Thermomechanical Pulping Process Research Articles

Isolation and purification of high-molecular weight hemicelluloses from radiata pine wood chips prior to thermo-mechanical pulp (TMP) production

Abstract A novel thermo-mechanical pulping (TMP) process has been developed to produce a by-product rich in high-molecular weight (MW) hemicelluloses, a potential raw material for barrier coatings and films. This process uses prehydrolysis to solubilise the hemicelluloses followed by chip compression to separate the soluble material from the wood matrix. The pressate from the chip compression stage was dark-coloured and had a high content of high-MW hemicelluloses and lignin. However, isolating the high-MW material from the pressate directly by ultrafiltration was not feasible because of membrane fouling by dissolved lignin and wood extractives, while coloured impurities are undesirable for many potential applications. To solve these problems the pressate was purified using XAD adsorbent resin to remove low-MW lignin, extractives and colour. Ultrafiltration of the purified pressate yielded lightly coloured high-MW hemicellulose with a low content of lignin and well suited for barrier films and coatings.

Energy Modeling of a Refiner in Thermo-Mechanical Pulping Process Using ANFIS Method

In the pulping industry, thermo-mechanical pulping (TMP) as a subdivision of the refiner-based mechanical pulping is one of the most energy-intensive processes where the core of the process is attributed to the refining process. In this study, to simulate the refining unit of the TMP process under different operational states, the idea of machine learning algorithms is employed. Complicated processes and prediction problems could be simulated and solved by utilizing artificial intelligence methods inspired by the pattern of brain learning. In this research, six evolutionary optimization algorithms are employed to be joined with the adaptive neuro-fuzzy inference system (ANFIS) to increase the refining simulation accuracy. The applied optimization algorithms are particle swarm optimization algorithm (PSO), differential evolution (DE), biogeography-based optimization algorithm (BBO), genetic algorithm (GA), ant colony (ACO), and teaching learning-based optimization algorithm (TLBO). The simulation predictor variables are site ambient temperature, refining dilution water, refining plate gap, and chip transfer screw speed, while the model outputs are refining motor load and generated steam. Findings confirm the superiority of the PSO algorithm concerning model performance comparing to the other evolutionary algorithms for optimizing ANFIS method parameters, which are utilized for simulating a refiner unit in the TMP process.

In situ real-time investigations on adsorptive membrane fouling by thermomechanical pulping process water with quartz crystal microbalance with dissipation monitoring (QCM-D)

Membrane processes are essential for the success of lignocellulosic biorefineries, but membrane fouling is still a major problem and the single most important reason for the relatively slow acceptance of membrane technology in this industrial application. It is therefore of the utmost importance to find methods that enable the study of the fouling development when processing new types of feed solutions. Although ex situ analysis allows the composition of the fouling layer to be determined, the processes leading to its build-up remain unknown. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study adsorptive fouling in situ. By using QCM-D, the development of fouling over time can be studied. Fouling of three fractions of a thermomechanical pulping process water (feed, microfiltration retentate and permeate) were studied on QCM-D sensors coated with a polymer used in commercial polysulfone membranes. The retentate contained mainly colloidal extractives and the permeate hemicelluloses. In the case of the retentate, adsorption was almost immediate and the greatest increase in mass was observed. In case of the permeate, the increase in mass was slowest but at steady state the adsorbed mass was similar to the adsorbed mass of the process water. After rinsing with water, an irreversibly attached network of hemicelluloses remained on the polymer surface while the colloidal extractives were washed away. Overall, the study shows that in situ real-time monitoring of adsorptive membrane fouling combined with additional ex situ analysis generates valuable understanding on the evolution of membrane fouling in lignocellulosic biorefineries.

Aggregation and Sedimentation Performance of Lignin and Hemicellulose Derived Flocs in the Spent Liquor of Thermomechanical Pulping Process

Spent liquors produced in the pulping industry contain dissolved lignocellulosic macromolecular components that are currently burned or treated in wastewater treatment systems. However, they can be isolated by flocculation to make added-value products. In this work, lignin and hemicelluloses were extracted from spent liquor (SL) of a thermomechanical pulping process (TMP) and treated by polydiallyldimethylammonium chloride (PDADMAC). The flocculation of lignocellulosic compounds of SL with three different molecular weights of PDADMAC was studied comprehensively in this work. The settlement of the generated flocs was also investigated by means of advanced techniques, and the results were related to the characteristics of PDADMAC and lignocellulosic compounds. The maximum removals of lignin (57%) and hemicellulose (36%) were achieved by larger PDADMAC with a molecular weight of 1045 kg/mol at the dosages of 100 mg/L and 80 mg/L, respectively. The properties of lignin and hemicelluloses, as well as zeta potential and focused beam reflectance measurement (FBRM) analyses, confirmed that the flocculation of lignin was mainly based on charge interaction, while that of hemicellulose was based on bridging mechanism. PDADMAC/pure lignin system showed a faster sedimentation rate with more compact flocs than both PDADMAC/pure hemicellulose and PDADMAC/industrial SL (TMP) systems. The PDADMAC/hemicellulose system had flocs with the loosest structure and poorest settling performance. The results of this study provide a means to extract and use lignocellulosic compounds of spent liquor via selective flocculation and separation strategies. Lignin/PDADMAC flocs and hemicellulose/PDADMAC flocs can be separated from their solutions by sedimentation and filtration, respectively.

Analysis of membrane fouling by Brunauer-Emmett-Teller nitrogen adsorption/desorption technique

Membrane fouling is the major factor limiting the wider applicability of the membrane-based technologies in water treatment and in separation and purification processes of biorefineries, pulp and paper industry, food industry and other sectors. Endeavors to prevent and minimize fouling requires a deep understanding on the fouling mechanisms and their relative effects. In this study, Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique was applied to get an insight into pore-level membrane fouling phenomena occurring in ultrafiltration of wood-based streams. The fouling of commercial polysulfone and polyethersulfone membranes by black liquor, thermomechanical pulping process water and pressurized hot-water extract was investigated with BET analysis, infrared spectroscopy, contact angle analysis and pure water permeability measurements. Particular emphasis was paid to the applicability of BET for membrane fouling characterization. The formation of a fouling layer was detected as an increase in cumulative pore volumes and pore areas in the meso-pores region. Pore blocking was seen as disappearance of meso-pores and micro-pores. The results indicate that the presented approach of using BET analysis combined with IR spectroscopy can provide complementary information revealing both the structure of fouling layer and the chemical nature of foulants.

Biorefining of spruce TMP process water: Selective fractionation of lipophilic extractives with induced air flotation and surface active additive

Lignocellulose biomass plays an important role in reducing the dependency on fossil fuels and ameliorating the dire consequences of climate change. It is therefore important that all the components of lignocellulose biomass are exploited. These components include hemicelluloses and extractives that are liberated and sterically stabilized during the thermomechanical pulping and that form the dissolved and colloidal substance (DCS) in the process water. Biorefining of this process water can extract these substances, which have a number of promising applications and can contribute to the full exploitation of lignocellulose biomass. This paper presents a simple treatment of unbleached Norway spruce (Picea abies) process water from TMP (thermomechanical pulping) production using induced air flotation (IAF) and cationic surfactant, dodecyl trimethylammonium chloride (DoTAC) to refine the extractives and prepare the waters so that hemicellulose could be easily harvested at a later stage. By applying 80 ppm of DoTAC at a pH of 3.5 and 50 °C before induced air flotation, 94% of the lipophilic extractives were recovered from process water. Dissolved hemicellulose polysaccharides were cleansed and left in the treated process water. The process enabled efficient biorefining of lipophilic extractives and purification of the process water to enable more selective harvesting of hemicelluloses in subsequent steps.

Unveiling TMP Process Water Potential As an Industrial Sourcing of Valuable Lignin–Carbohydrate Complexes toward Zero-Waste Biorefineries

The development of zero-waste biorefineries is a promising yet challenging pathway toward a sustainable bioeconomy. Deep insights on the composition of biorefineries side streams along with the development of green technologies are mandatory to achieve such a goal. In this Article, a sustainable pilot-scale membrane process was used to recover valuable organic matter dissolved in the main side stream of a thermomechanical pulping (TMP) plant. A great number of analytical tools were combined to get an extensive characterization of the generated fraction, including inductively coupled plasma atomic emission spectroscopy (ICP-AES), high-performance ion chromatography coupled with pulse amperometric detection (HPIC-PAD), Fourier transform infrared (FTIR), size-exclusion chromatography (SEC), and C-13 and 2D heteronuclear single quantum correlation (HSQC) NMR. The results revealed the presence of a considerable amount of native lignin-carbohydrate complexes (LCCs) in the fraction representing 40% of the dry weight. The LCCs are composed of partially acetylated galactoglucomannans (GGMs) covalently linked to low condensed and ) beta-O-4-rich lignin through phenyl glycosidic bonds (25.5 bonds/100 aromatic rings (ar)) and characterized by a relatively low molecular weight around 7 kDa. Such complexes present an interesting potential for valorization with unique properties resulting from the combination of their aromatic and sugar moieties. Different applications are discussed in regards to the generated data in this work as an industrial sourcing of LCC is reported.

Isolation of lignocelluloses from the spent liquor of thermomechanical pulping process with fly ash and cationic polymer

In this work, fly ash (FA) and polydiallyldimethylammonium chloride (PDADMAC) were utilized to treat the spent liquor (SL) of thermomechanical pulping (TMP) process in an effort to remove its lignocelluloses. The incorporation of PDADMAC into the system reduced the dosage of FA required for achieving acceptable lignocellulose removals. The maximum lignocellulose removals of 81%, 78%, 56%, 53% and 97% were achieved for lignin, hemicellulose, COD, BOD, and turbidity via treating SL with 100 g/L of FA at 25 °C for 60 min and subsequently treating with 100 mg/L of PDADMAC at 25 °C for 30 min, respectively. Comparing the two-step processes, FA pretreatment with PDADMAC post treatment was more effective than the two step process of PDADMAC pretreatment and FA post treatment. In this case, the FA pretreatment generated metal-organic complexes, and the addition of PDADMAC facilitated the formation of large flocs that could be separated from the system readily. A one stage process of combined PDADMAC and FA was less effective than the two-stage process of FA and PDADMAC treatments in removing lignocelluloses from SL.

Separation of hemicelluloses and lignins from synthetic hydrolyzate and thermomechanical pulp mill process water via liquid-liquid extraction

The separation of hemicelluloses from thermomechanical pulping (TMP) process water is of particular interest because it yields a biopolymer suitable for various value-added biomaterials production and reduces the organic loading on the water treatment facility. However, during the TMP process, hemicellulose is released in the process water at relatively low concentrations that are difficult to recover by many methods efficiently. Liquid-liquid extraction (LLE) has been deemed as a potentially viable separation technique in modern industrial processes for valuable materials recovery and undesirable impurities removal. In this work, the extraction of hemicellulose from the process water and synthetic hydrolyzate using LLE was investigated. In particular, the effects of the major experimental variables (the type of solvent, hydrolyzate to solvent volume ratio, and pH) on extraction performance were explored. The tested solvents have shown varying affinity and selectivity for the recovery of hemicellulose. It was found that the hemicellulose extraction efficiency of n-hexane (71.03%) and tributyl phosphate (TBP) (72.34%) was higher than that of 1-butanol (62.36%), and toluene (67.03%) at a solvent: hydrolyzate volume ratio of 1:3. Although TBP showed a high degree of hemicellulose extraction (72.34), it was characterized by a low selectivity coefficient, while n-hexane achieved the highest selectivity. The average selectivity coefficients of n-hexane were 7.3, 5.1, and 8.7 followed by toluene 2.7, 2.7, and 2.9 for pH values of 9.5, 7, and 4.3, respectively. Changing the pH of the hydrolyzate has resulted in varying effects depending on the type of the solvent used. The optimum extraction pH, phase ratio, and extraction time were at 4.3, 1:3 mL/mL and 30 min, respectively.

Investigations of Alkaline and Enzymatic Membrane Cleaning of Ultrafiltration Membranes Fouled by Thermomechanical Pulping Process Water

The pulp and paper industry is one of the most important industrial sectors worldwide, and has considerable potential for the sustainable fractionation of lignocellulosic biomass to provide valuable compounds. Ultrafiltration (UF) is a suitable separation technique for the profitable production of hemicelluloses from process water from thermomechanical pulping (ThMP), but is limited by membrane fouling. Improvements in cleaning protocols and new alternative cleaning agents are required to ensure a long membrane lifetime, and thus a sustainable process. This study, therefore, focuses on the cleaning of polymeric UF membranes after the filtration of ThMP process water, comparing alkaline with enzymatic cleaning agents. The aim was to develop a cleaning procedure that is efficient under mild conditions, resulting in a lower environmental impact. It was not possible to restore the initial permeability of the membrane when cleaning the membrane with enzymes alone, but the permeability was restored when using a two-step cleaning process with enzymes in the first step and an alkaline cleaning agent in the second step. Scanning electron microscopy gave a deeper inside into the cleaning efficiency. Attenuated total reflectance Fourier-transform infrared spectroscopy analysis confirmed that not only polysaccharides, but also extractives are adsorbed onto the membrane surface.

Pretreatment and in Situ Fly Ash Systems for Improving the Performance of Sequencing Batch Reactor in Treating Thermomechanical Pulping Effluent

In this work, two methods were applied for improving the performance of activated sludge in treating the effluent of thermomechanical pulping process. In one attempt, the effluent of the pulping process was pretreated with 0.2 wt.% of fly ash (FA) at room temperature and 100 rpm for 1 h, and the FA-pretreated samples were further processed by a sequencing batch reactor (SBR) system. In another work, FA (0.2 wt.%) and activated sludge were mixed with the effluent simultaneously in an in-situ system. The results showed that FA asimilation would benefit the removal of non-biodegradable substances, and thus facilitate the decomposition of contaminants by activated sludge in both systems, especially in the in-situ system. The removal efficiencies of 96.1%, 99.1%, 95.2%, 90.51% and 99.5% were achieved for COD, BOD, TOC, lignin and sugar from the effluent, respectively. In addition, the sludge volume index (SVI) of the FA-pretreated and in-situ systems decreased to 100.7 and 75.5 mL/g and the effluent suspended ...

Flocculation of thermomechanical pulping spent liquor with polydiallyldimethylammonium chloride

Currently, the dissolved lignocelluloses in the spent liquor (SL) of a thermomechanical pulping process are treated in wastewater treatment systems and thus they are wasted. In this work, polydiallyldimethylammonium chloride (PDADMAC), with different molecular weights, was used for flocculating lignocelluloses of SL and thus isolating them from SL. Results showed that the maximum removals were 38% via treating SL with 100 mg/L of PDADMAC (with 1045 kg/mol molecular weight) at 25 °C for 30 min. The focused beam reflectance measurement of the flocculation process revealed that the chord length of the flocs with the maximum square weighted counts was increased from 70 to 100 μm and also their maximum square weighted counts was increased from 5 to 25 μm2/s. The flocs contained 60.71–74.41 wt% PDADMAC, the balance of lignocelluloses and the heating value of 24–25 MJ/kg. The high molecular PDADMAC generated flocs with more organics and a higher heating value.

Treating thermomechanical pulping wastewater with biomass-based fly ash: Modeling and experimental studies

Abstract In the present study, biomass based fly ash was used to remove lignocellulose from the spent liquor (SL) of a thermomechanical pulping process. The effect of independent parameters, e.g. time, temperature and dosage, on the performance of fly ash in treating SL was studied using an optimal design of response surface methodology. Under the optimal conditions (time 160 min, temperature 40 °C and fly ash dosage of 150 g/L), the removals of turbidity, COD and lignin were 75.1%, 61.3% and 63.5%, respectively. Furthermore, the sedimentation and drainability of fly ash/SL systems were investigated to separate fly ash from SL after the treatment. The sedimentation analysis showed that fly ash would not be settled from the system fast, but sedimentation was improved at a higher temperature of 60 °C than 30 °C. Interestingly, the drainability analysis showed that fly ash could be separated from the SL by filtration. Increasing the fly ash dosage from 120 g/L to 180 g/L reduced the average filtrate rate from 95 mL/min to 25 mL/min, and it was improved from 35 mL/min to 75 mL/min with the temperature increasing from 25 °C to 75 °C. Agitation intensity did not affect the filtration performance, but it increased the solid content of the filtrate from 0.30 wt.% to 0.35 wt.%.

Enzymatic treatment of hemicelluloses and lignin isolated from thermomechanical pulp mill process water

Hemicelluloses dissolved in thermomechanical pulp (TMP) mill process streams can be used to manufacture high-value-added products. The molecular mass of the dissolved hemicelluloses is about 10kDa. In some applications, it would be beneficial with larger molecules. It was therefore investigated whether it is possible to increase the size of hemicelluloses isolated by microfiltration and ultrafiltration from TMP process water using enzymatic treatment with laccase. No significant increase of the size of hemicelluloses was achieved, probably due to only a small percentage of lignin carbohydrate complexes in the process water. The molecular mass of lignin increased however markedly from a peak molecular mass of 1kDa to about 60kDa. Diafiltration was used to purify large molecules after the enzymatic treatment. Low-molecular-mass sugar and lignin molecules in the diafiltration permeate were concentrated by nanofiltration. The retention of sugars and lignin was about 98% during nanofiltration to a volume reduction of 80%. Average flux during nanofiltration was 49l/m2h.

Pulp property development Part I: Interlacing undersampled pulp properties and TMP process data using piece-wise linear functions

Thermo-Mechanical Pulp (TMP) refiners served in this work as an example of how to combine oversampled and undersampled variables on a common timeframe for further analysis. To get more information from the refining process, temperature measurement arrays in the refining zones were studied alongside process measurements such as motor load, production rates, plate gaps, dilution waters, pulp properties and manually measured blow-line consistency. The undersampled data set consisted of 63 laboratory samples obtained at a Swedish TMP mill, which were tested for tensile index, mean fiber length and Somerville shives content. The pulp samples were obtained at five different periods during three months to cover a large dynamic operating window. The data set was expanded using a piece-wise linear approach. The measurements inside the refining zone were shown to be important variables when interlacing the undersampled pulp properties with the oversampled process data set, consisting of 350 000 samples. Use of an extended entropy model provided a palette of information about the process conditions inside the refining zone. Particularly, the residence time and the consistency in the refining zones were essential for the pulp property development, as a link between the refining segment pattern used and the current state of refiner operation.

Process for Treating Spent Liquor of the TMP Process with Biomass-Based Fly Ash

The spent liquor (SL) of the thermomechanical pulping (TMP) process has a high effluent load. In this work, biomass-based fly ash was used for adsorbing lignin of SL and thus for reducing the COD and turbidity of SL prior to sending SL to a wastewater treatment system. By treating SL with fly ash in a one-stage adsorption process under the conditions of a fly ash/SL ratio of 55 mg/g and 3 h at 30 °C, 67 mg/g of lignin was adsorbed on fly ash at room temperature. Adjusting the pH of SL had an insignificant influence on the lignin isolation from the system but affected the turbidity of SL. The lignin removal was 68% in a two-stage fly ash adsorption process, while the COD and turbidity removal were 70% and 94%, respectively. On the basis of the results, a process for reducing the effluent load of SL using fly ash was proposed.

Antisolvent precipitation of water-soluble hemicelluloses from TMP process water

During the thermomechanical pulping (TMP) of spruce, hemicelluloses (mainly galactoglucomannans, GGMs) are released into the process water at relatively low concentrations that are currently impossible to efficiently recover. This paper examines the recovery of hemicelluloses precipitated from TMP process water via solubility reduction by adding antisolvents such as methanol, ethanol, and acetone. The phase separation was monitored by turbidity measurements. Gravimetric analysis, FTIR, GC–MS, UV spectroscopy, and ICP-OES were used to determine the yield, purity, and composition of the precipitates. Gel permeation chromatography and pulsed field-gradient self-diffusion NMR were used to measure the molecular mass distribution of the precipitates. Acetone was found to be the most efficient antisolvent, giving the highest yield at the lowest addition. The contents of lipophilic extractives and lignin impurities were below 0.5% and 1.6%, respectively, and the metal content was approximately 2% in the precipitates obtained with acetone.

Isolating lignin from spent liquor of thermomechanical pulping process via adsorption

Wood chips are pretreated with steam prior to refining in the thermomechanical pulping process. The steam treatment dissolves part of lignin of wood chips in the spent liquor (SL) of this process, and subsequently the SL is sent to the wastewater system of the process. However, the lignin of SL can be used in the production of value-added chemicals, but it should first be separated from the SL in order to have a feasible downstream process. In this study, activated carbon (AC) was considered as an adsorbent to isolate lignin from SL. The results showed that the maximum adsorption of lignin on AC was166 mg/g under the optimal conditions of pH 5.2, 30 °C and 3 h treatment. Furthermore, the separation of lignin from SL was improved from 45% to 60% by having a two-stage adsorption process at pH 5.2, which also reduced the turbidity and chemical oxygen demand of SL by 39% and 32%, respectively.

Selective purification of bleached spruce TMP process water by induced air flotation (IAF)

Abstract The environmentally benign closure of water systems in paper mills leads to the problem of accumulation of dissolved and colloidal wood substances (DCS) in process water. Notably, pitch affects the pulp and paper production negatively and increases the demand for additional treatment of the process water. In the present article, the purification of thermomechanical pulping process water from the alkaline peroxide bleaching stage has been investigated, with the induced air flotation (IAF) in focus. The following parameters were considered concerning the IAF efficiency to remove detrimental substances: concentration of cationic foaming agent, pH value, calcium concentration, and temperature. The amounts and characteristics of residual DCS were determined by gas chromatography and turbidity measurements. Residual concentrations of the foaming agent dodecyltrimetylammonium chloride were determined by electrospray ionization mass spectrometry. Up to 90% of pitch was removed, whereas hemicelluloses, which are important in preventing pitch problems, remained in the waters. Up to 70% of the pectic acids accounted for the high cationic demand of the process waters were removed by optimization of the IAF parameters. The presented separation process gives new opportunities to a selective purification of the process waters.

Potential of pulp and paper secondary sludge as co-adhesive and formaldehyde scavenger for particleboard manufacturing

This study investigated the potential of secondary sludge (SS) as urea–formaldehyde (UF) co-adhesive for particleboard manufacturing. Three proportions of SS from three conventional pulping processes were added in the formulation of particleboard manufacturing. A 33 factorial design was used. All panels were tested for thickness swell (TS), linear expansion (LE), internal bond strength (IB), flexural modulus of elasticity (MOE), flexural modulus of rupture (MOR) and formaldehyde emission. Results indicated that particleboards made with SS from thermomechanical pulp (TMP) and kraft pulp (Kraft) met the ANSI standards for LE, IB, MOE, and MOR (with 7 and 9 % UF). However, the TS of panels made with SS was higher than that of control panels and adding SS to the formulation affected negatively this property. Most of the properties studied in the particleboards made with SS from chemical–thermomechanical pulping (CTMP) process failed to meet the ANSI standards. The main advantage of using SS as co-adhesive is the reduction of formaldehyde emission, in the best case here, about 50 %, with CTMP sludge added, of the particleboards.