My Family in Myself

Keluarga adalah tempat dimana aku bisa berbagi tawa

Keluarga adalah tempatku melepaskan air mata

Dan keluarga juga tempatku belajar segalanya

Walau dalam hidup sederhana

Walau hidup terkadang seadanya

Tapi keluarga membuat hidupku istimewa

Satu cita-cita

Walau berat mencapainya

Ingin kubuat mereka bahagia

Baca Selengkapnya - My Family in Myself

History of Bleaching

The first bleaching agent was probably sunlight. The yellow color of textile was removed by fading in the sun. The word bleach comes from the Anglo-Saxon word blaechan. The meaning of this word is "to fade". The first known commercial bleaching was carried out in The Netherlands in the seventeenth century. The Dutch received linen from surrounding countries and bleach it on the grassy meadow in the summer. The climate in The Netherlands was considered to be especially suited for this bleaching. Until World War II bleaching of linen on the snow in the spring was common practice in Scandinavia. This bleaching method would probably not have seen very useful for the bleaching of wood pulp because sunlight contains considerable ultraviolet radiation.

At the end of the eighteenth century chlorine and hypochlorite  became available and the commercial sun bleaching of textiles was soon replaced by bleaching with hypochlorite. Calcium hypochlorite, called bleaching powder, became the most useful bleaching compound because it could be prepared and transported as a powder. For a long time calcium hypochlorite was the only bleaching agent for rag and other fibers use for papermaking. The next change in bleaching came about 1930 when elementary chlorine was commercially applied as a bleaching agent for pulp. Multistage of sulfite pulp, using chlorination, alkaline extraction, and hypochlorite expanded rapidly. The bleaching of kraft pulp by this method came after it was discovered that hot alkali extraction dissolved the products formed by chlorination and that several bleaching stages would bleach kraft pulp to a high brightness.The effectiveness of chlorine as an agent for lignin-removal in pulp had been known for a long time, but there had been no suitable equipment for carrying out the chlorination process on an industrial scale. The breakthrough of chlorination came with development of stainless steel , which could resist the attack chlorine. The next major advance in pulp bleaching, the introduction of chlorine dioxide, was also closely connected with development of more corrosion-resistant. construction materials. Chlorine dioxide had been known as bleaching agent for pulp from about 1920, but the first commercial application was not until 1946. Besides the problem with equipment materials there also were problems arising from the fact the chlorine dioxide is highly toxic and explosive when the concentration in the gas phase exceeds 15%.

Bisulfite was used in the nineteenth century for the brightening of mechanical pulp. Dithionite (hydrosulfite) was introduced later for the brightening of mechanical pulp and also to give a slight brightening to kraft pulp. Peroxide, as sodium peroxide or hydrogen peroxide, was introduced as a bleaching agent for pulp about 1940.

Oxygen has been will known for many years as a strong oxidizing agent. Separation of oxygen from air is also relatively cheap is large-scale plant. It was logical, therefore, that oxygen should be tried as a pulping and bleaching agent , but the first really promising result with oxygen bleaching were not obtained until about 1955. The first commercial installation for oxygen bleaching was made in 1970, and there are significant number of other plants in operation or under construction.

Bleaching of pulp is in a changing state. The effluents from bleaching plants are among the most troublesome ones in the pulp and paper industry and nobody can at the present time predict what the final solution will be. There is general arrangement that we should see great changes in the next decade. New bleaching agents will probably be introduced. Ozone appears to be on the threshold of industrial application and chlorine monoxide is a potential bleaching agent. New methods for the application of the conventional bleaching agents are being introduce and even newer methods can be expected in the future.


(Source: Casey, J.P., (1980). Pulp and Paper Chemistry and Chemical Technology)

Baca Selengkapnya - History of Bleaching

Is Washing Necessary in Bleaching?

The purpose of washing between the bleaching stages is explained in previous post, but is it really necessary? Its necessity can be demonstrated by examining what happens if the impurities are present in the next bleaching stage. Nivelon et al (1996) showed that the consumption of bleaching chemicals in ECF and TCF bleaching was 20-50% higher when there was a carry-over of organic substances. Fiskari et al (1999) also noted that bleach plant closure and inefficient washing resulted in a dramatic increase in the consumption of bleaching chemicals.

The first two bleaching stages are the most important ones, because they remove most of the lignin and inorganic material from the pulp (Dence & Reeve 1996). Therefore, efficient washing in the first two washers provides good chemical and economically profitable conditions for bleaching. Inefficient washing increases the consumption of bleaching chemicals in the following stage and reduces pulp brightness.

Furthermore, the importance of washing depends on the bleaching chemical applied in the next bleaching stage. Pulp washing between the ozone and chlorine dioxide stages is not necessary and it is possible to reduce the need for chlorine dioxide in the AD stage by means of acid treatment without interstage washing (Henricson 1997, Chirat & Lachenal 1997, Fuhrmann et al 1998, Pikka & Vehmaa 2002). An ozone stage, on the other hand, can be quite sensitive to impurities as Vuorinen et al (1997) have proved. For example, filtrate from the A-stage is very detrimental in the subsequent ozone stage and washing is beneficial between the A and ozone stages. Since ozone reacts very sensitively with dissolved organic solid (Lindholm & Malkov 1997), only a low carry-over of these solids can be tolerated in bleaching sequences that employ this chemical. This leads to an increased demand for efficient washing before the ozone stage.

Beside transition metals, reduced sugars have also been observed to retard peroxide bleaching and accelerate the catalytic decomposition of hydrogen peroxide, so their removal requires good washing (Heikkila et al 2000). On mill scale, it has been observed that the bleaching efficiency of the peroxide stage is reduce due to reactions with circulated dissolved material (Fuhrmann et al 2000).

After the final D-stage, washing is essential to minimise the carry-over of corrosive material into the pulp dryer or paper machine and to minimise the brightness reversion of the pulp in storage towers.

(Source: Silanpaa, Mervi (2005). Studies on Washing in Kraft Pulp Bleaching. Finland: Oulu University Press)

Baca Selengkapnya - Is Washing Necessary in Bleaching?

Brownstock Washing and Washing in Bleaching. What's the Difference?

Washing during kraft pulping can be divided in two separate areas each with this own distinct features, namely brownstock washing and washing in bleaching. The main purposes of brownstock washing are to remove dissolved organic and inorganic substances that would contaminate the pulp during subsequent steps in the process and to recover the maximum amount of spent chemicals with the minimum dilution. Efficient washing improves the recovery of spent chemical, reduces the consumption of reagents in the subsequent bleaching, and essentially limits effluent load from the plant.

The aim of washing in bleaching is to remove both dissolved organic and inorganic matter, which will disturb the subsequent bleaching stage and enhance the consumption of bleaching reagent. As the optimum chemical conditions in successive bleaching stages vary, one very important purpose of washing is to render the conditions more suitable for the next bleaching stage. This may include modifying the pH, the metal content of the pulp and the temperature. Thus, an additional aim of washing is also to serve as chemical conditioning and a heat exchanger during the purification procedure.

During the past decade, environmental concern have created new pressures to reduce effluent loading from kraft pulp bleaching. Pulp mills also have intrinsic needs to cut down their use of water and reduce effluent. Efficient and rational water use to provides improve heat balance and chemical recovery. Intrinsic and extrinsic demands have forced both pulp mills and the related engineering industries to develop and optimise pulping process equipment to meet these demands. Improve pulp washers and washing system connected with the introduction of oxygen-based reagents have in particular provided considerably improved tools for the reuse of process water and have thereby essentially reduced effluent discharge or even allowed the implementation of a closed water circulation system in kraft pulp bleaching.

This ongoing trend has placed increasing requirements on pulp washing particularly in the interstage washing in bleaching. Less fresh water is used for pulp washing, but at the same time the quality and cleanliness of the pulp should remain high. The more closed the water re-circulation system is, the dirtier the wash water will be during bleaching, probably resulting in an increased reagent consumption and poorer pulp quality. Since more expensive bleaching chemicals are use and the loss of bleaching chemicals is not acceptable, more specific washing is needed.

(Source: Silanpaa, Mervi (2005). Studies on Washing in Kraft Pulp Bleaching. Finland: Oulu University Press)

Baca Selengkapnya - Brownstock Washing and Washing in Bleaching. What's the Difference?