Patent Application
20220410126
The present invention relates to a catalyst and process for pre-treatment of acidic charges consisting of sulfated zirconia and cerium for the production of biofuels, characterized by the catalyst having greater activity and resistance to deactivation with acidic charges.
In the research for low carbon footprint fuels and bioproducts, and also in the production of biodiesel and biolubricants, the esterification reaction plays an important role. For example, the production of biodiesel by esterification involves the reaction of fatty acids with alcohols, such as methanol and ethanol. The esterification reaction can also be used in the pre-treatment of bio-oil, where the acidity of this raw material is reduced. Bio-oil is a raw material for renewable fuels obtained by means of pyrolysis processes in the absence of oxygen.
However, the esterification reaction requires that the heterogeneous catalyst has adequate properties, such as acidity, porosity and hydrophobicity. The formulation of esterification catalysts for acidic charges, such as fatty acids and bio-oil, must necessarily have greater catalytic activity, in addition to high reaction stability, using smaller amounts of alcohol in the reaction. Leaching in a liquid medium is recognized as one of the main causes of deactivation of catalysts in these processes of reducing acidity of acidic charges, which may be caused by the presence of alcohols and other compounds present in the reaction medium. The deactivation process is also due to the presence of unconverted products and reactants in the catalyst pores, which is favored under low conversion conditions and facilitated by the existence of small pores.
There is a great effort being applied in the development of heterogeneous acidic catalysts, since esterification reactions require catalysts with adequate properties. One of the great difficulties encountered is that the catalysts can quickly deactivate under the reaction conditions employed, in addition to having low activity. This is a critical point of acidic solids, since most of the preparations lead to the loss of the functional group and, consequently, of its catalytic activity.
The esterification processes aimed at the production of biodiesel that use fatty acids employ high pressures and temperatures, as reported in U.S. Pat. No. 7,256,301 (2 to 100 bar (0.2 to 10 MPa), 50 to 300° C.), U.S. Pat. No. 6,147,196 (40 to 100 bar (4 to 10 MPa), 220 to 250° C.) and U.S. Pat. No. 8,704,003 (10 to 75 bar (1 to 7.5 MPa), 150 to 250° C.). Another aggravating factor is the fact that high temperatures and pressures cause the formation of undesirable by-products, such as dimethyl ether and compounds derived from the cracking of the charge. The methanol/charge molar ratio (R) should also be minimized, as it leads to a reduction in the operational costs of recovering this reagent. Therefore, active catalysts capable of carrying out this process under milder conditions are desirable.
The low activity of some inorganic oxides, the limitation of access to the active sites of the zeolites, which are naturally microporous, due to the triglyceride molecules being very bulky, the deactivation of some catalysts in successive cycles and the leaching of catalyst compounds based on anchored metallic complexes are some of the problems faced. Commonly used catalysts contain Ti, Zn, Sn in the form of aluminates and silicates (U.S. Pat. No. 6,147,196), commercial ion exchange resins (U.S. Pat. No. 4,698,186), binary oxides of La and Zn (U.S. Pat. No. 8,163,946), functionalized silicate-based solids (U.S. Pat. Nos. 7,122,688 and 9,062,081), sulfonated carbons obtained from glucose (U.S. Pat. No. 8,445,400), tungsten-doped and sulfated zirconia (WO2004096962 A1) and binary oxides (e.g., Zn, Ce, La, Si, Ti, Nd) supported on oxide of zirconia (US20120283459 A1). The class of superacidic solids is the most promising; however, catalysts often deactivate easily due to the loss of acidic groups, as in the case of sulfonated carbons and sulfated oxides.
The pre-treatment of bio-oil, also considered an option for the use of heterogeneous solid acidic catalysts, would provide improvement in chemical stability, reduction of acidity and water content, enabling the production of renewable fuels from this input. Esterification, transesterification and acetalization reactions with alcohols decrease the content of carboxylic acids, ketones and aldehydes, transforming them into esters and acetals (Hu et al, Fuel Processing Technology 106: 569-576, 2013; Lu, J., Guo, S., Fu, Y., Chang, J., Fuel Processing Technology 161: 193-198, 2017). A limiting factor is the low esterification temperature, preventing the favoring of parallel reactions, requiring a catalyst with high reaction activity.
The catalysts used are mostly acids, such as acidic resins, zeolites, SBA-15-SO3H, and others, generally, superacids (Milina, M., Mitchell, S., Pérez-Ramiréz, J., Catalysis Today 235: 176-183, 2014; Lohitharn, N., Shanks, B. H., Catalysis Communications 11: 96-99, 2009; Prasertpong, P., Jaroenkhasemmeesuk, C., Regalbuto, J., Lipp, J., Tippayawong, N., Energy Reports 6: 1-9, 2020). Liu et al. esterified the crude bio-oil with ethanol (mass ratio=2:1), and 2% m/m SO4−2 50% ZrO2/TiO2 (in relation to the total mixture), 80° C., in a Parr reactor with stirring of 300 rpm. Sondakh et al. (2018), in turn, performed the esterification reaction using homogeneous catalysis, with H2SO4, HCl and citric acid. It is observed that the use of catalysts with higher acidity, such as H2SO4 and HZSM-5, would promote undesirable parallel reactions, with the formation of ethers as by-products (LIU, Y., Li, Z, LEAHY, J. J., KWAÌNSKE, W., Energy Fuels 29: 3691-3698, 2012).
The choice of the catalyst involves adequate acidity (Bronsted acidic sites), and adequate porosity, with the presence of macropores or a wide distribution of pores, since the catalysts can be deactivated; both by the formation of water and by the retention of the products in the pores. Note that the acidity of the bio-oil or other acidic charge can interfere with the integrity of the catalyst, as, for example, dealuminization of zeolites can occur, or a decrease in Bronsted acidic sites, leading to the loss of catalytic activity (Milina M., Mitchell, S., Pérez-Ramirez, J., Catalysis Today 235: 176-183, 2014).
Document BR 10 2015 031632-1 discloses a process for obtaining biodiesel from charges with fatty acids and triglycerides with sulfated zirconia catalysts with bifunctional activity (esterification and transesterification). Document BR 10 2018 009940-0 teaches the preparation of suitable catalysts for the production of biodiesel from alternative sources (oils and fats with higher levels of free fatty acids and of lower market value), being active for the esterification and transesterification reactions, as well as its obtaining process and a process that uses such catalysts for the production of biodiesel. The catalyst formulations are zirconia-titania sulfated and optionally modified with cerium. Similar to BR 10 2015 031632-1, the catalysts are also bifunctional. Document BR 10 2018 009940-0 is also characterized by using 1 to 4 reaction stages.
The paper of Banerjee et al. studied a sulfated zirconia-based nanocrystalline catalyst formulation with an ionic liquid as a porogen for the esterification of fatty acids with methanol (Banerjee, B.; Bhunia, S.; Bhaumik, A. Applied Catalysis A: General 502: 380-387, 2015).
In view of the disclosure, solid acidic catalysts are needed for processes of acidity reduction of acidic charges via esterification that have activity at low temperatures, and that do not leach in the reaction medium; this can be achieved with optimized formulations with large pores, low sulfur or sulfate content. The use of large amounts of sulfate to provide acidity to the catalyst can cause operational problems, such as corrosion from sulfate leaching, in addition to loss of catalyst activity over time.
The solution taught by the present invention allows obtaining heterogeneous catalysts with a greater amount of macropores and greater acidity, allowing greater activity and resistance to deactivation, therefore more active for reducing acidity in acidic charges such as fatty acids, mixtures of fatty acids with triglycerides and bio-oil. The prepared catalyst consists of zirconia sulfated with cerium, where simple and low-cost porogens are used in its production process, which lead to unexpected technical effects: greater quantity of macropores and greater acidity, making it an efficient catalyst for the reduction of acidity of acidic charges. The porogen enlarges the pores of the catalyst during the calcination step and decomposes entirely.
An advantage of the developed solid acidic catalyst is the possibility of carrying out the esterification reaction in relatively mild conditions when compared to homogeneous acidic catalysis, increasing the economicity of the process and minimizing the formation of by-products.
The present invention will be described in more detail below, with reference to the attached figures which, in a schematic form and not limiting the inventive scope, represent examples thereof. In the drawings, there are:
Preliminarily, it is noted that the description that follows will start from preferred embodiments of the invention. As will be apparent to any technician skilled on the subject, however, the invention is not limited to these particular embodiments, but only to the scope of protection defined in the claims.
The catalyst of the present invention is obtained by introducing the active phases of cerium, or titanium and sulfur in the zirconium-based catalyst, which can be introduced separately or simultaneously.
Thus, according to an embodiment of the invention, the process for obtaining the catalysts according to the present invention comprises the following steps:
The source of zirconium can be zirconium oxychloride or zirconium nitrate, and the base can be ammonium hydroxide, or sodium carbonate, or sodium hydroxide. The source of cerium may be cerium nitrate. The source of sulfur can be ammonium sulfate. In this way, a low sulfur zirconium/cerium catalyst is obtained. The deposition takes place by a method selected from wet spot impregnation, mud impregnation or chemical vapor phase deposition, preferably by mud impregnation. Aging is carried out at a pH in the range between 8 and 11, for a period of time of up to 24 hours, and dried at a temperature between 100 and 140° C., for a period of between 10 and 24 hours. The calcination step takes place at a temperature between 350° C. and 800° C., for a period between 2 h and 10 h, using a heating rate between 1° C./min and 10° C./min.
The catalysts thus obtained have a Ce/Zr mass ratio: 0.02 to 0.10; Ti/Zr=0.05 to 0.50; and sulfur content in the range of 1.0 to 5.0% m/m.
Next, in order that the invention can be better understood, experiments that illustrate the invention are presented, without, however, being considered limiting.
A: in the first step, the precipitation of zirconium hydroxide was made using Zr oxychloride (1 M) and NH4OH (14.5% m/m), at room temperature, pH in the range of 10 to 11, dripping the precursor of Zr under ammonium hydroxide for 60 minutes. After the addition of the precursor, corn starch was preferably incorporated, and the porogen may originate from other sources such as: potato, yam, arrowroot, banana, among others (35% m/m in relation to the desired amount of ZrO2); the sample remained for 1 hour under stirring, followed by aging for 22 hours, washing/filtering and drying at 100° C. for 16 hours.
With the dry material, the impregnation was made with cerium nitrate and ammonium sulfate (Ce/Zr=0.05 and 6.5% m/m of ammonium sulfate in relation to the ZrO2) simultaneously in zirconium hydroxide (mass ratio H2O:Zr(OH)x:2.4:1). The mud was stirred for 24 hours at 300 rpm. After this step, the sample was dried at 100° C. for 24 hours in a fluidized bed reactor with air flow, followed by calcination at 600° C. for 5 h using 3° C./min using air flow rate (40 cm3/min).
B: in this preparation, the porogen incorporation was made during the sulfation/incorporation of cerium in zirconium hydroxide prepared previously by precipitation (6.5% m/m ammonium sulfate, Ce/Zr=0.05, mass ratio H2O:Zr(OH)x:2.4:1, and 42% m/m corn starch in relation to ZrO2). Note that starch can come from other sources such as: potato, yam, arrowroot, banana, among others. The step was carried out at 25° C. for 24 hours at 300 rpm. After this step, the sample was dried at 100° C. for 24 hours in a fluidized bed reactor with air flow, followed by calcination at 600° C. for 5 h, using 3° C./min, using air flow rate (40 cm3/min).
C: In the first step, the precipitation of zirconium hydroxide was made using Zr oxychloride (1 M) and NH4OH (14.5% m/m), pH in the range of 10 to 11, at room temperature. After the addition of the precursor, corn starch was incorporated (17.5% m/m in relation to the desired amount of ZrO2), the sample remained for 1 hour under stirring, followed by aging for 22 hours, washing/filtering and drying at 100° C. for 16 hours.
With the dry material, the impregnation was made with cerium nitrate and ammonium sulfate (Ce/Zr=0.05 and 6.5% m/m of ammonium sulfate in relation to ZrO2) simultaneously in zirconium hydroxide (mass ratio H2O:Zr(OH)x:2.4:1). The mud was stirred for 24 hours at 300 rpm. After this step, the sample was dried at 100° C. for 24 hours in a fluidized bed reactor with air flow, followed by calcination at 600° C. for 5 h using 3° C./min using air flow rate (40 cm3/min).
This example illustrates the catalyst preparation using an EO-PPO-PEO triblock copolymer (poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) copolymer) with ratio 20:70:20) with 20:70:20 (EO:PO:EO), as a porogen.
D: In the first step, the precipitation of zirconium hydroxide was made using Zr oxychloride (1 M) and NH4OH (14.5% m/m), pH in the range of 10 to 11, at room temperature, dripping the precursor of Zr under ammonium hydroxide for 60 minutes. After the addition of the precursor, the EO-PPO-PEO triblock copolymer (35% m/m in relation to the desired amount of ZrO2) was incorporated, the sample remained for 1 hour under stirring, followed by aging for 22 hours, washing/filtration and drying at 100° C. for 16 hours.
With the dry material, the impregnation was made with cerium nitrate and ammonium sulfate (Ce/Zr=0.05 and 6.5% m/m of ammonium sulfate in relation to ZrO2) simultaneously in zirconium hydroxide (mass ratio H2O:Zr(OH)x:2.4:1). The mud was stirred for 24 hours at 300 rpm. After this step, the sample was dried at 100° C. for 24 hours in a fluidized bed reactor with air flow, followed by calcination at 600° C. for 5 h using 3° C./min using air flow rate (40 cm3/min).
E: Zirconium hydroxide was obtained by precipitation with ammonium hydroxide, at room temperature and at controlled pH (9 to 10) by dripping zirconium oxychloride (1.5 M) for 40 minutes over the solution of ammonium hydroxide (14.5% m/m). At the end of the precursor addition, EO-PPO-PEO triblock copolymer (6.7% m/m in relation to ZrO2) was added, the system aged at room temperature for 21 hours, being filtered and washed with deionized water, and then dried in a static atmosphere at 120° C. for 16 hours.
With the dry material, the sulfation was made with titanium oxysulfate and ammonium sulfate (Ti/Zr=0.18 and 6.5% m/m of ammonium sulfate in relation to ZrO2), with mass ratio H2O:Zr(OH)x:2.4:1. The mud was stirred for 24 hours at 300 rpm. After this step, the sample was calcined at 600° C. for 5 h using 3° C./min using air flow rate (40 cm3/min). After this step, the solid was impregnated with cerium nitrate (Ce/Zr=0.035) in excess of solution, for 2 hours at room temperature with stirring. The solid was dried at 40° C. for 16 h and calcined with air flow 40 cm3/min at 400° C. for 4 hours, using a rate of 3° C./min.
This example illustrates the preparation of catalysts without the use of a porogen.
Zirconium hydroxide was obtained by precipitation with ammonium hydroxide, at room temperature and at controlled pH (9 to 10) by dripping zirconium oxychloride (1.5 M) for 40 minutes over the solution of ammonium hydroxide (14.5% m/m). The system was aged at room temperature for 21 hours, being filtered and washed with deionized water, and then dried in a static atmosphere at 120° C. for 16 hours.
With the dry material, the sulfation was made with ammonium sulfate (6.5% m/m of ammonium sulfate in relation to ZrO2), with a mass ratio H2O:Zr(OH)x:2.4:1. The mud was stirred for 24 hours at 300 rpm. After this step, the sample was calcined at 600° C. for 5 h using 3° C./min using air flow rate (40 cm3/min). After this step, the solid was impregnated with cerium nitrate (Ce/Zr=0.05) in excess of solution, for 2 hours at room temperature with stirring. The solid was dried at 40° C. for 16 h and calcined with an air flow of 40 cm3/min at 400° C. for 4 hours, using a rate of 3° C./min.
This example illustrates the preparation of catalysts without the use of a porogen.
Zirconium hydroxide was obtained by precipitation with ammonium hydroxide, at room temperature and at controlled pH (9 to 10) by dripping zirconium oxychloride (1.5 M) for 40 minutes over the solution of ammonium hydroxide (14.5% m/m). The system was aged at room temperature for 21 hours, being filtered and washed with deionized water, and later dried in a static atmosphere at 120° C. for 16 hours.
With the dry material, sulfation was performed with titanium oxysulfate and ammonium sulfate (Ti/Zr=0.18 and 6.5% m/m of ammonium sulfate in relation to ZrO2), with mass ratio H2O:Zr(OH)x:2.4:1. The mud was stirred for 24 hours at 300 rpm. After this step, the sample was calcined at 600° C. for 5 h using 3° C./min using air flow (40 cm3/min). After this step, the solid was impregnated with cerium nitrate (Ce/Zr=0.035) in excess of solution, for 2 hours at room temperature with stirring. The solid was dried at 40° C. for 16 h and calcined with an air flow of 40 cm3/min at 400° C. for 4 hours, using a rate of 3° C./min.
This example illustrates the characterization results and reaction tests.
Table 1 shows that the changes in the preparation of catalysts A to E provided an increase in acidic properties in relation to the catalyst Reference 1 (1). The results can be analyzed as follows:
Table 2 presents the textural results of the series of catalysts studied, showing the increase of macropores in the samples with the use of porogens.
Additionally, all samples from A to D had higher conversions than the reference catalysts, even D and C, which had smaller average diameters than the reference catalysts, as can be seen in
The percentage of the catalyst in relation to the acidic charge is from 1 to 8% m/m, both for fatty acids or mixtures of fatty acids with triglycerides and for bio-oil charge.
Therefore, the catalyst can be used in the pre-treatment of acidic charges such as fatty acids, mixtures of fatty acids with triglycerides and bio-oil. The mixtures of fatty acids with triglycerides have contents of 0.05 to 99.5% m/m of fatty acid in the mixture. The alcohols used in this process are low molecular weight aliphatic alcohols, ranging from 1 to 4 carbon atoms, preferably methanol and ethanol.
The catalyst can also be used with bio-oil, which comes from pyrolysis processes in the absence of oxygen, at temperatures from 400 to 600° C. Bio-oil comes from plant biomass, such as sugarcane bagasse, sugarcane straw, wood, rice husk, waste from the paper industry such as black liquor, etc.
Note that the esterification reaction occurs naturally during the aging of bio-oil. Esterification, transesterification and acetalization reactions with alcohols decrease the content of carboxylic acids, ketones and aldehydes, transforming them into esters and acetals (Lu, J., Guo, S., Fu, Y., Chang, J., Fuel Processing Technology 161: 193-198, 2017). These reactions can occur, to some extent, promoted by acidity and storage temperature, and can even happen at room temperature (Diebold, J. P., NREL/SR-570-27613). Controlled esterification can be used in a pre-treatment of bio-oil, allowing the partial removal of oxygenated compounds, increasing the useful life of HDO catalysts, consequently reducing the severity of the reaction, enabling the use of renewable charges in refining.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 012721 0 | Jun 2021 | BR | national |
