What are the steps in the pulp production process?

The Brazilian pulp and paper industry is the largest producer of hardwood pulp in the world. This is because the Brazilian climate favors the planting of eucalyptus, which is the raw material for this type of pulp. This product is one of the most exported in the country, contributing to the Brazilian economy on a large scale.

On the other hand, other producing countries stand out for the production of softwood pulp, as their climates favor the planting of pine, used to manufacture this type of product.

Since 2012, Brazil has been investing in the pulp and paper industry, and according to data from the Comexstat website, in the first half of 2019, exports by the pulp and paper industry reached US$ 5.6 billion. A highlight is that China alone purchased US$ 3.3 billion in products of the sector in 2019.

In 2020, even with the Covid-19 pandemic situation, the IBÁ (Indústria Brasileira de Árvores, translated into Brazilian Industry of Trees) announced that Brazil had a 6.4% increase in pulp production, reaching 21 million tons manufactured.

Unlike 2019, in 2020 there was a reduction in the volume of pulp purchased by China. The Asian country spent US$ 2.9 billion, 11.7% less than in the previous year.

Domestic market x Export

In Brazil, although much of the paper production is self-sufficient, newsprint needs to be imported. Thus, 70% of the newsprint used in the country is imported, and 80% of this volume comes from Canada.

This import is necessary because it is a type of paper made from softwood pulp, which is not abundant in Brazil.

According to data from IBÁ, in 2016 31% of the pulp production in Brazil was used in the domestic market, while 69% was destined for export. The production of paper, on the other hand, had 80% of the volume destined for the domestic market, therefore only 20% for the export of the product.

Also considering the source IBÁ, it was disclosed that in 2020 15.6 million tons of pulp were exported, a volume 6.1% higher than in 2019.

Products from the pulp and paper industry which are common in people’s routine

Cellulose is the raw material for the production of paper, used in people’s lives all the time. Often, people do not even know what types of paper they use in their daily lives, after all, everything ends up being considered a single material.

But in the pulp and paper industry, depending on the type of paper to be produced, it is necessary to submit the pulp to different treatments.

When the production is for writing paper, for example, the final product needs to be able to absorb ink from pen or pencil and be rough enough to do so.

On the other hand, the packages must have a certain rigidity and strength, according to its use.

In addition to these, other papers produced in the pulp and paper industry are sulfite, couché, newspaper, recycled, kraft, vegetable, photographic, supreme, among others.

Raw material preparation

In nature, trees are felled, delimbed, and logs are cut to be sent to industries. There, they are separated by size and then enter the production process.

Also in the debarking stage, materials that are not used such as bark, branches, and leaves are left in the wood extraction site to serve as organic matter.

The logs that arrive at the industries are then sent to the chipper, where they will be transformed into chips (small pieces of wood). On the other hand, logs that cannot be used in production are transferred to the energy generation area.

After the chips are standardized, storage takes place in silos, which will then be sent to the digesters.

Pulping

To produce paper, it is necessary to have cellulose pulp or cellulose paste. The pulping process takes place from mechanical, semi-chemical, and chemical processes.

In mechanical pulping, a wet press is used against a rotating roller of abrasive material. As a result, it is possible to achieve a yield of 90 to 95%, which is considered high. However, in this process, there is no complete separation of fibers from other components of the plant. And as there is no bleaching, in this case, this type of paper is used to make newspaper and magazines.

In the case of semi-chemical processes, there is the use of some chemical reagents. It is possible to use sulphite, carbonate or sodium hydroxide with a neutral pH level. With this, it is possible to dissolve lignin and carbohydrates, and fibers are separated more easily and without using as much energy as it happens in the mechanical process. Here the process yield is between 65 and 90%.

Finally, when it comes to chemical processes, there are a few options. Currently, the chemical process most used by the pulp and paper industry is called Kraft. This consists of combining sodium hydroxide and sodium sulfide to act on wood chips. The yield, in this case, is between 40 and 65%, and the bleaching process is facilitated.

Cooking and dissociation of lignin

The cooking step is when the lignin dissociates. It is also at this point that the chips give rise to a brown pulp (called unbleached pulp).

In order for this process to take place, the temperature of the digesters needs to be at 150 ºC. In addition, sodium sulfate and caustic soda are added, as it is from these elements that lignin dissolves and cellulose pulp has better quality. This process takes approximately 120 minutes.

Bleaching

This step serves to provide the cellulose with its natural color. For this, it is possible to carry out a chemical or enzymatic treatment. Sieves are used to remove impurities from pulp, making its properties more interesting for the industry.

In chemical treatment, some products are added: hydrogen peroxide, chlorine dioxide, oxygen, and sodium hydroxide. All to guarantee the desired properties for cellulose.

One factor that makes bleaching more difficult is the high concentration of lignin. Its presence gives a more yellowish color to the paper, as explained in the mechanical pulping process above.

Drying

Finally, drying ends the paper production process. In this final step, water is removed from the pulp and it is placed on the flat table, which is a machine that transforms the paper into a continuous, smooth sheet.

At this point, the objective is for the pulp to reach a balance of humidity with the relative humidity of the air. Thus, the pulp sheet passes through rollers for pressing and drying with hot air.

Finally, the cutter reduces the paper into smaller pieces that are distributed in bales, which will be used in the production of different types of paper.

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