Method for purifying exhaust gas of an internal combustion engine

A method for purifying the exhaust gas of an internal combustion engine comprising:

• a step for contacting the exhaust gas of an internal combustion engine containing sulfur oxide with a sulfate absorbent at a temperature lower than a releasing temperature, said sulfate absorbent absorbing sulfur oxide in the exhaust gas when the temperature is lower than said releasing temperature and releasing the absorbed sulfur oxide when the temperature becomes higher than said releasing temperature or when the concentration of oxygen in the exhaust gas becomes low;
• a step for determining whether the temperature of the sulfate absorbent has reached said releasing temperature;
• and
• a step for lowering the concentration of oxygen in the exhaust gas when it is determined that the temperature of the sulfate absorbent has reached said releasing temperature to, thereby cause the sulfate absorbent to release the absorbed sulfur oxide.

A method for purifying the exhaust gas of an internal combustion engine comprising:

• a step for contacting the exhaust gas of an internal combustion engine containing sulfur oxide with a sulfate absorbent, said sulfate absorbent absorbing sulfur oxide in the exhaust gas and releasing the absorbed sulfur oxide when the concentration of oxygen in the exhaust gas becomes low;
• a step for determining whether the amount of sulfur oxide absorbed by the sulfate absorbent has reached a predetermined value;
• and
• a step for lowering the concentration of oxygen in the exhaust gas when it is determined that the amount of the sulfur oxide absorbed by the sulfate absorbent has reached said predetermined value to, thereby cause the sulfate absorbent to release the absorbed sulfur oxide.

A method for purifying the exhaust gas of an internal combustion engine containing soot and sulfur oxide comprising:

• a step for collecting soot in the exhaust gas of an internal combustion engine;
• a step for contacting the exhaust gas after collecting soot with a sulfate absorbent at a temperature lower than a releasing temperature, said sulfate absorbent absorbing sulfur oxide in the exhaust gas when the temperature is lower than said releasing temperature and releasing the absorbed sulfur oxide when the temperature becomes higher than said releasing temperature;
• a step for burning the collected soot;
• and
• a step for supplying the combustion exhaust gas generated by the combustion of the soot to the sulfate absorbent to cause the sulfate absorbent to release the absorbed sulfur oxide.