Stability Of Bio-oil Research Articles

Impact of Miscanthus x giganteus senescence times on fast pyrolysis bio-oil quality

In this study the impact of senescence and harvest time in Miscanthus on the quality of fast pyrolysis liquid (bio-oil) was investigated. Bio-oil was produced using a 1kgh−1 fast pyrolysis reactor to obtain a quantity of bio-oil comparable with existing industrial reactors. Bio-oil stability was measured using viscosity, water content, pH and heating value changes under specific conditions. Plant developmental characteristics were significantly different (P⩽0.05) between all harvest points. The stage of crop senescence was correlated with nutrient remobilisation (N, P, K; r2=0.9043, r2=0.9920, r2=0.9977 respectively) and affected bio-oil quality. Harvest time and senescence impacted bio-oil quality and stability. For fast pyrolysis processing of Miscanthus, the harvest time of Miscanthus can be extended to cover a wider harvest window whilst still maintaining bio-oil quality but this may impact mineral depletion in, and long term sustainability of, the crop unless these minerals can be recycled.

Results of the IEA Round Robin on Viscosity and Stability of Fast Pyrolysis Bio-oils

An international round robin study of the stability of fast pyrolysis bio-oil was undertaken. Fifteen laboratories in five different countries contributed. Two bio-oil samples were distributed to the laboratories for stability testing and further analysis. The stability test was defined in a method provided with the bio-oil samples. Viscosity measurement was a key input. The change in viscosity of a sealed sample of bio-oil held for 24 h at 80 °C was the defining element of stability. Subsequent analyses included ultimate analysis, density, moisture, ash, filterable solids, and TAN/pH determination, and gel permeation chromatography. The results showed that kinematic viscosity measurement was more generally conducted and more reproducibly performed versus dynamic viscosity measurement. The variation in the results of the stability test was great and a number of reasons for the variation were identified. The subsequent analyses proved to be at the level of reproducibility, as found in earlier round robins on bio-oil analysis. Clearly, the analyses were more straightforward and reproducible with a bio-oil sample low in filterable solids (0.2%), compared to one with a higher (2%) solids loading. These results can be helpful in setting standards for use of bio-oil, which is just coming into the marketplace.

Development of the Basis for an Analytical Protocol for Feeds and Products of Bio-oil Hydrotreatment

Methods for easily following the main changes in the composition, stability, and acidity of bio-oil as a result of hydrotreatment are presented in this paper. The methods provide the basis for the development of an analytical protocol, which can be used for bio-oil, as well as the hydrotreated products from bio-oil. The correlation to more conventional methods is provided; however, the use of these methods for the upgrading products is different than previously recognized. The differences in the properties of bio-oil and the hydrotreated products will also create challenges for the analytical protocol. Polar pyrolysis liquids and their hydrotreated products can be divided into five main groups with solvent fractionation, and the change in the proportions of the groups as a result of handling or processing is easy to follow. Over the past 10 years, this method has been successfully used for comparison of fast pyrolysis bio-oil quality and the changes during handling and storage and provides the basis of the analytical protocol presented in this paper. This paper describes the use of the method for characterization of bio-oil hydrotreatment products. A discussion of the use of gas chromatographic and spectroscopic methods is also included. In addition, fuel oil analyses suitable for fast pyrolysis bio-oils and hydrotreatment products are discussed.

Chromatographic approaches for determination of low-molecular mass aldehydes in bio-oil

HPLC-UV and GC/MS determination of aldehydes in bio-oil were evaluated. HPLC-UV preceded by derivatization with 2,4-dinitrophenylhydrazine allows separation and detection of bio-oil aldehydes, but the derivatization affected the bio-oil stability reducing their quantitative applicability. GC/MS determination of aldehydes was reached by derivatization with o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride. Two approaches for this reaction were evaluated. The first: "in solution derivatization and head space extraction" and the second: "on fiber derivatization SPME", the latter through an automatic procedure. Both sample treatments allows the quantification of most important aliphatic aldehydes in bio-oil, being the SPME approach more efficient. The aldehyde concentrations in bio-oil were ~2% formaldehyde, ~!0.1% acetaldehyde and ~0.05% propionaldehyde.

An Approach for Stability Measurement of Wood-Based Fast Pyrolysis Bio-Oils

This paper presents a simple stability test method based on changes in carbonyl compounds. Whereas the method of identifying carbonyl groups by means of titration is in itself well-known, its use in determining the stability of fast pyrolysis bio-oils has previously not been established. Pyrolysis oil stability is typically measured as viscosity increase under specified conditions. The increase in viscosity occurs due to an increase in the amount and molecular weight of water insolubles present in the oil. The change in carbonyl compounds is due to reactions of aldehydes and ketones during storage, the reaction products of which end up in the water-insoluble fraction. This paper shows that the carbonyl titration method, based on changes in aldehydes and ketones, correlates with the viscosity increase-based stability test and that, due to this clear correlation, both methods can be used and comparison between the methods is possible.

Properties of Bio-oil from Fast Pyrolysis of Rice Husk

Physicochemical properties of bio-oil obtained from fast pyrolysis of rice husk were studied in the present work. Molecular distillation was used to separate the crude bio-oil into three fractions viz. light fraction, middle fraction and heavy fraction. Their chemical composition was analyzed by gas chromatograph and mass spectrometer (GC-MS). The thermal behavior, including evaporation and decomposition, was investigated using thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR). The product distribution was significantly affected by contents of cellulose, hemicellulose and lignin. The bio-oil yield was 46.36% (by mass) and the yield of gaseous products was 27% (by mass). The chemicals in the bio-oil included acids, aldehydes, ketones, alcohols, phenols, sugars, etc. The light fraction was mainly composed of acids and compounds with lower boiling point temperature, the middle and heavy fractions were consisted of phenols and levoglucosan. The thermal stability of the bio-oil was determined by the interactions and intersolubility of compounds. It was found that the thermal stability of bio-oil was better than the light fraction, but worse than the middle and heavy fractions.

Study of the Effect of Ultraviolet Exposure on Bio-oil by Laser-Induced Fluorescence Spectroscopy

Laser-induced fluorescence was used to simulate and monitor the effect of ultraviolet (UV) exposure on the chemical stability of bio-oil. Bio-oil obtained from fast pyrolysis of biomass has potential for replacing fossil fuel in the future as liquid fuels. Pyrolysis-derived bio-oil contains up to 400 chemical compounds and tends to be very unstable, both physically and chemically. Bio-oil produced from four different sources (pine lumber, pine bark, oak bark, and oak wood) was used in this study. Synthetic bio-oil composed of 10 chemicals but having a similar weight percentage (wt %) of compound groups and having a similar spectroscopic property as bio-oil was prepared. Synthetic bio-oil simplifies the limitation in the study posed by complex chemical composition in bio-oil. It was concluded that phenols present in the bio-oil show chemical instability by giving time-dependent fluorescence intensity.

O-Methylation of the Phenolic Bio-oil with Dimethyl Carbonate in an Ionic Liquid [bmim]Cl

O-Methylation of phenols has been studied as an important organic reaction, and its products, aryl methyl ethers, are valuable intermediates in fine chemicals. The phenolic component is one of the factors leading to the thermal instability of biomass pyrolysis oils. O-Methylation of phenols is helpful to improve the stability of bio-oil. Using dimethyl carbonate (DMC) as a methylation reagent, model O-methylations of three phenols (phenol, guaiacol, and eugenol) have been investigated in an ionic liquid, 1-butyl-3-methylimidazolium chloride ([bmim]Cl), in the presence of water and carboxylic acid, separately. In [bmim]Cl at 130 °C, both hydrolysis of DMC and esterification of acetic acid with DMC would occur and compete with the O-methylation of phenol and decrease the yield of the methylation. However, the esterification of carboxylic acids is helpful for bio-oil upgrading. Under the same reaction conditions, the methylation was performed for a phenolic bio-oil, which is the ether extractive from the bot...

Different solid acid catalysts influence on properties and chemical composition change of upgrading bio-oil

Several solid acid catalysts are prepared and compared in upgrading bio-oil using ethanol and acetic acid as raw materials through the catalytic esterification reaction model. The SO 4 2−/SiO 2–TiO 2 catalyst in the optimum experimental conditions achieved higher catalytic activity. The bio-oil was stabilized by ester reaction over SO 4 2−/SiO 2–TiO 2 catalyst in the conditioned experiment with lowered dynamic viscosity and enhanced fluidity, which was sustained after aging for 6 months in a refrigerator under about 5 °C. The gas chromatography–mass spectrometry analysis of the composition before and after the catalytic esterification proved that the proportion of esters in the upgraded bio-oils increased remarkably, suggesting that the catalytic esterification can vary the composition and properties obviously thus enhances the stability of bio-oil.

Upgrading of Bio-oil by Catalytic Esterification and Determination of Acid Number for Evaluating Esterification Degree

Bio-oil was upgraded by catalytic esterification over the selected catalysts of 732- and NKC-9-type ion-exchange resins. The determination of the acid number by potentiometric titration was recommended by the authors to quantify the total content of organic acids in bio-oil and also to evaluate the esterification degree of bio-oil in the process of upgrading. We analyzed the measurement precision and calibrated the method of potentiometric titration. It was proven that this method is accurate for measuring the content of organic acids in bio-oil. After bio-oil was upgraded over 732 and NKC-9, acid numbers of bio-oil were lowered by 88.54 and 85.95%, respectively, which represents the conversion of organic acids to neutral esters, the heating values increased by 32.26 and 31.64%, and the moisture contents decreased by 27.74 and 30.87%, respectively. The accelerated aging test and aluminum strip corrosion test showed improvement of stability and corrosion property of bio-oil after upgrading, respectively.

Comparison of three accelerated aging procedures to assess bio-oil stability

The current study utilizes three stability ranking methods to compare oxidative and thermal stability of alcohol-stabilized and un-stabilized slow pyrolysis bio-oil. Procedures were based on standard methods established by ASTM (D5304 and E2009) for hydrocarbon fuels and on a widely used method that assesses viscosity change over time. Each method involves an accelerated aging procedure ranging from several minutes to 24 h. Average stability rankings for bio-oils produced from two biomass feedstock (pine and peanut hull) in two pyrolysis units were compared. Bio-oils in order from most to least stable included; methanol-stabilized pine pellet oil, un-stabilized pine pellet oil, ethanol spray-condensed pine pellet oil, methanol-stabilized peanut hull oil, and un-stabilized peanut hull pellet oil. FT-IR spectra from pre- and post-aging showed an increase in the relative concentration of C–O (phenols, carboxylic acids, esters, and ethers) and C O (carbonyl) functional groups for aged samples.

Esterification of biomass pyrolysis model acids over sulfonic acid-functionalized mesoporous silicas

Esterification of acetic acid with methanol, which was used as a model reaction in the stabilization of bio-oil, was tested over propylsulfonic acid-functionalized SBA-15 materials. Due to the significant amount of water content in bio-oil, the water tolerance properties of the materials were also investigated in detail. The results showed that the functionalized mesoporous materials demonstrated a comparable site activity to H 2SO 4 in acetic acid esterification proving its potential for application. The effect of propylsulfonic acid loading showed that the intrinsic per site activity increased with the number of acid sites, which suggested the presence of acidic site cooperativity. Water tolerance experiments showed that SO 3H-SBA-15 exhibited less reaction inhibition due to water than did H 2SO 4, which was at least partially ascribed to the hydrophobic propyl groups bonded to sulfonic acid groups. Further functionalization of SO 3H-SBA-15 with hydrophobic propyl groups further increased the water tolerance property of the catalyst in the esterification reaction. The reusability of the catalyst was also investigated and showed multiple cycle stability for acetic acid esterification without significant loss of activity.

Effects of high-pressure homogenization on physicochemical properties and storage stability of switchgrass bio-oil

A high-pressure homogenization (HPH) technique was used to improve the physicochemical properties and storage stability of switchgrass bio-oil. The viscosity, ethanol-insoluble fraction, and mass average molecular weight ( Mw) of the bio-oil decreased significantly, and particle size became smaller after HPH processing; however, no significant changes were detected in heating value, water content, density, pH value, or ash content. The bio-oil's chemical composition changed after HPH: amounts of some compounds (furfural, levoglucosan, diethoxymethyl acetate, and lignin-derived compounds) increased, while others (acetic acid and 1,2-ethanediol) decreased. The homogenization processing remarkably improved switchgrass bio-oil stability: the viscosity of bio-oil homogenized at 100 MPa increased by only 13.9% after storage at 40 °C for 60 days, whereas that of unhomogenized oil increased 56% after the same storage period. The operating cost was very modest at only $0.0102/L for bio-oil HPH processing at 100 MPa.

Bio-oil upgrading by means of ethyl ester production in reactive distillation to remove water and to improve storage and fuel characteristics

Abstract Several solid acids (SO42−/MxOy) were prepared and compared in upgrading bio-oil using ethanol and bio-oil as raw materials through reactive rectification. Two kinds of upgraded bio-oil were obtained in the upgrading process. The densities of two kinds of upgraded bio-oil were reduced from 1.16 to 0.91 and 0.95 g cm−3, and the gross calorific value increased from 14.3 to 21.5 and 24.5 MJ kg−1 and the acidity of upgraded bio-oil was also alleviated from 2.82 to 7.06 and 5.35, respectively. The results of 1H NMR, gas chromatography-mass spectrometry (GC–MS) and FT-IR analysis showed that the ester reaction in the bio-oil was promoted by solid acid catalysts. The stability of upgraded bio-oil was investigated by storing at room temperature. After 3 months of aging, the upgraded bio-oil did not show much viscosity increase.

Evaluation of the Influence of Stainless Steel and Copper on the Aging Process of Bio-Oil

The thermal stability of bio-oils obtained from softwood bark (SWBR) and hardwood rich in fibers (HWRF) residues was studied under aging conditions at 80 °C in sealed glass bottles in the presence of stainless steel and copper. SWBR-derived bio-oil separated into oily and aqueous phases during aging, while HWRF-derived oil remained as a single phase during the entire aging period. Dynamic rheological tests and GPC analyses were used to follow the effect of aging on the properties of bio-oils. Bio-oil aging was determined following the changes in bio-oil macrofractions using solvents of different polarities. The main difference observed between the oils analyzed was the tendency of SWBR to form materials insoluble in methanol, while HWRF aging reactions led to the formation of compounds insoluble in water and CH2Cl2. Methanol-insoluble and water-/CH2Cl2-insoluble fractions of aged oils were characterized by thermogravimetry, GPC, and Py−GC/MS techniques. The bio-oil aging reactions seem not to be affected by the presence of metals.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part II: Stability and ageing of bio-oil and its blends with methanol and a pyrolytic aqueous phase

This paper completes a study the ultimate objective of which was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a gas turbine liquid fuel. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. The stability and ageing of the bio-oil and mixtures thereof were evaluated. The samples were stored at 40, 50 and 80°C for up to 168 h and at room temperature for up to one year, period after which the phase separation time, viscosity, solid and water content and average molecular weight were measured. The results indicated that the properties of the bio-oil were significantly altered when the bio-oil was heated at 80°C, but that the variations after heating at 40 and 50°C were not critical. It was found that the molecular weight increase after heating the bio-oil for one week at 80°C was equivalent to keeping the sample for one year at room temperature. The addition of aqueous phase to the bio-oil lowered its thermal stability significantly. A rapid phase separation occurred after heating at 80°C and, therefore, the total aqueous phase concentration in the bio-oil must be limited to 15%. Ageing of the raw bio-oil at room temperature resulted in a dramatic viscosity increase during the first 65 days, period after which a plateau was reached. The addition of methanol to the bio-oil was beneficial for the bio-oil properties as well as for the stability of the bio-oil and its mixtures. Methanol dissolved some structured components of the bio-oil and thus reduced the viscosity increase rate. Moreover, the addition of methanol to the bio-oil/pyrolytic aqueous phase mixtures delayed the phase separation process.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part I: Properties of bio-oil and its blends with methanol and a pyrolytic aqueous phase

The objective of this study was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a liquid fuel for gas turbine applications. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. Alkali metal content, viscosity, solid content, heating value, surface tension, moisture content and density of the bio-oil were investigated. The effect of the addition of methanol and/or a pyrolytic aqueous phase on the physicochemical properties of the bio-oils was also investigated. The pyrolytic aqueous phase is the sum of the water contained in form of moisture in the feedstock plus the water formed during biomass pyrolysis reactions. The results indicated that the bio-oil sample investigated is a valuable gas turbine fuel: it has a relatively low Na+K+Ca content (21 ppm), a low viscosity ( 5.3 cSt@90° C ), a high net heating value (32 MJ/kg, as-received basis) and a low solid content (0.34 wt%). The addition of methanol to the oil was beneficial. It was also found that the pyrolytic aqueous phase addition had no significant effect on the viscosity, but that its “flowability” effect was beneficial for other properties. A concentration of 10–15% of the aqueous phase in the bio-oil seemed to be optimal. The second phase of this study investigated the storage and thermal stability of bio-oils and their mixtures. This was carried out using a method performed in our laboratory. The results are presented in Part II of this study.

Characterization and stability analysis of wood-derived bio-oil

The stability characteristics of a bio-oil, produced by the high pressure liquefaction of aspen wood were studied by observing the changes in its physical properties, composition and distillation characteristics with time. Distillation characteristics of the fresh bio-oil showed that maximum amount of organic distillate was obtained at 172 Pa and 200°C. This distillate fraction mainly consisted of aromatic, aliphatic and naphthenic hydrocarbons and oxygenated compounds such as phenols, furans, alcohols, acids, ethers, aldehydes and ketones. The bio-oil viscosity, and chemical composition were found to change substantially over time probably due to polymerization of some components. Upon storage, the concentration of aromatic hydrocarbons and phenols decreased while the concentration of aldehydes and ketones increased. Also, the oxygen content of the distillate decreased from 22.7 wt% for the fresh bio-oil to 18.8 wt% after 31 days. However, when the bio-oil was mixed with tetralin it was observed that the properties of the mixture remained unchanged with time. Tetralin was found to donate hydrogen leading to the improvement in bio-oil stability. A free radical mechanism is proposed to explain the effect of tetralin.