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“It’s just a movie,”parents answered to their kids in awe of the visionary technology seen in the ’80s blockbuster Back to the Future. While hover boards are still not commercially available, the movie’s prediction of future cars running on garbage is pretty spot-on!

In this sequence, Doc Brown is fueling his DeLorean directly from a trash can (go to 1:00).

In reality, it requires more steps to get to this point, but it is what we are trying to do in our research! As shown in the diagram below, the steps are as follows:

(1) Gasify the organic waste into syngas, which is a mix of  hydrogen gas (H2), carbon monoxide (CO) and impurities such as methane (CH4), carbon dioxide (CO2), water and light hydrocarbons;

(2) Make the liquid biofuel via chemical synthesis. This biofuel is usually ethanol, but it can also be similar to diesel or gasoline as well depending on the catalyst used. It would directly feed to an actual car, so it is more convenient than the proposed vision in the movie;

(3) Transform the tail gas (unreacted organic impurities from the synthesis reactor that are now in high concentration) into syngas with a H2/CO ratio of 2. Then, replenish the synthesis reactor.

image_car

In my research project, we work on step (3). The most common way to produce syngas is to use a process called steam reforming, in which water and methane are mixed at high temperatures in the presence of a catalyst.

A catalyst is a material that accelerates the rate or increases yield of a chemical reaction without being consumed in the process. The main components of biogas and tail gas are methane (CH4) and carbon dioxide (CO2). Using this CO2 instead of paying to remove it will improve the global efficiency of the process. The catalysts used for steam reforming produces a lot of carbon deposition if used with CO2 and so, the aim of this project is to produce a catalyst that prevents carbon deposition covering its active site, plugging up the reactor or making the catalyst’s pellets collapse.

The catalyst we use is a nickel-alumina spinel of formulation NiAl2O4 mixed with zirconia (ZrO2) and it has the appearance of a sky blue powder. The catalyst was used for 19 days without any hint of deactivation or carbon deposition. In that test, the ratio of CO2/CH4 was 2 and in result, the ratio of H2/CO was only 0.58. To improve the syngas quality, we managed to reduce the CO2/CH4 ratio to 1.2. We got a H2/CO ratio of 0.86 with the same carbon performance over the course of the 12 day-test. We then added water (1CH4/1CO2/0.3H2O) and the result was an increase of the H2/CO ratio to 1.2. At 1CH4/0.5CO2/0.8H2O, the ratio of H2/CO increases to 2.1 but the CH4 conversion decreases continuously to 81% over a 29-hour period. The reason of this loss of conversion is the oxidation of the nickel particles that normally form over the surface of the catalyst. A gas containing a high concentration of water is more corrosive and prevents or reverses the reduction of the spinel. However, the loss of conversion is modest and with some optimization the objective will be fully accomplished. In future work, we plan to test the catalyst with other contaminants so we can get closer to feeding Doc Brown’s car with trash.

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