油質性微藻類之培養與固體觸媒在生質柴油製程之應用

Cultivation of oleaginous microalgae and the application of solid catalytic process to biodiesel production

蘇家弘(Chia-Hung Su)

指導教授 ： 吳文騰 ； 朱一民

國立清華大學/工學院/化學工程學系/博士(2007年)

https://doi.org/10.6843/NTHU.2007.00660

摘要

在本研究中，我們主要進行油質性單細胞微藻類之培養系統設計與固體觸媒在生質柴油製程之應用。在藻類培養系統設計方面，由於藻類運動強度正比於藻類的比生長速率（R2=0.82），因此藻類運動強度可做為篩選藻類最適化培養基之指標。此外，藻類在培養過程中顏色的變化（生長期的深綠色至停滯期之黃綠色），被認為與藻體內部成分組成變化有關。根據這項理由，藻類顏色所發生的變化以三原色來進行分析，並與葉綠素與油脂含量作對應可得線性關係式。利用此關係式估計藻類葉綠素或油脂含量之預測值，也以實際實驗驗證其可靠性（判定係數高於0.94）。利用這樣的影像分析可以改善傳統分析方法的不便，進而協助我們快速的瞭解藻類的生理狀態以及決定藻類最佳培養策略。由於藻類生長與油脂累積的機制各自所需的條件相異，因此開發藻類兩階段培養程序以同時符合各自所需的要求。在兩階段培養策略中，第一階段培養提供富含藻類營養成分的培養環境以促進藻類大量的生長；接著再將藻類培養至第二階段培養程序內。由於第二階段為氮源缺乏的培養條件，因此藻類油脂預期會在此階段進行大量的累積。相較於傳統單一階段批次培養，此程序可獲高於2.82倍的油脂產率。
在另一方面，以大豆油做為研究藻類油脂生產生質柴油之基礎，來探討固體觸媒於生質柴油製程之應用。本研究中，先以酵素法將大豆油進行水解反應以獲得脂肪酸。在強酸性陽離子交換樹脂的催化下，水解獲得之脂肪酸與甲醇進行酯化反應生成脂肪酸甲酯。觸媒使用量、反應溫度與醇酸莫耳比對於此酯化反應的影響，也在此做完整探討。此外，以擬均相數學模型來描述此含有固體觸媒之酯化反應行為。此數學模型更進一步的用來預測在轉化率為0.99的要求下，其初始醇酸莫耳比、反應溫度與反應時間分別是14.9、372.15K與9.5小時。這樣預測的結果與實際實驗值進行驗證，其相對誤差小於0.5％。

關鍵字

微藻類 ； 運動強度 ； 三原色 ； 兩階段培養 ； 生質柴油 ； 擬均相動力學模型

並列摘要

The aim of this study was to develop a microalgal cultivation system for intracellular lipid production and a solid catalytic process for biodiesel production. The motile intensity of microalgae, which was strongly related to specific growth rate, was used as the index for selecting a suitable cultivation medium. It was observed that the color of microalgae changed from green in the growth phase to yellow in the stationary phase during cultivation porcesses, mainly due to the changes of the biochemical composition in the microalgae. The color was analyzed by image analysis and an RGB (Red, Green, and Blue) model was developed to correlate the change in color to chlorophyll a and lipid contents of microalgae. The model was used to predict the chlorophyll a and lipid contents of microalgae and the experimental results were well correlated by the model (R2 > 0.94). This colorimetric method was more suitable in monitoring chlorophyll a and lipid contents in the microalgae as compared to the standard analytical methods.
The culture condition for lipid production differs from that of cell growth; it is possible to separate the growth and the production phases into two separate stages. The maximum lipid accumulation occurs under the nitrogen-limited growth. A two-stage cultivation strategy was developed. The microalgae was cultivated in a nitrogen-sufficient phase for cell growth and transferred into a nitrogen-deficient phase to induce the lipid production. The production of lipid obtained from the two-stage process was 2.82-fold higher than that from the traditional single stage cultivation.
Furthermore, a solid catalytic process for converting microalgal lipid into biodiesel was developed by using soybean oil as the source. Fatty acids obtained from enzymatic hydrolysis of soybean oil were esterified with methanol by using strong acidic cation-exchange resin as a heterogeneous catalyst. The kinetic study of esterification was carried out with different levels of catalyst loading, reaction temperature and molar ratio of methanol to fatty acids. The experimental data can be well-correlated by a second order kinetic equation. The kinetic model was used to predict the optimal operating conditions at a fatty acids conversion of 99%. The optimal operating conditions numerically calculated by the kinetic model were found to be reactants molar ratio of 14.9, reaction temperature of 99oC and reaction time of 9.5 h. The predicted results were verified with experimental results and the relative error was less than 0.5%.

並列關鍵字

microalgae ； motile intensity ； primary colors ； two-stage cultivation ； biodiesel ； pseudo-homogeneous kinetic model

參考文獻

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