Drugs and the pharmaceutical sciences

Ozone Applications in Biotech and Pharmaceuticals 769
It can be appropriate to use either air or oxygen to produce ozone, however for high purity
applications, including pharmaceuticals, oxygen rich (90 þ %) feed gas is highly
recommended by equipment manufacturers. It is also recommended that the feed gas
be; clean and particle free above 0.4 mm, dry to 60 C dew point or lower, and oil and
hydrocarbon free. It is also extremely important that the feed gas be plumbed using
appropriate materials of construction to avoid contamination, especially particulate that
can either react with ozone, compromise the process, or both. With lower levels of
impurities in the feed gas higher concentrations (wt.%) of ozone can be achieved, and as a
result, increased gas absorption into the water is possible resulting in more effective
disinfection, lower operating cost, and possibly even lower costs for capital equipment
based on physical size and purchase expense. Although lower concentrations of ozone are
common, in the range of 5%, higher concentrations, in the range of 10–12% by weight are
considered optimal. As an example, note the difference in oxygen (O2) required to
produce 10 pounds of O3 at 5% concentration (200#) versus that required at 12%
concentration (83#).
Appropriately sized plant compressed air systems that meet the purity requirements
noted above can be used to produce ozone, however, many facilities chose an alternate
route since upgrading and maintaining a large diverse system simply to accommodate a
single user may prove cost prohibitive. Plant compressed air systems are seldom
categorized critical direct contact systems although that status would most likely change
if ozone production were added to the list of uses. Therefore, it is not uncommon for
system design to include a dedicated source of oxygen that has been earmarked solely for
supply of oxygen to the ozone generation system. One possible method of providing
oxygen for the ozone system is from the vaporization of liquid oxygen (LOX) stored
on-site in cylinders or in a bulk storage vessel. This can become expensive and can also
result in outages if refilling is delayed. Furthermore, reliance on a vendor for delivery
combined with the requirements for vendor qualification and subsequent auditing can
substantially increase the per-unit cost making this option less desirable.
Alternatively, oxygen generation equipment can be sized and selected solely to
supply oxygen to the ozone generation system. Two primary types of oxygen generators are
produced and they are designated as pressure swing adsorption (PSA) type and vacuum
swing adsorption (VSA) type generators. For smaller applications, and most pharmaceutical
applications fall into this category, PSA generation is most practical. Pressure swing
adsorption technology involves the passage of compressed (30–90 psig) air through a vessel
containing molecular sieve material. The sieve, having a greater affinity for nitrogen and
other gasses, including moisture, retains all but the oxygen and about 4% argon. Prior to
becoming fully saturated, the sieve, is regenerated by depressurization (desorption)
followed by an oxygen purge. The majority of PSA generators utilize at least two
(2) pressure vessels, also known as adsorbers or beds, to allow one vessel to be regenerated
while the other is in service. An oxygen receiver tank connected to the outlet of the system
stores the 90–95% pure oxygen at constant pressure to eliminate fluctuations and possible
downtime. The product oxygen is typically produced between 5–60 psig, has a dew point of
approximately -100 Fahrenheit and is 90–95% pure.
Vacuum swing adsorption, also known as vacuum pressure swing adsorption
(VPSA) is similar to PSA however, low pressure, high volume blowers are utilized for the
adsorption and vacuum blowers are used for desorption. Reduced air inlet pressure
translates to lower oxygen output pressure, most commonly in the range of 3–5 psig
unless an oxygen booster or compressor is added. Oxygen produced is in the range of
88–94% pure and a dew point at -100 F parallels that from the PSA generator. Both PSA
and VSA/VPSA employ the same 3:1 ratio of adsorption pressure to regeneration