Chapter 4
Production of C1-C6 Alcohols from Synthesis Gas Ph. Courty1, A. Forestiere1, N. Kawata2, T. Ohno2, C. Raimbault1, and M. Yoshimoto2 1Institut Français du Pétrole, B.P. 311, 92506 Rueil-Malmaison-Cédex, France
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2Idemitsu Kosan Co. LTD, No1-1,3-Chome, Marunouchi, Chiyoda-ku, Tokyo, Japan Despite the current decrease of oil prices, the conversion of syngas to alcohols remains an attractive objective. Many companies are involved in alcohols synthesis projects, based on high pressure or low pressure technologies, with motorfuels and octane boosters as targets. The I.F.P. (France), Idemitsu (Japan) R&D program is focused on the co-produc-
tion of methanol and light C2+
alcohols. These product
mixtures yield favorable octane and methanol-compatibilizing properties. Pure linear saturated alcohols are selectively produced by highly-dispersed multi-metallic catalysts. The extent of chain-growth and related alcohols selectivity
depend strongly on the steady-state active phases composition, which is determined by the operating parameters of reaction.
Recent demonstration of the process, under the RAPAD R&D program, has proven its feasibility and good operability. Process economics are described. The development of such new technologies is of concern to countries lacking petroleum reserves or rich in natural gas. Syngas from natural gas is the most promising feedstock.
The development of new syngas-based processes is one of the objectives for the near future, despite the current low price of oil. Syngas
can be produced from various carbonaceous sources, including coal, heavy residue, bio m ass and gas, the latter being the most economical and abundant feedstock.
Chemical valorization of natural or associated
gas is a priority objective, since liquefaction of remote gas via alcohol synthesis permits convenient shipping to markets not directly connected to the gas source by pipeline.
Another near future objective is to ensure development of technology that enables production of motor-fuel substitutes from non petroleum sources. The production of m ethanol-higher alcohols mixtures from natural gas, via syngas, remains a priority objective to obtain octane boosters capable of replacing lead alkyls and to allow the use of additional low-priced methanol.
I.F.P. (France) and Idemitsu Kosan (Japan), as a member of
RAP AD (Research Association for Petroleum Alternative Development), are involved in process and catalysts development for alcohols synthesis. This paper details most of our recent results. 0097-6156/87/0328-0042$06.00/0
© 1987 American Chemical Society Fahey; Industrial Chemicals via C1 Processes ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
4. COURTY ET AL.
Production of CrC6 Alcohols
43
Present status of alcohols synthesis from syngas Table I details most of the recent developments regarding direct synthesis of m ethanol-higher alcohol mixtures.
Chain-growth can be initiated with high operating temperatures and pressures, in the presence of alkalinized zinc-chromium mixed oxides
(1, 2) possibly modified with other metals (3)- Such promoted catalysts allowed industrial scale production of alcohol mixtures containing up to 30 wt % of C
alcohols.
Low Hp/C (T ratios under more moderate temperatures and pressures,
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with copperHDased
methanol synthesis catalysts possibly alkalinized» yield
m ethanol-higher alcohol mixtures (4-6) with rather high contents (512 wt %) of other oxygenated molecules (ketones, esters) - (7>8). Copper-cobalt based catalysts induce a classical chain-growth mecha-
nism (9-1 1). A heavier alcohol content ranging between 20 and 70 % wt
can be obtained under moderate operating conditions. The actual target for
scale-up
studies
is
the
production of alcohol mixtures
containing 35-45 wt J of C2 (12,13). Sulilded and alkalinizeS
molybdenum
based catalysts have recently
been claimed (14,15) ; mixed Mo(Co)K sulfides yield similar alcohol distributions under su bstoichio metric syngas and HS (0.05-0.1 vol %), (16,17). d Direct synthesis of alcohols on Cu-Co based catalysts Reaction stoichiometry and mechanism. This process, which selectively produces linear alcohols ranging from Q to about C is based on the
chemical reactions of Table H. Main reactions (fa,b) produce alcohols
and their related unavoidable by-products, C0p and HO, the former being favored at low
H /CO ratios
due to side or consecutive shift
reaction (c). Secondary reactions produce light hydrocarbons (d,e). The reactions' stoichiometry (H /CO) varies between 0.6 and 3, depending on the nature of the products and the number of carbon atoms involved.
Most of these reactions are strongly exothermic. The reaction mechanism which obeys a Schultz-Flory polymerization
law (9) leads to a simultaneous production of alcohols and hydrocarbons, according to the basic flow-scheme of Figure 1. On Cu-Co based catalysts, formation of formate and acetate species has been confirmed (18) by chemical trapping under reaction conditions. C-C bond formation could occur by reaction of R C H species with either formyl or formate, yielding
dioxy m ethylenic and acetate dérivâtes.
Dioxymethylenic species have
already been postulated, or isolated, as intermediates of direct synthesis
of oxygenated compounds from syngas (19,20) and LR. spectroscopy and chemical trapping have confirmed the appearance of methoxy, formyl,
formate and acetate species in similar syngas-based reactions (21-23). A similar
chain-growth
mechanism
was said
to
occur
with
the
first molybdenum -sulfur-potassium based catalysts of table I (J_5). For such
a chain-growth mechanism, the heavier the average molecular weight of alcohols, the greater the formation of heavy compounds and, more often than not, the lower the alcohols1 selectivity. Furthermore, in FischepTropsch type catalysts (24,25) diffusion limitations, mostly due to the presence of liquid products condensed in the micro porosity, increase with the size of diffusing molecules. These molecules are capable of
Fahey; Industrial Chemicals via C1 Processes ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Downloaded by IOWA STATE UNIV on April 16, 2017 | http://pubs.acs.org Publication Date: December 16, 1987 | doi: 10.1021/bk-1987-0328.ch004
44
INDUSTRIAL CHEMICALS VIA C, PROCESSES
TABLE I : PRESENT STATUS OF ALCOHOLS SYNTHESIS "CHAIN GROWTH" DUE TO:
RANGE OF OPERATING CONDITIONS
Operating parameters ^^,^1
^ and'press^T b/ low H2/CO
C/ use of metals inducing chain-
Pr-.ur,
alkali metals
.
Cu-Zn
P„Pa
" H2/COmol.
C2t0H(wt%)
380-420
12-25
2-3
20-30
qnn
(alkali metals)
~CJUU
Cu-Co
.
alkali metals
-growth
.
others
db + c
•
________________________ I
T'C
M°S2(a)
promoter
K
|
in
1
90-10
-1 U
, ~'
270"320
6" 10
1.5 ±Q5
35-45
240-325W
10-28 (a)
__1
