By-pass adsorber system

Claim 2

An engine exhaust system for a hydrocarbon-containing engine exhaust stream comprising: a housing having disposed therein at least two molecular sieve structures connected in parallel each having a desorption temperature, the molecular sieve structures and the housing both having an inlet and an outlet end; a burn-off catalyst having a light-off temperature, disposed downstream from the molecular sieve structure; an exhaust pipe connecting an engine to the burn-off catalyst, the exhaust pipe being connected to the inlet end of the housing at an upstream junction and to the outlet end of the housing at a downstream junction; and a flow diverter disposed in the upstream junction for diverting exhaust gases from the engine to the housing and an additional flow diverter for directing exhaust stream between the two molecular sieve structures.

Claim 3

The exhaust system of claim 1, further comprising a main catalytic converter disposed downstream from the adsorber housing.

Claim 4

The exhaust system of claim 2, wherein the main catalytic converter is a three-way catalyst having a light-off temperature, for converting carbon monoxide, hydrocarbon, and NOx to carbon dioxide, water and nitrogen.

Claim 5

The exhaust system of claim 1, wherein the molecular sieve structure comprises zeolites supported on a substrate.

Claim 6

The exhaust system of claim 4, wherein the substrate is a honeycomb structure.

Claim 7

The exhaust system of claim 1, wherein the adsorber further comprises a catalyst.

Claim 8

The exhaust system of claim 1, wherein the molecular sieve structure is a monolithic honeycomb structure.

Claim 9

The exhaust system of claim 1, wherein the molecular sieve structure is a zeolite selected from ZSM-5, Beta, ultra-stable Y, mordenite, and combinations of these.

Claim 10

The exhaust system of claim 1, further comprising an electrically heated catalyst or pre-converter disposed in a location selected from the group consisting of (1) upstream from the junction, (2) in the exhaust pipe, and (3) between the burn-off catalyst and a second junction connecting the outlet end of the housing to the exhaust pipe.

Claim 11

The exhaust system of claim 1, wherein the molecular sieve structure comprises an extruded honeycomb structure having a frontal area, and having a plurality of cells running longitudinally parallel between the inlet and the outlet ends of the structure.

Claim 12

The exhaust system of claim 10, wherein the flow diverters are connected to a secondary air source.

Claim 13

The exhaust system of claim 1, wherein the molecular sieve structure comprises extruded zeolites selected from the group consisting of ZSM-5, USY, Mordenite, Beta zeolites and combinations of these.

Claim 14

The exhaust system of claim 1, wherein the molecular sieve structure comprises zeolites supported on a substrate.

Claim 15

The exhaust system of claim 13, wherein the substrate is in a form selected from the group consisting of pellets and cellular monoliths.

Claim 16

The exhaust system of claim 14, wherein the substrate is an extruded cordierite structure.

Claim 17

The exhaust system of claim 1, wherein the molecular sieve structure further comprises a catalyst.

Claim 18

The exhaust system of claim 1, wherein the burn-off catalyst is selected from the group consisting of segmented catalyst, multistage catalyst, three-way catalyst, and combinations of these.

Claim 19

The exhaust system of claim 12, further comprising a main catalytic converter disposed between the engine and the upstream junction.

Claim 20

The exhaust system of claim 18, wherein the main catalytic converter comprises a three-way catalyst.

Claim 21

Method of treating a hydrocarbon-containing engine exhaust stream by (1) providing the exhaust system of claim 1 having two molecular sieve structures; (2) during cold-start, first flowing the exhaust stream from the engine through a first molecular sieve structure until the first molecular sieve structure approaches its desorption temperature, and then flowing the exhaust stream through a second molecular sieve structure until the second molecular sieve structure approaches its desorption temperature; (3) after light-off, directing a substantial amount of the exhaust gases through the exhaust pipe while continuing to flow a small portion of the exhaust through the adsorbers to bring the molecular sieve structures to the desorption temperatures to thereby desorb hydrocarbons therefrom; and (4) during desorption, contacting the molecular sieve structure with additional air from a secondary air source to effect oxidation of the desorbed hydrocarbons and to cool the molecular sieve structure.

Claim 22

Method of treating a hydrocarbon-containing engine exhaust stream by (1) providing the exhaust system of claim 1; (2) during cold-start, apportioning the exhaust stream from the engine through the at least two molecular sieve structures until the molecular sieve structures approach desorption temperatures; (3) after light-off, directing a substantial amount of the exhaust stream through the exhaust pipe while continuing to flow a small portion of the exhaust through the adsorbers to bring the molecular sieve structures to the desorption temperatures to thereby desorb hydrocarbons therefrom; and (4) during desorption, contacting the molecular sieve structure with additional air from a secondary air source to effect oxidation of the desorbed hydrocarbons and to cool the molecular sieve structure.

Claim 23

The exhaust system of claim 1 wherein the flow diverter is adapted to adapted to direct a substantial portion of the exhaust stream through the burn-off catalyst and a minor portion of the exhaust through the molecular sieve structure, after the burn-off catalyst has attained its light-off temperature.