National Renewable Energy Laboratory 

Innovation for Our Energy Future 

A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 

Equipment Design and Cost 

Estimation for Small Modular 

Biomass Systems, Synthesis 

Gas Cleanup, and Oxygen 

Separation Equipment 

Task 9: Mixed Alcohols From Syngas — 

State of Technology 

Nexant Inc. 

San Francisco, California 

Subcontract Report 

NREL/SR-510-39947 

May 2006 
Equipment Design and Cost 

Estimation for Small Modular 

Biomass Systems, Synthesis 

Gas Cleanup, and Oxygen 

Separation Equipment 

Task 9: Mixed Alcohols From Syngas — 

State of Technology 

Nexant Inc. 

San Francisco, California 

NREL Technical Monitor: Kelly Ibsen 

Prepared under Subcontract No. ACO-5-44027 

Subcontract Report 

NREL/SR-510-39947 

May 2006 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

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Operated for the U.S. Department of Energy 

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Contract No. DE-AC36-99-GO10337
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Executive Summary

Due to limited incentives and significant risks involved in the mixed alcohols 

process, little commercial development has occurred this decade. Most original 

technology developers, who first investigated the technology in the mid-1980s, 

have since abandoned the technology. However, new catalysts, new project 

developers, and a desire to find alternatives for petroleum based fuels and 

oxygenates has brought new life to this technology. 

The major catalysts commercially available for mixed alcohol production from 

syngas are modified methanol catalysts, modified Fischer-Tropsch catalysts, and 

alkali-doped molybdenum catalysts. Recent work has also been performed on 

zirconium catalysts that show potential for process improvements. None of the 

catalysts investigated are clearly superior to the others; criteria prioritization must 

be performed by project developers to determine which catalyst aspects are of 

greatest importance. While no catalyst had a significant advantage in syngas 

conversion, molybdenum catalysts performed well on alcohol yield, selectivity, 

and impurity resistance criteria. A more direct comparison of each catalyst on a 

weighted set of process criteria would be helpful to better defining R&D plans. 

Recent research efforts have focused on changing base catalyst formulations 

instead of developing entirely new catalysts. These efforts have included doping 

of catalysts with different metals, novel catalyst preparation techniques, 

optimizing process conditions, and new catalyst support materials. While many 

of these research efforts have improved catalyst performance, an evaluation of 

the economics of each improvement needs to be performed. 

The tolerance of modified methanol and Fischer-Tropsch catalysts to sulfur 

remains very low (<1 ppm). Sulfided catalysts represent an improvement in this 

area, but it is unclear if this improves the economics of the process. If required to 

maintain between 50 and 100 ppm of sulfur in the syngas, only very small 

improvements in the overall process economics are possible. In addition, low 

sulfur requirements, especially to H2S and mercaptans, for transportation and 

chemicals applications of the mixed alcohol product may require additional 

cleanup anyway, potentially eliminating any economic advantage. 

The technical and economic risks include feasibility to produce the desired 

product slate, scale-up considerations, designing for severe process conditions, 

catalyst sensitivities, competitiveness versus petroleum fuels, and catalyst prices. 

Studies have shown that current mixed alcohol technologies can compete with 

wholesale gasoline prices at $1.25 to $1.70 per gallon, assuming $0/ton 

feedstock prices and no production credits. Consideration must be made for the 

impacts this product will have on transportation fuel specifications, especially 

octane, volatility, sulfur, and corrosion. Fluctuations in price for rare and high 
demand metals also add considerable risk to the commercial feasibility of this 

process. 
Contents 

Section Page 

i Introduction and Methodology i 

1 Current Mixed Alcohol Technologies 1-1 

 1.1 Technology Description 1-1 

 1.2 Catalysts 1-2 

 1.3 Reactors 1-11 

 1.4 Technology Developers 1-12 

 1.5 Conclusions and Future Research Needs 1-15 

2 Sulfur Removal 2-1 

 2.1 Sulfur Removal Requirements and Options 2-1 

 2.2 Summary and Conclusions 2-5 

3 Technical and Economic Risks 3-1 

 3.1 Introduction 3-1 

 3.2 Technical Risk Analysis 3-2 

 3.3 Economic Risk Analysis 3-10 

 3.4 Summary and Conclusions 3-17 

Tables 

1 Modified High Pressure Methanol Catalysts Process Conditions 1-2 

2 Modified Low Pressure Methanol Catalyst Process Conditions 1-3 

3 Modified Fischer-Tropsch Catalyst Process Conditions 1-5 

4 Alkali-Doped Molybdenum-Based Catalysts Process Conditions 1-6 

5 Alkali-Doped ZrO2-Based Catalysts Process Conditions 1-11 

6 2000 TPD Wood Gasification Plant Compression Requirements 3-6 

7 Stoichiometric H2/CO Ratio, Different Alcohols 3-9 

8 Mixed Alcohol Economic Study Comparisons 3-11 

9 Metals Considered for Use in Mixed Alcohol Catalysis 3-14 

Figures 

1 Molybdenum Oxide Prices, 1998 to 2004 3-15 
Introduction and Methodology 

This deliverable is for Task 9, Mixed Alcohols from Syngas: State of Technology, 

as part of NREL Award ACO-5-44027, “Equipment Design and Cost Estimation 

for Small Modular Biomass Systems, Synthesis Gas Cleanup and Oxygen 

Separation Equipment”. Task 9 supplements the work previously done by NREL 

in the mixed alcohols section of the 2003 technical report entitled, “Preliminary 

Screening – Technical and Economic Assessment of Synthesis Gas to Fuels and 

Chemicals with Emphasis on the Potential for Biomass-Derived Syngas”. It is 

assumed that NREL’s knowledge of higher alcohol synthesis is extensive, as 

demonstrated in the 2003 technical report. Thus, information presented by 

NREL in 2003 that is still current will not be elaborated upon in detail. Rather, 

confirmation will be provided, along with information on recent developments of 

higher alcohol synthesis technologies. 

This report updates the preliminary NREL work in the following three areas: the 

current state-of-the-art technologies for the production of mixed alcohols from 

syngas; interaction between different mixed alcohol catalysts and sulfur removal 

technologies; and areas of technical and economic risk in the mixed alcohols 

process. Suggestions are made for the appropriate sulfur removal technologies 

for different catalysts, with recommendations for suitable combinations for NREL 

designs. Finally, the risks section gives a comprehensive overview of R&D 

requirements, policy drivers, and economic hurdles that must be overcome to 

bring about commercialization of the mixed alcohol from biomass technologies. 

Besides using Nexant’s previous experience and information database, the 

current information was obtained by conducting literature searches, contacting 

commercial vendors of the mixed alcohol technologies, and using the Nexant 

developed IGCC economic model. 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

i 
Section 1 Current Mixed Alcohol Technologies

1.1 Technology Description

In the early 1980’s commercial chemical companies, such as Dow and 

Snamprogetti, patented their own higher alcohol synthesis (HAS) technologies in 

response to the oil embargo of the 1970’s and the phase out of lead as an octane 

enhancer in gasoline. However, commercial interest decreased with the 

increased supply of cheap petroleum and the use of methyl tert-butyl ether 

(MTBE) as an octane booster. Because MTBE has excellent blending properties 

and good economics, it has become the primary oxygenate chosen by refineries 

outside of the Midwest to meet the reformulated gasoline standards of the 

Federal Clean Air Act Amendments of 1990. The recent phase-outs of MTBE 

from much of the gasoline pool has renewed interest in ethanol and mixed 

alcohols as an alternative oxygenate. 

As of April 2005, there are no commercial plants that exist solely to produce 

mixed alcohols in the C2 to C6 range from syngas. In fact, many of the 

companies that had once pursued research to commercialize the production of 

mixed alcohols have now abandoned it. The status of these commercialization 

attempts will be further discussed in Section 1.4. 

The main process steps for higher alcohol synthesis do not differ from what was 

outlined by NREL in 2003. The main steps are synthesis gas production, 

followed by gas clean up and conditioning, alcohol synthesis, and product 

purification.1 This is a typical route regardless of how the syngas is used. The 

items that are unique to mixed alcohol production are the process conditions for 

product synthesis, level of clean up (depending on the catalyst chosen), and 

purification/recycle steps. 

It is worth mentioning that Sasol has commercial plants in South Africa that utilize 

the mixed alcohol by-product of their coal to Fischer-Tropsch liquids process for 

other commercial needs. However, this is not optimized for mixed alcohols 

production2

, and, thus, does not qualify as a commercial plant for mixed alcohol 

production. 

 

1

 U.S. Department of Energy. National Renewable Energy Laboratory. “NREL/TP-510-34929: Preliminary 

Screening – Technical and Economic Assessment of Synthesis Gas to Fuels and Chemicals with Emphasis 

on the Potential for Biomass-Derived Syngas.” Golden, CO.: December 2003. 

2

 Sasol currently has an FT facility that yields 4800 BPD of alcohols comprised of 2% methanol, 66% 

ethanol, and the remainder higher alcohols. However, the stream is used predominantly as a petrochemical 

intermediate. Information from Dr. Michael S. Graboski, “An Analysis of Alternatives for Unleaded Petrol 

Additives for South Africa”, UNEP sponsored report, May 2003. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-1 
1.2 Catalysts 

Higher alcohol synthesis catalysts have undergone a number of improvements in 

the past few years. The majority of the incremental improvements relate to better 

characterization of higher alcohol yields for different catalyst compositions. In 

addition, potentially significant improvements in yields have come from research 

done on new catalyst formation processes. 

This additional work that has been performed on mixed alcohol catalysts requires 

new categorization. Three of the four categories remain the same as in the 

NREL 2003 technical report; one category was expanded to include all 

molybdenum-based catalysts, and another category was added for additional 

catalysts. The categories are as follows: 

 

1. Modified high pressure methanol synthesis catalysts – alkali-doped 

ZnO/Cr2O3 

2. Modified low pressure methanol synthesis catalysts – alkali-doped 

Cu/ZnO and Cu/ZnO/Al2O3

3. Modified Fischer-Tropsch catalysts – alkali-doped CuO/CoO/Al2O3

4. Alkali-doped molybdenum based catalysts 

5. Other catalysts, mainly ZrO2 based 

If some of the new research continues to yield improvements and advances over 

existing catalysts, it may be possible for molybdenum-based catalysts to be more 

active than oxide-based catalysts if prepared under new methods. This is an 

area that NREL should follow closely to assure the most up-to-date data is 

included in mixed alcohol designs. 

1.2.1 Modified High Pressure Methanol Synthesis Catalysts 

Modified high pressure methanol synthesis catalysts are primarily alkali doped 

ZnO/Cr2O3. The typical process conditions are summarized in Table 1. Unless 

otherwise noted, data for process conditions tables are derived from the 2003 

NREL mixed alcohols analysis: 

Table 1: Modified High Pressure Methanol Catalysts Process Conditions

H2/CO 

Ratio 

T 

(F)

P 

(psia) 

CO2

Sensitivity 

CO conversion 

(per pass) 

Main Product 

Yield 

Total alcohol 

STY (g/kgcat/hr) 

1 572 - 

800

1810 - 

3625

significant 

at 6%

5 - 20% Branched 

Primary 

Alcohols

2033

 

3

 W.S. Epling, et. al, “Higher alcohol synthesis reaction study VI: effect of Cr replacement by Mn on the 

performance of Cs- and Cs, Pd-promoted Zn/Cr spinel catalysts”, Applied Cat. A: General, (1999) 335-343. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-2 
The benefits of these catalysts include: 

• Significant data exists to be able to predict the performance and 

effectiveness of Zn/Cr catalysts. 

• Highest isobutanol production rates of any catalyst group. 

The drawbacks to these catalysts include: 

• Significantly decreased C2+OH yields with CO2 rich (~6%) syngas 

stream.4 

• High pressure requirements. 

The group of George W. Roberts of North Carolina State University has 

published research dealing with isobutanol synthesis from such ZnCr catalysts.5

 

His work has been directed towards the use of ZnCr catalysts for HAS in slurry 

reactors and is further discussed in section 1.3.2. His work was not discussed in 

the 2003 technical report, but NREL may be interested in his attempts to use 

ZnCr in a slurry reactor to increase selectivity and yields of higher alcohols. 

However, no such improvements of selectivity or yields have been made at this 

time. 

1.2.2 Modified Low Pressure Methanol Synthesis Catalysts 

The difference between modified low pressure and high pressure methanol 

synthesis catalysts is whether the catalyst formulation contains copper. The 

typical process conditions are summarized in Table 2. The ranges given cover 

the conditions that most catalysts of this type would operate under. 

Table 2: Modified Low Pressure Methanol Catalyst Process Conditions

Catalyst H2/CO 

Ratio 

T (F) P (psia) CO 

Conversion 

(per pass) 

C2+OH 

Selectivity 

Primary 

Product 

Yields 

Lurgi: 

Octamix 

1–1.2 482-752 725–1,450 20-60% 41.9 wt% 

The benefits of these catalysts include: 

 

4

 E. Tronconi, L. Lietti, P. Forzatti, and I. Pasquon, “Synthesis of Alcohols from Carbon Oxides and 

Hydrogen .17. – Higher Alcohol Synthesis over Alkali Metal-Promoted High- Temperature Methanol 

Catalysts.” Applied Catalysis 47, no.2, (1989): 317-333. 5

 Xiaolei Sun, N.W. Jones, J.C. Gesick, L. Xu, and G.W. Roberts, "Liquid/Catalyst Interactions in Slurry 

Reactors: Changes in Tetrahydroquinoline Composition during Methanol Synthesis over Zinc Chromite", 

Applied Catalysis A. General 231 (2002): no. 269. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-3 
• Lower pressure requirements than high pressure methanol catalysts. 

• Effectiveness of process has been detailed in the literature.6

The drawbacks to these catalysts include: 

• High CO conversion can decrease higher alcohol selectivity and yield. 

• Lower production of higher alcohols and other oxygenated products than 

modified high pressure methanol synthesis catalysts.7

• Cu sintering limits the upper temperature of the process. 

NREL’s 2003 technical report mentions that modified low pressure methanol 

catalysts mainly produced primary alcohols. In addition, literature indicates that 

modified low-pressure methanol synthesis catalysts also produce branched 

primary alcohols as a significant product. Specifically, K-promoted/Cu/ZnO/Al2O3

catalysts fall into a group of catalysts that predominantly produce branched 

alcohols, such as isobutanol.8 This is particularly important for understanding the 

mixed alcohol product composition that will be produced by this catalyst. 

Also, recent research conducted by Ismail Boz of Istanbul University has 

improved the understanding of modified low pressure methanol catalysts with Co 

and K added. The research found that a 5% K2O promoter concentration yields 

the greatest higher alcohol selectivity for a Co2O3/CuO/ZnO/Al2O3 catalyst, and 

that 563 K maximizes higher alcohol selectivity over methanol with an H2/CO = 2 

at 580 psia.9

 In addition, using lower space velocities than those used for 

methanol synthesis can improve higher alcohol selectivity. Furthermore, 

increasing CO conversion beyond 10%, which is shown to be dependent on 

temperature, reduces higher alcohol selectivity and yield in favor of 

hydrocarbons. Thus, in order to increase higher alcohol selectivity and yield with 

a modified low pressure methanol synthesis catalysts, it will be necessary to 

lower the space velocity and to use the correct amount of promoter. Also, it is 

important to recognize that there may be a trade off between maximizing CO 

conversion and maximizing the higher alcohol selectivity and yield. 

 

6

 Refers to articles referenced in National Renewable Energy Laboratory paper. These include: Elliott, D.J. 

and Pennella, F. (1988); Nunan et al. (1989); Smith and Anderson. (1984). Smith and Klier (1992). 

7

 P. Forzatti, E. Tronconi, and I. Pasquon. “Higher Alcohol Synthesis” Catalysis Reviews-Science and 

Engineering 33, no.1-2 (1991): 109-168. 8

 J.M. Campos-Martin, A. Guerrero-Ruiz and L.G. Fierro, J. Catal. 156 (1995) 208. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-4 

9

 Ismail Boz. “Higher Alcohol Synthesis over a K-promoted Co2O3/CuO/ZnO/Al2O3 catalyst.” Catalysis 

Letters. Vol. 87, Nos. 3-4, April 2003. 
1.2.3 Modified Fischer-Tropsch Catalysts 

The majority of previous information available on the modified Fischer-Tropsch 

catalyst originated from the commercial process developed by the Institut 

Francais de Petrole (IFP) over 15 years ago. There have, however, been recent 

independent developments related to new catalyst preparation techniques. 

The general process conditions are summarized in Table 3. Depending on the 

type of alcohols desired, H2/CO ratio, temperature, and pressure can all be 

manipulated to promote heavier or lighter alcohol production. 

Table 3: Modified Fischer-Tropsch Catalyst Process Conditions

Catalyst H2/CO 

Ratio 

T (F) P (psia) CO 

Conversion 

(per pass) 

C2+OH 

Selectivity 

Primary 

Product 

Yields 

IFP 1-2 500-608 850-1450 5-30% 30-50% Straightchained 

alcohols 

The benefits of these catalysts include: 

• Greater selection for higher linear alcohols than modified methanol 

processes. 

• New catalyst preparation techniques can significantly improve CO 

conversion rates. 

The drawbacks of these catalysts include: 

• Decreasing H2/CO ratio increases higher alkane yield.10 This should not 

be an issue with biomass because biomass tends to have a high H2/CO 

ratio relative to coal derived syngas. 

Different catalyst preparation techniques have shown different conversion rates 

for the syngas feed. The typical method of catalyst preparation has been coprecipitation. However, alternative techniques for catalyst preparation have been 

shown to increase overall conversion rates. For example, researchers have 

recently claimed that preparing catalyst with the sol-gel/oil-drop method can 

increase CO conversion rates by ~14 - 30% over catalysts prepared by coprecipitation methods. This has important implications when considering the 

maximum yield of mixed alcohols a process can expect from a given modified 

Fischer-Tropsch catalyst. 

 

10 S. Naidu, U. Siriwardane, “Novel Preparation and Magneto Chemical Characterization of Nano-Particle 

Mixed Alcohol Catalysts” DOE Grant Number: DE-FG26-00NT40836. 8/31/2003. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-5 
Work carried out by Arislete Dantas de Aquino from Brazil in 2001 has helped 

characterize the effect of alkali metals on the higher alcohol yield and selectivity 

of Al-Cu-Co based catalysts.11 Specifically, Li, Na, K, and Cs were tested and 

the following information was found: 

• Li increased selectivity of methanol and C2-OH yield while decreasing that 

of hydrocarbons 

• Na increased catalyst deactivation, but the selectivity of hydrocarbon and 

alcohol remained relatively constant. 

• K reduces overall higher alcohol yield and produces only methanol and 

ethanol. It also reduces hydrocarbon yield. 

• Cs considerably lowers alcohol yield selectivity. 

These results should be taken into consideration if a modified Fischer-Tropsch 

catalyst is used. From the current research, it appears that the use of Li as a 

promoter would have the most beneficial effect upon alcohol yield and selectivity 

of the available alkali promoters. 

1.2.4 Alkali-Doped Molybdenum-Based Catalysts 

The category of alkali-doped sulfide catalysts has been expanded to include all 

molybdenum-based catalysts. The discussion will be divided between sulfided 

molybdenum-based catalysts and pre-reduced catalysts, expanding the coverage 

of this catalyst type from NREL’s 2003 analysis. Table 4 summarizes the basic 

process conditions for sulfided catalysts. 

Table 4: Alkali-Doped Molybdenum-Based Catalysts Process Conditions

Catalyst H2/CO 

Ratio 

T (F) P 

(psia) 

CO Conversion 

(per pass) 

Alcohol 

Selectivity 

Alcohol Yield 

(g/kg/hr) 

General 

Literature 

1 500-

662 

435-

2538 

10% 75-90% 

Dow <40%12

K-CoMoS2

13

2 581 1515 39% 75.7% 115 

K-CoMo/Al2O3

14

2 650 1515 - 59% 370 

K-CoMo/SiO2

15

2 482 725 7.2% 59% 370 

 

11 Arislete Dantas de Aquino, and Antonio Cobo, “Synthesis of higher alcohols with cobalt and copper 

based model catalysts: effect of the alkaline metals.” Catalysis Today, 65, no. 2-4, 2001, 209-216. 12 G. Quarderer, “Mixed Alcohols from Synthesis Gas”. April 1986. 78th Spring National AIChE Meeting. 13 R.R. Stevens, U.S. Patent 4,882,360, 1989. 

14 D.A. Storm, Top. Catal. 2 (1995): 91. 

15 K. Fujimoto, T. Oba, App., Catal. 13 (1985): 289. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-6 
The benefits of these catalysts include the following: 

• The sulfide-based catalysts require 50-100 ppm H2S in syngas stream to 

maintain the sulfidity of the catalyst. Thus, they are sulfur resistant, and 

sulfur clean up costs may be able to be reduced.16 

• The catalysts are less sensitive to CO2 in the syngas stream than other 

catalysts. However, catalysts activity can still be inhibited with high 

amounts of CO2 (>30%).17

• Carbon laydown (coking) does not become a problem even with low 

H2/CO ratio (i.e. <2).18

• Primarily produce non-branched linear alcohols. 

These catalysts have the following drawbacks: 

• Oxide-based catalysts tend to be more active than these sulfide-based 

catalysts.19

1.2.4.1 Molybdenum-Sulfide Catalysts 

Catalyst Characterization 

There has been important research recently conducted on alkali-doped sulfide 

catalyst for higher alcohol synthesis. The sulfide-based catalysts have been 

better characterized, and the new developments may enable increased higher 

alcohol yields. As an example, when K and Cs are used as promoters on a CoMoS2/clay catalyst, the alcohol yield was found to increase with reaction 

temperature; however, alcohol selectivity decreased with an increase in reaction 

temperature.20 

Further developments have characterized the effect of alkali promoters on the 

yield and composition of C2+OH. The space-time yield of C2+OH was strongly 

 

16 P. Courty, P. Chaumetter, C. Raimbault, and P. Travers, “Production of methanol-higher alcohol 

mixtures from natural gas via syngas chemistry.” Revue de l’Institut Francais du Petrole, 45, no.4 (1990): 

561-578. 

17 R.G. Herman “Chapter 7 – Classical and Non-classical Routes for Alcohol Synthesis.” New Trend in 

CO Activation, 265-349, (New York: Elsevier, 1991). 

18 G. Quarderer, ibid. 

19 R.G. Herman, “Advances in catalytic synthesis and utilization of higher alcohols.” Catalysis Today 55 

no. 3, 200: 233-245. 

20 J. Iranmahboob, H. Toghiani, D. Hill. “Dispersion of alkali on the surface of Co-MoS2/clay catalyst: a 

comparison of K and Cs as a promoter for synthesis of alcohol.” Applied Catalysis A: General. 247, no.2 

(2003): 207-218. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-7 
correlated with the alkali metal promoter to MoS2 ratio (M/MoS2).21 The 

maximum space-time yield was found to be at a maximum around an M/MoS2

ratio of ~.2 independent of the alkali metal promoter chosen. Of the alkali metal 

promoters chosen (M: K, Rb, and Cs), the Rb/MoS2 catalyst with an Rb/Mo ratio 

of .25 demonstrated the highest space-time yield of C2+ alcohol, and it also had 

the highest chain growth probability, .35. Finally, it was found that MoS2 catalysts 

could achieve higher alcohol yields than Cu based catalyst, but it requires 

pressures greater than 1,450 psia to achieve. 

Catalyst Formation 

Novel developments in catalyst formation techniques have contributed to 

potentially significant improvements in higher alcohol synthesis yields. 

The traditional way to prepare MoS2 catalyst is thermal decomposition or 

reduction of (NH4)2MoS4 (ATTM), where ATTM refers to ammonium 

tetrathiomolybdate. However, recent techniques have been identified that could 

increase the surface area of the catalyst significantly by preparing the catalyst by 

the reduction of ATTM in the presence of water.22 The technique used involves 

the presence of a long chain alkane, tridecane, to increase the surface area of 

MoS2 by nearly a factor of four, increasing catalyst activity. 

1.2.4.2 Pre-Reduced Molybdenum-Based Catalysts. 

Catalyst Characterization 

A large amount of work has also been done on pre-reduced molybdenum-based 

catalysts. For example, a Mo-Ni-K/SiO2 catalyst was found to perform the best of 

other pre-reduced molybdenum-based catalysts as measured by largest spacetime yield.23 Additional work on a similar Mo-Ni-K/SiO2 catalyst demonstrated that 

space time yield of alcohols could be further increased with a novel method of 

catalyst formation known as Metal Oxide Vapor Synthesis (MOVS).24 Given the 

promise of Mo-based catalysts, the Division of Fossil Energy under the National 

Energy Technology Laboratory has recently sponsored work on higher alcohol 

synthesis from Mo-based catalyst.

 

21 Naoto Koizumi, et. al., “Development of sulfur tolerant catalysts for the synthesis of high quality 

transportation fuels.” Catalysis Today 89 (2004): 465-478. 22 Y. Yoneyama, C. Song, Catalysis Today 50 (1999): 19-27 

23 T. Tatsumi, A.Muramatsu, “Molybdenum Catalysts for synthesis of mixed alcohols from synthesis gas.” 

Sekiyu Gakkaishi (J. Jpn. Petrol. Inst.) 35, 1992: 233 24 E.C. Alyea, D. He, J. Wang “Alcohol Synthesis from syngas. I. Performance of alkali-promoted Ni-Mo 

(MOVS) catalysts.” Appl. Catal. A: General104, (1993): 77. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

1-8 
Recent DOE sponsored research on calcined Mo-Ni-K/C catalysts have helped 

characterize the higher alcohol synthesis that can be achieved by this catalyst. 

Four major areas of interest were elaborated upon by this research. 

1. The space-time yield of both alcohols and hydrocarbons are increased 

with an increase in reaction temperature; however, this causes an 

overall decrease in total alcohol selectivity as temperature increases.25 

2. Addition of Ni and K increases the total alcohol selectivity, but the 

catalysts must, in general, be reduced first. 

3. Alcohol yield decreases with increasing partial pressure of H2 and 

increases with greater partial pressures of CO. 

4. Increased gas hourly space velocity (GHSV) is favorable for total 

alcohol yields. The general trends of the Mo-Ni-K catalyst supported 

by carbon are very similar to that seen in molybdenum-sulfide catalysts 

already discussed. 

The information obtained by this research helps establish the process 

conditions—H2/CO ratio, GHSV, Temperature—and catalyst composition that will 

optimize higher alcohol yields and selectivity for the desired product slate. 

Catalyst Formation and Support 

Research has also been conducted on the catalyst support structure and 

preparation for molybdenum catalysts. For instance, higher catalytic activity 

resulted from a Mo-K catalyst supported by activated carbon compared to a MoK catalyst supported by Al2O3.

26 This research done has also revealed that the 

space-time yield of alcohol synthesis is optimized at MoO3 loading of 48%. 

Similar to the research conducted on sol-gel preparation techniques for modified 

Fischer-Tropsch catalysts, the effect of sol-gel preparation of a K-Co-Mo/C 

catalyst was also studied. The sol-gel method was shown to produce a high 

alcohol yield, particularly for C2+OH.27 

An additional area of potential interest is the effect of metal doping. In one 

study, the addition of rhodium as a promoter to a Mo-K/γ-Al2O3 catalyst nearly 

tripled the space-time yield of higher alcohols from 370 to 1,100 g/(hr*kg) of 

 

25 Lawrence Norcio, et al. “Synthesis of Hydrocarbons and Alcohols from Syngas.” C1 Chemistry for the 

Production of Clean Liquid Transportation Fuels and Hydrogen: DOE 2002 Annual Report. DE-FC26-

99FT40540. 

26 Zhong-rui Li, Y Fu, M. Jiang, T. Hu, T. Liu, and Y. Xie, “Active Carbon Supported Mo-K Catalysts 

Used for Alcohol Synthesis.” Journal of Catalysis, 199, 2, (2001): 155-161. 27 J. Bao, Y Fu, Z. Sun, C. Gao, “A highly active K-Co-Mo/C catalyst for mixed alcohol synthesis from CO 

+ H2.” Chem. Commun. no. 6 (2003): 746-747. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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catalyst.28 Additional work has been done characterizing the increased alcohol 

selectivity that K doping has upon a Mo/AC catalyst.29 These results could 

possibly increase the attractiveness of sulfide-based catalysts that are promoted 

by rhodium and potassium; however, rhodium has previously been optimized for 

ethanol synthesis only, and it is much more expensive than potassium, as will be 

discussed in Section 3.3. 

1.2.5 Other Catalysts 

There are a variety of other catalysts that have some capability to produce higher 

alcohols, but they are not given much attention because their overall selectivity 

for higher alcohols has historically been low or they have been developed for 

other end products. For example, rhodium based catalysts were briefly 

mentioned in the 2003 technical report as such a catalyst group, yet they are 

more capable of yielding ethanol than being effective for higher alcohol 

synthesis. 

Other Sulfide Based Catalysts 

The higher alcohol yields of catalysts similar to molybdenum sulfide-based 

catalysts have also been explored. Because research had only been previously 

conducted with Mo and W sulfide catalysts, the space-time yields of Rh, Pd, Re 

and Os sulfide catalysts were tested in recent research. Rhodium was found to 

have a higher alcohol formation rate than Mo and W.30 This research suggests 

that rhodium sulfide catalysts could be superior, in terms of alcohol yields, for 

higher alcohol synthesis. However the high costs of rhodium would likely prevent 

its usefulness as a widespread catalyst. 

ZrO2 Catalysts 

Another new catalyst type are ZrO2-based catalysts. A ZrO2 based catalyst, 

promoted by Pd, has proven itself as an effective catalyst for the production of 

ethanol or isobutanol.31 The study also demonstrated that adding methanol or 1-

 

28 D.A. Storm, “The production of higher alcohols from syngas using potassium promoted Co/Mo/Al2O3

and Rh/Co/Mo/Al2O3.” Topics in Catalysis. 2 (1995): 91. 

29 X. Li, L. Feng, L. Zhang, D. Dadyburjor, E. Kugler, “Alcohol Synthesis over Pre-Reduced Activated 

Carbon-Supported Molybdenum-Based Catalysts.” Molecules 8 (2003): 13-30. 30 Naoto Koizumi, et. al. “Development of sulfur tolerant catalysts for the synthesis of high quality 

transportation fuels.” Catalysis Today 89 (2004): 465-478. 31 Daiping He, Y. Ding, H. Luo, and Can Li, “Effects of Zirconia phase on the synthesis of higher alcohols 

over zirconia and modified zirconia.” Journal of Molecular Catalysis A: Chemical. 208, Issues 1-2. 

(2004): 267-271. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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propanol into the feed of the reactor can increase isobutanol yields by 17% and 

72%, respectively. Representative process conditions are contained in Table 532: 

Table 5: Alkali-Doped ZrO2-Based Catalysts Process Conditions

Catalyst H2/CO 

Ratio 

Temp. 

(F) 

Pressure 

(psia) 

CO 

Conversion 

Alcohol 

Selectivity 

Alcohol 

Yield 

(g/ml/hr) 

Primary 

Products 

KPdCuMn

ZrO2

.9 608-

671 

1740 22.6-29.3 

mol % 

37.7-51.7 .41-.81 71.3 – 88.4 

wt% 

CH3OH 

LiPdZrO22 752 1160 7-8 % 146.3 

g/kg/hr 

The C2+OH selectivity of ZrO2 catalysts modified with a number of metals, 

copper, iron, cobalt, nickel, and manganese, has also been studied. The addition 

of manganese to the catalyst was found to increase the higher alcohol selectivity 

and suppress the formation of methane. Iron addition, in general, hindered 

mixed alcohol formation, and increased the selectivity to hydrocarbons.33 This 

should not be surprising, as iron is a common catalyst for the production of 

Fischer-Tropsch liquids. Adding Ni and Co made improvements in the higher 

alcohol selectivity of a Cu/Mn/ZrO2 catalyst to the catalyst.34 The use or 

absence of these metals in a Cu/Mn/ZrO2 catalyst could significantly increase 

higher alcohol selectivity. Ni and Co should be present in the catalyst in the right 

proportion while minimizing the presence of Fe. 

1.3 Reactors 

Standard fixed-bed reactors are currently employed in experimental HAS 

systems. Investigations have been made into two novel processes, multiple 

reactors and slurry reactors, to improve system performance. While neither of 

these are commercially available, the discussion below provides an update for 

the status of both technologies. 

1.3.1 Multiple Reactors 

Because HAS is an extremely exothermic process, there is interest to optimize 

the heat removal process. A multiple reactor design, or a “double bed” 

configuration, has been one idea explored to accomplish this. In this 

 

32 C. Yang, Minggui Lin, Z. Ma, W. Li, Y. Sun, M. He, “Novel Catalyst and Process Development for CO 

Hydrogenation”. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy 

of Sciences. 

33 Run Xu, C. Yang, W. Wei, W. Li, Y. Sun, and T. Hu, “Fe-modified CuMnZrO2 catalysts for higher 

alcohol synthesis from syngas.” Journal of Molecular Catalysis A: Chemical 221. (1-2). (2004): 51-58. 34 N. Zhao, R. Xu, and W. Wei, “Cu/Mn/ZrO2 catalyst for alcohol synthesis by Fischer-Tropsch modified 

elements.” Reaction Kinetics and Catalysis Letters. 75 (2), (2002). 297-304.

Task 9: Mixed Alcohols from Syngas: State of Technology 

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configuration, methanol production from syngas can be optimized in the first bed 

with a Cu catalyst and low temperatures, and the higher alcohol synthesis yield 

can be maximized in a second reactor with a higher temperature and a non-Cu 

Zn-chromite based catalyst.35 

Promising work on optimizing a double-bed reactor design has been conducted 

at Lehigh University. The first reactor was optimized for the production of shortchain alcohols over a Cs-promoted Cu/ZnO/Cr2O3 catalyst, and the second 

reactor was optimized to synthesize isobutanol over a Cs-promoted ZnO/Cr2O3

catalyst. The synergy of these two tubular bed reactors increased isobutanol 

production by 62% above what could be obtained with two reactor beds with the 

Cu catalyst alone36. Further research was halted in 1996 because the process 

was not considered economically promising at the time. 

1.3.2 Slurry Reactors 

The use of slurry reactors is of considerable interest for higher alcohol synthesis, 

because the formation of higher alcohols is extremely exothermic requiring 

significant heat removal. Breman conducted earlier research of higher alcohol 

synthesis in slurry reactors compared to fixed bed reactors. His work 

demonstrated that the presence of n-octacosane (a type of paraffin crystal) as a 

slurry liquid lowered higher alcohol to methanol selectivity and increased 

hydrocarbon yields.37 Over the past decade, the Roberts group at North Carolina 

State University has conducted a significant amount of research on alcohol 

synthesis in high temperature, 650 K, slurry bed reactors with a ZnCr catalyst. 

They have utilized three different slurry liquids for testing: tetrohydroquinoline 

(THQ), tetrahydronapthalene (Tetralin), and decahydroquinoline (Decalin). 38 

This could be of future interest if significant breakthroughs can be made, but too 

little data is currently available to make this a practical choice for higher alcohol 

designs. 

1.4 Technology Developers 

The development of a commercialized higher alcohol synthesis process has not 

significantly changed since the 2003 NREL report. No commercial plants have 

been built, and no pilot plants have been funded. In fact, some of the most 

 

35 K.A.N. Verkerk, B. Jaeger, C.H. Finkeldi, and W. Keim, W. “Recent developments in isobutanol 

synthesis from synthesis gas.” Applied Catalysis, A: General 186 (1,2)(1999): 407-431. 36 United States Department of Energy. “Development of Alternative Fuels and Chemicals from Synthesis 

Gas” DE-FC22-95PC93052. May 2003. 

37 B.B. Breman, A.A.C.M Beenackers, H.A. Schuurmann, H.A., E. Oesterholt, “Kinetics of the gas-slurry 

methanol-higher alcohol synthesis from CO/CO2/H2 over a Cs-Cu/ZnO/Al2O3 catalyst, including 

simultaneous formation of methyl esters and hydrocarbons.” Catalysis Today 24 (1995 :) 5-14. 38 Xiaolei Sun “Promoted Zinc Chromite Catalyst for Higher Alcohol Synthesis in a Slurry Reactor, Ph.D 

Thesis, North Carolina State University, 2001. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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interesting updates to the status of commercialization given in the 2003 technical 

report is the decrease in interest by technology developers to further advance 

HAS technologies. 

1.4.1 Snamprogetti (also referred to as SEHT – Snamprogetti, Enichem, and Haldor Topsoe) 

In the 1980’s Snamprogetti and Haldor Topsoe jointly developed a HAS process 

known as MAS (Metanolo piu Alcoli Superiori – methanol plus higher alcohols). 

The process was similar to a high pressure, high temperature methanol synthesis 

process, but the drawbacks of the modified methanol catalysts were supposedly 

avoided. They started a 12,000 tonne/yr pilot plant in 1982, and they sold the 

alcohol mixture as a 5 vol% blend in a gasoline called SUPER E.39 Despite the 

initial interest and promise, the MAS process is no longer available from these 

companies for the production of mixed alcohols.40

1.4.2 Dow 

While Dow was one of the first to develop and advance HAS technology, Dow is 

no longer pursuing the commercial development of their mixed alcohols process. 

In 1997, they offered to sell their patents for their Sygmal mixed alcohol 

production process to Power Energy Fuels, Inc. (PEFI). PEFI did not buy the 

patents, and subsequently, the patents have expired. PEFI is currently 

attempting to commercialize a modified version of Dow’s technology; Dow is no 

longer involved. 

1.4.3 Lurgi 

Lurgi developed their HAS process, known as OCTAMIX, with a low pressure 

methanol synthesis process in the 1980s and early 1990s. The process tended 

to yield higher alcohols, and 2 TPD demonstration plant was built in 1990. Lurgi 

indicated that they are no longer pursuing this technology; no detailed technical 

information is available. 

1.4.4 Institut Francais de Petrole (IFP) 

The latest development in IFP’s commercial mixed alcohols process occurred in 

the late 1980’s when they built their 20 BPD pilot plant in Chiba, Japan. Since 

that time, they have not ventured forth with any new units. In fact, according to 

their Strategic Marketing division, IFP has not further their work since they built 

 

39 G.A. Mills, and E.E. Ecklund, E.E. “Alternative Fuels – Progress and Prospects-2.” Chemtech, 19, no.10 

(1989): 626-631. 

40 Niels Udengaard, Haldor-Topsoe: Syngas Technology Group. May 4, 2005. Office Communication 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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1-13 
the pilot plant, and they have no commercial interest in pursuing a mixed 

alcohols process.41

1.4.5 EcaleneTM

The EcaleneTM mixed alcohol process continues to be developed by Power 

Energy Fuels, Inc, based in Lakewood, Colorado. The process is a modification 

of Dow’s Sygmal process using its polysulfite catalyst. Currently, the process 

has not moved beyond the bench scale, and the planned 500 gallon/day pilot 

plant is no longer being pursued.42 However, there are 2-3 other pilot plants 

under funding consideration that would produce mixed alcohols from various 

biomass sources, such as tires, wood chips, and refused derived fuel (RDF). 

One of the pilot plants in consideration is a 2,000 gallon/day pilot plant at the 

Wabash River Coal Gasification facility in conjunction with ConocoPhillips. PEFI 

management predicts that the EcaleneTM process will be ready for 

commercialization in 2006, and will be able to produce 1 gallon of mixed alcohols 

per 270 SCF of syngas. 

1.4.6 EnviroleneTM

The Standard Alcohol Company of America currently has a bench scale process 

to produce a mixed alcohols product known as EnviroleneTM. EnviroleneTM is 

composed of methanol through octanol. Approximately 50% of the product is 

ethanol, but a more detailed breakdown of its composition is not available due to 

its proprietary nature43. The process uses a modified high pressure methanol 

synthesis catalyst. The company is currently seeking funding for a pilot plant. 

1.4.7 Pearson Technologies 

Pearson Technologies has developed a 30-ton per day biomass gasification and 

alcohols conversion facility in Aberdeen, Mississippi. While both the gasifier and 

catalyst design are proprietary, it is believed that the catalyst is a modified FT 

catalyst formulated to selectively increase the production of ethanol. The overall 

Pearson design includes alcohol fractionation and recycle in an effort to purify the 

desired ethanol product44. 

 

41 Colin Baudouin, IFP Strategic Marketing. April 22, 2005, Office Communication. 

42 Gene Jackson, Power Energy Fuels, Inc, President, April 21, 2005, Office Communication. 43 Bob Dergay, Standard Alcohol Company Project Manager, April 29, 2005, Office Communication. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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44 Descriptions of this technology can be found at “The Manufacture of Synthetic Gas and Ethanol from 

Biomass using the Pearson Thermochemical Steam Reforming and Catalytic Conversion Process”, Pearson, 

Stanley, presented at the 5th International Biomass Conference of the Americas, 2001, and “Gridley Ethanol 

Demonstration Project Utilizing Biomass Gasification Technology: Pilot Plant Gasifier and Syngas 

Conversion Testing”, NREL/SR-510-37581, February 2005. 
A project is currently under development by the Worldwide Energy Group and the 

State of Hawaii to demonstrate gasification of sugarcane bagasse and production 

of ethanol using the Pearson technology on the island of Kauai. Funding for this 

project includes $50MM raised from special purpose revenue bonds issued by 

the state45. At the time of this report, it does not appear that a size or confirmed 

project timeline has been established. 

1.5 Conclusions and Future Research Needs 

Catalyst Selection 

There is no one catalyst that is best suited for every mixed alcohol process 

design. A set of criteria to evaluate each catalyst should be developed, project 

developers must determine which of the criteria is most important, and finally, 

evaluation of the trade-offs should occur. The key criteria that should be used in 

each analysis are per-pass conversion, alcohol yield, product selectivity, 

operating conditions required, sensitivity to impurities, and cost. The 

performance criteria—conversion, yield, and selectivity—will be summarized 

here. 

• Conversion: No one catalyst is clearly superior when it comes to per-pass 

conversion. Conversions are dependent on a number of factors, including 

catalyst formulation, doping agents, syngas impurities, and process 

conditions. Regardless of the catalyst chosen, recycle of anywhere from 

~40 to 90% of the process stream will be necessary to maximize 

production of mixed alcohols. 

• Alcohol Yield: Both modified methanol and molybdenum catalysts have 

shown higher alcohol yields than modified Fischer-Tropsch catalysts. The 

most recent research into process conditions, catalyst formulations, and 

metal promoters have shown that molybdenum catalysts can outperform 

modified methanol catalysts in this criteria under certain conditions. 

• Selectivity: Molybdenum catalysts have shown superior performance for 

selection of higher alcohols over either modified methanol or FischerTropsch catalysts. The relative benefit of this must be evaluated on an 

economic basis. 

The tolerance of molybdenum catalysts to both sulfur and carbon dioxide give it 

another advantage over the other types of catalysts. These benefits must be 

weighed against process condition requirements, catalyst costs, and final product 

specifications to determine the catalyst appropriate for each design. 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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45 Honolulu Star Bulletin, 23 June 2004, Star-Bulletin Staff. These bonds were originally authorized in 

2000. 
Future Research Needs 

The data that is currently available for mixed alcohol synthesis is adequate to 

perform an overall systems analysis. However, a broad R&D program would be 

helpful to more accurately determine the best catalyst formulations for 

downstream product requirements. A comprehensive R&D program should 

include: 

• Additional data gathering on clearly defined catalyst performance 

conditions to allow more direct comparisons between catalysts. The 

current literature available makes this type of comparison difficult due to 

different operating conditions, processes, and evaluation methods. 

• A determination of catalyst sensitivities to other impurities that may exist in 

a biomass-derived syngas stream. This could include metals, halides, 

ammonia, heavy hydrocarbons, nitrogen, and others. 

• Optimization of yields and selectivities for the desired product. For 

example, if use as a transportation fuel is desired, a set of specifications 

for the mixed alcohol product should be defined that is desired and 

compatible with this goal. Catalysts should then be optimized with these 

goals in mind. 

• Greater investigations into reactor configurations and conditions to 

improve process performance. 

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Section 2 Sulfur Removal 

2.1 Sulfur Removal Requirements and Options 

The gas clean up issues for mixed alcohol synthesis processes fall into two 

different categories. The first category is for modified methanol and FischerTropsch synthesis catalysts. Because the sulfur allowance for the modified 

catalysts is similar to the unmodified catalysts, the sulfur clean up issues will be 

the same. Sulfur limits are .1 ppmv and 60 ppb for the modified methanol and 

Fischer-Tropsch catalysts, respectively. The second category includes sulfidebased catalysts, such as MoS2, that do not have the strict sulfur clean up 

requirements of the other catalysts. In fact, these catalysts may require relatively 

high levels of sulfur in the syngas in order to operate most efficiently. While 

these catalysts may not require significant syngas sulfur treating, the final 

product sulfur specification for use as a motor fuel or chemical blendstock may 

require additional sulfur removal. 

2.1.1 Modified Methanol and Fischer-Tropsch Synthesis Catalysts 

The sulfur removal technology chosen for syngas cleanup depends upon the 

sulfur removal requirement, the total amount of sulfur in the syngas, and the 

downstream process conditions. The modified catalysts for higher alcohol 

synthesis have the same sensitivity to sulfur in the syngas feed stream as the 

unmodified methanol and Fischer-Tropsch catalysts. Sulfur levels below .1 ppmv 

are preferred in order to avoid poisoning the methanol synthesis catalysts. 

Similarly, the Fischer-Tropsch synthesis catalysts can require sulfur levels as low 

as 60 ppb. All of these catalysts require very low levels sulfur that will dictate the 

use of a physical absorption unit or ZnO beds as a polishing step. 

In general biomass to syngas cases, the total amount of sulfur to be removed is 

relatively small. Because the total amount of sulfur is likely to be under 20 TPD 

for even the largest plant, the most economic sulfur removal technology would 

most likely be the LO-CAT® process. The use of a physical (Selexol or Rectisol) 

or chemical (amine-based) solvent system would require a sulfur recovery unit, 

such as a LO-CAT® process or a CLAUS plant. LO-CAT® is used for small-scale 

applications with less than 20 TPD of sulfur to be removed, while a CLAUS plant 

is generally economic for large-scale applications with greater than 20 TPD. LOCAT® can also be used independently to achieve 99.9%+ H2S removal efficiency. 

Therefore, for sulfur removal applications of less than 20 TPD, a LO-CAT® unit 

followed by a ZnO adsorbent bed is recommended to achieve the necessary 

sulfur removal. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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However, it is important to consider the CO2 concentration of the syngas feed 

and recycle streams and the catalyst’s sensitivity to CO2. Small amounts of CO2

in the syngas streams can have detrimental effects upon higher alcohol yields for 

modified methanol catalysts. Depending upon the catalyst’s sensitivity to CO2, it 

may be beneficial to use a physical or chemical solvent system that can remove 

CO2 as well as sulfur to ensure the optimal syngas feed for a catalyst.46 This 

would have to be decided by an economic analysis of additional capital costs for 

sulfur removal and the increase in mixed alcohol yield that can be attained. 

If the total amount of sulfur in the syngas feed were to significantly increase 

(above 20 TPD) as a result of a different feedstock or a larger plant size, other 

technologies may become more economically reasonable. Sulfur removal 

technologies that could achieve the same levels of sulfur removal would be 

selected based upon the process conditions of the higher alcohol synthesis 

reactor. For instance, physical solvents might be favored over amine-based 

solvents, because physical solvents operate more effectively at higher pressure. 

The ZnO bed would still be required as a polishing step for Selexol with all 

catalysts, but it would only be required for Rectisol when used with the modified 

Fischer-Tropsch catalyst. 

2.1.2 Sulfide-Based Catalysts 

The nature of a sulfide-based catalyst changes the requirements for upstream 

sulfur removal. Sulfide-based catalysts are activated by the presence of sulfur in 

the syngas feed stream, particularly in the 50 – 100 ppm range.47 Thus, 

upstream acid gas removal as extensive as the modified methanol and FischerTropsch catalysts is not required. In fact, the EcaleneTM process being 

developed by Power Energy Fuels, Inc. claims that there is no need to do any 

upstream acid gas removal regardless of the origin of syngas.48 Because the 

sulfur requirements in the syngas stream vary depending upon the type of 

sulfide-based catalyst used, two options for sulfur removal will be discussed. 

2.1.2.1 Upstream Acid Gas Removal from Syngas 

The first option to consider is removing sulfur in the syngas stream to the 50 – 

100 ppm range. The base assumption for removal will be for a 2000 TPD 

biomass-fed gasification plant, using either direct or indirect gasification 

technology. The most economically justifiable sulfur removal technology would 

be the LO-CAT® process. Capable of achieving a 99.9%+ H2S removal 

 

46 Dow and Union Carbide assumed the use of MDEA as a CO2 removal process in their systems. 

47 P. Courty, et.al. (1990). “Production of methanol-higher alcohol mixtures from natural gas via syngas 

chemistry.” Revue de l’Institut Francais du Petrole, 45, no.4 (1990): 561-78. 48 Gene Jackson. PEFI – President. April 21, 2005. Office Communication.

Task 9: Mixed Alcohols from Syngas: State of Technology 

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2-2 
efficiency, the LO-CAT® process could reduce the sulfur levels in the syngas feed 

to that required by the higher alcohol synthesis reactor. A physical or chemical 

solvent process is still not economically justifiable, because the total amount of 

sulfur removal required is less than 20 TPD. The most notable change between 

the sulfur removal technologies required by the modified catalyst and the sulfidebased catalysts is the lack of need for a ZnO bed; since no polishing step will be 

needed, costs can be reduced. 

Reducing sulfur removal requirements will lead to some savings related to sulfur 

removal capital and operating costs, but it may not be as substantial or as 

beneficial as it first appears. First, there will be savings associated with a turneddown LO-CAT® process. In order to achieve a sulfur level of 50-100 ppm in the 

syngas, smaller equipment and less chelating agent would be used than required 

for a 99.9%+ H2S removal. This would slightly decrease capital and operating 

costs, although it is not likely to be significant since capital must still be spent to 

install a LO-CAT® unit. Second, removal of the ZnO beds will not reduce capital 

costs significantly; the beds cost roughly 1/10th that of a LO-CAT® unit, and only 

made up 0.2% of the installed capital costs in the 2005 NREL Biomass to 

Hydrogen report (~$350,000 in a $152MM project).49 Because the savings may 

not be significant to the overall cost of a plant, an economic analysis should be 

performed when comparing sulfur tolerant and non-tolerant catalysts based on 

incremental changes in cleanup requirements. 

The second option to consider is to eliminate a sulfur removal unit altogether. If 

assured that sulfur levels in the syngas feed will not poison a sulfide-based 

catalyst, sulfur removal steps may be able to be eliminated. The benefits would 

come from the capital cost reduction and elimination of waste sulfur removal 

requirements. However, it is important to understand that some form of 

downstream product cleanup may be required if upstream syngas cleanup is not 

done. A project developer must also be sure that the feedstocks selected will 

never have high levels of sulfur if a design without sulfur cleanup is chosen. 

The third option would be to do more extensive sulfur clean up in the syngas than 

required by the sulfide-based catalyst. This option arises from future federal 

sulfur specifications for gasoline that would not be met if there were no 

downstream sulfur removal. Choosing this cleanup option would depend upon 

an economic analysis comparing upstream acid gas and downstream sulfur 

removal costs. This option may actually be detrimental to sulfided catalysts that 

require some sulfur to operate most efficiently. 

 

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49 Pamela Spath, et al. “Biomass Syngas to Hydrogen Production Design Report.” National Renewable 

Energy Laboratory, January 31, 2005. 
2.1.2.2 Downstream Sulfur Removal 

The benefit of sulfide-based catalyst is avoiding some degree of syngas sulfur 

removal. However, because H2S is not removed in its entirety, significant sulfur 

concentrations may be present in the mixed alcohols product. Regardless of if 

the end use of the product is for use as a transportation fuel or for chemical 

applications, it is likely that additional sulfur may need to be removed if this is not 

performed in the syngas stream. 

The breakdown of sulfur species present in the mixed alcohols product could 

vary based on the feedstock and sulfur removal technology. Certain sulfur 

species, such as H2S and mercaptans, can be a problem if not removed to 

extinction. These compounds are extremely corrosive and damaging to gasoline 

and diesel engines. Any H2S would cause the gasoline to fail fungible gasoline 

specifications. Mercaptans can also be a problem depending on the regional 

regulation and standard. Thus, if these species are present in the mixed alcohols 

above allowable limits, either additional syngas sulfur removal or downstream 

sulfur cleanup will be required. The downstream product usage sulfur 

specification may reduce or eliminate any advantage that sulfided catalysts bring 

to the process. 

If sulfur in the syngas stream remained above 30 ppm, downstream sulfur 

cleanup would be required to meet future national sulfur requirements for 

gasoline. The Environmental Protection Agency’s Tier 2 Gasoline Sulfur 

requirements will phase in a 30 ppm sulfur limit by 2011 on gasoline.50 The 

mixed alcohol blend would therefore have to have a sulfur level of 30 ppm or 

lower, with no H2S, and very limited mercaptans. This would require one of two 

sulfur cleanup choices: either upstream acid gas removal from syngas, or 

removal of excess sulfur from the mixed alcohol product. An economic and 

catalyst performance analysis should be performed to determine the appropriate 

sulfur removal option. 

When considering the type of catalysts to be used for HAS it will be important to 

identify the desired use for the mixed alcohols, the end product sulfur 

specifications, and the type of sulfur species present in the syngas. There is 

potential savings in eliminating sulfur removal units for sulfide-based catalysts, 

but this should be carefully evaluated versus product requirements and catalyst 

costs. 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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50 Tier 2 Gasoline Sulfur Final Rule with Amendments. 8/29/02. available at http://www.npra.org/issues 

/fuels/pdf gasoline.pdf 
2.2 Summary and Conclusions 

In order to choose the catalyst and appropriate sulfur cleanup technologies to 

meet design needs, an economic analysis should be done that will incorporate 

the following factors: desired mixed alcohol product slate, sulfur specifications, 

CO2 removal requirements, and cost of sulfur removal. 

• Desired alcohol product slate: The different catalysts for HAS have 

distinct conversion rates and yields for methanol, ethanol, isobutanol and 

other higher alcohols. A decision should be made considering what the 

desired composition of the final mixed alcohol product slate is before a 

determining the sulfur cleanup required. However, it may still be possible 

that sacrificing some yield of a desired product could be compensated for 

by reduced cleanup costs. 

• Sulfur specifications: NREL should follow the expected federal and state 

sulfur specifications for transportation fuels and chemical grade alcohols. 

If sulfur cleanup for product, not catalyst, requirements are necessary, an 

evaluation of the best way to perform this step should be made. This 

analysis should be compared against using catalysts that are not sulfur 

tolerant. 

• CO2 Removal: Because CO2 can inhibit certain catalysts, particularly 

modified methanol synthesis catalysts, the right combination of CO2

removal and H2S removal should be explored. If CO2 removal needs to be 

incorporated into a HAS process, more costly sulfur removal technologies 

may become necessary. This would provide extra incentive to use sulfur 

tolerant catalysts, since they are also more tolerant to high levels of CO2. 

• Sulfur Removal: Actual costs for the needed sulfur removal technologies 

should be developed. This would help with an overall economic analysis 

of what catalyst would be the most economically attractive and, thus, 

commercially viable. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

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Section 3 Technical and Economics Risks 

3.1 Introduction 

In general, a considerable amount of uncertainty and risk exists in the biomass to 

mixed alcohols process. Not only does the biomass gasification section of the 

plant have risk by itself, but unlike alternative syngas-to-liquids processes such 

as Fischer-Tropsch (FT), no commercial plants exist solely for the manufacture of 

mixed alcohols from syngas. The limited experience from both a feedstock 

conversion and product synthesis side creates a number of risks that must be 

considered when moving forward with a concentrated effort to make this 

technology a commercial reality. 

This section will outline the major technical and economic considerations that 

should be addressed in order to progress the current state of the technology. 

Amongst the items that will be addressed include: 

Technical Risk

• Feasibility of Producing the 

Desired Product Slate 

• Scale-Up Considerations 

• Reactor and Overall Unit 

Process Conditions 

• Catalyst Sensitivities and Run 

Life 

Economic Risk

• Competitiveness versus 

Petroleum Transportation 

Fuels 

• Catalyst Manufacture and 

Prices 

• Overall Process Economics 

for Gasification and Synthesis

Besides a literature survey and analysis of past Bechtel/Nexant reports, efforts 

were made to find analogies in similar technologies in determining the barriers 

that had to be overcome for commercialization. For example, in order for FT 

liquids production to be successful, commercial facilities must be able to find 

markets where FT from syngas has an advantage over petroleum based fuels. 

While this study is not a comprehensive marketing analysis, efforts have been 

made to identify potential solutions to mitigate some of the risk that this 

technology faces. 

3.1.1 Drivers for Additional Research on Mixed Alcohols Synthesis 

Due to the lack of large-scale production data, along with a number of 

outstanding questions and research areas for mixed alcohol synthesis from 

biomass, incentives and focus needs to be provided in order to place appropriate 

emphasis on this technology. This will help to provide a common basis for what 

needs to be accomplished to bring the technology to commercial fruition. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-1 
Definition of Research Needs 

Currently, the available data for production routes, potential catalysts, and 

commercial application is fairly diverse, covering a wide range of areas. In order 

to progress the technology, a greater definition must be made for what the 

commercial use of the products will be. This will help to define what the catalyst 

yields, process set-up, and downstream refinement requirements are. Catalysts 

and technologies that are less promising for the eventual commercial use can be 

excluded from current consideration. Niche opportunities can also be identified 

at this stage in order to help establish the most attractive technologies to be 

pursued. 

Policy Options 

As with many other emerging technologies, research efforts can be spurred by 

government policy intervention. If biomass derived mixed alcohols had support 

from a concerted agricultural, security, and/or economic basis, focus could be 

placed on promotion of this technology. This support could come in the form of 

credits, such as the 51 cents/gallon ethanol credit, mandates, such as state 

renewable energy requirements, or focused research funding that would 

encourage additional research and development. While the appropriate policy 

tool is outside the scope of this analysis, consideration should be made of the 

options available to assist with technology promotion. 

3.2 Technical Risk Analysis 

A number of unanswered technical questions exist at this stage of mixed alcohol 

process research. The main items include the overall process feasibility to 

produce the desired product slate, the ability to scale-up the process to a 

commercial level, the appropriate process conditions both in the reactor and 

upstream units, performance of various catalysts at commercial conditions, 

catalyst sensitivities, and appropriate syngas compositions. After establishment 

of the desired product slate, each of these risk areas should be evaluated with 

prioritization placed on ways to reduce the inherent risk. This section will provide 

greater detail for the major areas of technical risk, and suggest ways to handle 

the risks involved. 

Since NREL has been given the priority of exploring options for biomass derived 

fuels to displace petroleum, the assumption will be made that the end product 

desired is mixed alcohols as a transportation fuel. Each risk area will be 

analyzed with that priority in mind. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-2 
3.2.1 Feasibility 

From a technical perspective, questions must be answered if catalysts are 

suitable to produce the product slate desired with reasonable performance 

characteristics (such as catalyst life, process efficiency, and once-through 

product yield). This is one of the few areas that has had considerable research 

performed. However, much of the research has only been performed on a 

bench-top level, with little optimization or tests under “real” industrial conditions. 

Key to answering this question is analysis of three areas: what product slate is 

desired, what catalysts are currently available or hold promise, and the impact 

that synthesis side products have on the downstream application. 

Product Slates and Catalysts Available 

When considering the optimum mixed alcohol slate that could be produced for 

use as a transportation fuel, the following items should be considered for their 

impact on the gasoline or diesel pool51. A more in-depth review of these items 

will be made in the Economic Risk section. 

• Effect on Octane/Cetane Number 

• Effect on fuel volatility: V/L ratio and Reid Vapor Pressure (RVP) 

• Effect on fuel distillation curve 

• “Enleanment” effect of mixed alcohols 

• Effect on fuel economy 

• Effect on water solubility and phase separation 

• Effect on pool sulfur and aromatics content 

These items should be prioritized based on the market where they are expected 

to be introduced. For example, in US markets that require reformulated gasoline, 

RVP and aromatics content are of greater concern than other fuels 

specifications. A general product slate can be theorized that is optimum given 

the transportation fuel constraints, and then catalysts chosen that best fit this 

desired slate. Many times, disconnects that exist between the desired product 

slate and the catalysts available will set research priorities. 

In general, heavier alcohols (C3+) are superior to light alcohols (methanol and 

ethanol) on a number of these criteria. Heavier alcohols have better octane 

ratings, lower RVPs, a distillation curve more comparable to gasoline than light 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-3 

51 Parts of this list are derived from a similar one established by Chandra Prakash, Motor Vehicles 

Emissions and Fuels Consultant, “Use of Higher Than 10 Volume Percent Ethanol/Gasoline Blends in 

Gasoline Powered Vehicles”, Environment Canada, November 1998. 
alcohols, and superior energy content52. Focus should potentially be placed on 

catalysts that have higher yields of these types of alcohols. Another advantage 

of the higher alcohols are their ability to act as a co-solvent that allows methanol 

and ethanol to be blended in higher proportions without hitting pool constraints 

relative to these alcohols alone. Trade-off studies for catalysts producing 

different proportions of light versus heavy alcohols should be performed to 

determine the most promising catalyst for future research. Besides just 

considering the different product yields, downstream processing, such as 

fractionation of the light alcohols for other uses, should also be considered53. 

Side Products 

Each catalyst has a unique quantity of side products (potentially up to 20%) that 

will be produced, which may either benefit or hinder the ability of the final product 

to be blended into transportation fuels. Compounds such as FT liquids and 

DME, have been identified as potential side products from mixed alcohol catalyst. 

• FT Liquids, a potential co-product of cobalt-based catalysts, may be 

beneficial depending on the ratio of naphtha to diesel (the catalyst “alpha 

value”). While octane values may be impacted negatively, the resulting 

product would likely be heavier, leading to a lower volatility. As 

mentioned in Section 1, other hydrocarbons have also been witnessed 

from catalysts where the alkali-doping has been reduced. This side 

product will hurt product octane value, but will have a varying impact on 

other properties, depending on the carbon content of the hydrocarbon. 

• DME is derived from Cu/ZrO2 containing catalysts, and have been found 

to be less prevalent as CO2 concentrations in the syngas decrease, while 

being more prevalent at higher reaction temperatures54. This high cetane 

product is an excellent diesel fuel substitute, and could be advantageous 

to mixed alcohol blends depending on the downstream application. 

An analysis of the downstream application for the mixed alcohol product will help 

to provide focus and determine what catalyst is best suited for the selected 

application. It is unlikely that one catalyst will be both technically feasible and 

optimized economically, which is why prioritization is key. Preliminary analysis 

would suggest that modified methanol catalysts containing copper might be less 

desirable due to the relatively high methanol yield. Modified FT catalysts 

 

52 Information for part of this analysis provided by Smith and Workman, “Alcohol for Motor Fuels”, 

Colorado State University, 15 February 2005. 

53 Methanol was fractionated off the mixed alcohol product, vaporized, and used as fuel gas in one scenario 

of Fluor’s “Co-Production of Fuel Alcohols and Electricity via Refinery Coke Gasification”, Gasification 

Technologies 2003 Conference, San Francisco, October 2003. 

54 Klier and Herman, et. al., “Oxygenates via Synthesis Gas”, Lehigh University, as a subcontractor to Air 

Products and Chemicals, US DOE subcontract DE-FG22-95PC93052, April 1999. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-4 
containing cobalt could have superior performance depending on the 

downstream application. Molybdenum catalysts, which selectively produce high 

ethanol content products, are also beneficial due to their lower methanol yields. 

One final feasibility consideration that should be made revolves around how 

policy will impact gasoline formulations. The product selected should take into 

consideration likely future fuels policy that may change requirements for 

oxygenates, RVP, aromatics, and sulfur, while also keeping in mind how current 

ethanol policy will influence mixed alcohols derived from biomass gasification. 

Mandates on ethanol blending may drive technical research toward higher 

ethanol, rather than heavier alcohol, yields. In addition, mixed alcohol fuel 

blends will need to be certified by appropriate federal and state agencies for 

blending into the motor fuel pool. Since two mixed alcohol products, from Lurgi’s 

OCTAMIX and PEFI’s Ecalene processes, have already been certified by the 

EPA, the technical hurdles to achieving certification should be limited. 

3.2.2 Scale-Up 

To varying extents, limited operational information exists on both biomass 

gasification operation and mixed alcohol synthesis on a commercial level. While 

analogies exist for the scale-up of other technologies, such as FT synthesis, it 

will be difficult to estimate with certainty the technical performance and economic 

impact of a commercial biomass to mixed alcohols plant. This is a risk inherent 

to any emerging energy technology. 

Some performance data exists on pilot-level and small commercial size biomass 

gasification plants that can be used for scale-up purposes. Units such as those 

run in Scandinavia, Hawaii, and the Eastern United States may provide adequate 

information for scale-up purposes, as well as pilot scale facilities tested by a 

number of commercial vendors. In addition, larger gasification facilities have 

been built for coal and petroleum coke that can also provide performance and 

sizing data. 

Additional technical risk comes in scaling-up a mixed alcohols reactor. Since 

little information on pilot or commercial scale performance exists, a testing 

program using either an existing gasifier or syngas derived from natural gas 

would help to provide important scaling data. In addition, analogies in processes 

such as FT synthesis, DME production, or other catalytic processes (such as 

COS or hydrotreating reactors), may be useful in estimating the major issues 

involved in scaling from the current plant sizes. 

3.2.3 Process Conditions 

The overall process conditions required for mixed alcohol synthesis represents 

another major technical risk to successful commercial operation. The high 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-5 
temperatures and pressures required will not only place a severe strain on 

catalyst performance, but will also require careful engineering of compressors, 

reactors, piping, and containment vessels to assure robust performance. 

Engineering analysis must take these conditions, which may be unlike other 

gasification designs, into account in order to obtain the most realistic estimates of 

the process performance and cost. 

Reactor Operating Conditions 

The process conditions required for conversion of syngas to mixed alcohols are 

severe, even by alternative liquid product from syngas standards. While 

methanol and FT synthesis require reactor pressures in the 500 to 1200 psia 

range and temperatures from 300 to 500 degrees F, mixed alcohol synthesis 

usually operates at around 1800 psia and 700 degrees F, but can vary 

depending on the catalyst. These process conditions are necessary due to the 

low activity of the catalysts used. 

Requiring this level of temperature and pressure will add cost due to the need to 

compress the syngas to a much higher degree, and from incorporation of 

materials necessary for operation at these conditions. Available software for 

performance and cost estimation may not always be suitable for pressure 

vessels of this thickness, requiring special estimates. While materials exist that 

should be able to handle the severe operating conditions, careful consideration 

should be made for what materials are appropriate, and how this will impact plant 

performance and cost. 

As an initial example of the higher cost for mixed alcohol synthesis, a preliminary 

estimate of the additional cost that would be required to compress a biomass 

derived syngas stream to 1800 psia relative to 450 psia (appropriate for 

hydrogen and FT reactors) and 1160 psia (appropriate for methanol reactors) 

was made. This estimate shows a net plant increase of 5 to 10% total installed 

cost (TIC) using the NREL Biomass Syngas to Hydrogen design as a base case 

and two different estimation methods55. The difference in horsepower can be 

seen in Table 6. 

 

55 TIC estimate of the compressor used in the NREL “Biomass Syngas to Hydrogen Production Design 

Report”, Spath P., et. al., January 2005, was used as the base. The increase in cost was estimated both 

using the NREL scaling factor and a HYSIS derived estimate for the increase in HP, along with Bechtel 

data on cost for refrigeration compressors at different HP loads. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-6 
Table 6: 2000 TPD Wood Gasification Plant Compression Requirements56

Compression Required Horsepower (BHP)

16 to 450 psia (for H2/FT synthesis) ~35,000 

396 to 1160 psia 

 (for methanol synthesis) ~10,000 

1160 to 1800 psia (for mixed alcohols) ~4,000 

The lower compression ratio required as stream pressure increases reduces the 

marginal horsepower requirement. Please note that this estimate does not take 

into account the different pipe, flange, and downstream unit thicknesses required 

to handle the higher pressure. These additional costs to accommodate mixed 

alcohol synthesis represent another risk to future commercial application. 

Catalyst Life 

Due to the severe process conditions of higher alcohol synthesis, it would be 

expected that catalyst life would not be significantly long. As a benchmark, it 

could be helpful to recognize that the catalyst life for the typical Fe-Co FischerTropsch catalyst can be longer than 5 years.57 Information on catalyst life is not 

abundant because most research into HAS is bench scale and not commercial. 

However, the catalyst life data available does not demonstrate the longevity of 

the typical Fe-Co Fischer-Tropsch catalyst. 

The majority of information available on catalyst life comes from the earlier 

commercialization attempts of different catalyst and processes in the 1980’s. As 

an example, Dow and Union Carbide found the longest life for their MoS2 catalyst 

to be in excess of 8 months (~5,700 hr), and at that time it retained 80% of it 

C2+OH selectivity at a 20% CO conversion rate.58 Also, Snamprogetti’s MAS 

process demonstrated that their methanol-synthesis like catalyst has a catalyst 

life over 8,000 hr at temperatures between 626 – 806 oF.59 Short catalyst life 

would produce high operating costs due to frequent replacement of the catalyst, 

and decreased performance during the relatively catalyst run life.

 

56 The HYSIS model developed for the Nexant LP clean-up design case was used for the flowrate and 

composition. 

57 Energy Research Centre for the Netherlands. Biomass – Fischer-Tropsch Synthesis. Available at 

http://www.ecn.nl/biomassa/research/poly/ftsynthesis.en.html 

58 G. Quarderer, ibid. 

59 A. Paginni, D. Sanfilippo, D. “MAS Process: From Research to Commercialization”. Paper presented at 

78th Spring National AIChE Meeting. New Orleans, LA, April 1986. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-7 
Catalyst Activity 

The amount of activity in mixed alcohols catalyst can vary widely based on a 

number of factors. This creates a significant technical design difficulty when 

estimating the per-pass conversion, the amount of recycle necessary, and the 

appropriate downstream treatment required. Activity and conversion will not be 

steady throughout the life of a catalyst, requiring designers to include 

considerable flexibility in plant designs. 

Priority will have to be placed on catalyst activity relative to other items such as 

sensitivity to stream impurities and catalyst cost. Since each design will have a 

different set of criteria priorities, it is difficult to say at this time how this factor 

should be taken into consideration. It should be estimated with as much certainty 

as possible, with design factors included to keep activity stable and predictable. 

Catalyst Sensitivities Other Than Sulfur 

Impurities in the syngas that could impact mixed alcohol yield and selectivity are 

a major technical risk to successful plant operation. Catalyst sensitivities to 

sulfur were discussed at length in Section 2.1. Some impurities, such as CO2

and water, have been researched specifically for their impact on mixed alcohols 

production, while the impact of others, such as metals, halides, ammonia, and 

nitrogen, can be predicted with some accuracy if modified methanol or FT 

catalysts are used. For catalysts with a more limited testing database, such as 

MoS2, greater research should be performed to reduce the risk that a previously 

unknown poison will impact the process. 

The impact of some of the potential stream impurities are listed below: 

• Carbon Dioxide: In research performed by Lehigh University60, it was 

found that increasing levels of CO2 increase the product methanol yield for 

Cu/ZrO2 catalysts. This is not surprising, for the fast reaction between 

CO2 and H2 over methanol catalysts is well known. As with methanol 

catalysts, high levels of CO2 may be undesirable due to the lowered 

process efficiency and the impacts of higher methanol concentrations in 

the final mixed alcohol product. 

However, as mentioned in Section 1.2.4, molybdenum catalysts are 

relatively tolerant to CO2. The level of impurity tolerance will be very much 

dependent on the catalyst chosen. 

• Water: Lehigh also found that increasing the water concentration would 

promote CO2 production and decrease alcohol formation. Surprisingly, the 

higher CO2 yield does not then produce proportionally higher amounts of 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-8 

60 Klier and Herman, ibid. 
methanol, as what may be expected. If an amine scrubber is included 

after the mixed alcohol reactor in the recycle loop, the additional CO2 will 

be removed, potentially reducing process efficiency. It is unlikely that 

syngas entering the synthesis reactor at 1800 psia will have water, making 

this impurity of reduced interest. 

Little other research on the impact that water has on other catalyst types 

exists. 

• Known FT and Methanol Catalyst Poisons: Metals, halides, ammonia, 

and nitrogen all act to reduce catalyst activity and catalyst life. As with 

other syngas to FT and methanol designs, steps should be made to 

reduce these impurities if modified FT or methanol catalysts are used. A 

greater level of testing should be performed to determine if the sensitivity 

to these poisons are as great as with straight FT or methanol catalysts. 

Hydrogen to Carbon Monoxide Ratio 

Depending on the alcohol product slate desired and the type of catalyst used, the 

appropriate ratio will vary. Whatever ratio chosen should be strictly maintained to 

optimize process performance. In general, a lower ratio has been found to be 

better for higher alcohol synthesis, as the table below shows: 

Table 7: Stoichiometric H2/CO Ratio, Different Alcohols 

Product Stoichiometric Ratio

Methanol 2.0 

FT Liquids 2.0 

Ethanol 1.0 

Propanol 0.8 

Butanol 0.71 

In the 2003 Fluor/Ecalene co-production study61, a 1:1 ratio was applied, while 

the 1996 Bechtel study62 used a lower ratio (0.5 to 0.7) to promote more C4 

alcohol production for MTBE synthesis. Maintaining this ratio will be more 

challenging in a plant with full recycle, while a limited recycle plant with either 

purge or co-production will run less risk of unoptimized product yields. 

Depending on the feedstock and gasification process, efforts may be necessary 

to reduce the H2/CO ratio in the syngas stream in order to promote heavy alcohol 

 

61 Fluor 2003 Gasification Technologies Conference paper, ibid. 

62 “Economics of MTBE via Mixed Alcohol Synthesis”, as a subcontractor to Air Products US DOE Study 

Alternative Fuels and Chemicals from Synthesis Gas, cooperative agreement DE-FC22-95PC93052. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-9 
production. This is especially true in biomass gasification systems. The main 

options that should be considered for reducing this ratio include: 

1. Pressure Swing Absorption (PSA) to remove hydrogen. While this step 

would be easiest to control relative to other options, a use for the pure 

hydrogen stream must be found and incorporated into the design. 

2. Unreacted CO recycle. Some degree of recycle will occur in all mixed 

alcohol designs. The type of catalyst chosen and desired product slate 

will greatly impact how the recycle will impact the inlet reactor stream 

composition. 

3. Injection of CO2 into the tar cracker. If a relatively pure CO2 stream is 

removed from the process, introduction of CO2 into the tar cracker may 

promote a reverse water-gas shift, increasing the CO concentration. The 

amount of CO2 and type of tar cracking catalyst will dictate the amount of 

extra CO that will be produced from this process. 

4. Minimizing steam injection into the gasifier. Since excess steam may 

cause unnecessary hydrogen production, efforts should be made to 

eliminate steam injection beyond what is required for fluidization or 

thermal control. Testing of both steam injection into the gasifier and CO2

injection into the tar cracker should be performed to determine how these 

efforts would impact the ratio. 

The appropriate design to reduce the ratio is very dependent on the mixed 

alcohol catalyst chosen, the desired product slate, the gasifier technology used, 

the feedstock selected, and other process steps. Each design case must be 

uniquely evaluated to determine the preferred method for producing the desired 

H2/CO ratio. 

3.3 Economic Risk Analysis 

Besides the obvious impact that mixed alcohol synthesis has on process design 

economics, the other major areas of economic risk are the competitiveness of the 

mixed alcohols product versus petroleum based transportation fuels and the risk 

inherent to new catalyst formulations. This section will elaborate on the major 

economic risks in the process, and suggest areas for future study and research. 

Once the externalities of petroleum based fuels are taken into consideration, 

policy makers may find that pursuing mixed alcohols from biomass as a motor 

fuel is an attractive option. In fact, some states have already started to take 

action in this area. California Assembly Bill AB2076 mandates that the California 

Energy Commission explore efforts to “reduce petroleum dependence” in motor 

fuels, which has been interpreted as an effort to pursue alternative transport 

fuels. States such as New York, Massachusetts, New Jersey, Connecticut, 

Rhode Island, Vermont, and California have also enacted some form of low, ultra 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-10 
low, or zero emission vehicle programs that, depending on the policy structure, 

may also stimulate the use of alternative fuels. These sorts of efforts, coupled 

with potential tax incentives, may be the driving force that stimulates additional 

work in this field. 

3.3.1 Comparison with Petroleum Based Transportation Fuels 

If the key use of mixed alcohols from syngas is as a replacement for petroleum 

based fuels, a direct evaluation of the advantages, disadvantages, and 

compatibility with the current fuels infrastructure is necessary. This analysis 

would determine what economic drivers exist for application of the fuel, and what 

roadblocks must be overcome to incorporate mixed alcohols into the fuels 

system. 

Price 

At least two comprehensive studies have evaluated the economics of producing 

alcohols from petroleum coke—a 1996 Bechtel study specific to MTBE 

production with C1 and C4 alcohols as a intermediate, and a 2003 Fluor/Ecalene 

study for co-production of mixed alcohols and electricity. Both studies were 

mentioned in the technical risk section of this paper. A comparison of the two 

cases is shown below: 

Table 8: Mixed Alcohol Economic Study Comparisons 

Bechtel (1996) Fluor/Ecalene (2003)

Product(s) MTBE from C1/C4 

alcohols 

Ethanol, Propanol, and 

Power 

Feed Rate (Pet Coke) 1800 TPD 4758 TPD 

Feed Cost $0/ton $0/ton 

Plant Cost $350-400MM estimated at >$1 billion63

Product Value $0.85 cents/gal MTBE 

$1.15 cents/gal for 

alcohols, 4.4 cents/kWh 

power 

Return on Investment ~13% ~15% 

The entries from these studies were placed in the Nexant IGCC Financial 

Model64 in order to test key study sensitivities and competitiveness of the 

 

63 Details of plant cost were not provided in the Fluor study. This estimate is derived from the Nexant 

IGCC Financial Model, using the inputs and output flowrates, along with estimated feedstock and product 

values shown by Fluor. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-11 
products versus petroleum fuels. Assuming the alcohols produced are used for 

fuels blending and not either MTBE production or for chemicals value, taking into 

account the lower energy content of mixed alcohols relative to gasoline, and 

assuming that this level of return is acceptable to investors, these studies show 

mixed alcohols to be competitive with gasoline at a wholesale value of $1.25 to 

$1.70 a gallon, depending on the cases being evaluated. 

Two unevaluated items in these studies could swing the economics considerably. 

One is the assumption of the feedstock cost. While petroleum coke may be 

ample and low cost for gasification applications, it is unclear if this would be the 

case with biomass. Sensitivity analysis performed by Nexant at $30 and $50/ton 

feedstock cost, making assumptions for general plant inputs not covered by the 

studies, show that the price of gasoline would have to rise by 20-25% in the 

$30/ton case and 30-40% in the $50/ton case for the pet coke based alcohols to 

be competitive. The other unevaluated input is the application of a production 

credit like that levied to ethanol (51 cents/gallon). A credit of this nature could 

swing the plant economics of an unattractive investment to very attractive if the 

full credit could be realized. 

While a complete design and economic analysis is outside the scope of this 

evaluation, projecting these plant economics to a biomass based system gives 

perspective to the economic hurdle that must be overcome for biomass to mixed 

alcohols plants to be pursued commercially. 

Blending

Blending mixed alcohols into existing gasoline and diesel pools will be beneficial 

for some fuels specifications and detrimental to others. Mixed alcohol blending 

will be similar in impacts to ethanol blending for many gasoline specifications. 

The key specifications that will be impacted were mentioned in Section 3.2.1. 

Impacts on octane, volatility, sulfur, aromatics, and corrosivity will be elaborated 

upon here. 

• Octane: Mixed alcohols provide a considerable octane boost to petroleum 

gasoline pools, with octane values generally rising as the carbon content 

increases. Some commercial marketers of mixed alcohol for fuels use 

market their fuels with octane values of over 120 or 13065. Mixed alcohols 

would be of considerable benefit in octane-constrained markets. 

• Volatility: Although the RVP of neat alcohols is lower than gasoline, when 

blended in small amounts (5 to 25%), alcohols have a negative impact on 

 64 Nexant, Inc. developed the ICGG Financial Model Version 3 for the US DOE, National Renewable 

Energy Laboratory, under a task order from E2

S, Subcontract Agreement No. 7000002220, 2003. 65 Power Energy Fuels, Inc. markets their Ecalene product as 124 octane, while Standard Alcohol Company 

of America, Inc. claims an octane rating of 138. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-12 
pool RVP66. Lighter alcohols adversely impact pool RVPs more, but the 

presence of heavier alcohols act as a “co-solvent” for light alcohols, 

allowing higher levels of light alcohols to be blended relative to blending 

them neat. For model purposes, commercially available mixed alcohols 

are marketed as blending like ethanol for volatility purposes67. 

• Sulfur and Aromatics: The tightening of fuels specification throughout the 

world has recently led to demands for lower sulfur and aromatics content 

fuels. Since mixed alcohols would largely be free of or very low on both 

accounts (although sulfur may be higher in sulfur tolerant catalysts, an 

issue dealt with in Section 2), mixed alcohols produced in this fashion 

could be beneficial to meeting lower targets for both these specifications. 

• Corrosivity: Depending on the level of alcohols blended, the type of 

alcohols, and the amount of phase separation that occurs, alcohols have 

been found to be corrosive to certain materials used in engines68. In 

general, higher blends and lighter alcohols create more corrosive 

environments. Based on the formulation that is created, modifications to 

vehicles may need to be performed, adding to the economic hurdles that 

must be overcome to widely use mixed alcohol fuels. 

A number of studies have evaluated the economic impact on both fuels markets 

and federal economies from the addition of ethanol to fuel pools. A similar 

analysis should be performed with mixed alcohols, based on the expected 

product make-up, to determine the level of economic risk that wider commercial 

application will have. 

Transport and Storage 

Special issues have arisen in transporting and storing methanol and ethanol for 

transportation fuels applications. Due to their limited solubility in gasoline in the 

presence of small quantities of water, pipeline transport rarely occurs, and 

special consideration must be made for the storage of alcohol/gasoline blends. 

Only 1-2% water can be tolerated in 25-40% alcohol mixtures, with the tolerance 

decreasing as the alcohol content decreases69. Water making its way into 

storage tanks has led to phase separation and corrosive environments. 

 

66 Volatility information provided by Meridian Corporation, “Properties of Alcohol Transportation Fuels”, 

prepared for the Biofuels Systems Division of the US DOE, July 1991. 

67 Testimony by Mark Radosevich, Standard Alcohol Company of America, in front of the California 

Environmental Policy Council, January 18, 2000. 

68 Smith and Workman, ibid. 

69 Meridian Corporation, ibid. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

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Fortunately, the presence of higher alcohols acts as effective co-solvent for 

lighter alcohols such as methanol and ethanol. Mixed alcohol blends that have 

sufficient quantities of these higher alcohols may be less susceptible to transport 

and storage problems that neat methanol and ethanol face. Greater analysis of 

the proposed fuel for blending should be performed to gauge the level of risk. 

3.3.2 Catalyst Prices 

Depending on the catalyst chosen to perform mixed alcohols synthesis, the price 

of the metals that go into the catalyst production will impact the cost of the 

production route to some extent. While this is less important for more common 

metals such as copper and zinc, exotics such as molybdenum, cesium, and 

rhodium prices may make certain synthesis routes cost prohibitive. An analysis 

of the metals that will go into the desired catalyst for mixed alcohols production 

will provide insight into the level of economic risk involved. A list of the metals 

considered for application, their prices, alternative uses, and risk level are shown 

below. 

Table 9: Metals Considered for Use in Mixed Alcohol Catalysis 

Metal Price70 Other Uses Risk Level

Molybdenum $2 to 40/lb Steel alloys; price tracks 

well with steel price Moderate 

Rhodium $600 to 1800/ounce Turbine engines, electric 

connections High 

Copper $1 to 2/lb Major industrial metal; 

electricity and telecom Low 

Chromium $3 to 6/lb Steel and nonferrous 

alloys Low 

Zinc $0.30 to 0.60/lb 

Major industrial metal; 

iron and steel coating, 

alloys 

Low 

Cobalt $20 to 40/lb Gas turbine superalloys, 

steel Moderate 

Cesium $30 to 60/gram 

Specialty chemical, 

medical, & electrical 

apps. 

Very High 

Less common industrial metals that are considered for mixed alcohols synthesis 

bring an extra level of economic risk to the catalysis operation. For example, 

molybdenum’s major industrial application, as an alloying element in steels and 

cast irons, can lead to a high level of volatility based on the demand for these 

 

70 The range presented is from a number of sources, looking at the current market and volatility over the 

past 10 years. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

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products. This was witnessed in 2004 when world steel demand pushed 

molybdenum prices to $35/lb, a 1300% increase from 200271. A graph of the 

recent trends in molybdenum oxide prices, which track closely with the metals 

price, can be seen in Figure 1. 

Figure 1: Molybdenum Oxide Prices, 1998 to 200472

Other factors such as the cost and activi

.3.3 Process Economics 

uilding upon what was mentioned in the technical risk section, the overall 

t 

cted 

lant 

 

Metals Week Moly Oxide Quarterly Averages 1998 - Sept 2004

1

3

5

7

9

11

13

15

17

19

Q1 - 1998

Q3 - 1998Q1 - 1999Q3 - 1999Q1 - 2000Q3 - 2000

Q1 - 2001

Q3 - 2001

Q1 - 2002Q3 - 2002Q1 - 2003

Q3 - 2003Q1 - 2004

Q3 - 2004

US$/lbMo

ty of support materials (alumina oxides 

and activated carbon), and the complexity of mass production of this catalyst, 

creates economic risk that must be better understood. 

3

B

process to convert biomass feedstock to mixed alcohols carried a significan

amount of economic risk. The considerable uncertainty in developing cost 

estimates for a process with no current commercial application must be refle

by adding contingency factors to the overall process, with a special process 

contingency placed on the mixed alcohol synthesis unit. While much of the p

process cost can be estimated from other biomass gasification facilities, unique 

considerations and design requirements for a mixed alcohol facility adds 

additional cost and risk. 

71 Dave Forest, Casey Research LLC, March 2005. 

72 From the International Molybdenum Association, www.imoa.info, London, UK. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-15 
Contingency Estimates 

The major areas of economic risk in a biomass to mixed alcohol facility are from 

the gasification unit, syngas cleanup costs, purification and fractionation of 

alcohols (if required), and stream recycle with carbon dioxide removal. In 

addition, uncertainty exists around how the mixed alcohol synthesis unit will 

perform, making estimates for economic purposes difficult. Contingency 

estimates outlined below are based upon DOE’s “Quality Guidelines for Energy 

Systems Studies73”, which provides a consistent basis for evaluating energy 

technologies. 

• Gasification Plant: As mentioned earlier, biomass gasification itself is not 

a mature technology. Reliability of the gasifier is key to long run lengths 

and attractive plant economics. Process contingency = 25% 

• Cleanup Costs: Much of the technology used in syngas cleanup, such as 

particulate removal, sulfur extraction, reforming, and water 

quench/scrubbing has a number of industrial applications. Special 

technologies, such as warm sulfur removal and advanced tar cracking 

catalysts, may require higher contingencies if used in this application. 

Process contingency = 15% for commercially proven technologies, 

higher for advanced ones. 

During the cleanup stage of the process, the syngas will need to be 

compressed and heated to the mixed alcohol reactor conditions. The 

severe conditions, coupled with the swings between hot gas exiting the 

gasifier, cooling for treatment, then reheating for reactor requirements, 

creates additional cost and higher levels of economic risk. These 

conditions will require a cleanup section more expensive than typical for 

biomass systems. 

• Alcohol Purification and Fractionation: Depending on the catalyst 

selectivity and the products desired, a purification or fractionation step 

may be required downstream of the reactor. As this is a mature 

technology, little risk is added, but this step represents a cost unseen in 

most gasification plants. 

Process contingency = 5%, yet costs are added to the plant that may 

increase the TIC by 1 to 5%. 

• Recycle and CO2 removal: Due to low once-through conversion, the 

unreacted syngas will need to be recycled back to the reactor in plants 

where mixed alcohols are the main product. This recycled stream must be 

treated, likely with a CO2 removal step, in order to maintain a constant 

 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-16 

73 “Quality Guidelines for Energy Systems Studies”, Gilbert McGurl, et.al., Office of Systems and Policy 

Support, US DOE, National Energy Technology Laboratory, January 2005. 
H2:CO ratio in the reactor inlet. The design of this plant section must take 

into account contingencies for different H2:CO ratios in the fresh feed, and 

the impact of different conversion in the reactor as the catalyst ages. 

Process contingency = 15%, since CO2 removal is fairly mature, yet 

additional capacity should be designed into the recycle loop to handle the 

range of process conditions that will likely occur. 

• Reactor Design: The uncertainty in performance of this high pressure, 

high temperature reactor will require significant contingency built into the 

cost estimate. While assumptions can be made for conversions and 

yields throughout the lifetime of the plant, additional data should be 

gathered to confirm these assumptions. Process contingency = 40%+

Conversion Optimization 

A number of steps can be taken, based on the catalyst and desired products 

chosen in the design, to modify reaction conversion. These include: 

• Changes in the H2:CO ratio 

• Level of stream impurities 

• Level of unconverted syngas recycle 

• Co-products desired and plant flexibility 

• Number of gasification, cleanup, and conversion trains 

The impact that these changes have on the process economics should be 

evaluated to determine the best scenario for each plant design. The 1996 

Bechtel study looked at a number of different per-pass and total conversion 

assumptions for both systems integrated with a refinery and as a stand-alone 

plant. For the integrated facility, they found an optimum total syngas conversion 

at around 51%. Above this conversion rate, the costs of recycling, due to larger 

reactor requirements, multiple trains, and recycle compression, outweighed the 

benefit of additional alcohol production. For the stand-alone facility, increasing 

per-pass conversions generally improved the plant economics.

3.4 Summary and Conclusions 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-17 

In order to advance research and assist in commercial promotion, better 

definition for how the product will be used and what the long-term goal of the 

design effort is will be critical to developing an integrated analysis approach. 

Once these definitions are set, more focus can be placed on the appropriate 

catalyst to use, design conditions to meet goal targets, how the product can be 

integrated into the market, and what policy options can be used to assist in 

technology promotion. A clear R&D effort can then be developed to minimize 

and prioritize the inherent technical and economic risks. 
Recommendations for technical R&D focus were made in Section 1.5. From the 

process side, a complete systems analysis should be performed to provide a 

preliminary basis for overall design requirements and costs. Once the systems 

analysis is complete, a plan should be established to demonstrate greater 

commercial feasibility. Part of this work can be accomplished along side the 

technical and economic systems analysis work: 

• Testing of pilot scale reactors on syngas (can be derived from natural 

gas). 

• Incorporation of pilot scale reactors with functioning gasifiers. Ideally, 

biomass derived syngas should be used, but data from coal and coke 

gasifiers will also be useful to the design process. 

• Establish economic and policy drivers to promote commercial use of 

biomass to mixed alcohol technology. These may include alternative fuel 

credits, mandates to replace petroleum based fuels, or incentives to build 

and run biomass gasifiers. 

• A greater analysis of the impact that the mixed alcohol product will have 

on the gasoline and diesel pools. May be able to use some of the 

information in the ethanol literature as a starting point. 

NREL will play key roles in all stages of the development of mixed alcohol 

technology from biomass. The following are the main items that NREL should 

focus on at this stage and in the near future: 

• Definition of the product use and appropriate process conditions 

• Conceptual design and cost estimates for commercial mixed alcohol 

plants. The contingencies listed in the economic risk section should be 

used to provide the best estimate of the technology cost at this time. The 

systems analysis in this area should cover a range of sensitivities: 

o Different biomass feedstock types 

o Different catalysts, assuming advances in technology, that can help 

to set research drivers and goals 

o Different plant sizes 

o Different product uses, including chemicals, fuels, and power. 

Should consider co-production scenarios that could improve plant 

economics. 

• Different R&D paths should be established based on the different product 

uses. The R&D paths would define what catalysts are most appropriate 

for each product, and what research needs to be focused on to enhance 

the current technology. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-18 
• Market analysis to determine feedstock availability, impact of mixed 

alcohol product on fuels and chemicals markets, and potential niche 

opportunities. 

Finally, although outside of NREL’s likely scope, a policy analysis of the most 

appropriate options to assist in technology advancement would be very useful 

along side technical and economic analysis. The policy analysis would help to 

determine how R&D funding could be promoted within the current system, and 

how the economics of the process could potentially be impacted by federal or 

state policies. 

Task 9: Mixed Alcohols from Syngas: State of Technology 

United States Department of Energy/National Renewable Energy Laboratory

3-19 
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DE-AC36-99-GO10337 

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4. TITLE AND SUBTITLE

Equipment Design and Cost Estimation for Small Modular Biomass 

Systems, Synthesis Gas Cleanup, and Oxygen Separation 

Equipment; Task 9: Mixed Alcohols From Syngas — State of 

Technology 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-510-39947 

5e. TASK NUMBER

BB06.3710 

6. AUTHOR(S)

Nexant Inc. 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Nexant Inc. 

101 Second St., 11th Floor 

San Francisco, CA 94105 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ACO-5-44027 

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NREL 

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14. ABSTRACT (Maximum 200 Words)

This deliverable is for Task 9, Mixed Alcohols from Syngas: State of Technology, as part of National Renewable 

Energy Laboratory (NREL) Award ACO-5-44027, “Equipment Design and Cost Estimation for Small Modular 

Biomass Systems, Synthesis Gas Cleanup and Oxygen Separation Equipment”. Task 9 supplements the work 

previously done by NREL in the mixed alcohols section of the 2003 technical report “Preliminary Screening – 

Technical and Economic Assessment of Synthesis Gas to Fuels and Chemicals with Emphasis on the Potential for 

Biomass-Derived Syngas”. 

15. SUBJECT TERMS

biomass; Nexant; small modular; synthesis gas; syngas; scaling; cost estimation; equipment design; mixed alcohols; 

National Renewable Energy Laboratory; NREL 

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