Importance of catalysis and carbon active sites in lignite char gasification

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1982

OSTI ID:5602038

Radovic, L R

A detailed study of the gasification of a North Dakota lignite was undertaken. Chars were prepared from raw and pretreated lignite under widely varying conditions of pyrolysis heating rate, temperature and residence time. Coal pretreatment consisted of essentially complete demineralization, selective removal of exchangeable cations and selective cation loading. Rapid pyrolysis was performed in an entrained-flow reactor. Slow pyrolysis was effected in a horizontal-tube furnace. The gasification reactivity of the chars was determined by isothermal thermogravimetric analysis mostly in 0.1 MPa air, but also in 0.1 MPa CO/sub 2/ and 3.1 kPa H/sub 2/O. A detailed analysis of the surface properties of the chars was performed. A very wide range of reactivities of the chars was achieved by varying the conditions of coal pyrolysis and pretreatment. It was shown that total surface area is not a relevant parameter. In the predominantly uncatalyzed gasification, the concentration of carbon active sites was shown to be the relevant index of reactivity, both for the demineralized lignite chars and for carbons of increasing crystallinity, from Saran char to natural graphite. In the case of raw (Ca-containing) lignite chars, it was shown that CaO is the predominant catalyst responsible for the relatively high gasification reactivity of lignite compared to higher-rank coals. Litnite char gasification should be regarded, therefore, as a catalyzed gas-solid reaction, with the catalyst dispersion being the relevant reactivity parameter. Indeed, when the rates are expressed as turnover frequencies, observed differences per unit mass of char as large as two hundred times are reduced to within one order of magnitude. Thus, the commonly observed and heretofore empirically treated coal char deactivation with increasing severity of pyrolysis conditions was correlated with a decrease in measurable fundamental properties of the chars: carbon active surface area and catalyst dispersion.

• OSTI ID: 5602038
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010401* -- Coal & Coal Products-- Carbonization-- (-1987)
ACTIVATION ENERGY
ALKALINE EARTH METAL COMPOUNDS
BROWN COAL
CALCIUM COMPOUNDS
CALCIUM OXIDES
CARBONACEOUS MATERIALS
CATALYSTS
CATALYTIC EFFECTS
CHALCOGENIDES
CHARS
CHEMICAL ANALYSIS
CHEMICAL REACTIONS
COAL
COAL GASIFICATION
DECOMPOSITION
DEMINERALIZATION
ENERGY
ENERGY SOURCES
FEDERAL REGION VIII
FOSSIL FUELS
FUELS
GASIFICATION
GRAVIMETRIC ANALYSIS
HEATING RATE
KINETICS
LIGNITE
MATERIALS
NORTH AMERICA
NORTH DAKOTA
OXIDES
OXYGEN COMPOUNDS
PYROLYSIS
PYROLYSIS PRODUCTS
QUANTITATIVE CHEMICAL ANALYSIS
REACTION KINETICS
REACTIVITY
SEPARATION PROCESSES
SURFACE AREA
SURFACE PROPERTIES
THERMAL ANALYSIS
THERMAL GRAVIMETRIC ANALYSIS
THERMOCHEMICAL PROCESSES
USA