Assessment of Q(OP)D(PO) bleachability of softwood kraft pulp

Bleachability is evaluated as how easily a pulp sample is bleached and it depends on the structure of residual lignin and carbohydrates. Also, the bleachability varies depending on the bleaching sequence. ECF light sequences have been improved significantly in the recent years. However, we still don’t fully understand how ECF light bleach plants are optimally run. This work studies the bleachability of softwood kraft pulp in an ECF light bleaching sequence, (OO)Q(OP)D(PO). Three pulp samples with brown stock kappa number 27, 32 and 35 were bleached and studied for residual lignin, hexenuronic acid and carbohydrate content. It was found that in the bleaching stages that are highly delignifying, it is beneficial with a higher kappa number for the delignifying bleachability. However, in the bleaching stages where the objective is brightness increase, the brightness gain bleachability is improved by a lower kappa number. We also intended to determine which of the three samples had the best suited kappa number for this particular bleaching sequence. According to our results, the bleaching was most effective with kappa number around 32. Although an even higher kappa number resulted in higher yield after cooking, it seemed that this bleaching sequence cannot preserve the yield gain.

Pre-bleaching of kraft acacia pulp

Kraft pulps from acacia hybrid, Acacia mangium of 8 years old and Acacia auriculiformis of 6, 8 and 10 years old were pre-treated with oxygen, peroxyformic acid and acid treatment prior to bleaching. The kappa number reduction was 52–63 % by oxygen delignification, 31–35 % by peroxyformic acid (PFA) pre-treatment and 11–13 % by acid pre-treatment. Oxygen delignified pulp required less chlorine dioxide charge to reach target brightness. At the consumption of 30 kg ClO2/ton of pulp, the pulp brightness reached to 65–71 % for the untreated pulp, 81–85 % for the oxygen delignified pulp, 81–82 % for the PFA treatment and 79–80 % for acid pre-treated pulp. COD load in bleached effluent was much lower in oxygen delignified pulp. Cold alkali extraction of unbleached and oxygen delignified pulps was also carried out with varying alkali charge to remove hexenuronic acid (HexA) from the pulp. Xylan removal from the pulp was insignificant and resulted in no removal of HexA. Acid pretreatment removed 55.7 % to 17.8 % HexA from acacia hybrid, 57.5 % to 16.3 % from A. auriculiformis of 10 years and 58.6 % to 20.1 % from A. auriculiformis of 6 years old, resulting in improved final pulp brightness.

Kandungan Hexenuronic Acid pada Pulp serta Pengaruhnya terhadap Kualitas Pulp dan Air Limbah: Tinjauan

Proses pemasakan kayu dengan cara alkali aktif akan menghasilkan hexenuronic acid (HexA) yang berasal dari grup glucuronoxylan, tepatnya 4-O-methylglucuronoxylan pada hemiselulosa. Proses hidrolisis HexA menghasilkan dua jenis senyawa furan, yaitu 2-furancarboxylic acid (FA) dan 5-formyl-2-furancarboxylic acid (FFA). Proses hidrolisis HexA hasil proses pemasakan dan terkandung dalam pulp dan kertas merupakan salah satu penyebab proses penguningan pada kertas akibat adanya paparan kelembapan dan panas dari lingkungan. Selain itu, kandungan HexA pada pulp juga dapat meningkatkan konsumsi bahan kimia pada proses produksi pulp dan kertas, terutama pada proses pemutihan dan pengujian parameter bilangan Kappa, serta dapat berkontribusi pada kandungan senyawa organik klorin terlarut dalam air limbah industri pulp dan kertas. Metode untuk menurunkan kandungan HexA dari pulp dan kertas antara lain dengan mengaplikasikan proses oksidatif kimia pada proses pemutihan atau dengan menggunakan proses enzimatis. Kandungan HexA yang rendah, akan dapat mempertahankan pulp dan kertas dari terjadinya proses penguningan, menghemat konsumsi bahan kimia serta menurunkan kandungan adsorbable organic halides (AOX) pada air limbah.Kata kunci: hexenuronic acid, pemasakan kayu, bilangan Kappa, AOX, enzimatis Hexenuronic Acid Content on Pulp and its Effects on Pulp Quality and Wastewater: a ReviewAbstractThe wood active alkali cooking process will produce hexenuronic acid (HexA) originating from 4-O-methylglucuronoxylan of the glucuronoxylan group in hemicellulose. Hydrolysis process of HexA produces two types of furan compounds, namely 2-furancarboxylic acid (FA) and 5-formyl-2-furancarboxylic acid (FFA). The HexA hydrolysis process contained in pulp and paper resulting from the cooking process is one of the causes of the yellowing process on paper due to exposure to moisture and heat from the environment. In addition, the HexA content of pulp can also increase the consumption of chemicals in the pulp and paper production process, especially in the bleaching process and testing of Kappa number parameters, and can also contribute to the content of organic chlorine soluble compounds in the waste water of the pulp and paper industry. There are several methods for reducing the HexA content of pulp and paper including by applying the oxidative chemical process to the bleaching process or by using an enzymatic process. Low HexA content, will be able to maintain pulp and paper from the occurrence of the pulp yellowing process, save on chemical consumption and reduce the adsorbable organic halides (AOX) content in wastewater.Keywords: hexenuronic acid, wood cooking, Kappa number, AOX, enzymatic

Does the kappa number method accurately reflect lignin content in nonwood pulps?

The traditional kappa number method was developed in 1960 as a way to more quickly determine the level of lignin remaining in a completed or in-progress pulp. A significantly faster approach than the Klason lignin procedure, the kappa number method is based on the reaction of a strong oxidizing agent (KMnO4) with lignin and small amounts of other organic functional groups present in the pulp, such as hexenuronic acid. While the usefulness of the kappa number for providing information about bleaching requirements and pulp properties has arguably transformed the pulp and paper industry, it has been mostly developed for kraft, sulfite, and soda wood pulps. Nonwood species have a different chemical makeup than hardwood or softwood sources. These chemical differ-ences can influence kappa and Klason measurements on the pulp and lead to wide ranges of error. Both original data from Sustainable Fiber Technologies’ sulfur and chlorine-free pulping process and kappa and Klason data from various nonwood pulp literature sources will be presented to challenge the assumption that the kappa number accurately represents lignin content in nonwood pulps.

Effects of lignin chemistry on oxygen delignification performance

The present work focused on characterizing the chemical and structural properties of isolated lignin from six hardwoods and their kraft pulps in an attempt to better understand the relationship between lignin’s chemical properties and resultant oxygen delignification performance. Several hardwood samples were cooked under the same conditions with varying alkali charges to obtain unbleached pulps with kappa numbers between 19 and 20. These pulps were then subjected to an oxygen delignification stage. Both processes were evaluated for pulp quality, residual lignin, and O-stage delignification efficiency. The oxygen delignification stage was carried out under fixed conditions and evaluated with regards to kappa number, which was corrected for hexenuronic acid (HexA) contributions.Results revealed that different hardwood species exhibited differing oxygen delignification efficiencies. A high correlation was found between the O-stage delignification efficiency and the content of phenolic groups in the unbleached lignin, which confirmed that free phenolic groups are the reactive site for molecular oxygen attack. When different hardwood species were compared, the HexA contents were not found to affect O-stage delignification efficiencies.

Enzymatic delignification and hexenuronic acid removal in cellulosic papermaking pulp using a haloperoxidase

A novel approach for lignin and hexenuronic acid removal from cellulosic pulp based on the combination of a vanadium haloperoxidase and a tertiary amine co-catalyst.