Effect of organic solvents and acidic catalysts on biodiesel yields from primary sewage sludge, and characterization of fuel properties

Biodiesel is considered the most convenient biofuel, due to its direct use in existing combustion engines; however, its production is not economically optimal due to processes that utilize costly substrates, require high energy expenditure or achieve low biodiesel yields. We used primary sewage sludge for the production of biodiesel and compared yields at different temperatures (40, 50 and 60 °C) and with different organic solvents (chloroform, toluene and hexane), acid catalysts (HCl and H₂SO₄) and catalyst concentrations (3, 5 and 7%). A maximum of 18 wt% biodiesel was obtained using chloroform with 3% H₂SO₄ at 40 °C. The conversion efficiency of the primary sludge to biodiesel under these conditions was 86.4%. Based on the fatty acid methyl ester composition of the obtained biodiesel and measured fuel properties, it was deduced that fuel from primary sludge is more suitable for areas with warmer climates than ones that reach temperatures close to 0 °C. However, the fuel properties of the produced biodiesel were within the limits of accepted international standards. We conclude that production of biodiesel from primary sewage sludge under optimized conditions reduces the impact of the feedstock on the environment, decreases overall costs and produces fuel with acceptable properties.

生物柴油（biodiesel）被认为是最为便捷的生物燃料，因其可直接在现有内燃机中使用；然而其生产并不具备经济最优性，缘由在于现有生产工艺多使用高成本底物、能耗较高，且生物柴油产率偏低。本研究采用原生污水污泥（primary sewage sludge）制备生物柴油，并对比考察了不同温度（40、50与60 ℃）、不同有机溶剂（氯仿（chloroform）、甲苯（toluene）、己烷（hexane））、酸催化剂（acid catalysts，即氯化氢（HCl）与硫酸（H₂SO₄））以及催化剂浓度（3%、5%与7%）条件下的产率差异。在40 ℃、以3%硫酸（H₂SO₄）搭配氯仿的反应体系中，可获得最高达18重量百分比（wt%）的生物柴油产率；在此工况下，原生污水污泥向生物柴油的转化效率可达86.4%。基于所制生物柴油的脂肪酸甲酯（fatty acid methyl ester）组成与实测燃料性能，可推断出原生污水污泥制备的燃料更适配气候温暖的地区，而非温度接近0 ℃的低温环境。不过所制生物柴油的各项燃料性能均处于公认的国际标准限值范围内。综上，在优化条件下以原生污水污泥制备生物柴油，可降低原料对环境的负面影响、压缩整体生产成本，并获得性能符合要求的燃料产品。