Edwards, Robin

Lachaud, Jean

Mansour, Nagi N.

Peck, Jay

Reinisch, Guillaume

Wong, Hsi-Wu

English

University of Kentucky

Experimental Determination of Pyrolysis Products from Carbon/Resin Ablative MaterialsHsi-Wu Wong, Jay Peck, and Robin EdwardsAerodyne Research, Inc., Billerica, MAGuillaume ReinischUniversity of Texas at Austin, Austin, TXJean LachaudUniversity of California at Santa Cruz, Moffett Field, CANagi MansourNASA Ames Research Center, Moffett Field, CADetailed Pyrolysis Speciation and Production Rates Are Needed A class of low-density carbon/resin ablative materials has been developed, made of carbon fiber preform impregnated with phenolic resin The gas production rate from phenolic pyrolysis have an impact on the material response during ablation2Taken from Lachaud et al., 2012Current Understanding of Phenolic Pyrolysis Current understanding of phenolic pyrolysis consists of three general steps:1) Crosslink of phenolic and formation of water, aromatics, and phenol derivatives from condensation reactions (550-800 K)2) Crosslink breaking and the production of permanent gases such as methane, carbon monoxide and carbon dioxide (700-1100 K)3) Charring and the formation of hydrogen gas (> 850 K) A five-step reaction mechanism describing this behavior is used in PATO Quantitative understanding of detailed chemical composition (speciation) of pyrolysis gases and rates of production of these species, which is critical to developing a more robust finite-rate chemistry model, is dated (Sykes, 1967) 3A Batch Reactor System Was Designed and Constructed4A graphite ferrule was used to seal the quartz-stainless steel interfaceQuartz reactor was used:1) Light weight2) Transparent3) High temperature capability4) Good thermal shock resistanceThe Setup and the Configuration of the Reactor and the Furnace5 The condenser was placed into the liquid nitrogen bath Only the reactor was placed into the furnace, allowing larger species with low volatility to condense and reducing system pressureExperimental Procedure● 50 mg of cured phenolic sample were loaded in the reactor● Quartz reactor tube was weighted by electronic balance before being attached to the assembly● Furnace was preheated to the temperature of interest (first step was 323 K)● Reactor assembly was pumped down to < 0.1 torr● Reactor was inserted into the furnace; while condenser was inserted into the liquid nitrogen bath● After 1 hour of reaction, reactor was quenched in a water bath to room temperature (< 300 K)● Reactor pressure was measured, and an internal standard (C5H12, pentane) was added● Gas phase products were analyzed with gas chromatography (GC)● Quartz reactor was weighted for mass loss and preserved for the next run (step)● Liquid phase products were extracted with solvent (dichrolomathane) and analyzed with GC● The procedure was repeated with the preserved sample at a temperature 50 K higher6Sample and Ferrule Temperature● Sample temperature increased linearly with furnace set temperature● Ferrule temperature was no higher than 450 K, suggesting a large thermal gradient in the headspace of the reactor 7Chemical Species Were Identified and Quantified by Gas Chromatography● A mixture of chemical species is injected into a heated inlet and carried by a carrier gas● The compounds are separated by a column that is programmed to heat up with time:− Packed column: permanent gases− PLOT column: volatile vapors (< C8)− Capillary column: non-volatile liquids (> C6)● Lighter species reach the detector earlier● Different types of detectors can be used:− Flame ionization detector: hydrocarbons− Thermal conductivity detector: permanent gases− Mass spectrometer: mainly used for identification 8Representative ChromatographsReaction temperature ~ 850 K9Mass Loss Was Measured by Electronic Balance and Quantified by GC● Mass loss peaked at about 750 K● Water dominated at low temperatures, and permanent gases dominated at higher temperatures 10Reactor Pressure Measured after Each Step11● Pressure peaked at about 900 K, higher than mass loss peak● Pressure is more associated with molar loss rather than mass loss, suggesting lighter species were produced at higher temperaturesAccumulated Mass Loss Measured by Balance Agreed Well with GC Results12● GC quantification captured the trend and the amount of mass loss measured by the laboratory electronic balance● Total mass loss reached about 40%Speciation Results: 1) Permanent Gases and Water Vapor13● Water vapor was produced at a temperature below 800 K● Permanent gases were produced at a temperature higher than 700 K● Hydrogen gas had the highest molar yields, followed by methane and carbon monoxideSpeciation Results: 2) Phenol and Derivatives14● Phenol, Cresol had higher yields than dimethylphenol and trimethylphenol● Phenol and its derivatives were the most dominant liquid products and responsible for the peaked mass loss● Production peaked at about 750 KSpeciation Results: 3) Aromatics15● Benzene, toluene, xylene (BTX) all peaked at about 800 K● BTX had the lowest yields compared with other families of speciesSpeciation Results: 4) Hydrocarbons16● Smaller alkanes, such as ethane, had higher yields than larger alkenes● The overall yields of light hydrocarbons were much lower than permanent gases● Production peaked at about 1000 KConclusions● Batch pyrolysis of phenolic polymers was performed from room temperature up to 1300 K● Chemical speciation was measured by gas chromatography:− Water was found to be only important below 800 K− Phenol and its derivatives were responsible for the peaked mass loss, and their yields peaked between 600 – 850 K17− Minor molar yields of aromatic species were present between 750 – 850 K− Permanent gases were mostly produced between 700 – 1200 K− Yields of light hydrocarbons peaked at 1000 K− Lighter species were found to form at higher temperatures, consistent with the three-stage mechanism● The molar production of these species will be used for the construction of a finite-rate chemistry model for phenolic pyrolysisOngoing and Future Work● Two sets of pyrolysis experiments will be performed:− Pyrolysis of PICA− Pyrolysis of generic phenolic through carbon preform● The time-dependent pressure will be recorded:18Acknowledgement1. This work was originally supported by NASA’s Fundamental Aeronautic Program Hypersonic NRA grant NNX12AG47A and is currently supported by the 19Space Technology Research Grant Program2. Comments and suggestions from Drs. Ioana Cozmuta, Richard Jaffe, and Francesco Panerai

Experimental Determination of Pyrolysis Products from Carbon/Resin Ablative Materials

https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1019&amp;context=ablation

Experimental Determination of Pyrolysis Products from Carbon/Resin Ablative Materials

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