Stability Of Bio-oil Research Articles

Storage Stability of Bio-oils Derived from the Catalytic Conversion of Softwood Kraft Lignin in Subcritical Water

The stability of lignin-derived bio-oil obtained from a continuous process [base (K2CO3)-catalyzed, using phenol as a capping agent] under subcritical conditions of water (25 MPa, 290–370 °C) was investigated. The lignin-derived bio-oil obtained was stored at ambient temperature for 2 years. Our results show that the base concentration in the feed solution affects the stability of this lignin-derived bio-oil during its long-term storage. It was found that, at low base concentrations (i.e., 0.4%–1.0%), the yields of all lignin-derived bio-oil fractions were relatively stable. At high base concentrations (i.e., 1.6%–2.2%), however, the yield of high-molecular-weight (high-Mw) structures increased and that of low-molecular-weight (low-Mw) structures decreased after storage. This indicated that the low-Mw materials had been polymerized to form high-Mw materials. In addition, it was found that the yield of gas chromatography-mass spectrometry (GC-MS)-identified compounds (excluding phenol) in this lignin-deriv...

Optimization of composite additives for improving stability of bio-oils

Composite additives of ethanol, acetonitrile, and methyl acetate were added to bio-oils to assess the effects of these additives on stability of bio-oil using D-optimal experimental mixture design (DMD). A systematic analysis of the influence of different proportions of composite additives on bio-oil properties such as viscosity, water content and pH was carried out. The results showed that bio-oil had a lower viscosity, water content and higher pH when the additive formulation consisted of 6.58wt% ethanol, 1wt% acetonitrile and 2.42wt% methyl acetate that was determined to be an optimal composite additive (OCA). Experimental trials were performed to validate the models. A fast aging test at 80°C for 24h confirmed that the composite additive was better than single additives to improve stability of bio-oils. The viscosity of bio-oil with OCA was 27.25mm2/s and was reduced by 33–47% compared to the bio-oil with a single additive; while reduced by 95% with no additives. GC–MS analysis showed that several compounds such as 4-hydroxy-Butanoic acid, p-Cresol, and Vanillin were virtually eliminated in bio-oil with addition of the composite additive. This research illustrated the beneficial effect of the composite additive for storage of bio-oils.

Thermal and Storage Stability of Bio-Oil from Pyrolysis of Torrefied Wood

The objective of this paper is to investigate the biomass torrefaction effect on bio-oil stability by comparing the physicochemical and compositional properties of aged bio-oils. Two aging methods, accelerated aging (held at 80 °C for 24 h) and long-term natural aging (12-month storage at 25 °C), were employed to produce aged bio-oils for such comparison. The results indicate that bio-oils made from heat-treated wood had similar aging behavior in terms of increase of water content, acid content, molecular weight, and viscosity. The increase rate, however, was found to be different and dependent on the aging method. The accelerated method found parallel water and total acidity number (TAN) increments between raw and torrefaction bio-oils, while the natural aging method found torrefaction bio-oils, especially those made from heavily treated wood, had much slower water and acid accumulation than that of raw bio-oil. As a negative effect, both methods identified the viscosity of torrefaction bio-oils increased more significantly than that of raw bio-oil, while their molecular weights were unexpectedly lower. The correlation study showed that bio-oil viscosity is more tied to the content of bio-oil–water insoluble fraction rather than its average molecular weight. In addition, the characterization of aged bio-oils using NMR, GC/MS, and solvent fractionation indicated that torrefaction bio-oils had less compositional alternation after accelerated aging than the raw bio-oil. Also, they were more stable during the first 6 months of storage at room temperature. During the long-term storage, the raw bio-oil completely phase-separated after 6 months. However, two distinct torrefaction bio-oils (LP-280T and LP-330T) had enhanced phase stability, as a stable uniform oil phase without gum formation can be maintained during the entire 12-month storage.

Stabilization of pyrolysis oil: Comparison of reactive distillation and reactive chromatography

The present study, evaluates the applicability of reactive distillation and reactive chromatography for stabilization of bio-oil, obtained from pyrolysis of wood. Bio-oil, along with several oxygenated organic compounds, contains substantial amounts of carboxylic acids (e.g., acetic acid, 5–10%). The presence of acids results in a shorter shelf life of bio-oil, as it catalyzes condensation reactions of furfural-like components leading to an increase in viscosity over a time period. Thus, we investigate the ability of multifunctional reactor for stabilization of bio-oil through esterification of acid with suitable alcohol in the presence of ion-exchange resin catalyst. Reactive distillation is performed at higher a temperature which is dictated by the bubble point of the mixture, reactive chromatography allows one to perform reaction at relatively low temperatures and with lower alcohols. It results in an improvement in the characteristic properties of bio-oil, thereby increasing the shelf life. The main limitation of this approach is that the catalyst used for esterification also catalyzes simultaneous polymerization of furfural-like components which deactivate the catalyst. Deactivation of Amberlyst-15 with ethanol after 20h of continuous run in a fixed-bed chromatographic-reactor was found to be less compared to RD making RC a promising candidate for this particular application.

Controlling the Phase Stability of Biomass Fast Pyrolysis Bio-oils

Fast pyrolysis bio-oil oil is a promising alternative to fossil fuels and is currently entering the heating oil market. However, there is a lack of available information about the phase stability of bio-oil. The water-soluble and water-insoluble compounds in bio-oil can either be in one homogeneous phase or form two individual phases, to which we refer to as phase separation. Phase separation can occur immediately after condensation of the pyrolysis vapors to bio-oil because of certain pyrolysis conditions or type of raw material or after years of aging because of changes in composition caused by repolymerization reactions. We present how the phase separation of bio-oils is related to the chemical composition and show that the probability of phase separation can be predicted with a numerical stability index based on the chemical composition. The chemical composition of the bio-oils studied was characterized using a solvent extraction scheme that describes the composition of bio-oil as a blend of three mac...

Effective evaluation of catalytic deoxygenation for in situ catalytic fast pyrolysis using gas chromatography–high resolution mass spectrometry

Effective deoxygenation in catalytic fast pyrolysis (CFP) is crucial for bio-oil stabilization and its successful commercialization. Herein, we utilize a new analytical platform that couples gas chromatography (GC) to dopant-assisted atmospheric pressure chemical ionization (dAPCI) time-of-flight mass spectrometry (TOF MS) to evaluate catalytic deoxygenation of cellulose pyrolysis. Soft ionization and accurate mass measurement through dAPCI-TOF MS allows direct chemical composition analysis of GC-separated molecules, regardless of their presence in the database. The analytical approach was successfully demonstrated for its ability to evaluate catalytic efficiency of different catalysts and to monitor the change in CFP reaction products with catalyst-to-biomass load ratio. A total of 142 compounds could be analyzed with this approach compared to 38 compounds in traditional Py-GC-EI-MS analysis.

Physical and Chemical Properties and Accelerated Aging Test of Bio-oil Produced from in Situ Catalytic Pyrolysis in a Bench-Scale Fluidized-Bed Reactor

In situ catalytic upgrading is a promising technique to improve the properties of bio-oil because the bio-oil produced from the conventional method has several negative attributes, such as low heating value and highly acidic nature, and is also unstable during storage. In this study, the catalytic effect of CaO, MgO, and ZSM-5 as in situ upgrading catalysts during biomass pyrolysis was studied in a fluidized-bed reactor. Southern pine sawdust was subjected to pyrolysis with inert bed material (quartz sand) and subsequently with the catalysts. The quality of bio-oil obtained was compared to the baseline values (i.e., with the use of sand as bed material without any catalyst) in terms of its chemical composition, heating value, viscosity, pH, total acid number (TAN), and oxygen and water contents. The use of CaO resulted in an improvement in pH (2.39–3.98) and TAN (88.9–46.6) of the bio-oil when compared to the results when using only sand. In comparison, MgO was a mild catalyst because it altered the bio-oil quality slightly, while ZSM-5 had no effect on the acid content in bio-oil, although it produced bio-oil with the least oxygen content at a significantly lower yield and higher water content (38.5%). In terms of chemical composition, the catalysts exhibited different behaviors to various groups of compounds. Anhydrosugars were reduced by all of the catalysts tested to different extents, but CaO significantly altered the quality of bio-oil by reducing organic acids, while CaO and ZSM-5 reduced the abundance of phenolic compounds with a higher oxygen content. An accelerated aging test was performed to compare the efficacy of these in situ catalysts on improving the stability of bio-oil, and it was observed that the bio-oil produced using CaO was the most stable when compared to the baseline and other catalytic bio-oils tested in this study.

Lifecycle assessment of microalgae to biofuel: Comparison of thermochemical processing pathways

Abstract Microalgae is being investigated as a renewable transportation fuel feedstock based on various advantages that include high annual yields, utilization of poor quality land, does not compete with food, and can be integrated with various waste streams. This study focuses on directly assessing the environmental impact of two different thermochemical conversion technologies for the microalgae-to-biofuel process through life cycle assessment. A system boundary of “well to pump” (WTP) is defined and includes sub-process models of the growth, dewatering, thermochemical bio-oil recovery, bio-oil stabilization, conversion to renewable diesel, and transport to the pump. Models were validated with experimental and literature data and are representative of an industrial-scale microalgae-to-biofuel process. Two different thermochemical bio-oil conversion systems are modeled and compared on a systems level, hydrothermal liquefaction (HTL) and pyrolysis. The environmental impact of the two pathways were quantified on the metrics of net energy ratio (NER), defined here as energy consumed over energy produced, and greenhouse gas (GHG) emissions. Results for WTP biofuel production through the HTL pathway were determined to be 1.23 for the NER and GHG emissions of −11.4 g CO 2-eq (MJ renewable diesel) − 1 . Biofuel production through the pyrolysis pathway results in a NER of 2.27 and GHG emissions of 210 g CO 2-eq (MJ renewable diesel) − 1 . The large environmental impact associated with the pyrolysis pathway is attributed to feedstock drying requirements and combustion of co-products to improve system energetics. Discussion focuses on a detailed breakdown of the overall process energetics and GHGs, impact of modeling at laboratory-scale compared to industrial-scale, environmental impact sensitivity to systems engineering input parameters for future focused research and development, and a comparison of results to literature.

Formate assisted pyrolysis of pine sawdust for in-situ oxygen removal and stabilization of bio-oil

Pine sawdust was pretreated with several calcium compounds and then pyrolyzed in a fluidized bed pyrolysis reactor at 500°C. The catalytic action of the calcium compounds varies depending on the anion. Analysis of pyrolysis gas, liquid and char yields and compositions demonstrates that calcium sulfate is inert during pyrolysis while calcium formate, carbonate, hydroxide and oxide show significant deoxygenation activity. Of the salts which showed deoxygenation activity, calcium formate had the highest relative yield. This effect is likely attributable to the activity of calcium formate as a hydrogen donor at the pyrolysis temperature.

Fast pyrolysis processing of surfactant washed Miscanthus

Miscanthus×giganteus was subjected to pre-treatment with deionised water, hydrochloric acid or Triton X-100 surfactant, and subsequently fast pyrolysed in a fluidised bed reactor at 535°C to obtain bio-oil. Triton X-100 surfactant was identified as a promising pre-treatment medium for removal of inorganic matter because its physicochemical nature was expected to mobilise inorganic matter in the biomass matrix. The influence of different concentrations of Triton X-100 pre-treatment solutions on the quality of bio-oil produced from fast pyrolysis was studied, as defined by a single phase bio-oil, viscosity index and water content index. The highest concentration of Triton X-100 surfactant produced the best quality bio-oil with high organic yield and low reaction water content. The calculated viscosity index from the accelerated ageing test showed that bio-oil stability improved as the concentration of Triton X-100 increased.

Toward Understanding of Bio-Oil Aging: Accelerated Aging of Bio-Oil Fractions

Pyrolysis bio-oil from biomass is a promising intermediate for producing transportation fuels and platform chemicals. However, its instability, often called aging, has been identified as a critical hurdle that prevents bio-oil from being commercialized. The objective of this research is to explore the bio-oil aging mechanism by an accelerated aging test of fractionated bio-oil produced from loblolly pine. When water soluble (WS), ether insoluble (EIS), and pyrolytic lignin (PL) fractions were aged separately, the increased molecular weight (Mw) was observed with increasing aging temperature and the presence of acids. WS and EIS fractions had high Mw brown solids formed after aging. Adjusting the pH of WS and EIS fractions from 2.5 to 7.0 significantly reduced the tendency of a Mw increase. Similar Mw rise was also observed on a PL fraction with an elevated temperature and acid addition. Formaldehyde was found to react with the PL fraction in the presence of any acid catalysts tested, i.e., 8-fold Mw increase in acetic acid environment, while other bio-oil aldehydes did not significantly promote lignin condensation. To better understand bio-oil stability, a potential bio-oil aging pattern was proposed, suggesting that bio-oil can be aged within or between its fractions.

Bio-oil from pyrolysis of Tunisian almond shell: Comparative study and investigation of aging effect during long storage

Bio-oil from fast pyrolysis of Tunisian almond shell (TN-AS) in fluidized bed reactor was investigated. TG (Thermogravimetric) and DTG (Derivative Thermogravimetric) analyses were performed to quantify the kinetic of its thermal degradation by comparison with other Mediterranean almond shell feedstocks from Spain (SP-AS) and Turkey (TR-AS).The obtained bio-oil was characterized in terms of its composition and energy content using FTIR, 13C NMR and GC-MS. The analyses showed that TN-AS bio-oil was similar to the Turkish one and was slightly different from the Spanish bio-oil.Aging effect at room temperature over a long storage period (5years) was also investigated to assess bio-oil stability. The aged TN-AS bio-oil had a higher viscosity (705.16±3.76mm2·s−1 at 50°C) while pH, water content and HHV remained unchanged. The increase of viscosity may be due to the increase in the molecular weight resulting of re-polymerization reactions taking place during the long storage period.

Hydrogenation of Furfural as Model Reaction of Bio-Oil Stabilization under Mild Conditions Using Multiwalled Carbon Nanotube (MWNT)-Supported Pt Catalysts

Pt nanoparticles supported on multiwalled carbon nanotubes (MWNT) were synthesized and applied in the catalytic hydrogenation of furfural, the model reaction of mild stabilization of reactive bio-oil. The catalytic properties of the catalysts were modified by changing the surface concentration of oxygen-containing groups (OCGs) of MWNT. Various characterization techniques, including fluorescent labeling, nitrogen physisorption, powder X-ray diffraction, transmission electron microscopy, and in situ DRIFTS analysis, were employed to study both the supports and catalysts. Pt nanoparticles supported on MWNT with high OCGs show high activity and selectivity, attributed to the formation of small Pt particles as a result of the high concentration of OCGs.

A mild approach for bio-oil stabilization and upgrading: electrocatalytic hydrogenation using ruthenium supported on activated carbon cloth

Electrocatalytic hydrogenation (ECH) offers a new approach for bio-oil stabilization (a.k.a. partial upgrading). Water-soluble bio-oil, obtained by aqueous extraction of the liquid product of biomass pyrolysis, was hydrogenated using ECH at room conditions. A new electrocatalyst, ruthenium supported on activated carbon cloth, was used as the catalytic cathode. After electrocatalytic hydrogenation, aldehydes and ketones were reduced to the corresponding alcohols or diols, forms less prone to condensation chemistry. Carbon recovery into the liquid product, important when making liquid fuels from biomass, was more than 80%, while less than 0.1 wt% of the water-soluble bio-oil formed solid precipitate. The stability of the ECH-treated water-soluble bio-oil was checked via an accelerated aging test followed by size exclusion chromatography analysis and viscometry. Besides stabilization of bio-oil for subsequent fuel production, hydrogen and valuable diols were produced during ECH. Strategies to optimize the energy efficiency of this approach by altering the cell design, modifying the catalyst and adjusting the reaction conditions were also explored.

Identification of free radicals in pyrolysis oil and their impact on bio-oil stability

The existence of radicals in pyrolysis oil generated from loblolly pine in three different reactor systems was verified with electron paramagnetic resonance (EPR) spectroscopy.

Tuning cellulose pyrolysis chemistry: selective decarbonylation via catalyst-impregnated pyrolysis

Improving bio-oil stability through aldehydic furan decarbonylation by impregnating cellulose with supported palladium catalysts.

Co-pyrolysis of biomass with waste tyres: Upgrading of liquid bio-fuel

Co-pyrolysis of forestry wastes and waste tyres is carried out using different facilities: a fixed bed reactor and a continuous auger reactor. Remarkably, only one phase is found in the liquid fraction, which is not achieved by mixture of the pure liquids. In addition, positive effects between waste tyre and biomass are evidenced, being more notable even synergetic in the auger reactor. It is found that whilst acidity, density and oxygen content decrease, pH and calorific value increase with respect to the merely biomass pyrolysis liquid, leading to upgraded bio-oil. Upgrading process is linked to the presence of radical interactions between waste tyres and biomass pyrolysis products. In addition, it is observed that the addition of waste tyres to the feedstock blend is significantly decreasing the amount of aldehydes and phenolic compounds, which is beneficial for improving the stability of the new bio-oils.

Bio-oil Stabilization and Upgrading by Hot Gas Filtration

The objective of this research project was to test the hypothesis that separation of char with its associated mineral matter from pyrolysis vapors before condensation will lead to improved bio-oil ...

Recent Advances in Hydrotreating of Pyrolysis Bio-Oil and Its Oxygen-Containing Model Compounds

Considerable worldwide interest exists in discovering renewable energy sources that can substitute for fossil fuels. Lignocellulosic biomass, the most abundant and inexpensive renewable feedstock on the planet, has a great potential for sustainable production of fuels, chemicals, and carbon-based materials. Fast pyrolysis integrated with hydrotreating, one of the simplest, most cost-effective, and most efficient processes to convert lignocellulosic biomass to liquid hydrocarbon fuels for transportation, has attracted significant attention in recent decades. However, effective hydrotreating of pyrolysis bio-oil presents a daunting challenge to the commercialization of biomass conversion via pyrolysis-hydrotreating. Specifically, the development of active, selective, and stable hydrotreating catalysts is problematic due to the poor quality of current pyrolysis bio-oil feedstock (i.e., high oxygen content, molecular complexity, coking propensity, and corrosiveness). Significant research has been conducted to address the practical issues and provide fundamental understanding of hydrotreating and hydrodeoxygenation (HDO) of bio-oils and their oxygen-containing model compounds, including phenolics, furans, and carboxylic acids. A wide range of catalysts have been studied, including conventional Mo-based sulfide catalysts and noble metal catalysts. Noble metal catalysts have been the primary focus of recent research because of their excellent catalytic performances and because they do not require the use of environmentally unfriendly sulfur. Recently, the reaction mechanisms of the HDO of model compounds on noble metal catalysts and their efficacy for hydrotreating or stabilization of bio-oil have been reported. This review provides a survey of relevant literature, published over the past decade, reporting advances in the understanding of the HDO chemistry of bio-oils and their model compounds, mainly on noble metal catalysts.

Effect of hydrothermal pretreatment on properties of bio-oil produced from fast pyrolysis of eucalyptus wood in a fluidized bed reactor

Eucalyptus wood powder was first subjected to hydrothermal pretreatment in a high-pressure reactor at 160-190°C, and subsequently fast pyrolyzed in a fluidized bed reactor at 500°C to obtain high quality bio-oil. This study focused on investigating effect of hydrothermal pretreatment on bio-oil properties. Hemicellulose and some metals were effectively removed from eucalyptus wood, while cellulose content was enhanced. No significant charring and carbonization of constituents was observed during hydrothermal pretreatment. Thus pretreated eucalyptus wood gave higher bio-oil yield than original eucalyptus wood. Chemical composition of bio-oil was examined by GC/MS and (13)C NMR analyses. Bio-oil produced from pretreated eucalyptus wood exhibited lower contents of ketones and acids, while much higher levoglucosan content than bio-oil produced from original eucalyptus wood, which would help to improve thermal stability of bio-oil and extract levoglucosan from bio-oil. Hydrothermal pretreatment also improved bio-oil fuel quality through lowering water content and enhancing heating value.