Biorefining: the role of endoglucanases in refining of cellulose fibers

With an annual production of more than 400 million tons, paper is the main product of the largest biorefinery process industrially implemented. Enzymes have been used for pulp refining to dramatically reduce energy consumption. However, exact mechanisms related to the individual enzymes are hardly understood. Yet, this knowledge would be important to predict enzyme performance in industrial processes. Three commercial refining enzyme formulations showed different endoglucanase (1.25 nkat mg−1–13.7 nkat mg−1), β-glucosidase (0.57 nkat mg−1–1.34 nkat mg−1) and xylanase activities (1.78 nkat ml−1–62.1 nkat mg−1) on model substrates. Additionally, distinct amounts of reducing sugars from hardwood sulfate pulp were released. Endoglucases were purified from each formulation by using hydrophobic interaction and anion exchange chromatography and showed molecular weights from 20 to 55 kDa and specific activities ranging between 3.11 and 26.3 nkat mg−1 according to endoglucanase specific derivatized cellopentaose (CellG5). Refining trials of hardwood sulfate pulp were conducted using a PFI laboratory mill and fiber properties such as degree of refining or fiber length and properties of formed sheets like tensile index were monitored. Thereby, enzymes were dosed based on identical endoglucanase activity on CellG5. Enzyme formulations and purified endoglucanases led to an increase of the degree of refining of up to 47.9 [°SR] at 6000 PFI revolutions while the tensile index was improved by up to 76.0 Nm g−1. In summary, refining effects can be primarily attributed to endoglucanases indicating activity on CellG5 being a suitable parameter for enzyme dosing.

Identification of comparability indicators of the pulp mill discharged treated effluents quality with the technological parameters of the production nature intensity

В соответствии с изменением природоохранного законодательства проблема минимизации природоёмкости сульфат-целлюлозного производства, влияющего на экосистему озера, неразрывно связана с изучением вопроса трансформации и превращения загрязняющих веществ в воде с учетом гидрологических характеристик водоема. Природоёмкость целлюлозного производства определяется следующими показателями: количество и качество используемого сырья – древесина, щепа, химические реагенты, вода; технологический процесс производства целлюлозы, бумаги, картона, побочных продуктов – скипидар, талловое масло; эффективность систем очистки сбросов и выбросов предприятия, а также применяемые природоохранные технологии по их управлению. Решались задачи снижения негативного воздействия сульфат-целлюлозного производства на водную экосистему. Совместно с лабораторией отдела охраны окружающей среды целлюлозного завода в летне-осенний период 2020 г. проведен ряд лабораторных исследований сточных вод разной степени очистки после варки разных марок целлюлозы с целью изменения показателей экологичности состава сточных вод ЦБП по критериям региональной экологической техноёмкости. Реализована модель исследования трансформации загрязняющих веществ очищенных и неочищенных сточных вод сульфат-целлюлозного производства при различных разбавлениях природной водой. Представлены целевые и репрезентативные показатели щелокосодержащих сточных вод с учетом наилучших доступных технологий (НДТ) в области производства целлюлозы. Проведены исследования параметров кинетики биохимического окисления при пяти кратностях разбавления водой, имитирующих зону начального и основного разбавления. Произведено соизмерение определяющих технологических характеристик производственно-территориального комплекса в рамках решения задачи эколого-технологического нормирования. In accordance with the changes in environmental legislation the issue of minimizing the nature intensity of sulfate-pulp production, which affects the ecosystem of the lake, is inextricably linked with the study of the transformation and transformation of pollutants in the water, taking into account the hydrological characteristics of the reservoir. The natural intensity of pulp production is determined by the quantity and quality of the raw materials used – wood, wood chips, chemical reagents, water; the technological process of production of pulp, paper, cardboard, as well as by-products such as turpentine, tallow oil and efficiency and applied environmental technologies for the management of discharges, emissions and waste of production and consumption. The tasks of reducing the negative impact of sulfatecellulose production on the aquatic ecosystem were solved. Together with the laboratory of the environmental protection department of the pulp mill, a number of laboratory studies of treated and untreated waste water after cooking of different grades of pulp were carried out in the summer-autumn period of 2020 in order to implement the procedure for rationing waste water of the pulp and paper mill according to the criteria of regional environmental technology intensity. A model is presented for studying the transformation of pollutants in treated and untreated wastewater from sulfate-pulp production at various dilutions with natural water. Target and representative indicators of alkaline-containing wastewater are presented, taking into account the best available technologies (BAT) in the field of pulp production. The parameters of the biochemical oxidation kinetics were studied at five water dilution multiplicities simulating the initial and main dilution zones. The main characteristics of the production and territorial complex were measured within the framework of the tasks of environmental rationing.

Minimizing the Chlorine Content in Bleached Sulfate Pulp for Sanitary Tissue products and Food Packaging

The increasing consumption of pulp for chemical processing, including production of sanitary tissue products and other medical products, food packaging, as well as fillers for food products leads to new requirements for the quality of raw materials. The task of improving the characteristics of pulp has become particularly acute in connection with the COVID-19 epidemic: the demand for disposable nonwoven materials in direct contact with the human skin has increased several times over. The elemental chlorine free (ECF) sulfate pulp bleaching process, which uses chlorine dioxide as a bleaching agent, dominates bleached pulp production worldwide. The chlorine-containing compounds formed as a result of bleaching pollute not only waste water, but also the product itself. In the near future, it is expected that paper products made with chlorine-based bleaches may be banned for the production of sanitary tissue products and food packaging. If the products of the pulp and paper industry do not meet international consumer requirements, the pulp market for these purposes may face undesirable results. The most promising direction of modernization the existing bleaching schemes, both in terms of the process consumption parameters and the quality of the produced pulp, is the use of oxygen-alkaline bleaching in the first stage. Determination of total and organically bound chlorine content in pulp materials in accordance with ISO 11480:2017 on the advanced plant has shown, that the introduction of bleaching schemes using oxygen-alkaline agents will ensure the recommended content of chlorine compounds while maintaining the necessary characteristics of pulp for the manufacture of medical and sanitary tissue products, food packaging. However, high quality of finished products that meet consumers’ requirements is possible only if the chlorine content is controlled at all stages of pulp production, since the quantitative indicators of this substance content remain close to the upper allowable limit. For citation: sofronova e.D., Lipin v.A., Dubovy v.K., Sustavova t.A. Minimizing the Chlorine Content in bleached sulfate pulp for sanitary tissue products and food packaging. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 3, pp. 186–195. DOI: 10.37482/0536-1036-2021-3-186-195

TOTAL CHLORINE-FREE BLEACHING OF SULFATE HARDWOOD PULP WITH HYDROGEN PEROXIDE

The work is devoted to the study of the possibility and feasibility of environmentally safe bleaching of sulfate hardwood pulp by TCF-technology without the use of traditional oxygen and ozone as a delignifying reagent. The TCF-technology of sulphate hardwood pulp bleaching (scheme Pa-EP-Pd-Aac-P-A) was developed with only one oxidizing reagent – hydrogen peroxide. It is proposed to carry out of pulp delignification with hydrogen peroxide in an acid medium conditions, additional delignification and bleaching – with hydrogen peroxide in an alkaline medium conditions. Soft oxidizing effect of hydrogen peroxide used at all stages of bleaching provides selectivity of the process along with ecological compatibility of the scheme. The mechanical strength of pulp varies during bleaching in accordance with the change of the degree of delignification and is very moderate, and the total loss of pulp fibers is only 6.1%. Production of hardwood sulfate pulp, as well as sulfite, is associated with difficulties caused by a "harmful" resin at a small proportion of extractives. The proposed scheme of bleaching provides a high degree of resin removal and contributes to the depitching, i.e. decision of very important problems in sulphate hardwood pulp production.

Absorption of H2S with sodium hydroxide from the black liquid of sulfate pulp production

При обработке черного щелока сульфат-целлюлозного производства серной кислотой (с целью частичного или полного высаждения сульфатного лигнина) происходит выделение сероводорода и других серосодержащих газов. Рассмотрен процесс поглощения этих газов путем абсорбции водным раствором гидроксида натрия. Процесс подкисления черного щелока серной кислотой сопровождается выделением сероводорода, который должен подвергаться абсорбции. Промышленные методы получения сульфатного лигнина предусматривают применение абсорбции сероводорода водными растворами гидроксида натрия. В качестве абсорбентов при поглощении серосодержащих газов применяют растворы щелочи или воду в зависимости от состава сероводородных газов и дальнейшего использования продуктов абсорбции. Водные растворы гидроксида натрия применяются для абсорбции в тех случаях, когда обработке подвергаются значительные объемы газов, содержащих преимущественно сероводород. При этом в процессе абсорбции получается раствор сульфида натрия. В случае подкисления черного щелока серной кислотой абсорбции подвергается сероводород, который содержит и другие примеси. Для того чтобы абсорбция сероводорода гидроксидом натрия прошла с образованием конечного продукта сульфида натрия, необходимо использовать определенную концентрацию щелочи. Для достижения необходимого результата использовался симплекс-метод по целочисленной матрице, который позволил выбрать оптимальные параметры проведения процесса абсорбции сероводорода гидроксидом натрия. В результате получен раствор белого щелока с высокой сульфидностью, что является положительной характеристикой процесса варки сульфатной целлюлозы, так как уменьшает продолжительность варки до определенной степени провара, облегчает процесс делигнификации, а также увеличивает выход целлюлозы. Это позволяет уменьшить расход реагентов при приготовлении белого щелока, подаваемого на варку технологической щепы. По предложенному методу осаждение лигноуглеводного комплекса из черного щелока проводят без применения содорегенерационных котлов, где процесс получения белого щелока связан с получением плава щелочей и последующим получением из него зеленого щелока, с дальнейшей регенерацией белого щелока, используемого для варки сульфатной целлюлозы. В результате установлена принципиальная возможность абсорбции сероводорода раствором гидроксида с выполнением требований, предъявляемых к белому щелоку. While black liquor from sulfate pulp process treatment with sulfuric acid (for partial or full sulfate lignin precipitation) emission of hydrosulfide and other sulfur containing gasses happens. It is reviewed process of the gasses absorption by sodium hydroxide solution. The process of acidification of black liquor with sulfuric acid is accompanied by the release of hydrogen sulfide, which must undergo absorption. Industrial methods for producing sulphate lignin involve the use of hydrogen sulfide absorption by aqueous solutions of sodium hydroxide. Alkali solutions or water are used as absorbents for absorption of sulfur-containing gases, depending on the composition of hydrogen sulfide gases and the further use of absorption products. Aqueous solutions of sodium hydroxide are used for absorption in cases where significant volumes of gases containing predominantly hydrogen sulfide are processed. In the process of absorption is obtained a solution of sodium sulfide. In the case of acidification of black liquor with sulfuric acid, hydrogen sulfide is subjected to absorption, which contains other impurities. In order for the absorption of hydrogen sulfide by sodium hydroxide to form the final product of sodium sulfide, it is necessary to use a certain concentration of alkali. To achieve the required results, a simplex method was used for the integer matrix, which allows choosing the optimal parameters for the process of hydrogen sulfide absorption by sodium hydroxide. As a result of the experiment, a solution of white liquor with high sulfidity is obtained. which is a positive characteristic of the sulphate pulp boiling process, as it reduces the cooking time to a certain degree of penetration, facilitates the delignification process, and also increases the cellulose yield. This allows reducing the consumption of reagents in the preparation of white liquor fed to the cooking chips. According to the proposed method, the precipitation of the black liquor lignohydrocarbon complex is carried out without the use of soda recovery boilers, where the process of obtaining white liquor is associated with obtaining alkaline water and subsequent production of green liquor from it, with further regeneration of white liquor used for cooking sulphate pulp. As a result of the experiment, the principal possibility of hydrogen sulfide absorption by a hydroxide solution was established with the fulfillment of the requirements for white liquor.

Биоповреждение бумаги микромицетами в условиях эксперимента: исследование методами колебательной спектроскопии

Damage to paper (sulfate pulp, cotton half-stuff, and flax half-stuff) caused by the Aspergillus niger , A. sclerotiorum , and Penicillium chrysogenum fungi is investigated by Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. It is shown that the use of application infrared Fourier-transform absorption spectroscopy allows one to identify the initial stages of damage from a decrease in the degree of crystallinity of the cellulose contained in paper. The absorption band near 900 cm^–1 is used as an indicator of early stages of damage. An increase in the amide II peak at 1550 cm^–1 and spectral changes in the region of valence vibrations of the C–H bonds (2800–3000 cm^–1) are observed in the case of heavier damage. The obtained data indicate that the vibrational spectroscopy techniques are promising in the study of damage of archive documents.