Shirazi Yaser, Viamajala Sridhar, Varanasi Sasidhar
Department of Chemical and Environmental Engineering, University of Toledo, Toledo, OH, United States.
Department of Chemical Engineering, Manhattan College, New York City, NY, United States.
Front Chem. 2020 Sep 10;8:786. doi: 10.3389/fchem.2020.00786. eCollection 2020.
Microalgae are attractive feedstocks for biofuel production and are especially suitable for thermochemical conversion due to the presence of thermally labile constituents-lipids, starch and protein. However, the thermal degradation of starch and proteins produces water as well as other O- and N-compounds that are mixed-in with energy-dense lipid pyrolysis products. To produce hydrocarbon-rich products from microalgae biomass, we assessed and catalytic pyrolysis of a lipid-rich sp. in the presence of the HZSM-5 zeolite catalyst over a temperature range of 450-550°C. Results show that product yields and compositions were similar under both and conditions with benzene, toluene and xylene produced as the primary aromatic products. Yields of aromatics increased with increasing temperature and the highest aromatic yield (36.4% g aromatics/g ash-free microalgae) and selectivity (87% g aromatics/g bio-oil) was obtained at 550°C. Also, at this temperature, oxygenates and nitrogenous compounds were not detected among the liquid products during catalytic pyrolysis. We also assessed the feasibility of a two-step fractional pyrolysis approach integrated with vapor phase catalytic upgrading. In these experiments, the biomass was first pyrolyzed at 320°C to degrade and volatilize starch, protein and free fatty acids. Then, the residual biomass was pyrolyzed again at 450°C to recover products from triglyceride decomposition. The volatiles from each fraction were passed through an catalyst bed. Results showed that net product yields from the 2-step process were similar to the single step catalytic pyrolysis at 450°C indicating that tailored vapor phase upgrading can be applied to allow separate recovery of products from the chemically distinct biomass components-(1) lower calorific value starch and proteins and (2) energy-dense lipids.
微藻是生物燃料生产中颇具吸引力的原料，由于存在热不稳定成分（脂质、淀粉和蛋白质），特别适合热化学转化。然而，淀粉和蛋白质的热降解会产生水以及其他与能量密集型脂质热解产物混合的含氧化合物和含氮化合物。为了从微藻生物质中生产富含烃类的产品，我们评估了在HZSM - 5沸石催化剂存在下，在450 - 550°C温度范围内对富含脂质的小球藻进行热解和催化热解的情况。结果表明，在热解和催化热解条件下，产物产率和组成相似，主要芳香族产物为苯、甲苯和二甲苯。芳香族化合物的产率随温度升高而增加，在550°C时获得了最高的芳香族产率（36.4% g芳香族化合物/g无灰微藻）和选择性（87% g芳香族化合物/g生物油）。此外，在此温度下，催化热解过程中液体产物中未检测到含氧化合物和含氮化合物。我们还评估了与气相催化提质相结合的两步分级热解方法的可行性。在这些实验中，生物质首先在320°C下热解，以降解和挥发淀粉、蛋白质和游离脂肪酸。然后，残余生物质在450°C下再次热解，以从甘油三酯分解中回收产物。各馏分的挥发物通过一个催化剂床。结果表明，两步法的净产物产率与450°C下单步催化热解相似，这表明可以应用定制的气相提质来分别从化学性质不同的生物质组分（1）低热值的淀粉和蛋白质以及（2）能量密集型脂质中回收产物。
