Top Catal DOI 10.1007/s11244-016-0554-6
ORIGINAL PAPER
Raw Material Change in the Chemical Industry Martin Dieterle1 • Ekkehard Schwab1
Ó Springer Science+Business Media New York 2016
Abstract In the past Raw Material Change in the chemical industry followed always the availability of different fossil raw materials like coal, oil or gas for the energy market combined with improved physical properties of the raw material leading to an improved technology. Currently, however it is expected that near and midterm price developments for carbon containing raw materials most probably will no longer be identical in all parts of the world. Different regions of the world are relying on different carbon sources. The cost of the required conversion technology from raw materials to basic chemicals determines investment decisions. Different research activities of BASF on such conversion technologies, either syngas related conversions or direct conversions are briefly discussed. Keywords Petrochemical raw materials Chemistry and energy Energy equivalent Cost of carbon Fischer– Tropsch to Olefin Methane to Benzene Catalysis
1 Introduction Until the early 19th century chemicals and energy were essentially derived from renewable resources. This changed with the development of the steam engine which on the one hand allowed the exploitation of deep lying coal reserves due it’s ability to pump water efficiently out of the mines and at the same time created a demand for & Ekkehard Schwab
[email protected] 1
BASF SE, Process Research and Chemical Engineering M301, 67056 Ludwigshafen, Germany
inexpensive energy in large quantities which could no longer be covered by wood. Once available, coal could also be gasified to ‘‘town gas’’ for lighting and heating purposes. A byproduct of coal gasification is coal tar, and it was soon discovered that this tar contained a number of valuable chemicals which could be used for the synthesis of artificial dyestuffs which due to their superior properties soon replaced plant-derived natural colors. The roots of many European chemical companies go back to this time. It happens that BASF as one of those is celebrating its 150th anniversary in 2015 (Fig. 1), and it was exactly the idea to use the byproduct of a ‘‘town gas’’ factory as a raw material for dyestuff manufacturing. However, coal itself is only of limited interest for chemical synthesis: elemental carbon first has to be converted into a reactive form, typically by gasification into a mixture of carbon monoxide and hydrogen. Therefore, the use of coal as a raw material for chemicals rapidly declined when crude oil became available as an alternative. As a mixture of different hydrocarbons, crude oil can be converted into chemicals with much less effort than coal, and therefore until today is the by far preferred source of carbon [1]. Besides its chemical properties, availability and cost are the other decisive factors that determine the choice of a raw material, especially for large volume chemical processes, where raw material cost is above 80 % of the total production cost. Rather, than comparing the cost of the raw material itself, it is very informative to use the specific cost of carbon in a certain raw material. It turns out, that carbon from coal is the most inexpensive (Table 1). As mentioned above, conversion cost for coal is high, especially because it involves solid handling thus making it less attractive than it might look at first glance. Moreover, an additional hydrogen source is needed to convert coal into olefins which are the basis for petrochemical
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Top Catal Table 1 Comparison of cost per ton of carbon and cost per GJ for various carbon containing raw materials
Fig. 1 BASF’s operating permit issued by the Bavarian Government (May 2nd, 1865)
downstream chemistry. If this is done by water gas shift, large CO2 emissions are unavoidable. Natural gas is much more attractive with respect to the latter point and also avoids the difficulties associated with solid handling. Therefore, depending upon the price gap between oil and gas (Fig. 2), gas has become a very attractive raw material, although here, too, conversion cost is higher than for oilbased processes. Two more conclusions can be drawn from the data in Table 1: Edible biomass is not a cheap source of carbon, and even C in Carbon Dioxide comes at a significant cost. Finally, there is a good correlation between cost per carbon
$/tonc
$/GJ
Reference
–CH2– (Oil)
730 (365)
21 (10.5)
@ 100 (50) $/bbl @ 4 $/MMBTU (USA)
CH4 (Gas)
135
3.8
–CH– (Coal)
98
3.1
@ 90 $/ton (NWE)
Saccharose
1000 (630)
26 (16)
@ 19 (12) ct/lb
CO2
180
–
@ 50 $/ton
and cost per GJ, which reflects the fact that all raw materials in Table 1 (except CO2) are energy carriers that are used only to a minor extent for the production of chemicals. Near and midterm price developments for carbon containing raw materials most probably will no longer be identical in all parts of the world, and one may be confronted with a situation that is illustrated in Fig. 3 with different regions of the world relying on different carbon sources. A closer look to the fraction of fossil energy carriers that are used in the chemical industry is given in Fig. 4 and Table 2: it is estimated that only around 3 % of the world’s total consumption of fossil carbon sources end up in the chemical industry. Out of those approximately 75 % end up in chemicals, whereas the remaining 25 % are needed to drive the conversion processes. It was mentioned above that besides cost—be it calculated as cost per ton of carbon or the cost of the raw material—and availability, the cost of the required conversion technology determines investment decisions. Of course this goes along with benchmarking of alternative raw materials which are available. In fact, there are only very few missing technology links between the available raw materials and the basic chemicals which form the foundation of today’s petrochemical industry (Fig. 5).
2 Examples for Research Targets in the Conversion Technology Landscape
Fig. 2 Decoupling of oil and gas prices since 2005
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Although the pathways in the conversion technology map are fairly complete, there are a few desirable shortcuts missing. These shortcuts may start directly from the carbon containing raw material or from the intermediate syngas stage. Figure 6 shows a simplified scheme of today’s applied processes downstream of the syngas stage: Starting from any carbon containing raw material (including biomass). Syngas with varying ratios of H2 and CO can be obtained. Using Methanol as a platform intermediate, there are two established processes that either lead to Propylene (with a significant fraction of Gasoline as a byproduct,
Top Catal Fig. 3 Regional diversification of C-containing raw materials in the future
Fig. 4 Energy production determines today’s global raw material mix
Table 2 Material and energetic use of fossil raw material in the chemical industry Fossil energy carrier
D
World
Material use
18.7
630
Mio ton/year
Energetic use
7.6
225
Mio tons/year
Industry turnover (2012)
237.4
4.9732
Billion US $
Sources VCI: Energieverbrauch und Rohstoffe, 2011; DECHEMA: Technology Roadmap Energy & GHG Reductions in the Chemical Industry via Catalytic Processes 2013; ACC: Global Chemical Shipments by Country 2013
‘‘MTP’’) or to a mixture of Ethylene and Propylene (MTO). In both cases Dimethyl Ether occurs as an intermediate. The red arrow ‘‘shortcuts’’ in this scheme would either be the direct or ‘‘1-step’’ synthesis of Dimethyl Ether (DME) from Syngas or the direct conversion of Syngas into
olefins, depicted here as ‘‘FTTO’’—Fischer–Tropsch-toOlefins’’. The 1-step DME synthesis takes advantage of the fact that it is possible to couple 3 reactions (Methanol synthesis, Methanol dehydration, and water gas shift) in one reactor, thereby overcoming the equilibrium limitation of the Methanol synthesis as shown in Fig. 7: For the 1-step DME synthesis, the highest equilibrium conversion is obtained for a syngas with a stoichiometric ratio of H2:CO=1; if the hydrogen content in the Syngas increases, the difference between 1-step DME and Methanol synthesis becomes smaller. Overall, this allows the design of a more energy efficient process if the DME synthesis is back-integrated into the syngas stage. The 1-step DME technology has been investigated since the early eighties [2] and is currently intensively revisited [3]. Besides the potentially improved energy efficiency of a
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Top Catal
Fig. 5 Known technology pathways between carbon sources and basic chemicals
Fig. 6 Simplified scheme ‘‘Syngas to Olefins’’
back-integrated process scheme, the other attraction is, that the chemistry fits nicely to coal-based CO-rich Syngas. CO-rich syngas can also be produced from Methane which has become an economically very attractive source of carbon with the development of shale gas production technologies (see Table 2). The established technology in
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this case is partial oxidation with pure oxygen; technologies under development are Methane Dry Reforming or Reverse Water Gas Shift [4]—both in addition to inexpensive Methane requiring an appropriate source of pure CO2. Fischer–Tropsch technology currently is mainly run for the production of fuels, using cobalt catalysts at relatively low temperatures. There is, however also a version of the technology that runs at higher temperature, applying ironbased catalysts. If these catalysts are operated under proper conditions, it is possible to obtain relatively high yields of lower olefins [5]. As shown in the schematic mechanism in Fig. 8, hydrogenation of the primary olefin products needs to be avoided, and the Anderson–Schulz–Flory kinetics needs to be tuned to the maximum yield in the C2–C4 cut. Figure 9 puts the FTTO technology in perspective with MTO, MTP and Naphtha steam cracking, respectively: ‘‘unwanted’’ fractions are counted negative, wanted fractions positive on the y-axis. If only the carbon containing fractions are considered, and the byproduct water is neglected, MTO/MTP have the highest yields. FTTO comes close to Naphtha steam cracking, and it needs to be noted that the C4? olefins here are mostly a-olefins. On the other hand, Butadiene is missing, and the C5? fraction does not contain aromatics. All in all, with the currently obtainable selectivities, Fischer–Tropsch technology will most probably remain best suited for fuel production.
Top Catal Fig. 7 CO equilibrium conversion as a function of Temperature and syngas composition
Fig. 8 Schematic mechanism ‘‘Fischer–Tropsch to Olefins’’
Fig. 10 Assumed reaction pathway on a MoC/ZSM 5 catalyst
Fig. 9 Product mix of FTTO in comparison with MTO/MTP and Naphtha steam cracking
There are only few known pathways that are able to build C–C bonds while using Methane as a starting point. One of those is the so-called Dehydro-Aromatization (DHAM) reaction. The reaction involves two elementary steps—activation of methane and C1 coupling and the subsequent oligomerization and aromatization—for which a multifunctional catalyst is used. Methane activation is believed to occur at Molybdenum- or Tungsten-Carbide species which are placed in close proximity to an acidic catalytic site incorporated into a zeolite. The employed zeolite induces a shape selectivity by the spacial constraints so that Benzene is the main product (Fig. 10).
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Benzene is an important building block for the chemical industry. It is mainly used for the production of styrene or polyurethanes. On-purpose production of benzene using a low-cost raw material, such as methane, is an attractive technology option even at today’s benzene prices. It may fill an expected benzene supply gap caused by the shift of crackers mainly in the US to lighter feedstocks. The development of such a process faces many challenging technical hurdles. Due to severe thermodynamic limitation, the process has to be operated at temperatures exceeding 700 °C. Due to the highly endothermic reaction special care has to be taken to supply sufficient heat input into the reactor. Therefore, novel catalyst and reactor designs are required to endure such harsh conditions while selectively producing benzene and hydrogen instead of coke—the formation of which is thermodynamically favored under such conditions. The regeneration of the catalyst has to done at high
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temperatures without harming the zeolitic structure. Due to the low thermodynamic equilibrium conversion a highly efficient way to remove hydrogen in low concentrations from the product stream has to be developed.
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