Conversion of ethanol to gasoline range hydrocarbons using a zeolite catalyst (HZSM-5)


The investigation of alternative and renewable sources of fuel is of special interest to countries lacking petroleum reserves. Some years ago, a project in the Department of Chemistry focussed on the conversion of ethanol to petrol by the use of the synthetic zeolite HZSM-5.

A related process, which uses methanol as substrate (obtained by converting methane from natural gas) has been developed to industrial scale in New Zealand and has the capacity to supply about one third of their petrol requirements.
Our study was concerned with catalyst design for the conversion of ethanol with regard to the manufacture of liquid and gaseous fuels.
HZSM-5 can be considered as a derivative of silica and alumina, both very cheap reagents. It acts as a solid acid since for each Al3+ substituted for Si4+ in the structure, an H+ ion is also needed to maintain the overall neutrality of the molecule.
The 3-D lattice built up, consists of channels through which certain small molecules can pass and react inside by a process called shape selectivity. Bulky molecules can not enter the channels and reaction of smaller molecules to larger ones is hindered by the size of the channels, Figure 1.
This restriction means that only molecules with less than say 10 carbons are produced in the reactions inside the catalyst.
Our results indicate total conversion of the ethanol and the liquid fuel produced is comparable to commercial unleaded grade petrol with a good range of aromatic and aliphatic hydrocarbons, Table 2.

GC of synfuel

The hydrocarbons were identified by GC and GC/MS analysis.
A simulation of a GC/MS showing spectra and molecular graphics is available using JSpecView and Jmol.

Table 1. The major peaks identified in Synfuel
Peak Hydrocarbon
1 1-butene
2 2-methylpropene
3 2-methylbutane
5 4-methylpentene
7 methylcyclopentane
8 benzene
15 toluene
16 ethylbenzene
17 m- and p-xylene
18 o-xylene
21 1-ethyl-4-methylbenzene
24 1,2,4-trimethylbenzene
25 1-methyl-4-(ethylmethyl)-benzene
30 1,2-diethylbenzene
31 1-ethyl-2,4-dimethylbenzene
32 2,3-dihydro-1-methyl-1-indene
33 naphthalene
37 2-methylnaphthalene
39 1,8-dimethylnaphthalene
41 2-(1-methylethyl)-naphthalene

In addition, other potential catalysts, including substituted aluminophosphates, have been prepared and characterised by X-ray powder techniques, scanning electron microscopy, FTIR, magic angle NMR and neutron activation analysis.
These materials have been shown to be more useful for conversion of ethanol to gaseous products such as ethylene.
Their reactions with ethanol have significant potential for the production of petrochemicals.
For more information on the methanol to gasoline (MTG) process see the pages at UCSD

Table 2. Comparison of HZSM5 sample CI1/C/H and Mobil's MZIIO used in the catalytic conversion of EtOH a.
ZSM-5 sample CI1/C/H MZI110/C/H
Conversion (%) >99 >99
Distribution of conversion products (wt%)
Hydrocarbons 62.8 63.4
Water 37.6 36.9
Distribution of total hydrocarbons (wt %):
Permanent gases 58.3 46.4
C5+ 41.7 53.6
Selectivity within permanent gases (wt%)
C1 0.3 0.1
C2 9.8 10.3
C3 42.6 33.3
C4 46.9 56.3
Selectivity for aromatics in C5+ (wt%)
Nonaromatics in C5+ 29.1 40.5
Aromatics 71.9 59.5
Benzene 4.3 2.8
Toluene 21.7 11.2
Ethylbenzene 3.9 2.9
m- and p-Xylene 17.4 12.5
o-Xylene 4.4 3.1
EMB** 5.8 10.7
TMB*** 1.5 3.7
2-Methylnapthalene 1.0 0.4
Others 11.9 12.2
a Reactor temperature: 3750C, WHSV:6.48hr-1, N2 flow rate: 20cm3/min, wt of catalyst: 1.0g.

*Zeolite composition:
CI1/C/H-Na0.8H3.4Al4.2Si92O 192.19H2O (Si/Al=21.9)
MZ110/C/H-Na0.1H2.9Al3.0Si93O 192.7H2O (Si/Al=26.3)
Included in the non-aromatic hydrocarbons are:
dimethyl (cyclo) pentanes, methylcyclopentane, ethylcyclopentane and di- and trimethylbutanes, etc.
**EMB: 1-Ethyl-4-methylbenzene
***TMB: 1,2,4-trimethylbenzene

For the answers to some frequently answered questions on gasoline, oxygenates etc., see FAQS.ORG.

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The Department of Chemistry, University of the West Indies,
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Created Feb 1995. Links checked and/or last modified 26th November 2013.