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Journal ArticleDOI

Study of an ethylic biodiesel integrated process: Raw-materials, reaction optimization and purification methods

01 Aug 2014-Fuel Processing Technology (Elsevier)-Vol. 124, pp 198-205

Abstract: No studies are reported on ethylic biodiesel integrated processes, considering raw materials, reaction optimization and product purification. The present study aims to: i) select key variables for experimental optimization of ethanolysis using a virgin vegetable oil; ii) perform an optimization study using a waste oil; and iii) evaluate the effectiveness of water free purification methods. Sunflower oil ethanolysis was conducted at different temperatures (30 – 80 °C), catalyst concentrations (0.3 – 2 wt.%), reaction times (0.5 – 4 h) and ethanol: oil molar ratios (2:1 – 12:1). Optimization experiments on waste oil ethanolysis were performed at different temperatures (30 – 50 °C) and ethanol: oil molar ratios (6:1 – 12:1), during 1 h and using 1 wt.% catalyst. Quality parameters were measured according to EN 14214. A cation-exchange resin and a ceramic membrane were evaluated for water-free purification. Regarding sunflower oil ethanolysis, when successful, conversion ranged from 75.2 to 97.7 wt.%. Using both oils under optimized conditions (45 °C, 6:1 ethanol:oil molar ratio), a product with a very high purity (> 98.0 wt.%) was obtained after water washing purification. The 0.1 μm ceramic membrane was more effective than the cation-exchange resin, but it was not possible to obtain a good quality product using both methods.
Topics: Waste oil (59%), Vegetable oil (58%), Biodiesel (55%), Sunflower oil (55%), EN 14214 (51%)

Summary (3 min read)

1. Introduction

  • In agreement with what was previously stated, the present study aims to: i) select key variables for experimental optimization of ethanolysis reaction using a virgin vegetable oil; ii) perform an optimization study on ethanolysis, by varying reaction conditions, using a waste oil as raw material; and, iii) evaluate the effectiveness of currently proposed water free methods for biodiesel purification, obtained from waste oil or refined oil.

2.1. Materials

  • The most relevant reagents used during synthesis, purification and quality evaluation procedures were: ethanol absolute (P.A, Panreac), sodium hydroxide powder 98 % (Sigma-, Reagent Grade), heptane (analytical grade, ), ethyl pentadecanoate , sodium standard for AAS (TraceCERT ® , 1000 mg/L Na in nitric acid, FLUKA) and CombiCoulomat frit Karl Fischer reagent for the coulometric water determination for cells with diaphragm .

2.2.2. Dry purification processes

  • Regarding the ceramic membrane separation system, 250 mL of crude biodiesel was poured into a feed vessel and cross-filtered once by the membrane ceramic tube, using a peristaltic pump at 6.25 L h -1 (Aspen, Standard model).

2.2.3. Evaluation of raw materials and biodiesel quality

  • After, the solid was treated with 5 mL of nitric acid and heated at 200 ºC until reduced to 200 µL.
  • Finally, 5 mL of nitric acid were added and this solution was diluted with distilled water up to 50 mL, for further analysis.

3.1 Raw materials

  • In the present work, a sunflower oil (acid value of 0.19 mg KOH g -1 ; water content of 0.06 wt.%; composition: C16:0 = 5.5 wt.%, C18:0 = 3.6 wt.%; C18:1=35.2 wt.%; C18:2 = 54.2 wt.%; others = 1.5 wt.%)) and a pre-treated waste frying oil (acid value of 0.62 mg KOH g -1 , water content of 0.07 wt.% ; composition: C16:0 = 7.3 wt.%, C18:0 = 3.8 10 wt.%; C18:1= 29.1 wt.%; C18:2 = 58.5 wt.%; others  1.2 wt.%)) were used as raw materials.
  • The virgin oil presents the characteristics required to be used for food purposes and it was used as reference oil for preliminary experiments and for comparison with the results obtained with the waste oil.
  • The characteristics of both oils agree with the range of values reported in the literature and reference books [3, 10, 22] .

3.2 Preliminary experiments

  • The reaction conditions were established taking into account a literature review, namely considering the review by Brunschwig et al. [17] that evaluates bioethanol use for biodiesel production.
  • Taking into account the great amount of work on ethanolysis conducted at 80 C, initially, experiments were conducted at that temperature and by varying the ethanol:oil molar ratio, the catalyst concentration and the reaction time.

Results are presented in Table 1 (exp. 1 -6).

  • It can be seen that using a lower ethanol to oil molar ratio, of 7:1 (experiments 1 -4), independently of the catalyst concentration and reaction time, there was no phase separation, reason why such conditions were considered to be inefficient; also, using 2.0 wt.% of catalyst, a great amount of soap was observed.
  • Using this oil, such molar ratio, and at a catalyst concentration of 1 wt.%, immediate soap production occurred which impaired the reaction (experiment 10).
  • The best preliminary reaction conditions, that led to a product conversion of 97.7 wt.% were found after 1 h of reaction using 1 wt.% of catalyst (experiment 14).
  • The ethyl ester content of waste frying oil biodiesel (WFOB) is very close to the one obtained with the SFOB, meaning that the reaction time of 1 h is also adequate for the conversion of this oil.
  • Since the European Standard is based on rapeseed oil, it makes sense the differences found, that agree with studies on the use of such type of oil [3] ; the iodine value of the WFOB shows similar degree of unsaturation.

3.2 Optimization experiments

  • Taking into account the results obtained during preliminary studies and also that the use of high alcohol:oil molar ratios in the transesterification reaction is known to significantly increase separation and purification costs [20] , the optimized conditions were selected as 45 ºC and 6:1 ethanol to oil molar ratio.

3.3 Evaluation of purification methods

  • On the other hand, the ceramic membrane seemed to retain the fatty acids [20] allowing the reduction of this parameter to acceptable values.
  • The raw materials water content was between 600 and 700 ppm (section 3.1) and although the resin selectively absorbs hydrophilic components, the membrane did not retain the water molecules and did not enable a low water content of the product.
  • As previously stated, the final purity obtained was lower than that obtained with the water washing method.
  • Finally, although these methods are referred to as effective for catalyst removal [20, 21, 25] , to confirm the efficiency towards sodium removal, sodium was measured in the water washed product as well as in the product purified with the water free methods, when the virgin oil was used as raw material.
  • Better results might be achieved by optimization studies, since membrane separation efficiency depends upon conditions such as temperature, transmembrane pressure and flow [19] .

Conclusions

  • The present work allowed the study of an integrated biodiesel production process through ethanolic route, using virgin and waste oil as raw materials.
  • The preliminary results on ethanolic biodiesel production using sunflower oil showed the importance of optimizing reaction conditions and the difficulties and complexity of this process.
  • Taking into account the results from preliminary and optimization experiments, the best conditions were selected as: reaction temperature of 45 ºC and 6:1 ethanol:oil molar ratio (considering 1.0 wt.% of catalyst and 1 h of reaction).
  • Under such conditions, a good quality product could generally be obtained after water washing, using both the virgin and the waste oil.
  • Under the conditions studied for water-free processes, better results were obtained using the 0.1 m ceramic membrane compared with the cation-exchange resin; the major problems related with the lower product purity, compared to the water washing product; the acid value in the case of the resin and the sodium content in both methods (although with the membrane a much higher metal removal was achieved) ,which did not allow obtaining a good final quality of the product.

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Content maybe subject to copyright    Report

1
This article was published in Fuel Processing Technology, 124, 198-205, 2014
1
http://dx.doi.org/10.1016/j.fuproc.2014.02.026
2
3
Study of an Ethylic Biodiesel Integrated Process: Raw-materials,
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Reaction Optimization and Purification Methods.
5
6
Dias, J. M.
a,
*, Santos, E.
a
, Santo, F.
a
, Carvalho, F.
a
, Ferraz, M. C. M.,
b
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Almeida, M. F.
a
8
9
LEPABE, Faculdade de Engenharia, Universidade do Porto, R. Dr. Roberto Frias, 4200-465, Porto,
10
Portugal
11
a
Departamento de Engenharia Metalúrgica e de Materiais
12
b
Departamento de Engenharia Química
13
* Corresponding author. Tel.: +351 22 5081422; Fax: +351 22 5081447. E-mail address: jmdias@fe.up.pt
14
15

2
Abstract
16
Up to date, no studies exist on integrated processes for ethylic biodiesel production,
17
focusing on raw materials (including wastes), reaction optimization and product
18
purification (using water-free methods). Therefore, the present study aims to: i) select
19
key variables for experimental optimization of ethanolysis reaction using a virgin
20
vegetable oil; ii) perform an optimization study on ethanolysis using a waste oil as raw
21
material; and iii) evaluate the effectiveness of currently proposed water free methods for
22
product purification using the waste and refined oils as raw materials. Preliminary
23
experiments on sunflower oil ethanolysis were conducted at different temperatures (30
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80 ºC), catalyst concentrations (0.3 2 wt.%), reaction times (0.5 4 h) and ethanol to
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oil molar ratios (2:1 12:1). Optimization experiments on waste oil ethanolysis were
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further performed by varying the temperature (30 50 ºC) and the ethanol to oil molar
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ratio (6:1 12:1), during 1 h and using 1 wt.% catalyst. Several quality parameters were
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measured in the products (considering EN 14214). A cation-exchange resin and a
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ceramic membrane were evaluated as alternative purification agents. Preliminary studies
30
reflected the difficulties on performing ethanolysis; when successfully conducted,
31
conversion ranged from 75.2 97.7 wt.%. Using both oils under optimized conditions
32
(45 ºC and 6:1 ethanol:oil molar ratio), a product with a very high purity (> 98.0 wt.%)
33
could be obtained after water washing purification. Better purification results were
34
obtained using the 0.1 m ceramic membrane compared to the cation-exchange resin,
35
but it was not possible to obtain a good quality product under the studied conditions
36
using both water-free processes.
37
38
39
Keywords: Ethanolysis; Waste oil; Optimization; Ceramic membrane; Resin.
40

3
1. Introduction
41
Biodiesel is being studied since several years as a renewable and environment-friendly
42
alternative to fossil diesel [1, 2]. Chemically, biodiesel is a mono-alkyl ester obtained
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through a transesterification reaction, by which more complex triglyceride molecules are
44
converted into smaller molecules of fatty acid esters (biodiesel), that present physical and
45
chemical characteristics similar to fossil diesel [3]. Vegetable food oils, such as soybean
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oil, rapeseed oil, palm oil and sunflower oil are used in more than 95 % of biodiesel
47
production plants throughout the world [4]. The transesterification reaction is reversible
48
and involves three steps to convert the initial triglyceride into a mixture of biodiesel and
49
the by-product glycerol (according to stoichiometry, roughly 1 kg of biodiesel and 0.1 kg
50
of glycerol per 1 kg of oil). The technology employed by most industries dedicated to
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biodiesel production consists of a methanolic route for the reaction, catalysed by a
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homogeneous alkali reagent (e.g. NaOH, KOH, CH
3
ONa, CH
3
OK) [3, 5].
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To contribute for a sustainable biodiesel production, there are two fundamental aspects:
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raw material diversification and process optimization. These aspects should be studied
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not only aiming the reduction of costs but also to enable the implementation of “greener”
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alternatives, with reduced environmental impacts.
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Virgin vegetable oils might account for up to 95% of the biodiesel production costs [6];
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therefore, raw-material diversification might have significant impact on improving the
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economic viability of the process. In order to do that, animal fats might be used [7]; in
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addition, when possible, waste streams, namely from the food processing industry and
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domestic activities, should be recycled for biodiesel production [7-9]. By using wastes as
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resources, both the energetic and the waste management problems might be mitigated.
63

4
Among the research work which considers the improvement of current production
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processes, heterogeneous catalysts appear as a very valid contribute, although catalytic
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activity, leaching and reusability issues still need further developments [10, 11].
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Another very relevant subject is the alcohol used; the problems associated with the
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hazardous nature of methanol, used in most of the industrial plants, and its non-
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renewable origin (almost 100% is fossil derived) motivated the research towards the use
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of an ethanolic route, since ethanol might be easily produced from renewable resources
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and presents very low toxicity [12], which makes the overall biodiesel production
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process greener. Although the price of ethanol is higher than that of methanol [12], this
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alcohol presents much higher solubility in vegetable oils and its extra carbon slightly
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increases the energy content of the fuel [13]. The higher cost of ethanol results mostly
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from the fact that it derives from the conversion of biomass, and, currently, essentially
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from food and animal feed crops (e.g. corn and sugarcane) that have great implications
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on the production cost [14]. The production of bioethanol from cellulosic biomass
77
resources has potential to lower the bioethanol production costs [15], although the
78
complexity of cellulosic ethanol production (the difficulties in breaking down such
79
materials, due to the plant cell wall structure) also increases associated costs. Research
80
is still ongoing regarding the production of engineering improved energy feedstocks and
81
other potentially alternative feedstocks for bioethanol production [14]. In the future,
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biomethanol produced from biomass might also be used [16], but extensive research is
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still required to make this alternative economically viable. The ethanolic route is in fact
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more promising; however, the process is much more sensitive and it still needs to be
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optimized, namely regarding reaction conditions and product separation constraints, to
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be competitive with the methanolic route [17].
87

5
Finally, biodiesel purification is also a major issue, even when using heterogeneous
88
catalysts [10, 18]. Conventional purification process includes water washing to remove
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the alcohol (usually used in excess), and residual glycerol, soaps and catalyst [19]. After
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washing, the remaining water in biodiesel is evaporated, usually using vacuum flash
91
processes. Water washing of biodiesel is generally implemented because it allows
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fulfilling the stringent biodiesel standards such as EN 14214 and ASTM D6751;
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however, it leads to the production of wastewater that requires further treatment,
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causing significant economic and environmental impacts [20]. In addition, this process
95
is responsible for high energy and time consumptions and also for low biodiesel yields
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(there is always product loss during washing stages) [6, 16]. No data could be found
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regarding the quantification of the operational costs of biodiesel purification.
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It is known that an effective biodiesel separation and purification is crucial, because
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impurities resulting from ineffective processes can cause operational problems during
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engine functioning, such as filter plugging, injector coking, additional carbon deposits,
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remarkable engine wear, among others [16]. Therefore, purification technologies to be
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developed must be effective and without risks of causing the mentioned problems.
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Alternative water-free purification processes have been developed, employing the use of
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different materials such as absorbents (e.g. ®magnesol), adsorbents (e.g. activated
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carbon), solvents (e.g. ether), resins (e.g. Purolite®) and membranes (organic or
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inorganic) [16].From the existing processes, dedicated ion exchange resins are being
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highly promoted for biodiesel purification. For instances, Purolite® (PD206) is a
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commercial cation-exchange resin, manufactured to purify biodiesel with the purpose of
109
removing residual catalyst, water and other impurities, being however known for acting
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mostly as an adsorbent [18, 20]. The use of membranes on the treatment of organic
111
solutions is emerging. Taking into account biodiesel purification, inorganic, ceramic
112

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