Smith, DM
1991
Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals
White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 4:180-209, 1991. Funded by ACERC.
Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.
1990
Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals
White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 1990 (In press). Funded by ACERC.
Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.
1989
Pore Structure Characterization of Coals & Chars Via NMR
Davis, P.J.; Smith, D.M.; Bartholomew, C.H.; White, W.E. and Hecker, W.C.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Due to the wide pore size range and complexity of coals and chars, it is difficult to study the pore structure. Multiple techniques such as gas adsorption, mercury porosimetry, and density measurements are often used. These techniques suffer from limited pore size range, pore shape assumption, network/percolation effects, and sample changes during analysis. To obtain a more complete description of coals and chars, NMR spin-lattice relaxation measurements of water saturated coals and chars have been performed. The NMR technique does not suffer from network/percolation effects, sample changes, pore shape assumption (rp>5nm). Three coals and their chars were compared.
Surface Areas and Pore Structures of ANL and PETC Coals and Derived Chars
Bartholomew, C.H.; White, W.E. ; Hecker, W.C.; Smith, D.M.
4th Annual Meeting of the Western States Catalysis Club, Denver, Colorado , 1989. (Also presented at the Western States Section,The Combustion Institute, Livermore, California, 1989). Funded by ACERC (National Science Foundation and Associates and Affiliates).
Surface areas, pore volumes, and pore size distributions of five Argonne National Lab (ANL) coals (Pittsburgh No. 8, Illinois No. 6, Pocahontas No. 3, Beulah Zap lignite, and Utah Blind Canyon) and of two PETC coals (Lower Wilcox and Dietz) and chars derived from these coals area being measured in an ongoing study. Data obtained for several of these coals and chars will be reported. Surface areas, pore volumes and pore size distributions were measured by nitrogen and carbon dioxide adsorptions at 77 K and 195-300 K respectively; pore volumes and pore size distributions were also determined by NMR spin-relaxation measurements of samples saturated with water. Comparisons of accuracy and precision for static vacuum and flow desorption methods were made. Surface areas and pore volumes measured by adsorption in a static vacuum system and by desorption in a flow/TC detector system agree to better than 1-5% where adsorption equilibrium has obtained.
The results provide new insights into the surface and pore structure of coals and chars as functions of rank and charification. Surface areas of coals generally increase with decreasing rank. Chars have larger surface areas and pore volumes than the parent coals; indeed surface areas measured by nitrogen adsorption are up to two orders of magnitude larger, while those measured by carbon dioxide adsorption are 2-3 times larger. Pore volumes of chars measured by nitrogen adsorption are 10-20 time those of the parent coals. Large fractions of the internal surfaces of coals and pore diameters are microporous (pore diameters of 1 nm or smaller) and are not easily penetrated by nitrogen molecules at 77 K. In the case of some coals, while the pore volume increases during devolatilization, the shape of the pore size distribution stays the same. For other coals, the pore size distribution changes radically during devolatilization. This systematic study of surface areas and pore structures of coals and chars provides insights into physical changes that occur during coal devolatilization and char burnout. This information can be useful in characterizing the evolution of pore structure and its effect on diffusion of reactant in and products out during combustion of coal chars.
1988
Surface and Pore Properties of ANL and PETC Coals
Bartholomew, C.H.; White, W.E.; Thornock, D.; Wells, W.F.; Hecker, W.C.; Smoot, L.D.; Smith, D.M. and Williams, F.L.
Preprint ACS Fuels Chem. Divl., 1988, Los Angeles. 9 pgs. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Surface areas, pore volumes, pore size distributions, and solid densities were measured for three ANL coals (Pittsburgh No. 8, Wyodak, and Beulah Zap Lignite), two PETC coals (Lower Wilcox, and Dietz) and a Utah Scofield coal and for chars derived from these coals. Surface areas were measured using nitrogen and carbon dioxide adsorptions; pore volumes were determined using nitrogen adsorption, mercury porosimetry, and NMR spin-lattice relaxation measurements of samples saturated with water. Solid densities were obtained using helium displacement. The results indicated that chars have larger surface areas and pores relative to coals; large fractions of the internal surfaces of coals are not penetrated by nitrogen molecules but are penetrated by carbon dioxide suggesting that the pores are mostly smaller than 1 NM
Smith, DM
1991
Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals
White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 4:180-209, 1991. Funded by ACERC.
Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.
1990
Changes in Surface Area, Pore Structure and Density During Formation of High-Temperature Chars from Representative U.S. Coals
White, W.E.; Bartholomew, C.H.; Hecker, W.C. and Smith, D.M.
Adsorption Science & Technology, 1990 (In press). Funded by ACERC.
Multiple techniques (CO2 and N2 adsorptions, NMR spin relaxation of adsorbed water, He pycnometry, and Hg porosimetry) were combined in a comprehensive study to determine changes in surface area (CO2 and nitrogen), density (solid, particle, and bulk), and pore structure (pore size and volume distributions of micro-, meso-, and macropores) in high temperature char formation from rank-representative U.S. coals of the ANL and PETC Banks (i.e. Beulah Zap, Dietz, Utah Blind Canyon, Pittsburgh No. 8, and Pocahontas No. 3). Chars were formed at high heating rates in a flat flame burner (maximum temperature of 1473 K), a process representative of char formation in pulverized coal combustion. It was determined that most of the surface area of coals was found in micropores with radii less than 1.5 nm, while 95% or more of the pore volume in the coals (85% of that in chars) is contained in mesopores (radii > 20 nm). During high temperature formation of char in a flame: (1) CO2 surface areas (involving mainly micropores, rpore < 1.5 nm) increase 2-3 fold, while N2 surface areas, (involving mesopores, 1.5 nm < rpore < 20 nm) increase 20-200 fold, (2) solid densities increase about 25% due to graphitization, while particle densities decrease by about a factor of two due to large increases in particle porosity, (3) pore volumes are increased 5-10 fold, and (4) total porosities are increased 3-4 fold, most of this increase occurring in the macropore range. The larger surface areas and porosities of chars relative to coals may be explained by (i) the removal by pyrolysis of strongly adsorbed molecules or volatile hydrocarbons from micropores and small mesopores that would otherwise hinder access of CO2 and N2, (ii) creation of new pores during the restructuring process involved in charification, and (iii) opening up by gasification with oxygen of new pores previously blocked to gas adsorption. Preparation conditions (e.g. atmosphere, heating rate, and temperature) greatly affect the physical properties including surface area, porosity and density of the resulting chars. The degree of carbon burnout is an important correlating factor affecting these properties.
1989
Pore Structure Characterization of Coals & Chars Via NMR
Davis, P.J.; Smith, D.M.; Bartholomew, C.H.; White, W.E. and Hecker, W.C.
Twelfth Symposium of the Rocky Mountain Fuels Society, Denver, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Due to the wide pore size range and complexity of coals and chars, it is difficult to study the pore structure. Multiple techniques such as gas adsorption, mercury porosimetry, and density measurements are often used. These techniques suffer from limited pore size range, pore shape assumption, network/percolation effects, and sample changes during analysis. To obtain a more complete description of coals and chars, NMR spin-lattice relaxation measurements of water saturated coals and chars have been performed. The NMR technique does not suffer from network/percolation effects, sample changes, pore shape assumption (rp>5nm). Three coals and their chars were compared.
Surface Areas and Pore Structures of ANL and PETC Coals and Derived Chars
Bartholomew, C.H.; White, W.E. ; Hecker, W.C.; Smith, D.M.
4th Annual Meeting of the Western States Catalysis Club, Denver, Colorado , 1989. (Also presented at the Western States Section,The Combustion Institute, Livermore, California, 1989). Funded by ACERC (National Science Foundation and Associates and Affiliates).
Surface areas, pore volumes, and pore size distributions of five Argonne National Lab (ANL) coals (Pittsburgh No. 8, Illinois No. 6, Pocahontas No. 3, Beulah Zap lignite, and Utah Blind Canyon) and of two PETC coals (Lower Wilcox and Dietz) and chars derived from these coals area being measured in an ongoing study. Data obtained for several of these coals and chars will be reported. Surface areas, pore volumes and pore size distributions were measured by nitrogen and carbon dioxide adsorptions at 77 K and 195-300 K respectively; pore volumes and pore size distributions were also determined by NMR spin-relaxation measurements of samples saturated with water. Comparisons of accuracy and precision for static vacuum and flow desorption methods were made. Surface areas and pore volumes measured by adsorption in a static vacuum system and by desorption in a flow/TC detector system agree to better than 1-5% where adsorption equilibrium has obtained.
The results provide new insights into the surface and pore structure of coals and chars as functions of rank and charification. Surface areas of coals generally increase with decreasing rank. Chars have larger surface areas and pore volumes than the parent coals; indeed surface areas measured by nitrogen adsorption are up to two orders of magnitude larger, while those measured by carbon dioxide adsorption are 2-3 times larger. Pore volumes of chars measured by nitrogen adsorption are 10-20 time those of the parent coals. Large fractions of the internal surfaces of coals and pore diameters are microporous (pore diameters of 1 nm or smaller) and are not easily penetrated by nitrogen molecules at 77 K. In the case of some coals, while the pore volume increases during devolatilization, the shape of the pore size distribution stays the same. For other coals, the pore size distribution changes radically during devolatilization. This systematic study of surface areas and pore structures of coals and chars provides insights into physical changes that occur during coal devolatilization and char burnout. This information can be useful in characterizing the evolution of pore structure and its effect on diffusion of reactant in and products out during combustion of coal chars.
1988
Surface and Pore Properties of ANL and PETC Coals
Bartholomew, C.H.; White, W.E.; Thornock, D.; Wells, W.F.; Hecker, W.C.; Smoot, L.D.; Smith, D.M. and Williams, F.L.
Preprint ACS Fuels Chem. Divl., 1988, Los Angeles. 9 pgs. Funded by ACERC (National Science Foundation and Associates and Affiliates).
Surface areas, pore volumes, pore size distributions, and solid densities were measured for three ANL coals (Pittsburgh No. 8, Wyodak, and Beulah Zap Lignite), two PETC coals (Lower Wilcox, and Dietz) and a Utah Scofield coal and for chars derived from these coals. Surface areas were measured using nitrogen and carbon dioxide adsorptions; pore volumes were determined using nitrogen adsorption, mercury porosimetry, and NMR spin-lattice relaxation measurements of samples saturated with water. Solid densities were obtained using helium displacement. The results indicated that chars have larger surface areas and pores relative to coals; large fractions of the internal surfaces of coals are not penetrated by nitrogen molecules but are penetrated by carbon dioxide suggesting that the pores are mostly smaller than 1 NM