[Quinone.com] Environment

Applications, physical properties and features

Environment

1.Environment and quinones

Quinones, with its unique characteristics, have important roles in living organism (for example, electron transfer body of photosynthesis, vitamin K), and are used in wide variety of applications in industries (desulfurization, generation control of hydrogen sulfide, recovery of precious metals, pulping, oxygen absorber and catalyst of hydrogen peroxide manufacturing).
Quinones consists of mainly benzoquinones, naphthoquinones and anthraquinones. The greatest feature of quinones is the ability to compose a reversible oxidation-reduction cycle.


The oxidation form	The reduction form

The standard redox potentials of quinones are widely distributed from +0.9V to +0.1V. For example, the standard redox potential of the 1,4-benzoquinone is +0.715V, the 1,4-naphthoquinone is +0.485V, and the 9,10-anthraquinone is +0.154V. The potential of the quinones becomes low by introducing of electron-donating groups such as OH, and with electron-withdrawing groups such as Cl and

the potential becomes high.
So, it is possible that quinones can have various value of the standard redox potential governed by their functional groups. Therefore, Quinones can play the important roles in chemical reactions, and are used in various industrial applications, especially in environmental conservation scene, as described below.

2.Recovery of precious metals by quinones

    Precious metals represented by gold have been used as valuable goods for the purpose of ornament from ancient times because they are very stable and shine their beautiful color. But their amount of deposits in the earth is very small, differing from base metals such as iron, aluminum etc.Therefore, they are very expensive, since they are limited resources, even if they are very useful to industries.
    Besides ornament uses, recently they have been rapidly consumed in the various applications such as electronic wiring, non-electric plating, auto catalyst and so on, because of their physical properties.
     While, the discharge of precious metals to the environment is also increasing. In the plating field of electronic industries, the discharged precious metals usually exist into the effluent as the complex ions, and they are recovered by treatments of sedimentation, filtration and combustion.
    But it is difficult to recover these metals selectively because many other metals are also contained in the effluent.
    However, it has become possible to recover these precious metals by the quinones.     The quinones have their own oxidation-reduction (redox) potentials, and they are able to selectively reduce only precious metal ions to the elemental form. Precious metals such as gold, silver, palladium and platinum have the redox potential which is higher than those of quinones.
    On the other hand, the standard redox potentials of quinones are generally higher than that of base metals, therefore the quinones don ft reduce the base metal ions. And, the redox potential greatly changes by pH of the solution. Half cell reaction formula of the quinone is shown in following formula.

The Relationship of Redox Potential between Metals and Quinone

Half cell reaction formula of the quinone

From Nernst's equation, redox potential E is shown as E =

+ (RT/2F) ln(H+) =

0.0295*pH (

is the standard oxidation-reduction potential).
    The potential lowers, when pH rises.
    Therefore, it is possible to control the potential of the quinones for the desirable value by the control of pH.
    KAWASAKI KASEI CHEMICALS LTD. has developed Metal Control (MC

), a recovery compound for precious metals which is composed of a unique quinone, and realized the system of precious metal recovery.

3.Papermaking and quinone compounds

    Papermaking is very important manufacture, because paper is indispensable for human life. On the other hand papermaking industry consumes large forest resources.     And paper demand is increasing at developing countries year by year. This demand promotes tree-planting projects for stable supply of forest resources. The continuous resources recycling by tree planting enables us to protect the environment from big problems such as the Earth warming.
    Quinone compounds are used by pulp and paper industries worldwide as cooking additives. There are two types of quinones, anthraquinone(AQ) and SAQ. SAQ is a trade name of KAWASAKI KASEI CHEMICALS LTD's product. One of the characteristics of these quinone compounds is that the chemical structure carries out reversible "Redox Reaction". This means that these can work as redox catalyst when these are added to the appropriate cooking reaction in the digester.
    The effects of this "Redox Reaction" starting from quinone compounds are stabilization of carbohydrates by oxidation of terminal aldehyde groups of cellulose and hemicellulose and acceleration of delignification through cleavage of ß-phenylether bond of lignin.
    Above mentioned effects provide cooking process with many advantages as increase of pulp yield by stabilization of carbohydrates and improvement of pulp quality by milder cooking conditions, such as lower cooking temperature, shortening the cooking time or saving of active alkali, by acceleration of delignification. And accelerating the rate of delignification makes it possible to lower sulfidity for overcoming of the odor problem and produce the pulp of lower Kappa number for lowering of bleaching load.
In Japan, SAQ is used in many pulp mills. The reason is that SAQ is alkaline aqueous solution of disodium salt of DDA (1,4-dihydro-9,10-dihydroxyanthracene). Therefore SAQ can be mixed with cooking liquor immediately and can penetrate into wood chip easily.     On the other hand, AQ is solid. It must be crushed into fine powder and be dispersed in cooking liquor. This difference of two types of quinones causes effect difference as cooking additive. SAQ is superior to AQ.
    Pulp and paper industry of Japan had obtained advantages, such as chip saving, pulp yield improvement and resolving of bottlenecks of digester, caustification, kiln and recovery boiler, by using the functions of SAQ skillfully.

Figure of the quinone effect