Improvement of bio-oil stability in wood pyrolysis process

Pyrolysis is one of several thermochemical technologies that convert solid biomass into more useful and valuable bio-fuels. Pyrolysis is thermal degradation in the complete or partial absence of oxygen. Under carefully controlled conditions, solid biomass can be converted to a liquid known as bie-oil in 75% yield on dry feed. Bio-oil can be used as a fuel but has the drawback of having a high level of oxygen due to the presence of a complex mixture of molecular fragments of cellulose, hemicellulose and lignin polymers. Also, bio-oil has a number of problems in use including high initial viscosity, instability resulting in increased viscosity or phase separation and high solids content. Much effort has been spent on upgrading bio-oil into a more usable liquid fuel, either by modifying the liquid or by major chemical and catalytic conversion to hydrocarbons. The overall primary objective was to improve oil stability by exploring different ways. The first was to detennine the effect of feed moisture content on bio-oil stability. The second method was to try to improve bio-oil stability by partially oxygenated pyrolysis. The third one was to improve stability by co-pyrolysis with methanol. The project was carried out on an existing laboratory pyrolysis reactor system, which works well with this project without redesign or modification too much. During the finishing stages of this project, it was found that the temperature of the condenser in the product collection system had a marked impact on pyrolysis liquid stability. This was discussed in this work and further recommendation given. The quantity of water coming from the feedstock and the pyrolysis reaction is important to liquid stability. In the present work the feedstock moisture content was varied and pyrolysis experiments were carried out over a range of temperatures. The quality of the bio-oil produced was measured as water content, initial viscosity and stability. The result showed that moderate (7.3-12.8 % moisture) feedstock moisture led to more stable bio-oil. One of drawbacks of bio-oil was its instability due to containing unstable oxygenated chemicals. Catalytic hydrotreatment of the oil and zeolite cracking of pyrolysis vapour were discllssed by many researchers, the processes were intended to eliminate oxygen in the bio-oil. In this work an alternative way oxygenated pyrolysis was introduced in order to reduce oil instability, which was intended to oxidise unstable oxygenated chemicals in the bio-oil. The results showed that liquid stability was improved by oxygen addition during the pyrolysis of beech wood at an optimum air factor of about 0.09-0.15. Methanol as a postproduction additive to bio-oil has been studied by many researchers and the most effective result came from adding methanol to oil just after production. Co-pyrolysis of spruce wood with methanol was undertaken in the present work and it was found that methanol improved liquid stability as a co-pyrolysis solvent but was no more effective than when used as a postproduction additive.

A comparison of integrated biomass to electricity systems

This thesis presents a comparison of integrated biomass to electricity systems on the basis of their efficiency, capital cost and electricity production cost. Four systems are evaluated: combustion to raise steam for a steam cycle; atmospheric gasification to produce fuel gas for a dual fuel diesel engine; pressurised gasification to produce fuel gas for a gas turbine combined cycle; and fast pyrolysis to produce pyrolysis liquid for a dual fuel diesel engine. The feedstock in all cases is wood in chipped form. This is the first time that all three thermochemical conversion technologies have been compared in a single, consistent evaluation.The systems have been modelled from the transportation of the wood chips through pretreatment, thermochemical conversion and electricity generation. Equipment requirements during pretreatment are comprehensively modelled and include reception, storage, drying and communication. The de-coupling of the fast pyrolysis system is examined, where the fast pyrolysis and engine stages are carried out at separate locations. Relationships are also included to allow learning effects to be studied. The modelling is achieved through the use of multiple spreadsheets where each spreadsheet models part of the system in isolation and the spreadsheets are combined to give the cost and performance of a whole system.The use of the models has shown that on current costs the combustion system remains the most cost-effective generating route, despite its low efficiency. The novel systems only produce lower cost electricity if learning effects are included, implying that some sort of subsidy will be required during the early development of the gasification and fast pyrolysis systems to make them competitive with the established combustion approach. The use of decoupling in fast pyrolysis systems is a useful way of reducing system costs if electricity is required at several sites because• a single pyrolysis site can be used to supply all the generators, offering economies of scale at the conversion step. Overall, costs are much higher than conventional electricity generating costs for fossil fuels, due mainly to the small scales used. Biomass to electricity opportunities remain restricted to niche markets where electricity prices are high or feed costs are very low. It is highly recommended that further work examines possibilities for combined beat and power which is suitable for small scale systems and could increase revenues that could reduce electricity prices.

Technical and economic simulation of biomass pyrolysis processes for fuels and electricity

There is considerable concern over the increased effect of fossil fuel usage on the environment and this concern has resulted in an effort to find alternative, environmentally friendly energy sources. Biomass is an available alternative resource which may be converted by flash pyrolysis to produce a crude liquid product that can be used directly to substitute for conventional fossil fuels or upgraded to a higher quality fuel. Both the crude and upgraded products may be utilised for power generation. A computer program, BLUNT, has been developed to model the flash pyrolysis of biomass with subsequent upgrading, refining or power production. The program assesses and compares the economic and technical opportunities for biomass thermochemical conversion on the same basis. BLUNT works by building up a selected processing route from a number of process steps through which the material passes sequentially. Each process step has a step model that calculates the mass and energy balances, the utilities usage and the capital cost for that step of the process. The results of the step models are combined to determine the performance of the whole conversion route. Sample results from the modelling are presented in this thesis. Due to the large number of possible combinations of feeds, conversion processes, products and sensitivity analyses a complete set of results is impractical to present in a single publication. Variation of the production costs for the available products have been illustrated based on the cost of a wood feedstock. The effect of selected macroeconomic factors on the production costs of bio-diesel and gasoline are also given.

High temperature gas cleaning for advanced syngas utilization:Paper # 95

Biofuels and chemicals from biomass mean the gasification of biogenic feedstocks and the synthesis via methanol, dimethylester (DME) or Fischer-Tropsch products. To prevent the sensitive synthesis catalysts from poisoning the syngas must be free of tar and particulates. The trace concentrations of S-, C1-, N-species, alkali and heavy metals must be of the order of a few ppb. Moreover maximum conversion efficiency will be achieved performing the gas cleaning above the synthesis conditions. The concept of an innovative dry HTHP syngas cleaning is presented. Based on the HT particle filtration and suitable sorption and catalysis processes for the relevant contaminants a total concept will be derived, which leads to a syngas quality required for synthesis catalysts in only 2 combined stages. The experimental setup for the HT gas cleaning behind the 60 kWtherm entrained flow gasifier REGA of the institute is described. Results from HT filter experiments in pilot scale are presented. The performance of 2 natural minerals for HC1 and H2S sorption is discussed with respect to the parameters temperature, surface and residence time. Results from lab scale investigations on low temperature tar catalysts' performance (commercial and proprietary development) are discussed finally.

Biofuel subsidies and international trade

This paper explores optimal biofuel subsidies in a general equilibrium trade model. The focus is on the production of biofuels such as corn-based ethanol, which diverts corn from use as food. In the small-country case, when the tax on crude is not available as a policy option, a second-best biofuel subsidy may or may not be positive. In the large-country case, the twin objectives of pollution reduction and terms-of-trade improvement justify a combination of crude tax and biofuel subsidy for the food exporter. Finally, we show that when both nations engage in biofuel policies, the terms-of-trade effects encourage the Nash equilibrium subsidy to be positive (negative) for the food exporting (importing) nation. © 2013 John Wiley & Sons Ltd.

Intermediate pyrolysis studies of aquatic biomass and potential applications in the BtVB-process

Aquatic biomass is seen as one of the major feedstocks to overcome difficulties associated with 1st generation biofuels, such as competition with food production, change of land use and further environmental issues. Although, this finding is widely accepted only little work has been carried out to investigate thermo-chemical conversion of algal specimen to produce biofuels, power and heat. This work aims at contributing fundamental knowledge for thermo-chemical processing of aquatic biomass via intermediate pyrolysis. Therefore, it was necessary to install and commission an analytical pyrolysis apparatus which facilitates intermediate pyrolysis process conditions as well as subsequent separation and detection of pyrolysates (Py- GC/MS). In addition, a methodology was established to analyse aquatic biomass under intermediate conditions by Thermo-Gravimetric Analysis (TGA). Several microalgae (e.g. Chlamydomonas reinhardtii, Chlorella vulgaris) and macroalgae specimen (e.g. Fucus vesiculosus) from main algal divisions and various natural habitats (fresh and saline water, temperate and polar climates) were chosen and their thermal degradation under intermediate pyrolysis conditions was studied. In addition, it was of interest to examine the contribution of biochemical constituents of algal biomass onto the chemical compounds contained in pyrolysates. Therefore, lipid and protein fractions were extracted from microalgae biomass and analysed separately. Furthermore, investigations of residual algal materials obtained by extraction of high valuable compounds (e.g. lipids, proteins, enzymes) were included to evaluate their potential for intermediate pyrolysis processing. On basis of these thermal degradation studies, possible applications of algal biomass and from there derived materials in the Bio-thermal Valorisation of Biomass-process (BtVB-process) are presented. It was of interest to evaluate the combination of the production of high valuable products and bioenergy generation derived by micro- and macro algal biomass.

Pyrolysis and gasification of biomass and acid hydrolysis residues

This research was carried for an EC supported project that aimed to produce ethyl levulinate as a diesel miscible biofuel from biomass by acid hydrolysis. The objective of this research was to explore thermal conversion technologies to recover further diesel miscible biofuels and/or other valuable products from the remaining solid acid hydrolysis residues (AHR). AHR consists of mainly lignin and humins and contains up to 80% of the original energy in the biomass. Fast pyrolysis and pyrolytic gasification of this low volatile content AHR was unsuccessful. However, successful air gasification of AHR gave a low heating value gas for use in engines for power or heat with the aim of producing all the utility requirements in any commercial implementation of the ethyl levulinate production process. In addition, successful fast pyrolysis of the original biomass gave organic liquid yields of up to 63.9 wt.% (dry feed basis) comparable to results achieved using a standard hardwood. The fast pyrolysis liquid can be used as a fuel or upgraded to biofuels. A novel molybdenum carbide catalyst was tested in fast pyrolysis to explore the potential for upgrading. Although there was no deoxygenation, some bio-oil properties were improved including viscosity, pH and homogeneity through decreasing sugars and increasing furanics and phenolics. AHR gasification was explored in a batch gasifier with a comparison with the original biomass. Refractory and low volatile content AHR gave relatively low gas yields (74.21 wt.%), low tar yields (5.27 wt.%) and high solid yields (20.52 wt.%). Air gasification gave gas heating values of around 5MJ/NM3, which is a typical value, but limitations of the equipment available restricted the extent of process and product analysis. In order to improve robustness of AHR powder for screw feeding into gasifiers, a new densification technique was developed based on mixing powder with bio-oil and curing the mixture at 150°C to polymerise the bio-oil.

Effects of engine cooling water temperature on performance and exhaust emission characteristics of a multi-cylinder CI engine operated with Jatropha-Butanol blend

Renewable alternatives such as biofuels and optimisation of the engine operating parameters can enhance engine performance and reduce emissions. The temperature of the engine coolant is known to have significant influence on engine performance and emissions. Whereas much existing literature describes the effects of coolant temperature in engines using fossil derived fuels, very few studies have investigated these effects when biofuel is used as an alternative fuel. Jatropha oil is a non-edible biofuel which can substitute fossil diesel for compression ignition (CI) engine use. However, due to the high viscosity of Jatropha oil, technique such as transesterification, preheating the oil, mixing with other fuel is recommended for improved combustion and reduced emissions. In this study, Jatropha oil was blended separately with ethanol and butanol, at ratios of 80:20 and 70:30. The fuel properties of all four blends were measured and compared with diesel and jatropha oil. It was found that the 80% jatropha oil + 20% butanol blend was the most suitable alternative, as its properties were closest to that of diesel. A 2 cylinder Yanmar engine was used; the cooling water temperature was varied between 50°C and 95°C. In general, it was found that when the temperature of the cooling water was increased, the combustion process enhanced for both diesel and Jatropha-Butanol blend. The CO2 emissions for both diesel and biofuel blend were observed to increase with temperature. As a result CO, O2 and lambda values were observed to decrease when cooling water temperature increased. When the engine was operated using diesel, NOX emissions correlated in an opposite manner to smoke opacity; however, when the biofuel blend was used, NOX emissions and smoke opacity correlated in an identical manner. The brake thermal efficiencies were found to increase slightly as the temperature was increased. In contrast, for all fuels, the volumetric efficiency was observed to decrease as the coolant temperature was increased. Brake specific fuel consumption was observed to decrease as the temperature was increased and was higher on average when the biofuel was used, in comparison to diesel. The study concludes that the effects of engine coolant temperature on engine performance and emission characteristics differ between biofuel blend and fossil diesel operation. The coolant temperature needs to be optimised depending on the type of biofuel for optimum engine performance and reduced emissions.

The influence of harvest and storage on the properties of and fast pyrolysis products from Miscanthus x giganteus

The research investigates the fuel property variations associated with the time of harvest and the duration of storage of Miscanthus x giganteus over a one year period. The crop has been harvested at three different times: early (September 2009), conventional (April 2010) and late (June 2010). Once harvested the crop was baled and stored. Biomass properties of samples taken from different storage zones were compared. The thermochemical properties have been investigated using a range of analytical equipment including thermogravimetric analysis (TGA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). In addition, bio-oil has been produced from the early, conventional and late harvest using a laboratory scale (300gh) fast pyrolysis unit. The potential organic liquid yield (ondry basis, also excluding the reaction water generated) based on the laboratory fast pyrolysis processing undertaken in this study, was found to vary between 2.82 and 3.18 dry tha for the early and the late harvest respectively. The bio-oil organic yield was reduced by approximately 11% (0.36tha) between the early and the late harvest. Char yield was also reduced by approximately 18% (0.61tha). The highest gas yield (18.03%-1.60tha) was observed for the conventional harvest. Gas chromatography-mass spectrometry (GC-MS) analysis of the bio-oil shows that levoglucosan, methylbenzaldehyde and 1,2-benzenediol all increase as a consequence of delayed harvest. It was also observed that by delaying the harvest time the O:C atomic ratio is reduced and a more carbonaceous feedstock is produced. © 2013 Elsevier Ltd.

Upgrading biomass fast pyrolysis liquids

A comprehensive examination is made of the characteristics and quality requirements of bio-oil from fast pyrolysis of biomass. An appreciation of the potential for bio-oil to meet a broad spectrum of applications in renewable energy has led to a significantly increased R&D activity that has focused on addressing liquid quality issues both for direct use for heat and power and indirect use for biofuels and green chemicals. This increased activity is evident in North America, Europe, and Asia with many new entrants as well as expansion of existing activities. The only disappointment is the more limited industrial development and also deployment of fast pyrolysis processes that are necessary to provide the basic bio-oil raw material. © 2012 American Institute of Chemical Engineers (AIChE).

Saccharomyces Cerevisiae as a biotechnological tool for ageing research:studies on translation and metabolism

The yeast Saccharomyces cerevisiae is an important model organism for the study of cell biology. The similarity between yeast and human genes and the conservation of fundamental pathways means it can be used to investigate characteristics of healthy and diseased cells throughout the lifespan. Yeast is an equally important biotechnological tool that has long been the organism of choice for the production of alcoholic beverages, bread and a large variety of industrial products. For example, yeast is used to manufacture biofuels, lubricants, detergents, industrial enzymes, food additives and pharmaceuticals such as anti-parasitics, anti-cancer compounds, hormones (including insulin), vaccines and nutraceuticals. Its function as a cell factory is possible because of the speed with which it can be grown to high cell yields, the knowledge that it is generally recognized as safe (GRAS) and the ease with which metabolism and cellular pathways, such as translation can be manipulated. In this thesis, these two pathways are explored in the context of their biotechnological application to ageing research: (i) understanding translational processes during the high-yielding production of membrane protein drug targets and (ii) the manipulation of yeast metabolism to study the molecule, L-carnosine, which has been proposed to have anti-ageing properties. In the first of these themes, the yeast strains, spt3?, srb5?, gcn5? and yTHCBMS1, were examined since they have been previously demonstrated to dramatically increase the yields of a target membrane protein (the aquaporin, Fps1) compared to wild-type cells. The mechanisms underlying this discovery were therefore investigated. All high yielding strains were shown to have an altered translational state (mostly characterised by an initiation block) and constitutive phosphorylation of the translational initiation factor, eIF2a. The relevance of the initiation block was further supported by the finding that other strains, with known initiation blocks, are also high yielding for Fps1. A correlation in all strains between increased Fps1 yields and increased production of the transcriptional activator protein, Gcn4, suggested that yields are subject to translational control. Analysis of the 5´ untranslated region (UTR) of FPS1 revealed two upstream open reading frames (uORFs). Mutagenesis data suggest that high yielding strains may circumvent these control elements through either a leaky scanning or a re-initiation mechanism. In the second theme, the dipeptide L-carnosine (ß-alanyl-L-histidine) was investigated: it has previously been shown to inhibit the growth of cancer cells but delay senescence in cultured human fibroblasts and extend the lifespan of male fruit flies. To understand these apparently contradictory properties, the effects of L-carnosine on yeast were studied. S. cerevisiae can respire aerobically when grown on a non-fermentable carbon source as a substrate but has a respiro-fermentative metabolism when grown on a fermentable carbon source; these metabolisms mimic normal cell and cancerous cell metabolisms, respectively. When yeast were grown on fermentable carbon sources, in the presence of L-carnosine, a reduction in cell growth and viability was observed, which was not apparent for cells grown on a non-fermentable carbon source. The metabolism-dependent mechanism was confirmed in the respiratory yeast species Pichia pastoris. Further analysis of S. cerevisiae yeast strains with deletions in their nutrient-sensing pathway, which result in an increase in respiratory metabolism, confirmed the metabolism-dependent effects of L-carnosine.

Heterogeneous catalysts for converting renewable feedstocks to fuels and chemicals

The combination of dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change is driving the urgent development of routes to utilise renewable feedstocks as sustainable sources of fuel and chemicals. Catalysis has a rich history of facilitating energy-efficient selective molecular transformations and contributes to 90% of chemical manufacturing processes and to more than 20% of all industrial products. In a post-petroleum era, catalysis will be central to overcoming the engineering and scientific barriers to economically feasible routes to biofuels and chemicals. This chapter will highlight some of the recent developments in heterogeneous catalytic technology for the synthesis of fuels and chemicals from renewable resources, derived from plant and aquatic oil sources as well as lignocellulosic feedstocks. Particular attention will be paid to the challenges faced when developing new catalysts and importance of considering the design of pore architectures and effect of tuning surface polarity to improve catalyst compatibility with highly polar bio-based substrates.

Nanoengineering the active site in heterogeneous catalysis

Here we demonstrate the first application of time-resolved synchrotron X-ray absorption spectroscopy to simultaneously follow dynamic nanoparticle surface restructuring and the evolution of surface and gas-phase products during an organic reaction. Surface palladium oxide, and not metal, is identified as the catalytic species responsible for the selective oxidation (selox) of crotyl alcohol to crotonaldehyde. Elevated reaction temperatures facilitate reversible nanoparticle redox processes, and concomitant catalytic selectivity loss, in response to reaction conditions. These discoveries highlight the importance of stabilizing surface palladium oxide and minimizing catalyst reducibility in order to achieve high selox yields, and will aid the future design of Pd-derived selox catalysts. This discovery has important implications for the design of future liquid and vapor phase selox catalysts, and the thermochemical behavior of Pd nanostructures in general.

Heterogeneous catalysts for biodiesel production

The combination of dwindling oil reserves and growing concerns over carbon dioxide emissions and associated climate change is driving the urgent development of clean, sustainable energy supplies. Biodiesel is non-toxic and biodegradable, with the potential for closed CO2 cycles and thus vastly reduced carbon footprints compared with petroleum fuels. However, current manufacturing routes employing soluble catalysts are very energy inefficient and produce copious amounts of contaminated water waste. This review highlights the significant progress made in recent years towards developing solid acid and base catalysts for biodiesel synthesis. Issues to be addressed in the future are also discussed including the introduction of non-edible oil feedstocks, as well as technical advances in catalyst and reactor design to ensure that biodiesel remains a key player in the renewable energy sector for the 21st century.

In situ aberration corrected-transmission electron microscopy of magnesium oxide nanocatalysts for biodiesels

Biofuels are promising renewable energy sources and can be derived from vegetable oil feedstocks. Although solid catalysts show great promise in plant oil triglyceride transesterification to biodiesel, the identification of active sites and operating surface nanostructures created during their processing is essential for the development of efficient heterogeneous catalysts. Systematic, direct observations of dynamic MgO nanocatalysts from a magnesium hydroxide-methoxide precursor were performed under controlled calcination conditions using novel in situ aberration corrected-transmission electron microscopy at the 0.1 nm level and quantified with catalytic reactivity and physico-chemical studies. Surface structural modifications and the evolution of extended atomic scale glide defects implicate coplanar anion vacancies in active sites in the transesterification of triglycerides to biodiesel. The linear correlation between surface defect density (and therefore polarisability) and activity affords a simple means to fine tune new, energy efficient nanocatalysts for biofuel synthesis. © 2009 Springer Science+Business Media, LLC.