Yinzhi Zhang

Synthesis of pitch materials from hydrogenation of anthracite

Abstract A Pennsylvania anthracite was ground, carefully dried and hydrotreated into materials with properties resembling those of pitches. The hydrotreatment was carried out using two hydrogen donors, 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydronaphthalene (THN), and two catalysts, molybdenum hexacarbonyl (Mo(CO) 6 ) and ammonium tetrathiomolybdate (ATTM). Due to the high reactivity at low temperatures, the degree of hydrogenation was probed in the temperature range 300, 350 and 400 °C. The optimum hydrogen donor, catalyst and hydrogenation temperature were 1,2,3,4-tetrahydronaphthalene, ammonium tetrathiomolybdate and 300 °C, respectively. This was reflected in an increase in the hydrogen-to-carbon atomic ratio (H/C) from 0.33 for the original anthracite to 0.42 for the pitch-like material from anthracite. Further, differential scanning calorimetry (DSC) showed that the anthracite-derived pitch material had a glass transition temperature ( T g ) around 81.6 °C and softening point of 205.7 °C. This indicates that the softening behavior of the anthracite-derived pitch is similar to that of high-softening-point coal tar pitches. The anthracite-derived pitch material was evaluated by producing a small carbon body directly from the anthracite-derived pitch, and partial binding was observed.

Development of Value-Added Products from Fly Ash Carbons

The implementation of increasingly stringent Clean Air Act Regulations by the coal utility industry has resulted in an increase in the concentration of unburned carbon in coal combustion fly ash. Unburned carbon, also referred to as fly ash carbon, is nowadays regarded as a waste product and its fate is mainly disposal, due to the present lack of efficient routes for its utilization. However, the increasingly severe regulations on disposal may demand the utility industry to begin offsetting coal combustion with natural gas, or require additional coal cleaning to remove the ash prior to combustion, or simply start utilizing the unburned carbon. Accordingly, this work focuses on the development of two routes for the generation of premium carbon products from the unburned carbon present in fly ash: (1) feedstock for the production of activated carbons and (2) replacement for calcined petroleum coke in the production of carbon artefacts. Steam activation of the unburned carbon generated activated carbons with surface areas up to 688m2/g, and increasing the activation time from 60 to 120 minutes resulted in higher surface areas at the expense of some solid yield. However, increasing the steam activation time resulted in widening of both micro- and mesopores due to pore enlargement and removal of some pore walls. For the carbon artefacts, the baking yields are very similar for all the carbon bodies investigated, around 90%, as expected from the similar thermal history of petroleum coke and fly ash carbons. The densities of the green and baked carbon bodies produced with only petroleum coke are slightly higher than those of the carbon bodies prepared using fly ash carbon, probably due to the small particle size distribution of the formulations when using fly ash carbons.

INTEGRATED CARBONATION: A NOVEL CONCEPT TO DEVELOP A CO2 SEQUESTRATION MODULE FOR VISION 21 POWER PLANTS

The greatest challenge to achieve no environmental impact or zero emissions for the Vision 21 plants is probably greenhouse gases, especially CO{sub 2} emissions that are inevitably associated with fossil fuel combustion. Mineral carbonation, that involves the reaction of CO{sub 2} with non-carbonate minerals to form stable mineral carbonates, has been lately proposed as a promising CO{sub 2} sequestration technology due to the vast natural abundance of the raw minerals, the long term stability of the mineral carbonates formed, and the overall process being exothermic, and therefore, potentially economic viable. However, carbonation efficiency is being considered a major hurdle for the development of economically viable sequestration technologies, where present studies require extensive mineral particle communition, high pressures and prior capture of the CO{sub 2}. Consequently, mineral carbonation will only become a viable cost-effective sequestration technology through innovative development of fast reaction routes under milder regimes in a continuous process. The objective of the proposed novel active carbonation concept is to promote and accelerate reaction rates and efficiencies through surface activation to the extent that extensive mineral particle communition and high temperatures and pressures are not required. In this research program, serpentine was used as the carbonation feedstock material. Physical and chemical surface activation studies were conducted to promote its inherent carbonation reactivity. The activated materials were characterized by a battery of analytical techniques to determine their surface properties and assess their potential as carbonation minerals. Active carbonation studies were conducted and the carbonation activity was quantitatively determined by the increase of the weight of solid products and the percent of stoichiometric conversion. This work has shown that chemical activation was more effective than the physical activation in terms of increasing the surface area (330 vs. 17m{sup 2}/g). The steam activated serpentine had a 73% conversion to magnesite at 155 C and 1850 psig after 1 hour reaction, while under the same operating conditions, the parent sample only had 8% conversion. However, heat treatment is very energy intensive, and therefore, this steam activation route was not further considered. For the chemical activation, the most effective acid used was sulfuric acid, that resulted in surface areas of over 330 m{sup 2}/g, and more than 70% of the magnesium was dissolved from the serpentine (100{micro}m), and therefore, made available for carbonation. As a consequence, the subsequent carbonation reaction could be conducted at ambient temperatures (20 C) and low pressures (600psi) and it was possible to achieve 73% conversion after only 3 hours. This is indeed a significant improvement over previous studies that required temperatures over 185 C and very high pressures of around 1950 psig. Finally, this project has been awarded a Phase II, where the active carbonation process developed during this Phase I will be optimized in order to design a CO{sub 2} sequestration module.

Integrated Carbonation: A Novel Concept to Develop a CO2 Sequestration Module for Power Plants

Publisher Summary Anthropogenic emissions have increased the CO2 concentrations in the atmosphere with over 30% compared to pre-industrial levels. It is estimated that future global CO2 emissions will increase from 7.4 GtC/year in 1997 up to 26 GtC/year in 2100. Mineral carbonation has been proposed as a promising CO2 sequestration technology, while serpentine minerals have been identified as suitable feedstocks for mineral carbonation. This is because of the vast natural abundance of the raw minerals, the long term stability of the mineral carbonates formed, and the overall process being exothermic, and therefore, potentially economic viable. However, carbonation efficiency is being considered a major hurdle for the development of economically viable sequestration technologies. Consequently, mineral carbonation will only become a viable cost-effective sequestration technology through innovative development of fast reaction routes under milder regimes in a continuous process. This chapter focuses on surface activation studies of serpentine minerals to accelerate the carbonation reaction efficiency. The work presented has shown that it is possible to increase the surface area of the serpentine minerals to ∼330m2/g, compared to only ∼8m2/g for the raw serpentine. The SEM studies show that the structure of the activated serpentines has been significantly altered. The thermogravimetric analyses (TGAs) profile for the activated serpentines, particularly the physically activated sample, shows significantly smaller weight loss than the parent untreated sample (3wt% vs. 15 wt%).

Reducing Emissions of Polyaromatic Hydrocarbons from Coal Tar Pitches

Coal tar pitches are widely used as a binder in the production of carbon artifacts, and during baking of these artifacts significant amounts of polyaromatic hydrocarbons (PAHs) are emitted. This study has identified a green engineering approach to reduce the emissions of PAHs from coal tar pitches using a wide range of environmental benign polymerization additives that increase the yield of the carbon artifacts during baking. These additives have been tested against conventional sulfur additives, and an improvement of 97% in the pitch retention levels was observed. Several techniques, including pyrolysis GC/MS studies, were used to ascertain the role of the polymerization additives during the pyrolysis of coal tar pitches. It was observed that the novel additives react with the low molecular weight compounds present in the pitch.