Michael Boot

Catalytic depolymerization of lignin in supercritical ethanol.

One-step valorization of soda lignin in supercritical ethanol using a CuMgAlOx catalyst results in high monomer yield (23 wt%) without char formation. Aromatics are the main products. The catalyst combines excellent deoxygenation with low ring-hydrogenation activity. Almost half of the monomer fraction is free from oxygen. Elemental analysis of the THF-soluble lignin residue after 8 h reaction showed a 68% reduction in O/C and 24% increase in H/C atomic ratios as compared to the starting Protobind P1000 lignin. Prolonged reaction times enhanced lignin depolymerization and reduced the amount of repolymerized products. Phenolic hydroxyl groups were found to be the main actors in repolymerization and char formation. 2D HSQC NMR analysis evidenced that ethanol reacts by alkylation and esterification with lignin fragments. Alkylation was found to play an important role in suppressing repolymerization. Ethanol acts as a capping agent, stabilizing the highly reactive phenolic intermediates by O-alkylating the hydroxyl groups and by C-alkylating the aromatic rings. The use of ethanol is significantly more effective in producing monomers and avoiding char than the use of methanol. A possible reaction network of the reactions between the ethanol and lignin fragments is discussed.

Ethanol as capping agent and formaldehyde scavenger for efficient depolymerization of lignin to aromatics

Obtaining renewable fuels and chemicals from lignin presents an important challenge to the use of lignocellulosic biomass to meet sustainability and energy goals. We report on a thermocatalytic process for the depolymerization of lignin in supercritical ethanol over a CuMgAlOx catalyst. Ethanol as solvent results in much higher monomer yields than methanol. In contrast to methanol, ethanol acts as a scavenger of formaldehyde derived from lignin decomposition. Studies with phenol and alkylated phenols evidence the critical role of the phenolic –OH groups and formaldehyde in undesired repolymerization reactions. O-alkylation and C-alkylation capping reactions with ethanol hinder repolymerization of the phenolic monomers formed during lignin disassembly. After reaction in ethanol at 380 °C for 8 h, this process delivers high yields of mainly alkylated mono-aromatics (60–86 wt%, depending on the lignin used) with a significant degree of deoxygenation. The oxygen-free aromatics can be used to replace reformate or can serve as base aromatic chemicals; the oxygenated aromatics can be used as low-sooting diesel fuel additives and as building blocks for polymers.

Reductive fractionation of woody biomass into lignin monomers and cellulose by tandem metal triflate and Pd/C catalysis

A catalytic process for the upgrading of woody biomass into mono-aromatics, hemi-cellulose sugars and a solid cellulose-rich carbohydrate residue is presented. Lignin fragments are extracted from the lignocellulosic matrix by cleavage of ester and ether linkages between lignin and carbohydrates by the catalytic action of homogeneous Lewis acid metal triflates in methanol. The released lignin fragments are converted into lignin monomers by the combined catalytic action of Pd/C and metal triflates in hydrogen. The mechanism of ether bond cleavage is investigated by lignin dimer models (benzyl phenyl ether, guaiacylglycerol-β-guaiacyl ether, 2-phenylethyl phenyl ether and 2-phenoxy-1-phenylethanol). Metal triflates are involved in cleaving not only ester and ether linkages between lignin and the carbohydrates but also β-O-4 ether linkages within the aromatic lignin structure. Metal triflates are more active for β-O-4 ether bond cleavage than Pd/C. On the other hand, Pd/C is required for cleaving α-O-4, 4-O-5 and β–β linkages. Insight into the synergy between Pd/C and metal triflates allowed optimizing the reductive fractionation process. Under optimized conditions, 55 wt% mono-aromatics – mainly alkylmethoxyphenols – can be obtained from the lignin fraction (23.8 wt%) of birch wood in a reaction system comprising birch wood, methanol and small amounts of Pd/C and Al(III)-triflate as catalysts. The promise of scale-up of this process is demonstrated.

Effective release of lignin fragments from Lignocellulose by Lewis Acid Metal triflates in the lignin-first approach

Adding value to lignin, the most complex and recalcitrant fraction in lignocellulosic biomass, is highly relevant to costefficient operation of biorefineries. We report the use of homogeneous metal triflates to rapidly release lignin from biomass. Combined with metal-catalyzed hydrogenolysis, the process separates woody biomass into few lignin-derived alkylmethoxyphenols and cellulose under mild conditions. Model compound studies show the unique catalytic properties of metal triflates in cleaving lignin-carbohydrate interlinkages. The lignin fragments can then be disassembled by hydrogenolysis. The tandem process is flexible and allows obtaining good aromatic monomer yields from different woods (36-48 wt %, lignin base). The cellulose-rich residue is an ideal feedstock for established biorefining processes. The highly productive strategy is characterized by short reaction times, low metal triflate catalyst requirement, and leaving cellulose largely untouched.

Spray impingement in the early direct injection premixed charge compression ignition regime

The main goal of this paper is to acquire more insight into the relationship between wall and piston impingement of liquid fuel and unburnt hydrocarbon emissions (UHC) emissions, under early direct injection (EDI) premixed charge compression ignition (PCCI) operating conditions. To this end, the vaporization process is modeled for various operating conditions using a commercial CFD code (StarCD). Predicted values for liquid core penetration, or liquid length LL , have been successfully checked against experimental data from literature over a wide range of operating conditions. Next, the correlation between the CFD results for wall and piston impingement and measured UHC emissions is studied. The diesel fuel used in the experiments is modeled as n-dodecane and n-heptadecane, representing the low and high end of the diesel boiling range, respectively. A distinction is made between liquid spray impingement on the piston surface and cylinder liner. For a conventional DI diesel nozzle, the high UHC emissions in the EDI PCCI regime correlate well with modeled cylinder wall impingement. Conversely, piston impingement is negligible in this regime. Accordingly, it may be assumed that the primary cause for high UHC emissions in the EDI PCCI regime, using conventional DI nozzles, is caused by liquid spray impingement against the cylinder liner. In this regime it was found that a higher intake and fuel temperature, as well as an elevated intake pressure have a positive effect on both UHC emissions and the spray impingement against the cylinder wall. This provides additional evidence that the two parameters (i.e. UHC and wall impingement) are linked. Lastly, the impact of nozzle cone angle is investigated. When adopting a narrow cone angle nozzle in the EDI PCCI regime, wall impingement is negligible and piston wetting becomes the dominant source of UHC emissions.

Assessment of the Effect of Low Cetane Number Fuels on a Light Duty CI Engine: Preliminary Experimental Characterization in PCCI Operating Condition

The goal of this paper is to acquire insight into the influence of cetane number (CN) and fuel oxygen on overall engine performance in the Premixed Charge Compression Ignition (PCCI) combustion mode.

Low Cetane Number Renewable Oxy-fuels for Premixed Combustion Concept Application: Experimental Investigation on a Light Duty Diesel Engine

This paper illustrates the results of an experimental study on the impact of a low cetane number (CN) oxygenated fuel on the combustion process and emissions of a light-duty (LD) single-cylinder research engine. In an earlier study, it was concluded that cyclic oxygenates consistently outperformed their straight and branched counterparts at equal oxygen content and with respect to lowering soot emissions. A clear correlation was reported linking soot and CN, with lower CN fuels leading to more favorable soot levels. It was concluded that a lower CN fuel, when realized by adding low reactive cyclic oxygenates to commercial diesel fuel, manifests in longer ignition delays and thus more premixing. Ultimately, a higher degree of premixing, in turn, was thought to suppress soot formation rates. Such compounds have the advantage to be stable in blends with fossil diesel fuel, to have a boiling point close to the diesel fuel range, and have the potential to be produced in a renewable way from lignin , which has a similar hexagonal hydrocarbon basis, albeit in polymer form. Lignin is currently a widely available second generation biomass waste stream, found in for example the paper pulp industry and cellulosic ethanol plants. In the present work, blends of diesel and cyclohexanone were tested in a LD single cylinder research diesel engine in order to evaluate its effects on the combustion process and pollutant emissions, employing both conventional (i.e. mixing-controlled) combustion (at medium/high engine loads) and premixed combustion (at medium/low loads). The results suggest that the combination of low CN and fuel oxygen appears to have a favorable impact on both fuel efficiency and overall emissions in premixed-mode. For mixing-controlled combustion, at medium/high engine loads, the negative effects of low CN (e.g. retarded combustion phasing) can be overcome with an appropriate calibration of the injection parameters. The high unburnt hydrocarbon emissions at low load, conversely, require a further development of the combustion system design, as well as the after-treatment device. Finally, to realize a more and more precise control of the in-cylinder air-fuel charge, before and during the combustion, the future PCCI fuels have to be tailored to the specific combustion process characteristics. In this framework, renewable low CN oxygenated fuels might function as an enabler for PCCI combustion engines.

Throttle loss recovery using a variable geometry turbine

Two of the most pressing challenges of the automotive sector are reduction of fuel consumption and corresponding emission of greenhouse gases, especially when taking into account the growing degree of luxury in modern passenger cars, which increases the auxiliary load on the engine. Preferably, this increase in auxiliary load is compensated by the recovery of waste energy. To accomplish this, a technology called WEDACS (Waste Energy Driven Air Conditioning System) is being developed to recover throttling losses. WEDACS uses a turbine to induce provide the engine with the same air mass flow rate as a throttle valve while producing mechanical energy and cold air. An alternator coupled to this turbine converts mechanical energy into electrical energy and the cold air is used to cool A/C fluid. This way the load of both the engine-mounted alternator and A/C compressor is reduced or eliminated, resulting in higher efficiency. A previous paper provides a proof of principle, using a turbine from a turbocharger, but also discusses a challenge in the form of a limited operating range. The present paper focuses on addressing this challenge. To expand the control range of the engine, a turbocharger with variable nozzle turbine is used. Due to limitations in the variable nozzle mechanism, the range is limited to higher engine powers. It is shown that between 50 W and 1.3 kW of energy can be recovered from a 2-liter engine, depending on the operating point. A second turbochargers variable nozzle mechanism is adapted to enable control of a 2-liter engine from idle to about 50% engine power. With decreasing engine power, the energy recovery efficiency eventually drops to zero. The root cause for this is identified and an attempt is made to improve efficiency. Finally the drive cycle model from the previous paper is expanded and a new drive cycle simulation shows a fuel consumption improvement over the NEDC of about 5 to 8% for a mid-sized passenger car with a 2-liter engine.

Waste Energy Driven Air Conditioning System (WEDACS)

In the port injected Spark Ignition (SI) engine, the single greatest part load efficiency reducing factor are energy losses over the throttle valve. The need for this throttle valve arises from the fact that engine power is controlled by the amount of air in the cylinders, since combustion occurs stoichiometrically in this type of engine. In WEDACS (Waste Energy Driven Air Conditioning System), a technology patented by the Eindhoven University of Technology, the throttle valve is replaced by a turbine-generator combination. The turbine is used to control engine power. Throttling losses are recovered by the turbine and converted to electrical energy. Additionally, when air expands in the turbine, its temperature decreases and it can be used to cool air conditioning fluid. As a result, load of the alternator and air conditioning compressor on the engine is decreased or even eliminated, which increases overall engine efficiency. A model and validating experiment both indicate throttle losses of about 1.25 kW in a modern 2 liter engine at common operating points. On the same engine in a different operating point, an automotive turbocharger is used in another experiment to recover 1.1 kW of these throttling losses. Based on these measurements, a simulated MVEG-A drive cycle predicts a fuel efficiency improvement of 15 to 19 %.

Uncooled EGR as a means of limiting wall-wetting under early direct injection conditions

Collision of injected fuel spray against the cylinder liner (wall-wetting) is one of the main hurdles that must be overcome in order for early direct injection Premixed Charge Compression Ignition (EDI PCCI) combustion to become a viable alternative for conventional DI diesel combustion. Preferably, the prevention of wall-wetting should be realized in a way of selecting appropriate (most favorable) operating conditions (EGR level, intake temperature, injection timing-strategy etc.) rather than mechanical modification of an engine (combustion chamber shape, injector replacement etc.). This paper presents the effect of external uncooled EGR (different fraction) on wall-wetting issues specified by two parameters, i.e. measured smoke number (experiment) and liquid spray penetration (model). Experiments performed in a dedicated heavy-duty direct injected (HDDI) diesel engine suggest that the elevation of intake temperature caused by delivery of external uncooled exhaust gases led to significant reduction in wall wetting. This is combined with IMEP improvement. In-house spray- and ignition modeling was used to gain insight into the measured trends. Copyright