Conventional Heating Pretreatment Research Articles

An innovative study for pretreatment of high-phosphorus oolitic hematite via high-temperature heating: phase, microstructure, and phosphorus distribution analyses

To investigate the effects of heating pretreatment on the distribution of phosphorus elements, phase transformation, and microstructure evolution mechanisms of high-phosphorus oolitic hematite (HPOH), particularly from the Tindouf regions of Algeria, several analyses, including HSC Chemistry software, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Image-Pro Plus software, specific surface area, pore size distribution (BJH), and N2 adsorption–desorption isotherms. The results show that the conventional heating pretreatment has a significant effect on the phase and microstructure of HPOH. Cracks appeared within mineral phases and around the interphase boundaries owing to the co-promotion of different thermal expansions of minerals and dehydration and chemical reactions via the heating treatment of ore samples. As the pretreatment temperature increased within the studied range, increases in crack perimeter (from 8.062 to 87.236 μm), percentage of crack area (from 0.135 to 7.988 %), and BJH desorption average pore diameter (from 6.1788 to 23.4384 nm) were observed. The specific surface area and pore volume decreased from 23.2054 to 1.0661 m2/g and 0.0237 to 0.0017 cm3/g, respectively. In addition, the distribution of phosphorus did not change or repartition during the heating pretreatment period in the mineral phases.

Heating Pre-Treatment of Copper Ores and Its Effects on the Bond Work Index

Comminution is the stage with the largest energy consumption in the mining process. Therefore, several pre-treatments have been proposed to reduce the energy requirements of this stage. This work analyzed the effect of a heating pre-treatment on the Bond index. A conventional heating pre-treatment was applied to a Chilean copper ore. The ore was heated to temperatures from 300 to 600 °C using a conventional furnace, resulting in a reduction of 19% in the Bond work index. Due to the pre-treatment, the mineral cracked in several areas. Microfracture and composition analyses of these areas confirmed that crack generation in the ore is due to the thermal stress produced by the pre-treatment. The fracture analysis explains the reduction in the Bond work index, since crack generation started at similar temperatures to those at which the reduction in the Bond work index was observed. In addition, the analysis also shows that micro-cracks occur between and through different phases, which may have an impact on mineral liberation. These results also show that, under a moderate high temperature, an important reduction in energy consumption can be obtained.

Thermally Assisted Grinding of Cassiterite Associated with Pollimetallic Ore: A Comparison between Microwave and Conventional Furnaces

We investigated the influence of microwave and conventional heating pretreatments on the grinding of cassiterite associated with pollimetallic ore. The minerals that exhibited a stronger microwave absorption ability crushed first, which is the main difference between the microwave and the traditional heating pretreatments. The distribution of Fe, Pb, Zn, and Sn increased in the fine size range (−0.425 mm). The Fe and Pb grades in the size ranges of −3.2 + 2 mm and −2 + 1 mm after the microwave pretreatment (6 kW, 1 min) were lower than those of the traditional heating (12 kW, 400 °C, 20 min), indicating that the microwave selective heating was beneficial for pyrite and jamesonite. The grade and distribution of Sn decreased significantly in the size ranges of −3.2 + 2 mm and −2 + 1 mm and increased in the size ranges of −0.425 + 0.15 mm and −0.15 + 0.074 mm. Microwave heating treatment promoted the grinding of sulfide ore and reduced the cassiterite overgrinding.

Evaluation of chemical-free microwave pretreatment on methane yield of two grass biomass with contrasted parietal content

As a result of increasing demand for alternatives to fossil energy, the agricultural biogas sector is in expansion and lignocellulosic biomass (LCB) represents an interesting renewable feedstock. Nevertheless, due to the recalcitrance and complexity of its structure, deconstructive pretreatments are necessary to render possible biochemical conversions and efficient biomass exploitation. In this work, chemical-free, mild microwave pretreatment was evaluated (through BMP tests) as a method to improve anaerobic biodegradability of two grass biomass of industrial relevance and contrasted parietal content: corn stalks (low parietal content, high soluble content) and miscanthus (high parietal content, low soluble content). BMP tests carried out on raw biomass before pretreatment highlighted the negative correlation of BMP value to lignin and cellulose contents and the positive correlation to soluble and hemicellulose contents.Efficiency of microwave pretreatment under two conditions, open vessel and high pressure (4 bars), with water as unique solvent was tested for tackling recalcitrance and results were compared to conventional heating pretreatment and a control treatment. Solid and liquid phases were separated after pretreatment with the aim to elucidate if microwave treatment had an impact on organic matter solubilisation and/or on the residual solid phase, which could improve the biodegradability of the pretreated solid fraction. To the authors' knowledge, this is the first study to dissociate methane production of the solid phase from that of the liquid phase after microwave pretreatment.Observed BMP values in mesophilic conditions of raw biomass samples were 286 NLCH4/kgVS for corn stalks and 228 NLCH4/kgVS for miscanthus respectively (in agreement with literature). No significant improvement in BMP value nor in CH4 production kinetics were observed following microwave pretreatment, while a harsh chemical pretreatment (10 h soaking in 10% w/w NaOH) allowed 30% increase in BMP value. These results highlight the significant chemical effect -compared to thermal- on the biomass deconstruction and fibers breakdown during chemical-free microwave pretreatment. A synergy microwave-NaOH effect could allow to achieve higher impact on biomass recalcitrance using lower NaOH amounts than chemical treatment alone.

Thermochemical pretreatments of maize stem for sugar recovery: Comparative evaluation of microwave and conventional heating

Microwave (MW) heating is attracting great attention in biorefinery processes, because of its special dipole rotation heating mechanism. In the current study, MW and conventional heating methods were employed to assist the thermochemical pretreatments (H2O, H2SO4 or NaOH) of maize stem biomass. Their influences on sugar release and biomass compositions during pretreatments were comparably evaluated. Compared to conventional heating pretreatment, MW thermochemical pretreatments are highly efficient in sugar recovery, contributing to 4.3 times higher amount of sugar release (1.25 vs 0.30 μmol/mg biomass) with reaction time 8 times shorter (5 vs 40 min) and selectively producing glucose as the major constituent (0.75 μmol/mg biomass) using 0.2 M H2SO4 as pretreatment media. MW thermochemical pretreatment also effectively removed lignin (up to 91.6 %) within 5 min, which was significantly higher than conventional heating pretreatment (51.2 %). Conventional heating pretreatment successfully removed hemicellulose and converted the crystalline cellulose into amorphous cellulose, which is probably due to its longer heating time. Rapid MW thermochemical pretreatments efficiently fractionated hemicellulose and removed lignin content while keeping the crystalline cellulose structure. MW and conventional heating pretreatments led to similar digestibility of biomass solid residues. Overall, MW thermochemical pretreatment represents an energy efficient alternative strategy, as it consumed 25–34 folds less energy than conventional heating pretreatment for effective biomass fractionation and value-added chemical production.

Evaluation Solvent Level Effect on Sugar Yield during Microwave-Assisted Pretreatment

An efficient pretreatment step is essential to ensure maximum and economical recovery of the fermentable sugar from enzymatic hydrolysis of lignocellulosic biomass. Microwave-assisted pretreatment was found to be a good alternative of conventional heating pretreatment of acid or alkali due to its direct heating of sample which reduce the energy consumption. The present study aims to evaluate the effect of using very diluted solvent (acid and alkali) on monomeric sugar yield during microwave-assisted pretreatment of lignocellulosic biomass (sago palm bark wastes). The changes of the surface structure of untreated and pretreated lignocellulosic biomass were detected using SEM analysis. Three solvents were employed at three concentrations (0.01, 0.05 and 0.1 N). The solvents that utilized in the microwave-assisted pretreatment were sulphuric acid (MA), sodium hydroxide (MH) and sodium bicarbonate (MB) and compared with distilled water (MW). Sago palm bark (SPB) was soaked in these solvents as a substrate at 5% w/v and subjected to microwave power at 800 W in a modified household microwave oven for 5 minutes. Immersing feedstock in distilled water and heating using microwave heating released 5.32 mg/g of monomeric sugar. Highest yield of monomeric sugar was found using 0.1N H2SO4 which yielded 10.28 mg/g during. Applying the pretreatment using the similar concentrations of NaOH and NaHCO3 released 9.35 and 4.31 mg/g of monomeric sugar, respectively. Decreasing chemical solvent level from 0.1 to 0.05 and 0.01 N shows a negative influence on sugar yield for MA and MH pretreatment while MB pretreatment displays a positive effect by extracting some useful components such as xylose.

Efficient sugar production from sugarcane bagasse by microwave assisted acid and alkali pretreatment

Sugarcane bagasse represents one of the best potential feedstocks for the production of second generation bioethanol. The most efficient method to produce fermentable sugars is by enzymatic hydrolysis, assisted by thermochemical pretreatments. Previous research was focused on conventional heating pretreatment and the pretreated biomass residue characteristics. In this work, microwave energy is applied to facilitate sodium hydroxide (NaOH) and sulphuric acid (H2SO4) pretreatments on sugarcane bagasse and the efficiency of sugar production was evaluated on the soluble sugars released during pretreatment. The results show that microwave assisted pretreatment was more efficient than conventional heating pretreatment and it gave rise to 4 times higher reducing sugar release by using 5.7 times less pretreatment time. It is highlighted that enrichment of xylose and glucose can be tuned by changing pretreatment media (NaOH/H2SO4) and holding time. SEM study shows significant delignification effect of NaOH pretreatment, suggesting a possible improved enzymatic hydrolysis process. However, severe acid conditions should be avoided (long holding time or high acid concentration) under microwave heating conditions. It led to biomass carbonization, reducing sugar production and forming ‘humins’. Overall, in comparison with conventional pretreatment, microwave assisted pretreatment removed significant amount of hemicellulose and lignin and led to high amount of sugar production during pretreatment process, suggesting microwave heating pretreatment is an effective and efficient pretreatment method.

Conventional heating vs. microwave sludge pretreatment comparison under identical heating/cooling profiles for thermophilic advanced anaerobic digestion

This research evaluates whether there is any advantage of selecting one of the thermal methods of sludge pretreatment, conventional heating (CH) and microwave hydrolysis (MW), over another to enhance municipal sludge disintegration and performance of thermophilic anaerobic digestion (AD). For this purpose, a custom-built CH system simulating MW hydrolysis under identical heating and cooling profiles was used. The effects of three main pretreatment parameters including pretreatment method (CH and MW), heating ramp rate (3, 6 and 11°C/min) and final temperature (80, 120 and 160°C) on sludge solubilization and performance of thermophilic batch AD were evaluated. The effects of CH and MW hydrolysis were observed to be similar for sludge disintegration and digester performance (p-value>0.05), while the effects of final temperature and heating ramp rate were proven to be different (p-value<0.05). According to the results, it is essential to apply MW and CH pretreatments under identical experimental condition for an unbiased comparison which supports the findings of the author’s earlier study under mesophilic condition. Failing to address this issue explains the significant inconsistency observed among the findings of the previous CH vs. MW comparison studies that were unable to implement identical thermal profiles (between CH and MW) during sludge pretreatment. In comparison with mesophilic AD, thermophilic AD revealed lower biodegradation rate constant at the highest pretreatment temperature tested (160°C), suggesting its higher sensitivity to the inhibitory effects of thermal pretreatment at the elevated temperatures.

Microwave assisted chemical pretreatment of Miscanthus under different temperature regimes

Miscanthus is a major bioenergy crop in Europe and a potential feedstock for second generation biofuels. The most efficient and realistic method to produce fermentable sugars from lignocellulosic biomass is by enzymatic hydrolysis, assisted by thermo-chemical pretreatment. Recently, microwave technology has drawn growing attention, because of its unique effects and performance on biomass. In this work, microwave energy was applied to facilitate NaOH and H2SO4 pretreatment for Miscanthus under different temperatures (130–200 °C) for 20 min. The yields of reducing sugars from Miscanthus during the pretreatment process increased up to 180 °C and then declined with increasing temperature. Out results here showed a remarkable sugar yield from available carbohydrate (73 %) at the temperature of 180 °C by using 0.2 M H2SO4. In comparison with conventional heating pretreatment studied at same temperature with same biomass material, the reducing sugar release in this study was 17 times higher within half the time. It was highlighted that the major sugar component could be tuned by changing pretreatment temperature or pretreatment media. Optimally, the glucose and xylose yield from available carbohydrate are 47 and 22 % by using 0.2 M H2SO4 and NaOH respectively when temperature was 180 °C. The digestibility of pretreated Miscanthus was 10 times higher than that of untreated biomass. 68–86 % of the lignin content was removed from biomass by 0.2 M NaOH. Simultaneous saccharification fermentation (SSF) results showed an ethanol production of 143–152 mg/g biomass by using H2SO4/NaOH microwave assisted pretreatment, which is 7 times higher than that of untreated Miscanthus. Biomass morphology was studied by SEM, showing temperature has a strong influence on lignin removal process, as different lignin deposits were observed. At the temperature of 180 °C, NaOH pretreated biomass presented highly exposed fibres, which is a very important biomass characteristic for improved enzymatic hydrolysis. Compared to conventional pretreatment, microwave assisted pretreatment is more energy efficient and faster, due to its unique heating mechanism leading to direct interaction between the polar part of biomass and electromagnetic field. The results of this work present promising potential for using microwave to assist biomass thermo-chemical pretreatment.

Thermally assisted liberation of high phosphorus oolitic iron ore: A comparison between microwave and conventional furnaces

This paper aims to investigate the effects of microwave, and conventional heating pretreatment on the liberation of iron bearing minerals from high phosphorus oolitic iron ore, specifically iron ore from the Aswan region of Egypt. These effects were analyzed by examining intergranular fractures generated between the oolitic/matrix and in the oolitic layers. Grindability and energy consumption were also measured after both microwave and conventional heating pretreatments.Scanning electron microscope (SEM) photomicrographs indicated that intergranular fractures are formed between the gangues (fluoroapatite and chamosite) and hematite after microwave treatment (resulting in improved liberation of the iron ore) while only a small number of micro-cracks were observed between the oolitic/matrix and in the oolitic layers after conventional heating of iron ore. Grindability tests indicated that microwave treated iron ore could be more easily ground compared with iron ore treated in a conventional furnace. This improved grindability is attributable to the large amount of intergranular fractures which are formed on the oolitic iron ore after treatment with microwave radiation. Energy consumption measurements also revealed that microwave treatment consumes much smaller quantities of energy compared with conventional heating ovens.

Low temperature microwave and conventional heating pre-treatments to improve sludge anaerobic biodegradability

This paper presents the results of lab-scale experiments on low temperature thermal pre-treatment (less than 100 °C) prior to anaerobic digestion of sewage sludge. Two heating ways, microwave heating (MH) and conventional heating (CH), and two types of sludge, primary and waste activated sludge, were compared under the same experimental conditions. The degree of solubilisation produced by MH and CH up to 72, 82 and 93 °C was firstly estimated. For both types of heating, increase in soluble chemical oxygen demand (COD) caused by the pre-treatment was about 14% on waste activated sludge and only 3% on primary sludge. The final temperature of 72 °C resulted as the most cost-effective in terms of additional soluble COD per unit of energy required. Subsequently, five series of biochemical methane potential mesophilic assays were run in 120 mL serum bottles on sludge samples pre-treated at 72 °C. When compared with control reaction vessels, no significant differences were noticed in net methane production of pre-treated primary sludge, whereas a relevant increase occurred regarding the pre-treated waste activated sludge. It was also observed that the trend of methane content in biogas during the batch tests can be described by a second order polynomial.

Effects of Microwave Irradiation Pre-Treatment of Egg White Proteins on Ant Oxidative Activity of Their Hydrolysates Prepared with Pepsin

The effects of Conventional Heating (CH) and Microwave Irradiation (MWI) pre-treatment of Egg White Proteins (EWPs) on antioxidative activity of their hydrolysates prepared with pepsin were investigated. MWI pre- treatment of EWPs resulted in a higher degree of hydrolysis (DH) and the highest hydroxyl radical scavenging activity (40.67±1.30%), superoxide anion scavenging activity (75.53±2.79%), inhibitory activity of tea oil autoxidation (67.68±2.50%) and reducing power (0.34±0.01) of Egg White Proteins Hydrolysates (EWPHs) in comparison with CH pre-treatment, although there was no significant difference in DPPH radical scavenging activity between the EWPHs originated from the proteins pre-treated by CH and MWI (p>0.05). According to the experimental results, MWI pre-treatment could improve the antioxidant activities of EWPHs compared with CH treatment.

Mechanisms of microwave irradiation pretreatment for enhancing anaerobic digestion of cattail by rumen microorganisms

In this study, the mechanisms of anaerobic digestibility of cattail improved by microwave irradiation pretreatment were explored. Both Box–Behnken design and response surface methodology (RSM) were used to optimize the microwave irradiation pretreatment with regard to chemical oxygen demand equivalent of the products formed in the anaerobic digestion. The optimum products obtained was as follows: substrate loading of 17.0gvolatile solids/L, microwave intensity of 500W, and irradiation time of 14.0min. The product formation rate increased by 32% and product yield by 19% after microwave irradiation pretreatment at 100°C, as compared with the conventional water-heating pretreatment under the same conditions. The X-ray diffraction (XRD) analysis showed that the crystallinity index of cattail was reduced by 9.4% with the microwave irradiation, compared with the conventional heating pretreatment. The atomic force microscope analysis further confirmed that the recalcitrant structure of wax and lignin covering on the cattail surface was disrupted by microwave irradiation. These results demonstrate that the breakdown of the crystalline and physical structure of cattail caused by microwave irradiation pretreatment improved its anaerobic digestibility.

A Feasibility Study on a Continuous-flow-type Microwave Pretreatment System for Bioethanol Production from Woody Biomass

Efficient pretreatment prior to enzymatic saccharification process is essential for profitable bioethanol production from woody biomass. Microwave pretreatment is expected as an efficient and energy-cost-saving method to enhance enzymatic susceptibility. The objective of the present study is to develop an efficient, high-volume, and continuous microwave pretreatment system toward commercially-based bioethanol production. As a feasibility study, we developed prototypes of a continuous-flow-type microwave pretreatment system for bioethanol production from woody biomass. A unit of the microwave irradiation sections of a continuous-flow-type microwave pretreatment system was designed with a 3D electromagnetic simulator. Prototype experiments and quantitative estimation of energy balance were also conducted. Microwave pretreatment provided 45.9% of the total saccharide yield woody biomass weight by electric consumption of 552 kJ; whereas conventional heating pretreatment provides 43.6 % of the total saccharide yield by 498 kJ, when the mixture was composed of 70 g of woody biomass (Japanese cedar sapwood chips) and 770 g of solvents (ethylene glycol : phosphoric acid = 95 : 5). We estimated 14.8g of bioethanol and 439 kJ of bioethanol energy could be produced by the prototype microwave pretreatment. Although heat dissipation from the metal pipe to the air and the ratio of solvents to woody biomass are immediate problems, microwave is a future potential energy-saving pretreatment method without loss of the saccharide yield.

Alkali (NaOH) Pretreatment of Switchgrass by Radio Frequency-based Dielectric Heating

Radio-frequency (RF)-based dielectric heating was used in the alkali (NaOH) pretreatment of switchgrass to enhance its enzymatic digestibility. Due to the unique features of RF heating (i.e., volumetric heat transfer, deep heat penetration of the samples, etc.), switchgrass could be treated on a large scale, high solid content, and uniform temperature profile. At 20% solid content, RF-assisted alkali pretreatment (at 0.1 g NaOH/g biomass loading and 90 degrees C) resulted in a higher xylose yield than the conventional heating pretreatment. The enzymatic hydrolysis of RF-treated solids led to a higher glucose yield than the corresponding value obtained from conventional heating treatment. When the solid content exceeded 25%, conventional heating could not handle this high-solid sample due to the loss of fluidity, poor mixing, and heating transfer of the samples. As a result, there was a significantly lower sugar yield, but the sugar yield of the RF-based pretreatment process was still maintained at high levels. Furthermore, the optimal particle size and alkali loading in the RF pretreatment was determined as 0.25-0.50 mm and 0.25 g NaOH/g biomass, respectively. At alkali loading of 0.20-0.25 g NaOH/g biomass, heating temperature of 90(o)C, and solid content of 20%, the glucose, xylose, and total sugar yield from the combined RF pretreatment and the enzymatic hydrolysis were 25.3, 21.2, and 46.5 g/g biomass, respectively.