METHOD FOR CATALYTIC CONVERSION OF GLYCERIN INTO PRODUCTS OF HIGH ADDED VALUE, AND USE

Abstract

Disclosed is a catalyst based on synthetic silica, in a heterogeneous catalysis method, to promote the effective conversion of residual glycerin, resulting from the production of biodiesel, into formic acid with high selectivity and stability, in a continuous flow reaction. The conversion of residual glycerin occurs by homogeneous catalysis, by the action of components remaining from the synthesis of biodiesel, with the formation of major compounds, such as formic acid, cyclic ethers and diglycerol, in continuous flow and reflow reactions. The reaction can also be carried out by adding sodium salts in the homogeneous catalytic conversion process of commercial glycerin. The process values the residual glycerin, without the need for purification before its transformation into products with high added value, but of renewable origin, adding more interest and potential.

Claims

1. A method of catalytic conversion of glycerin into high added value products, the method comprising: a) Homogenizing the residual glycerin containing salts and impurities in peroxide solution by means of a static mixer; b) Pumping the solution obtained in a) to a reactor containing silica catalyst inside; c) Leaving the mixture b) in the reactor for a residence time of 2 hours; and d) Collecting the products obtained in c) and separating them by distillation.

2. The method according to claim 1, wherein it comprises the synthesis steps of a pure silica catalyst with a high specific surface area (>1000 m2 g1) and presence of acidic groups, applied in the process of heterogeneous catalysis.

3. The method according to claim 1, wherein it employs 35 to 50% of peroxides as oxidizing agents, such as, but not restricted to, hydrogen peroxide (H.sub.2O.sub.2) and benzoyl peroxide, in the process of homogeneous catalysis.

4. The method according to claim 1, wherein characterized in that the residual glycerin comes from the process of obtaining biodiesel.

5. The method according to claim 1, wherein it promotes the conversion of residual glycerin into formic acid, via heterogeneous catalysis, at a temperature of 100 to 250 C.

6. The method according to claim 5, wherein it promotes the conversion of residual glycerin into formic acid, via heterogeneous catalysis, using a continuous flow reactor, also being used batch or semi-batch reactors.

7. The method according to claim 1, wherein it promotes the conversion of residual glycerin into formic acid and green ethers, via homogeneous catalysis, at a temperature of 100 at 250 C.

8. The method according to claim 7, wherein it promotes the conversion of residual glycerin into formic acid and green ethers, via homogeneous catalysis, using a continuous flow reactor or in a semi-batch system.

9. The method according to claim 1, wherein the conversion of residual glycerin by homogeneous catalysis occurs by the action of components remaining from the synthesis of biodiesel, with the formation of major compounds such as formic acid, cyclic ethers and diglycerol.

10. The method according to claim 1, wherein it promotes the conversion of commercial glycerin into formic acid and green ethers, via homogeneous catalysis, at a temperature of 100 to 250 C.

11. The method according to claim 10, wherein it promotes the conversion of commercial glycerin into formic acid and green ethers, via homogeneous catalysis, using a continuous flow reactor or in a semi-batch system.

12. The method according to claim 1, wherein it adds sodium salts before step a) of homogenization of commercial glycerin with peroxide solution.

13. The method according to claim 12, wherein it employs inorganic or organic salts.

14. (canceled)

15. The method according to claim 13, wherein the inorganic or organic salts are selected from the group consisting of sodium chloride and sodium methylate.

16. The method according to claim 13, wherein the inorganic or organic salts are dissolved in the glycerin, in water, or in methanol.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described in greater detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of its embodiment. The figures are:

[0026] FIG. 1, which represents: Infrared absorption spectrum for the SiO.sub.2 catalyst, a) after pyridine adsorption, and b) corresponds to the result after addition of H.sub.2O.sub.2 and subsequent pyridine adsorption. Raman spectrum for SiO.sub.2 catalyst, c) before the treatment with H.sub.2O.sub.2 and d) corresponds to the result after the treatment with H.sub.2O.sub.2. In the Raman spectra, bands 1, 2 and 3 were attributed to the different SiOSi vibrations and band 4 was attributed to a new bond between the silicon atom and the oxygen deposited by H.sub.2O.sub.2, in vacant sites to SiO.sub.2.

[0027] FIG. 2 represents a general schematic of the continuous flow reactor. The system consists of a loading vessel (1), where the reaction mixture, residual glycerin and peroxide, is added, which is taken to the reactor through a pump (2). Before the reactor inlet, there is a safety valve (3), which helps to control the internal pressure of the reactor. The feed is provided by the lower part of the reactor (4) and in the upper part (5) there are 3 (three) thermocouples (6a, 6b, 6c), which make it possible to control the temperature in the different zones of the reactor. The reactor, which is inside an oven during the entire reaction, is divided into three parts, zone I, filled with an inert material (silicon carbide), is the place for preheating the reagents, zone II, in which a mixture of silicon carbide and catalyst is placed and where the reaction takes place, and zone III, which is also filled with silicon carbide only. On the side of the reactor, at the end of zone III, there is a gas outlet (7), coupled to a condenser (8), which liquefies the reaction products and these are collected in a collection flask (9) throughout the reaction.

[0028] FIG. 3, which represents the glycerol conversion and selectivity data for one of the reaction products using the SiO.sub.2 catalyst. The bars represent the percentages of glycerol conversion and the solid line with squares, the percentages of selectivity for formic acid.

[0029] FIG. 4, which represents the glycerol conversion and selectivity data for the main reaction products. The bars represent the percentages of glycerol conversion, the solid line with squares, the percentages of selectivity for formic acid, the solid line with circles, the percentages of selectivity for diglycerol, and the solid line with triangles, the percentages of selectivity for dioxanes.

[0030] FIG. 5, which illustrates the schematic representation of a reactor in an experimental reflow system, used in residual glycerin conversion reactions. There are identified: outlet of products (a), addition of H.sub.2O.sub.2 (b), condenser (8), magnetic plate (10), volumetric flask (11).

[0031] FIG. 6, which illustrates the conversion data of residual (e) and commercial (f) glycerin, and selectivity for the main reaction products in a reflow system. The bars represent the percentages of glycerol conversion. In (e) and (f), the solid line with squares represents the percentages of selectivity for formic acid, the solid line with circles, the percentages of selectivity for diglycerol, the solid line with triangles, the percentages of selectivity for dioxanes, and the solid line with diamonds, the percentages of selectivity for hydroxypropanone.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention addresses to a method of obtaining compounds of high added value, from residual glycerin, derived from the synthesis of biodiesel, or commercial. The glycerin conversions carried out in this invention occur through two catalytic processes: (i) heterogeneous catalysis, using a synthetic silica catalyst (without the use of metals), with acidic properties and presenting mesopores; (ii) homogeneous catalysis, where the catalyst used constitutes an impurity of the residual glycerin, adding only an oxidizing agent, such as benzoyl peroxide or hydrogen peroxide (H.sub.2O.sub.2).

[0033] The catalytic conversion reactions, object of this invention, were carried out in a continuous flow reactor (fixed-bed reactor, PBR) and in a semi-batch system, at a temperature of 100 to 250 C.

[0034] In flow and semi-batch systems, residual and commercial glycerin were tested. In homogeneous catalysis, the main reaction products in the semi-batch reactor, using residual glycerin, were formic acid and 1-hydroxypropanone. On the other hand, in the reaction using commercial glycerin, diglycerol was obtained as the major product. In PBR, both residual and commercial glycerines were converted into dioxanes (cyclic ethers).

[0035] Still in the case of homogeneous catalysis, it is worthy to highlight that, even in the absence of the catalyst, only in the presence of the oxidizing agent, it is possible, with the method employed in this invention, to promote the conversion of residual and commercial glycerin by the action of remaining components of biodiesel synthesis.

[0036] The reaction is also carried out by adding sodium methylate to convert commercial glycerin. Sodium methylate provides the methoxide anion (proving complementary homogeneous catalytic action) when using commercial glycerin.

[0037] In heterogeneous catalysis, the use of synthetic silica-based catalysts promotes the effective conversion of residual glycerin from biodiesel production into formic acid with high selectivity and stability, in a continuous flow reaction.

[0038] The method described in this invention allows obtaining compounds with high selectivity and the reactions, via heterogeneous or homogeneous catalysis, are performed without the need to use organic solvents, which makes the process less costly and environmentally friendly.

[0039] The catalytic conversion method of glycerin developed in this invention involves the production steps of pure silica catalyst, in the case of heterogeneous catalysis, followed by conversion reactions. In the homogeneous catalysis of residual and/or commercial glycerin, the products formed are formic acid and green ethers (such as diglycerol, cyclic ethers and/or 1-hydroxypropanone), so named because they are derived from residual glycerol from biodiesel synthesis, using 35 to 50% peroxides as oxidizing agents. In heterogeneous catalysis, there is the use of heterogeneous catalyst formed by pure synthetic silica (SiO.sub.2) with high specific surface area (>1000 m.sup.2 g.sup.1) and presence of acidic groups.

[0040] Both reactions take place at a temperature of 100 to 250 C. in a continuous flow reactor and/or in a semi-batch system.

[0041] The present invention can be better understood through the steps highlighted below, which involve the development of the pure silica catalyst and the glycerin conversion reactions via homogeneous and heterogeneous catalysis.

Step 1: Synthesis of pure silica catalyst

[0042] A solution of NaOH and CTAB (Cetyltrimethylammonium bromide) is added to a beaker. In the resulting mixture, a solution of TEOS (Tetraethylortosilicate) is slowly dripped, and the system is left under magnetic stirring. The formation of a white solid is observed, which is filtered under vacuum and washed with distilled water until neutral pH. After filtration and washing, the solid is taken to the oven, subsequently macerated and subjected to a thermal treatment, following a heating ramp.

[0043] The catalyst obtained in Step 1 was subjected to several analyses in order to characterize the material. To determine the acidity, the surface of the compound was subjected to cleaning, at a temperature of 150 C., under N.sub.2 flow and subsequent adsorption of pyridine. The interaction between this basic molecule and the acidic sites of the catalyst is evaluated by the presence of a specific absorption band in the Infrared region, as shown in FIG. 1a, wherein the 1447 cm.sup.1 band is related to the interaction between the pyridine molecule and the Lewis acidic sites. These Lewis acidic sites are associated with the presence of vacant oxygen sites on some silicon atoms.

[0044] The oxidizing character of the catalyst is related to its ability to decompose H.sub.2O.sub.2 and the consequent deposition of an oxygen atom in vacant sites of silicon atoms, or vacant sites of oxygen, as represented in FIG. 1b. The presence of this oxygen atom on the Lewis vacant site was proposed from the analyses of the absorption spectrum in the Infrared region for the sample, after the addition of H.sub.2O.sub.2 and subsequent adsorption of pyridine (FIG. 1b), and the Raman spectrum of the catalyst before the addition (FIG. 1c), and after the addition of H.sub.2O.sub.2 (FIG. 1d). It was observed that the sample, after being in contact with H.sub.2O.sub.2, did not present Lewis acidic sites, indicating a possible occupation of these vacant sites. In addition, after the addition of H.sub.2O.sub.2 to the catalyst, the presence of a band in the Raman was observed, which was attributed to a new bond between the silicon atom and the oxygen (active species) deposited after the decomposition of H.sub.2O.sub.2. The other bands (1, 2 and 3) in the Raman spectra are the same for the material before and after the addition of H.sub.2O.sub.2 and were attributed to the different SiOSi vibrations (FIGS. 1c and 1d).

Step 2: Catalytic Tests for Conversion of Residual Glycerin Using Pure Silica Catalyst: Reactions in Continuous Flow.

[0045] The reactions in continuous flow carried out in this invention occur in a reactor that remains inside an oven throughout the process, as shown in FIG. 2. In the load vessel (1), there is the reaction mixture that is taken to the reactor through a pump (2). The feed is provided by the lower part of the reactor (4) and in the upper part (5) there are 3 (three) thermocouples (6a, 6b, 6c) that allow the control of the temperature in the different zones of the reactor. The reactor is divided into three parts, zone I, which is filled with an inert material, silicon carbide; in zone II, a mixture of silicon carbide and catalyst is placed, and zone III is also filled only with silicon carbide. On the side, at the end of zone III, there is a gas outlet (7), coupled to a condenser (8), which liquefies the reaction products, which are collected in a collection flask (9) during the entire reaction.

[0046] For the reaction in question, zones I and III of the reactor are filled with silicon carbide and zone II is filled with a solid mixture of silicon carbide and catalyst. The reaction mixture consists of a residual glycerine and hydrogen peroxide solution, with a feed flow of 1 mL.Math.min.sup.1 to the reactor.

[0047] At intervals of one hour, the volume and mass of the product formed during this period were determined, with the maximum reaction time in the test corresponding to 8 hours. Collected samples taken during the reaction were analyzed by GC-MS. Conversion and selectivity were determined from a calibration curve.

[0048] The pure silica catalyst, called SiO.sub.2, showed a constant conversion (approximately 90%) during the 8 uninterrupted hours of reaction, suggesting that the catalyst has a high stability in the reaction of conversion of residual glycerin. In addition, the SiO.sub.2 catalyst was able to promote the conversion of glycerol with high selectivity to formic acid (approximately 80%) during the entire time studied, as can be seen in FIG. 3.

[0049] Since formic acid is an oxidative cleavage product of glycerol, the catalyst in question is capable of promoting dehydration and oxidation of the glycerol molecule.

Step 3: Catalytic Tests for Conversion of Residual Glycerin Via Homogeneous Catalysis

[0050] The transesterification of triglycerides for the production of biodiesel generates as a co-product a glycerin that undergoes a neutralization process, giving rise to the blond or residual glycerin exported by the biodiesel production units, which is the main component of the reactions of the present invention. The impurities present in residual glycerin, in the presence of an oxidizing agent such as H.sub.2O.sub.2, are capable of converting the same into products of commercial interest, via homogeneous catalysis. This result was observed using only residual glycerin and H.sub.2O.sub.2, in a continuous flow system. The reaction was carried out in a continuous flow reactor described in Step 2.

[0051] Products such as formic acid, diglycerol and dioxanes were identified in the GC-MS as products of this reaction and their respective selectivities are shown in FIG. 4.

[0052] Dioxanes are the major products of this reaction and are compounds that can be used as additives in biodiesel formulation, improving its properties at low temperatures and reducing its viscosity. Then, the formation of formic acid is observed, which is a product of the oxidation of glycerol and stands out for its wide application in the textile, agricultural, pharmaceutical and chemical industries. Currently, formic acid is used as a hydrogen storage compound, since it can be decomposed into hydrogen and CO.sub.2. In lower concentration, diglycerol can be observed as a product of the reaction. Diglycerol is formed due to the etherification of glycerol and has numerous applications in the food, pharmaceutical and cosmetics industries.

[0053] Reflow reactions were employed to study reactions in a semi-batch system. Furthermore, these reactions allowed us to understand the formation mechanism of its main products. The reactions at reflow were carried out according to the system shown in FIG. 5.

[0054] The reaction mixture consisted of residual or commercial glycerin and H.sub.2O.sub.2 solution. The reactions took place at 150 C. for 3 hours and, every 30 minutes, aliquots of the sample were taken and taken for analysis in the GC-MS. The results are shown in FIG. 6.

[0055] In a system at reflow, the conversion of residual glycerin presents as main products formic acid, hydroxypropanone and dioxanes, as observed in FIG. 6a. Diglycerol is only formed at the end of the reaction, after 160 minutes. The relative selectivity for the production of formic acid gradually increases up to 120 minutes, reaching 55% selectivity. The same behavior can be observed for hydroxypropanone. After this time, the selectivity reduces and there is an increase in selectivity for diglycerol, reaching 60%. The presence of formic acid can be explained by the oxidative cleavage mechanism of glycerol with the aid of the oxidizing agent (H.sub.2O.sub.2). The formation of formic acid from glycerol can be explained firstly by the dehydration of glycerol, forming hydroxypropanone, and then by the generation of formic acid from the oxidation of hydroxypropanone and/or direct oxidation of glycerol. Hydroxypropanone can be obtained from glycerol via dehydration. This substance is an important intermediate used in the production of polyols and acrolein. In addition, it can be used in the textile industry, in cosmetics and as flavoring agents.

[0056] In FIG. 6b, the formation of diglycerol is observed as the major product, around 70%, in the reflow reaction of conversion of commercial glycerol. Dioxane, formic acid and hydroxypropanone molecules were also identified as minor products in the reaction (10%). The main product is probably obtained by the oligomerization of glycerol in the presence of an oxidizing agent, such as hydrogen peroxide, in the reaction medium.

[0057] Comparing the results presented, it is clear that there is a preference in the formation of formic acid and diglycerol using residual and commercial glycerin, respectively. This difference in the products obtained is probably due to impurities present in glycerin (such as sodium chloride and methanol) which, when reacting with hydrogen peroxide, generate species responsible for dehydrating and oxidizing the glycerol molecule, forming hydroxypropanone and formic acid.

[0058] As the reaction progresses, sodium chloride is consumed, there is the reduction in the formation of these products, and the increase in diglycerol is observed. The production of diglycerol, in turn, is directly related to the reaction of hydrogen peroxide with glycerol, resulting in the oligomerization of glycerin. This effect occurs both for residual glycerin and for commercial glycerin; however, it is more significant in commercial glycerin, due to the fact that it does not have impurities. In both situations, starting from glycerin as a by-product of biodiesel production, it is highlighted the obtention of industrially important products, in the absence of a heterogeneous catalyst and in mild reaction conditions.

[0059] This invention shows the importance of using hydrogen peroxide as a green oxidizing agent in glycerol conversion reactions, but is not restricted to the same. Hydrogen peroxide has low cost and high availability, which makes it very attractive, making the glycerin conversion process a simple and inexpensive process.