Agriculture Reference
In-Depth Information
chemistry of formate and persulfate. The chemical reaction system involved the use
of a unique chemical effector and was described using a 20-step mechanism capable
of predicting the controlled heat released by this system (Curtin and others 2004).
Through the similar use of a chemical effector, a second alternative chemical heater
based on oxyhalogen oxidation-reduction chemistry was found. The chlorite-sulfi te
reaction generates abundant heat exothermically, but it could also be adjusted to
produce the disinfectant chlorine dioxide at near-neutral pH without the use of caustic
acids (Doona and others 2004, 2007). Understanding the complex reaction kinetics
and mechanism of this novel chemical combination has furnished insight that was
used to control the rate and quantity of chlorine dioxide produced and which provided
the conceptual basis for designing the PCS. That is to say, the PCS is designed to
accommodate this unique reaction chemistry and unlocks its inherent capabilities for
producing chlorine dioxide disinfectant and effi ciently inactivating bacterial spores
and vegetative pathogens on foodstuffs and contaminated surfaces.
Table 14.1 shows a simplifi ed version of the chemical reaction mechanism that
produces chlorine dioxide in the PCS. The core chemical species are an oxidant (chlo-
rite, chemical symbol ClO
2
−
), a reductant (sulfi te, chemical symbol SO
3
2−
), and a
chemical effector (called either ascorbic acid negative ion or sodium ascorbate, chemi-
cal symbol C
6
H
7
O
6
Na) that induces the reaction between the oxidant and reductant
while also undergoing oxidation. In a typical formulation, the symbols shown in Table
14.1 are the following: Ox
−
= ClO
2
−
, Ox
A
−
= ClO
−
, Eff
−
= AH
•
(ascorbyl
free radical), Eff = A (dehydroascorbic acid), Salt
1
= SO
4
2−
, Salt
2
= Cl
−
. A similar
scheme would complete the mechanism by reduction of ClO
−
to Cl
−
.
The PCS is an innovative device that represents a major technological breakthrough
(Doona and others 2005) for portable, energy-independent, point-of-use medical ster-
ilization, where no preexisting commercial technologies were available to fi ll this
need. For the purposes of sterilizing surgical instruments with chlorine dioxide gener-
ated by the novel chemical combination specifi ed above, the Pelican case was embel-
lished with special features designed to accommodate the chemical reaction, prevent
the accumulation of excess heat and pressure inside the sterilization chamber, fl ush,
and safely fi lter chlorine dioxide during evacuation of the chamber poststerilization
using a disposable, homemade scrubber device, thereby ensuring the health and safety
of the user and the environment (Fig. 14.4).
−
, Eff
•
= AH
Microbiological Validation of the PCS
The easy - to - operate PCS units were confi gured to achieve sterility by inactivating
resistant bacterial spores (live cultures and bioindicators) in 30 min. Microbiological
validation studies verifi ed that the PCS achieved sterility by inactivating bioindicators
Table 14.1.
Simplifi ed 3-step reaction mechanism proposed for the production of chlorine
dioxide by the novel chemical combination of chlorite (Ox
−
), sulfi te (Red
2
−
), and ascorbate
(Eff
−
)
2Ox
−
E f f
−
O x
A
−
E f f
i
.
+
→
+
ClO
2
+
ii
.
Ox
−
+
Red
2−
→
O x
A
−
+
Salt
1
iii
.
2Ox
−
+
O x
A
−
+
E f f
→
Eff
+
2ClO
2
+
Salt
2
