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.
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.
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.
At the coating were used two substrates, commercial base paper and base paper produced in pilot experimental paper machine. The printing quality varied at both base papers. The coating colours contain commercial silica and precipitated calcium carbonate pigments. As a binder was used polyvinyl alcohol and cationic starch combined with high-cationic polymer SMAI 1000. Colour gamut significantly improved when the inkjet ink contact angle decreased below 14° independently of the base paper. The order of coating colours effect on the base papers was similar. Application of silica pigment in the coating colour provided papers with the largest inkjet ink wetting, the best colour gamut area, print sharpness and smoothness. By using of polyvinyl alcohol, a high colour gamut area was reached but it resulted in a markedly low print sharpness in comparison with cationic starch. Coating of base paper produced in pilot experimental paper machine introduces papers with higher colour gamut and also print sharpness.
This study presents the influence of retention reagents and multi-component retention systems on properties of pulp suspension which is used during toilet paper production. The following relationships were evaluated: influence of retention systems on rate of pulp suspension water drainage, values of specific cationic and anionic demand, Zeta potential of fibers, WRV values of fibers and water turbidity. The best results were achieved from applying three-component retention system which consisted of micro-milled bentonite Hydrocol OT, modified cationic polyethylenimin Polymín SK and cationic polyacrylamide Percol 830. The above mentioned three-component retention system resulted in increased rate of pulp suspension drainage by 43 %, improvement of water turbidity by 50 % and decrease of specific cationic demand by 33 %. The proposed retention system resulted in improved values of WRV pulp suspensions, which led to decrease of values by about 10 %. Influence of three-component retention system resulted only in minimal decrease of Zeta potential values for fibers.
The effect of silica and calcium carbonate pigments, polyvinyl alcohol and cationic starch binders combined with high-cationic polymers on physical-chemical and printing properties of coated papers were studied. The best printing properties were obtained with coating colour based on silica. Colour gamut significantly improved when the inkjet ink contact angle decreased below 15°. The water fastness was influenced with specific charge density of coating colour. Application of silica provided papers with the largest inkjet ink wetting, colour gamut area, print sharpness and surface roughness. By using of polyvinyl alcohol a high colour gamut area was reached but it resulted in a low print sharpness in comparison with cationic starch. High-cationic polymer poly-DADMAC showed a more significant effect on all printing properties of coated paper in comparison with SMAI 1000. The final inkjet print quality depends on structural and chemical properties of coating.
Extrusion pretreatment of wheat straw in a single screw extruder was investigated in terms of effectiveness of enzymatic hydrolysis and the formation of fermentation inhibitors. The effect of sodium hydroxide in extrusion pretreatment was compared with calcium hydroxide. The accessibility of wheat straw structure to hydrolytic enzymes increased with NaOH and Ca(OH)2 loadings, whereby more with the addition of NaOH. With 6% w/w of NaOH loading, the conversion of polysaccharides was 76.1% and with the same Ca(OH)2 loading it was 47.3%. The conversion of polysaccharides with 12% w/w of Ca(OH)2 loading was 66.6%. Without alkali in extrusion pretreatment, the conversion of polysaccharides was only 36.7%. The polysaccharides conversion of original extruded wheat straw was about 1.5 to 3.3% higher in comparison to washed extruded wheat straw. Fermentation inhibitors such as lignin, acetic and formic acid are primarily formed in the presence of alkali during extrusion pretreatment, most of which was lignin. Alkaline extrusion is a suitable method for pretreatment of lignocellulosic biomass.
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 %.
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%.
The paper describes a process for the preparation of fibre from waste wood particleboards (PB), oriented strand chipboard (OSB) and medium density fibreboard (MDF). The purpose of recycling of agglomerated wood materials is to reuse them for the production of fibrous materials. The agglomerated materials disintegrated after the initial destruction were further processed under the specified conditions with respect to the moisture content, their type, adhesive used, and properties of final particles – wood chips. The obtained wood particles were characterized by the fractional composition of chips. The resulting chips were mechanically defibred with subsequent characterization of fiber obtained for its reuse in the manufacture of MDF. A quantity of formaldehyde released into the water when cooking waste MDF and PB was set up depending on the cooking time. Residual level of formaldehyde is the main chemical load that determines the amount of waste material that can be reused for production of new panels based on ureaformaldehyde adhesives.
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.
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.
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.
The influence of tree species on basic density of wood, bark and small-wood was investigated here. Experimental material was obtained from 73 trees of 7 tree species, namely alder (Alnus glutinosa (L.) Gaertn.), beech (Fagus sylvatica L.), birch (Betula pendula Roth.), hornbeam (Carpinus betulus L.), Black locust (Robinia pseudoacacia L.), Sessile oak (Quercus petraea (Matt.) Liebl.) and Turkey oak (Quercus cerris L.) from the territory of Slovakia. Wood and bark samples were taken from discs cut from three trunk sections and from small-wood and branch parts coming from tree crowns. The volume of green samples was measured in graduated cylinders with a precision of 1 ml; a dry matter was measured with a precision of 0.01 g. The statistically significant effect has been shown in tree species, biomass fractions and locations on the tree. The average basic density of all species varies from 440 to 650 kg.m-3 for wood, for bark it is 380-670 kg.m-3 and for small-wood outside bark it reaches 490-650 kg.m-3. Alder and Black locust tree species have the lowest and highest wood density, Black locust and Turkey oak of bark and alder and Turkey oak of small-wood.
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.
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).
Experimental material was obtained from 43 trees of four tree species, namely pine, fir, larch and spruce from the territory of Slovakia. Wood and bark samples were taken from the discs in three locations on a stem and from small-wood, branches coming from tree crowns. The volume of fresh samples was measured in calibrated graduated cylinders with a precision of 1 ml; a dry matter was measured with a precision of 0.01 g. The statistically significant effect has been shown in tree species, fractions of biomass and locations on the tree using a special software based on ANOVA. The average basic density of wood for all species ranges from 373 to 508 kg. m-3. For bark it is 333-551 kg. m-3 and for small-wood outside bark it reaches 406-535 kg. m-3. The fir and larch have the lowest and highest values for wood density; pine and fir for bark density and pine and spruce species for small-wood density.
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.