Synthesis Gas Utilization
As shown in Table 3 (Khan, 2018) synthesis gas can be produced from a variety of feed sources, with coal accounting for 48.3%. Once the synthesis gas is produced, there are several downstream processes for synthesis gas to chemicals, fuels and power.
The following discussion on conversion of synthesis gas to chemicals applies to monetization of coal as well as remote natural gas. Table 4 shows the 2018 applications (Khan, 2018) of synthesis gas.
As seen in Figure 5 (Vora, 2015), once coal or natural gas is converted to synthesis gas, it opens up a number of options for making different products. Lee (1997) provides an excellent review of various processes for methane derivatives via synthesis gas. Chang (1984) provides a good review of chemicals from methanol. The question becomes: Producing which product from which feedstock is most economical? For most petrochemical processes, raw materials account for 60-70% of the cost of production. Therefore, a first analysis requires a look at the differential between the product value and the feed cost. Table 5 shows this differential using 2018 average product values at various natural gas as feed prices. One can do a similar analysis for coal. This shows the production of olefins, ethylene and propylene via methanol has the highest differential, making methanol an important intermediate. Coal at 100S/MT is equivalent to 3.80S/mmBTU.
Table 3. Feed sources for synthesis gas production.
Table 4. Applications for synthesis gas production in 2018.
Figure 5. Natural gas and coal utilization.
Table 5. Product-feed price differential, 2018 product value at different NG price.
Assumption: NG to Synthesis Gas efficiency 80% Synthesis gas to Methanol-95%
MTG-90%, FT-90%, MTO-90%, MTP-65%
From the previous discussion, it is clear that synthesis gas can play an important role in the utilization of coal or remote natural gas reserves. Since methanol is a key intermediate in this conversion, it is important to discuss developments in methanol markets and technology. The world methanol demand balance for its different uses is shown in Table 6. From 1995 to 2010 methanol production grew at an annual rate of 4.7%. The recent new application of methanol for the production of ethylene and propylene has given a further boost to methanol production, with 2018 total methanol production reaching 90 million MTA. Alvarado (2016) compared methanol uses in 2010 and 2015, as shown in Figure 6.
An interesting point to note is that in 2010, the use of methanol for the production of ethylene/ propylene via MTO MTP was negligible and is not represented on the chart. However, in 2015 at 18% it is the second largest application after formaldehyde.
There are several methanol technology suppliers. Lurgi GmbH, Davy and Haldor Topsoe are some of the main licensors (HP, 1993). Until 2000, a typical large methanol plant capacity was 2500 metric tons per day (MT D). Some trends in methanol synthesis technology are particularly important for the production of light olefins from gas. First, plant capacity is increasing significantly, as exemplified by several mega-scale plants (~ 5000 MT/D) that came into operation during the 2010s, as reported by Bonarius (2005). Second, lower feedstock costs in specific geographic areas are having a major impact on methanol production economics. Technology for the production of methanol from synthesis gas is available from several licensors (Chem System, 2012), as seen in Table 7.
The early development in methanol technology is credited to Imperial Chemical Industries Ltd. (ICI). ICI first introduced the Low-Pressure Methanol (LPM) Process in 1966. In 1994, ICI Katalco introduced the Leading-Concept Methanol (LCM) Process. Later, this became part of Johnson Matthey. The overall reaction from methane to synthesis gas to methanol can be summarized as:
Table 6. Products from methanol in 1995 and 2010.
Figure 6. Methanol applications in 2010 and 2015.
Table 7. Major methanol technology licensors.
Synthesis gas is processed over a fixed bed of catalyst forming methanol and water. Two reactor types are most popular: An adiabatic reactor with multiple quenches of a cold stream (ICI system) or a multi-tubular reactor with internal heat exchange (Lurgi system). Both types are operated at a temperature range of 200-280 °C and low pressure of 5-7 MPa using Cu ZnO/AfO. catalyst. More details are given by Lee (1990). Typical methanol properties and specifications are shown in Table 8.
Methanol production economics
Capital investment costs and the feedstock costs vary significantly for different geographic areas. In some parts of the Middle East, the natural gas price in 2018 was 1.00-1.5OS/imnBTU. In the USA it ranged between S2.50 to $4 per nmiBTU. It was over $8 to $12 per mmBTU in China, Japan. India and other Asian countries where LNG is imported.
During the 1980s-l 990s, high feed cost units in North America and Western Europe led to significant capacity shut downs. By 1990, all production in Japan was shut down (Chem System, 2012). Subsequently, almost all new methanol units were located where natural gas was relatively low in cost, typically in the Middle East and South America. This development led to a dramatic change in the methanol industry. Since 2010, with the development of shale gas, methanol production in North America is reviving again. At the same time, China has been aggressively moving into chemicals from coal, where methanol is a key intermediate. This led to significant coal-based production of methanol in China. As was seen earlier, in Table 2, from 2000 to 2018 the coal price has ranged between 30 and 110 dollars per ton (BP. 2019). Table 9 shows the cost of methanol production for a unit producing 5000 metric tons of methanol per
Table 8. Methanol properties and specifications.
Table 9. Methanol production economics m 2018.
day. based on 2018 coal prices in China and the USA and 2018 natural gas prices in China, Middle East and the USA.