Steam Pretreatment Research Articles

Effect of Different Types of Thermochemical Pretreatment on the Enzymatic Hydrolysis and the Composition of Hazelnut Shells

Hazelnut shells were pretreated with acid (1% H2SO4), alkali (2.25% NaOH) and steam at different temperatures (120, 150 and 200 °C) and pretreatment times (15, 30 and 60 min). The pretreated hazelnut shells were subjected to enzymatic hydrolysis with a mixture of cellulase (60 FPU/g dry biomass) and β-glucosidase (40 CBU/g dry biomass). Compared with acid and steam pretreatment, 2.25% NaOH pretreatment provided highest lignin removal (73.28%) at 200 °C for 60 min. Almost 60% cellulose and 100% of hemicellulose solubilized after pretreatment of hazelnut shells with 1% H2SO4 at 200 °C. Cellulose recovery was highest in the biomass pretreated with steam (76.25% at 200 °C, 60 min). The highest glucose recovery (58.66%) was achieved at 150 °C for 60 min pretreatment time in the alkali pretreated shells. The pretreatment energy efficiencies (ηpretreatment) were 4.75, 4.98, 1.53 g glucose/MJ for acid, alkali and steam pretreatments, respectively. This study demonstrated that NaOH pretreatment of hazelnut shells is superior to both acid and steam pretreatments in terms of glucose recovery and energy efficiency.

The effect of blending spruce and poplar on acid-catalyzed steam pretreatment and enzymatic hydrolysis

The aim of this work was to explore the possibility of mixed feedstocks utilization using acid-catalyzed steam pretreatment in the context of forest biomass. Three steam pretreatment conditions were applied to characterize the interactions between spruce (softwood) and poplar (hardwood) that were concurrently processed by SO2-catalyzed steam pretreatment and enzymatic hydrolysis. The effects of blending feedstocks were evaluated in terms of composition and enzymatic digestibility. The combined sugar yields after steam pretreatment and enzymatic hydrolysis ranged from 58% to 71%. No synergistic or antagonistic interactions were observed in the concurrent use of spruce and poplar—our linear interpolation model accurately predicted the overall sugar recovery after steam pretreatment and enzymatic hydrolysis for a 50:50 blend to within 3%, based on the results of the individual feedstocks.

Effects of saturated steam pretreatment on the drying quality of moso bamboo culms

Bamboo (Phyllostachys heterocycla f. pubescens) culms were pretreated by the saturated steam with the temperature of 140, 160, and 180 °C and subsequently dried by the kiln drying method. Results indicated that steam pretreatment has a significantly positive effect on the drying quality of the bamboo culms. The steam treatments with a temperature of 160–180 °C and duration of 25–15 min are suggested for the rapid drying of bamboo culms.

Physical and Mechanical Properties of Binderless Particleboard Made from Steam-Pretreated Oil Palm Trunk Particles

Formaldehyde emissions from conventional particleboards raise issues of health and safety. One of the potential solutions is binderless particleboards made without using synthetic adhesives. However, the physical and mechanical properties of untreated binderless particleboards are relatively poor compared to conventional particleboards. This research aims to reveal the potential of using steam pretreatment to improve binderless particleboard properties made from oil palm trunk. The oil palm trunk particles were treated with steam pretreatment for different durations of time (20, 40, 60 min). The chemical constituents of the treated and untreated particles were evaluated. The binderless particleboards were made from treated and untreated particles. In addition, panels using untreated oil palm trunk particles with 10% urea–formaldehyde resin were made and used as a comparison. The boards were evaluated according to European Standards. The results indicated that the hemicellulose and starch content gradually reduced with the progression of steam pretreatment. The physical and mechanical properties were improved by increasing steam pretreatment duration. The steam pretreatment was able to improve the properties of binderless particleboards made from oil palm trunk. However, the performance of steam-pretreated binderless particleboard in this study is not compatible with the particleboards made using 10% urea–formaldehyde.

Effect of Asparaginase Enzyme in the Reduction of Asparagine in Green Coffee

Coffee is the most consumed beverage in the world, especially in Nordic countries. Its composition has substances considered to have high value for human health, such as chlorogenic and phenolic acids. However, the roasting of coffee can form substances such as acrylamide that are considered toxic and carcinogenic, depending on the time and the heat of roasting. However, there are some ways of reducing acrylamide formation during the processing of coffee beans. The reduction of its precursor asparagine is one of these ways. This can be achieved by the treatment of beans with the enzyme asparaginase. This study aimed to test the effectiveness of applying asparaginase (Acrylaway™) and evaluate the reduction of the amount of asparagine in Coffea arabica and C. canephora beans. The results showed the effectiveness of the enzyme in the reduction of free asparagine in green coffee beans of both species (C. arabica and C. canephora). Steam pretreatment was effective for the two species but required different times (30 min for C. arabica and 45 min for C. canephora). This can be attributed to the different chemical compositions found in the two species.

Microwave and steam mediated alkaline pretreatments of sweet sorghum bagasse: Study of the energy efficiency

The effects of microwave and steam mediated pretreatments were evaluated and compared relative to the hydrolysis of sweet sorghum bagasse (SSB) in the presence of sodium hydroxide. The results established the optimum parameters for energy consumption and sugar production after hydrolysis of the pretreated SSB. The energy balance was better in microwave treatment compared with the steam treatment. The results recommended pretreatment at 300 watts power setting in the microwave oven up to 10 min. At higher wattage setting and longer exposure time, increased sugar yields were obtained, although the efficiency of the process decreased when the energy balance was calculated. The energy balance was calculated as the proportion of energy consumed during the pretreatments to the energy that can be produced by fermenting released glucose to ethanol. In this study, the energy consumed during the different pretreatments varied from 1/33 to 1/200 of the energy obtainable by fermenting released glucose to ethanol. Overall, the pretreatment of SSB to produce fermentable sugars was effective, and the energy balance was positive both in microwave and steam pretreatments of alkaline suspension of SSB. In microwave treatment the energy applied can be more accurately dosed, and consequently the energy balance was improved compared to steam treatment.

Optimization of dilute sulfuric acid, aqueous ammonia, and steam explosion as the pretreatments steps for distillers’ dried grains with solubles as a potential fermentation feedstock

Distillers’ dried grains with solubles (DDGS) is the by-product of bioethanol production from starch-rich grains through dry-mill fermentation. In this study, dilute sulfuric acid hydrolysis, aqueous ammonia, and steam explosion as the pre-treatment methods were optimized. The central composite response surface methodology (RSM) design was used for optimization of dilute acid pretreatment, aqueous ammonia pretreatment. The steam explosion trials were evaluated. The results show that the dilute acid pretreatment at 121 °C is the most effective way of obtaining simple fermentable sugars (0.382 g/g DDGS). The levels of furfural and HMF was also 5.2 mg/g DDGS) and 1.6 mg/g DDGS, respectively, in the dilute sulfuric acid pretreated DDGS. On the other hand, maximum sugar yield for ammonia pretreatment was 0.129 g/g DDGS and 0.055 g/g DDGS for the steam pretreatment, while no significant amounts of furfural and HMF were observed for these two pretreatment methods.

Effect of Steam Pre-treatment of Bagasse as Fiber Reinforcement SCG Composite

Steam pre-treatment has been examined to sugarcane bagasse fibers (BF). Steam pressure plays an important role in the fibrillation process that is capable in dissolving fibers up to micron scale. Values of fiber diameter with steam pre-treatment (BFP) significantly decreased by 57%. Decrease of the size of fiber can increase the active area of bonding interaction between the fiber surface and the composite matrix. The investigation resulted in mechanical characteristics of unsaturated polyester composite matrix (UP) containing a filler of spent coffee grounds (SCG).When compared between UP-SCG-BF composites to UP-SCG-BF8, it has an increase in tensile strength and flexural strength by 53.57% respectively.

Effect of Pretreatment Methods on the Moisture State and Drying Quality of Balsam Pear (Momordica charantia L.) Slices Using a Microwave Vibratory Fluidized Bed

Abstract In order to improve the uniformity of microwave absorption and obtain good drying quality, a vibratory fluidized bed was used during the microwave drying of balsam pear slices. The temperature distribution of the materials during drying is discussed. The water state and drying quality of the balsam pear slices with blanching, ultrasonic, and superheated steam pretreatment were measured using low-field nuclear magnetic resonance and scanning electron microscopy. As a result, the drying uniformity of balsam pear slices was improved, and the drying temperature decreased more than 10 °C using the microwave vibratory fluidized bed. By using an ultrasonic pretreatment step, the activity of the water molecules was improved, and the drying time was reduced by 10 min, but the product was discolored during drying. Blanching and superheated steam pretreatment did not improve the activity of water molecules, but the product color changes were minimal and drying time was reduced by 20 min. The microstructure of dehydrated balsam pear slices was destructed seriously caused by this heat–moist pretreatment. Therefore, a variety of pretreatments should be integrated for the comprehensive control of the processing characteristics, such as enzyme deactivation and improving water activity, to further improve the drying efficiency and quality of balsam pear slices.

Technologies for Lignocellulose Pretreatment to Produce Fuel Ethanol

Bioethanol is one of the alternatives to fossil fuels. Bioethanol production from lignocellulose has advantages on source richness, but it has poor performance on the conversion yield. In order to destroy the structure of lignocellulose and promote the cellulose and other components release, lignocellulose treatment was necessarily prior to bioethanol fermentation. In this paper, eight methods for lignocellulose pretreatment were reviewed, including physical method, dilute acid pretreatment method, dilute alkali pretreatment method, steam pretreatment method, ammonia pretreatment methods, organic solvent pretreatment method, ionic liquid pretreatment method and biological pretreatment, and those principles and novel progresses were briefly introduced.

Bioethanol Production from Musambi Peel by Acid Catalyzed Steam Pretreatment and Enzymatic Saccharification: Optimization of Delignification Using Taguchi Design

Citrus waste is an attractive feedstock for second generation bioethanol due to its richness in carbohydrates. For the production of bioethanol, removal of lignin through pretreatment to liberate more cellulose with minimal loss is essential. In the present work, the removal of lignin from musambi (Citrus limetta) peel by acid-catalyzed steam pretreatment and the characterization of musambi peel before and after pretreatment was studied. A Taguchi design was used to optimize solid loading, sulphuric acid concentration and time, for steam pretreatment with delignification as the response. The optimum conditions of process variables were 17% (w/v) for solid loading, 0.25% (v/v) for acid concentration with a time of exposure of 60 min with maximum delignification of 65%. The decrease in peak intensity in FTIR spectra and increase in the crystallinity index of pretreated peel indicated the reduction in pectin, hemicellulose, and lignin. The scanning electron micrographs of pretreated peel clearly showed the delignified microfibrils of cellulose. Enzymatic saccharification of pretreated musambi peel and the effect of peel loading, temperature, time, pH and the loading of cellulase, beta-glucosidase, and pectinase on reducing sugar were also investigated. The maximum reducing sugar obtained after the enzymatic hydrolysis was 386 mg/g for steam pretreated musambi peel at the optimum conditions whereas it was only 258 mg/g for the raw musambi peel. Thus, steam pretreatment of musambi peel resulted in better hydrolysis than untreated musambi peel. The yield of bioethanol production at the end of 48 h of fermentation was 85.97%.

Sequential fractionation of the lignocellulosic components in hardwood based on steam explosion and hydrotropic extraction

BackgroundThe forest biorefinery plays an important part in the evolving circular bioeconomy due to its capacity to produce a portfolio of bio-based and sustainable fuels, chemicals, and materials. To tap into its true potential, more efficient and environmentally benign methods are needed to fractionate woody biomass into its main components (cellulose, hemicellulose, and lignin) without reducing their potential for valorization. This work presents a sequential fractionation method for hardwood based on steam pretreatment (STEX) and hydrotropic extraction (HEX) with sodium xylene sulfonate. By prehydrolyzing the hemicellulose (STEX) and subsequently extract the lignin from the cellulose fraction (HEX), the major wood components can be recovered in separate process streams and be further valorized.ResultsUsing autocatalyzed STEX and HEX, hemicellulose (> 70%) and lignin (~ 50%) were successfully fractionated and recovered in separate liquid streams and cellulose preserved (99%) and enriched (~ twofold) in the retained solids. Investigation of pretreatment conditions during HEX showed only incremental effects of temperature (150–190 °C) and hold-up time (2–8 h) variations on the fractionation efficiency. The hydrolyzability of the cellulose-rich solids was analyzed and showed higher cellulose conversion when treated with the combined process (47%) than with HEX alone (29%), but was inferior to STEX alone (75%). Protein adsorption and surface structure analysis suggested decreased accessibility due to the collapse of the fibrillose cellulose structure and an increasingly hydrophobic lignin as potential reasons.ConclusionThis work shows the potential of sequential STEX and HEX to fractionate and isolate cellulose, hemicellulose, and a sulfur-free lignin in separate product streams, in an efficient, sustainable, and scalable process.

Anthocyanin profile, color and antioxidant activity of blueberry (Vaccinium ashei) juice as affected by thermal pretreatment

ABSTRACT The effects of hot water bath and steam pretreatments were investigated, considering color, anthocyanin profile and antioxidant activity of blueberry (Vaccinium ashei) juice. The juice maximum total phenolic content, anthocyanin, and antioxidant activity were observed using the steam pretreatment processing method. Eleven anthocyanins were isolated from the blueberry juice of steam treatment processing, while only 10 from the hot water bath and 8 from the control sample. After storage at 40°C for 10 days, the anthocyanin retention rate of the juice from steam treatment processing was higher than in that from hot water bath and control sample (30.71%, 23.77%, and 19.91%, respectively). The antioxidant capacity was also significantly higher and the hue angle (H°) was lower in the juice from steam pretreatment processing. Steam pretreatment process could prevent color deterioration, increase variety and content of anthocyanins, and improve antioxidant activity in the blueberry juice.

Utilisation of superheated steam in oil palm biomass pretreatment process for reduced chemical use and enhanced cellulose nanofibre production

In this study, superheated steam (SHS) pretreatment was used as a green approach to partially remove hemicellulose from oil palm mesocarp fibre (OPMF). OPMF was treated with SHS at 260°C for 30 min prior to delignification by NaClO2 to obtain mainly cellulose fibre. Hemicellulose removal by KOH was conducted as a control experiment. Both SHS- and KOH-treated OPMF were later nanofibrillated using a wet disk mill (WDM). The characteristics of CNF produced were analysed in terms of morphological, crystallinity and thermal properties. Based on the chemical compositional analysis, SHS-treated OPMF had residual hemicellulose content of 11% (w/w), and there was no hemicellulose residue in KOH-treated OPMF. The presence of hemicellulose in SHS-treated OPMF was later found to enhance CNF formation during WDM process, whereby it was shown that nanofibrillation of SHS-pretreated OPMF occurred as early as 6th cycle, compared to KOH-pretreated OPMF (8th cycle). This observation could be explained by the presence of hemicellulose which prevented hornification of the cellulose microfibrils during milling process. This finding is significant as not only can the use of chemicals be reduced during pretreatment step, but the use of SHS pretreatment contributed greatly to the productivity of the CNF.

Comparison of SHF and SSF Processes under Fed Batch Mode on Ethanol Production from Pretreated Vegetable Processing Residues

Vegetable wastes containing high starch in contrast to lignocellulosic biomass cause environmental threat due to non-judicious disposal and have not been exploited for bioethanol production. The ethanol production from steam or dilute sulphuric acid (DSA) pretreated residues was compared under fed-batch Separate Hydrolysis and Fermentation (F-SHF) or Simultaneous Saccharification and fermentation (F-SSF). The volumetric ethanol productivity, ethanol yields and ethanol contents (g/L) were higher from DSA than steam pretreatment in F-SHF, while latter two did not differ significantly between the pretreatments under F-SSF mode. High RS utilization was observed towards the last phase (72-120 h) in steam pretreatment under F-SSF. Fermented broth from F-SSF had higher levels of inhibitors such as phenolics, furfural and Hydroxymethyl furfural compared to F-SHF and also in the DSA pretreatment. A comparison of the ethanol production from the processes vis-a-vis enzyme and yeast feeding and pretreatment conditions, overall processing time etc. showed that F-SSF had higher requirement of enzymes and yeast than F-SHF. Possibility to curtail fermentation at 24 h under F-SHF mode due to very low ethanol production after 24 h equated the processing time under the two modes to 120 h and this made F-SHF the most advantageous process for the selected residues.

Improvement of the yield and flavour quality of sesame oil from aqueous extraction process by moisture conditioning before roasting

SummaryThis study was to investigate the effect of conditioning and heat‐treatments on the yield and quality of sesame oil. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) were used to explore the microstructure of sesame cotyledon cells. It was found that cell microstructure and oil body membrane of sesame seeds underwent high‐pressure steaming pretreatment (HPS), roasting pretreatment (RP), moisture‐conditioning plus roasting pretreatment (MRP) was all damaged. All these thermal treatments, especially MRP, contributing to increased oil yield from 45.85 (untreated) to 91.69%. Furthermore, RP or MRP yielded a higher content of sesamol than untreated sesame, whereas sesamin and seasamolin content, fatty acid composition, acid value and peroxide value showed no significant changes (P > 0.05) between heat‐treatments. MRP increased the type and content of volatile compounds, which was beneficial to the strong nut‐like aroma. Additionally, MRP had a positive effect on oxidative oil stability (induction time of 10.80 h) with respect to untreated oil (7.82 h).

Reduced use of phosphorus and water in sequential dark fermentation and anaerobic digestion of wheat straw and the application of ensiled steam-pretreated lucerne as a macronutrient provider in anaerobic digestion

BackgroundCurrent EU directives demand increased use of renewable fuels in the transportation sector but restrict governmental support for production of biofuels produced from crops. The use of intercropped lucerne and wheat may comply with the directives. In the current study, the combination of ensiled lucerne (Medicago sativa L.) and wheat straw as substrate for hydrogen and methane production was investigated. Steam-pretreated and enzymatically hydrolysed wheat straw [WSH, 76% of total chemical oxygen demand (COD)] and ensiled lucerne (LH, 24% of total COD) were used for sequential hydrogen production through dark fermentation and methane production through anaerobic digestion and directly for anaerobic digestion. Synthetic co-cultures of extreme thermophilic Caldicellulosiruptor species adapted to elevated osmolalities were used for dark fermentation.ResultsBased on 6 tested steam pretreatment conditions, 5 min at 200 °C was chosen for the ensiled lucerne. The same conditions as applied for wheat straw (10 min at 200 °C with 1% acetic acid) would give similar sugar yields. Volumetric hydrogen productivities of 6.7 and 4.3 mmol/L/h and hydrogen yields of 1.9 and 1.8 mol/mol hexose were observed using WSH and the combination of WSH and LH, respectively, which were relatively low compared to those of the wild-type strains. The combinations of WSH plus LH and the effluent from dark fermentation of WSH plus LH were efficiently converted to methane in anaerobic digestion with COD removal of 85–89% at organic loading rates of COD 5.4 and 8.5 g/L/day, respectively, in UASB reactors. The nutrients in the combined hydrolysates could support this conversion.ConclusionsThis study demonstrates the possibility of reducing the water addition to WSH by 26% and the phosphorus addition by 80% in dark fermentation with Caldicellulosiruptor species, compared to previous reports. WSH and combined WSH and LH were well tolerated by osmotolerant co-cultures. The yield was not significantly different when using defined media or hydrolysates with the same concentrations of sugars. However, the sugar concentration was negatively correlated with the hydrogen yield when comparing the results to previous reports. Hydrolysates and effluents from dark fermentation can be efficiently converted to methane. Lucerne can serve as macronutrient provider in anaerobic digestion. Intercropping with wheat is promising.

Comparison of ethanol yield from pretreated lignocellulo-starch biomass under fed-batch SHF or SSF modes

The ethanol yields from lignocellulo-starch biomass (peels of sweet potato, elephant foot yam, tannia, greater yam and beet root) by fed-batch separate hydrolysis and fermentation (F-SHF) and simultaneous saccharification and fermentation (F-SSF) using Saccharomyces cerevisiae were compared. Fed-batch saccharification of steam or dilute sulphuric acid pretreated biomass enhanced the reducing sugar yield which resulted in high RS consumption, volumetric ethanol productivity and ethanol yield during the first 24 h fermentation under F-SHF mode, while continuous production and utilization of reducing sugars occurred up to 72 h in F-SSF. Dilute sulphuric acid pretreated residues under F-SHF gave higher ethanol yield (34–43 g/L) and productivity (274–346 ml/kg dry biomass) than steam pretreatment (27–36 g/L and 223–295 ml/kg respectively), while F-SSF was superior for steam pretreated peels of sweet potato, elephant foot yam and tannia giving ethanol yields from 281 to 302 ml/kg. Glucose and xylose were present in all the hydrolysates with a preponderance of glucose and fermentation resulted in significant reduction in glucose levels in both F-SHF and F-SSF. Higher levels of total soluble phenolics and hydroxymethyl furfural were observed in the hydrolysates from dilute sulphuric acid pretreatment and yeast assimilated/detoxified part of the inhibitors, while only trivial amounts of furfural were present due to the low xylose content in the hydrolysates. Continuous formation led to higher accumulation of inhibitors in F-SSF despite supplementation with the detoxification mix comprising Tween 20, polyethylene glycol and sodium borohydride. F-SHF of dilute sulphuric acid pretreated biomass could be considered as a comparatively advantageous process where only one time feeding of enzyme cocktail and yeast was adopted compared to multiple feeds of enzymes and yeast along with other additives such as detoxification mix or nutrient solution in F-SSF.

Two-stage pretreatment with alkaline sulphonation and steam treatment of Eucalyptus woody biomass to enhance its enzymatic digestibility for bioethanol production

This work proposed a two-stage pretreatment with alkaline sulphonation and steam treatment, and investigated its efficiency for converting Eucalyptus woody biomass to fermentable sugars and bioethanol. Comparing with steam pretreatment and subsequent sulphonation, this alkaline sulphonation-steam pretreatment improved carbohydrate recovery by maintaining a more neutral pH throughout the pretreatment process, while promoting the enzymatic digestibility of biomass through lignin removal and modification. Results showed that the alkaline sulphonation-steam pretreatment caused lignin removal of 69.37% and 120.28 mmol/kg acid groups incorporation into substrate, both of which could lead to significantly improved cellulose accessibility. About 80% of the sugars present in the original carbohydrate (cellulose and hemicellulose) were released, which could be recovered after pretreatment and enzymatic hydrolysis. The sugars released from enzymatic hydrolysis of substrate pretreated by alkaline sulphonation-steam pretreatment could be efficiently converted to ethanol, indicating that alkaline sulphonation-steam two-stage pretreatment is a promising pretreatment approach of lignocellulosic biomass for the production of biofuels.

Removal of non-structural components from poplar whole-tree chips to enhance hydrolysis and fermentation performance

BackgroundWhole-tree chips will be a likely feedstock for future biorefineries because of their low cost. Non-structural components (NSC), however, represent a significant part of whole-tree chips. The NSC can account for more than 10% of whole-tree poplar mass when the trees are grown in short rotation cycles. The influence of NSC, however, on the production of fuels and chemicals is not well known. In this study, we assessed the impact of NSC removal from poplar whole-tree chips on pretreatment and enzymatic hydrolysis yields, overall sugar recovery, and fermentation yield. In addition, we evaluated the economics of preprocessing as a new unit operation in the biorefinery.ResultsPoplar whole-tree chips were preprocessed by neutral or acidic washing before steam pretreatment, enzymatic hydrolysis, and fermentation. Preprocessing of poplar reduced ash and extractives content as much as 70 and 50%, respectively. The overall sugar yield after pretreatment and hydrolysis was 18–22% higher when the biomass had been preprocessed, which was explained by higher sugar yields in liquid fraction and more efficient enzymatic hydrolysis of the solid fraction. The liquid fraction ethanol fermentation yield was 36–50% higher for the preprocessed biomass.ConclusionsIt appears that preprocessing reduced the buffering capacity of the biomass due to ash removal, and thereby improved the enzymatic hydrolysis. Removal of extractives during preprocessing improved the fermentation yield. The economic modeling shows that a preprocessing unit could have significant economic benefits in a biorefinery, where poplar whole-tree chips are used as bioconversion feedstock.