(638g) Fischer-Tropsch Synthesis over Alumina Supported Cobalt Catalyst in a Fixed-Bed Reactor

Approximately 30% of the energy is consumed in transportation in the form of gasoline, diesel and jet fuels. The ever-rising energy demands especially in the transportation sector and the depletion of fossil fuels has raised the interest in production of transportation fuels from renewable and potentially neutral source. Among the renewable source biomass stand first for the production of liquid fuels.The biomass is converted to liquid fuels in a two-step process. In the first step, the biomass is converted to syngas (a mixture of carbon monoxide and hydrogen) under controlled atmosphere. In the second step, the biomass derived syngas will be converted to liquid fuels via Fischer-Tropsch synthesis over a catalyst.

In this work, Fischer-Tropsch Synthesis was carried out using 12wt% cobalt catalyst supported over γ-Al₂O₃. The catalyst was synthesized using wetness impregnation technique using cobalt nitrate solution. After the impregnation, the catalyst was reduced using sodium borohydride (in the liquid-phase), whose addition was controlled by a timer-assisted peristaltic pump. After reduction, the catalyst is washed multiple times with ultrapure water to obtain neutral pH. The catalyst was loaded into a fixed-bed stainless steel reactor. The reactor temperature at the desired conditions was maintained by using a 3-zone tubular furnace (Carbolite make) and the reactor pressure was maintained using a backpressure regulator. All the experiments were carried out under isothermal conditions. The temperature was varied from 220-310oC, the pressure was varied from 5-20 atm, the hydrogen to carbon moxide ratio was varied from 0.75 to 3 and the gas hourly space velocity was varied from 5 – 100 1/hr. The products were characterized using Shimadzu GC-MS QP-2010 Plus employing Rt-Alumina Bond / Na₂SO₄ column and FID detector.

From the concentration of the compounds it was observed that the conversion of carbon monoxide increases with increase in temperature and pressure. But, the selectivity to hydrocarbons decreases with increase in temperature, increases with increase in pressure and also increase with increase in pressure and hydrogen to carbon monoxide ratio. The selectivity to hydrocarbons was calculated using chain growth probability (α) using Anderson-Sluz-Flory (ASF) distribution. The chain growth probability was found to vary from 0.48 to 0.76 depending on the reactor and flow conditions.