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The effect of supercritical water treatment on the composition of bio-oil was investigated. Preliminary studies were carried in batch mode using a bio-oil simulant. This bio-oil simulant was designed to mimic crude bio-oil by possessing the same functional groups as are found in crude bio-oil, but with reduced complexity. Experiments of this type allow to be gained of the reaction chemistry involved. These were then followed up by experiments using crude bio-oil. Critical process parameters for all these experiments were reaction time, bio-oil/water ratio, reaction temperature and pressure. One of the objectives of this work was to identify processing conditions that would either suppress formation of, or elimination of the coke precursors. This would then result in a bio-oil with improved storage characteristics and a reduced tendency towards coke formation during catalytic upgrading. The results suggest that supercritical water treatment can effectively eliminate the coke pre-cursors resulting from bio-oil, resulting in a bio-oil with improved properties.

Bio-oil is produced by the rapid pyrolysis of biomass and is a source of renewable fuel. The increase in viscosity during storage is a major problem that can be controlled by the addition of methanol or other alcohols. The objective of this research was to determine how alcohols stabilize bio-oil by investigating the reactions of alcohols with low molecular weight aldehydes and acids. The reaction of methanol with hydroxyacetaldehyde (HA) and acetic acid to form the respective acetal or ester was catalyzed by the 7 x 10-4 M strong acids such as sulfuric, hydrochloric, p-toluene sulfonic acid, and methylsulfonic acid. HA formed 2,2-dimethoxyethanol (DME) and AT 60°C, equilibrium was reached in less than one hour. Smaller amounts of DME were formed in the absence of strong acid. HA, acetaldehyde, and propanal formed their corresponding acetals when reacted with methanol, ethanol, 1-propanol or 1-butanol. Esters of acetic acid and hydroxyacetic acid were observed from reactions with these same four alcohols. Other acetals and esters were observed by GC/MS analysis of the reaction products. The results from accelerated aging experiments at 90°C suggest that the presence of methanol slows polymerization by formation of acetals and esters from low molecular weight aldehydes and organic acids. The other objective of this study was to improve the bio-oil quality as fuel in a single step by adding methanol to the pyrolysis gases. Therefore, a methanol/sulphuric acid mixture was injected into the pyrolysis vapor zone prior to the water cooled condensers of the auger reactor. The chemical and physical properties of bio-oils were determined and the results of these tests were compared with the results of tests with raw bio-oils. The amount of methanol injection varied from 1 to 20 wt % with and without catalysts. The results showed that the addition of 10% methanol was required for stability with the accelerated aging test. The bio-oil viscosity was reduced to 11.7 cSt from 15.45 cSt with the 10% methanol addition and after 5 days of ageing at 90°C the viscosity only increased by 17% whereas raw bio-oil turned into a highly viscous phase separated material. GC/MS analysis indicated the formation of the esters and quantified the amount of methanol present in the bio-oil after the reaction. The acid value was 87 compared to 99.8 for raw bio-oil. The lower acid value of the esterified bio-oil supports the hypothesis that the formation of esters lowered the amount of free acids present. The flash point of the bio-oil was improved to 37°C and it burned intensely in the waste oil burner. A Principal component analysis supported these findings by indicating that the esterified bio-oil properties differed significantly from the raw bio-oil.

Raw bio-oil is produced by fast pyrolysis of biomass. The high level of oxygen content in bio-oil causes negative properties of polymerization over time, high acidity, pungent odor and low heating value relative to petroleum fuels. The objective of this study was to develop and identify upgrading processes to produce a boiler fuel with reduced acid value, reduced polymerization over time and increased higher heating value. By one upgrading method, raw bio-oil was upgraded by esterification over acid catalyst by batch reaction; a second approach was an in-reactor reaction, produced by injecting methanol or 1-butanol with acid catalyst into the pyrolysis vapor stream. An olefination reaction method combined with an alcoholation reaction was also studied. The resulting fuel produced from in-reactor esterification fuel was compared in terms of physical and chemical properties with esterifed bio-oil produced by the batch method. The olefination reaction was examined in terms of higher heating value, acid value, viscosity, and water content. The influence of reaction conditions such as reaction time, reaction temperature, and catalyst content relative to upgraded bio-oil properties were examined, and optimal conditions were identified. Analysis of variance (ANOVA) and empirical analysis was utilized to analyze the difference in physical and chemical properties between treatment groups.

Future predicted shortages in fossil fuel resources and environmental regulations from fossil fuel combustion have led to great research interest in developing alternatives to fossil fuels. Biomass-derived bio-oils will have the potential to replace conventional transportation fuels because of their sustainability and environmental advantages. However, the presence of high percentages of chemical oxygenates cause negative properties such as high water content, low volatility, lower heating value, corrosiveness, immiscibility with fossil fuels and instability during storage and transportation. Moreover, polymerization, esterification, condensation and other reactions occur between these highly reactive oxygenates in bio-oil (Diebold 2000). These negative properties hinder both bio-oil direct use as a fuel and the fuel conversion process (Mohan, et al. 2006). Hydrodeoxygenation has proven itself effective in converting of bio-oil to pure hydrocarbons. However, the large consumption of expensive hydrogen prevents the industrialization of bio-oil. Therefore, development of more efficient hydrodeoxygenation approaches with less capital cost will be desirable. The objective of this current research was to upgrade raw and distilled bio-oil by oxidation to a stabilized precursor to the final hydrocracking step of hydrodeoxygenation. In the second chapter, raw bio-oil, two pretreated bio-oils and hydrotreated bio-oil were hydrodeoxygenated to produce liquid hydrocarbons in the continuous reactor. In the third chapter, raw bio-oil, oxidized raw bio-oil, distilled bio-oil and oxidized distilled bio-oil were hydrodeoxygenated to liquid hydrocarbons with hydrogen in the batch reactor. In the fourth chapter, oxidized distilled bio-oil was hydrotreated with model syngas to organic liquid products followed by hydrocracking with hydrogen to produce liquid hydrocarbons. In the fifth chapter, oxidized distilled bio-oil was upgraded with syngas (H2/CO molar ratios of 4:6) in a single stage to produce organic liquid products. The resultant stabilities of these organic liquid products were investigated by application of accelerated aging. The research results showed that oxidized distilled bio-oil could be upgraded by the syngas in a single stage to produce stabilized bio-oil. This success will replace hydrogen by syngas for first stage hytrotreating and save shipping fee by transportation less weight of upgraded bio-oil rather than the bulky and high moisture content biomass.

This dissertation research is based on two reactions, including those of cyclic ketene acetals with acid chlorides and acid catalyzed olefination reactions in bio-oil. In first four chapters, reactions of in situ generated cyclic ketene acetals were explored. Highly functionalized heterocycles such as pyrrollo-[1,2-c]imidazolediones, were synthesized in one-pot reactions of 2-alkylimidazoles or 2-methylbenzimidazoles with 1,3-diacid chlorides. Some reactions proceed through in situ generated cyclic-N,N′-ketene acetal intermediates. 2-Alkylimidazoles and 2-methylbenzimidazole can be considered as tridentate nucleophiles in these reactions that can give four consecutive attacks on electrophiles which ultimately generate new heterocycles. Reactions of substituted oxazoles and thiazoles with different acid chlorides in the presence of different bases were explored. Arylvinyl esters of substituted benzoic acids containing substituted oxazoles or thiazoles were formed when aroyl chlorides were used. Most reactions occurred through in situ generated cyclic ketene acetals. Reactions of 2-methylbenzoxazole and 5-phenyl-2-methylbenzoxazole with acid chlorides and base in THF generated a series of ortho-amidoesters. All of these reactions showed that aromatic heterocycles based in situ generated cyclic ketene acetals could be used to make highly functionalized heterocycles under mild conditions. These one-pot reactions generated various heterocycles, which might have useful bioactivities. For example, arylvinyl esters of substituted benzoic acids have been reported to show insecticidal activities. The last two chapters describe the olefinations of bio-oil and model bio-oil compounds using acid catalysts. Two different branched olefins were used, representative of those available at petroleum refineries. Amberlyst-15 and Nafion NR-50 were used as heterogeneous acid catalysts. The acid catalyzed olefination of bio-oil was explored using an excess of 1- octene. Some olefinations were performed in the presence of ethanol. Ethanol was used to make the olefin and bio-oil phases partially miscible. Acid catalyzed olefination of raw bio-oil induced some changes in the resulting bio-oil by generating variety of alcohols, ethers and oligomeric mixtures of the starting olefin. Olefination with excess 1-octene showed the decrease of the water content and the acid value and increase of the heating value of the bio-oil. Thus, the acid catalyzed olefination of bio-oil can be considered as a potential bio-oil upgrading technique.

Eight alcohols in their supercritical states were used individually to treat crude bio-oil and pine wood chips. All supercritical alcohols studied, with the exception of tertbutanol, exhibited the ability to decrease the oxygen content, acid value and/or remove unstable compounds from the crude bio-oil. For supercritical 1-butanol, its use for upgrading of crude bio-oil resulted in a product with much lower oxygen content, lower acid value and fewer unstable compounds. Two CoMo catalysts were examined for their impact on the bio-oil upgrading process with supercritical alcohol. Their influence on the oxygen content, acid value and concentrations of unstable compounds in the processed bio-oil was examined. The basic CoMo/MgO catalyst was demonstrated to effectively eliminate acid content from the bio-oil, regardless of the alcohol employed. Compared with crude bio-oil produced by fast pyrolysis of pine wood lumber, the liquid products produced from supercritical alcohol treatment of pine wood chips possessed one or more of the desirable characteristics: lower acid value, lower oxygen content and fewer unstable compounds. Generally, supercritical butanol isomers produced liquid fuels with lower oxygen content. However, the bulky structure of branched alcohol isomers (secondary and tertiary alcohols) appeared to hinder the degradation of pine wood chips. The CoMo/MgO catalyst exhibited the ability to decrease the acid value, but not to decrease the oxygen content in the liquid product. Wood chip size, wood chip/methanol mass ratios, temperatures, pressures and reaction time were examined in this work. However, the influence of these variables on liquid yield from supercritical methanol treatment of pine wood chips was not substantial.

Highly oxygenated compounds in bio-oil produce negative properties that have hampered fuel development. Copyrolysis with plastics has increased hydrogen content in past research. Py-GC/MS analyses for two wood types (pine and oak) and three plastic types (polystyrene, polypropylene and high density polyethylene) established temperature, heating rate and residence time to produce a typical bio-oil. Analysis of various plastics to wood ratios by Py-GC/MS showed that a 50:50 wt/wt ratio produced the highest level of low molecular weight compounds best for fuel viscosity. Copyrolysis was performed on a laboratory-scale reactor at these temperature and wood-to-plastic ratios. Copyrolysis lowered bio-oil oxygen content and increased carbon content. Lower water content, acid value and viscosity also resulted, improving bio-oil suitability for fuels. Cross reactions between wood and plastics formed no new chemical species during copyrolysis. These results indicate that copyrolysis of waste plastics with woody biomass has potential for improving bio-oil properties for fuels production.

Levoglucosan is the major anhydrosugar component of bio-oil produced by fast pyrolysis. Previous research has shown that levoglucosan yield can be greatly increased if a mild acid pretreatment is applied to demineralize the feedstock prior to pyrolysis. The interest in levoglucosan production is that it provides a route to production of monomeric sugars, primarily glucose, which can be utilized to produce biochemically derived fuels (ethanol, butanol, etc.) In one study, four different lignocellulosic biomass were subjected to pyrolysis as feedstocks to produce bio-oils via fast pyrolysis in a 7 kg/h feed rate auger reactor. Feedstocks were pretreated with dilute phosphoric acid and bio-oils were produced and analyzed to compare the bio-oil characteristics from both untreated and treated feedstocks. The results shown in this study strongly indicate that the ash content and alkali metal content are very important parameters which can greatly affect the yield and many properties of bio-oils produced during fast pyrolysis. The dilute acid pretreatment performed in this study significantly reduced the total ash content and alkali metal content in the feedstocks, resulting in a great increase in the bio-oil and levoglucosan yields. It was also shown that dilute acid pretreatment was more effective in treating herbaceous feedstocks than woody biomass in terms of increasing bio-oil production yield and improving bio-oil properties. In one study, bio-oil composed of high levoglucosan concentration was produced via fast pyrolysis of dilute acid pretreated loblolly pine wood in an auger reactor. Water-to-bio-oil ratio, temperature, and time were selected as the three parameters to investigate the optimal condition for extracting the maximum amount of levoglucosan from the bio-oil. The optimal condition for levoglucosan extraction determined was 1.3 : 1 (water-to-bio-oil ratio), 25 oC, and 20 min, producing a levoglucosan yield of 12.7 wt %. The final study developed a new method based on pyrolysis of dilute acid pretreated loblolly pine wood and modification of the pyrolysis process. This new method resulted in a significant 30.7 wt % increase in levoglucosan concentration in the bio-oil organic portion. The results indicated that this method successfully suppressed the levoglucosan decomposition during fast pyrolysis.

Contaminated stormwater discharge is a major concern in the United States due to a steady increase of harmful pollutants entering fresh water sources. The many congressional mandates that require local governments to reduce the impact of storm water discharge on the natural ecology have greatly increased the need for economically and environmentally viable solutions to pollution reduction. One such solution is that of constructed wetlands. Previous research conducted at the Sustainable Bio-products Department at Mississippi State University demonstrated the feasibility of kenaf fiber and wood shavings to remove toxins and crude oil from the bio-oil process water. This study proposes to amend contaminated storm water runoff from a biomass to bio-oil conversion facility through a simulated constructed wetland. The constructed wetlands were contaminated with varying dilution levels of bio-oil process water in a series of six phases. It was hypothesized that the contaminated rainwater can be remediated by constructed wetlands and safely released back into the native waterways. This study concluded that there was a significant decrease in biological oxygen demand (BOD) and micro-toxicity over a ten day cycle within the constructed wetlands for the lower levels of contaminated stormwater. A comparative screen of the bacterial community within the wetlands during the contamination process showed a similar trend in species richness and composition for the first three Phases of contamination. There was a shift in richness and diversity for the final three Phases of contamination after ten days within the constructed wetlands. The constructed wetlands were successful at lowering BOD and toxicity levels and achieving permissible pH levels when the concentration of contaminated stormwater was less than or equal to 400x dilution. Much of the BOD reduction was due to volatilization of the contaminated wastewater. When the concentration of contaminated water exceeded 300x dilution, the constructed wetland were only successful at achieving permissible pH discharge levels. Better results may be achievable with longer residence time in the wetlands.