Oxidation of carbonaceous materials in flames is a key phenomenon in determining the final emission of these compounds in the atmosphere both in terms of concentrations and particle sizes. Oxidation is generally considered as a surface process able to subtract carbon atoms from the particles reducing their size. However, fragmentation of particles can also occur if the oxidizing species is able to penetrate the particles and remove C atoms from weak points causing the break-up of the particles. This process can be referred to as oxidation - induced fragmentation and can be seen as particular events of oxidation. It produces a huge number of very small size particles increasing their subsequent burn-out. Recent experimental data obtained in flames have shown the importance of oxidation-induced fragmentation and have individuate O 2 as the main responsible for particle fragmentation because of its relatively slow oxidation rate and the capability to penetrate the particles. Fragmentation can involve large aggregates containing a large number of individual particles leading to smaller aggregates, but also primary particles where internal burning fragments single particle into smaller clusters. In order to have more insights on the process of oxidation - induced fragmentation of soot, the oxidation of various carbonaceous materials has been carried out in a quartz tubular flow micro reactor electrically heated to controlled temperatures ranging from 800 to 1300K. Continuous analysis of CO and CO 2 concentrations allowed the evaluation of carbon conversion at varying temperatures and material characteristics. Measurements of specific surface area of the fresh carbon materials and of the samples after partial carbon conversion have also been carried out. Results showed a huge increase of the specific surface area as the carbon conversion proceeds. The increase was more evident in the low temperature range where the specific surface area was increased up to 800%. Analysis of the data have shown that fragmentation of the particles occurs particularly at lower temperatures where molecular oxygen is able to penetrate the pores to internally oxidize the particle causing their break-up. A fragmentation kinetic constant has been retrieved from the experimental data and compared with literature data.

Oxidation-induced fragmentation of carbonaceous materials at low and intermediate temperatures

VACCARO, Salvatore;
2013

Abstract

Oxidation of carbonaceous materials in flames is a key phenomenon in determining the final emission of these compounds in the atmosphere both in terms of concentrations and particle sizes. Oxidation is generally considered as a surface process able to subtract carbon atoms from the particles reducing their size. However, fragmentation of particles can also occur if the oxidizing species is able to penetrate the particles and remove C atoms from weak points causing the break-up of the particles. This process can be referred to as oxidation - induced fragmentation and can be seen as particular events of oxidation. It produces a huge number of very small size particles increasing their subsequent burn-out. Recent experimental data obtained in flames have shown the importance of oxidation-induced fragmentation and have individuate O 2 as the main responsible for particle fragmentation because of its relatively slow oxidation rate and the capability to penetrate the particles. Fragmentation can involve large aggregates containing a large number of individual particles leading to smaller aggregates, but also primary particles where internal burning fragments single particle into smaller clusters. In order to have more insights on the process of oxidation - induced fragmentation of soot, the oxidation of various carbonaceous materials has been carried out in a quartz tubular flow micro reactor electrically heated to controlled temperatures ranging from 800 to 1300K. Continuous analysis of CO and CO 2 concentrations allowed the evaluation of carbon conversion at varying temperatures and material characteristics. Measurements of specific surface area of the fresh carbon materials and of the samples after partial carbon conversion have also been carried out. Results showed a huge increase of the specific surface area as the carbon conversion proceeds. The increase was more evident in the low temperature range where the specific surface area was increased up to 800%. Analysis of the data have shown that fragmentation of the particles occurs particularly at lower temperatures where molecular oxygen is able to penetrate the pores to internally oxidize the particle causing their break-up. A fragmentation kinetic constant has been retrieved from the experimental data and compared with literature data.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/4214054
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