Continuous Steam Explosion Research Articles

Separate hydrolysis and fermentation of softwood bark pretreated with 2-naphthol by steam explosion

Background2-Naphthol, a carbocation scavenger, is known to mitigate lignin condensation during the acidic processing of lignocellulosic biomass, which may benefit downstream processing of the resulting materials. Consequently, various raw materials have demonstrated improved enzymatic saccharification yields for substrates pretreated through autohydrolysis and dilute acid hydrolysis in the presence of 2-naphthol. However, 2-naphthol is toxic to ethanol-producing organisms, which may hinder its potential application. Little is known about the implications of 2-naphthol in combination with the pretreatment of softwood bark during continuous steam explosion in an industrially scalable system.ResultsThe 2-naphthol-pretreated softwood bark was examined through spectroscopic techniques and subjected to separate hydrolysis and fermentation along with a reference excluding the scavenger and a detoxified sample washed with ethanol. The extractions of the pretreated materials with water resulted in a lower aromatic content in the extracts and stronger FTIR signals, possibly related to guaiacyl lignin, in the nonextractable residue when 2-naphthol was used during pretreatment. In addition, cyclohexane/acetone (9:1) extraction revealed the presence of pristine 2-naphthol in the extracts and increased aromatic content of the nonextractable residue detectable by NMR for the scavenger-pretreated materials. Whole-slurry enzymatic saccharification at 12% solids loading revealed that elevated saccharification recoveries after 48 h could not be achieved with the help of the scavenger. Glucose concentrations of 16.9 (reference) and 15.8 g/l (2-naphthol) could be obtained after 48 h of hydrolysis. However, increased inhibition during fermentation of the scavenger-pretreated hydrolysate, indicated by yeast cell growth, was slight and could be entirely overcome by the detoxification stage. The ethanol yields from fermentable sugars after 24 h were 0.45 (reference), 0.45 (2-naphthol), and 0.49 g/g (2-naphthol, detoxified).ConclusionThe carbocation scavenger 2-naphthol did not increase the saccharification yield of softwood bark pretreated in an industrially scalable system for continuous steam explosion. On the other hand, it was shown that the scavenger's inhibitory effects on fermenting microorganisms can be overcome by controlling the pretreatment conditions to avoid cross-inhibition or detoxifying the substrates through ethanol washing. This study underlines the need to jointly optimize all the main processing steps.

Enhanced biobased carbon materials made from softwood bark via a steam explosion preprocessing step for reactive orange 16 dye adsorption

The growing textile industry produces large volumes of hazardous wastewater containing dyes, which stresses the need for cheap, efficient adsorbing technologies. This study investigates a novel preprocessing method for producing activated carbons from abundantly available softwood bark. The preprocessing involved a continuous steam explosion preconditioning step, chemical activation with ZnCl2, pyrolysis at 600 and 800 °C, and washing. The activated carbons were subsequently characterized by SEM, XPS, Raman and FTIR prior to evaluation for their effectiveness in adsorbing reactive orange 16 and two synthetic dyehouse effluents. Results showed that the steam-exploded carbon, pyrolyzed at 600 °C, obtained the highest BET specific surface area (1308 m2/g), the best Langmuir maximum adsorption of reactive orange 16 (218 mg g−1) and synthetic dyehouse effluents (>70 % removal) of the tested carbons. Finally, steam explosion preconditioning could open up new and potentially more sustainable process routes for producing functionalized active carbons.

Multifunctional bamboo-based composites in-situ coated with graphene via continuous steam explosion

Biomass materials like bamboo have received much attention in studies of triboelectric nanogenerators (TENGs) electrode materials because its sustainability, however, it is a major challenge to construct high-quality conductive networks, originating from the agglomeration of conductive fillers and inferior interfacial properties. In this work, the continuous steam explosion in-situ coating technique (CSEICT) was innovatively adopted to fabricate bamboo/graphene/PVA composites (BGP) with an advanced structure of graphene in-situ coated on the surface of bamboo fibers. The BGP-based triboelectric nanogenerator (BGP-TENG) possessed a high output charge density of 155.86 μC/m2, 1.57 times higher compared with that of natural wood. The BGP-TENG was proven to be used as smart floors to harvest human walking energy. Notably, the BGP had extremely high electromagnetic interference (EMI) shielding effectiveness of 51.51 dB, electrical conductivity of 101.86 S/m with ultra-low percolation threshold of 0.06 vol%, and outstanding and stable electro-thermal management capabilities. On this basis, this work can provide a novel strategy for preparing bio-based composites and further expand the multiple functions of bio-based TENGs.

Effect of a promising CSESE pretreatment on the morphological structure and properties of jute fibers

Plant fiber has a complex aggregated structure, high crystallinity and a large number of hydrogen bonds, and has low chemical reaction activity. Therefore, in order to improve the reactivity, the plant fiber needs to be pretreated before chemical modification. Therefore, the pretreatment method has an important influence on the chemical modification of plant fibers. In this paper, Jute fibers were successively treated by particular continuous screw-extrusion steam explosion (CSESE). The effects on the morphological ructure, composition, thermal and crystalline properties of jute fibers before and after treated were investigated. Scanning electron microscopy (SEM) showed that the morphological structure changed significantly after CSESE pretreatment, the diameter was smaller, the surface cracks and the specific surface area increased. There was no new functional groups appeared in fourier transform infrared spectroscopy (FTIR). Composition analysis demonstrated that the content of hemicellulose and extractive decreased, but cellulose and lignin increased. The crystallinity of JSE increased from 66.31 % to 70.19 %. X-ray photoelectron spectroscopy (XPS) suggested that the cellulose and lignin content increased. Thermogravimetric analysis (TGA) demonstrated that the initial decomposition temperature of JSE increased from 334.4 to 355.2°C. DMA indicated that the Tg of JSE reduced from 92.6 to 90.0°C. Therefore, for jute fiber, the CSESE pretreatment is an effective and promising pretreatment method for further chemical modification, biofuels and chemical products.

Sustainable thermoplastic bio-based materials from sisal fibers

Thermoplastic bio-based materials from lignocellulosic fibers are of great importance in a sustainable society. To enhance their preparation to an industrial scale, a facile strategy is proposed that combines continuous steam explosion (CSE) with periodate oxidation/borohydride reduction to modify sisal fibers. In the CSE pretreatment, the aldehyde content of oxidized products was increased by a maximum of ∼17%, and the yield of oxidized/reduced products was increased by a maximum of 25%. Furthermore, the tensile strength of hot-pressed sheets was increased to 42.2 MPa, representing a 175% improvement compared with sheets without CSE pretreatment, and a decreased glass transition temperature of ∼132 °C. Results indicated that CSE pretreatment was favorable for improving the modification efficiency and uniformity of sisal fibers, simultaneously achieving much better mechanical properties and thermoplasticity. Appropriate oxidation level of sisal fibers also achieved the better performances. The combined strategy was facile and scalable, and might significantly impact the widespread preparation and utilization of thermoplastic bio-based materials.

Preparation and Properties of Jute Fiber Long-Chain Fatty Acid Esters in Supercritical Carbon Dioxide.

A two-step method involving continuous screw-extrusion steam explosion (CSESE) pretreatment and esterification in supercritical carbon dioxide (scCO2) is used to prepare long-chain fatty acid-modified jute fiber. The weight gain percentage (WG %) of CSESE-pretreated jute laurate (JL) was 110.7% when esterification was carried out in scCO2 at 14 MPa and 100 °C for 2 h. The corresponding WG % was 105.5% when esterification was instead carried out in pyridine at 100 °C for 2 h. Scanning electron microscopy and X-ray diffraction indicated that CSESE pretreatment enhanced the reactivity of jute fiber, with esterification in scCO2 simultaneously occurring on the fibers surface and internal walls. The glass transition temperature of esterified jute was approximately 119 °C, indicating that it could be hot processed over a wide temperature range. The esterified jute had an oil absorption ratio of 17.01 g/g, so it can be used as an oil absorption material.

Towards sustainable thermoplastic woody materials prepared from continuous steam explosion followed by oxidation-reduction

Converting plant fibers into thermoplastic materials are challenging in a sustainable society. Herein, continuous steam explosion pretreatment was used to improve the reactivity of plant fiber. Meanwhile, periodate oxidation and subsequent sodium borohydride reduction were used to plastify plant fiber. SEM and BET results showed that steam explosion pretreatment can gradually dissociate bundle structure of eucalyptus fiber and increase its specific surface area, which improve the reaction efficiency significantly. The FTIR and NMR indicated that the eucalyptus fiber had been successfully oxidized and reduced. XRD and TGA tests showed that the crystallinity and thermal stability of the modified fibers decreased with the increase of oxidation time. When the oxidation time is 8 h, the mechanical properties of the modified material are optimal, and the glass transition temperature is significantly reduced. These results suggest that this all-component plant fiber material is a possible alternative to petroleum-based materials.

Enhanced properties of poly(vinyl alcohol) composite films filled with microfibrillated cellulose isolated from continuous steam explosion

The objective of this research was to analyze the enhanced properties of poly(vinyl alcohol) composite films reinforced with microfibrillated cellulose obtained from continuous steam-explosion. Irregular and unsmooth external surfaces were observed in PVA/MFC composite films along with the high incorporation of MFC concentration. Voids and aggregates localized in PVA/MFC composite films induced the fractures of the films. Opacity of the obtained films increased with the high inclusion of MFC. However, all the tested composite films had higher transmittance of above 50% at visible wavelength of above 400 nm. Oxygen increased and N decreased with the incorporation of high MFC concentration. Chemical functional groups were changed due to intermolecular linkages between PVA and MFC. PVA/MFC composite films had good thermal stability with higher temperature of melting point and maximum degradation than neat PVA film. PVA matrix reinforced with MFC 5% had the highest tensile strength because of percolation network in the films during intercalation and exfoliation process. PVA/MFC composite films have the potential as food packaging plastics because of these above enhanced properties.

Synthesis of a bioadsorbent from jute cellulose, and application for aqueous Cd (II) removal

A low-cost, high-adsorption-capacity, eco-friendly bioadsorbent for removing Cd2+ from aqueous solution is reported. J-g-P(AM-co-AANa) was prepared by hydrolysis of the grafted copolymer, which was synthesized by free radical polymerization of acrylamide (AM) with jute fibers (JSE) pretreated by continuous screw-extrusion steam explosion. Fourier transform infrared and solid-state 13C nuclear magnetic resonance spectroscopies, confirmed that amino and carboxylate groups were introduced into J-g-P(AM-co-AANa). X-ray diffraction showed that the crystallinity of J-g-P(AM-co-AANa) was significantly lower than that of JSE. The surface morphology of bioadsorbent was investigated by scanning electron microscopy (SEM). The adsorption capacity of Cd2+ on J-g-P(AM-co-AANa) was evaluated for different solution pH values, contact times, and initial Cd2+ concentrations. The adsorption kinetics followed the pseudo-second-order kinetic model, and the rate controlling step was chemisorption. The adsorption isotherm was well fitted by the Freundlich model, and the adsorption process was multilayer adsorption. The maximum adsorption capacity was 344.8 mg/g, which indicated that the bioadsorbent was effective for removing Cd2+ from aqueous solution.

Characteristics and environmentally friendly extraction of cellulose nanofibrils from sugarcane bagasse

This study reports an environmentally friendly process to prepare cellulose nanofibrils (CNFs) from sugarcane bagasse (SCB), by ultrasonication combined with various mechanochemical pretreatments. The pretreatments included continuous steam explosion, dilute alkali-catalyzed (0.4wt% NaOH) hydrothermal treatment, and bleaching with hydrogen peroxide. The morphology and physiochemical properties of the fibers obtained after each stage of treatment were characterized by various techniques. Suspensions of fibers subjected to different pretreatments were prepared by the same mechanical process. The result proved that continuous steam explosion pretreatment could strip the primary wall and the binding materials related to middle lamella, loosen the structure of fiber cell wall, and promote sequent nanofibrillation of the cellulose fibers. Therefore, the total energy consumption is reduced. The current pretreatments effectively removed non-cellulosic constituents of the raw fibers, using very small amount of chemical reagents. Individual CNFs typically had diameters of 20–40nm, high aspect ratios, a fine web-like structure, and good thermal stability.

Production of Microfibrillated Cellulose by Novel Continuous Steam Explosion Assisted Chemo-Mechanical Methods and Its Characterizations

In this study, microfibrillated cellulose (MFC) was successfully isolated with different time treatments of steam explosion, which were combined with chemo-mechanical stages. The objectives of this study were to isolate and characterize MFC obtained from steam explosion—assisted novel chemo-mechanical methods, and to investigate the effects of different steam explosion times on obtained MFC. Characterizations used were SEM, TEM, PSA, GC–MS, EDS, XRD, FTIR, and STA. The result of this study showed an optimal diameter range of MFC samples was between 23.45 and 77.65 nm at 1 h steam explosion time. However, MFC fibers were aggregated until its particle size distribution by number was about 645.83 nm. That lignocellulose MFC comprised C, N, and O with a dramatic decrease of Si. Most of the samples had many transmittance peaks, indicating the presence of cellulose with –OH, –CH2, C–H, and C–O functional groups whereas IR peaks designated to hemicellulose and lignin were almost absent. The presence of n-heptadecanol-1; n-nonadecanol-1; n-nonadecanol; hexadecanoic acid, ethyl ester; ethyl oleate; and octadecanoic acid, ethyl ester was linked with existance of cellulose and cementing agents (hemicellulose and lignin). There was an increase of cellulose crystallinity along with the increase in steam explosion time. Native cellulose or cellulose I was the initial nature of obtained MFC. The decrease of thermal stability of hemicellulose was correlated with acid treatment and acetyl groups, while the increase of cellulose thermal stability was in accordance with the increase of cellulose crystallinity index.

Recovery of pectic hydrocolloids and phenolics from huanglongbing related dropped citrus fruit

Citrus pre-harvest fruit drop, caused by huanglongbing infection, has increased dramatically concomitant with declining tree health and crop harvest size. This loss of harvestable fruit is damaging to both growers and juice processors. Recovering and converting this fruit to alternative value added products would benefit the citrus industry. Therefore, we have explored the potential of using this fruit as a feedstock in our newly developed pilot scale continuous steam explosion process. Whole fruits were converted to steam-exploded biomass using a continuous pilot scale process. The sugar composition of raw fruit and steam-exploded biomass was determined. Recovered pectic hydrocolloids and phenolic compounds were characterized. Pectic hydrocolloids comprised 78 g kg-1 of the dry material in the dropped fruit. Following the steam explosion process almost all of the pectic hydrocolloids were recoverable with a water wash. They could be functionalized in situ or separated from the milieu. Additionally, approximately 40% of the polymethoxylated flavones, 10% of the flavanone glycosides, 85% of the limonoids and almost 100% of hydroxycinnamates were simultaneously recovered. The continuous steam explosion of pre-harvest dropped citrus fruit provides an enhanced, environmentally friendly method for the release and recovery of valuable coproducts from wasted biomass. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Effects of Continuous Steam Explosion on the Microstructure and Properties of Eucalyptus Fibers

Laboratory-designed continuous steam explosion (CSE) equipment was used to prepare continuous steam-exploded eucalyptus fibers (CSEEFs). The pretreatment intensity was varied by changing treatment time, and effects of CSE on the composition, microstructure, surface composition, thermal properties, and crystallinity of CSEEFs were investigated. Composition analysis showed that CSE had a significant impact on lignin and hemicellulose, but little on cellulose. Scanning electron microscopy indicated that the middle lamella, primary wall, and outer secondary wall were progressively stripped as the CSE time increased. X-ray photoelectron spectroscopy demonstrated that concentrations of extractives and lignin were higher on the surface of eucalyptus wood than CSEEFs’, and the exposed carbohydrate fraction increased with increasing CSE time. Differential scanning calorimetry showed that eucalyptus wood has one glass transition (193.5 °C), whereas two glass transitions at 56.7 and 138.5 °C were observed for CSEEF-5. X-ray diffraction results suggested that crystallinity of samples decreased with increasing CSE time. Thermogravimetric analysis showed the pyrolysis peak temperature of samples first increased and then decreased slightly as CSE time increased. These data will be useful for the optimization and application of CSE technology.

Effect of pretreatment severity in continuous steam explosion on enzymatic conversion of wheat straw: Evidence from kinetic analysis of hydrolysis time courses

Focusing on continuous steam explosion, the influence of pretreatment severity due to varied acid loading on hydrolysis of wheat straw by Trichoderma reesei cellulases was investigated based on kinetic evaluation of the saccharification of each pretreated substrate. Using semi-empirical descriptors of the hydrolysis time course, key characteristics of saccharification efficiency were captured in a quantifiable fashion. Not only hydrolysis rates per se, but also the transition point of their bi-phasic decline was crucial for high saccharification degree. After 48h the highest saccharification was achieved for substrate pretreated at relatively low severity (1.2% acid). Higher severity increased enzyme binding to wheat straw, but reduced the specific hydrolysis rates. Higher affinity of the lignocellulosic material for cellulases does not necessarily result in increased saccharification, probably because of lignin modifications occurring at high pretreatment severities. At comparable severity, continuous pretreatment produced a substrate more susceptible to enzymatic hydrolysis than the batch process.

Thermal and Flexural Properties and Water Absorption of Caulis Spatholobi Residue Fiber Reinforced Biodegradable Poly(propylene carbonate) Composites

Abstract This paper investigated and compared the thermal and flexural properties and water absorption of natural caulis spatholobi residue fibers reinforced PPC/CSRF composites. Polypropylene carbonate (PPC) was reinforced by caulis spatholobi residue fibers (CSRF) which had been pretreated by continuous steam explosion. The effect of fiber content (10 to 60 wt%) on the properties and water absorption of PPC/CSRF biodegradable composites was investigated. The thermal properties of PPC/CSRF composites indicated that the addition of CSRF could improve the thermal stability of the composites. The flexural strength and modulus of the composites were found to be improved as the content of fiber increased. From the SEM micrographs, it was found that a small amount of fibers were pulled out on fractured surfaces of the composites, showing good network structure between the fiber and PPC matrix. The water absorption amount of the composites increased with increasing the fiber content. This paper demonstrates that the incorporation of low-cost and biodegradable caulis spatholobi residue fiber into PPC provides a practical way to produce completely biodegradable and cost-competitive composites with good mechanical properties.

Study on Toughening of Chinese Herb Residue Fiber/Recycled ABS Composites

The Chinese herb residue (CHR) fiber obtained by blasting through a continuous steam explosion device, and recycled acrylonitrile-butadiene-styrene (ABS) were blended to prepare reABS/CHR fiber composites by a vane extruder. Three kinds of thermoplastic elastomers: POE, SEBS and TPU were used to toughen composites. The results of toughening effects, mechanical properties and thermal stability properties show that: there were significant effects of these agents on impact strength; the compatibility not only affects toughening result, but also other properties; the best toughening agent for reABS/CHR fiber composites is TPU.

Caulis spatholobi residue fiber reinforced biodegradable poly (propylene carbonate) composites: The effect of fiber content on mechanical and morphological properties

Adding caulis spatholobi residue fiber (CSRF) to reinforce biodegradable poly (propylene carbonate) (PPC) as a reinforcement was investigated. The morphology of CSRF before and after continuous steam explosion, the mechanical and morphological properties of PPC/CSRF bio-composites with different fiber content were investigated using scanning electron microscopy (SEM), mechanical tests and infrared spectroscopy. The tensile strength and modulus, and impact strength of the bio-composites increased as the content of fiber increased in composites, the elongation at break declined. It was found that a small stay-segment in the stress–strain curves and pulled-out fibers on fractured surfaces of the composites. Infrared spectra result showed esterification and formation of hydrogen bonds between the matrix and CSRF. The fractured surface of the composites addressed a promotion of the interfacial interactions. POLYM. COMPOS., 35:208–216, 2014. © 2013 Society of Plastics Engineers

Pilot-scale study on the acid-catalyzed steam explosion of rice straw using a continuous pretreatment system

A continuous acid-catalyzed steam explosion pretreatment process and system to produce cellulosic ethanol was developed at the pilot-scale. The effects of the following parameters on the pretreatment efficiency of rice straw feedstocks were investigated: the acid concentration, the reaction temperature, the residence time, the feedstock size, the explosion pressure and the screw speed. The optimal presteaming horizontal reactor conditions for the pretreatment process are as follows: 1.7rpm and 100–110°C with an acid concentration of 1.3% (w/w). An acid-catalyzed steam explosion is then performed in the vertical reactor at 185°C for 2min. Approximately 73% of the total saccharification yield was obtained after the rice straw was pretreated under optimal conditions and subsequent enzymatic hydrolysis at a combined severity factor of 0.4–0.7. Moreover, good long-term stability and durability of the pretreatment system under continuous operation was observed.

Mechanical Properties of Poly(Butylene Succinate) Reinforced with Continuously Steam-Exploded Cotton Stalk Bast

Poly(butylene succinate) (PBS) was reinforced by cotton stalk bast fibers (CSBF), which had been pretreated by the continuous steam explosion method. The influence of water content in CSBF during the explosion and fiber content on the mechanical properties of CSBF/PBS biocomposites was investigated. The results showed that the incorporation of CSBF decreased the tensile and impact strength, while significantly enhanced the flexural strength, flexural modulus and tensile modulus. The mechanical properties of biocomposites reinforced by exploded fibers were much better than that of the biocomposites reinforced by non-exploded fibers. Biocomposites reinforced by fibers with 40 and 50 wt% water contents during the explosion had the best mechanical properties. The morphology of CSBF and biocomposites was evaluated by SEM, which demonstrated that fibers with 40 and 50 wt% water contents had better separation and rougher microsurfaces, indicating a better adhesion between PBS matrix and fibers.

Continuous seam explosion of wheat straw by high pressure mechanical refining system to produce sugars for bioconversion

This study demonstrated the use of a pressurized mechanical refining system for the continuous steam explosion pretreatment of wheat straw. Wheat straw was first impregnated with either dilute acid (0.5% sulfuric acid) or water and then steam exploded in an Andritz pressurized refiner. The effect of a range of pretreatment conditions, including refining retention time and steam pressure/temperature on the resulting substrate composition and hydrolysability as well as overall sugars yield was investigated. For autohydrolysis, the optimum conditions, 198 oC/6 min gave an enzymatic hydrolysis yield of 93.3% and an overall glucose yield of 85.8%, while 198 oC/4 min gave an enzymatic hydrolysis yield of 88.7% and overall glucose yield of 88.4%. Longer retention time increased the enzymatic hydrolysability but reduced the overall glucose yield owing to the degradation reaction during pretreatment. For acid pretreatment, the most favourable condition for enzymatic hydrolysis and overall glucose yield coincided at 178 oC /6 min.