Aachen team develops framework for model-based formulation of biofuel blends with tailored properties
28 March 2017
A team at RWTH Aachen University has developed a framework for the model-based formulation of biofuel blends with tailored properties by considering the fuel’s molecular composition as the fundamental design degree of freedom. A paper on their work is published in the ACS journal Energy & Fuels.
The researchers envision that the model-based approach can (i) guide fundamental experimental investigations of the combustion behavior of blended biofuels toward the most favorable mixtures and (ii) identify promising conversion pathways for further elaboration by means of reaction engineering and conceptual process design. The latter is ultimately needed to bridge the gap from a mass- and energy-based molecular level analysis to a process level analysis addressing the economics of the involved conversion and separation steps.
Whereas biofuel production based on gasification or pyrolysis is thought to yield mixtures of hydrocarbons designed to match the properties of fossil fuels, the aqueous phase processing of carbohydrates derived from hydrolysis of cellulose and hemicellulose enables selective access to one or few oxygenated fuel components, e.g., ethanol, 2-methyltetrahydrofuran, γ-valerolactone, ethyl- levulinate or 2-methylfuran. The molecular structure of such oxygenated fuel can be tailored to exhibit desired physicochemical properties that unlock the full potential of advanced internal combustion engines.
In an attempt to optimize both production and quality of the fuel, an integrated product and pathway design problem is posed on the molecular level in the present contribution. The complexity of this design problem is driven (i) by the rich variety of oxygenated fuel components that can be obtained from refunctionalization of bioderived sugars in principle, (ii) by the numerous conversion pathways that connect these molecules with the biomass feedstock, and (iii) by the interactions between physicochemical fuel properties and the performance of an internal combustion engine.
… The focus of this contribution lies on the rational formulation of well-defined blends of few bioderived fuel components. As such we will not consider thermochemical biofuel production pathways which typically yield complex multicomponent mixtures of (oxygenated) hydrocarbons. Instead, we will focus on biofuels made through hydrolysis of cellulose and hemi-cellulose followed by selective synthesis of few oxygenated species via chemical and/or fermentation routes. The blends are formulated to maximize a process-related performance indicator, such as mass of fuel produced for a fixed input of biomass, while certain fuel quality requirements, including constraints on the derived cetane number, fuel density, or volatility, are met.
—Dahmen and Marquardt
The method combines optimization-based reaction pathway screening with mathematical fuel property prediction by means of structural group contribution and quantitative structure–property relationship modeling in order to formulate and solve an integrated product and pathway design problem.
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| Blend design framework: integrated product and pathway design. The framework comprises four main stages. Based on the selection of a palette compound (Stage 1), a conversion pathway is created in Stage 2. Stage 3 sets up and solves the specific mixture design problem. Stage 4 is dedicated to a detailed analysis of the resulting mixtures, including the inspection of blend compositions, fuel properties and material flow diagrams. Credit: ACS, Dahmen and Marquardt. Click to enlarge. |
Case study. The paper describes a case study on the identification of promising blends and respective production routes for a spark-ignition (SI) engine. The goal of the exercise, said Manuel Dahmen and Wolfgang Marquard, both from the Aachen Process Systems Engineering group, was to produce a 100% bio-derived fuel with tailored properties from hexoses and pentoses from lignocellulosic biomass by utilizing renewable hydrogen from carbon-free energy sources such as wind or solar to boost the energy of fuel produced for a given quantity of biomass supplied.
The target engine was a boosted direct-injection spark-ignition engine. The objective was to maximize the energy of fuel produced (in terms of lower heating value) given a fixed feed of biomass; for the exercise, they decided not to constrain the supply of hydrogen, considering it instead as an enabler for directing as many carbon as possible from the carbohydrates toward the fuel, thereby maximizing the energy of fuel produced.
They considered 12 biobased intermediates which can be produced from hexoses and pentoses in large volumes. Reflecting the importance of knock-resistance and fuel volatility, two criteria were applied to select the palette compounds: (i) The normal boiling point of each blend component was below the final boiling point of a typical gasoline (∼225 °C). (ii) No blend component could exhibit a diesel-like autoignition tendency; the derived cetane number (DCN) of all blend components had to be smaller than ∼30.
In the case study, the maximization of the energy of fuel produced yielded a five-components blend rich in 1-butanol (44 mol %), cyclopentane (31 mol %), and ethyl acetate (15 mol %). This design features a high degree of hydrogenation (4.6 molH2/molfuel) and yields 0.75 MJfuel/MJbiomass (Blend A).
If DCN was constrained to ≤9, the result was a seven-components blend comprising 42 mol % ethanol, 26 mol % cyclopentanone, 15 mol % 2-butanone, 7 mol % 1-butene, 6 mol % 1-butanol, 3 mol % cyclopentane, and <1 mol % 1-propanol. (Blend B)
A simpler ternary blend was 1-butanol (45 mol %), ethanol (29 mol %), and cyclopentane (27 mol %). (Blend C). An optimal ternary blend consisted of ethanol (58 mol %), cyclopentane (27 mol %), and 2,5-dimethyltetrahydrofuran (15 mol %). (Blend D).
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| Number of active conversion steps and energy of fuel produced for all optimal binary (2 circles) and ternary (149 squares) blends. For comparison, the graph also includes the more complex blends A and B (2 stars). Credit: ACS, Dahmen and Marquardt. Click to enlarge. |
Resources
Manuel Dahmen and Wolfgang Marquardt (2017) “Model-Based Formulation of Biofuel Blends by Simultaneous Product and Pathway Design” Energy & Fuels doi: 10.1021/acs.energyfuels.7b00118
This opens the window a little to valuable info on boutique fuel blends. The ability of customizing processing and feed stocks with optimum ICE technology to maximize efficiency and lower emissions. Notice they use 100% biofuel. Also, I've heard the hydrogen blending does have some terrific fuel attributes. It may be an excellent biofuel additive and good way to easily utilize renewable hydrogen in most efficient form. Also, they didn't mention it, but water (thermal electrolysis) dislocation to hydrogen and oxygen is becoming more of a attractive element of high compression engines. They have yet to maximize that.
Posted by: Trees | 28 March 2017 at 04:36 AM
We can make bio synthetic and synthetic fuels, we have known how to do this for more than 50 years.
Posted by: SJC | 28 March 2017 at 12:06 PM
Fuel has been produced for 50 years. Problem is fuel has never been engineered to complement efficiency, power, and lower emissions. Now, the opportunity exists to desing fuel to maximum potential for efficiency and environment. This has never been done before.
Posted by: Trees | 30 March 2017 at 01:50 PM
It's not as if there is spare Hydrogen. If anything demand for traditional uses is increasing and then there are rapid deployment of fuel cells, upgrading of fossil and bio oils and chemical and plastics industry products being increasingly utilised.
My point here is that demand will outstrip supply for decades.Synthetic HC products have many advantages and value adding is usually environmentally beneficial. Whether high uptake as a blended fuel additive will be possible or a best use is not obvious.
From wiki
According to the U.S. Department of Energy, only in 2004,
53 million metric tons were consumed worldwide.
In 2006, the United States was estimated to have a production capacity of 11 million tons of hydrogen. 5 million tons of hydrogen were consumed on-site in oil refining, and in the production of ammonia (Haber process) and methanol (reduction of carbon monoxide)
Posted by: Arnold | 30 March 2017 at 04:06 PM
It is good to see this applied to bio fuel manufacture and would seem to be an important and possibly necessary application.
There have been articles describing economic benefits from supplementary hydrogen 20% and methane 80% injected into the air intake of diesel engines giving power boost emission reduction etc.
Hythane fuel enhancement.
Posted by: Arnold | 30 March 2017 at 04:28 PM
Ya, the post is just about R&D of biofuels, This team has developed a modeling tool to assess and improve the work of optimum alternative fuels. Starting from the ability to flex the hydrolysis of cellulose (ethanol process) to produce slightly different fuel character. Then blending gas or liquid constituents to optimize power and minimize harmful emissions. As you know lots of work within attempting to find an optimum fuel blend of which oxygenate rich ethanol is at the forefront. Usually, making fossil fuels burn better. I think the diesel engine is ripe for a new fuel that emits less harmful particles. The fuel can mixed with ethanol, usually up to 30%. NOX is always a problem and this is the primary target to minimize.
Hydrogen is such a valuable gas and research is continually looking for easier, cheaper, and renewable processes. The best outcome and key to beneficial, economical, and practical wind and solar energy may lie within hydrogen production.
Posted by: Trees | 31 March 2017 at 02:03 AM