旋轉填充床真空氣提生質柴油中甲醇

Abstract

在生質柴油快速發展之際，本研究利用旋轉填充床在負壓下進行氣提程序，來處理生質柴油製程中甲醇與生質柴油分離的重要步驟。實際實驗中以甲醇濃度1%、4%、8%之生質柴油進行真空氣提、系統絕對壓力操作於40至120Torr，溫度操作於30至45℃，並以氣提百分比評估氣提效率。結果顯示氣提百分比隨壓力降低與溫度升高而升高。當液體流量由10mL/min增加至100~150mL/min時氣提百分比會有20%以內的下降，但與空氣氣提相比下降程度較不劇烈。在較低壓力、較高溫度與較低進料甲醇濃度實驗，氣提百分比幾乎與液體流量及轉速無關，顯示液體濃度已接近氣液相平衡濃度，故可知在高溫與低壓下，質傳速率較快，而主要原因為質傳驅動力的增加。在較高濃度實驗中，氣提百分比隨轉速的提升而提升的效果更加明顯，以8%甲醇進料濃度實驗為例，轉速由600rpm增加至2400rpm，氣提百分比有10%以上的增加。本實驗中最大氣提百分比在1%甲醇進料濃度實驗為70%，4%進料甲醇濃度實驗為90%而8%進料甲醇濃度實驗為72%。而單以本實驗數據可直接串連兩旋轉填充床進行真空氣提，處理含8%甲醇濃度的生質柴油達到95%或更高的甲醇去除率。 真空氣提時，旋轉填充床內外溫差隨轉速的升高而降低。最大溫差出現於8%進料甲醇濃度實驗，在溫度30℃，壓力80Torr，轉速600rpm下，在旋轉填充床徑向長度為4公分時溫差達到12.6℃。本研究中詳盡記錄不同操作條件下旋轉填充床的內外溫度，除了有助於未來更多旋轉填充床真空氣提程序的開發外，亦對旋轉填充床應用於具有溫度差異的化工程序如蒸餾等基礎研究有所幫助。

This work presented a vacuum stripping process in a rotating packed bed (RPB or HIGEE) to intensify the methanol recovery step in the biodiesel production. The study conducted at system temperatures of 30, 45℃, pressure ranging from 40 to 120Torr, and 1% to 8% of methanol concentration in biodiesel. The stripping ratio increased with increasing temperature and decreasing pressure. Increasing liquid flow rates from 10mL/min to 100~150mL/min lowered stripping ratio by 20% or less. However, the stripping ratio decreased less than that by air stripping. At lower pressure, higher temperature and, the stripping ratio was almost independent of rotor speed and liquid flow rates, which indicated that the liquid concentration was relatively close to equilibrium value. It implied better mass transfer rate, mainly due to higher mass transfer driving force. At the higher methanol concentration, obvious mass transfer intensification was noted with increased rotor speeds. For 8% feed concentration, stripping ratio increased more than 10% when rotor speed increased from 600 to 2400rpm. The highest stripping ratio was 70% for 1% feed concentration, 90% for 4% feed concentration and 72% for 8% feed concentration in our experiments. According to the experimental data, more than 95% stripping efficiency was obtained for 8% feed concentration with two rotating packed bed in series. The temperature difference between inner and outer edge of the RPB decreased as increasing rotor speed in this vacuum stripping process, suggesting both mass transfer and radial direction heat transfer increasing with rotor speed. At 30℃, 80Torr, 600rpm and 8% feed concentration, 12.6℃ temperature difference was observed in a 4cm packing depth RPB. All temperature differences were carefully recorded in this HIGEE system. Hopefully, it would show some light not only for the further study of vacuum stripping processes, but also for the investigation of temperature-sensitive chemical engineering processes in the rotating packed beds.