- Email: [email protected]
H2
M. de Pontes, R.L. Espinoza, C.P. Nicolaides, J.H. Scholz and M.S. Scurrell (Editors) Natural Gas Conversion IV
Studies in Surface Science and Catalysis, Vol. 107 9 1997 Elsevier Science B.V. All rights reserved.
139
ETHERMIX PROCESS: SYNTHESIS OF ETHERS FROM CO/H2 E. Micheli, G.B. Antonelli, D. Sanfilippo, Snamprogetti S.p.A., Research Division, via Maritano 26, 1-20097 S.Donato Milanese B. Cometa, G.C. Pecci, Euron S.p.A., via Maritano 26, 1-20097 S.Donato Milanese
Abstract
In the last two decades increasing interest has been devoted world-wide to the conversion of natural gas (NG) to valuable chemical products and fuels, due to its huge reserves and geographic distribution. This paper deals with a multi-step process, under development, for the transformation of natural gas, particularly of methane, into ethers, mainly MTBE. The process is performed in a series of steps that includes the preparation of a mixture of hydrogen and carbon monoxide in the desired ratio, their reaction addressed to the synthesis of a mixture of methanol and higher alcohols, mainly isobutanol, the dehydration of the higher alcohols fraction to olefins eventually followed by their reaction with methanol to produce the mixture of ethers. Economic evaluations of the process indicate high values of IRR and other indexes that allow the Ethermix technology to be the most convenient route for the transformation of NG into liquid products for motor fuel components.
INTRODUCTION In the last two decades fuel manufacture has been determined not only by economic considerations but also by public concerns about social and environmental factors. In the late 70s, environmental concerns led to phase down the lead content in gasoline, and, at the same time, to reduce the dependence from oil by producing synthetic components for gasoline blends has represented a common target; for these reasons it was necessary to provide new alternatives for transportation fuel, and oxygenates, alcohols and mainly ethers, have become a very well accepted option for gasoline blending. MTBE (methyl t-butyl ether), which emerged as the most attractive ether for the gasoline pool [1], is manufactured from methanol and isobutylene; the latter is usually obtained as a side product from steam crackers or FCC units. In 1995 MTBE production has reached 19 million MTPY and, since future demand is expected to exceed the potential isobutylene supply from traditional feedstock, alternative sources are highly desirable. Light hydrocarbons (C 3 - C4) of the NG wet fraction or of associated gas represent a low cost source of carbon and have found an attractive utilization through their dehydrogenation to olefins, becoming in this way an alternative feedstock for the refinery and the chemical industry
[2]. Also the dehydration of isobutyl alcohol is a possible route to produce isobutylene and technologies for the synthesis of methanol/higher alcohols mixture represent a way to
140 manufacture ethers, via syngas, from methane or other low cost raw materials like coal or refining tar.
1. E T H E R M I X PROCESS Ethermix is a process for the transformation of natural gas, particularly of methane into ethers, mainly MTBE; because of the low cost and the large availability of the raw materials this route represents a virtually endless source of C4 olefins. Via the intermediate formation of syngas, carbon-carbon bonds are formed in order to build the desired skeletal structure of an iso-C 4 molecule which is the basis of MTBE. The overall process scheme (figure 1) consists of 5 main steps: 1 - syngas preparation 2 - synthesis of methanol and higher alcohols (HA), mainly isobutanol 3 - separation of methanol from the higher alcohols fraction 4 - dehydration of HA from step 3 to oleflns 5 - etherification of olefins with methanol from step 3.
Figure 1 Ethermix process: flow diagram
Preparatl~J"~"t~t
L separation
HA 1
natural gas tar
Ethermix
synthesis )
,,, r-.,.).
@
(~._therlflcatlo e n) Oleflne$ ale~ ~'I ~ (Ldehydratlonj r MeOH
All the five sections listed above are based on well established technologies but the feasibility of the overall process mainly depends on the productivity and selectivity to isobutanol in the synthesis step 2, to enhance the relative production of MTBE.
2. B A C K G R O U N D IN T H E SYNTHESIS OF H I G H E R A L C O H O L S The Ethermix process derives from the know-how gained in the development of the MAS technology for the production of a mixture of methanol and higher alcohols to be blended into gasoline as an octane booster component [3]. It has been well known for many years [4] that methanol and higher alcohols may be manufactured from syngas by alkali promotion of methanol synthesis catalysts and by a
141 convenient modification of reaction conditions; industrial plants for the production of methanol and higher alcohols mixtures were in operation in the USA and in Germany from 1927 to 1947. In the late 1970s, due to the opportunity to reduce the oil dependence by producing synthetic fuel components, many companies focused their attention on the catalytic conversion of syngas to mixture of C1-C4 alcohols for fuel use and more recently also the trend to lead phase down renewed the industrial interest for the synthesis of higher alcohols. Higher alcohols have several favorable characteristics for motor fuel use: they have good octane-enhancing properties, are miscible with gasoline and behave as solutizers increasing the water tolerance and inhibiting the methanol phase separation. The MAS technology for the production of mixed alcohols, jointly developed by Snamprogetti, Enichem and H.Topsoe A/S, was based on a modified high-temperature methanol synthesis catalyst which gives a non Schultz-Flory distribution of products with a high content of branched alcohols. Methanol was the major component in the product and the content of higher alcohols was typically 30 wt%. From 1982 to 1986 in Italy, a commercial unit for MAS synthesis (15,000 MTPY) was operated for a demonstrative run. The product, whose characteristics are reported in table 1, was blended into gasoline at 5% level, and was successfully marketed but, as oil price decreased in the last quarter of 1985, economics became not favorable and this technology has been kept in standby. Table 1 MAS characteristics
Typical composition Methanol Ethanol Propanol Isobutanol C5+
68 2310 7-
72 wt% 3 wt% 5 wt% 15 wt% 12 wt%
Blending properties RON MON (R+M)/2 RVP (psi) O ~ e n content wt%
120 - 135 93 - 106 100 - 121 3.4 41
3. E T H E R M I X PROCESS OVERVIEW 3.1 The alcohols synthesis In the meanwhile ethers like MTBE became the preferred oxygenate as an octane booster requiring large supply of isobutylene. Recent developments in the Snamprogetti know-how for higher alcohols synthesis led to significant improvements with respect to the MAS process and the obtained mixture of higher alcohols represents a convenient precursor of isobutylene and other olefins. The development of a second generation proprietary catalyst allowed to increase the productivity ofisobutanol with a gain up to ten times with respect to the previous technology. The carbon chain grows according to a J3-addition mechanism, and, apart from methanol, mainly branched alcohols are obtained in the liquid product, isobutanol being the most abundant C2+ alcohol produced. Isobutanol content ranges typically from 55 to 60 wt% of the whole C4+ fraction which contains some C5 and C6 "iso-" alcohols too.
142 The new catalyst is also highly selective towards the synthesis of oxygenated compounds with respect to the production of undesired light hydrocarbons. A stoichiometric ratio between alcohols precursor of olefins and methanol is obtained in the outlet stream from the higher alcohols synthesis section. Reactor configuration includes fixed mukibed adiabatic converter operating at relatively high temperature and pressure, interstage cooling and feed-etiluent heat exchanger.
3.2 The alcohol separation A specific separation cycle has been studied [5] in order to obtain an effective separation of the alcoholic mixture (step 3). Two main streams are obtained, containing respectively methanol and Ca+ oxygenated compounds. 3.3 The alcohol dehydration The stream containing the C4 + alcohols is dehydrated in step 4 using a proprietary catalyst which totally and selectively converts the higher alcohols to the corresponding olefins without skeletal isomerization or cracking. 3.4 The ethers synthesis The olefmic stream undergoes etherification by means of the methanol obtained from the distillation of the total alcohols mixture in step 2. The etherification reaction, which leads to the final product, is carried out according to the consolidated Snamprogetti's technology for MTBE and TAME (t-amyl methyl ether) synthesis. 3.5 Ethermix properties This technology provides an effective route to transform natural gas to liquid products having a substantial added value. The final product mainly consists of ethers which amount to about 90 wt% of the total: typical composition ranges are reported in table 2. Table 2 Ethermix typical composition MTBE TAME Higher ethers Other oxygenates Hydrocarbons (*)
73 - 80 wt% 5- 10wt% 5 - 8 wt% 1 - 2 wt % 8 - 10 wt%
* boiling in the gasoline range
MTBE is the major component, but significant amounts of TAME and higher ethers are also present (10 - 18 wt%). Other oxygenates in the product, esters and ketones, are as low as 2 wt%, while the remaining is constituted by hydrocarbons boiling in the gasoline range. Ethermix has been tested for motor fuel use as an octane booster showing properties very close to the ones of the well-known TAME. Blending properties are summarized in table 3 in comparison with the MTBE and TAME ones.
143 Table 3
Blending properties RON MON (R+M)/2 Spec. Gravity (Kg/1), 15 ~ RVP (psi) Oxygen content (wt%)
Ethermix 111 94 103 .755 7.2 15.7
MTBE 116 98 107 .745 9.4 18.2
TAME 113 95 104 .768 2.9 15.7
4. E C O N O M I C EVALUATION The transformation of NG, via syngas, into a mixture of higher alcohols offers an alternative endless source of C4 for the manufacture of ethers for fuel transportation use; economic evaluations here presented are based on 500,000 MTPY plant capacity, located in Saudi Arabia and with a 15 years life. Economic evaluations of the process have been performed in several scenarios. As an example, for an Ethermix plant located in Saudi Arabia with a capacity of 500,000 MTPY the investment cost has been estimated to be 281 MUSS and 384 MUSS including other utilities, interconnections and storage units. Table 4 summarizes the assumed economic scenario and the main profitability indexes. Table 4
Economic evaluation, price scenario and profitability indexes Price scenario Economic indexes Oil, constant during 19.7 US$/bbl IRR before taxes project life (1998 - 2012) Premium Gasoline (PG) 225 US$/ton Payout time before taxes Natural Gas 0.5 US$/MBTU NPV before taxes MTBE 281 US$/ton Total production costs Ethermix value (*) 260 US$/ton (*) Ethermix value = 1.25 PG - 23 US$/ton as transportation costs
17.7
%
5 232 180
years MUSS US$/ton
As shown in table 4 the production cost is close to 180 US$/ton and the economic indexes are very interesting: payout time results to be 5 years (before taxes) and also NPV and IRR indicate the high potentiality of this technology that has still margins for optimization.
5. CONCLUSIONS On the basis of these evaluations the Ethermix technology appears a convenient route for the transformation of abundant and low cost raw material into liquid products for motor fuel use having a substantial added value and premium in terms of quality.
144 The proposed scheme results also to be the more convenient route to exploit natural gas towards the market of high quality and clean fuels when compared to other possible processes.
REFERENCES
1. D. Sanfilippo, Chemtech, 23, (8), August 1993, 35 - 39 2. Fuel Reformulation, 5, (2) March/April 1995, 31 - 43 3. A. Paggini, D. Sanfilippo, G. Pecci, I. Dybkjaer, VII Int. Symposium on Alcohol Fuels, Paris, Oct 1986, 62- 67. Ed. Technip 4. G. Natta, U. Colombo, I. Pasquon, Catalysis, 5 (1957), 131-174 5. C. Rescalli, F. Cianci, It. MI 92/A 002658 to Snamprogetti
Studies in Surface Science and Catalysis, Vol. 107 9 1997 Elsevier Science B.V. All rights reserved.
139
ETHERMIX PROCESS: SYNTHESIS OF ETHERS FROM CO/H2 E. Micheli, G.B. Antonelli, D. Sanfilippo, Snamprogetti S.p.A., Research Division, via Maritano 26, 1-20097 S.Donato Milanese B. Cometa, G.C. Pecci, Euron S.p.A., via Maritano 26, 1-20097 S.Donato Milanese
Abstract
In the last two decades increasing interest has been devoted world-wide to the conversion of natural gas (NG) to valuable chemical products and fuels, due to its huge reserves and geographic distribution. This paper deals with a multi-step process, under development, for the transformation of natural gas, particularly of methane, into ethers, mainly MTBE. The process is performed in a series of steps that includes the preparation of a mixture of hydrogen and carbon monoxide in the desired ratio, their reaction addressed to the synthesis of a mixture of methanol and higher alcohols, mainly isobutanol, the dehydration of the higher alcohols fraction to olefins eventually followed by their reaction with methanol to produce the mixture of ethers. Economic evaluations of the process indicate high values of IRR and other indexes that allow the Ethermix technology to be the most convenient route for the transformation of NG into liquid products for motor fuel components.
INTRODUCTION In the last two decades fuel manufacture has been determined not only by economic considerations but also by public concerns about social and environmental factors. In the late 70s, environmental concerns led to phase down the lead content in gasoline, and, at the same time, to reduce the dependence from oil by producing synthetic components for gasoline blends has represented a common target; for these reasons it was necessary to provide new alternatives for transportation fuel, and oxygenates, alcohols and mainly ethers, have become a very well accepted option for gasoline blending. MTBE (methyl t-butyl ether), which emerged as the most attractive ether for the gasoline pool [1], is manufactured from methanol and isobutylene; the latter is usually obtained as a side product from steam crackers or FCC units. In 1995 MTBE production has reached 19 million MTPY and, since future demand is expected to exceed the potential isobutylene supply from traditional feedstock, alternative sources are highly desirable. Light hydrocarbons (C 3 - C4) of the NG wet fraction or of associated gas represent a low cost source of carbon and have found an attractive utilization through their dehydrogenation to olefins, becoming in this way an alternative feedstock for the refinery and the chemical industry
[2]. Also the dehydration of isobutyl alcohol is a possible route to produce isobutylene and technologies for the synthesis of methanol/higher alcohols mixture represent a way to
140 manufacture ethers, via syngas, from methane or other low cost raw materials like coal or refining tar.
1. E T H E R M I X PROCESS Ethermix is a process for the transformation of natural gas, particularly of methane into ethers, mainly MTBE; because of the low cost and the large availability of the raw materials this route represents a virtually endless source of C4 olefins. Via the intermediate formation of syngas, carbon-carbon bonds are formed in order to build the desired skeletal structure of an iso-C 4 molecule which is the basis of MTBE. The overall process scheme (figure 1) consists of 5 main steps: 1 - syngas preparation 2 - synthesis of methanol and higher alcohols (HA), mainly isobutanol 3 - separation of methanol from the higher alcohols fraction 4 - dehydration of HA from step 3 to oleflns 5 - etherification of olefins with methanol from step 3.
Figure 1 Ethermix process: flow diagram
Preparatl~J"~"t~t
L separation
HA 1
natural gas tar
Ethermix
synthesis )
,,, r-.,.).
@
(~._therlflcatlo e n) Oleflne$ ale~ ~'I ~ (Ldehydratlonj r MeOH
All the five sections listed above are based on well established technologies but the feasibility of the overall process mainly depends on the productivity and selectivity to isobutanol in the synthesis step 2, to enhance the relative production of MTBE.
2. B A C K G R O U N D IN T H E SYNTHESIS OF H I G H E R A L C O H O L S The Ethermix process derives from the know-how gained in the development of the MAS technology for the production of a mixture of methanol and higher alcohols to be blended into gasoline as an octane booster component [3]. It has been well known for many years [4] that methanol and higher alcohols may be manufactured from syngas by alkali promotion of methanol synthesis catalysts and by a
141 convenient modification of reaction conditions; industrial plants for the production of methanol and higher alcohols mixtures were in operation in the USA and in Germany from 1927 to 1947. In the late 1970s, due to the opportunity to reduce the oil dependence by producing synthetic fuel components, many companies focused their attention on the catalytic conversion of syngas to mixture of C1-C4 alcohols for fuel use and more recently also the trend to lead phase down renewed the industrial interest for the synthesis of higher alcohols. Higher alcohols have several favorable characteristics for motor fuel use: they have good octane-enhancing properties, are miscible with gasoline and behave as solutizers increasing the water tolerance and inhibiting the methanol phase separation. The MAS technology for the production of mixed alcohols, jointly developed by Snamprogetti, Enichem and H.Topsoe A/S, was based on a modified high-temperature methanol synthesis catalyst which gives a non Schultz-Flory distribution of products with a high content of branched alcohols. Methanol was the major component in the product and the content of higher alcohols was typically 30 wt%. From 1982 to 1986 in Italy, a commercial unit for MAS synthesis (15,000 MTPY) was operated for a demonstrative run. The product, whose characteristics are reported in table 1, was blended into gasoline at 5% level, and was successfully marketed but, as oil price decreased in the last quarter of 1985, economics became not favorable and this technology has been kept in standby. Table 1 MAS characteristics
Typical composition Methanol Ethanol Propanol Isobutanol C5+
68 2310 7-
72 wt% 3 wt% 5 wt% 15 wt% 12 wt%
Blending properties RON MON (R+M)/2 RVP (psi) O ~ e n content wt%
120 - 135 93 - 106 100 - 121 3.4 41
3. E T H E R M I X PROCESS OVERVIEW 3.1 The alcohols synthesis In the meanwhile ethers like MTBE became the preferred oxygenate as an octane booster requiring large supply of isobutylene. Recent developments in the Snamprogetti know-how for higher alcohols synthesis led to significant improvements with respect to the MAS process and the obtained mixture of higher alcohols represents a convenient precursor of isobutylene and other olefins. The development of a second generation proprietary catalyst allowed to increase the productivity ofisobutanol with a gain up to ten times with respect to the previous technology. The carbon chain grows according to a J3-addition mechanism, and, apart from methanol, mainly branched alcohols are obtained in the liquid product, isobutanol being the most abundant C2+ alcohol produced. Isobutanol content ranges typically from 55 to 60 wt% of the whole C4+ fraction which contains some C5 and C6 "iso-" alcohols too.
142 The new catalyst is also highly selective towards the synthesis of oxygenated compounds with respect to the production of undesired light hydrocarbons. A stoichiometric ratio between alcohols precursor of olefins and methanol is obtained in the outlet stream from the higher alcohols synthesis section. Reactor configuration includes fixed mukibed adiabatic converter operating at relatively high temperature and pressure, interstage cooling and feed-etiluent heat exchanger.
3.2 The alcohol separation A specific separation cycle has been studied [5] in order to obtain an effective separation of the alcoholic mixture (step 3). Two main streams are obtained, containing respectively methanol and Ca+ oxygenated compounds. 3.3 The alcohol dehydration The stream containing the C4 + alcohols is dehydrated in step 4 using a proprietary catalyst which totally and selectively converts the higher alcohols to the corresponding olefins without skeletal isomerization or cracking. 3.4 The ethers synthesis The olefmic stream undergoes etherification by means of the methanol obtained from the distillation of the total alcohols mixture in step 2. The etherification reaction, which leads to the final product, is carried out according to the consolidated Snamprogetti's technology for MTBE and TAME (t-amyl methyl ether) synthesis. 3.5 Ethermix properties This technology provides an effective route to transform natural gas to liquid products having a substantial added value. The final product mainly consists of ethers which amount to about 90 wt% of the total: typical composition ranges are reported in table 2. Table 2 Ethermix typical composition MTBE TAME Higher ethers Other oxygenates Hydrocarbons (*)
73 - 80 wt% 5- 10wt% 5 - 8 wt% 1 - 2 wt % 8 - 10 wt%
* boiling in the gasoline range
MTBE is the major component, but significant amounts of TAME and higher ethers are also present (10 - 18 wt%). Other oxygenates in the product, esters and ketones, are as low as 2 wt%, while the remaining is constituted by hydrocarbons boiling in the gasoline range. Ethermix has been tested for motor fuel use as an octane booster showing properties very close to the ones of the well-known TAME. Blending properties are summarized in table 3 in comparison with the MTBE and TAME ones.
143 Table 3
Blending properties RON MON (R+M)/2 Spec. Gravity (Kg/1), 15 ~ RVP (psi) Oxygen content (wt%)
Ethermix 111 94 103 .755 7.2 15.7
MTBE 116 98 107 .745 9.4 18.2
TAME 113 95 104 .768 2.9 15.7
4. E C O N O M I C EVALUATION The transformation of NG, via syngas, into a mixture of higher alcohols offers an alternative endless source of C4 for the manufacture of ethers for fuel transportation use; economic evaluations here presented are based on 500,000 MTPY plant capacity, located in Saudi Arabia and with a 15 years life. Economic evaluations of the process have been performed in several scenarios. As an example, for an Ethermix plant located in Saudi Arabia with a capacity of 500,000 MTPY the investment cost has been estimated to be 281 MUSS and 384 MUSS including other utilities, interconnections and storage units. Table 4 summarizes the assumed economic scenario and the main profitability indexes. Table 4
Economic evaluation, price scenario and profitability indexes Price scenario Economic indexes Oil, constant during 19.7 US$/bbl IRR before taxes project life (1998 - 2012) Premium Gasoline (PG) 225 US$/ton Payout time before taxes Natural Gas 0.5 US$/MBTU NPV before taxes MTBE 281 US$/ton Total production costs Ethermix value (*) 260 US$/ton (*) Ethermix value = 1.25 PG - 23 US$/ton as transportation costs
17.7
%
5 232 180
years MUSS US$/ton
As shown in table 4 the production cost is close to 180 US$/ton and the economic indexes are very interesting: payout time results to be 5 years (before taxes) and also NPV and IRR indicate the high potentiality of this technology that has still margins for optimization.
5. CONCLUSIONS On the basis of these evaluations the Ethermix technology appears a convenient route for the transformation of abundant and low cost raw material into liquid products for motor fuel use having a substantial added value and premium in terms of quality.
144 The proposed scheme results also to be the more convenient route to exploit natural gas towards the market of high quality and clean fuels when compared to other possible processes.
REFERENCES
1. D. Sanfilippo, Chemtech, 23, (8), August 1993, 35 - 39 2. Fuel Reformulation, 5, (2) March/April 1995, 31 - 43 3. A. Paggini, D. Sanfilippo, G. Pecci, I. Dybkjaer, VII Int. Symposium on Alcohol Fuels, Paris, Oct 1986, 62- 67. Ed. Technip 4. G. Natta, U. Colombo, I. Pasquon, Catalysis, 5 (1957), 131-174 5. C. Rescalli, F. Cianci, It. MI 92/A 002658 to Snamprogetti