Industrial Chemicals via C1 Processes - ACS Publications - American

tives for the near future, despite the current low price of oil. ... tional low-priced methanol. ..... deal mostly with selectivity improvements from ...
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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

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

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,

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

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