Skip to main content
ARS Home » Research » Publications at this Location » Publication #203895
Title: Development of acid functional groups during the thermal degradation of wood and wood components

Author
item RUTHERSFORD, DAVID - USGS
item WERSHAW, ROBERT - USGS
item Reeves Iii, James

Submitted to: USGS - Scientific Investigations Report
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2006
Publication Date: 3/31/2008
Citation: Ruthersford, D.W., Wershaw, R.L., Reeves III, J.B. 2008. Development of acid functional groups during the thermal degradation of wood and wood components. U.S. Geological Survey Scientifc Investigations Report. 2007-5013:43.

Interpretive Summary: This study provides data on acid functional groups in charcoals and how the acid functional group content varies with the formation conditions. Chars were created from purified cellulose, purified lignin (a non-carbohydrate polymer found in woody plants), pine wood, and pine bark. The charring temperatures and charring duration were controlled in a laboratory furnace with an inert atmosphere and ranged from 200 C to 400 C and for 1 hour to 168 hours charring time. The total acidity of chars from cellulose and cellulose containing materials (wood and bark) was maximized at low charring temperatures and long charring times. At a charring temperature of 250 C, total acidity from cellulose continued to increase for times greater than 72 hours. For a fixed charring time, total acidity from cellulose char decreased as charring temperature increased. Total acidity in lignin did not change significantly with low temperature charring (250 to 400 C). The oxygen and carbon content of the chars were determined. Upon charring, both oxygen and carbon are lost from the starting material, but at unequal rates. Oxygen is lost more rapidly than carbon at the beginning of the charring process but for longer durations of heating, carbon continues to be lost while oxygen remains fairly constant. Diffuse reflectance mid-infrared spectra were obtained for the chars. For all materials, charring caused a reduction in absorbance associated with OH groups and a decrease in absorbance related to the overall loss of oxygen. Charring also caused a reduction in absorbance in the band associated with CH and the decrease in absorbance can be related to the overall loss of aliphatic carbon. For cellulose and cellulose containing materials (wood and bark), there were increases in absorbance in the bands associated with CO groups and the increase in absorbance which can be related to the creation of the acidic materials.

Technical Abstract: This study provides data on acid functional groups in charcoals and how the acid functional group content varies with the formation conditions. Chars were created from purified cellulose, purified lignin, pine wood, and pine bark. The charring temperatures and charring duration were controlled in a laboratory furnace with an inert atmosphere and ranged from 200 C to 400 C and for 1 hour to 168 hours charring time. The acid functional content and composition of these chars were measured using the Boehm titration method. This method measures the amount of NaOH, NaHCO3, and Na2CO3 neutralized by the char and allows the determination of total acidity and the fraction of acidity associated with strong, moderate and weak acids. The total acidity of chars from cellulose and cellulose containing materials (wood and bark) was maximized at low charring temperatures and long charring times. At a charring temperature of 250 C, total acidity from cellulose continued to increase for times greater than 72 hours and reached levels of 8.8 meq/g. For a fixed charring time, total acidity from cellulose char decreased as charring temperature increased. Total acidity in lignin did not change significantly with low temperature charring (250 to 400 C). The oxygen and carbon content of the chars were determined. Upon charring, both oxygen and carbon are lost from the starting material, but at unequal rates. Oxygen is lost more rapidly than carbon at the beginning of the charring process but for longer durations of heating, carbon continues to be lost while oxygen remains fairly constant. For charring at a given temperature, this disparity in loss results in the percentage carbon reaching a maximum in the first one to eight hours and then decreasing with time, while percentage oxygen reaches a minimum during this period and then increases with time. Neither the percentage oxygen, nor the carbon to oxygen atomic ratio, correlate with the observed increases in acid functional groups. Diffuse reflectance mid-infrared spectra were obtained for the chars. For all materials, charring caused a reduction in absorbance in the broad band between 3500 and 3300 wavenumbers. This band is associated with OH stretching and the decrease in absorbance can be related to the overall loss of oxygen. Charring caused a reduction in absorbance in the band at approximately 2900 wavenumbers for all materials. This band is associated with CH stretching and the decrease in absorbance can be related to the overall loss of aliphatic carbon. For cellulose and cellulose containing materials (wood and bark), there were increases in absorbance in the sharp bands at 1750 and 1620 wavenumbers. These bands are associated with carbonyl stretching and the increase in absorbance can be related to the creation of lactones and carboxylic acids.