Biomass to Butyl Esters and γ-Valerolactone (GVL)
...we have described an integrated biorefining strategy for the production of butyl esters and GVL starting from cellulose and utilizing reactive extraction of levulinic and formic acids with butene. This strategy simplifies the recovery and recycle of sulfuric acid for cellulose deconstruction and enables downstream catalytic processing in the absence of sulfur. The mixture of levulinic and formic esters, along with residual levulinic and formic acids, can be converted to an aqueous solution of GVL and 2-butanol in a single step over a dual-catalyst- bed consisting of Pd/C followed by Ru/C, in which H2 generated from FA and its ester over Pd/C is used for the reduction of LA and its ester to GVL over Ru/C.
—Gürbüz et al _GCC
Chemical engineering has barely begun to work on the problem of lignocellulosic biomass-to-energy. Up until now, the price of oil has not been consistently high enough to justify the research costs. But that is beginning to change. A team at UW-Madison is working on an approach to streamline a biomass to butene process.
The new process relies on the use of butene—produced by the decarboxylation of GVL during the process—as an extracting solvent in lieu of using alcohols, as proposed in other work. The new biorefining strategy simplifies earlier processes, is adaptable to various extraction conditions, and potentially advances the cost-effective production of alkenes from renewable lignocellulosic resources, the researchers say.
In the hunt for cost-effective, high-yield ways to convert biomass into renewable liquid hydrocarbons, one attractive approach is the controlled reduction of the oxygen content in the feedstock to produce platform chemicals that retain sufficient functionality for upgrading to a variety of useful end products (biorefining). Levulinic acid (LA) is an attractive platform molecule that can be converted to, among others, GVL.
...The new process comprises the following steps:
Production of an aqueous solution containing equimolar concentrations of LA and formic acid (FA) by hydrolysis of cellulose at 423 K (150 °C) using sulfuric acid (0.5m);
Some of the water and the FA co-product are then removed by an evaporation step to obtain a more concentrated solution of LA and sulfuric acid, containing residual amounts of water and FA.
The FA product in water is retained for downstream hydrogen production in a dual-catalyst-bed system, and the concentrated LA product is contacted with butene, generating sec-butyl levulinate (BL) and sec-butyl formate (BF) esters as major and minor products, respectively, using H2SO4 as a catalyst. The team has demonstrated that high yields, 85%, of the levulinate ester can be attained at moderate temperatures (<373 K, 100 °C) and short contact times (<120 min). Excess butene is recovered by vaporization, and the concentrated ester product is then contacted with water, during which the hydrophobic ester separates spontaneously from the aqueous phase, the latter of which retains 99% of the sulfuric acid to be recycled for use in biomass deconstruction. The BL and BF esters are subsequently processed in combination with the aqueous FA product stream (obtained from the evaporation step) using a dual-catalyst-bed in a single reactor to produce GVL in nearly quantitative yields with 2-butanol and CO2 as coproducts. The liquid effluent from this reactor, consisting of an aqueous solution of GVL and 2-butanol, can undergo decarboxylation and dehydration (of GVL and butanol, respectively) over a catalyst to obtain butene and CO2. _GCC
As more engineers, microbiologists, nanotechnologists, plant scientists, and thermodynamics experts become involved in the problem of creating renewable liquid fuels, expect to see significant progress.
The economics will take longer to catch up with the science and engineering.
In a rational energy climate, there would be more than enough coal, gas, and unconventional hydrocarbons, and nuclear energy to ride out the current storm of "political peak oil." Lacking a rational energy climate, we must hope that the energy starvation regime of Obama and company gets tangled in its own intrigues.