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Techno-Economic Evaluation of Biodiesel Production from Waste Cooking Oil—A Case Study of Hong Kong
Raffel Patria, Sanjib Karmee, Carol Lin


Published: 18 February 2015 by MDPI in International Journal of Molecular Sciences
MDPI, Volume 16; 10.3390/ijms16034362
Abstract: Fossil fuel shortage is a major challenge worldwide. Therefore, research is currently underway to investigate potential renewable energy sources. Biodiesel is one of the major renewable energy sources that can be obtained from oils and fats by transesterification. However, biodiesel obtained from vegetable oils as feedstock is expensive. Thus, an alternative and inexpensive feedstock such as waste cooking oil (WCO) can be used as feedstock for biodiesel production. In this project, techno-economic analyses were performed on the biodiesel production in Hong Kong using WCO as a feedstock. Three different catalysts such as acid, base, and lipase were evaluated for the biodiesel production from WCO. These economic analyses were then compared to determine the most cost-effective method for the biodiesel production. The internal rate of return (IRR) sensitivity analyses on the WCO price and biodiesel price variation are performed. Acid was found to be the most cost-effective catalyst for the biodiesel production; whereas, lipase was the most expensive catalyst for biodiesel production. In the IRR sensitivity analyses, the acid catalyst can also acquire acceptable IRR despite the variation of the WCO and biodiesel prices.
Keywords: biodiesel, Economic Evaluation, Equipment Costs, Capital Investment Costs, Internal Rate of Return (irr)

Comments on this paper Get comment updates
Soulayman Soulayman
Comments on published article
Karmee, Patria and Lin [1] used in their economic analyses of the biodiesel production from WCO in Hong Kong with acid, base and lipase catalysts the optimum reaction conditions. As reaction conditions for base catalyst production, namely: reaction temperature was 65 °C, molar ratio of oil to methanol was 1:4, reaction time was 6 h, are not optimum but they could be accepted for providing the economic analyses, the reaction conditions for acid catalyst production, namely: reaction temperature was 65 °C, molar ratio of oil to methanol was 1:4, reaction time was 6 h, are not optimum but they could not be accepted for providing the economic analyses. Reaction time for acid catalyst biodiesel production is much longer 48h [2].

The present letter is but to correct conclusions provided in [1].
2. Comments
2.1. First Comment
When applying the production scheme proposed in [2] on WCO using methanol and sulfuric acid, the main results of [2] were obtained. In contrast, following the proposed in [1] biodiesel production conditions using acid catalyst, namely scheme 2 entitled "Biodiesel production process using acid catalyst" and the Table 1 entitled "Operating conditions and simulation results using chemical and enzyme catalysts" in addition to the sentence which determines the reaction time "The reaction time was 6 h for chemical and enzymatic reactions" and to the sentence which determines the methanol/WCO volume ratio "5 wt % of chemical catalysts (acid/base)" the result was negative. So, the optimum conditions for acid catalyst production are those of [2] and not of [1]. As a consequence, the acidic base production conditions mentioned in [1] are underestimated. Moreover, it is mentioned in [1] that "It is assumed in this study that the plant working days are 330 days, the working time is 15 h per day, and two biodiesel batches are produced each day". So, the economic analysis based on non accurate assumptions especially regarding reaction time, biodiesel batches/day and required energy to accomplish the reaction could not lead to conclusions given in [1].

2.2. Second Comment
In [1] it mentioned clearly the used quantity of methanol and hydroxide (see Table 1 entitled "Operating conditions and simulation results using chemical and enzyme catalysts"). From Table 1 in [1] it is easy to calculate methanol/WCO volume ratio and catalyst/WCO weight ratio. These values are 16.16% and 5% wt respectively. When comparing these values with those mentioned in [3] as optimum conditions for basic catalyst biodiesel production from WCO, namely methanol/WCO volume ratio is of 18.17% and catalyst/WCO weight ratio is of 0.4%, it becomes clear that the used in [1] value for catalyst/WCO weight ratio is 12.5 times overestimated. Moreover, optimum reaction temperature is 60 °C and optimum reaction time is 2h. Thus, the used in [1] reaction time is 3 times overestimated. As a consequence, the basic base production conditions mentioned in [1] are overestimated and this fact should be taken into consideration.

2.3. Third Comment
When comparing scheme 2 entitled "Biodiesel production process using acid catalyst" with scheme 1 entitled "Biodiesel production process using base catalyst" provided in [1] the real difference in initial investment is restricted to the WCO pretreatment complex which consists of mixer, pretreatment of WCO and decanter. The base tank drawn in scheme 1 is also required in scheme 2 and indirectly hidden by adding hydroxide to the neutralization process. The mentioned WCO pretreatment complex could be totally removed using the complex of reaction 1 (see scheme 1). So, the real difference in initial investment could be made zero. As a consequence, the results provided in [1] for base and acid catalyst, namely, in Tables 2 & 3 entitled "Total equipment costs (TEC)" and "Capital investment cost (CIC)" respectively become identical.




2.4. Fourth Comment
According to optimum biodiesel production conditions for basic catalyst mentioned in [3], a pilot biodiesel production unit using base catalyst was constructed and exploited. The plant working days are 312 days, the working time is 24 h per day, and 8 biodiesel batches are produced each day. So, the proposed in [1] 2 batches/day is 4 times lower the real possibility. This argument should be considered.
2.4. Fourth Comment
According to the above mentioned comments, the provided data of [1] in Table 4 entitled "Biodiesel production cost (BPC)" should be modified with regard to required correction in items: raw material cost and electricity.

References
1. Karmee, S.K.; Patria, R.D.; Lin, C.S.K. Techno-economic evaluation of biodiesel production from
waste cooking oil—A case study of Hong Kong. Int. J. Mol. Sci. 2015, 16, 4362-4371; doi:10.3390/ijms16034362.
2. Canakci, M.; Van Gerpen, J. Biodiesel production via acid catalysis. Transactions of ASAE 1999, 42(5), 1203-1210; doi: 10.13031/2013.13285.
3. Soulayman, S; Mustafa, F., Hadba, A. Assessment of optimal parameters synthesis of biodiesel from frying oils wastes. ICRE'2012, 15/16 April 2012, University of A. Mira, Bejaia, Algeria.

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