04 June 2006

Soy Biodiesel Review

The topic of discussion is Sheehan, J., V. Camobreco et al. (1998) . Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus. Golden, National Renewable Energy Laboratory. It's a big, inclusive report (314 pages) on the the energy balance of soy derived biodiesel and fossil diesel.

Energy Return

Let's start on p. V of the executive summary:
Biodiesel yields 3.2 units of fuel product energy for every unit of fossil energy consumed in its life cycle. The production of B20 yields 0.98 units of fuel product energy for every unit of fossil energy consumed.
That first number, 3.2 units of fuel product energy for every unit of fossil energy. What does this mean? It's in a big bold block quote in the executive summary. It looks like the EROEI, right? Unfortunately it's not. On p. 207 we find that Fossil Energy Ratio = Fuel Energy/Fossil Energy Inputs. In other worlds, any power input that is not a fossil source is not accounted for. For the purposes of this study, this means the hydroelectric and nuclear power share. What we actually want to know is the total process energy required. The energy inputs for biodiesel are predominately electricity (to run machinery) and low grade steam (50 - 70 °C), along with natural gas (to produce methanol) in addition to the standard farm inputs.

Fortunately, the results are not that badly off due to this factor. The study divides the production of biodiesel into five stages:
  1. Agriculture
  2. Transport from farm to processing plant
  3. Soybean crushing and oil separation operations
  4. Conversion of soy oil to methyl ester fuel.
  5. Transport and distribution of biodiesel to consumers.
The study also accounts for transport from the separation plant to the conversion plant but this energy input is left out of the end results. I agree with this because it is overly high due to the small number of biodiesel plants in the USA at the time of the study. For large scale biodiesel production the two operations would be naturally collocated.

I went through the study to attempt to figure out what the difference was between fossil and absolute energy inputs. Annoyingly, for Stage 4 (Conversion), the energy of the soy oil is incorporated as an input. What makes this frustrating is that the authors at no point in the study actually define what they consider the energy content of soy oil to be, which makes deconstructing this part of the study difficult.

Table 1: Energy Allocation to Biodiesel Production Stages



(MJ/kg biodiesel)




Table 62, p. 116



Table 63, p. 118



Table 83, p. 137



Table 105, p. 166



Table 106, p. 169



Higher Heating Value


Table 108, p. 173

Lower Heating Value


Table 108, p. 173



As it happens, I get a better result (3.24 > 3.2) but that's due to the fact that I employ the Higher Heating Value -- the original authors' calculation uses the LHV. As it happens, this is only a minor bone I have to pick with the study. The big problem is with what's called "Allocation of Lifecycle Flows." Anyone who has read into ethanol studies will know this as 'coproducts'.

Funny Coproduct Accounting

The first giant problem associated with 'coproducts' appears in the Separation (or crushing) stage. The oil content of soybeans is rather low − around 18.4 %. For this entire study, allocation of energy consumption between biodiesel and coproducts is done purely on a mass basis. Unfortunately, this leads to a silly assumption. Table 82 (p. 136) allocates 18 % of energy consumption for the Separation stage to soy oil and 82 % to meal. This in turn propagates back through the allocations for transport and agricultural energy consumption. Is this fair? Take a look at Table 64 (p. 121):

Table 2: Mass composition of soybeans


18.4 %


0.8 %


7.4 %


16.0 %


57.4 %

That's right boys and girls, the authors are allocating the same value to oil as dirt and water. Realistically if the mass of dirt, water, and hulls were discarded then the oil would have to assume 24.2 % of energy use for the first three stages. Furthermore, it probably makes more sense to compare the ratio between the wholesale price of soy oil versus soy meal to determine the proper value of the coproducts. Free hint: the oil is worth more per kilogram than the meal.

This process is repeated for the Conversion stage is similar for the allocation between methyl ester (biodiesel) and glycerin. For this stage, 82 % of the energy is allocated to biodiesel and 18 % to glycerin. Once again this allocation is propagated back through the previous steps. However, this calculation is actually unfavourable to the biodiesel. Separating the glycerin and excess methanol consumes approximately 65 % of the energy for the Conversion stage (Table 96, p. 159). The reason is distillation. As anyone who has looked at ethanol systems will know, distillation is a killer because it requires so much energy to vapourize water. Also, the NREL numbers come out quite high compared to some European plants also presented in the report.

From my point of view, I want to know if biodiesel is energy positive, regardless of coproducts. For soy, the answer appears to be no. Going back and removing the coproduct credits appears to give the following results:

Table 3: Energy Consumption for Biodiesel Production
with Zero Coproduct Credits



(MJ/kg biodiesel)















Before we all fall into a state of depression, it is fairly clear from the report that there is a lot of promise in reducing the energy inputs for the conversion stage. Methanol inputs constitute approximately half the energy inputs. I have previously hypothesized that anaerobic digestion of the meal could produce methane which in turn could be made into methanol in addition to providing heat energy. The NREL numbers require approximately three times as much energy as some quoted European operations (Table 98, p. 161).

There are potential improvements to be made to the efficiency of the Conversion stage as well. Research and development on catalysts offers the potential to reduce the reaction temperature. In particular I think a zeolite could be ideal for separating the glycerol from the methyl ester chains. Most of the energy (65 %) is used not for the actual conversion but for distilling out glycerin and excess methanol post-transesterfication − normally an excess of methanol is added to carry through the reaction to completion. Reducing the amount of water and methanol used will have a direct result on the distillation requirements.

Like ethanol, biodiesel would benefit significantly from combined heat and power generation. The temperature requirements for most processes is low enough (50 - 70 °C) that the use of solar thermal systems to augment the heat production is feasible.

To a certain extent glycerin might be the biodiesel analogue to sulfur for petroleum oil. Sulfur is a chemical with its uses, but oil refining produces mountains of the stuff. Will glycerin be a product worth distilling in a biodiesel nation, or should it just go into the anaerobic digester to make more methane?

Soy versus Rapeseed (Canola)

Any way you cut it soy is not an ideal crop for biofuel production. Soy does have one significant advantage in that it's a legume and hence fixes atmospheric nitrogen. As such, the energy requirements for fertilizer for soy is very low compared to everyone's favourite biomass villain, corn. However, the foremost quantity on my mind is the low oil content of soybeans. It's about 18 % (Table 64, p. 121) versus 40 % for rape and jatropha or 70 % for coconut. Rape appears to be the best temperate crop for biodiesel production. Its oil quality is high as its content, and its moisture content low.

The NREL study uses an average yield of 36 bushels/acre for soy which works out to 445 kg (oil)/hectare. (Here is a useful webpage for converting agricultural units from US Customary nonsense to more sensible metric units. Oh, and soybeans are 60 lbs./bushel, not 56 or 48 or 25 lbs./bushel but you all knew that, right? Next thing you know they'll be measuring the volume of biodiesel in barrels.) In comparison Canadian Canola yields about 640 kg (oil)/ha. The same source gives European Rapeseed a much higher yield of approximately 1280 kg (oil)/ha, largely due to the greater use of irrigation.

Aside from the oil content issue there are a number of other drawbacks for soy. For the most part, soy appears to take a great deal of work to get the oil separated from the meal. Soy has a high moisture content of 16.0 % water by mass (Table 64, p. 121) which necessitates drying.
In comparison, Canola is about half that if properly sun dried, and hence can be processed without drying. Soy also needs to be flaked into regular sized small pieces, which constitutes about a quarter of the electricity requirements for the Separation stage.


Anonymous said...

Biodiesel is not a solution. It is politics, it is spin, it is agribusiness profits, it is a hobby.

Soy and canola and oil palm are food, they are not fuel. Do you really want humans to be competing with cars for their food source?

A human consumes on average 20 liters of edible oil a year. 20 liters - around five and a quarter gallons. Per year. How long does it take your car to consume five gallons of fuel? Half a day?

Worldwide, we are consuming around 85 million barrels of petroleum every day - that's 13.5 billion liters per day. The entire human population only eats around 328 million liters of food oil a day. So, let's compare: 13,500 million liters of fuel oil consumed every day vs. 328 million liters of food oil consumed every day. That's 41 times more fuel oil than food oil consumed.

What makes biodiesel proponents think that biodiesel is an alternative to petroleum? How could we possibly increase food oil production by 41 times? Cut down the rest of the mangrove swamps for oil palm plantations? Raze the rest of the rain forest for soy bean fields? Just to run the world on B10 (10% biodiesel, 90% petroleum diesel - hardly an end to petroleum dependency) we'd have to increase plant oil production by a factor of four. That alone would require destroying the rest of our suffering ecosystem, and that type of food oil consumption would likely raise food prices to the point where the majority of the world's population living on just a few dollars a day would starve to death - the world's poor simply can't compete with our cars.

So, the world running on 10% biodiesel = ecological disaster and mass starvation. Not an optimal solution. We're still dependent on petroleum, but manage to bury the ecosystem and starve billions of people.

No, biodiesel is not a solution. It's something for a small group of hobbyists. It is something for politicians to make hay off of. It is something for fools and people who can't do simple math to fall for.

What is the solution - solar? Wind? Nukes? I can't say, but it is certainly not dreaming that we can farm our way out of this, and the solution is certainly not in wasting our time and resources pursuing this dead end.

Robert McLeod said...

Thank you for not reading my blog before, or you would know my answer to this.

Anonymous said...

Mark Harrison, I agree that it's not a great solution for now - but remembering that new technologies need not be a panacea, I also think that cultured oil production in algae farms promises to more than provide for the balance, but also supply a healthy supply of cooking oil to replace other conventional products.

Anonymous said...

This is the absolutely worst possible mode of criticism, and one that's practically ingrained in these discussion circles. The flinging of the agrabusiness' profiteering off of an expansive biofuel industry at some myopic idea of impending famine and petrol figures.

All major infrastructures are made possible by profiteering. It's the world we live in. The only alternative to major corporations and private interests buoying up green technologies is wholesale investment by the government, and you're out in space somewhere if you think THAT'S a good idea.

I should say that I agree with the basic premise. Cars can't supplant humanity, and we can't sustain our ridiculous current fuel usage standards on soybeans. But to rant on as such and then admit that you've got no clue as to what alternative-alternative solutions are out there speaks to the fact that you MIGHT want to do some homework aside from knee-jerk reactivity.

With that in mind, I'd suggest you actually take the time to read this blog and LEARN something about what you're trying to debunk. Dumping every biofuel source and prospective technology in development under the blanket of ethanol's shortcomings isn't just dumb, it's downright WRONG.

Ecacofonix said...

Anyone has an idea of how good is castor oil as a feedstock for biodiesel? I got some inputs from this page on biodiesel from castor oil from CastorOil.in ...are there other resources?

I understand castor oil can be quite cost effective, and has excellent lubricating properties...the above mentioned web site states the only problem could be the high viscosity of castor oil...any ideas?


Anonymous said...

For checking feasibility, you can find pricing and specifications of a small biodiesel unit at http://www.altenergy.in/biodieselunit.html

Anonymous said...

Yes, and on average humans are grossly obese...do you have any idea how much arable land exists in Brazil that is unused?

Mark Harrison is typical of the shortsighted nature of people...forget that pollution is ruining the earth...and that human beings require very little fat to exist. I do agree Palm oil is a poor choice, but after that, I completely disagree.

Farmer on Mars said...

..."do you have any idea how much arable land exists in Brazil that is unused? "

This "unused" land is called the Cerrado; it is a quite biodiverse grassland that releases massive amounts of carbon when converted to farmland. Of course, they are also slashing and burning the Amazon for soy on a massive scale in Brazil, Bolivia, and Argentina.

That said, global food demand is rising rapidly anyway, due to rising population and meat consumption around the world, and there really isn't any "extra" land once you take that into consideration. Plus, you might want some intact ecosystems when you've finished feeding everyone and running their vehicles.

Anonymous said...

Domestic and International energy consumption is at its highest level in history. Increases in the global population and the modernization of developing countries such as China and India have caused demand to outpace supply. The price of refined crude oil is rising due to restrictions in new oil exploration and a lack of refinery capacity. Political conflicts and civil unrest in oil producing nations continue to restrict production.

In addition, increased consumption has resulted in the increased production of greenhouse gases. Governments worldwide are working to restrict the production of greenhouse gases such as carbon dioxide which has been linked to potentially dangerous global warming.

As a result, the United States and many other countries are searching for ways to reduce their dependence on foreign oil and develop a cost effective, eco-friendly renewable fuel source.

So, what does that fuel source look like? Ideally, it is:

Continuously harvestable (not seasonal).
Is ecologically friendly, using everything, wasting nothing.
Does not steal one resource for the sake of another (food versus fuel).
Competes with fossil fuels in the open market (does not require high oil prices to justify its production profitability).
Produces more oil per acre than other bio mass sources.
Not limited by climate.

Currently, the only bio mass able to meet all of these requirements is algae. Grown in virtually all climates, algae has been shown to produce in excess of 130,000 gallons/acre/year (see the U.S. governments Aquatic Species Studies). It can double in volume approximately every 52 hours. It consumes large quantites of greenhouse gas (570 metric tons of carbon dioxide per acre, per year). While oils from certain algae can be used to make food supplements or cosmetic oils, it is not a food source and does not compete with food sources such as corn, soy or palm. Using newly developed bioreactor technologies, alge based fuel oils can compete in the sub-$50/barrel market. Done properly, algae grown in a closed loop system is able to be harvested while recovering CO2, O2, and water for future use. In addition to the production of a fuel oil that does not require transesterfication, by-products of the production process may include methane, butanol, industrial grade charcoal and/or synthesis gas.

So, if all this is possible, why hasn't algae based fuel oil been become a significant player in the bio fuels business? The answer is cost. If you look at almost every company who has demonstrated the growing of algae for oil production purposes, cannot affordably scale their systems to hundreds and even thousands of acres.

In 2008 that changed. Stellarwind Bio Energy recently announced the establishment of their pilot production facility in central Indiana (NW Indianapolis). With a 100 acre field trial scheduled for the summer of 2010, the current pilot production facility is demonstrating a massively scalable, low cost bioreacter. While details are still forthcoming, all indications are that this is the first inexpensive to build, simple to construct, easy to maintain, and above all, affordable algae oil mass production system soon to be on the market.

Keith M.