Process integrated enzyme production: the cost-efficient way to commercially viable 2G cellulosic ethanol

By Dr. Markus Rarbach, Head of Biofuels & Derivatives, Clariant

Special to The Digest

Cellulosic ethanol is no longer a topic solely discussed in scientific papers or conferences, or by the academic world. It has made its way through the stages of technology development, from lab scale to pilot, to demo and now to commercial-scale plants. It is safe to say that at the end of 2016 our industry has managed some of the main technological hurdles; today, the main talk is about the economic competitiveness of the technology.

Our approach at Clariant when developing the sunliquid® technology was to deliver an entirely integrated process from feedstock to finished product including our proprietary enzyme and fermentation organism platform, where all process steps are optimized to guarantee technical as well as commercial performance. In addition, we offer a self-sustained solution to our clients. Here the process integrated enzyme production was key to reach these goals while at the same time increasing the efficiency and reducing the cost of enzymes for cellulosic ethanol production. That this is key to a competitive cellulosic ethanol production process which has now been confirmed by a recent study, comparing different enzyme production approaches.1

What do we mean by integrated enzyme production?

Basically there are three different scenarios of how to get the enzymes you need for your cellulosic ethanol production facility (Figure 1). First, you buy them from a third-party supplier (off-site production). Second, you (or a third-party) build a small enzyme plant at your cellulosic ethanol facility (on-site or the “OSM” approach). The feedstock for enzyme production in this case is conventional carbohydrates like glucose. And third, you make enzyme production a part of your cellulosic ethanol production process by using the same biomass as a carbon source to produce the enzymes. Both, biomass and energy flows are integrated with the main production plant. The main advantage of this third approach is, that you substitute a rather expensive feedstock (glucose) by a cheaper one, biomass. In addition, this substitution of feedstock allows to produce 100% advanced ethanol with the lowest carbon intensity possible as no food or feed feedstock enters the production process, neither directly nor indirectly. Plus, you produce the enzymes you need when and where you need them, eluding dependence on suppliers, formulation, stabilization and transportation costs.

Figure 1. Different enzyme production approaches (simplified graphic)

How does the enzyme production approach impact on cellulosic ethanol costs?

A recent study* analyzed and compared these three production methods and their effect on overall cellulosic ethanol production costs, coming to the following conclusions:

• The cost of enzyme is one of the most significant cost factors in cellulosic ethanol production
• Integrated enzyme production is the most cost efficient way
• The cost of enzyme production is the most variable single input item by production approach

Let’s look at these three findings in more detail.

The cost of enzyme production

The study examined a base case cellulosic ethanol plant with an annual ethanol output approx. 23.4 million gallons (70.000 metric tons). In a first step mass balances for all three production approaches were calculated. In the second step annual cash costs and full costs per gallon were calculated.

The cost of enzymes makes up a significant percentage of overall cellulosic ethanol production costs, ranging from 28% for off-site production to 22% for on-site and 10% for integrated enzyme production (Figure 2). Together with the costs for feedstock, overhead & insurance and capital/finance costs, enzyme production ranks among the TOP 4 cost factors, that together make up for more than 80% of full costs.

Figure 2. Cost of enzyme production as percentage of overall cellulosic ethanol production cost

Breaking down the enzyme production costs, it is shown, that by changing from off-site to on-site to integrated enzyme production, the cost for enzymes can be lowered by 23% and 52% respectively, and thus enzyme production is the most variable of cost factors (Figure 3). This quite dramatic decrease is mainly attributed to the difference in feedstock for enzyme production and the huge price difference between biomass for integrated production versus sugars in the off-site and on-site case.

Figure 3. Comparison of enzyme costs, * includes all operating and capital cost, but does not include transport cost for offsite enzymes which will further increase costs.

The cost of cellulosic ethanol production

We have seen that enzyme costs are one of the most significant cost factors for cellulosic ethanol production. Hence, it is not surprising, that a reduction in enzyme costs has a significant impact on overall cellulosic ethanol costs. The study looked at the annual cash costs, which showed a reduction of 8% and 20%, respectively, by shifting from off-site to on-site to integrated production, and at annual full costs (including capital costs), with a reduction of 7% and 19% respectively. Overall cellulosic ethanol production costs were calculated to decrease from 2.78 USD/gallon to 2.61 USD/gallon to 2.36 USD/gallon, with enzyme costs making up 0.78, 0.58 and 0.23 USD/gallon respectively (Table 1).

Table 1. Cellulosic ethanol full costs, USD/gallon

Conclusion and Outlook

Integrated enzyme production has proven to be the most cost efficient way for cellulosic ethanol processes. The substitution of expensive sugars with biomass (and thus the elimination of a 1G feedstock) significantly reduces costs, in addition to the elimination of transport and formulation costs. Furthermore, the integration into the ethanol production process, ensures flexible on-site supply of feedstock and process specific enzymes, continuous performance improvement, and thus, again, cost efficiency. We strongly believe that integrated enzyme production is the way forward in cellulosic ethanol production and will continue to be one of the key features enabling competitive production now and in the future.

*Johnson E, Biofuels, Bioprod. Bioref 10:164-174 (2016),