Alkali Impregnation Research Articles

Functionalisation of alkali-resistant nanoporous glass via Au nanoparticle decoration using alkaline impregnation: catalytic activity for CO removal.

The concerted use of nano-metal particles with catalytic functions and nanoporous materials holds promise for effective air purification and gas sensing; however, only a few studies have used porous glasses as supports for Au nanoparticles. Furthermore, Au/nanoporous glasses with activities comparable to that of Au/TiO2, which is a typical Au catalyst, have not been reported to date. This study demonstrates that a nanoporous glass, which is highly acid- and alkali-resistant and chemically stable, can be decorated with Au nanoparticles using an alkali impregnation method. The resulting composite exhibits high catalytic activity in CO oxidation. The catalysts reported herein are as active as Au/TiO2 catalysts per active site. Further optimisation of the pore properties of the glass and sizes of the Au nanoparticles is expected to result in excellent catalytic systems for CO removal and sensing.

Combined alkali impregnation and poly dimethyl diallyl ammonium chloride-assisted cellulase absorption for high-efficiency pretreatment of wheat straw

Combined alkali impregnation and poly dimethyl diallyl ammonium chloride-assisted cellulase absorption for high-efficiency pretreatment of wheat straw

Adsorptive properties of Flamboyant seed pod activated carbon for the removal of anionic dye in wastewater

Flamboyant seed pods were used as a sustainable and cost-effective adsorbent for the removal of anionic dyes from wastewater. The activated carbon was obtained via Carbonization and subsequent chemical activation with Sodium Hydroxide at 600 o C for 60 minutes. The adsorbent was characterized using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Optimization of adsorption parameters, including dosage, contact time, and initial concentration were performed to determine the optimum adsorption performance of the activated carbon. It is evident from the result that, there were good enhancements in pores of the absorbent FS-AC due to alkali impregnation in addition the several functional groups that took part in the adsorption process. The adsorption capacity of methyl orange increased with contact time until it reaches the saturation limit and later decrease, indicating that the adsorbent can no longer adsorbed more dye beyond it saturation limit. There was a decrease in the dye uptake with increase in dosage of the FS-AC. The amount of methyl orange adsorbed onto FS-AC increased with time and subsequently decreased at some point in time with maximum uptake at 100 mg/L.

Simple Alkali-Modified Persimmon Peel–Montmorillonite Composite Hydrochar for Rapid and Efficient Removal of Methylene Blue

Modified persimmon peel–montmorillonite composites (PMHC-KOH/NaHCO3) for efficient and rapid removal of methylene blue (MB) were synthesized using hydrothermal carbonization and simple alkali impregnation. The surface properties and material compositions of the hydrochars were determined with SEM, zeta potential, and XRD, and the adsorption mechanism of MB on two modified hydrochars was analyzed with FTIR, XPS, and DFT calculation. The results showed that modified hydrochars with a rough surface structure and rich oxygen-containing groups exhibited a strong affinity for MB, and the adsorption capacity of PMHC-NaHCO3 and PMHC-KOH for MB reached 121.28 mg/g and 278.41 mg/g, respectively, with PMHC-KOH achieving more rapid adsorption of MB, at a rate of 0.043 g/mg/min. After five adsorption/desorption cycles, the two modified hydrochars still maintained a high adsorption rate of MB (92.32%/98.43%). The excellent adsorption performance of the modified hydrochars was attributed to hydrogen bonding, π-π interaction, electrostatic attraction, and ion exchange. DFT calculations revealed that oxygen-containing groups of the modified hydrochars played an important role in the adsorption of MB and confirmed that electrostatic attraction, hydrogen bonding, and π-π interactions were the key forces for rapid and efficient adsorption of MB. The prepared adsorbents gave full play to the regenerative applicability of agricultural waste, the simple alkali impregnation method eliminated the need for the additional cost of pyrolysis and activation, and their application in MB adsorption realized the treatment of waste with waste.

Study of the interaction between a Mn ore and alkali chlorides in chemical looping combustion

Chemical looping combustion (CLC) is a novel technology for heat and power generation with inherent CO2 capture. Using biomass in CLC (bio-CLC), negative CO2 emissions can be attained. Biomass usually contains high content of alkalis (mainly K and Na) which can be problematic in the process, such as potential alkali-bed interaction, and this is the focus of current work. This work uses charcoal with and without the impregnation with alkali chlorides, KCl and NaCl. The results are compared to previous data from samples impregnated with K2CO3 and Na2CO3. A low-alkali braunite manganese ore is used as bed material to study the oxygen carrier interaction with the alkalis in cyclic experiments at 950 °C in a quartz batch fluidized-bed reactor. As compared to charcoal without alkali impregnation, the impregnation with KCl, NaCl, K2CO3, and Na2CO3 can improve the rate of gasification by a factor of 4, 3, 10, 8, respectively. Partial-defluidization of the braunite particles was found with all the alkali-fuels, although the extent differed, e.g., K2CO3 and KCl resulted in earlier onset of defluidization than Na2CO3 and NaCl. Further, indications of partial defluidization were earlier and more permanent with the carbonates than the chlorides. Partial agglomeration with soft agglomerates of the bed was observed, while hard agglomerations were never seen. Accumulation of K, Na, Si, and Ca was found in the agglomerates after cycles with K2CO3-charcoal and Na2CO3-charcoal, while little K and Na was detected in the bridges between particles after the KCl and NaCl cycles. A significant fraction of the alkali added was found in the oxygen carrier, with 80% or more being retained for the Na salts, and around 40% for the K salts. There was no clear difference between chlorides and carbonates with respect to retention. The fresh and used braunite have very similar reactivity with CH4 and H2, whereas some decrease in reactivity is noticed with CO.

The impact of bleaching on the yield of softwood kraft pulps obtained by high alkali impregnation

AbstractHigh alkali impregnation (HAI) increases the total yield of softwood pulps following kraft cooking. This yield improvement is also maintained after oxygen delignification. This study evaluates how bleaching with either chlorine dioxide or hydrogen peroxide affects the final yield of samples obtained with standard and HAI. The chemical composition, viscosity, brightness, mechanical and morphological properties were studied. Compared to cooking after standard impregnation the yield improvement achieved by HAI was preserved in both types of bleaching sequences (2 % units for chlorine dioxide and 4 % units for hydrogen peroxide). The introduction of charged groups into the cellulose fibers was higher with hydrogen peroxide bleaching than with chlorine dioxide however, no significant impact was seen on the swelling or mechanical properties. The brightness was higher for the pulps bleached with chlorine dioxide compared with hydrogen peroxide. Hydrogen peroxide bleaching resulted in similar brightness development for both standard and HAI. Fibers bleached with chlorine dioxide had the highest curl index (16–17 %) compared to the fibers bleached with hydrogen peroxide (15 %).

Alkali Impregnation and Steam Explosion of Cogon Grass for Improved Enzymatic Saccharification

Process parameters for the alkali-impregnation of cogon and its combination with steam explosion were evaluated and optimized using Response Surface Modeling (RSM). Dried cogon (10% w/v) was impregnated in diluted base (1, 2, 3% (w/w) NaOH) at different ranges of temperature (50, 85,120 °C) and time (15, 32.5, 50 min), and then subjected to enzymatic saccharification using 60 FPU/g Accelerase 1500TM. The concentration of reducing sugar released was measured using Nelson-Somogyi Colorimetric Method. The RSM showed that the optimum condition, predicting 10% Reducing Sugar Yield (RSY), was treatment of 10 % (w/v) cogon with 1.5% NaOH (w/v) at 73 °C for 15 min. Upon validation, done in triplicates, 13+1.0% RSY was obtained. The optimally-impregnated cogon was subjected to a steam explosion treatment to improve its saccharifiability. The factors varied were temperature (170 to 225 °C) and exposure time (250 to 800 s). Upon saccharification of the steam-exploded samples, the RSM indicated that the best steam explosion condition, predicting 14% RSY, was 225 °C and 800 s. Upon validation, 15+0.5% RSY was obtained. Steam explosion improved the saccharifiability of NaOH-impregnated cogon by 15%.

The effects of high alkali impregnation and oxygen delignification of softwood kraft pulps on the yield and mechanical properties

Abstract This study investigated whether the yield improvement after high alkali impregnation (HAI) is maintained after oxygen delignification and whether the potential of oxygen delignification to increase the mechanical properties is affected by high alkali impregnation. The yield improvement achieved by high alkali impregnation (1 %) was preserved after oxygen delignification, particularly of glucomannan. The total fiber charge and swelling increased after oxygen delignification regardless of the type of impregnation in the cooking step. The tensile index improvement obtained by oxygen delignification was retained if this was preceded by high alkali impregnation. The stiffness index was higher and elongation slightly lower after HAI impregnation than after a standard (REF) impregnation. Fibers obtained through high alkali impregnation seem to be slightly less deformed and slightly wider than fibers obtained after a standard impregnation.

Statistical investigation of the bioprocess conditions of alkali combined twin-screw extrusion pretreatment to enhance fractionation and enzymatic hydrolysis of bulgur bran.

Bulgur bran (BB) is a potential source for the production of value-added products such as fermentable sugars and xylooligosaccharides (XOs). In this study, alkali combined twin-screw extrusion pretreatment was performed and statistically optimized to enhance fractionation and enzymatic hydrolysis of BB. The pretreatment conditions (barrel temperature, screw speed and alkali impregnation) were optimized by Box-Behnken design (BBD) to obtain the highest hemicellulose separation from BB. The obtained fractions were analyzed for the production of fermentable sugars and XOs. The results revealed that twin-screw extrusion of BB performed at 67 °C barrel temperature and 250 rpm screw speed after alkali impregnation at 0.02 g alkali g-1 biomass concentration provided 40.4% higher hemicellulose separation yield compared to the untreated BB. Alkali combined twin-screw extrusion pretreatment increased the enzymatic hydrolysis yield of BB fourfold, whereas a 13-fold increase was achieved after the separation of hemicellulose from pretreated BB. Xylose (X1)-free xylobiose (X2) was the main product after xylanase hydrolysis of hemicellulose fraction. SEM images confirmed the morphological modifications in BB, which were in agreement with the enhanced fractionation performance and the higher enzymatic hydrolysis yield. The results of this study suggested that pretreatment by alkali combined twin-screw extrusion followed by alkali extraction could be a reliable and effective process for fractionation of BB and production of fermentable sugars and XOs. © 2022 Society of Chemical Industry.

Hydrothermal Carbonization of Waste Sugarcane Bagasse for the Effective Removal of Emerging Contaminants from Aqueous Solution

Porous carbon spheres were fabricated from sugarcane bagasse using a sustainable hydrothermal carbonization process followed by alkali impregnation inert atmosphere activation. Developed spheres were technically analysed for their chemical science, structural morphology, texture, porosity with respect to size distribution, and thermal degradation. Spheres are functionally enriched with oxygenated groups showing amorphous nature portraying as a smooth surface. After activation, intensity of functional groups is reduced due to reduction reaction by KOH thereby yielding highly rich porous carbon. The active surface area developed on spheres is 111 m2 g-1 holding pores that are mesoporous in nature. Resistance to thermal exposure using TGA showed that decomposition of hemicelluloses followed by cellulose yielded aromatized carbon-rich skeleton through thermal degradation of carboxyl and hydroxyl groups. Developed carbon was found to be effective in removing Ciprofloxacin Hydrochloride from water with maximum adsorption capacity of 110.008 mg g-1. Mechanistic removal followed pseudo-second-order kinetics along with Freundlich mode of adsorption. The presence of carboxylic and hydroxyl groups in porous carbon favoured elimination of CPF from water. The development of HTC-derived carbon helped conserving the energy thereby reducing the cost requirement.

Impact of Alkali Impregnation on Physicochemical Properties of Macro-Scale Sugarcane Bagasse

Impact of Alkali Impregnation on Physicochemical Properties of Macro-Scale Sugarcane Bagasse

Multi-step preparation of Fe and Si modified biochar derived from waterworks sludge towards methylene blue adsorption

A magnetic nitrogen-doped sludge-based biochar (NAlSB–Fe–Si) was prepared based on waterworks sludge for raw material and dicyandiamide for nitrogen source to adsorb methylene blue (MB) from water. And the magnetic particles loaded on the adsorbent were obtained through functionalizing iron and silicon ions which were extracted from the biochar by acid and alkali impregnation. Physicochemical properties of sludge-based biochar (SB) were analyzed by SEM, BET, FTIR, XRD, XPS and VSM. Compared with the original biochar, NAlSB–Fe–Si had richer pore structure and higher pore volume, and the SiO2 and Fe3O4 loading made the specific surface area increased by 200%. Possible adsorption mechanism was proposed by exploring the initial pH, MB concentration and reaction time. Results revealed that alkaline environment was more conducive to the rapid removal of cationic dyes such as MB. Pseudo-second-order kinetic model and intra-particle diffusion model could describe the adsorption behavior of MB on NAlSB–Fe–Si. The fitting results of Langmuir model showed that adsorption temperature is positively correlated with adsorption capacity, and the maximum adsorption capacity of MB on nitrogen-doped sludge-based biochar (NSB) and NAlSB–Fe–Si at 25 °C was 26.47 and 300.36 mg/g, respectively. Finally, the MB removal rate of NAlSB–Fe–Si could still reach 70% after four cycles, indicating that the composite was an efficient cationic dye adsorbent, and its preparation could be regarded as a way of resource utilization of waterworks sludge.

Process parametric optimization toward augmentation of silica yield using Taguchi technique and artificial neural network approach

This study was attempted towards the retrieval of silica from rice husk ash to annihilate the local problems of disposal from the rice milling industries for enhancement of silica purity. Optimization of process factors using the Taguchi technique involved variation in sodium hydroxide concentration (NaOH), alkali impregnation volume per unit weight of the rice husk ash, and reaction time for designing the experimental matrix utilizing L16 orthogonal array at four different levels. The maximum silica extraction was 98.26% obtained with 4 N of NaOH, 20 ml/g of alkali volume, and treatment time 60 min. The identical experimental data set was also applied to an artificial neural network model (ANN) with the LM algorithm for predicting the feasibility of the extraction process. Both Taguchi and neural networks suggested a high coefficient of determination and a satisfactory correlation between experimental and predicted silica recovery values. The detailed characterization of the synthesized silica powder and residual rice husk ash was executed using field emission scanning electron microscopy (energy-dispersive spectroscopy), Fourier transform infrared spectroscopy, thermogravimetric, Brunauer Emmett Tellet surface area, and particle size analysis. The simultaneous reuse of residual ash and silicate was performed to ensure the best possible reclamation of silica and reusability of rice husk ash. The detailed cost estimation of the synthesized silica powder further suggested the effectiveness of the optimized process. Thus, a comprehensive approach for enhancement of the silica yield and purity by adopting Taguchi and ANN optimization proved to be useful in this study.

Study on reaction mechanism of superior bamboo biochar catalyst production by molten alkali carbonates pyrolysis and its application for cellulose hydrolysis

Biochar has attracted wide interest due to its important role in the synthesis of functionalized carbon materials. Molten alkali carbonates (MC) pyrolysis as a novel mean was explored to obtain superior bamboo biochar compared with alkali impregnation pretreating bamboo powder associated with pyrolysis. The properties of biochar produced by MC pyrolysis were enhanced, suggesting an increase in BET surface area of 43.59 m2/g compared with non-pretreat biochar of 5.76 m2/g, and possessed preferable pore structure than the alkali impregnation one of 39.82 m2/g and 16.98 nm for catalyst support. Besides, pyrolysis temperature reinforced the porosity and the degree of carbonization as it rising, however, the optimized temperature for top-grade biochar materials was 450 °C. The MC weakened the hydrogen bonds network in bamboo powder acting a similar role just as alkaline pretreated, meanwhile neutralized the acid produced during pyrolysis process supported by the analysis of FTIR and TGA. The potential pathways of biomass pyrolysis with MC had also been proposed. In addition, the biochar obtained was utilized as a catalyst support of biochar-bearing sulfonic acid groups, which achieved the remarkable yields of TRS and glucose (52.8% and 43.5%) in hydrolysis of cellulose.

Steam explosion pre-treatment of alkali-impregnated lignocelluloses for hemicelluloses extraction and improved digestibility

The application of steam explosion pre-treatment to extract xylan-rich biopolymers from alkali-impregnated lignocelluloses, while simultaneously increasing the enzymatic digestibility of cellulose, was investigated. Steam-enhanced extraction of xylan from sugarcane trash (SCT) and aspen wood (AW) was performed at varying temperatures (176–204 °C) and retention times (3–17 min) after the impregnation of biomass samples with sodium hydroxide at 1:20 (w/w) solid loading ratio. Xylan extraction and cellulose digestibility results were statistically analysed to fix the condition/s for significantly enhanced values. Accordingly, maximum xylan yields of 51 and 24%, and highest cellulose digestibility of 92 and 81%, were attained for SCT and AW respectively following their pre-treatment at 204 °C for 10 min. At this most-severe condition, neither xylose nor furfural – a degradation product from xylose – were observed in the hemicellulose extract, indicating steam explosion pre-treatment with alkali impregnation of lignocelluloses as viable biorefinery approach to co-produce xylan biopolymers and bioethanol.

Autohydrolysis prior to poplar chemi-mechanical pulping: Impact of surface lignin on subsequent alkali impregnation

Chemi-mechanical pulping, a typical high-yield pulping method, combined with autohydrolysis pretreatment prior to pulping is an efficient and value-added utilization method for biomass in pulp and paper industry. This study investigated the surface lignin changes of poplar sapwood chips in autohydrolysis pretreatment and their effect on the subsequent alkali impregnation for chemi-mechanical pulping. The results showed that the surface lignin content went up with the increase of autohydrolysis intensity, and that the existence of the surface lignin had nearly no impact on the subsequent alkali impregnation in making chemi-mechanical pulps (CMPs) compared to the volume porosity, which was validated by using the stepwise regression analysis. It can be further concluded that autohydrolysis can facilitate the subsequent alkali impregnation of the autohydrolyzed sapwood chips in making CMP, which would be of significance for the combination of biomass refinery and pulp and paper industry.

Consequences in a softwood kraft pulp mill of initial high alkali concentration in the impregnation stage

Abstract Impregnation with high initial concentration is fast and efficient, leading to a homogeneous delignification in the subsequent cook, resulting in improved screened pulp yield. To obtain high initial alkali concentration, the white liquor flow needs to be significantly increased. The moisture content of the wood chips and the alkali concentration of the white liquor limit the initial alkali concentration of the impregnation liquor that can be reached. It is therefore of interest to evaluate the possibility to implement high alkali impregnation (HAI) industrially and the consequences this would have on the mill system. The effect of HAI on mass and energy balances in a kraft pulp mill has been studied using mill model simulations. The sensitivity to disturbances in important parameters for process control has been compared to impregnation scenarios used industrially. It was shown that high initial alkali concentration can be achieved on industrial scale by increased white liquor flow. HAI has a positive effect on recovery flows and reduces the need for make-up chemicals. The HAI concept is less sensitive to variations in process parameters, such as chip moisture and white liquor concentration, thus diminishing the risk of alkali depletion in chip cores.

Alkali enhanced biomass gasification with in situ S capture and a novel syngas cleaning. Part 2: Techno-economic assessment

Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning system comprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reduction with zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol production allowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantage derived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.

Effect of chemical modification with 4-vinylpyridine on dyeing of cotton fabric with reactive dyestuff

Cotton fabrics were pre-treated with 4-vinylpyridine before dyeing to increase dye uptake. Various treatments for the application of monomers to fabrics were tried in different combinations and after dyeing the best result was obtained with alkali impregnation and monomer exhaustion. After decisions had been made on the processes to be applied before dyeing, different amounts of monomer, dyestuff and salt were used in reactive dyeing baths at different pHs. The results were evaluated in terms of color coordinates, color strength, FT-IR and fastness to washing, rubbing and perspiration. The best results were obtained with 3 ml of 4-vinylpyridine dissolved in 10 ml of alcohol, in the presence of 25 g L−1 of salt and in neutral medium at 5% dyestuff concentration. Color strength from this dyeing process was higher than from the conventional dyeing at the same dyestuff concentration. FT-IR analysis demonstrated the presence of monomer on the surface of the fabric. Fastness values showed that this method could be used as an alternative to the conventional method.

Improved diffusivity of NaOH solution in autohydrolyzed poplar sapwood chips for chemi-mechanical pulp production

This work investigated the changes in the physical structure of autohydrolyzed poplar sapwood chips and the effect on the subsequent alkali liquor diffusion properties for chemi-mechanical pulping (CMP). An alkali impregnation process was conducted by using the autohydrolyzed poplar sapwood with different levels of autohydrolysis intensity. The results showed that the volume porosity, water constraint capacity, and saturated water absorption of the autohydrolyzed poplar sapwood chips increased. Also, the effective capillary cross-sectional area (ECCSA) in the radial direction and the diffusion coefficients of NaOH solution in both the radial and axial directions all increased. Autohydrolysis pretreatment enhanced the alkali liquor diffusion properties in poplar sapwood chips, and the diffusion coefficient was increased more greatly in the radial direction than that in the axial direction.