Oxidative Pretreatment Research Articles

Challenges and opportunities in mimicking non-enzymatic brown-rot decay mechanisms for pretreatment of Norway spruce

The recalcitrance bottleneck of lignocellulosic materials presents a major challenge for biorefineries, including second-generation biofuel production. Because of their abundance in the northern hemisphere, softwoods, such as Norway spruce, are of major interest as a potential feedstock for biorefineries. In nature, softwoods are primarily degraded by basidiomycetous fungi causing brown rot. These fungi employ a non-enzymatic oxidative system to depolymerize wood cell wall components prior to depolymerization by a limited set of hydrolytic and oxidative enzymes. Here, it is shown that Norway spruce pretreated with two species of brown-rot fungi yielded more than 250% increase in glucose release when treated with a commercial enzyme cocktail and that there is a good correlation between mass loss and the degree of digestibility. A series of experiments was performed aimed at mimicking the brown-rot pretreatment, using a modified version of the Fenton reaction. A small increase in digestibility after pretreatment was shown where the aim was to generate reactive oxygen species within the wood cell wall matrix. Further experiments were performed to assess the possibility of performing pretreatment and saccharification in a single system, and the results indicated the need for a complete separation of oxidative pretreatment and saccharification. A more severe pretreatment was also completed, which interestingly did not yield a more digestible material. It was concluded that a biomimicking approach to pretreatment of softwoods using brown-rot fungal mechanisms is possible, but that there are additional factors of the system that need to be known and optimized before serious advances can be made to compete with already existing pretreatment methods.

Comparison of mild alkaline and oxidative pretreatment methods for biobutanol production from brewer’s spent grains

In this study, a comparative analysis of different pretreatment strategies on hydrolysis and fermentation of brewers’ spent grain for biobutanol production by C. beijerinckii is presented. Ozone (2.7% w/w, 30 min, 40–60% w/w humidity), sodium hydroxide (1–5 % w/w NaOH, 30 min, 120 ºC, 5–15 % w/w BSG) and hydrogen peroxide (5% w/w H2O2, pH 11.5, 60–180 min, 50 °C, 5–15 % w/w BSG) were the pretreatments analyzed.Ozonolysis was not very effective for either the degradation of lignin or the recovery of fermentable sugars in the enzymatic process under the tested operation conditions. Maximum butanol and ABE concentrations, 5.3± 0.2 g butanol/L and 6.8 ± 0.2 g ABE/L, were observed when low moisture content was used (40% w/w).The peroxide alkaline pretreatment was found to be the most effective for BSG, when it was conducted at 5% BSG for 60 min. Under these conditions, sugar enzymatic yields of 62.8% for glucose and 28.1% for xylose and arabinose, referred to untreated BSG, and product concentrations of 11.0± 0.2 g butanol/L and 13.7 ± 0.2 g ABE/L, were achieved. The alkaline pretreatment at 15% BSG with 1% w/w NaOH also provided high butanol and ABE concentrations (7.3 ± 0.1 g butanol/L and 8.9 ± 0.1 g ABE/L).Both the sodium hydroxide alkaline and peroxide alkaline methods were highly successful as pretreatments of BSG for ABE production, with overall yields of 44.4 g butanol/kg BSG and 54.0 g ABE/kg BSG for NaOH pretreatment (15% BSG, 1% w/w NaOH) and 45.1 g butanol/kg BSG and 56.1 g ABE/kg BSG for H2O2 pretreatment (5% BSG, 60 min).

Environmentally friendly extraction of gold from refractory concentrate using a copper – ethylenediamine – thiosulfate solution

The growing environmental concerns associated with the use of cyanides and their toxicity have led to the prohibition of cyanidation-based gold leaching in many countries, necessitating the search for other extraction methods. Herein, we show that thiosulfate leaching presents an alternative green way of gold extraction from S- and As-rich refractory gold concentrates, revealing the importance of oxidative ore pretreatment. Prior to leaching, samples were oxidized by roasting, with the optimum roasting temperature (642 °C) and time (240 min) determined using the response surface method. Subsequently, the roasted residues were subjected to cyanidation, copper – ammonia – thiosulfate system, and copper – ethylenediamine – thiosulfate system treatment. As a result, 18-h cyanidation achieved a gold extraction efficiency of 80.6%, with the consumption of NaCN equaling 1.05 kg/t, whereas the corresponding values for 1.5 h copper – ammonia – thiosulfate treatment equaled 63.0% and 11.3 kg/t. Importantly, 4 h copper – ethylenediamine – thiosulfate system treatment (5 mM copper ion, 10 mM ethylenediamine, 0.1 M thiosulfate, pH = 8–11, liquid-to-solid ratio = 3, stirring speed = 250 rpm) achieved a gold extraction efficiency of 80.3%, with the corresponding thiosulfate consumption equaling only 4.14 kg/t. Thus, copper – ethylenediamine – thiosulfate leaching proved to be an efficient, environmentally friendly, and low-cost method, being well-suited for gold extraction from roasted residues.

Disintegration of biological sludge. A comparison between ozone oxidation and ultrasonic pretreatment

Disintegration of biological sludge. A comparison between ozone oxidation and ultrasonic pretreatment

Real-Time Weighted Data Fusion Algorithm for Temperature Detection Based on Small-Range Sensor Network.

Biological oxidation pretreatment, which can improve the yield of gold, is the main gold extraction technology for disposing refractory gold ore with high arsenic and sulfur. The temperature of the oxidation tank influences the oxidation efficiency between the ore pulp and bacteria, including the yield of gold. Therefore, measurement has consistently been an important subject for researchers. As an effective data processing method, data fusion has been used extensively in many fields of industrial production. However, the interference of equipment or external factors such as the diurnal temperature difference or powerful wind may constantly increase measurement errors and damage certain sensors, which may transmit error data. These problems can be solved by following a pretreatment process. First, we establish a heat transfer mechanism model. Second, we design a small-range sensor network for the pretreatment process and present a layered fusion structure of sharing sensors using a multi-connected fusion structure. Third, we introduce the idea of iterative operation in data processing. In addition, we use prior data for predicting state values twice in order to improve the effectiveness of extended Kalman filtering in one time step. This study also proposes multi-fading factors on the basis of a weighted fading memory index to adjust the prediction error covariance. Finally, the state estimation accuracy of each sensor can be used as a weighting principle for the predictive confidence of each sensor by adding a weighting factor. In this study, the performance of the proposed method is verified by simulation and compared with the traditional single-sensor method. Actual industrial measurement data are processed by the proposed method for the equipment experiment. The performance index of the simulation and the experiment shows that the proposed method has a higher global accuracy than the traditional single-sensor method. Simulation results show that the accuracy of the proposed method has a 55% improvement upon that of the traditional single-sensor method, on average. In the equipment experiment, the accuracy of the industrial measurement improved by 37% when using the proposed method.

Formation of Multiple Microstructures During the Reduction of Ironsand

Ironsand is a type of titanic-ferrous solution ore. As most ironsands come from rapidly cooled lava, raw ironsand particles consist of complicated distributions of elements and a variety of Ti–Fe solid solution phases. In this study, samples of raw and pre-oxidized ironsands were reduced by hydrogen at 900°C for different time intervals. The formation of multiple microstructures of ironsand during the reduction process were investigated. For raw ironsand, a three-layer core structure, an incompletely reduced core structure, and a lump/net structure appeared in order with the reduction procedure. However, for pre-oxidized ironsand, the unit cells of major phases of ironsand shrink, leading to the formation of microcracks during the oxidation pretreatment. These cracks in turn trigger unordered reduction structures, significantly accelerating the reaction kinetics.

Ligand Migration from Cluster to Support: A Crucial Factor for Catalysis by Thiolate-protected Gold Clusters.

Thiolate protected metal clusters are valuable precursors for the design of tailored nanosized catalysts. Their performance can be tuned precisely at atomic level, e. g. by the configuration/type of ligands or by partial/complete removal of the ligand shell through controlled pre‐treatment steps. However, the interaction between the ligand shell and the oxide support, as well as ligand removal by oxidative pre‐treatment, are still poorly understood. Typically, it was assumed that the thiolate ligands are simply converted into SO2, CO2 and H2O. Herein, we report the first detailed observation of sulfur ligand migration from Au to the oxide support upon deposition and oxidative pre‐treatment, employing mainly S K‐edge XANES. Consequently, thiolate ligand migration not only produces clean Au cluster surfaces but also the surrounding oxide support is modified by sulfur‐containing species, with pronounced effects on catalytic properties.

Effect of chemical input during wet air oxidation pretreatment of rice straw in reducing biomass recalcitrance and enhancing cellulose accessibility

The present study was aimed at evaluating the effect of variable sodium carbonate (Na2CO3) loading during wet air oxidation (WAO) pretreatment of rice straw in reducing biomass recalcitrance. The research study was intended to increase the cellulose recovery, hemicellulose solubilization, lignin removal in the solid fraction and limiting the generation of inhibitors in the liquid fraction while reducing the chemical input. The operating condition of 169 °C, 4 bar, 18 min and 6.5 g/L Na2CO3 loading resulted in maximum cellulose recovery of 82.07% and hemicellulose solubilization and lignin removal of 85.43% and 65.42%, respectively, with a total phenolic content of 0.36 g/L in the liquid fraction. The crystallinity index increased from 47.69 to 51.25 along with enzymatic digestibility with an increase in Na2CO3 loading from 0 to 6.5 g/L as a result of removal of barriers for saccharification via effective cleavage of ether and ester bonds cross-linking the carbohydrates and lignin as indicated by FT-IR spectroscopy. A further increase in the Na2CO3 loading to 9.5 g/L did not significantly increase the sugar release. Thus, it was concluded that 6.5 g/L Na2CO3 during WAO is sufficient to increase the delignification and deacetylation, leading to significant changes in apparent cellulose crystallinity inter alia improvement in cellulose accessibility and digestibility of rice straw.

Combined treatment of mezcal vinasses by ozonation and activated sludge.

In Mexico, mezcal production generates huge amounts of vinasses (MV) that cause negative environmental impacts. Thus, MV treatment is necessary before discharge to water bodies. Although there is no information for mezcal vinasses, similar effluents have been treated by biological processes (i.e. anaerobic and aerobic) usually complemented by oxidative chemical pretreatments (ozonation) and physico-chemical methods. In this work MV were first ozonated and followed by batch aerobic biological degradation. In the ozonation stage, organic matter removals were 4.5-11 % as COD, whereas the removal of aromatic compounds and phenols were 16-32 % and 48-83 % respectively. In the aerobic post-treatment, COD depletions up to 85 % were achieved; removals in ozone pre-treated vinasses were higher (80 to 85 %) than that of raw vinasse (69 %). It seems that ozonation preferentially attacked the recalcitrant fraction of organic matter present in the vinasses and increased its aerobic biodegradability.

Investigation on hydroxyapatite coatings formation on titanium surface

This study presents an alternative coating method based on biomimetic approach to grow the hydroxyapatite layers on the titanium surface. In order to increase the bioactivity of the titanium surface the anodization and alkali ÷ thermal oxidation pre-treatments have been applied. Titanium implants were then coated with a hydroxyapatite layer under biomimetic conditions by using a Simulated Body Fluid (SBF) solution. The apatite deposits were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR). The obtained results confirmed that the hydroxyapatite coatings on the titanium surface were obtained.

Study of The Reaction Mechanism to Produce Nanocellulose-Graft-Chitosan Polymer.

Cellulose and chitin are the most abundant polymeric materials in nature, capable of replacing conventional synthetic polymers. From them, cellulose nano/microfibers (CNFs/CMFs) and chitosan are obtained. Both polymers have been used separately in graft copolymerization but there are not many studies on the use of cellulose and chitosan together as copolymers and the reaction mechanism is unknown. In this work, the reaction mechanism to produce nano/microcellulose-graft-chitosan polymer has been studied. Recycled cellulose pulp was used, with and without a 2,2,6,6-tetramethylpiperidin-1-oxyl-radical (TEMPO)-mediated oxidation pretreatment, to produce CNFs and CMFs, respectively. For chitosan, a low-molecular weight product dissolved in an acetic acid solution was prepared. Grafted polymers were synthesized using a microwave digester. Results showed that TEMPO-mediated oxidation as the cellulose pretreatment is a key factor to obtain the grafted polymer CNF-g-CH. A reaction mechanism has been proposed where the amino group of chitosan attacks the carboxylic group of oxidized cellulose, since non-oxidized CMFs do not achieve the desired grafting. 13C NMR spectra, elemental analysis and SEM images validated the proposed mechanism. Finally, CNF-g-CH was used as a promising material to remove water-based inks and dyes from wastewater.

Evaluation of acidification and oxidation of sludge to improve the effect of a starch-based flocculant on the dewaterability of sewage sludge

Conditioning is essential for achieving effective sludge dewatering and easier disposal. In this study, a combined pretreatment of acidification and oxidation using potassium permanganate (KMnO4) as oxidant was conducted to improve the effect of a cationic starch-based flocculant (St-WH) on the dewaterability of sewage sludge. Synergetic dewatering mechanisms by acidification, oxidation, and flocculation are discussed in detail according to the analysis of the changes in bound water content, extracellular polymeric substances (EPS) fractions and components, zeta potentials, floc size, and surface microstructures of sludge cakes in the dewatering process. Acidification and oxidation could destroy the sludge flocs, thereby causing the degradation of EPS and formation of fine particles. Original loosely and tightly bound EPS partially converted to soluble EPS, resulting in release of trapped water, which can be reflected by the significant correlation between loosely bound EPS and filter cake moisture content (FCMC) (Rs = 0.83, P < 0.05). Those fine particles, simultaneously produced, were adverse to filtration efficiency. In addition to enhancing the oxidation effect of KMnO4, acidification treatment could still compress the protein-like materials in soluble EPS due to protonation effect, which was positively related to specific resistance to filtration (SRF) (Rs = 0.74, P < 0.05). The following flocculation using St-WH efficiently aggregated those fine particles and restrained the released EPS to bind with free water through charge neutralization and bridging effects, thereby resulting in improved filtration performance and enhanced removal of bound water (Rs = 0.88, P < 0.01). Response surface methodology was also applied to achieve an optimal condition and evaluate the effects of various environmental factors.

Microwave annealing promoted in-situ electrochemical activation of Ni3S2 nanowires for water electrolysis

Microwave is widely used to synthesize advanced nanomaterials for energy storage and conversion, whereas its applications remain limited in water electrolysis. Herein, we qualitatively explore the house-hold microwave annealing in atmosphere as chemical-free oxidation pretreatment strategy on Ni3S2 nanowires for hydrogen evolution reaction (HER). The microwave can induce fast surface oxidation to form metal hydroxides on catalyst which promotes in-situ electrochemical activation (ISEA) to improve the catalytic performance. The microwave annealing is superior to traditional oxidation such as chemical oxidation or Ar gas annealing. Thanks to faster reaction kinetics, better conductivity and larger electrochemical surface area, the formed NiOx/Ni3S2 hybrids by ISEA achieve 7-time higher activity and operate well for 12 h compared with pristine catalyst. The NiOx/Ni3S2 hybrids also perform well in acid (0.5 M H2SO4) and neutral (1.0 M phosphate buffer solution) media to realize all-pH water electrolysis. Moreover, the microwave annealing is found to be applicable for other transition metals such as cobalt sulfide to obtain higher HER properties. Therefore, such chemical-free modulation concept in our work might be a general access for many advanced materials in other electrocatalysis fields.

Gold recovery from refractory gold concentrates by pressure oxidation pre-treatment and thiosulfate leaching

Gold recovery from refractory gold concentrates by pressure oxidation pre-treatment and thiosulfate leaching

Development and Application of Carbon-Layer-Stabilized, Nitrogen-Doped, Bamboo-Like Carbon Nanotube Catalysts in CO2 Hydrogenation.

Nitrogen‐doped, bamboo‐like carbon nanotubes (BCNTs) were synthesized from butylamine by catalytic chemical vapor deposition (CCVD method). The nanotubes were oxidized by H2SO4/HNO3 treatment and used to prepare calcium alginate gelled BCNT spheres. These beads were first carbonized and then Pd, Rh and Ni nanoparticles were anchored on the surface of the spheres. These systems were then applied as catalysts in CO2 hydrogenation. The BCNT support was examined by Raman spectroscopy, dynamic light scattering (DLS) and X‐ray photoelectron spectroscopy (XPS). The prepared catalysts were characterized by HRTEM and SEM. The oxidation pretreatment of BCNTs was successful, with the electrokinetic potential of the water‐based dispersion of BCNTs measuring −59.9 mV, meaning the nanotube dispersion is stable. Pyridinic and graphitic types of incorporated nitrogen centers were identified in the structure of the nanotubes, according to the XPS measurements. The Pd‐containing BCNT sphere catalyst was the most efficient in the catalytic studies. The highest conversion was reached on the Pd catalyst at 723 K, as well as at 873 K. The difference in the formation rate of CO was much less at 873 K between the Pd and Rh compared to the 723 K values. Accordingly, the application of Pd‐containing BCNT/carbon‐supported catalyst favored the generation of CO. However, the Ni‐BCNT/carbon catalyst leads to the formation of CH4 as the major product.

Optimizing the alkaline oxidation pretreatment of a refractory gold ore using taguchi orthogonal array method

This study investigates the alkaline oxidation pretreatment process of Zarshuran refractory gold ore. Taguchi method-orthogonal array design (OAD) is applied to evaluate and optimize the influence of five main factors including solution pH, aeration rate, agitation speed, temperature, and oxidation time. In order to establish relationship between the gold dissolution rate and influential factors, a linear regression model with R2 of 0.9706 is fitted to experimental data. The results indicated that in the range studied, the agitation speed does not have any significant impact on the gold recovery, while oxidation time and temperature were the most significant factors. Au recovery increased with increasing the aeration rate, pretreatment time, and temperature as well as decreasing the solution pH. Using Taguchi orthogonal array optimization technique (OAOT), the maximum gold recovery was about 96.72%. Also, the optimal conditions were 11 for solution pH, 150 ml min−1 for aeration rate, 240 rpm for agitation rate, 50 °C for temperature, and 24 h for oxidation time.

Combined dilute hydrochloric acid and alkaline wet oxidation pretreatment to improve sugar recovery of corn stover

Two-stage dilute hydrochloric acid (DA)/aqueous ammonia wet oxidation (AWO) pretreatment was used to recover the sugars of corn stover. The morphology characterizations of samples were detected by SEM, BET and SXT. The results showed that DA-AWO process demonstrated a positive effect on sugar recovery compared to AWO-DA. 82.8% of xylan was recovered in the first stage of DA-AWO process at 120 °C for 40 min with 1 wt% HCl. The second stage was performed under relative mild reaction conditions (130 °C, 12.6 wt% ammonium hydroxide, 3.0 MPa O2, 40 min), and 86.1% lignin could be removed. 71.5% of glucan was achieved with a low enzyme dosage (3 FPU·g−1) in the following enzymatic hydrolysis. DA-AWO pretreatment was effective due to its sufficient hydrolysis of hemicellulose in the first stage and remarkably removal of the lignin in the second stage, resulting in high sugar recovery with a low enzyme dosage.

Low-Temperature Restructuring of CeO2-Supported Ru Nanoparticles Determines Selectivity in CO2 Catalytic Reduction

CO2 reduction to higher value products is a promising way to produce fuels and key chemical building blocks while reducing CO2 emissions. The reaction at atmospheric pressure mainly yields CH4 via methanation and CO via the reverse water-gas shift (RWGS) reaction. Describing catalyst features that control the selectivity of these two pathways is important to determine the formation of specific products. At the same time, identification of morphological changes occurring to catalysts under reaction conditions can be crucial to tune their catalytic performance. In this contribution we investigate the dependency of selectivity for CO2 reduction on the size of Ru nanoparticles (NPs) and on support. We find that even at rather low temperatures (210 °C), oxidative pretreatment induces redispersion of Ru NPs supported on CeO2 and leads to a complete switch in the performance of this material from a well-known selective methanation catalyst to an active and selective RWGS catalyst. By utilizing in situ X-ray absorption spectroscopy, we demonstrate that the low-temperature redispersion process occurs via decomposition of the metal oxide phase with size-dependent kinetics, producing stable single-site RuO x/CeO2 species strongly bound to the CeO2 support that are remarkably selective for CO production. These results show that reaction selectivity can be heavily dependent on catalyst structure and that structural changes of the catalyst can occur even at low temperatures and can go unseen in materials with less defined structures.

Fabrication of supported Au-CuOx nanohybrids by reduction-oxidation strategy for efficient oxidative esterification of 5-hydroxymethyl-2-furfural into dimethyl furan-2,5-dicarboxylate

5-Hydroxymethyl-2-furfural (HMF) is a key platform molecule for biomass utilization. The HMF derivative 2,5-furandicarboxylic acid (FDCA) by oxidation of HMF is a promising alternative for terephthalic acid as a monomer in polyethylene terephthalate. However, due to the facile purification of dimethyl furan-2,5-dicarboxylate (DMFD), an oxidative esterification derivative of HMF, is more desirable. In this work, supported Au–Cu bimetallic catalysts with Au–CuOx (x = 0–1) nanohybrids were prepared by a reduction–oxidation pretreatment strategy. The as-prepared catalysts were used for the oxidative esterification of HMF into DMFD under base-free conditions using oxygen as sole oxidant. Activity tests showed that the optimized Au–Cu/γ-Al2O3 catalyst displayed a remarkably high DMFD yield of up to 98% and a turnover frequency (TOF) value of 243 h–1, whereas the monometallic Au and Cu catalysts exhibited poor performance. Various characterizations confirmed the strong interaction between Au nanoparticles and CuOx species, and their synergistic effect on the enhanced performance of HMF oxidative esterification. The reduction–oxidation pretreatment promoted the dispersion of CuOx and intensified the interaction of Au nanoparticles with CuOx. A plausible reaction mechanism for the oxidative esterification of HMF over Au–Cu/γ-Al2O3 was proposed. This work provided new insights into the effect of reduction–oxidation pretreatment on the fabrication of supported Au–CuOx nanohybrids for the production of DMFD by HMF oxidative esterification.

Ligand-Free Nano-Au Catalysts on Nitrogen-Doped Graphene Filter for Continuous Flow Catalysis.

In this study, the authors rationally designed a high-performance catalytic filter for continuous flow catalysis. The catalytic filter consisted of ligand-free nanoscale gold (nano-Au) catalysts and nitrogen-doped graphene (N-rGO). The Au catalyst was fabricated in situ onto a pre-formed N-rGO support by the NaBH4 reduction of the Au precursor, and the size of the nano-Au was fine-tuned. A hydrothermal pretreatment of graphene oxide enriched nitrogen-containing species on the surface of two-dimensional graphene supports and enhanced the affinity of Au precursors onto the support via electrocatalytic attraction. The nano-Au catalysts acted as high-performance catalysts, and the N-rGO acted as ideal filter materials to anchor the catalysts. The catalytic activity of the as-designed catalytic filter was evaluated using 4-nitrophenol (4-NP) hydrogenation as a model catalytic reaction. The catalytic filters demonstrated superior catalytic activity and excellent stability, where a complete 4-nitrophenol conversion was readily achieved via a single pass through the catalytic filter. The as-fabricated catalytic filter outperformed the conventional batch reactors due to evidently improved mass transport. Some key operational parameters impacting the catalytic performance were identified and optimized. A similar catalytic performance was also observed for three 4-nitrophenol spiked real water samples (e.g., surface water, tap water, and industrial dyeing wastewater). The excellent catalytic activity of the nano-Au catalysts combined with the two-dimensional and mechanically stable graphene allowed for the rational design of various continuous flow catalytic membranes for potential industrial applications.