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 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 43, 2015 

A publication of 

The Italian Association 
of Chemical Engineering 
Online at www.aidic.it/cet 

Chief Editors: Sauro Pierucci, Jiří J. Klemeš 
Copyright © 2015, AIDIC Servizi S.r.l., 
ISBN 978-88-95608-34-1; ISSN 2283-9216                                                                               

 

Simulation, Optimization and Analysis of a Syngas to Ethanol 
and other Oxygenates Production Plant Using a Rh-Based 

Catalyst 

Júlio C. C. Miranda*a, Gustavo H. S. F. Poncea, Harvey Arellano-Garcíab, Rubens 
Maciel Filhoa, Maria R. M. Wolfa 
a Laboratory of Optimization, Design and Advanced Control. School of Chemical Engineering P.O. Box 6066, 13083-970, 
Campinas-SP, Brazil. 
b University of Bradford, Bradford, West Yorkshire, BD7 1DP, UK 
julioccmiranda@gmail.com 

Synthesis gas (syngas) is mostly known by its use on ammonia and hydrocarbons (Fischer-Tropsch process) 
production. However, a less explored route to produce chemical products, among them alcohols and other 
oxygenates, from syngas is gaining attention over the last few years. In this route, an initial feedstock as 
biomass is firstly gasified to synthesis gas, which is reformed, cleaned, compressed and finally catalytically 
converted in a mixture of alcohols and oxygenated products that after separation steps attain sufficient purity 
to be sold. In this case of study, the commercial simulator ASPEN Plus v7.3 is used to evaluate the application 
of a Rh-based (Rh-Mn-Li-Fe/SiO2) catalyst in a small scale plant with processing capacity of 100 kmol/h of 
pure syngas. This plant, besides methane, water, and CO2 produces 8 oxygenated products: methanol, 
ethanol, propanol, butanol, acetic acid, acetaldehyde, methyl and ethyl acetates, being necessary 9 further 
separation or concentration steps in order to obtain the products in their desired purity. The main goals of this 
work were to design and optimize a process so as to produce alcohols and other oxygenates using syngas as 
feedstock. After conceiving the process, an optimization was performed, which started by evaluating the 
reactor conversion/selectivity in order to produce more add-value products. Then, the downstream separation 
processes were optimized searching for less energy consumption and recovering as much as possible add-
value products. Lastly, we aimed at possible solutions and improvements concerning sustainability, feedstock 
and energy integration, and utilities consumption.  

1. Introduction 

The search for alternative and sustainable fuels has increased in the last decade pushed by the great energy 
consumption of processing industry, the growing demand of energy-based comforts and mobility and the 
perspective of depletion of the world’s petroleum reserves. Presently the focus of international policies 
regarding liquid and renewable fuels are associated with the search of sustainability and energy security. In 
this direction, we can cite the Biofuels Directive from the EU, which has as its main goal to achieve a minimum 
quota of 20 % consumption of renewable biofuels until 2020 and a mandatory quota to be attained by all EU 
members of 10 % of biofuels in transportation in the same year. In the same way, the USA approved the 
Renewable Fuels Standard, which has as one of its goals the reduction of 20 % of gas emissions related to 
the renewable fuels lifecycle (Kendall et al., 2009) 
With such attention directed to renewable biofuels and their sustainability, the development and improving of 
biofuels production processes are needed. In this scenario, the use of synthesis gas (syngas) to produce 
biofuels (and other by-products) through thermochemical conversion can be seen as a possible process 
alternative regarding the improvement on biofuels production and feedstock usage. 

                                

 
 

 

 
   

                                                  
DOI: 10.3303/CET1543245 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Miranda J., Ponce G., Arellano-Garcia H., Maciel Filho R., Wolf Maciel M.R., 2015, Simulation, optimization and 
analysis of a syngas to alcohols and other oxygenates production plant using a rh-based catalyst, Chemical Engineering Transactions, 43, 
1465-1470  DOI: 10.3303/CET1543245

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In the thermochemical route, syngas, which is a mixture of carbon monoxide (CO) and hydrogen (H2), is 
produced by gasification of biomass or coal and then reformed, cleaned, compressed, heated and finally 
catalytically converted in a mixture of oxygenated products of high molecular weight. These products are then 
purified and can be sold separately as fuel, solvent or used as feedstock to other processes (Subramani and 
Gangwal, 2008). 
In this work, the commercial simulator ASPEN Plus v7.3 is used to design, simulate and optimize the 
conversion of syngas to alcohols (methanol, ethanol, propanol and butanol) and oxygenated compounds 
(acetaldehyde, acetic acid, methyl and ethyl acetates) using a Rh-based (Rh-Mn-Li-Fe/SiO2) catalyst (Yin et 
al. 2003). After simulation and optimization of the whole process, an energy and production analysis was 
proposed while pointing out the major products and the major energy consumers in the process, making 
possible to propose some solutions and further developments for the process. 

2. Simulation 

The simulation was carried out using the commercial simulator ASPEN Plus v7.3. The thermodynamic 
package NRTL (non-random-two-liquid) was chosen based on the polarity of the components involved in the 
process. In the operations involving acetic acid, the Hayden-O'Connell (NRTL-HOC package) model was used 
so as to calculate the non-idealities of the gas phase. 

2.1 Reaction Kinetics 

The reaction kinetics used in the simulation was obtained from Yin et al. (2003) that used the catalyst Rh-Mn-
Li-Fe/SiO2, a Rh-based catalyst capable of promoting the direct synthesis of ethanol (Subramani and 
Gangwal, 2008). The kinetic data for Arrhenius model (Eq. 1), was originally obtained for methane, methanol, 
ethanol, acetaldehyde (R1-R4) and a mixture of oxygenated compounds with 2 or more carbons (C2+) which 
counts with the ethanol and acetaldehyde parts. Therefore, to calculate the proportion between the other 
components (propanol, butanol, acetic acid, methyl and ethyl acetates), the data was recomputed subtracting 
continuously the ethanol and the acetaldehyde portion. Thus, the data was divided based on the reaction 
enthalpy (∆HR) of each reaction (R1-R9) obtaining the final proportion between the components reflected in 
the pre-exponential factor. The kinetic data is shown in Table 1 as follows. = ⁄   (1) CO + 3H → CH + H O  (R1) 2CO + 3H → C H O + H O  (R4) 2CO + 2H → H CCOOH  (R7)CO + 2H → CH OH  (R2) 3CO + 6H → C H OH + 2H O (R5) 3CO + 4H → HCOOC H + H O  (R8)2CO + 4H → C H OH + H O (R3) 4CO + 8H → C H OH + 3H O (R6) 4CO + 6H → H C OOC H + H O (R9)
Table 1: Kinetic Parameters 

Reaction 
Ea 

(kJ/mol) 
x  

(adm) 
y  

(adm) 
A 

(kmol/kgRh.h.kPax+y)
K 

(kmol/kgRh.h.kPax+y) 
R1 126700.0 0.90 -0.76 2.33 x 1010 0.081 
R2 89900.0 0.53 0.14 3.13 x 105 0.003 
R3 114839.7 1.39 0.23 1.68 x 104 0.985 
R4 114839.7 1.39 0.23 2.24 x 104 2,553 
R5 114839.7 1.39 0.23 1.04 x 104 0.330 
R6 114839.7 1.39 0.23 1.25 x 104 0.476 
R7 114839.7 1.39 0.23 2.24 x 103 0.083 
R8 70600.0 0.16 -0.10 1.48 x 104 0.005 
R9 156800.0 0.79 -0.60 2.35 x1013 0.126 

2.2 Process Layout 

The process layout (Figure 1) is composed by a compressor, a PFR reactor, a flash drum, a gasification 
reactor and nine separation units, which are represented by general blocks for simplicity. The pure syngas 
enters in the system through the stream S-1001 at 1 bar and 25 °C is then mixed with the recycle stream (S-
1009, 300 °C, 1 bar), compressed (in the CPR unit) and sent to the reactor (R-1001). Inside the reactor, the 
products are synthesized, in the effluent stream (S-1004) can be found methane, methanol, ethanol, propanol, 
butanol, acetaldehyde, acetic acid, methyl and ethyl esters and non-reacted syngas. The stream S-1005 
enters the flash, which operates at 10°C and 6.5 bar, at 304.8 °C and 3 bar. This stream is then split in two 
other streams, one containing mostly CH4, CO and H2 (S-1006) and the other (S-1011) the oxygenated 
compounds. 

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Figure 1: Process Layout 

The bottom stream leaving the flash drum (S-1011) is directed to SEP-1 block (Figure 2a) in which the stream 
S-106 recovers the rest of syngas and methane that come from R-1001, and in the stream S-104 which 
contains 66,34 % w/w of the water entering the distillation column and 100 % w/w of the acetic acid. This 
stream is sent to SEP-2 (Figure 2b) while the stream S-105 with the mixture of other components is sent to the 
SEP-3 (Figure 2c). In SEP-2 the stream S-203 enters the distillation column with a mixture of water (90 % 
w/w) and acetic acid (10% w/w) and is separated in two streams S-204 (99.0 % w/w acetic acid) and S-205 
(99.9 % w/w water).  In the SEP-3 block, acetaldehyde at 99.7 % w/w (S-304) is recovered from the stream S-
303 and the stream S-305 is then directed to SEP-4 (Figure 2d). 

  

  

Figure 2: (a) SEP-1 layout; (b) SEP-2 layout; (c) SEP-3 layout; (d) SEP-4 layout 

CPR
R-1001 V-1001

F-1001

GASI V-1002

V-1003

SEP-8 SEP-9SEP-7SEP-6

SEP-3 SEP-1SEP-4SEP-5

S-1002 S-1003 S-1004 S-1005

S-1006S-1007

S-1001

S-1009

S-1011S-1013
S-1017

S-1018 S-1012

S-1022 S-1025 S-1027

SEP-2

S-1014S-1016

S-1019

S-1021

S-1024

S-1029

S-1034

S-1008

S-1031

S-1010

S-1015

S-1032

S-1033

S-1023

S-1020
S-1026

S-1028

S-1030

V-101
C-101

S-103

P-102

S-102

S-106 (S-1034)

S-104 (S-1014)

S-105 (S-1013)

S-101 (S-1012)

V-201
C-201

S-203

P-201

S-202

S-205 (S-1031)

S-204 (S-1015)

S-201 (S-1014)

V-301
C-301

S-303

P-301

S-302

S-304 (S-1016)

S-305 (S-1017)

S-301 (S-1013)

V-401
C-401

S-403

P-401

S-402

S-405 (S-1020)

S-404 (S-1018)

S-401 (S-1017)

(a) (b) 

(c) (d) 

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Figure 3: (a) SEP-5 layout; (b) SEP-6 layout; (c) SEP-7 layout; (d) SEP-8 layout; (e) SEP-9 layout 

In the bottom stream of the distillation column C-401 (SEP-4) is recovered, a mixture of butanol (46 % w/w) 
and water (54 % w/w), while this stream (S-404) goes to SEP-5 block (Figure 3a), the stream containing 
methanol, ethanol, propanol, methyl and ethyl acetates (S-405) goes to SEP-6 (Figure 3b). To separate the 
heterogeneous azeotrope butanol-water, a special design is needed (Luyben, 2008). The mixture enters the 
block and first is directed to a decanter, which receives also the top streams of the two distillation columns (S-
507 and S-512). The aqueous phase stream (S-504) goes to the distillation column C-501, which recovers the 
stream S-506 composed by approximately 100% w/w water. The organic phase of the decanter (S-509) with 
84 % w/w butanol and 16 % water w/w is sent to the distillation column C-502 responsible for the recovery of 
stream S-511 with 99.3 % w/w butanol. SEP-6 separates the stream S-405 originated in block SEP-4 in two 
other streams: one containing the acetates plus water, ethanol and methanol (S-605), and the other one 
containing the rest of alcohols plus water (S-604). The first stream is directed to block SEP-7 (Figure 3c) and 
the second one to the block SEP-8 (Figure 3d). In SEP-7, using a solvent (Ethylene Glycol, EG) the entering 
mixture is dehydrated in the first column (C-701) generating the top stream (S-707), consisting in an acetate-
rich stream and the bottom stream (S-708) that consists of solvent, water and ethanol (the proportion in mass 
solvent:feed stream is 1:3). The acetate-rich mixture is directed to de column C-703 and separated in its two 
components methyl acetate 96.3 % w/w (S-715) and ethyl acetate 99.9 % w/w (S-714). The bottom stream of 

C-501

C-502

D-501

S-507

S-509

S-508

S-505

S-506 (S-1032)

S-511 (S-1019)

S-512

K-501
K-503

S-513

S-503

S-502

V-503

S-504

V-504

S-510

V-501

S-515

S-514
V-505V-502

S-501 
(S-1018)

V-601
C-601

S-603

P-601

S-602

S-605 (S-1022)

S-604 (S-1021)

S-601 (S-1020)

C-701

C-702

C-703

V-701

V-702

V-703

P-701

K-701

S-707

S-708 S-709

S-712 (S-1025)

S-713

S-715 (S-1024)

S-714 (S-1023)

S-710S-711

S-706

S-703 S-705
S-701

(S-1022)
V-704

S-702

S-704

C-801

C-802

V-801

V-803

P-801

K-801

S-810 (S-1027)

S-811 S-812

S-813 (S-1026)

S-814S-815

S-809

S-805 S-807

S-801
(S-1021)

V-802

S-803

S-806 P-802

S-808

S-802
(S-1025)

S-804

C-901

C-902

V-901

V-902

P-901

S-905

S-904 (S-1028)

S-906

S-908 (S-1029)

S-902 S-903
S-901 

(S-1027) S-907 (S-1030)

(a) 

(b) 

(c) (d) 

(e) 

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C-701 goes to C-702, where the solvent is recovered at 99.9 % w/w in the bottom stream (S-710) and in the 
top stream is obtained a mixture of water, ethanol and methanol, directed to SEP-8. SEP-8 receives the 
streams containing alcohols (S-802 and S-801) originated from blocks SEP-6 and SEP-7. Using ethylene 
glycol in an extractive distillation (mass ratio of 2.35:1 related to the feed stream), the mixture water-alcohols 
is dehydrated in the first distillation column (C-801) which has as its top stream (S-810) a mixture of methanol, 
ethanol and propanol and as its bottom stream (S-811) the water-solvent. The solvent is then recovered in the 
bottom of the second column (S-814) and in the same column is obtained the stream S-813 composed by 
water 99.9 % w/w. From SEP-9 (Figure 3e), propanol (99.5 % w/w) in the first distillation column (C-901) and 
methanol (90 % w/w) and ethanol (99.4 % w/w) in the second distillation column (C-902) are obtained. It is 
important to notice (Figure 1) that the top stream of the flash drum passes through a reactor that generates 
pure syngas. This hypothetical operation calculates the amount of syngas that can be reintroduced to the 
system, being possible, for this reason turn the stream S-1009 “on” and “off” with no impact to the rest of the 
process by adjusting stream S-1001 to the reactor’s feed stream composition and mass flow. 

3. Results and Discussion 

The results were obtained after an optimization carried out through sensitivity analysis. For the distillation 
columns the number of stages, the feed stage(s) and the mass reflux ratio were varied, for the flash drum 
were varied temperature and pressure, aiming to attain the specifications with less energy consumption in 
both cases.The reactor’s feed stream is maintained at 100 kmol/h with a mole ratio of 1:2 CO:H2. This ratio 
was also obtained through sensitivity analysis. As shown in Figure 4, the mole ratio within the possible range 
of operation in which the conversion and ethanol selectivity attain their maximum is 1:2. The reactor is 
operated at 304.8 °C and 30 bar, the catalyst load of 12 kg (Rhodium basis). 

Figure 4: Reactor sensitivity analysis to mole ratio (a) Conversion (b) Ethanol selectivity 

3.1 Products 

In Figure 5 are shown the flow rate and the purity of the products obtained. As can be seen, ethanol is the 
major product of the process attaining 170.5 kg/h (99.4 % w/w) of production. Acetaldehyde and butanol are 
other products that can be highlighted with final mass flows of respectively 89.7 kg/h (99.8 % w/w) and 69.3 
kg/h (99.3 % w/w). Regarding the recycle stream (S-1009), after receiving a stream basically composed by 
methane (148.9 kg/h), CO (87.5 kg/h) and traces of hydrogen, acetaldehyde and ethyl acetate and a stream 
composed by pure oxygen (S-1010, 151.7 kg/h), the reactor GASI converts all products to syngas at the rate 
of 401.3 kg/h at 1:1.56 mol (CO:H2). The final production of water (S-1033) is 367.7 kg/h at 99.9 % w/w. 

 

Figure 5: Products Mass Flow (kg/h) and Purity (w/w %) 

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3.2 Energy Consumption 

Table 2 shows that there is a positive energy balance (1596.8 kW/h) between heated and cooled units. Due 
the exothermic nature of the reactions involved in the process, the reactor has an impact almost equivalent to 
all heated units in the process and is responsible for more than 40 % of the consumption of cooling utilities. 
Among the heated units, the blocks with higher consumption are related with the high inlet flows (as SEP-1 
and SEP-4) and complex separations as narrow boiling points (SEP-2/SEP-9) and azeotropes (as SEP-8).  

Table 2: Energy Consumption by Equipment 

Heated Units Cooled Units 
Equipment Energy (kW/h) % Consumption Equipment Energy (kW/h) % Consumption 
SEP-1 252.89 17.1 % R-1001 -1305.1 42.4 % 
SEP-2 217.44 14.7 % F-1001 -534.0 17.3 % 
SEP-3 94.86 6.4 % SEP-1 -224.7 7.3 % 
SEP-4 255.63 17.3 % SEP-2 -216.8 7.0 % 
SEP-5 25.15 1.7 % SEP-3 -35.0 1.1 % 
  C-501 (Reb.) 10.43 0.7 % SEP-4 -255.1 8.3 % 
  C-502 (Reb.) 14.72 1.0 % SEP-5 -25.9 0.8 % 
SEP-6 46.73 3.2 %  D-501 -19.0 0.6 % 
SEP-7 68.03 4.6 %  K-501 -3.8 0.1 % 
  C-701 (Reb.) 24.72 1.7 %  K-502 -3.1 0.1 % 
  C-702 (Reb.) 28.09 1.9 % SEP-6 -46.2 1.5 % 
  C-703 (Reb.) 15.22 1.0 % SEP-7 -68.3 2.2 % 
SEP-8 177.81 12.0 %  C-701 (Cond.) -9.7 0.3% 
  C-801 (Reb.) 115.04 7.8 %  C-702 (Cond.) -11.5 0.4 % 
  C-802 (Reb.) 62.77 4.2 %  C-703 (Cond.) -15.3 0.5 % 
SEP-9 189.64 12.8 %  K-701 -31.8 1.0 % 
  C-901 (Reb.) 127.97 8.6 % SEP-8 -177.2 5.8 % 
  C-902 (Reb.) 61.68 4.2 %  C-801 (Cond.) -58.6 1.9 % 
CPR-1001 153.73 10.4 %  C-802 (Cond.) -40.7 1.3 % 
Total 1481.92 100.0 %  K-801 -77.9 2.5 % 
   SEP-9 -190.3 6.2 % 
    C-901 (Cond.) -128.6 4.2 % 
    C-902 (Cond.) -61.6 2.0 % 
   Total -3078.7 100.0 % 

4. Conclusions 

The use of the catalyst Rh-Mn-Li-Fe/SiO2 results in a process with series of complex separations and a total 
production of 451 kg/h) of oxygenated products. With the proper energy integration, the positive net energy 
balance (1596.8 kW/h) can be used to reduce energy consumption making the process feasible and profitable. 
The use of syngas from different sources makes the process a sustainable alternative to the liquid fuels 
market and an option for process integration with first and second-generation ethanol production processes. 

Acknowledments 

The authors are grateful to CNPq, CAPES and FAPESP for the financial support. 

References 

Kendall, A., Chang, B., Sharpe, B., 2009, Acounting for time.dependent effects in biofuel life cycle greenhouse 
gas emission calculations, Environmental Science & Technology, 43(19), 7142-7147. 

Subramani, V. and Gangwal, S.K., 2008, A review on recent literature to search an efficient catalytic process 
for the conversion of syngas to ethanol, Energy and Fuels, 22(2), 814-839. 

Yin, H., Ding, Y, Luo, H, He, D., Chen, W., Ao, Z. Lin, Liwu, 2003, A Kinitic Study of Selective Hydrogenation 
of Carbon Monoxide to C2 Oxygenates on Rh-Mn-Li-Fe/SiO2 catalyst, Journal of Natural Gas Chemistry, 
12, 233-236. 

Luyben, W.L., 2008, Control of the Heterogeneous Azeotropic n-Butanol/Water Distillation System, Energy & 
Fuels, 22, 4249-4258. 

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