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© 2013 Published by Center for Pulp and Paper through REPTech2012
As the study results of chemicals that effectively remove HexA, we have discovered that
“peroxymonosulfuric acid” can most effectively remove HexA. Peroxymonosulfuric acid shortened
as MPS is manufactured by the reaction between high-concentration hydrogen peroxide and high-
concentration sulfuric acid. Because this reaction is highly exothermic, it is necessary to control the reaction
temperature to manufacture peroxymonosulfuric acid at high yield. Various manufacturing methods
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that are suitable to manufacture small amount of it were proposed. However, they are not suitable
to manufacture a large amount that is applicable to pulp bleaching. We overcame these dificulties
and have completed the irst industrial-scale on-site production equipment
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of peroxymonosulfuric acid in the world. We also studied the pulp bleaching using
the peroxymonosulfuric acid and found out that 1 it is effective as a countermeasure to discoloration
and 2 it is possible to reduce the bleaching cost.
Accordingly, we applied this peroxymonosulfuric acid to the Tomioka Mill of Oji Paper Company, attained
the successes in discoloration countermeasure and cost reduction, and have put the irst bleaching process
using peroxymonosulfuric acid into practical use in the world
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. This process is being operated at four mills and is planned to be started operation further in
two mills near future. In this paper, we are introducing the on-site
production of peroxymonosulfuric acid and its application to pulp bleaching.
2. Discoloration Problems of ECF Pulp
Table 1 shows the discoloration results of ECF pulp by acid papermaking. In the case of conversion to
ECF bleaching mainly by chlorine dioxide, the method where hydrogen peroxide is added to the alkaline
extraction stage E, Eo is generally executed to reduce the cost. As a result, a new problem of deterioration of
pulp discoloration by the decline of chlorine dioxide consumption, which has the capability of removing
impurities like lignin, has become clear.
Table 1 Discoloration of ECF Bleached Pulp
Color Reversion
Bleach Sequence add.
Brightness Brightness
D:ClO
2
, p: H
2
O
2
Before C.R. After C.R.
Extensi D0.5-Eop0.3-
D0.3 86.4
67.6 Minor
D0.9-Eo-D0.3 87.2
81.8
Acceleration Test Condition : 80°C, 65 RH, 24h It is said that residual lignin, residual HexA, and
sugars are related to the factors affecting the pulp discoloration. HexA is formed by alkaline conversion
of glucuronic acid, which is bonded to xylan, during cooking. Fig. 1 shows the structure. We noted
HexA and studied the relations among the HexA
quantity, discoloration PC value, and papermaking conditions. Fig. 2 shows the results. HexA quantity
and discoloration have proportional relations. Also, when comparing the discoloration at the same
HexA usage, acid paper and alkaline paper show different degree of discoloration, where acid paper is
especially problematic. We suppose that the causes are the decomposition products formed while being
unattended in the acid state and the aluminum of aluminum sulfate used in acid paper.
Accordingly, removing HexA is proved to be important as a countermeasure to the discoloration of
acid paper.
Fig. 1 Structure of Hexenuronic Acid
Fig. 2 Inluence of Amount of Hexenuronic Acid on PC Value
3. Comparison of Hexenuronic Acid Removal Abilities of Various Chemicals
As the results of the above studies, it has become clear that one of the causes of discoloration of ECF
bleached pulp is HexA. Therefore, we compared the various chemicals and methods having HexA
removing ability. Table 2 shows the results.
Chlorine dioxide, hypochlorites, and ozone, which have been long used in pulp bleaching, showed
good HexA removal eficiency. Activated hydrogen peroxide and peracetic acid are effective HexA
removal agents but the problems are their high cost. Acidic hydrogen peroxide and nitrous acid are cheap in
cost but their HexA removal eficiency is low. Acidic persulfate showed HexA removal ability but alkaline
persulfate showed almost no HexA removal ability.
ISBN : 978-602-17761-0-0
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© 2013 Published by Center for Pulp and Paper through REPTech2012
On the other hand, Oxone showed effective HexA removal ability on a par with ozone. However, Oxone
is expensive and contains low percentage of oxygen in the molecule. Therefore, it is dificult to make it into
practical use as it is. Accordingly, we have decided to use peroxymonosulfuric acid synthesized from
sulfuric acid and hydrogen peroxide.
Fig. 3 Relationship between Peroxymonosulfuric Acid Addition Rate and Hexenuronic Removal
Quantity Figure 3 shows the relations between
peroxymonosulfuric acid addition rate and HexA removal quantity. The peroxymonosulfuric acid addition
rate and HexA removal quantity showed an almost linear relationship; where 0.5 of peroxymonosulfuric
acid could have removed about 10 μmolg-pulp of HexA and 1.0 could have removed about 16 μmolg-pulp
respectively. Also, although peroxymonosulfuric acid can be effective not only in HexA removal but also in
lignin removal, it was more effective in HexA removal.
4. On-site Production of Peroxymonosulfuric Acid
