Activated carbons from end-products of tree nut and tree fruit production as sorbents for removing methyl bromide in ventilation effluent following postharvest chamber fumigation.

End-products of tree nuts and tree fruits grown in California, USA were evaluated for the ability to remove methyl bromide (MB) from ventilation effluent following postharvest chamber fumigation. Activated carbon sorbents from walnut and almond shells as well as peach and prune pits were prepared using different methods of pyrolysis, activation, and quenching. Each source and preparation was evaluated for yield from starting material (%, m/m) and performance on tests where MB-containing airstreams were directed through a columnar bed of the activated carbon. We report the number of doses needed to first observe the breakthrough of MB downstream of the bed and the capacity of the activated carbon for MB (%, m/m) based on a fractional percentage of MB mass sorbed at breakthrough relative to mass of the bed prior to testing. Activated carbons from prune pits, prepared either by steam activation or carbon dioxide activation coupled to water quenching, received the greatest number of doses prior to breakthrough and had the highest capacity, approximately 12 to 14 %, outperforming a commercially-marketed activated carbon derived from coconut shells. Experimental evidence is presented that links discrepancy in performance to the relative potential for activated carbons to preferentially sorb water vapor relative to methyl bromide.