Bruce E. Waymack

Low temperature formation of aromatic hydrocarbon from pyrolysis of cellulosic materials

The major chemical pathways for production of aromatic hydrocarbons in the pyrolysis and subsequent flaming combustion of biomass materials are high temperature secondary reactions of the primary pyrolysis products. The second and less explored route is the evolution of aromatics from the solid substrate in the temperature range of 400–600°C. Primary chars that form around 300–400°C, depending on the starting material, continue to undergo pyrolysis up to temperatures of 600°C and higher. In this work, the formation of aromatic hydrocarbons from the second route was investigated for cellulosic materials. Experimental work was performed primarily using TG/DSC/MS. In order to reduce the formation of hydrocarbons from secondary reactions of the primary pyrolysis products, small sample size, i.e., 2 –10 mg, and a high helium flow rate of 150 ml/min, were used. Heating rates of less than 60°C /Min were used to ensure uniform sample temperature. Py/GC/MS confirmed the identities and relative quantities of masses detected by TG/DSC/MS. Under slow heating conditions, which are typical of thermogravimetric analyzers, simple hydrocarbon products begin to evolve above 350°C, where the primary decomposition of cellulosic materials has completed and the remaining char has begun the carbonization/aromatization process. Most aromatic products such as benzene, toluene, naphthalene, anthracene are detected between 400 to 600°C. Detectable products formed at temperatures above 600°C are methane, benzene, and hydrogen, and carbon monoxide. Some kinetic parameters for the formation of hydrocarbon products are deduced from the experimental findings and discussed in this presentation.

The Initiation of Smolderin Combustion in Cellulosic Fabrics

The time and heat flux required for the initiation of smoldering com bustion in cellulosic fabrics depends on the properties of both the environment and the fabric. In the environment, there must be sufficient oxygen to support smolder ing combustion and there must be sufficient heat to raise the temperature of the fabric to the point where combustion becomes self supporting. The critical factors for the cellulosic fabrics are the potassium and/or sodium ion content and the ther mal characteristics of the fabric. A series of simple weave, raw cotton fabrics, com monly referred to as cotton ducks, and an upholstery fabric were examined. The requirements for the initiation of smoldering combustion were similar for both the ducks and the upholstery fabric. However, the situation for the upholstery fabric was complicated by the non-homogeneous distribution of ions in the material and spatial variations in fabric thickness and basis weight. Also, for fabrics with potas sium and sodium ion contents in the range of approximately 1500 to 2500 ppm, there was an increased sensitivity to the environmental factors.

Smolder Rates of Thin Cellulosic Materials

Linear burn rates were determined for thin, cellulosic materials (papers and cotton fabrics) held in the horizontal plane by measuring the rate of radial increase of the circular burn pattern. Linear burn rates were determined for freely smoldering materials and for materials in contact with polyurethane foam. The linear burn rates of the freely smoldering materials were found to be inversely proportional to basis weight. This relationship held over basis weights from 0.8 to 24 oz/yd2. The linear burn rates of the materials in contact with poly urethane foam were also inversely proportional to basis weight and were reduced about 16% from the free smolder rate. The effect of potassium ion content was also examined. A minimum level of potassium, approximately 1300 ppm, was re quired for sustained smoldering combustion. Above this minimum level, the ion content did not have a significant effect on the linear burn rate.

Modification of the NIST Test for Measurin the Ignition Propensity of Cigarettes

The NIST method for measuring the ignition propensity (IP) of cigarettes on a test mockup meant to represent the flat surface of upholstered furniture was revised and tested [1]. The revisions included a number of dele tions and additions. The most important addition to the original test was the in clusion of selected, smolderable upholstery fabrics. The deletions were, in general, procedural details known or believed to be unnecessary. Three replicate runs of the method using the same experimental and control cigarette pair, as well as a series of runs using experimental and control cigarette pairs with deliv eries of 5, 11 and 16 mg of tar, were performed. The modified method provides re peatable and statistically valid data. Adding commercial, nonreversal upholstery fabrics to the test did not add to the ability of the test to measure IP behavior and, therefore, they were eliminated in the final proposed method. A reversal-type fabric should be included in the test, but it should be specially pro duced for this purpose [9]. With these further modifications, the test is consider ably simpler to perform than the original test.