Renaissance of Syngas Technology
However recently, oil prices have repeatedly tested the $ 100/barrel threshold, and the experts at BP, Shell, etc. continue to revise their oil reserve scenarios. These developments have injected new life into technologies such as Fischer-Tropsch and syngas production. Even the Imbert wood gas generator is making a comeback, on a Ford just like years ago. “Syngas technologies run in cycles,” said Prof. Eckhard Dinjus, head of the Institute of Catalytic Research and Technology (IKFT) at the German Karlsruhe Institute of Technology (KIT).
Versatile Raw Material Can Be Used
Two industries are currently working on syngas production, one of them being the fuel industry which uses gas as an intermediate for biofuel. The Chemical Process Industry has also developed a renewed interest in the process. The reactive carbon monoxide-hydrogen mixture is highly versatile. Dr. Andreas Kreitmeier, who is in charge of research at BASF, sees this as a genuine advantage. He stated at a press conference three years ago that the use of syngas is likely to broaden the raw material base.
Syngas can be produced from nearly any raw material that contains carbon. Coal, natural gas, oil, plant residue, bio-waste, wood, plastic and even garbage have already been gasified. This gives the Chemical Process Industry the flexibility it needs and means that gas will play a major role in the search for new raw materials. There is good reason why BASF invested € 100 million in a research cluster between 2006 and 2008. Among other things, the company’s researchers are working on catalysts for Fischer-Tropsch synthesis which can be used specifically for production of olefins with two, three or four carbon atoms.
Syngas is raw material neutral
Once it has been produced, syngas is essentially raw material neutral. However the original input material has an influence on the hydrogen/carbon ratio. The range extends from 1:1 for coal and biomass to 4:1 for methane-rich natural gas. Oil lies in the middle at 2:1. In other words, synthesis in and of itself is not the whole story. There are also downstream cleaning stages, and in most cases catalytic conversion is used to increase the proportion of hydrogen in the hydrogen/carbon ratio depending on how the gas will be used.
That makes the use of biomass particularly challenging. “Biomass is a catch-all term for a very heterogeneous class of materials,” explained Dinjus, a co-developer of the Bioliq process. Biomass can mean grass cuttings, straw waste, wood chips, food residue, etc. It is invariably moist and non-homogeneous, and it has a low energy density. As a result, the key step in the Bioliq process is pyrolytic densification to produce a high-energy syncrude for subsequent gasification.
Scientists at Evonik are taking a totally different approach. They want to use a mixture of syngas and ordinary glucose directly as a fermentation raw material. This idea is appealing, because it side-steps the cleaning and conversion stages. “Bio-organisms are not too particular when is comes to the purity of syngas,” explained Dr. Thomas Haas from Evonik. However, he admits that the yields are still two or three orders of magnitude short of what can be achieved with chemical catalysts.
Due to the difficulties involved, the processes used to produce syngas take up several pages in the standard technical chemistry texts. Ten different processes exist for coal gasification alone, which use a packed bed, a fluidized bed or an entrained-bed gasifier, but extremely elaborate equipment is needed, as the coal has to be finely ground at the start of the process. The output gas is contaminated with coal particles, and it has to be scrubbed prior to downstream processing. Dr. Otto Machhammer from the Process Development group at BASF is on solid ground with his estimation that “twice the specific investment is needed compared to syngas production because of the solids handling issue.”