Special Report Refining Developments R. Kolodziej, Wood Group Mustang, Houston, Texas; and j. Scheib, Gevo Inc., Englewood, Colorado

Bio-isobutanol: The next-generation biofuelThe success of any new industry lies in its ability to innovate

and grow. Future growth in renewable fuels may require an evolution from first-generation products, such as ethanol and biodiesel, to next-generation products, such as isobutanol.

Isobutanol, a form of biobutanol, has many outstanding characteristics that allow it to be used in a variety of ways:

•  “As is”—i.e., as a solvent or as a gasoline blendstock•  Converted,  through  known  processes,  to  a  variety  of 

hydrocarbons for use in the petrochemical and/or refining industries

•  In existing production, distribution, marketing and end-user assets.

This  article  highlights  the  technology,  feedstocks  and market  growth opportunities  for  isobutanol, with  a  focus on potential new market offerings in 2012.

Technology pathway for bio-isobutanol. The specialized production process for bio-isobutanol is fermentation paired with an integrated separation technology. This approach, developed over the past seven years, has been successfully proven  at  bench  scale,  at  a  pilot  plant,  and  at  a  1  million-gallon-per-year (MMgpy) demonstration plant. In May 2012, the world’s first commercial, bio-based isobutanol production plant was started up in Luverne, Minnesota, with a capacity of 18 MMgpy.

Bio-isobutanol fermentation is very similar to the existing ethanol  process.  Ethanol  plants  can  be  repurposed  to make 

isobutanol relatively easily and cost-effectively, with two key modifications:

1. Modified biocatalyst. Isobutanol is a naturally occurring product of the fermentation process, found in many  items  such  as  bread  and  scotch  whiskey;  however,  its commercial use to date has been limited. However, through innovations in microbiology and biochemistry, traditional yeasts  have  been  modified,  making  possible  a  much  higher selectivity in producing isobutanol—i.e., turning up the yeast’s ability  to  make  isobutanol  while  also  limiting  the  ethanol production pathway.

2. Unique proprietary separation.  As  the  isobutanol  is produced, a stream is taken from the fermentation broth where the isobutanol is removed, and the remaining broth is returned for  further  conversion.  This  has  the  effect  of  keeping  the isobutanol concentration below the biocatalyst toxicity level, but it allows for improved conversion.

With these two additions to existing facilities, it is clear how the project completion time and CAPEX to make bio-isobutanol can be significantly lower than those for the construction of a greenfield  plant.  A  plant  conversion  can  nominally  be  20%–40%  of  the  CAPEX  of  a  greenfield  bio-isobutanol  plant.  As fermentation ethanol plants have been shut down or under-utilized due to recent poor economics (e.g., the US ethanol subsidy has been repealed, and the regulation “blend wall” has effectively been reached), the ability to repurpose these plants to isobutanol becomes an attractive opportunity.

Fig. 1. Conversion of a fermentation ethanol plant to an isobutanol plant in Luverne, Minnesota.

Originally appeared in:September 2012, pgs 79-85.Used with permission.

HYDROCARBON PROCESSING September 2012

Refining Developments

Upon fermentation plant conversion, the plant capacity will  be  approximately  80%  on  a  volumetric  product-yield basis (compared to ethanol), but comparable on an energy-equivalent basis (isobutanol contains more energy than ethanol).  Therefore,  the  utility  requirements  and  OPEX are comparable to ethanol production (which, again, limits CAPEX requirements).

There is over 20 billion gpy (Bgpy) of existing fermentation ethanol capacity in the world, located mostly in North and  South  America.  A  leading  company  in  bio-isobutanol is converting some of these ethanol plants to isobutanol production. That company’s business model is based on the flexibility to buy ethanol plant assets, form a joint venture with the current plant owner for the conversion, or to license the isobutanol production technology to ethanol plant owners.

Fig. 1 illustrates an isobutanol plant conversion. The “before” photo shows a facility in Luverne, Minnesota as a 22-MMgpy ethanol  plant.  The  “after”  photo  depicts  the  plant  as  it  was repurposed to produce up to 18 MMgpy of isobutanol.

Feedstock. One company’s proprietary fermentation process is designed to convert feedstocks of all types: grain, sugarcane, cellulose and/or nonfood-based materials. Almost anything that can be converted into a fermentable sugar can be used, whether it is a traditional C6 sugar, such as glucose, or a C5 sugar, such as pentose. The issue of feedstock selection is one of economics, but technology can be put into yeasts to allow them to digest C6 or C5 sugars. In fact, at bench scale, these yeasts have produced cellulosic isobutanol using a mixed stream of C5 and C6 sugars.

Bio-isobutanol has versatility. One of the main reasons that converted plants have such good projected economics is that bio-isobutanol is versatile as a platform molecule. In the chemicals arena, it can be sold as a solvent product (e.g., paints)

and/or converted into materials such as butyl rubber, paraxylene (PX) and other derivatives  for use  in market applications  such as tires, plastic bottles, carpets and clothing. (This conversion is accomplished through dehydration to isobutylene.) For fuels applications, isobutanol can be blended as a low-vapor-pressure gasoline  component  and/or  used  as  feedstock  to  make  other transportation fuels (e.g., iso-paraffinic kerosine for use as biojet) or other renewable products (e.g., renewable heating oil).

Bio-isobutanol as a gasoline blendstock. Bio-isobutanol’s properties  as  a  gasoline  blendstock  can  best  be  understood by comparing some of the blending properties to ethanol and alkylate. Table 1 summarizes some key aspects in the comparison.

Compared  to  ethanol,  isobutanol has  a much  lower Reid vapor pressure (RVP) and about a 30% higher energy content. The blend octane of isobutanol is high as well (although slightly lower than ethanol). Isobutanol also has a lower oxygen (O2) content than ethanol, so more isobutanol can be blended into gasoline for a given O2 content. Greater blend volume, plus higher energy content, means more renewable identification number (RIN) generation. See Table 2 for a RIN comparison summary.

Unlike ethanol, which is fully miscible in water, isobutanol has  limited  water  solubility  (about  8.5%).  Isobutanol  also does not cause stress corrosion cracking in pipelines. These factors result in major advantages in terms of blending logistics. Isobutanol can be blended as a drop-in renewable fuel at the refinery and shipped in pipelines to fuel terminals via existing infrastructure, which prospectively eliminates the  need  for  segregated  tankage  or  pipelines.  This  also affords refiners the opportunity to once again produce a finished-specification  gasoline  vs.  a  sub-octane  blendstock for oxygenate blending.

Isobutanol overcomes the regulation “blend wall” limitation of ethanol blending. Isobutanol blended into gasoline up to 12.5 vol% produces a substantially similar gasoline at a 2.7% O2 content. For refiners, this is a conservative first step for blending, and it generates 16.25 RINs per gallon of finished product. E10 has  3.5  vol% O2 , which is the currently accepted limit of O2 content by automobile engine manufacturers. For this same 3.5 vol% O2, a US Environmental Protection Agency (EPA) waiver (211b) exists that would potentially allow isobutanol blending of up to 16.1 vol%, yielding 20.93 RINs, or more than twice the number of RINs as E10 for an equivalent O2 content.

20070.0

0.5

1.0

1.5

2.0

2.5

2008 2009 2010 2011 2012

Domestic ethanolBrazilian ethanolBiodieselPyrolysis oil, FT liquids, green dieselEISA renewableEISA advanced

2013 2014Year

Millio

n bar

rels

per d

ay

2015 2016 2017 2018 2019 2020 2021 2022

Fig. 2. Projected RIN-gallons vs. EISA targets.

Table 1. Gasoline blendstock comparison: Ethanol vs. isobutanol

ethanol isobutanol alkylate

blend octane (R + M) ÷ 2 112 102 95

blend RVP (psi) 18–22 4–5 4–5

O2 content 34.7 21.6 0

Net energy (% of gasoline) 65 82 95

Fungible in infrastructure No Yes Yes

Table 2. Gasoline blend RIN generation summary

Volume in gasoline O2 content

RiN-gal per 100 gal of

finished product

e10 10% 3.5% 10

e15 15% 5.2% 15

isobutanol (substantially similar to gasoline)

12.5% 2.7% 16.25

isobutanol (ePa waivers allowing O2 content of 3.5 wt%)

16.1% 3.5% 20.93

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Refining Developments

Bio-isobutanol can be an advanced biofuel. To account for the relative amounts of renewable energy benefit, each biofuel generates a RIN based on its energy content. There are basically four types of RINs: renewable (e.g., first-generation, corn-based ethanol), biomass-based diesel, cellulosic and advanced.

Advanced  RINs  are  generated  with  the  production  of advanced biofuels with an approved US EPA pathway (i.e., rated as having at least a 50% reduction in greenhouse gas footprint vs. baseline hydrocarbon fuel). Since bio-isobutanol has a higher energy content than ethanol, bio-isobutanol generates 1.3 RINs per  gallon,  vs.  first-generation  ethanol’s  1.0  RINs  per  gallon. In addition, whereas today’s corn ethanol is precluded from qualifying  as  an  advanced biofuel,  bio-isobutanol—produced with a green energy source (e.g., biomass-fired combined heat and power) has the potential to qualify for advanced RIN status.

Fig. 2 summarizes the US Renewable Fuel Standard (RFS) projected gallons for implemented renewable and advanced biofuels, as compared to the requirements stated by the US Energy  Independence  and  Security Act  (EISA)  of  2007. As can be seen, there is a projected shortfall of advanced biofuels. Bio-isobutanol  offers  some  flexibility  for meeting  the RFS2 targets with domestically produced renewable fuels, as opposed to relying on sugarcane ethanol imports from Brazil, which is the main biofuel pathway currently approved by the EPA for advanced status.

Bio-isobutanol as renewable feedstock for biojet. Taking the bio-isobutanol and processing it further to isoparaffinic kerosine (IPK) biojet has been demonstrated at a hydrocarbon plant in Silsbee, Texas. The process is outlined in Fig. 3.

Producing  IPK  biojet  from  bio-isobutanol  involves  three sequential steps:

1.  Dehydration of the renewable isobutanol to isobutylene2.  Oligomerization of  the  isobutylene  to mostly  trimers/

tetramers to produce C12 and C16 molecules3.  Hydrogenation of olefins to IPK biojet.These processes present opportunities for retrofits of

existing, underutilized refining/petrochemical assets, in some cases.  Commercialization  and  integration  into  an  existing process plant should be straightforward.

Depending upon economics, the overall process also has the flexibility to make more or less isooctene and/or isooctane product  streams,  which  make  good  renewable  gasoline blending components. It should be noted that both renewable gasoline blendstocks (isobutanol and isooctene) are not tied to crude oil processing, so these are not likely to have crude oil volatility effects. Again, isobutylene, isooctene and isooctane can also be drawn off for the production of other renewable petrochemical products (e.g., PX).

This biojet process has been demonstrated in a small (10,000-gallon-per-month-capacity) unit for several months. The  alcohol-to-jet  (ATJ)  product  has  been  sold  to  the  US Air Force as part of the Alternative Fuels Certification Office (AFCO) process. Fig. 4 shows a picture of the demonstration plant in Silsbee, Texas.

IPK process steps.  There  are  three  steps  in  the  IPK production process.

Dehydration. Step  1  is  the  dehydration  of  isobutanol  to 

isobutylene and water. The reaction is endothermic, with a relatively low operating pressure (< 200 psig) and temperatures of around 550°F–650°F. The operating requirements are similar to  semi-regenerative  catalytic  reforming—older  technology that has since been upgraded in refineries and petrochemical plants. Therefore, idled semi-regenerative reformers are possibilities for retrofits to develop the dehydration step. The catalyst for the dehydration has been fully commercialized in similar applications.

The dehydration reaction can be efficiently designed to almost complete conversion, minimizing the downstream complexities of the separation of the butylene and water, and the effluence of the water.

It should be noted that isobutylene can be a hydrocarbon feedstock  for  other  refining  and  petrochemical  processes. Since the isobutylene is renewable, any resulting RINs would carry forward to any hydrocarbon product covered by RFS2.

Oligomerization.  Step  2  is  the  oligomerization  of  the isobutylene  to dimers  (isooctene),  trimers  (C12 olefins) and tetramers. There is some measure of flexibility in the amount of each olefin produced. Since IPK jet fuel primarily requires C12–C16 olefins, dimers are recycled to yield more trimer/tetramer product.

Oligomerization is an exothermic reaction, with operating conditions, heats of reaction, and catalysts that closely resemble MTBE production units and/or catalytic polymerization units;  these  units  are  possible  retrofit  candidates  for  this oligomerization step. In fact, after MTBE was banned in the US,  many  MTBE  units  were  converted  to  make  isooctene 

Oligomerization Hydrogenation

Hydrogen

Isooctene(if desired)

Isooctane(if desired)

DehydrationIsobutylene IPKIsobutanol

Fig. 3. Isobutanol-to-IPK jet fuel process flow diagram.

Fig. 4. IPK biojet demonstration plant.

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Refining Developments

(dimer). These units could be used with a minor retrofit. Depending upon economics, the dimer could be used for gasoline blending and/or further processing options.

Hydrogenation. Step  3  is  the  saturation  of  the  olefin product from the oligomerization section. This is also a well-known and practiced operation in refineries and petrochemical plants. The main reaction is the conversion of the trimers/tetramers  to  IPK.  The  operating  conditions  are  mild,  and they have relatively low operating pressure and temperature, and modest space velocity requirements. The hydrogenation reaction is exothermic and occurs with hydrogen consumption in the process, so some recycle and cooling design details are correlated with the reactor bed design to ensure proper heat removal and control of the reaction.

Olefin hydrogenation is well-known and practiced, so there may be an opportunity to retrofit existing assets, since lower-pressure hydrogenation units have been idled as hydrogenation requirements have become more severe. The operations learning curve is somewhat established already, as per catalyst preparation, unit startup, normal plant operations, etc.

Biojet properties.  IPK  biojet  has  some  properties  that enhance  its  value.  The  freeze  point  is  low  (–80°C),  while oxidation stability is high. Starting from isobutanol, a renewable IPK would also generate RINs at the rate of 1.6 per gallon, based on the process. The current specification limit for a jet fuel blend with synthetic blending components is a

maximum of 50%. For a 1:1 blend with petroleum jet fuel, 80 RINs are generated for every 50 gallons of IPK that are used to produce 100 gallons of blended jet product.

Scoping economics of biojet. One important aspect of understanding how bio-isobutanol can be a versatile alternative biofuel is the nominal economic incentive for its conversion  to  jet  fuel.  Preliminary  scoping  economics  were developed  for  making  biojet  from  renewable  isobutanol feedstock. Although a retrofit of existing units would help the economics, retrofits are not possible in all cases. Therefore, a new unit was used as the basis for this scoping evaluation.

In addition to CAPEX and efficiencies associated with the possible retrofit of some existing assets, the other sensitivity in scoping economics is the value and use of established RIN and other tax credit incentives, as allowed.

The CAPEX throughput basis was a nominal 3,000-barrels-per-stream-day (bpsd) grassroots plant. The unit was assumed with all new equipment (no retrofit or surplus or idled equipment). All  inside-battery-limit (ISBL) equipment was  sized,  specified and budget-estimated. The CAPEX was determined by applying factors to the equipment pricing to account for commodity materials and labor. Allowances were also made for engineering, escalation and contingency. A 30% allowance for offsites was assumed and added.

For the jet fuel price basis, a relatively conservative $2.60–$3.40-per-gallon  price  range  was  assumed,  although the price could be higher. Sensitivities for this price range were included in the scoping economic study.

With the advent of the jet fuel carbon tax on international flights landing in the EU, the airline industry and fuel suppliers have been looking for cost-effective, renewable alternatives to petroleum  jet  fuel.  A  scoping  sensitivity  examining  this  tax credit is shown in Fig. 5.

As can be seen, the EU tax credit has a significant effect on the scoping economics. As one might expect,  the RIN value also has a considerable impact. In summary, this nominal 3,000-bpsd  biojet  plant  study  illustrated  some  positive scoping economics, even at conservative jet fuel prices.

Bio-isobutanol for renewable PX for PET. Once the renewable hydrocarbon is made, there is the chance to make renewable hydrocarbon products via traditional or even newer processes. One new process uses isooctene to make PX, which then can be made into purified terephthalic acid (PTA), and then  into  renewable  polyethylene  terephthalate  (PET)  via traditional methods.

A pilot plant is being designed for this new process, which yields  PX  at  a  very  high  selectivity  vs.  other  xylenes.  High selectivity eliminates the need for xylene isomerization, separation  and  recycle  steps.  Additionally,  the  PX  can  be integrated with the rest of the biofuel plant, as shown in Fig. 6. Depending on the relative amounts of each renewable product, even the hydrogen made in the PX plant can be used in the biojet hydrogenation unit.

Takeaway. Isobutanol has gasoline blending, chemical and usage advantages vs. ethanol, which result in positive economics for the conversion of existing ethanol facilities to

$2.60 jet$2.80 jet$3.00 jet$3.20 jet$3.40 jet

1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.102.0005

10

15

20

25

30

35

40

Isobutanol advanced RIN value, $

Retu

rn on

inve

stmen

t, %

rate

of re

turn

Fig. 5. Biojet plant financial summary analysis. Source: Mustang Engineering

Corn

Sugarcane Isobutanolretrofitted ethanol plant

Isoocteneor C12

Fuels markets

Low-carbongasoline, jet

or diesel

Paraxylene

Chemicals markets

Agriculturalresidue

Wood

Fig. 6. Bio-isobutanol to paraxylene, gasoline blendstock and/or biojet.

HYDROCARBON PROCESSING September 2012

Refining Developments

bio-isobutanol production. Compared to other transportation fuel  blendstocks,  bio-isobutanol  is  a  better  environmental alternative (e.g., low vapor pressure, meaning lower volatility in finished fuel). Also, being made by fermentation of sugars (via normal or cellulosic biomass), these renewable fuels are not tied to crude oil prices or to petroleum supply fluctuations.

The process configuration for bio-isobutanol to IPK biojet fuel involves three sequential, straightforward steps. The process operates at moderate operating conditions, and it is similar to some existing refinery and petrochemical units that have been idled or underutilized. Revamps are possible, and  they  would  reduce  the  CAPEX  and  construction  time. Projected  RIN  values  and  EU  carbon  tax  incentives  would provide additional upside on the project economics. This three-step process has been demonstrated at a 10,000-gallon-per-month-capacity hydrocarbon plant in Silsbee, Texas. On-spec product is being made and sold to the US Air Force for the military certification process.

Bio-isobutanol has numerous process and product platforms that can be employed as economics dictate. These include, but are not limited to, solvent sales, use as a gasoline blendstock,  conversion  to  biojet  or  use  as  a  feedstock  for renewable  PX.  Bio-isobutanol  has  the  versatility  to  allow multiple options at the same time. For example, marine and small-engine fuels are niche options that can be addressed. Renewable diesel is another option.

The pathway for bio-isobutanol via fermentation has been  established,  and  the  business  model  makes  economic 

sense to revamp idled or underutilized fermentation ethanol plants. One company’s production of bio-isobutanol at demonstration  scale  was  proven  in  2009.  More  recently,  a commercial-scale, 18-MMgpy plant was started up. 

Furthermore, bio-isobutanol has versatility and environmental and economic advantages when compared to ethanol. Bio-isobutanol has the capability to provide significant impact as an advanced gasoline blendstock, or as a feedstock to make other advanced fuels or products; therefore, it should be considered a high-potential, next-generation biofuel.

RIck kolodzIEj is a process technology manager at Wood Group Mustang. He has over 30 years of experience in process and project engineering and development in the refining, petrochemicals, chemicals, polymers and gas processing industries. Mr. Kolodziej has been involved with several new technology development projects, including several bio-related projects. Most recently, Mr. Kolodziej was involved with Gevo’s projects in renewable isobutanol and various petrochemicals. He is also responsible for process plant project development for Wood Group Mustang in the Far East. Mr. Kolodziej has US and international patents in hydrotreatment technology. He holds a BS degree in chemical engineering from the University of Illinois (Chicago) and an MBA degree in finance from DePaul University, and is a registered professional engineer in the state of Illinois.

jEff SchEIb is vice president for fuels at Gevo Inc., overseeing sales, marketing and business development activities for isobutanol-into-fuels markets, including refining, biojet, gasoline distributors and marketers, marine and small-engine applications. He has over 20 years of fuels and biofuels leadership expertise, having worked 17 years within the petroleum sector with ARCO and BP, followed by four years in the renewable energy arena with Cilion and Chromatin, prior to joining Gevo in 2011. Jeff holds an MBA degree from the University of California (Los Angeles) and a BS degree in industrial engineering from Northwestern University.

Article copyright ©2012 by Gulf Publishing Company. All rights reserved. Printed in U.S.A.Not to be distributed in electronic or printed form, or posted on a website, without express written permission of copyright holder.

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