2.2.1 Use of Coal
Coal is used since the middle 1800s as source of carbon in synthetic chemistry, with
an apparent decline in the middle 1900s due to the competitive price and easier use
of oil and natural gas. As a matter of fact, for 100 years from 1850 to 1940, most
synthetic chemicals were produced from coal through the “coal chemistry.” From
1940s onward, the “coal chemistry” was progressively substituted by “petrochemistry,” based on use of oil and even methane. The reduction of the use of coal
was justified by several factors, such as the (i) competitive cost of oil and gas;
(ii) easier extraction techniques; and (iii) cleaner processes for hydrocarbons
work-up with respect to coal. As a matter of fact, environmental concerns, having
issues both in by-products produced and the effects of coal mining/extraction, were
a potent driver for the shift from coal to hydrocarbons, liquid and gaseous.
Recently, attempts to develop clean technologies for coal conversion have been
made. The use of coal had recently a revival, but still it is under severe control due
to the emissions. The rise of price of oil and gas will eventually bring back coal to
the chemical industry? This question will remain open until clean technologies are
developed. Countries rich of coal, and poor of oil and gas, have to weigh the cost of
investments for safe extraction–conversion of their own coal with respect to
external debt if they will use oil and gas purchased on the international market. The
main use of coal in the chemical industry is for producing syngas (CO+H 2 ) through
the Water–Gas Reaction (WGR) and Water–Gas Shift Reaction (WGSR) shown in
Eq. 2.1a and 2.1b, respectively. The overall reaction is shown in Eq. 2.1c.
C þ H 2 O ! CO þ H 2 syngas production
ð
Þ
ð 2:1aÞ
CO þ H 2 O ! CO 2 þ H 2 water-gas shift reaction
ð
Þ
ð 2:1bÞ
C þ 2H 2 O ! CO 2 þ 2H 2 overall reaction
ð
Þ
ð 2:1cÞ
By combining reactions 2.1a and 2.1b in the right ratio it is possible to produce
syngas [DI2.1] with a variable H 2 :CO ratio, from 1 to 2 and even higher values.
Such syngas is used for the synthesis of methanol (CH 3 OH) or, through the
Fischer–Tropsch (FT) process, for the synthesis of gasoline, diesel, and other
chemicals. Scheme 2.1 shows the many products that can be produced from
methanol [3].
It also finds utilization in several other fields, such as fuel cells. (Appendix C)
Coal clearly meets the interest of several industrialized countries, which are rich of
coal mines (such as USA, Australia, Poland, China, India, Malaysia, and South
Africa) and already have on stream an advanced FT technology. FT plants for
Syngas to Liquid (SGtL) may have a size of the order of 330 000 t/y (South Africa)
up to 1 Mt/y. Catalyst improvement for better specification of SGtL products
(gasoline fraction, mainly, with gaseous and wax fractions minimization) is a
continuous development because of the relevant economic interest: improving by
2.2 Fossil-C as Source of Carbon in Synthetic Chemistry
15
Coal is used since the middle 1800s as source of carbon in synthetic chemistry, with
an apparent decline in the middle 1900s due to the competitive price and easier use
of oil and natural gas. As a matter of fact, for 100 years from 1850 to 1940, most
synthetic chemicals were produced from coal through the “coal chemistry.” From
1940s onward, the “coal chemistry” was progressively substituted by “petrochemistry,” based on use of oil and even methane. The reduction of the use of coal
was justified by several factors, such as the (i) competitive cost of oil and gas;
(ii) easier extraction techniques; and (iii) cleaner processes for hydrocarbons
work-up with respect to coal. As a matter of fact, environmental concerns, having
issues both in by-products produced and the effects of coal mining/extraction, were
a potent driver for the shift from coal to hydrocarbons, liquid and gaseous.
Recently, attempts to develop clean technologies for coal conversion have been
made. The use of coal had recently a revival, but still it is under severe control due
to the emissions. The rise of price of oil and gas will eventually bring back coal to
the chemical industry? This question will remain open until clean technologies are
developed. Countries rich of coal, and poor of oil and gas, have to weigh the cost of
investments for safe extraction–conversion of their own coal with respect to
external debt if they will use oil and gas purchased on the international market. The
main use of coal in the chemical industry is for producing syngas (CO+H 2 ) through
the Water–Gas Reaction (WGR) and Water–Gas Shift Reaction (WGSR) shown in
Eq. 2.1a and 2.1b, respectively. The overall reaction is shown in Eq. 2.1c.
C þ H 2 O ! CO þ H 2 syngas production
ð
Þ
ð 2:1aÞ
CO þ H 2 O ! CO 2 þ H 2 water-gas shift reaction
ð
Þ
ð 2:1bÞ
C þ 2H 2 O ! CO 2 þ 2H 2 overall reaction
ð
Þ
ð 2:1cÞ
By combining reactions 2.1a and 2.1b in the right ratio it is possible to produce
syngas [DI2.1] with a variable H 2 :CO ratio, from 1 to 2 and even higher values.
Such syngas is used for the synthesis of methanol (CH 3 OH) or, through the
Fischer–Tropsch (FT) process, for the synthesis of gasoline, diesel, and other
chemicals. Scheme 2.1 shows the many products that can be produced from
methanol [3].
It also finds utilization in several other fields, such as fuel cells. (Appendix C)
Coal clearly meets the interest of several industrialized countries, which are rich of
coal mines (such as USA, Australia, Poland, China, India, Malaysia, and South
Africa) and already have on stream an advanced FT technology. FT plants for
Syngas to Liquid (SGtL) may have a size of the order of 330 000 t/y (South Africa)
up to 1 Mt/y. Catalyst improvement for better specification of SGtL products
(gasoline fraction, mainly, with gaseous and wax fractions minimization) is a
continuous development because of the relevant economic interest: improving by
2.2 Fossil-C as Source of Carbon in Synthetic Chemistry
15