New Metal Carbide Catalyst for Cost-Effective Direct Conversion of Cellulose into Chemical Intermediate
22 September 2008
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| Catalytic conversion of cellulose into polyols. Click to enlarge. Credit: Angewandte Chemie |
Researchers in the USA and China have developed a new inexpensive catalyst for the direct conversion of cellulose into ethylene glycol. As reported in the journal Angewandte Chemie, the catalyst is made of tungsten carbide and nickel on a carbon support.
The new process results in up to 29% yield over a tungsten carbide catalyst, and in up to 61% yield when the catalyst is promoted with a small amount of nickel. An attractive feature of this reaction is the low yields of other polyols with respect to ethylene glycol.
A team led by Tao Zhang at the Dalian Institute of Chemical Physics (China) and Jingguang G. Chen at the University of Delaware (Newark, USA) developed the more economical tungsten carbide catalyst system.
Ethylene glycol (EG) is an important intermediate in the chemical industry. In the plastics industry it is needed for the production of polyester fibers and resins, and in the automobile industry it is used as antifreeze.
The global production of EG in 2007 is estimated to be 17.8 million tonnes, an increase of 5.4% from 2006. In view of the increasing demand for EG for the manufacture of polyester fibers and resins in the plastics industry and as an antifreeze in the automotive industry, its direct production from cellulose will create a new method for reducing dependence on petroleum.
—Ji et al. (2008)
The catalytic conversion of cellulose has been demonstrated by other researchers, using a noble metal catalyst (Pt/Al2O3) as a catalyst to convert cellulose into sugar alcohols. These can be used as chemicals in their own right or as new starting materials for the production of fuels, as demonstrated by Dumesic at the University of Wisconsin. A disadvantage of this type of approach, however, is the cost of the catalyst.
In their paper, the researchers note that carbides of Groups 4–6 metals show catalytic performances similar to those of platinum-group metals in a variety of reactions involving hydrogen. Tungsten and molybdenum carbides show strong performances in the catalytic decomposition of hydrazine, comparable with those of expensive iridium catalysts. Tungsten carbides have been used as electrocatalysts because of their platinum-like catalytic behavior, stability in acidic solutions, and resistance to CO poisoning. However, they wrote, “to the best of our knowledge, there have been no attempts so far to utilize metal carbides as catalysts for cellulose conversion.”
...our results have demonstrated that tungsten carbide can replace precious metals to catalyze the degradation of cellulose in an environmentally friendly way. A remarkable advantage of the tungsten carbide over platinum and ruthenium catalysts is the high yield of EG relative to other polyols. More importantly, with the promotion of a small amount of nickel, the yield of EG was significantly increased to 61% by a synergistic effect between nickel and W2C. This is the first report that EG can be directly produced from cellulose in such a high yield.
In view of the importance of EG in the petrochemical industry, this approach may open a new avenue for the production of valuable chemicals from renewable resources. In addition, the substitution of noble metal catalysts with less expensive carbides in a variety of biomass conversion reactions will be of importance because of the limited resources and high prices of precious metals.
—Ji et al. (2008)
Resources
Na Ji, Tao Zhang, Mingyuan Zheng, Aiqin Wang, Hui Wang, Xiaodong Wang, and Jingguang G. Chen (2008) Direct Catalytic Conversion of Cellulose into Ethylene Glycol Using Nickel-Promoted Tungsten Carbide Catalysts. Angewandte Chemie International Edition, doi: 10.1002/anie.200803233
They have tried hydrogenation of cellulose in all possible ways in the past. The first was Bergius who demonstrated that cellulose and wood could indeed be hydrogenated to saturated hydrocarbons at high H2 pressures and temperatures similar to coal. Then a few researchers tried this with CO in supercritical water with an iron catalyst to promote the water gas shift of carbon monoxide to hydrogen.
The above mentioned catalysts platinum and tungsten are both hydrogenation catalysts. They break carbon-heteroatom bonds and make C-H instead. Examples are hydrodeoxygenation and hydrodesulfurization with H2 in the presence of W2S and Mo2S.
While these processes work they suffer from poor overall efficiency. Also, the high pressures needed necessitate expensive equipment.
Posted by: black ice | 22 September 2008 at 10:39 PM