Regeneration of adsorbents

Claim 1

In the process for pretreatment of landfill gas by selective adsorption for removal of trace impurities therein prior to bulk separation of CO 2 from CH 4 contained in the pretreated gas, the improvement which comprises: (A) passing said landfill gas at superatmospheric pressure into the feed end and through a column containing successive layers of adsorbent wherein hydrocarbons and halohydrocarbons boiling above methane are removed by selective adsorption in the first of such layers and water and sulfur compound are retained by adsorption in the succeeding layer, thereby producing a purified dry gas effluent discharge at the exit end of said column comprised of substantially purified CH 4 and CO 2 ; (B) thereafter regenerating the adsorbent layers in said column by the successive steps of: (a) depressurizing the column to near ambient pressure level by withdrawal of gas therefrom at its initial feed end; (b) passing hot regenerating gas into the column through the initial exit end thereof whereby said gas passes first through said water-retaining adsorbent layer at the highest regeneration temperature until a portion of said layer is heated to said highest regeneration temperature thereby driving off water and impurities earlier sorbed in said layer; (c) reducing the inlet temperature of the hot regenerating while continuing passage of the hot gas successively through said water-retaining adsorbent layer and said hydrocarbonladen layer, thereby thermally desorbing the hydrocarbon impurities from the hydrocarbon-laden layer without damage to the adsorbent in said layer; (d) cooling the column to about ambient temperature range by flowing unheated gas through the consecutive adsorbent layers; and (e) then restoring the column to the starting superatmospheric pressure level by introduction therein of a stream of purified dry gas comprised of CH 4 and CO 2 .