Recovery of oxygen used in ozone production
A method of continuous ozone production using a system of four absorbent beds to separate an ozone and oxygen gas mixture generated in an ozone generator. The beds are operated according to an offset sequence of cycles. Oxygen passing through the beds is at least partially recycled for use in further ozone generation. The concentration of oxygen in the ozone product can be reduced using the system to make it suitable for use in fine chemical applications.
1. A method for the continuous production of ozone having an oxygen concentration less than that of air and recovery of oxygen in a purge cycle adsorption process having four adsorbent beds, in which a first, second, third and fourth beds cycle sequentially through the following steps in an overlapping cycle:
a) Feeding an oxygen and ozone mixture from an ozone generator to a first bed, wherein ozone is adsorbed in the first bed and non-adsorbed oxygen passes through the first bed and is recycled back to the ozone generator;
b) Feeding a first nitrogen-rich purge gas in a counter current direction to step a) thereby desorbing an oxygen enriched ozone stream from the first bed to a customer process;
c) Feeding a second nitrogen-rich purge gas in the counter current direction to step a) thereby desorbing the oxygen-depleted ozone from the first bed to the customer process;
d) Feeding an oxygen and ozone mixture from the ozone generator to the first bed in the same direction as in step a) whereby ozone is adsorbed in the first bed and non-adsorbed oxygen rinse gas displaces a nitrogen-rich purge gas from the first bed through a vent, preparing the first bed to repeat step a);
e) Feeding an oxygen and ozone mixture from an ozone generator to a second bed, wherein ozone is adsorbed in the second bed and non-adsorbed oxygen passes through the second bed and is recycled back to the ozone generator;
f) Feeding a first nitrogen-rich purge gas in a counter current direction to step e) thereby desorbing an oxygen enriched ozone stream from the second bed to a customer process;
g) Feeding a second nitrogen-rich purge gas in the counter current direction to step e) thereby desorbing the oxygen-depleted ozone from the second bed to the customer process;
h) Feeding an oxygen and ozone mixture from the ozone generator to the second bed in the same direction as in step e) whereby ozone is adsorbed in the second bed and non-adsorbed oxygen rinse gas displaces a nitrogen-rich purge gas from the second bed and feeds the displaced nitrogen-rich purge gas through a vent, preparing the second bed to repeat step e);
wherein steps e) to h) are offset in time from steps a) to d) such that the beginning of steps a) and c) overlap with the end of steps e) and g) and the end of steps a) and c) overlap with the beginning of steps e) and g).
2. The method as claimed in claim 1 further comprising venting a portion of the nitrogen-rich purge gas to the atmosphere at the start of step b) and step f).
3. The method as claimed in claim 1 in which make-up oxygen is mixed with recycled oxygen before it is fed to the ozone generator.
4. The method as claimed in claim 3 in which the mixture of recycled oxygen and make-up oxygen is fed through a blower to increase its pressure before being fed to the ozone generator.
5. The method as claimed in claim 3 in which the mixture of recycled oxygen and make-up oxygen is passed through an inline ozone destruct unit prior to being fed to the blower.
6. The method as claimed in claim 2 in which vent streams from steps b) and f) are passed through one or more ozone destruct units before being released to the atmosphere.
7. The method as claimed in claim 3 in which the vent streams from steps d) and h) are passed through one or more ozone destruct units before being released to the atmosphere.
8. The method as claimed in claim 1 wherein the oxygen and ozone gas mixture that is fed to the adsorbent beds comprises about 1 to 30% by weight ozone.
9. The method as claimed in claim 6 wherein the oxygen and ozone gas mixture that is fed to the adsorbent beds comprises about 6 to 12% by weight ozone.
10. The method as claimed in claim 1 wherein the oxygen concentration of the ozone stream sent to the customer is less than 15% by volume.
11. The method as claimed in claim 1 wherein the oxygen concentration of the ozone stream sent to the customer is less than 10% by volume.
12. The method as claimed in claim 1 wherein the oxygen concentration of the ozone stream sent to the customer is less than 5% by volume.
13. The method as claimed in claim 1 wherein buffer tanks are connected to a source selected from the group consisting of the recovered ozone, the recycled oxygen and both.
14. The method as claimed in claim 1 wherein the first, second, third and fourth adsorbent beds contain an adsorbent material.
15. The method as claimed in claim 10 wherein the adsorbent material is selected from the group consisting of silica gel and high silica zeolites.
16. The method as claimed in claim 11 wherein the silica gel is of different particle sizes.
17. The method as claimed in claim 11 wherein the high silica zeolites are selected from the group consisting of DAY, MFI and dealuminated mordentite.
18. The method as claimed in claim 1 wherein the cycle is a concentration swing adsorption cycle.
19. The method as claimed in claim 1 wherein the duration of steps a) and c) and steps e) and g) are equal and in the range 5 to 600 seconds.
20. The method as claimed in claim 1 wherein the duration of steps a) and c) and steps e) and g) are equal and in the range of 30 to 500 seconds.
21. The method as claimed in claim 1 wherein the duration of steps a) and c) and steps e) and g) are equal and in the range of 60 to 120 seconds.
22. The method as claimed in claim 1 wherein the duration of steps b) and d) and steps f) and h) are equal and in the range of 5 to 50% of step a).
23. The method as claimed in claim 1 wherein the duration of steps b) and d) and steps f) and h) are equal and in the range of 25 to 40% of step a).