WOOD RESEARCH Volume 68, Number 3, 2023
Boháček Štefan, Pažitný Andrej, and Slámová Stela

Optimisation of energy consumption in paper production. Review

This article examines the current state of research on energy efficiency in the paper industry, focusing on the key strategies, technologies, and best practices for improving energy efficiency and reducing greenhouse gas emissions. The review covers a range of topics, including energy management systems, process optimisation, cogeneration, waste heat recovery, and renewable energy sources. Overall, the energy efficiency improvements can significantly reduce energy costs and carbon emissions in the paper industry. Still, there is a need for more comprehensive and integrated approaches that consider the entire value chain of paper production.

WOOD RESEARCH Volume 67, Number 6, 2022
Boháček Štefan, Pažitný Andrej, and Michaela Handlovská

Intensification of the freeze-thaw pretreatment of disintegrated poplar wood

This research was focused on the effect of water content in the cells of disintegrated Populus nigra L. on a freeze-thaw pretreatment method before an enzymatic hydrolysis. Two chipped and sieved fractions 2.5 mm and 0.7 mm and two milled fractions, characterized as 18°SR (Shopper–Riegler index) and 37°SR, of the disintegrated 5 years old poplar tree were used for our experiment. Glucose and xylose yields were measured after 24 and 48 hours of enzymatic hydrolysis with a 15% load of the enzyme measured to a total cellulose content. The influence of nine freeze-thaw cycles under -20°C and +20°C was considered. The results showed that an increase in moisture content positively affects yields in all fractions but a desirable result was achieved mainly for the 0.7 mm fraction where the total yield increased by about 16%. More effective way is a finer wet beating of wood mass, while wood fibre receives moisture already in the technological process. The highest glucan conversion 51,74% and the total hemicelluloses conversion 47,72% was achieved for the finest fraction 37°SR. The higher moisture content has a positive effect on the increase in the conversion of oligosaccharides, especially glucan, in chipped fractions.

WOOD RESEARCH Volume 67, Number 2, 2022
Halaj Michal, Boháček Štefan, Pažitný Andrej, Monika Stankovská, and Albert Russ

Methods of preparation of nanofibrillated cellulose for special filter papers with effective air filtration. Short notes

Nanofibrillated cellulose was prepared from distillery refuse based on maize starch using the extraction with NaOH and HCl involving centrifugation. SEM images of bleached kraft pulp with/without the addition of nanofibrillated cellulose were compared. The results showed that the application of nanofibrillated cellulose caused a visible reduction in the surface porosity. Conversely, mixing of the pulp with the nanofibrillated cellulose resulted in large pores among the fibres. The effect of the cationic retention aid on porosity was not significant, observed in the fines retention. A minimal difference in porosity was found among of fine and coarse fibres. When lyophilisation as drying method was used it yielded nanofibrillated cellulose with a size in the range of approximately 100 to 150 nm.

WOOD RESEARCH Volume 62, Number 5, 2017
Balberčák Jozef, Boháček Štefan, Peter Medo, VLADIMÍR IHNÁT, and HENRICH LÜBKE

Chemical processing of waste wood based agglomerates Part I: Evaluation of properties of fluting liners made of semichemical pulp obtained by a mildly alkaline sulphur-free cooking process

The article describes the method of evaluation and preparation of fluting liners produced from semichemical pulp of waste wood particle boards (PB) and oriented strand boards (OSB) and after the combination with old corrugated cardboards (OCC) to improve strength properties. The semichemical pulp was obtained by a mildly alkaline boiling process from two fractions of waste PB and OSB. Properties as thickness, bulk density, gurley, tensile strength, tensile index, breaking length, burst index, CMT30 and SCT were monitored on lab sheets 127 g.m-2 and 170 g.m-2. Values of pH and residual NaOH and Na2CO3 were determined in batch leachate.

WOOD RESEARCH Volume 62, Number 2, 2017
Pažitný Andrej, Boháček Štefan, Peter Medo, Balberčák Jozef, Jiří Schwartz, Kuňa Vladimír, and VLADIMÍR IHNÁT

Possibilities of removing condensate from a heat recovery unit utilizable in paper industry

Methods, processes and equipments currently used for heat recovery systems are very diverse in different branches of industry including paper industry. A very important process applied in heat recovery units is condensate removal from the heat recovery units because of optimization of the heat recovery process and extending the working life of heat recovery units. Using of heat recovery units with condensate removal in paper industry fits the innovation trends and means heat energy saving that can be realized by increase of heat recovery efficiency. Heat recovery system with condensate removal should be installed near a drying cover of a paper machine due to reduction of heat loss and pipeline length. Integration of designed spiral heat recovery unit with condensate removal into the existing dryer section of paper machine in a paper mill will lead to decrease of heat consumption and increase heat recovery efficiency up to 91.7 %.

WOOD RESEARCH Volume 63, Number 6, 2018
Kuňa Vladimír, Balberčák Jozef, Pažitný Andrej, Albert Russ, Boháček Štefan, and VLADIMÍR IHNÁT

Tackiness reducing of the stickies surfaces by inorganic agents and organic polymers

This paper present the results of application of inorganic minerals and organic polymers for elimination of sticky impurities “macrostickies” in the processing of recovered paper. The impact of individual agents has been monitored on different species of suspensions. On the dark suspension of recycled fibres VL5 with a brightness 53% ISO and an ash content of 17.6%, and the suspension VL1 with a brightness 64% ISO and an ash content of 29.4%. From inorganic minerals, the highest efficiency was achieved in the elimination of macrostickies using bentonite Hydrocol OT. At a dose of 5 kg bentonite.t-1 b.d. recycled fibres efficiency of 65.1% for suspension VL5 and 58.7% for VL1 was achieved. The highest performance of the Acefloc 2550 was achieved from the polymers. When applied to the VL5 suspension, the macrostickies were reduced by 57.1%, and when applied to the VL1 suspension, the macrostickies content dropped by 56.5%.

WOOD RESEARCH Volume 63, Number 1, 2018
Balberčák Jozef, Boháček Štefan, Pažitný Andrej, VLADIMÍR IHNÁT, and HENRICH LÜBKE

Chemical processing of waste wood based agglomerates Part II: Evaluation of properties of fluting liners made of semichemical pulp obtained by an alkaline cooking process

The article describes the method of evaluation and preparation of fluting liners produced from semichemical pulp obtained from waste wood particle boards (PB) and oriented strand boards (OSB). The semichemical pulp was obtained using an alkaline cooking process from a sorted fraction of the 4-8 mm chips. Properties as thickness, bulk density, air resistance of paper sheet, tensile strength, tensile index, breaking length, burst index, CMT30 and SCT were monitored on lab sheets 127 g. m-2 and 170 g. m-2. Values of pH and residual NaOH were determined in the batch leachate.

WOOD RESEARCH Volume 66, Number 4, 2021
Halaj Michal, Boháček Štefan, Pažitný Andrej, Kuňa Vladimír, and Balberčák Jozef

Influence of ultra low and high temperature on enzymatic pretreatment of beech branches wood

The publication is focused on the effect of ultra low and high temperature on enzymatic pretreatment of beech wood (Fagus sylvatica L.). Two fractions < 0.7 mm and 1.0 – 2.5 mm of disintegrated branches sawdust were used for experiments. Glucose and xylose yields were measured after 24, 48, and 72 hours of enzymatic hydrolysis with 15 % load of the enzyme measured to total cellulose content. The influence of freezing under -80°C and boiling under pressure at +160°C on samples before enzymatic hydrolysis was observed. Mutual combination of boiling under pressure to obtain the maximum water uptake and subsequent freezing was used to better understand the process of cell destruction. The results show that the boiling pretreatment has a positive influence on the total monosaccharide yields and the subsequent freezing may slightly increase these yields even further. The maximum monosaccharide conversion (73.24%) was achieved using the fraction < 0.7 mm.

WOOD RESEARCH Volume 65, Number 6, 2020
Boháček Štefan, Pažitný Andrej, Halaj Michal, Balberčák Jozef, and Kuňa Vladimír

Freeze-thaw pretreatment of poplar sapwood dust

The paper is focused on the effect of freezing and cyclic freezing-thawing pretreatment of poplar sapwood (Populus alba L.). The experimental comparison was carried out by the sawdust fraction 0.7 mm as (a) water-saturated and (b) dry. Monosaccharide yields, as well as an amount of acetic acid, were measured after 6, 24, 48, 72, and 96 hours of enzymatic hydrolysis with 15% load of the enzyme measured to total cellulose content. The influence of freezing rate on total yields was observed on equally prepared samples with different weights (31 g, 25 g, 62.5 g, 125 g, 250 g, 500 g, and 1000 g) by “cubic” tests. To increase the efficiency of pretreatment, a cyclic freezing-thawing experiment at temperatures -20°C and +25°C was performed. The results show that single freezing of grounded poplar sapwood impregnated by water or dry in its matter is not a sufficient pretreatment method, so cyclic freeze-thaw is needed to enhance the yield of monosaccharides. Analysis of cubic test showed that slower freezing process has a positive effect on enzyme accessibility.

WOOD RESEARCH Volume 65, Number 4, 2020
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, VLADIMÍR IHNÁT, and Štefan Šutý

Effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree

The effect of steam explosion on enzymatic hydrolysis of various parts of poplar tree (heartwood, sapwood and 1-year coppice) was investigated. These parts were milled, the obtained sawdust was chemically analysed and then steam explosion of 0.7 mm poplar particles at temperature of 205°C was performed. Concentration of monomers obtained after enzymatic hydrolysis was considered as the main indicator for cellulose accessibility. Analysis of high performance liquid chromatography showed that non-treated poplar sawdust does not enable sufficient cellulose accessibility, while excessively high temperature and rapid pressure release resulted in substantial breakdown of polysaccharides and lignin and formation of inhibitors. The concentration of monomers increased gradually in the order of coppice, sapwood and heartwood. Steam exploded heartwood gave the maximum monosaccharides concentration of 90.0 g.L-1 after 72 hours of enzymatic hydrolysis. However, glucose concentration culminated after 48 hours of this hydrolysis. This corresponds to the best holocellulose accessibility for enzymes. The maximum concentration of inhibitors (9.3 g.L-1) was determined for poplar coppice after 24 hours of enzymatic hydrolysis.

WOOD RESEARCH Volume 64, Number 3, 2019
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, VLADIMÍR IHNÁT, and Štefan Šutý

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part II. Effect of steam explosion temperature on beech enzymatic hydrolysis

Beech wood is one of the most abundant species and the most harvested hardwood in Slovak Republic. The structure and chemical composition predetermines beech wood for the second generation bioethanol production. Steam explosion of beech wood from industrial treatment was investigated as a suitable pretreatment method. The effect of steam explosion temperature on beech sawdust enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 180°C was determined based on concentration of monosaccharides in hydrolysates and concentration of enzymatic hydrolysis inhibitors such as formic acid and acetic acid from beech sawdust. This corresponds to creating conditions resulting in good disintegration to the lignocellulosic structure which leads to increased cellulose accessibility. Non-treated beech sawdust does not enable sufficient cellulose accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and formation of inhibitors. The concentration of inhibitors was also determined for each studied steam explosion temperature. Based on steam explosion of beech sawdust, the effect of severity factors was investigated to find the optimum conditions of steam explosion pretreatment on cellulose and xylan recovery of beech wood. The obtained optimum steam explosion temperature corresponds to severity factor R0 = 3.36 (180°C, 10 minutes).

WOOD RESEARCH Volume 64, Number 1, 2019
Pažitný Andrej, Albert Russ, Boháček Štefan, Monika Stankovská, and Štefan Šutý

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part I: Evaluation of wheat straw pretreatment processes

New requirements for the biofuels industry force individual enterprises to develop various procedures for newly selected substrates pretreatments that could be applicable in processing of large quantities of raw materials. Even greater pressures are on second-generation biofuels producers justified by selection of waste lignocellulosic substrates and methods of substrate processing. Among the most suitable lignocellulosic raw materials in Slovak Republic (SR) for 2G bioethanol production is wheat straw. This raw material (Senec region, SR) for enzymatic hydrolysis was pretreated by dry milling (Brabender), cyclic freezing and thawing, wet milling (Sprout Waldron), two-step process of steam explosion at 180°C and extrusion at 145°C and one-step process of steam explosion at different temperatures. Wheat straw holocellulose accessibility was tested by adsorption of three commercially available dyes (Pylam Products Company, Inc., USA). Absorptivity coefficient of each dye at its maximum wavelength was determined from individual calibration curves of dyes and their values resulted ranging from 13.78 to 19.52 dm3.g-1.cm-1. The absorption of solution was measured and concentration of residual dye was calculated at given wavelength. The accessibility of holocellulose contained in wheat straw pretreated by steam explosion was controlled by SEM (scanning electron microscope) in correlation with the ratio of adsorbed dyes according to the modified Simons’ method.

WOOD RESEARCH Volume 66, Number 2, 2021
Kuňa Vladimír, Balberčák Jozef, Boháček Štefan, and VLADIMÍR IHNÁT

Elimination of adhesive impurities of the recovered paper in flotation process

The article presents results of the elimination of sticky impurities from recovered paper in laboratory flotation of three pulp suspensions with different whiteness, obtained directly from the production line before entering flotation. A combination of commercial agents releasing undesirable substances from recovered paper and means for regulation and stabilization of froth and modified micronized bentonit was used. In the flotation purification of pulp suspension with a whiteness of 53%, the combination of Prodeink Extra, Prodeink AS10 and Hydrocol OT reduced the macrostickies content by 58%, the ash content decreased from 18.5% to 4.5%, the whiteness increased from 53% to 56.4% and the residual color content was reduced from 385 ppm to 294 ppm. The pulp suspension with a whiteness of 64% showed a reduction in the content of macrostickies by 66%, a reduction in the ash content by 23.2%, an increase in whiteness by 1.4% and a reduction in the residual color content from 245 ppm to 194 ppm. The pulp suspension with a whiteness of 68.3% showed a decrease in the content of macrostickies by 58.1%, the ash content decreased from 35.7% to 6.3%, the whiteness increased by 1.1% and the content of residual color decreased from 157 ppm to 117 ppm.