Energy and environmental research emphasizing low-rank coal: Task 5.7, Coal char fuel evaporation canister sorbent

Abstract

Atomobile evaporative emission canisters contain activated carbon sorbents that trap and store fuel vapors emitted from automobile fuel tanks during periods of hot ambient temperatures and after engine operation. When a vehicle is started, combustion air is pulled through the canister, and adsorbed vapors are removed from the sorbent and routed to the intake manifold for combustion along with fuel from the tank. The two primary requirements of an effective canister sorbent are that (1) it must be a strong enough adsorbent to hold on to the fuel vapors that contact it and (2) it must be a weak enough adsorbent to release the captured vapors in the presence of the airflow required by the engine for fuel combustion. Most currently available commercial canister sorbents are made from wood, which is reacted with phosphoric acid and heat to yield an activated carbon with optimum pore size for gasoline vapor adsorption. The objectives of Task 5.7 were to (1) design and construct a test system for evaluating the performance of different sorbents in trapping and releasing butane, gasoline, and other organic vapors; (2) investigate the use of lignite char as an automobile fuel evaporation canister sorbent; (3) compare the adsorbing andmore » desorbing characteristics of lignite chars with those of several commercial sorbents; and (4) investigate whether the presence of ethanol in fuel vapors affects sorbent performance in any way. Tests with two different sorbents (a wood-derived activated carbon and a lignite char) showed that with both sorbents, ethanol vapor breakthrough took about twice as long as hydrocarbon vapor breakthrough. Possible reasons for this, including an increased sorbent affinity for ethanol vapors, will be investigated. If this effect is real (i.e., reproducible over an extensive series of tests under varying conditions), it may help explain why ethanol vapor concentrations in SHED test evaporative emissions are often lower than would be expected.« less