titration curves indicates the strength of complexation between titrant and sample molecules. Aluminum ion interferes with the stoichiometry of charge titrations in a different way when compared with other inorganic ions such as Ca²⁺, Cl⁻ and Na⁺. It is possible to consider the aluminum ion itself as one kind of cationic sample to be titrated with standard anionic titrant under certain conditions. Turbidity and zeta potential tests indicated that there could be polynuclear species existing under the conditions in which the aluminum ions can be titrated as a cationic sample.
Integrating Black Liquor Gasification with Pulping - Process Simulation, Economics and Potential Benefits
(2008-05-08) Lindstrom, Mathias Erik Vilhelm; Hasan Jameel, Committee Chair; Hou-min Chang, Committee Member; Adrianna Kirkman, Committee Co-Chair; Michael Overcash, Committee Member
Gasification of black liquor could drastically increase the flexibility and improve the profit potential of a mature industry. The continuous efforts made in the area of black liquor gasification (BLG) are bringing this technology closer to commercial realization and potential wide-spread implementation. Research exploring the integration of BLG into the kraft process and the potential of BLG enabled modified pulping technologies on modern pulping operations is important to support this effort. The following effort is focused on such research, utilizing laboratory pulping experiments and process simulation. The separation of sodium and sulfur achieved through gasification of recovered black liquor can be utilized in processes like modified continuous cooking, split sulfidity and green liquor pretreatment pulping, and polysulfide-anthraquinone pulping to improve pulp yield and properties. Laboratory pulping protocols have been developed for these modified pulping technologies and different process options evaluated. The process simulation work around BLG has led to the development of a WinGEMS module for the low temperature MTCI steam reforming process, and case studies comparing a simulated conventional kraft process to different process options built around the implementation of a BLG unit operation into the kraft recovery cycle. The implementation of gasification, functioning as the core of wood pulping recovery operations in a biorefinery, would enable the application of modified pulping technologies while creating a synthetic product gas that could be utilized in the production of value added products in addition to wood pulp. The evaluated modified pulping technologies have indicated the potential of yield increases of 1-3% points with improved product quality, and the potential for capital and operating cost savings relative to the conventional kraft process. Process simulation work has shown that the net variable operating cost for a pulping process using BLGCC is highly dependent on the cost of lime kiln fuel and the selling price of green power to the grid. Under the initial assumptions taken in the performed case study, the BLGCC process combined with split sulfidity or PSAQ pulping operations had net variable operating cost 2-4% greater than the kraft reference. When comparing the BLG cases to the MCC reference, the net variable operating cost break even point based on lime kiln fuel cost is about $47⁄barrel for the split sulfidity and lower charge polysulfide processes, and about $38—barrel for the higher polysulfide charge process. This is significantly lower than assumed kiln fuel price of $60/barrel used in this work. If the sales price for power to the grid could be increased through green power credits from 3.5 to 6 ⁄KWh cost savings of about $40—ODtP could be realized in the investigated BLG processes. Other alternatives to improve the process economics around BLG would be to modify or eliminate the lime kiln unit operations, utilizing high sulfidity green liquor pretreatment, PSAQ with auto-causticization, or converting the process to mini-sulfide sulfite-AQ.
An Investigation of the Milled Wood Lignin Isolation Procedure by Solution- and Solid-State NMR Spectroscopy.
(2004-02-22) Holtman, Kevin Matthew; Jeffrey L. White, Committee Member; Hou-min Chang, Committee Member; Hasan Jameel, Committee Co-Chair; John F. Kadla, Committee Co-Chair
Milled wood lignin (MWL) is a fraction of the total lignin in wood but is considered the isolated lignin most representative of lignin in its native state. It is useful for lignin studies because it is isolated relatively free of carbohydrates, however structural changes occur during its isolation. This study presents attempts to evaluate the whole lignin structure with the goal of analysis its structure in intact wood. Solution-state and solid-state NMR experiments and degradative techniques were performed on soluble and insoluble lignins to make an estimation of the interunit linkages. MWL and cellulolytic enzyme lignin (CEL) exhibit only minor structural differences. MWL is lower in b-aryl ether content, has a higher degree of condensation, and a slightly higher amount of oxidized end group moieties. MWL may derive from the middle lamella to a larger extent than CEL. MWL and lignins isolated from milled wood and REL (Residual Enzyme Lignin) were dissolved using dimethyl sulfoxide (DMSO)/N-methylimidazole (NMI) for NMR analysis. HMQC showed that these lignins are similar from the standpoint of structural moieties present. Quantitative 13C NMR indicates that MWL has a b-O-4' content lower than that of the wood. Solid-state NMR suggests that MWL had a higher degree of condensation. The milled wood and REL contain a significant portion of high MW material (~55,000 g/mol) which contributes to their insolubility in aqueous dioxane. Solution-state NMR indicates that prolonged rotary ball milling results in more structural changes than the standard milling technique. There are few differences between samples milled in toluene or under N2 in a vibratory ball mill. Milling under N2 results in a higher MWL yield and the isolated lignin contains higher aliphatic and phenolic hydroxyl contents. The DFRC method is inefficient because it does not completely cleave all b-O-4' linkages. Inefficiency increases with molecular weight indicating that the cause is either accessibility or molecular mobility in the reductive cleavage step. Thioacidolysis completely degrades the b-aryl ether linkages in lignin and is therefore preferrable for analysis of these structures.