Engine exhaust system with reduced hydrocarbon emissions

Claim 2

An engine exhaust system for substantially converting hydrocarbons in a hydrocarbon-containing engine exhaust stream to water and carbon dioxide comprising molecular sieve means for adsorbing hydrocarbons from said engine exhaust stream, said means being capable of adsorbing hydrocarbons from said stream and further capable of having hydrocarbons desorbed therefrom upon heating to a desorption temperature; main catalytic converter means for substantially converting hydrocarbons in said stream to water and carbon dioxide, said main catalytic converter means having a light-off temperature; one or more conveying means for selectively conveying said engine exhaust stream within said engine exhaust system, whereby said conveying means operate to (i) convey, for a first period of time prior to said molecular sieve means attaining its desorption temperature, substantially all of said exhaust stream through said molecular sieve means and said converter means; (ii) convey, for a second period of time thereafter, substantially all of said exhaust stream through said catalytic converter means, bypassing said molecular sieve means; and (iii) convey, for a third period of time thereafter, after said catalytic converter means attains at least its light-off temperature, at least a portion of said exhaust stream through said molecular sieve means and thereafter through said main catalytic converter means, said conveyed portion of exhaust stream being sufficient to raise the temperature of said molecular sieve means to its desorption temperature and thereby effect desorption of hydrocarbons therefrom.

Claim 3

The engine exhaust system of claim 1 wherein said molecular sieve means comprises zeolite.

Claim 4

The engine exhaust system of claim 1 wherein said zeolite is a high silica zeolite.

Claim 5

The engine exhaust system of claim 3 wherein said high silica zeolite is selected from the group consisting of silicalite, ZSM-5, ZSM-8, ZSM-11, ZSM-12, Hyper Y, ultrastabilized Y, Beta, mordenite, and erionite.

Claim 6

The engine exhaust system of claim 1 wherein said molecular sieve means comprises a ceramic substrate coated or embedded with zeolite.

Claim 7

The engine exhaust system of claim 1 wherein said molecular sieve means comprises a zeolite crystallized on the surface of a ceramic substrate.

Claim 8

The engine exhaust system of claim 5 wherein said ceramic substrate comprises a honeycomb structure.

Claim 9

The engine exhaust system of claim 6 wherein said ceramic substrate comprises a honeycomb structure.

Claim 10

The engine exhaust system of claim 1 wherein said main catalytic converter means additionally converts carbon monoxide and NO x to non-toxic by-products.

Claim 11

The engine exhaust system of claim 1 wherein said conveying means comprise a thermostatically controlled valve.

Claim 12

The engine exhaust system of claim 1 wherein said one or more conveying means operate, for said third period of time, to convey through said molecular sieve means a portion of said exhaust stream sufficient to effect desorption of substantially all hydrocarbons from said molecular sieve means and to convey said desorbed hydrocarbons to said main catalytic converter means.

Claim 13

The engine exhaust system of claim 11 wherein, for a fourth period of time subsequent to the desorption of substantially all hydrocarbons from said molecular sieve, said one or more conveying means operate to convey substantially all of said exhaust to said converter means, bypassing said molecular sieve means.

Claim 16

The method of claim 13 wherein said molecular sieve means comprises zeolite.

Claim 17

The method of claim 13 wherein said zeolite is a high silica zeolite.

Claim 18

The method of claim 15 wherein said high silica zeolite is selected from the group consisting of silicalite, ZSM-5, ZSM-8, ZSM-11, ZSM-12, Hyper Y, ultrastabilized Y, Beta, mordenite, and erionite.

Claim 19

The method of claim 13 wherein said molecular sieve means comprises a ceramic substrate coated or embedded with zeolite.

Claim 20

The method of claim 13 wherein said molecular sieve means comprises a zeolite crystallized on the surface of a ceramic substrate.

Claim 21

The method of claim 17 wherein said ceramic substrate comprises a honeycomb structure.

Claim 22

The method of claim 18 wherein said ceramic substrate comprises a honeycomb structure.

Claim 23

The method of claim 13 wherein said main catalytic converter means additionally converts carbon monoxide and NO x to non-toxic by-products.

Claim 24

The method of claim 13 wherein, during said third period of time, said portion of said exhaust stream directed through said molecular sieve means is sufficient to effect desorption of substantially all hydrocarbons from said molecular sieve means and to convey said desorbed hydrocarbons to said main catalytic converter means.

Claim 25

The method of claim 22 comprising the additional step of conveying, for a fourth period of time subsequent to the desorption of substantially all hydrocarbons from said molecular sieve, substantially all of said exhaust stream to said converter means, bypassing said molecular sieve means.

Claim 26

A process for treating an engine exhaust gas stream containing hydrocarbons and other pollutants comprising directing the engine exhaust gas stream over an adsorbent zone comprising a molecular sieve bed which preferentially adsorbs the hydrocarbons over water, to provide a first exhaust stream, flowing the first exhaust gas stream and discharging the treated exhaust stream into the atmosphere, said process being carried out for a time until the molecular sieve bed temperature is about 150° C., at which time the engine exhaust gas stream is diverted completely away from the adsorbent zone and routed directly over the primary catalyst until such time as the primary catalyst reaches its operating temperature, at which time the engine exhaust gas stream is divided into a major and minor portion, flowing the major portion of the engine exhaust gas stream over the primary catalyst and then discharging the treated exhaust gas stream from the primary catalyst into the atmosphere, flowing the minor portion of the engine exhaust gas stream over the adsorbent zone for a time sufficient to desorb substantially all the hydrocarbons absorbed on the molecular sieve bed and provide a second exhaust gas stream containing desorbed hydrocarbons, flowing the second exhaust stream and discharging the treated exhaust stream to the atmosphere and after such time as necessary to desorb substantially all the hydrocarbons from the molecular sieve bed, the engine exhaust gas stream is completely directed over the primary catalyst to provide a treated exhaust gas stream to the atmosphere; the molecular sieve being selected from the group consisting of silicalite, mordenites, zeolite ultrastable Y, and ZSM-5.

Claim 27

A process for treating an engine exhaust gas stream containing hydrocarbons and other pollutants comprising directing the engine exhaust gas stream over an adsorbent zone comprising a molecular sieve bed which preferentially adsorbs the hydrocarbons over water, to provide a first exhaust stream, flowing the first exhaust gas stream and discharging the treated exhaust stream into the atmosphere, said process being carried out for a time until the molecular sieve bed temperature is about 150° C., at which time the engine exhaust gas stream is diverted completely away from the adsorbent zone and routed directly over the primary catalyst until such time as the primary catalyst reaches its operating temperature, at which time the engine exhaust gas stream is divided into a major and minor portion, flowing the major portion of the engine exhaust gas stream over the primary catalyst and then discharging the treated exhaust gas stream from the primary catalyst into the atmosphere, flowing the minor portion of the engine exhaust gas stream over the adsorbent zone for a time sufficient to desorb substantially all the hydrocarbons absorbed on the molecular sieve bed and provide a second exhaust gas stream containing desorbed hydrocarbons, flowing the second exhaust stream and discharging the treated exhaust stream to the atmosphere and after such time as necessary to desorb substantially all the hydrocarbons from the molecular sieve bed, the engine exhaust gas stream is completely directed over the primary catalyst to provide a treated exhaust gas stream to the atmosphere; the molecular sieve being selected from the group consisting of silicalite, mordenites, zeolite ultrastable Y, and ZSM-5.