Toward an Economical Production of Propane and Propylene from Biomass

Biomass can be fermented to produce butyric acid or 3-hydroxybutyrate, which can then be decarboxylated to produce propane or propylene. Here's the abstract from research done at MIT chemical engineering dept. describing their more economical process of producing propane and propylene from butyric acid :

We demonstrate a route for the production of C3 hydrocarbons from renewable biomass by the hydrothermal conversion of well-known fermentation end-products. Specifically, the major commercial C3 hydrocarbons, propane and propylene, can be obtained from butyric acid and 3-hydroxybutyrate (3HB) in substantial yields and industrially relevant productivities by hydrothermal decarboxylation. Butyric acid decarboxylates in supercritical water to give propane as the major product at 454 °C and 25 MPa. 3HB undergoes joint dehydration and decarboxylation in subcritical water to yield propylene at 371 °C and 25 MPa with yields of up to 48 mol %. Although catalysts may be found that increase yields and selectivities, these processes were demonstrated without any added heterogeneous catalysts, and have the further advantage of requiring no external H2 source. _ACS

This follows an earlier report from U. Michigan and Zhejiang U. (China) describing the synthesis of longer chain hydrocarbons by decarboxylation from fatty acids, without added hydrogen.

Propylene has many industrial uses, and propane is the third most commonly used fuel in the world. If these 3 chain hydrocarbons can be made cheaply enough from biomass, they will find a ready market.

More from GCC

Petroleum prices are currently over-hyped, but the longer they stay high, the more motivation research funders will have for funding alternative approaches to common fuels and industrial chemicals from alternative feedstocks.

A Promising Approach to Advanced Biofuels w/o Hydrotreatment

Finland's Neste Oil has proven its hydrotreatment approach to advanced biodiesel beyond question. But hydro-treating bio-oils is expensive, and more economical approaches are likely to find quicker and more widespread acceptance among advanced synthetic liquid fuels producers. Fortunately, a joint team from both China's Zhejiang University and the US University of Michigan, is hot on the trail of a process which achieves the advanced renewable synthesis of liquid hydrocarbons without requiring expensive hydrotreatment.

We report herein on the conversion of saturated and unsaturated fatty acids to alkanes over Pt/C in high-temperature water. The reactions were done with no added H2. The saturated fatty acids (stearic, palmitic, and lauric acid) gave the corresponding decarboxylation products (n-alkanes) with greater than 90 % selectivity, and the formation rates were independent of the fatty acid carbon number. The unsaturated fatty acids (oleic and linoleic acid) exhibited low selectivities to the decarboxylation product. Rather, the main pathway was hydrogenation to from stearic acid, the corresponding saturated fatty acid. This compound then underwent decarboxylation to form heptadecane. On the basis of these results, it appears that this reaction system promotes in situ H2 formation. This hydrothermal decarboxylation route represents a new path for using renewable resources to make molecules with value as liquid transportation fuels. _Wiley abstract_via_GCC

Here is more detail on the research from GreenCarCongress.com:

As described in the paper, the team of Jie Fu, Xiuyang Lu, and Phillip Savage converted five different fatty acids prevalent in nature—stearic, palmitic, lauric, oleic, and linoleic—to alkanes over a commercial 5% Pt/C catalyst in high-temperature water (330 °C). The reactions were done with no added hydrogen, in contrast to the processes that have adapted petroleum hydrotreatment technology to convert triglycerides and fatty acids into hydrocarbons.

Recent review articles have highlighted the significant research and development (R&D) efforts that have been devoted to using and adapting petroleum hydrotreatment technology to convert triglycerides and fatty acids into hydrocarbons...The high H2 consumption associated with these processes is their main drawback. H2 is not currently available in large quantities from renewable resources and H2 costs can be high. Moreover, H2 is made primarily from steam reforming of natural gas and CO2 is the byproduct. Thus, a near-term process for the production of fully renewable biofuels needs to operate without added H2.

—Fu et al.

_More at GCC

The GCC article goes on to describe the decarboxylation process adopted by the joint-university team, which produces CO2 as a byproduct of decarboxylation. The process is faster and perhaps more efficient using saturated fatty acides as feedstock, as opposed to unsaturated fatty acids. Oils such as palm oil, which are high in saturated palmitic acid, would seem to be ideal for the process.

If the world can ever pacify the carbon hysterics -- at least remove them from positions of high office and power -- the terrestrial and oceanic plants of the world can be freer to enjoy some extra free CO2, courtesy of the human animal.

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.

_GCC

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.