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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Conversion of MixAlco Process Sludge to Liquid Transportation Fuels

Teiseh, Eliasu 1973- 02 October 2013 (has links)
About 8 tons of dry undigested solid waste is generated by the MixAlco process for every 40 tons of food residue waste fed into the process. This MixAlco process produces liquid fuels and the sludge generated can be further converted into synthesis gas using the process of pyrolysis. The hydrogen component of the product synthesis gas may be separated by pressure swing adsorption and used in the hydrogenation of ketones into fuels and chemicals. The synthesis gas may also be catalytically converted into liquid fuels via the Fischer-Tropsch synthesis process. The auger-type pyrolyzer was operated at a temperature between 630-770 degrees C and at feed rates in the range of 280-374 g/minute. The response surface statistical method was used to obtain the highest syngas composition of 43.9 +/- 3.36 v % H2/33.3 +/- 3.29 v % CO at 740 degrees C. The CH4 concentration was 20.3 +/- 2.99 v %. For every ton of sludge pyrolyzed, 5,990 g H2 (719.3 MJ), 65,000 g CO (660 MJ) and 21,170 g CH4 (1055.4 MJ) were projected to be produced at optimum condition. At all temperatures, the sum of the energies of the products was greater than the electrical energy needed to sustain the process, making it energy neutral. To generate internal H2 for the MixAlco process, a method was developed to efficiently separate H2 using pressure swing adsorption (PSA) from the synthesis gas, with activated carbon and molecular sieve 5A as adsorbents. The H2 can be used to hydrogenate ketones generated from the MixAlco process to more liquid fuels. Breakthrough curves, cycle mass balances and cycle bed productivities (CBP) were used to determine the maximum hydrogen CBP using different adsorbent amounts at a synthesis gas feed rate of 10 standard lpm and pressure of 118 atm. A 99.9 % H2 purity was obtained. After a maximum CBP of 66 % was obtained further increases in % recovery led to a decrease in CBP. The synthesis gas can also be catalytically converted into liquid fuels by the Fischer-Tropsch synthesis (FTS) process. A Co-SiO2/Mo-Pd-Pt-ZSM-5 catalyst with a metal-metal-acid functionality was synthesized with the aim of increasing the selectivity of JP-8 (C10-C17) fuel range. The specific surface areas of the two catalysts were characterized using the BET technique. The electron probe microanalyzer (with WDS and EDS capabilities) was then used to confirm the presence of the applied metals Co, Mo, Pd and Pt on the respective supports. In addition to the gasoline (C4-C12) also produced, the synthesis gas H2:CO ratio was also adjusted to 1.90 for optimum cobalt performance in an enhanced FTS process. At 10 atm (150 psig) and 250 degrees C, the conventional FTS catalyst Co-SiO2 produced fuels rich in hydrocarbons within the gasoline carbon number range. At the same conditions the Co-SiO2-Mo-Pd-Pt/HZSM-5 catalyst increased the selectivity of JP-8. When Co-SiO2/Mo-Pd-Pt-HZSM-5 was used at 13.6 atm (200 psig) and 250 degrees C, a further increase in the selectivity of JP-8 and to some extent diesel was observed. The relative amounts of olefins and n-paraffins decreased with the products distribution shifting more towards the production of isomers.
12

Sugarcane juice extraction and preservation, and long-term lime pretreatment of bagasse

Granda Cotlear, Cesar Benigno 17 February 2005 (has links)
New technologies, such as an efficient vapor-compression evaporator, a stationary lime kiln (SLK), and the MixAlco process, compelled us to re-evaluate methods for producing sugar from cane. These technologies allow more water and lime to be used, and they add more value to bagasse. Extracting and preserving the sugars, and lime pretreating the bagasse to enhance biodigestibility, all at the same time in a pile, was demonstrated to be unfeasible; therefore, sugar extraction must occur before lime treating the bagasse. Sugar extraction should occur countercurrently by lixiviation, where liquid moves in stages opposite to the soaked bagasse (megasse), which is conveyed by screw-press conveyors that gently squeeze the fiber in each stage, improving extraction. The performance of a pilot-scale screw-press conveyor was tested for dewatering capabilities and power consumption. The unoptimized equipment decreased megasse moisture from 96 to 89%. Simulation of the process suggested that eight stages are necessary to achieve 98% recovery from typical sugarcane. The cumulative power for the screw-press conveyor system was 17.0±2.1 hp•h/ton dry fiber. Thin raw juice preserved with lime for several months showed no sucrose degradation and no quality deterioration, except for reducing sugar destruction. The lime loading needed for 1-year preservation is 0.20 g Ca(OH)2/g sucrose. Shorter times require less lime. After preservation, the juice was carbonated and filtered, and the resulting sludge pelletized. Due to their high organic content, the pellets were too weak for calcination temperatures used in the SLK. The organics must be decreased prior to pelletization and sodium must be supplemented as a binding agent. Long-term lime pretreatment of bagasse showed two delignification phases: bulk (rapid) and residual (slow). These were modeled by two simultaneous first-order reactions. Treatments with air purging and higher temperatures (50 – 57oC) delignified more effectively, especially during the residual phase, thus yielding higher cellulase-enzyme digestibilities after 2 – 8 weeks of treatment. At temperatures > 60oC, pure oxygen purging is preferred. Fresh bagasse was of better quality than old bagasse. Treatment with NaOH yielded a larger bulk delignification phase than Ca(OH)2. Long-term lime pulping of bagasse was unsuitable for copy-quality paper, but it was appropriate for strawboard and other filler applications.

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