Thursday, February 03, 2011

A Spanish Solution: Renewable Diesel from Waste

A team at the Universidad Politécnica de Valencia (Spain) has designed a new simple, energy-efficient process (that also does not require any organic solvents) for the production of renewable diesel from biomass waste. A paper on their work is published in the journal Angewandte Chemie International Edition. _GCC
The name of the game in biofuels is efficiency and affordability of both feedstock and every step in the pre-processing, refining, and synthesis processes -- plus efficient distribution. Given the upward creep of liquid fuel prices caused by emerging demand, speculation, and cartel shenannigans, it is crucial that renewable alternative liquid fuels be made affordable. To that end, teams of researchers and technologists are working on the problem around the world.
A number of routes have been and are being developed for the conversion of biomass into renewable fuels, including (but not limited to):
  • Gasification of biomass followed by Fischer-Tropsch synthesis;
  • Fast pyrolysis and upgrading of bio-oil;
  • Hydrolysis of biomass followed by the fermentation of the sugars by genetically modified microorganisms to hydrocarbons;
  • Dehydration of hydrolyzed sugars to 5-hydroxymethylfurfural (HMF) or into furfural (FUR) when starting from hexoses or pentoses, respectively, followed by aqueous phase processing;
  • Production of γ-valerolactone from biomass-derived carbohydrates via levulinic acid, followed by decarboxylation to produce butene and CO2, the former then being oligomerized to octenes and hexadecenes in a second step.
This list of processes to produce second-generation biofuels can be further expanded, but the extent to which one of these technologies will play an active role in the future biofuel industry will depend on economics, energy efficiency, and environmental issues. Surplus energy consumption and process limitations can be detected in most of the processes proposed to date. For example, the excessive cleavage of carbon–carbon bonds and subsequent reformation leads to energy losses. Extractions of products with organic solvents are energy and cost-intensive steps that change, to the worse, the overall energy balance of the process. Organic solvents as reaction medium should be avoided, as they enlarge process volumes with a negative impact on process economics and environment. A crucial point for the optimization of the overall process economics is the perfect overlap of the boiling point range of the product mixture, with diesel range C9 to C24 hydrocarbons.

Here is the Spanish solution devised by U. Politecnica de Valencia researchers:
The first step is the conversion of biomass into furfural—an established industrial process. In an adaptation of another current process, furfural can be converted with high selectivity into 2-methyl-furfural (2MF), a ring consisting of four carbon atoms and one oxygen atom, with a side chain consisting of a methyl group (-CH3).

Three molecules of 2MF are linked together. This requires water and an acid catalyst. This reaction causes one third of the rings to open and each to link to two other rings (hydroxy alkylation/alkylation). The aqueous phase, which also contains the catalyst, separates from the organic phase, which contains the intermediate product, on its own. It can easily be removed and the catalyst recycled. In a second reaction, the two other rings must also be opened and their oxygen atoms removed. This reaction uses a special platinum-containing catalyst (hydrodeoxygenation).
In the end we obtain 87% of the diesel fraction in the form of branched hydrocarbon chains with nine to 16 carbon atoms. This is the best yield reported in the literature thus far for biodiesel synthesis.
—Avelino Corma
The process is very stable at lab levels (more than 140h). Gas-phase and lower molecular weight byproducts can be used to produce heat. The resulting renewable hydrocarbon liquids are of excellent quality (cetane number 71, pour point -90 °C) and can be mixed directly with conventional diesel fuels.


A good use for used motor oil

Another wastewater to diesel conversion using algae

Questions about the validity and reliability of the recent Rand report on algal fuels for the US military are beginning to crop up. More on that later.

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