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ItemKinetics of the Titanate Causticization Reactions in a Potassium-Based Process(Georgia Institute of Technology, 2004-04-16) Ho, Luis HolingThe objective of this study was to model the kinetics of direct causticization of potassium-based chemical using titanium dioxide, TiO₂. The starting materials were K₂CO₃ and TiO₂. Potassium chemical was used because there is an indication that potassium carbonate, K₂CO₃, might offer benefits over sodium carbonate, Na₂CO₃, such as the elimination of potassium build-up in sodium-based pulping. Experiments were run at six different temperatures. Half were below potassium carbonate’s melting point while the other half were above. Reaction rates and conversions increased with temperature, and the maximum conversion achieved was 0.90. Several kinetic models were fitted to the data. Valensi-Carter showed a good fit for the solid-solid reaction, while ash diffusion control model was chosen to describe the solid-liquid reaction with TiO₂ stayed in solid phase. The samples from the heated experiments were then leached with water to produce KOH. The amount of KOH was found to increase with temperature. It implied that more 4K₂O•5TiO₂ was produced at higher temperatures. Reacting K₂CO₃ with K₂O•3TiO₂ might interest industry more because TiO₂ is added to the recovery system as a make up only. The models used did not show good fits for the whole conversions; therefore, additional study should be done to develop a model that could describe low conversions as well as high conversions.
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ItemDetermination of Reaction Kinetics of Barium Sulfide with Sodium Carbonate and Sodium Sulfate to Reduce Deadload in the Recovery Cycle(Georgia Institute of Technology, 2004-04-15) Branham, Joshua M.The following study deals with the characteristics of the reaction to form BaSO₄ and BaCO₃ from Na₂SO₄ and Na₂CO₃, respectively, using BaS as the other reactant. These reactions would theoretically increase the efficiency of the chemical recovery process in papermaking to near 100% by completely converting Na₂SO₄ to Na₂S and Na₂CO₃ to NaOH. Kinetic data were collected, and it was determined that both reactions were overall first order with rate constants of 0.037s⁻¹ for the formation of BaSO₄ and 0.021s⁻¹ for the formation of BaCO₃. Also, it was found that both reactions go to completion in under three minutes. The heats of reaction were studied and found to be negligible. BaSO₄ particle sizes averaged approximately 4.5μm and remained steady with respect to time while BaCO₃ particle sizes were approximately 21μm initially, but decreased over the course of several days. BaCO₃ formed agglomerates which began to break down immediately, but BaSO₄ did not form agglomerates at all. No explanation for why BaCO3 formed agglomerates and BaSO₄ did not could be determined experimentally or found in the literature. Attempts to increase the particle size of BaSO₄ included seeding the initial solution with BaSO₄ crystals and increasing the concentration of reactants from 0.100M solutions each to 0.292M for BaS and 1.31M for the sodium salts. Both seeding and increased reactant concentration had no effect on particle size. The settling rates of BaSO₄ and BaCO₃ particles were also studied. BaSO₄ exhibited mainly discrete and some flocculant settling characteristics, and the suspension as a whole settled quickly with some smaller particles remaining in suspension for a lengthy period of time. Hindered and mainly compression settling occurred with BaCO₃ because of the agglomerates that formed due to strong particle-particle interactions. BaCO₃ settled slowly, but virtually no particles remained in suspension after the bulk of the particles settled.
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ItemKinetics of Ba(OH)₂ Reaction with Na₂CO₃ and Na₂SO₄ & Particle Separation Characteristics from White Liquor(Georgia Institute of Technology, 2003-04-16) Quesada, Alexander L.The purpose of this study is to determining the feasibility of replacing causticizing (calcium based reactions and precipitate) with bausticizing (barium based reactions and precipitates). Bausticizing is not limited by chemical equilibrium and thus can proceed to full conversion eliminating the dead load of inert sodium carbonate in the white liquor. The comparison is centered on the kinetics and conversion as well as precipitate sedimentation. BaCO₃ and BaSO₄ approach full conversion (97.7% and 95.9% respectively) after a 5 to 10 second reaction at room temperature with 0.1M feed solutions (Ba(OH)₂, Na2CO₃, and Na2SO₄). Barium mud settling behavior is comparable to that of lime mud and can possibly be carried out by existing sedimentation tanks within a pulp mill.
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ItemGasification of Black Liquor with the Addition of Secondary Sludge(Georgia Institute of Technology, 2002-04-15) Hammond, DavidThe effects of secondary sludge addition on black liquor gasification were studied. Additions of 0, 5, 10, and 15% secondary sludge solids to hardwood black liquor solids were considered. Gasification temperatures were 700 and 900°C. Residence times were 0.2, 0.7, and 1.2 seconds. Gasification was performed in a laminar entrained flow reactor. Although both amount and rate of organic carbon conversion increased with temperature, the percentage of sludge addition did not affect percent of feed carbon recovered as organic carbon. Isobutyl and ethyl mercaptan, as well as carbon disulfide, were not produced in reportable quantities. Recoveries were expressed on a percentage-of-feed-element basis. Recovery of sulfur in char was higher for the 100/0 (black liquor/secondary sludge) feed than for the 85/15 feed. Recoveries of H2S were higher for purer (less sludge added) feed stocks for all experiments except those performed 900°C/1.2 seconds residence time. Recoveries of methyl mercaptan, n-propyl mercaptan, carbon disulfide, and ammonia were relatively independent of sludge addition. Recoveries in char of magnesium, vanadium, and aluminum were higher for the 85/15 feed stock.