| WO/2011/117474 | METHOD OF UTILIZING TALL OIL PITCH |
| WO/2009/067779 | VAPOUR PHASE ESTERIFICATION OF FREE FATTY ACIDS |
| JP2005015562 | METHOD FOR PRODUCING FATTY ACID ALKYL ESTER |
RAMOS LUIZ PEREIRA
CORDEIRO CLAUDINEY SOARES
WYPYCH FERNANDO
RAMOS LUIZ PEREIRA
CORDEIRO CLAUDINEY SOARES
| WO2006006033A1 | 2006-01-19 |
| EP0070492A2 | 1983-01-26 | |||
| EP0037172A2 | 1981-10-07 | |||
| GB573202A | 1945-11-09 | |||
| EP1092703A1 | 2001-04-18 |
| PATENT CLAIMS 1- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, characterized by the use of layered metal carboxylates whose general formulae is My+(carboxylate)y.zH2O, where My+ is a metal cation (Zn, Mn, Fe, Co, Ni, Cu, Al, Sn), "carboxylate" is an anion derived from saturated or unsaturated fatty acids with a hydrocarbon chain length varying from n = 8 to n = 22 and "z" is variable. 2- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIM 1 , characterized by the production of fatty esters by esterjfication of free fatty acids derived from vegetable oils (soybeans, babassu, peanuts, corn, Jatropha sp., palm, sunflower, among others), animal fat (|ard, tallow, fish and' chicken fat, among others) and waste oils (used frying oil, rendered materials, sewage oils/fats, among others). 3- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 AND 2, characterized by the use of a catalyst derived from the neutralization of a alkaline ethanolic solution containing the fatty acid of interest with an aqueous solution of a water-soluble salt containing the cation of interest, for the subsequent precipitation of the freshly synthesized metal carboxylate. 4- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL r CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 3, characterized by the use of a catalyst that is generated in situ by adding to the reaction media a layered hydroxide salt, a layered double hydroxide or an inorganic salt containing the cation of interest. 5- PROCESSO DE OBTENQAO DE ESTERES DE ACIDOS GRAXOS POR CATALISE HETEROGENEA EMPREGANDO CARBOXILATOS METALICOS LAMELARES, ACCORDING TO PATENT CLAIMS 1 TO 4, characterized by the possibility of recycling and/or reusing the solid catalyst quantitatively after extensive washing with organic solvents (to eliminate adsorbates from the surface of the catalyst) and drying and/or activation by a suitable thermal treatment. / 6- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS I LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 5, characterized by the esterification of free fatty acids present in oils and fats of high acid number. 7- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED , METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 6, characterized by the use of primary alcohols such as methanol and ethanol as the esterification agents whenever the production of fatty esters is associated with their use as diesel fuels (biodiesel). 8- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 7, characterized by esterification reactions that are carried out within the 40 to 1800C temperature range. 9- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 8, characterized by esterification reactions in which the concentration of the solid catalyst ranges from 1 to 20 wt% (dry basis) in relation to the dry mass of the fatty material used for conversion. 10- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 9, characterized by esterification reactions that are carried out for 2 to 12 hours in batch or fed-batch reactors, pressurized or not. 11- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO . PATENT CLAIMS 1 TO 9, characterized by esterification reactions ifi (wh'ich the alcohohfatty acid molar ratio ranges from 1 :1 to 1 :60. > 12- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 9, characterized by reactions in which methanol and ethanol are used for esterification, either anhydrous or containing up to 10 vol% of water in their composition. 13- PROCESS FOR OBTAINING FATTY ACID ALKYL ESTERS BY ESTERIFICATION USING HETEROGENEOUS LAYERED METAL CARBOXYLATES AS THE REACTION CATALYST, ACCORDING TO PATENT CLAIMS 1 TO 12, characterized by situations in which the solid catalyst is immobilized in a porous material of high mechanical properties for application in fixed bed or fluidized bed reactors with continuous operation. |
CARBOXYLATES
The present invention is referred to the process whereby fatty esters are produced from free fatty acids employing layered metallic carboxylates as reaction catalysts, whose general formulae is M y+ (carboxylate) y .zH 2 O, where M y+ is a metal cation (Zn, Mn, Fe, Co, Ni, Cu, Al, Sn) and "carboxylate" is one anion derived from saturated or unsaturated free fatty acids, with the latter being derived from renewable lipid sources such as vegetable oils or animal fats. The hydrocarbon chain length of the free fatty acids may vary from n = 8 to n = 22 and "z" is variable. The catalysts are water insoluble salts of synthetic origin that can be derived from the, chemical precipitation of a free fatty acid by neutralization with an alcoholic solution of an inorganic salt containing the metal of interest, or synthesized in situ by adding a layered hydroxide salt, a layered double hydroxide or a proper inorganic salt, containing the cation of interest, into the reaction environment were the esterification is supposed to occur. Freshly synthesized materials, prepared by chemical precipitation, must be utilized as is and/or after thermal treatment at temperatures between 50 and 150 0 C to promote its dehydration. The catalyst or catalyst precursors are added to a reaction medium containing free fatty acids (of either animal or vegetal origin) and the alcohol (a mono- alcohol or a poli-alcohol), in variable mass ratios, proportions or quantities. These reactions can be performed in agitated reaction vessels, pressurized ,όr not, under conditions that must be optimized for the different lipid sources that are considered for conversion. The proposed catalysts can be recycled quantitatively, after washing with organic solvents and drying and/or activation by thermal treatment. Under special circumstances, the catalysts may be also recycled and reused without purification or pre-activation immediately after recovery from the reaction environment. The process consists on the esterification of free fatty acids with mono-alcohols or poly-alcohols with the purpose of obtaining fatty esters. The catalyst can be used for biodiesel production, which is traditionally based on the transesterification of oils and fats using homogeneous base catalysts (for transesterification) and homogeneous acid catalysts (for both). These processes not only complicate the separation of reaction co-products (fatty esters and glycerin) but also require several operational uni.ts, particularly those related to the washing stages for the removal of impurities including the catalyst itself. By utilizing the catalysts proposed in this patent, phase separation will occur immediately after removal of the excess alcohol and the catalyst will be amenable to recycling after a simple filtration and/or centrifugation of the reaction media. Another advantage of the proposed catalytic system is the possibility of fluidizing the catalyst to boost the reaction kinetics and increase the reaction efficiency. Also, these catalysts will be suitable for biodiesel production in fixed bed reactors after .immobilization in porous matrices of good mechanical properties. The development of continuous processes is hardly achievable when traditional homogeneous catalysts are used for biodiesel production. Finally, the catalyst may be applied in the esterification of free fatty acids with glycerol to produce tailor-made mono-, di- and triacylglycerols. Example 1: Synthesis of the catalyst in vitro Layered carboxylates of divalent and trivalent metals, insoluble within the reaction media used for fatty acid esterification, can be synthesized by chemical precipitation in many different ways, using different free fatty acids and metal components. Synthesis is carried out by neutralization of the fatty acids with an alcoholic solution of an hydroxide, which is reacted with an inorganic salt that contains the cation of interest. The present example refers to the synthesis of zinc laurate, which can b,e, obtained by neutralizing lauric acid with an ethanojic solution of sodium hydroxide, under stoichiometric ratio, followed by addition of an aqueous solution of zinc chloride, also under stoichiometric ratio, for the precipitation of zinc laurate. The solid thus obtained is washed thoroughly with ethanol and water and dried in oven until constant weight. Example 2: Synthesis of the catalyst in situ
Layered carboxylates of divalent and trivalent metals can be synthesized within the reaction media (synthesis in situ) by adding a solid precursor, which might be a layered hydroxide salt (LHS), a layered double hydroxide (LDH) or an inorganic salt containing the cation of interest. Therefore, the synthesis of the catalyst is carried out simultaneously to the synthesis of fatty esters, which facilitates the whole process by condensing two process steps in a single experimental procedure,, In this example, the reactions were carried out in a pressurized reaction vessel (Bϋchiglass,, mbάei.miniclave drive), with 100 mL of total capacity and provided with mechanjcal agitation. The amount i of the catalyst precursor used in each experiment corresponded to 2 wt% in gelation to the oil mass present in the reaction media. In a typical experimental procedure, the fatty material, the acylating agent (alcohol) and the catalyst precursor were transferred to the reaction vessel and, after reaching thermal equilibrium at the desired reaction temperature (c.a. 40 min), the mixture was kept under agitation for 2 h. The pressure inside the reaction chamber, in all experiments described in this patent, corresponded to the vapor pressure of the most volatile reaction component (short chain alcohol). Also, mechanical agitation was routinely fixed at 500 rpm. Immediately after reaching the desired reaction time, the agitation was stopped and the mixture was cooled down to room temperature in approximately 40 min. Separation of the catalyst froiin the reaction media was achieved by filtration, followed by distillation at reduced pressure to eliminate the 75 excess alcohol and facilitate the purification of the mono-esters. The conditioning of the catalyst for a new reaction cycle, after filtration, was carried out by an extensive washing with an ethanol:hexane (1:1 vol/vol) mixture, followed by oven drying at 7O 0 C until constant weight. Example 3: Characterization of the Catalysts
80 Fourier-transformed infrared spectroscopy (FTIR) and X-ray powder diffraction (XRPD) were used to characterize the layered catalysts before and after recycling. Results bf these analytical procedures were included in this example for several metal carboxylates such as zinc laurate (ZL), zinc stearate (ZS) and zinc oleate (ZO), all of them synthesized according to the "Examples 1 and 2" of the experimental protocols.
• 85 The characterization by FTIR was carried out in a Bomem Michelson MB100 apparatus. Potassium bromide (KBr) disks were prepared after mixing anhydrous KBr with 1 wt% of the test specimen and pressing at 8 tons. Analyses were performed at the transmission mode in the 4000 to 400 cm '1 wavenumber range with a resolution of 2 cm "1 and 16 scans (Drawing 1). The XRPD results were obtained in a Shimadzu
90 XRD-6000 apparatus with CuKa radiation (λ = 0.15418 nm) at 40 kV, 30 mA and 1°/min from 4 to 60 of 2Θ (°) (Drawing 2). The first sample (ZL1) 1 was synthesized in vitro as described in "Example 1 " and the second sample (ZL2) was synthesized in situ (or inside the pressurized reaction vessel) from Zn(NOa) 2 -SH 2 O, according to the procedure described in "Example 2". The reaction was carried out at 100 0 C for 2 h with
95 a mefhanohlauric acid molar ratio of 6:1. Samples ZL3, ZL4 and ZL5 were obtained under the same conditions described for ZL2 from the layered hydroxide salt (LHS) Zn 5 (OH) 8 (NOa) 2 ^H 2 O and the layered double hydroxides (LDH) ZnAI-CI and Zn 3 AI- NO 3 , respectively. In all cases, the solid was recovered after the reaction was completed and treated as described in "Example 2". The Drawing 1 displays the FTIR00 spectra of the above mentioned samples, in which a band at 2953 cm "1 was observed and attributed to the asymmetric axial deformation of C-H bonds in methyl groups. The symmetric deformation of this bond, which was expected to appear at 2971 cm "1 , was not observed because this vibration mode in very sensitive to the ^structural rearrangements of the fatty acid alkyl groups and is usually shifted to higher05 frequencies with the an increase in the conformational disorder of the hydrocarbon chains. Both asymmetric and symmetric axial deformations of C=O bonds in carboxylate anions are observed at 1541 and 1397 cm '1 , respectively, while bands located at 1463 and 722 cm "1 are attributable to the angular deformations of C-H bonds in methylenic carbon atoms. The Drawing 1 also presents the FTIR spectra of10 zinc stearate (ZS) and zinc oleate (ZO). Both samples were obtained under the same conditions used for ZL2 but, in these cases, the lauric acid was replaced, respectively, by stearic acid and oleic acid. The same interpretation shown above for the FTIR spectra of ZL are also valid for ZS and ZO. The XRPD data displayed in this example are related to the ZL produced in vitro by chemical precipitation (Example 1) or
115 synthesized in situ from solid precursors such as inorganic salts (zinc chloride), LDHs (Zn 3 AI-NO 3 and ZnAI-CI) and LHS (Zn 8 (OH) 5 (NO 3 ) 2 .2H 2 O) (Example 2). The X-ray diffraction pattern of the solids prepared from these different precursors are practically identical, all of them showing a constant basal spacing of 29.3 A (Drawing 2), which is consistent with the intercalation of laurate anions within the resulting layered structure.
120 Therefore, the equivalence among the FTIR and XRPD data of freshly synthesized ZL (ZL1), as well as all solids derived from the LDHs Zn 3 Af-NO 3 and ZnAI-CI and the LHS Zn 8 (OH) 5 (NO 3 ) 2 .2H 2 O, was an unquestionable demonstrationi that ' ZL was synthesized in situ and probably acted as the real catalyst in this reaction system. Example 4: Synthesis of the Fatty Acid Monoesters
125 As discussed in "Examples 2 and 3", the synthesis of the solid catalyst (in this case, zinc laurate or ZL) occurs in situ, that is, simultaneously with the synthesis of the fatty acid monoesters. Therefore, the general procedure for the synthesis of the latter was basically the same as described in "Example 2". Example 5: Characterization of the Fatty Acid Monoesters
130 The fatty acid monoesters were analyzed for their acid number using the AOCS Ca-5a- 40 method and further characterized by high performance liquid chromatography (HPLC) in a Shimadzu LC10AD HPLC system, using a Waters Spherisorb÷C18 (4.6 x 250 mm, 5 μm) reverse phase column at 4O 0 C under isocratic elution with acetonitrrle:aceton (9:1 , Carlo Erba) at 1 mL/min. The HPLC system was controlled and the data was
135 treated with the CLASS 10 Shimadzu software package. Example 6: Esterification of Laurie Acid with Methanol
In "Example 3", zinc laurate (ZL) was shown to be the real reaction catalyst regardless of the procedure used for its synthesis which, as discussed before, could be achieved in vitro by chemical precipitation or in situ by adding inorganic salts like zinc chloride,
140 LDHs like Zn 3 AI-NO 3 and ZnAI-CI, and LHS like Zn 8 (OH) 5 (NO 3 )^H 2 O to the reaction media. Table 1 shows the experimental conditions and the results obtained with the use of this catalyst (ZL) for the esterification of lauric acid with methanol. However, in each of the situations described in Table 1 , ZL was introduced* as , the reaction catalyst in a different way. For instance, experiments LM013 and LM020 were carried out at
145 the same experimental conditions (Table 1), except for the solid inorganic material that was used as the catalyst (ZL) precursor. Results in Table 1 have shown that, for precursors of the LDH family, the use of Zn 3 AI-NO 3 was slightly better than ZnAI-CI, probably due to the higher zinc content of the former in relation to the latter, which is consistent with the generation of a higher amount of ZL in the reaction media. In all
150 experimental conditions described in Table 1 , the ZL catalyst produced in situ displayed the highest catalytic activity at elevated reaction temperatures. This trend can be easily seem from experiments LM015, LM019 and LM018, which were carried out at the same reaction conditions (Table 1) except for the reaction temperature. By contrast, for experiments LM018 and LM035 in Table 1 , an increase from 2:1 to 6:1 in
155 the methanoUauric acid molar ratio resulted in a very slight increase in the reaction efficiency, which was translated into an increase of around 2 points percent in the ester yield of the final product.
Table 1. Esterification of free fatty acids using several layered solid materials (layered double hydroxides and zinc hydroxide nitrate) as zinc carboxylate precursors.
Sample Alcohol Acid M LC J ( 0 C) % % R Acidity Ester
S
LM013 Methanol Laurie 6:1 Zn 3 AI-NO 3 , 100-- 60.38 l 37.54
LM020 Methanol Laurie 6:1 ZnAI-CI 1 IOO 57.95 . 20.16
EM004 Methanol Laurie 6:1 Zn 3 AI-NO 3 140 1.50 -
LM050 Methanol Oleic 6:1 Zn 3 AI-NO 3 140 18.5 -
TM006 ' Methanol Tall Oil 6:1 Zn 3 AI-NO 3 140 8.21 -
TM005 Methanol Tall Oil 6:1 Zn 5 (OH) 8 (NO 3 )2.2H 2 O 120 29.76 -
TM001 Methanol Tall Oil 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H2θ 140 5.21 -
LM015 Methanol Laurie 6:1 Zn 5 (OH) 8 (NO 3 )2.2H 2 O 100 51.90 39.40
LM019 Methanol Laurie 6:1 Zn 5 (OH) 8 (NOs) 2 ^H 2 O 120 38.63 48.05
LM018 Methanol Laurie 6:1 Zn 5 (OH) 8 (NOs) 2 ^H 2 O 140 4.84 87.07
LM035 Methanol Laurie 2:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 140 , 9.64 84.91
;
Anhydrous
LE004 Laurie 6:1 Zn 5 (OH) 8 (NOs) 2 .2H 2 O 140. 14.86 ' 77.17 ethanol f
LE005 Ethanol 95% Laurie 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O '14O 31.34 .
LE002 Ethanol 95% Laurie 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 100 62,14 21.83
LE003 Ethanol 90% Laurie 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 100 74.35 20.61
LE006 • Ethanol 90% Laurie 6:1 Zn 5 (OH) 8 (NOs) 2 .2H 2 O 140 45.39 -
OM08001 Methanol Oleic 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 100 43.58 -
OM08002 Methanol Oleic 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 120 11.8 -
OM08003 Methanol Oleic 6:1 Zn 5 (OH) 8 (NOs) 2 .2H 2 O 140 4.52 -
EM001 Methanol Stearic 6:1 Zn 5 (OH) 8 (NOs) 2 .2H 2 O 100 64.63 -
EM003 Methanol Stearic 6:1 Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O 120 15.16 -
Example 7: Esterification of Stearic Acid with Methanol
Zinc stearate (ZS) was obtained using LDHs and Zn 8 (OH) 5 (NO 3 ) 2 .2H 2 O as the solid precursors. Formation of ZS in the reaction media was demonstrated by FTIR and
165 XRD in Drawings 1 and 2. Table 1 shows the experimental conditions and the results obtained with the use of this catalyst (ZS) for the esterification of stearic acid with methanol. Likewise ZL, the catalytic activity of ZS increased considerably! with the reaction temperature. For instance, at 140 0 C in experiment EM002, the resulting material (methyl stearate) contained only 0.75% of the unreacted free fatty acid.
170 Example 8: Esterification of Oleic Acid with Methanol
Zinc oleate (ZO) was obtained using LDHs like Zn 3 AI-NO 3 and LHS like Zn 8 (OH) 5 (Nθ 3 ) 2 .2H 2 O as the solid precursors. Formation of ZO in the reaction media was demonstrated by FTIR and XRPD in Drawings 1 and 2. Table 1 shows the experimental conditions and the results obtained with the use of this catalyst (ZO) for
175 the esterification of oleic acid with methanol. Likewise ZL and ZS, the catalytic activity of ZO increased considerably with the reaction temperature as seem in experiments OM08001 , 8002 e 8003, respectively (table 1).
Example 9: Esterification of Tall Oil Fatty Acids with Methanol .
Esterification experiments were also carried out with tall oil fatty acids (TOFA), a
180 complex mixture of free fatty acids that is derived from a by-product (tall oil) of the kraft pulping industry. In this case, Zn 3 AI-NO 3 and Zn 8 (OH) 5 (NO 3 ) 2 .2H 2 O were used as zinc carboxylate precursors. Due to the chemical composition of the starting material (TOFA), a mixture of different zinc carboxylates was obtained as a result of this chemical reaction, including both saturated and unsaturated free fatty acids of different
185 chain lengths. When the reaction was carried out at 140 0 C for 2 h, using a methanohTOFA molar ratio of 6:1 and 2 wt% of the catalyst precursor, the total free fatty acid content of the starting material was reduced to only 5 wt%, as described in experiment TM001 , 005 and 006 in Table 1. However, this reaction was not further optimized, meaning that these yields could be improved 1 upon suitable optimization
190 procedures.
Example 10: Esterification of Laurie Acid with Ethanol '
Tests were carried out to evaluate the catalytic activity of ZL in the esterification of lauric acid with ethanol. Experiments LM015 and LE003 (Table 1) were carried out at 10O 0 C under the same experimental conditions, except for the chemical nature of the 195 acylating agent (alcohol). Methanol performed as a better acylating agent than ethanol, providing an increase of 12 points percent in the reaction efficiency in relation to the latter. Such behavior is very similar to situations in which homogeneous catalysts are used for esterification. The higher reactivity of methanol in relation to ethanol can also be detracted from experiments LM018 and LE004, which were carried out at 14O 0 C under the same experimental conditions used for experiments LM015 and LE003 (Table 1). At this temperature, the gap between methanol and ethanol was reduced to 10 points percent, suggesting that the lower reactivity of ethanol is minimized when the reaction is carried out at higher temperature ranges. The activity of the catalyst decreased with an increase in the level of ethanol hydration. This was demonstrated in experiments LE004, LE005 and LE006, which were carried out at 14O 0 C under the same reaction conditions except for the type of ethanol used for alcoholysis. However, the activity of the ZL catalyst was not severely compromised by water, with good catalytic performances being obtained when ethanol 90% was used as the esterification agent. The HPLC profiles of samples derived from experiments ' LE002 e LE004 are shown in Drawing 4, where the effect of higher temperatures on ester yields (ethyl laurate) is clearly demonstrated.
Example 11 : Recycling of Zinc Laurate in the Esterification of Laurie Acid with Methanol These experiments were carrried out with zinc laurate (ZL) synthesized in situ from zinc hydroxide nitrate (Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O). Samples of Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O and ZL were initially characterized by thermal analysis (data not shown) to determine the actual amount of zinc present in each one of these layered materials. Based on these results, the amount of solids, recycled from one reaction stage to another, was always calculated on the basis on their zinc content. Table 2 shows the results of ..several consecutive reaction cycles carried out with the same ZL sample as the lauric acid esterification catalyst.
Table 2. Esterification of lauric acid with methanol employing recycled solids: zinc hydroxide nitrate was used in the first reaction cycle (experiment LM015) and the solid catalyst was recycled thereof as zinc laurate (HLZLM series).
Sample MR T ( 0 C) % Acidity
HLZLM002 6:1 100 35.90
HLZLM003 6:1 100 54.28
HLZLM004 6:1 100 58.29
Reactions were always carried out at 10O 0 C for 2 h using a methanoklauric acid MR of 6:1. Experiments HLZLM002, HLZLM003 and HLZLM004 refer to the first three reaction cycles. By comparing experiments LM015 (the first reaction stage in which ZL was synthesized in situ) and HLZLM002 (the first recycling stage), there was an increase in the catalytic activity of the solid catalyst and this was readily attributed to changes in the chemical structure of the solid catalyst. Experiments HLZLM003 and HLZLM004 (second and third recycling stages, respectively), the acidity of the resulting methyl laurate was very similar to the value derived from experiment LM015, demonstrating that ZL could be recycled for at least four reaction cycles.
235 Example 12: Esterification of Laurie Acid with Methanol Using ZL synthesized in vitro
Table 3 also shows the results obtained in the esterification of lauric acid with methanol using ZL synthesized in vitro as the reaction catalyst. In this case, the conversion of lauric acid into methyl laurate was very similar to experiments carried out
240 under the same reaction conditions except for the type of reaction catalyst which, in this case, was ZL synthesized in situ from different solid precursors (Table 1). Reactions were carried out at 100 and 14O 0 C, with a methanoklauric acid/molar ratio of 6:1 and 2 h of reaction time. These results also confirmed that thφ catalytic activity of ZL, regardless of the method of its synthesis {in situ or in vitro), was considerably
245 higher at 14O 0 C (an increase of 40.82 point percent was observed when the temperature was raised in 4O 0 C). As mentioned previously, the results obtained in these experiments were comparable to those derived from reactions in which different solid precursors were used to generate ZL in the reaction media (Table 1). For instance, the final acidity of experiment LZ-M02 (3.42%) is comparable to that of
250 experiment EM004 (1.50%), while the final acidity of experiment LZ-M03 (44.24%) is also comparable to that of LM015 (51.90%).
Table 3. Esterification of lauric acid with methanol employing 7.4 wt% of freshly synthesized zinc laurate as the reaction catalyst.
Sample MR , T ( 0 C) % Acidity ^ i ,
LZ-M02 6:1 140 3.42
LZ-M03 6:1 100 44.24
255 DRAWING'S DESCRIPTION
Drawing 1: FTIR spectra of: (a) freshly synthesized zinc laurate (ZL1); (b) ZL synthesized in situ from Zn(NO 3 ) 2 .6H 2 O (ZL2); (c) ZL synthesized in situ from Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O (ZL3); (d) ZL3 after 3 consecutive reaction cycles (ZL3R); (e) ZL synthesized in situ from ZnAI-CI (ZL4); (f) ZL synthesized in situ from Zn 3 AI-NO 3
260 (ZL5); (g) zinc stearate (ZS) synthesized in situ from Zn 5 (OH) 8 (NOs) 2 ^HaQ; and (h) zinc oleate (ZO) synthesized in situ from Zn 3 AI-NO 3 .
1 I
J Drawing 2: X-ray diffraction patterns of zinc laurate (ZL). (a) ZL 1 as freshly synthesized in lab scale; (b) ZL2 as synthesized in situ from Zn 5 (OH) 8 (NO 3 ) 2 .2H 2 O; (c) ZL4 as synthesized in situ from ZnAI-CI e; (d) ZL5 as synthesized in situ from Zn 3 AI-NO 3 .
Drawing 3: HPLC profile of samples derived from experiments (a) LMOI 5 at 100 0 C and (b) LM018 at 140°C. <
Drawings 4: HPLC profile of samples derived from experiments (a) LE002 at 100 0 C and (b) LE004 at 14O 0 C.