WO2013151921A1

WO2013151921A1 - Solid zinc based catalysts

Info

Publication number: WO2013151921A1
Application number: PCT/US2013/034780
Authority: WO
Inventors: K. Y. Simon Ng; Steve O. SALLEY; Shuli Yan
Original assignee: Wayne State University
Priority date: 2012-04-02
Filing date: 2013-04-01
Publication date: 2013-10-10

Abstract

The present disclosure discloses Zn based catalysts modified by the oxide of a second metal. In one aspect, a catalyst comprises zinc oxide and the oxide of a second metal. The second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof. In another aspect, a catalyst comprises zinc oxide mixed with the oxide of a second metal, the second metal being more electronegative than zinc. In further another aspect, a process comprises contacting any catalyst of the present disclosure with a reaction. The catalyst catalyzes the reaction.

Description

SOLID ZINC BASED CATALYSTS

[0001] This application claims priority to U.S. Provisional Application No. 61/619,009, the entirety of which is herein incorporated by reference. This application is also relevant to U.S. Pat. Pub. Nos. 2009/0307966 and 2010/0010246, and PCT Pub. No. WO2010/148057, the entireties of all of which are herein incorporated by reference.

FIELD

[0002] The present disclosure relates to novel Zn based catalysts. More specifically, the present disclosure relates to Zn based catalysts modified by a second metal or oxide thereof, preferably on a support.

BACKGROUND

[0003] Due to growing worldwide demand for energy and its resulting impact on the environment, it is becoming increasingly important to search for sustainable alternative fuels. Among the many possible sources, biodiesel derived from natural oils attracted early attention as a promising fuel for substitution or blending with petroleum based diesel fuel because biodiesel and petroleum diesel share similar physical and chemical properties.

BRIEF SUMMARY

[0004] In one aspect, a catalyst comprises zinc oxide and the oxide of a second metal. The second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof.

[0005] In another aspect, a catalyst comprises zinc oxide mixed with the oxide of a second metal, the second metal being more electronegative than zinc.

[0006] In further another aspect, a process comprises contacting any catalyst of the present disclosure with a reaction. The catalyst catalyzes the reaction.

[0007] In yet still another aspect, a process comprises contacting a material that comprises a glyceride with an alcohol in the presence of any catalyst of the present disclosure such that at least some of the glyceride is converted into the corresponding alcoholic ester of the glyceride.

[0008] In yet another aspect, a process comprises contacting a material that comprises a free fatty acid with an alcohol in the presence of any catalyst of the present disclosure such that at least some of the free fatty acid is converted into the corresponding alcoholic ester.

BRIEF DESCRIPTION OF THE FIGURES

[0009] Figure 1 illustrates the catalytic activity of various metal compounds.

[0010] Figure 2 illustrates the yields of total fatty acid methyl esters (FAME), FAME from transesterification reaction and FAME from esterification reaction using the ZnO/Si0₂, ZnO/C, ZnO/Al₂0₃ or ZnO catalysts.

[0011] Figure 3 illustrates the yields of total FAME, FAME from

transesterification reaction and FAME from esterification reaction using the K, Na, Ca, Mg or La modified or unmodified ZnO catalysts.

[0012] Figure 4 illustrates the yields of total FAME, FAME from

transesterification reaction and FAME from esterification reaction using the Sn, Fe, Co, or V modified or unmodified ZnO catalysts.

[0013] Figure 5 illustrates the yields of total FAME using Pr, Ce, Yb, Cu, or Ag modified ZnO catalysts.

[0014] Figure 6 illustrates the yield of FAME in a control testing in the absence of catalysts (pure soybean oil at 200°C, 15:1 molar ratio of methanol to oil.)

[0015] Figure 7 illustrates the yield of FAME in a control testing in the absence of catalysts and at different temperatures (pure oleic acid, 10: 1 molar ratio of methanol to oil.)

[0016] Figure 8 illustrates the yield of FAME in a control testing in the absence of catalysts and using different percentages of oleic acid (at 200°C, 15:1 molar ratio of methanol to oil.)

[0017] Figure 9 illustrates the yield of yields of total FAME using the ZnPr catalyst at different stirring speeds. The stirring speeds are 150 rpm, 300 rpm, or 550 rpm (at 200°C, 15:1 molar ratio of methanol to oil, 1.5 % of catalyst loading, 50 % acidic oil.)

[0018] Figure 10 illustrates yields of total FAME using the ZnPr catalyst with different amounts of acidic oil. Oleic acid contents are 15 %, 33 %, 50 %, 67 %, 85 % or 100 % (at 200°C, 15:1 molar ratio of methanol to oil, 1.5 % of catalyst loading, at 300 rpm.)

[0019] Figure 11 illustrates yields of total FAME using the ZnPr catalyst at different temperatures (15: 1 molar ratio of methanol to oil, 1.5 % of catalyst loading, 50 % acidic oil, at 300 rpm.)

[0020] Figure 12 illustrates yields of total FAME using the ZnPr catalyst at different catalyst loadings (at 200°C, 15: 1 molar ratio of methanol to oil, 50 % acidic oil, at 300 rpm.)

[0021] Figure 13 illustrates yields of total FAME using the ZnPr catalyst at different molar ratios of methanol to oil (at 200°C, 1.5 % of catalyst loading, 50 % acidic oil, at 300 rpm.)

[0022] Figure 14 illustrates yields of total FAME using the ZnLaAl catalyst at various durations.

DETAILED DESCRIPTION

[0023] Traditional biodiesel is produced from some well refined vegetables oils, such as food grade soybean oil, rapeseed oil, palm oil etc. These oils contain a very low content of free fatty acids (generally lower than 0.5 %), and have a high market price. Recently, there is a trend to use some inexpensive oils as raw materials for biodiesel production, such as crude vegetable oils, waste cooking oil, and rendered animal fats. Free fatty acids (FFA) in these oils vary from 0.5 ~ 95 %. Therefore, these oils cannot be directly used in traditional biodiesel production process.

Development of heterogeneous catalysts, which can convert both triglyceride and FFA into FAME, becomes attractive to many biodiesel plants.

[0024] The present disclosure provides a screening of metal oxides for FAME synthesis. A series of binary catalysts which are active in catalyzing both transesterification and esterification reactions are disclosed. These catalysts have a potential for industrial applications.

[0025] According to one embodiment of the present disclosure, a catalyst comprises zinc oxide and a second metal or oxide thereof. The second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof. Preferably, the second metal is selected from the group consisting of Pr, Ce, Yb, Cu, Ag, Si, C, Al, Mg, La, Sn, V and combinations thereof. More preferably, the second metal is Pr or La.

[0026] The molar ratio of zinc to the second metal in the catalyst may vary. In one example, the molar ratio of zinc to the second metal is from about 100:1 to about 1 :100, preferably from about 10:1 to about 1: 10. In another example, the molar ratio of zinc to the second metal is from about 5: 1 to about 1 : 1. Preferably, the molar ratio of zinc to the second metal is about 3:1.

[0027] Preferably, zinc oxide in the catalysts is impregnated with the second metal or salt thereof.

[0028] According to another embodiment of the present disclosure, a catalyst comprises zinc oxide mixed with a second metal or oxide thereof, the second metal being more electronegative than zinc. Preferably, the second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr, and combinations thereof. More preferably, the second metal is selected from the group consisting of Sn, Fe, Co, V, Pr, La, Ce, Yb, Cu, Ag and combinations thereof. Still more preferably, the second metal is Pr or La.

[0029] According to yet another embodiment of the present disclosure, a catalyst is prepared by providing a zinc ion solution, impregnating a second metal, a salt thereof or an oxide thereof in the zinc ion solution to form a solid comprising zinc and the second metal, salt or oxide thereof, and calcining the solid to form a catalyst.

[0030] Preferably, the second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof. More preferably, the second metal is selected from the group consisting of Pr, Ce, Yb, Cu, Ag, Si, C, Al, Mg, La, Sn, V and combinations thereof. Even more preferably, the second metal is Pr or La. [0031] According to yet still another embodiment of the present disclosure, a catalyst comprises zinc oxide and the oxide of a second metal, and the catalyst is supported on a support. The second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, La, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof. Preferably, the second metal is selected from the group consisting of Pr, Ce, Yb, Cu, Ag, Mg, La, Sn, V and combinations thereof. More preferably, the second metal is Pr or La. Any suitable support, such as Si0₂, A1₂0₃, C, zeolite, ZSM-5, SBA-15, Zr0₂, Ce0₂, diatomite, a mesoporous material, a clay, and combinations thereof, can be used. Preferably, the support is selected from Si0₂, A1₂0₃, C and combinations thereof. Preferably, the catalyst comprises zinc oxide and either La oxide or Pr oxide supported on a support. More preferably, the catalyst comprises zinc oxide and La oxide supported on Si0₂, A1₂0₃, or C, and preferably on A1₂0₃. Also preferred is the catalyst comprising zinc oxide and Pr oxide supported on Si0₂, A1₂0₃, or C, and preferably on A1₂0₃.

[0032] Not wishing to be bound by any theory, it is believed that the effects of second metal oxides on the modified ZnO catalysts include physically promoting ZnO distribution on a support, such as Si, Al and C, which isolates nano-particles and greatly decreases the average particle size. These second metal oxides promote both transesterification and esterification reactions. Also, the second metal oxides change the electronic structure of ZnO catalysts. For the ions of Na, K, Ca, Mg, La and Pr, when they contact with the Zn ion, electrons tend to transfer from the second metal ions to the Zn ion, and enhances the transesterification reaction. For Sn, Fe, Co and V, electrons tend to transfer from the Zn ion to the second metal ions. Thus,

esterification is enhanced.

[0033] In some examples, the second metal or oxide thereof is calcined before the impregnating step. Preferably, the solid is dried before calcined. Preferably, the calcining is at about 450°C. Preferably, the calcining is for at least about 12 hours.

[0034] According to still another embodiment of the present disclosure, a process comprises contacting any catalyst of the present disclosure with a reaction. The catalyst catalyzes the reaction. The reaction can be an esterification reaction. The reaction can be a transesterification reaction. Preferably, the catalyst catalyzes both an esterification reaction and a transesterification reaction.

[0035] According to further another embodiment of the present disclosure, a process comprises contacting a material that comprises a glyceride with an alcohol in the presence of any catalyst of the present disclosure such that at least some of the glyceride is converted into the corresponding alcoholic ester of the glyceride. Any alcohol can be used. Preferably, the alcohol is methanol. Preferably, the catalyst catalyzes the alcoholic ester formation.

[0036] In some examples, the material further comprises a free fatty acid. At least some of the free fatty acid is converted into the corresponding alcoholic ester of the free fatty acid in the presence of the catalyst. Preferably, the catalyst catalyzes the formation of the alcoholic ester of the free fatty acid. More preferably, the catalyst simultaneously catalyzes the transesterification reaction of the glyceride and the esterification reaction of the free fatty acid.

[0037] The glyceride may be a triglyceride, a diglyceride, or a monoglyceride. The glyceride may be a mixed glyceride.

[0038] In some example, the material is a non-refined oil. For example, the material can be a crude oil, a waste oil, an animal fat, or combinations thereof. The material may further comprise water. The water content in the feed material may vary. For example, the water content in the feed material may be more than about 0.15 weight %, or more than about 2 weight %, or more than about 5 weight %, or more than about 10 weight %.

[0039] In some examples, the material may further comprise one or more free fatty acids. The free fatty acid content in the material may vary. For example, the free fatty acid content in the material may be more than about 0.5 weight %, or more than about 2 weight %, or more than about 3.5 weight %, or more than about 10 weight %.

[0040] According to yet still another embodiment of the present disclosure, a process comprises contacting a material that comprises a free fatty acid with an alcohol in the presence of any catalyst of the present disclosure such that at least some of the free fatty acid is converted into the corresponding alcoholic ester.

[0041] The catalysts according to the present disclosure are solid catalysts, a mixture of zinc oxide and other metal oxide species. The preferred catalysts include Zn-La, Zn-Pr, Zn-Ce, Zn-Cu, Zn-Al, Zn-Mg, Zn-Ti, Zn-Zr, and Zn-Ag catalysts.

More preferably, these catalysts are supported on a support, such as Zn-La or Zn-Pr supported on Si0₂, A1₂0₃ or C. Their catalytic ability in both triglyceride

transesterification and fatty acid esterification varies with catalyst composition.

These catalysts have the potential to convert all kinds of oil feedstocks into biodiesel, including high quality oil feedstock, whose FFA content is lower than 0.5 %, and lower quality oil feedstocks with FFA in the range of 0.5 - 100 %.

[0042] Using these catalysts can significantly reduce the cost of producing biodiesel. Currently, most of the commercial biodiesel produced in the U.S. comes from the transesterification of food grade vegetable oils with methanol using alkalis (KOH, NaOCH₃) as catalysts. With this conventional homogeneous method, FFA content in oils need to be lower than 0.5% and water content lower than 0.06 %. Thus, the high cost of food grade vegetable oils leads to high production cost of biodiesel.

[0043] The novel catalysts disclosed herein can utilize crude oils, waste cooking oil, and rendered animal fats that are less expensive compared to food grade vegetable oils. These inexpensive oils usually contain high content of FFA and water. FFA can react with homogeneous alkaline catalysts and poison the catalysts.

Likewise, water can lead to hydrolysis of triglycerides and fatty acid methyl esters (FAME or biodiesel). This technical difficulty had prevented unrefined or waste oils from being used directly in biodiesel production.

[0044] Recently, there have been reported an acid- and alkali-catalyzed two- step method for biodiesel production using some unrefined or waste oils as raw materials. An acidic catalyst (H₂S0₄, HCI) is initially used to convert FFA to the esters, and then in the second stage the transesterification of oil is performed using an alkaline catalyst. However, this production process is more lengthy and complicated.

[0045] Moreover, the use of homogeneous catalysts (strong acid or base) often lead to many engineering problems such as equipment corrosion, and some environmental problems such as the disposal of waste catalysts and contaminated wash water. Because homogeneous catalysts are mixed with biodiesel products, the purification of biodiesel becomes more complicated and costly. Heterogeneous base catalysts are less corrosive, easily separated from biodiesel products, and generate no waste water.

[0046] The oil feedstocks used in traditional processes and other

heterogeneous processes are high quality oils, such as food grade soybean oil, high purity rapeseed oil. The oil feedstocks that may be used with the novel catalysts of the present disclosure are inexpensive oils, such as waste cooking oil, yellow grease, brown grease, crude vegetable oil, rendered animal fats, crude algae oil, which generally contain a high FFA content, high water content and other impurities, like metal ions and biogel.

[0047] The novel catalysts of the present disclosure are active in both transesterification and esterification. Unlike some traditional homogeneous catalysts that have only one active center - either a base or an acid site, the novel catalysts of the present disclosure have two active sites found on the surface of these catalysts, including both base and acid sites. Moreover, the amount of active sites and catalytic strength of the present catalysts can be adjusted by the addition of metal oxides. Also, the novel catalysts of the present disclosure show a long catalyst life in acidic oil conditions in both batch and continuous reactor systems. For traditional

heterogeneous catalytic processes, a high molar ratio of methanol to oil is often exploited to get a high yield of FAME, which could be as high as 42: 1. However, recovery of excess methanol from final products is costly. The novel catalysts of the present disclosure can be used to minimize the ratio of methanol to oil to 9:1.

Accordingly, methanol recovery cost is greatly decreased.

[0048] The novel catalysts of the present disclosure have the potential to make biodiesel production more profitable. These catalysts can be used with unrefined or waste oils in biodiesel production as active heterogeneous base catalysts. For biodiesel production, the cost of oils accounts for up to 70- 90 % of biodiesel production cost. Therefore, reducing the cost of oil feedstock has substantial impact on the economics of biodiesel production. Also, from the catalyst aspect, traditional methods use homogeneous base catalysts which usually result in engineering and environmental problems, as well as considerable cost in separating them from the final product. Using the heterogeneous base catalysts of the present disclosure can alleviate these problems, and reduce preparation cost. Moreover, from an engineering aspect, currently availably heterogeneous catalytic processes incur a high cost in processing excess methanol. The novel catalysts of the present disclosure can be used to decrease the usage of methanol and decreases the recovery cost. The present catalysts are highly active and easy to be separated and recovered from biodiesel products, are low corrosive, and minimize the environmental problems associated with homogeneously catalytic methods.

Examples

Reagents

[0049] Oleic acid, methanol, urea, KOH, Ca(OH)₂, Sc₂0₃, Ti0₂, V₂(S0₄)₃, Cr(S0₄)₃, MnS0₄ ^«H₂0, Co(N0₃)₂ ^«6H₂0, Fe(N0₃)₃ ^»9H₂0, (Ν0₃)₂·6Η₂0,

Cu(N0₃)₂*6H₂0, and Ζη(Ν0₃)₂·6Η₂0 were purchased from Sigma-Aldrich Inc. (St. Louis, MO). Vegetable oil was purchased from Costco Warehouse (Detroit, MI). The amount of C]₆ in vegetable oil is about 10.31 %.

Catalyst Preparation

[0050] The catalytic activities of KOH and Ca(OH)₂ were directly tested. Sc₂0₃ and Ti0₂ were dried at about 150°C for about 5 hours before usage. V₂0₃, Cr₂0₃, Mn0₂, Fe₂0₃, CoO, NiO, CuO and ZnO were prepared by the improved homogeneous precipitation method as described in U.S. Patent Publication No. 2009/0307966 to Yan et al. (for example, in paragraph [0029] and Fig. 1), the entirety of which is hereby incorporated by reference. The clear solutions of V₂(S0₄)₃, Cr(S0₄)₃, MnS0₄ ^«H₂0, Co(N0₃)₂ ^«6H₂0, Fe(N0₃)₃ ^«9H₂0, Ni(N0₃)₂ ^«6H₂0,

Cu(N0₃)₂*6H₂0, and Zn(N0₃)₂*6H₂0 were separately mixed with urea with molar ratio of 1:5. Then the mixture solutions were agitated and heated to boiling, and kept boiling for at least 6 hours. The precipitants were removed and washed by distilled water. The wet precipitants were further mixed with urea solution and the molar ratio of metal to urea was still kept at 1 :5. The mixture was agitated and heated at boiling temperature until the mixture became a firm solid. The solid was then removed and dried at 100°C for about 1-5 hours, and then calcined at about 450 ~ 750°C for about 8 hours.

Reaction Conditions And Analysis Methods

[0051] Transesterification reactions were conducted with pure soybean oil and 42: 1 molar ratio of methanol to oil with a 0.8 % catalyst loading at 200°C and 500 Psi unless otherwise stated. Esterification reactions were conducted with pure oleic acid and 10: 1 molar ratio of methanol to oleic acid with a 0.8 % catalyst loading at 200°C and 500 Psi unless otherwise stated. The reactions were allowed to run for 0 - 3 hours unless specified otherwise.

[0052] For transesterification reactions, FAME contents were analyzed by GC- MS methods. When the reactions were completed, the catalysts were filtered out. The liquid products obtained were vaporized to remove excessive methanol, and then settled in a separating funnel. The upper layers in the separating funnel (mainly containing fatty acid methyl esters) were characterized by a GC-MS spectrometer (Claras 500 MS System, PerkinElmer, Shelton, CT) equipped with a capillary column (Rtx- WAX Cat. No.12426) (Bellefonte, PA). Methyl arachidate (Nu-Chek Prep Inc, Elysian, MN) was used as an internal standard. For esterification reaction, FAME contents were also analyzed by GC-MS methods.

Catalyst Screening

[0053] A series of catalysts made of oxides of fourth period metals were prepared and tested for their catalytic activities in esterification and transesterification reactions. Referring to Fig. 1, at 200°C, all catalysts tested (KOH, Ca(OH)₂, Sc₂0₃, Ti0₂, V₂0₃, Cr₂0₃, Mn0₂, Fe₂0₃, CoO, NiO, CuO and ZnO) showed high activities in oleic acid esterification reactions. However, only KOH, Ca(OH)₂, Sc₂0₃, Ti0₂ and ZnO showed high activities in triglyceride transesterification. It is noted that the d- electron configuration influences catalyst activities. The screening results showed that the catalysts with dO, or dlO structures had high activities in both

transesterification and esterification reactions.

Binary Catalysts - ZnO/Si0₂, ZnO/C and Zn/Al₂0₃ Catalysts

[0054] Raw materials and catalyst preparation. Si0₂, A1₂0₃ and C were purchased from Sigma- Aldrich Inc. (St. Louis, MO). In view of the catalyst screening results, ZnO was selected as the main catalyst component. A series of ZnO-based binary catalysts were prepared through an impregnation method. A 2 M Zn(N0₃)₂ solution was prepared as the impregnated liquid. Si0₂, A1₂0₃ and C were calcined at about 450°C for about 2 hours to stabilize their crystal structure before usage. 100 g of each of the pretreated Si0₂, A1₂0₃ and C were separately

impregnated in the Zn(N0₃)₂ solutions for about 3 hours. The resultant solids were removed from the solutions, dried at about 100°C for about 10 hours, and then calcined at about 450°C for about 12 hours. The obtained catalysts were labeled as Si0₂, A1₂0₃ and C in Fig. 2.

[0055] Product analysis. The FAME yields from triglyceride and from oleic acid were determined by GC-MS spectra. From the amount of C₁₆ methyl esters determined in the products, the amounts of the FAME from triglyceride and the FAME yield from oleic acid can be calculated as follows.

FAME yield from triglyceride = 9.69 * [C₁₆] and

FAME yield from oleic acid =

Total FAME yield - FAME yield from triglyceride

[0056] Reaction conditions. A mixture of soybean oil and oleic acid (about 50 % to 50 %) was prepared. The reactions were conducted with a 10: 1 molar ratio of methanol to oleic acid with a 0.8 % catalyst loading at 200°C and 500 Psi.

[0057] Results. In comparison with the ZnO catalyst, ZnO/Si0₂, ZnO/C and Zn/Al₂0₃ showed high yields of total FAME. As shown in Fig. 2, the yields of total FAME and the FAME fractions from transesterification and from oleic acid esterification were separately reported. The ratio of transesterification and esterification was maintained at about 0.97. Not wishing to be bound by any theory, the results suggested that Si0₂, C and A1₂0₃ act as structure promoters, which physically improved ZnO dispersion.

Binary Catalysts - Na, K, Ca, Mg, or La Modified ZnO Catalysts

[0058] Catalyst preparation. The Ca, Mg, or La modified ZnO catalysts were prepared using the improved homogeneous precipitation method described above. The Na and K modified ZnO catalysts were prepared using an incipient- wetness impregnation method. Concentrations of NaOH and KOH used were about 0.4 mol/mL. The obtained catalysts were labeled as Na, K, Ca, Mg and La in Fig. 3.

[0059] Reaction conditions. A mixture of soybean oil and oleic acid (about 50 % to 50 %) was prepared. The reactions were conducted with 10: 1 molar ratio of methanol to oleic acid with a 0.8 % catalyst loading at 200°C and 500 Psi.

[0060] Results. Referring to Fig. 3, it was shown that the addition of Na, K, Ca, Mg, or La to ZnO improved the transesterification reactions, but decreased the esterification reactions. The results also indicated that only Mg and La modified ZnO catalysts have higher total FAME yields than the ZnO catalyst. The electronegativity of the metals is as follows: K⁺ < Na⁺ < Ca²⁺ < Mg²⁺ < La³⁺ < Zn²⁺.

Binary Catalysts - Sn, Fe, Co, or V Modified ZnO Catalysts

[0061] Catalyst preparation. The Sn, Fe, Co, or V modified ZnO catalysts were prepared using the improved homogeneous precipitation method described above. The obtained catalysts were labeled as Sn, Fe, Co, and V in Fig. 4.

[0062] Reaction conditions. A mixture of soybean oil and oleic acid (about 50 % to 50 %) was prepared. The reactions were conducted with a 10: 1 molar ratio of methanol to oleic acid with a 0.8 % catalyst loading at 200°C and 500 Psi.

[0063] Results. Referring to Fig. 4, it was shown that the addition of Sn, Fe, Co, or V to ZnO improved the esterification reactions, but decreased the transesterification reactions. The electronegativity of the metals is as follows 2+

< Sn⁴⁺ < Fe 3+ < Co³⁺ < V³⁺.

Binary Catalysts - Pr, Ce, Yb, Cu, or Ag Modified ZnO Catalysts

[0064] Catalyst preparation. The Pr, Ce, Yb, Cu, or Ag modified ZnO catalysts were prepared using the improved homogeneous precipitation method described above. The obtained catalysts were labeled as Pr, Ce, Yb, Cu, or Ag in Fig. 5.

[0065] Reaction conditions. A mixture of soybean oil and oleic acid (about 50 % to 50 %) was prepared. The reactions were conducted with a 10: 1 molar ratio of methanol to oleic acid with a 0.8 % catalyst loading at 200°C and 500 Psi.

[0066] Results. Pr, Ce, Yb, Cu, or Ag was mixed with ZnO to adjust the electronegativity of the obtained catalysts. Referring to Fig. 5, it was shown that all Pr, Ce, Yb, Cu, or Ag Modified ZnO catalysts were active in converting acidic oils into FAME. Referring to Figs. 1-5, it was shown that Pr, Ce, Yb, Cu, Ag, Si0₂, C, A1₂0₃, Mg, La, Sn, or V modified ZnO catalysts are among the most active catalysts.

Optimization of Pr Modified ZnO Catalyst

[0067] Catalyst preparation. The Pr modified ZnO catalyst was prepared using the improved homogeneous precipitation method described above. The ratio of Zn to Pr was about 3: 1.

[0068] Results - control test. To optimize the reaction conditions of converting acidic oils, a series of control tests was conducted. Referring to Fig. 6, for pure soybean oil, there was almost no conversion at 200°Cin the absence of a catalyst. Referring to Fig. 7, for oleic acid, the rate of FAME formation increased with elevated reaction temperatures in the absence of a catalyst. FAME formation using acidic oils with different oleic acid contents was then tested. Referring to Fig. 8, it was shown that oleic acid can catalyze triglyceride conversion to FAME in the absence of a catalyst. [0069] Optimizing reaction conditions. Referring to Figs. 9-13, the effect of the stirring speeds, oleic acid contents, reaction temperatures, catalyst loadings and methanol to oil molar ratios on FAME yields were determined. The results suggested that the stirring speed was preferably at 300 rpm to obtain a high yield of FAME using the ZnPr catalysts. Preferably, the acid content was higher than 67 %.

Preferably, the reaction temperature was 200 °C. Preferably, the molar ratio of methanol to oil was 10: 1. Preferably, the catalyst loading was 0.8 %.

Binary Catalysts on Support - La or Pr Modified ZnO Catalysts on A1₂0₃ Support

[0070] Catalyst preparation. La modified ZnO catalysts on A1₂0₃ were prepared using the traditional impregnation method. Total Zn and La loading was about 15 wt % of the total weight of the La modified ZnO catalysts on A1₂0₃ and the mole ratio of Zn to La is 3:2. A 2 M of mixture of Zn(N0₃)₂ and La(N0₃)₃ solution was prepared as the impregnated liquid (Zn:La = 3:2 mol). A1₂0₃ was calcined at about 450°C for about 2 hours to stabilize their crystal structure before usage. 100 g of the pretreated A1₂0₃ was impregnated in the mixture solution for about 3 hours. The resultant solids were removed from the solutions, dried at about 100°C for about 10 hours, and then calcined at about 450°C for about 12 hours. If the total Zn/La loading is less than 15 wt %, a repeat impregnation will be processed. Pr modified ZnO catalysts on A1₂0₃ were prepared and tested similarly as well.

[0071] Reaction conditions. Oil extracted from DDGS (Dried Distillers Grains with Solubles) corn was used. DDGS is a kind of waste from the ethanol production process. The DDGS corn oil used contains 12 % of FFA, 88 % of triglyceride. The reaction was carried out in a lab scale continuous reactor. Diameter of the reactor tube is 1 inch with a length of 24 inch. 53.44 g of the ZnLaAl oxide catalyst was loaded. The mole ratio of methanol to oil was 12: 1. The reaction temperature was 200 °C and the pressure was 600 Psi, with a residence time of 80 minutes. [0072] Results. As shown in Figure 14, the ZnLaAl oxide catalyzed reaction was allowed to run for 140 days with an average FAME yield around 82.5 %. This catalyst showed a high activity in converting acidic oil and maintains activity for an extended period of time. Not wishing to be bound by any theory, it is believed that aluminum oxide in the ZnLaAl oxide catalyst acts as a physical promoter; La oxide acts as an electronic promoter. With the presence of La and Al oxides, the ZnO catalyst showed an enhanced activity and prolonged durability in converting acidic oils in comparison with pure ZnO catalysts.

[0073] The novel catalysts of the present disclosure can be used for any purpose. These catalysts can be used in transesterification reactions. These catalysts can also be used in esterification reactions. Preferably, these catalysts are used to catalyze both transesterification and esterification reactions. One application of these catalysts is catalyzing transesterification and esterification reactions in biodiesel production.

[0074] While the present disclosure has been described with reference to certain embodiments, other features may be included without departing from the spirit and scope of the present disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.

Claims

1. A catalyst, the catalyst comprising:

zinc oxide and the oxide of a second metal, the second metal selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof.

2. The catalyst of claim 1, wherein the second metal is selected from the group consisting of La, Pr, Ce, Yb, Cu, Ag, Si, C, Al, Mg, La, Sn, V and combinations thereof.

3. The catalyst of claim 1, wherein the second metal is Pr.

4. The catalyst of claim 1, wherein the second metal is La.

5. The catalyst of any of claims 1-4, further comprising a support, wherein zinc oxide and the oxide of the second metal are supported on the support.

6. The catalyst of claim 5, wherein the second metal is La.

7. The catalyst of claim 5, wherein the second metal is Pr.

8. The catalyst of claim 5, wherein the support is Si0₂, A1₂0₃ or C.

9. The catalyst of claim 5, wherein the support is A1₂0₃.

10. The catalyst of claim 5, which is zinc oxide and La oxide supported on aluminum oxide.

11. The catalyst of claim 5, which is zinc oxide and Pr oxide supported on aluminum oxide.

12. The catalyst of any of claims 1-4, wherein zinc oxide is impregnated with the second metal oxide or salt.

13. A catalyst, the catalyst comprising:

zinc oxide mixed with the oxide of a second metal, the second metal being more electronegative than zinc.

14. The catalyst of claim 13, wherein the second metal is selected from the group consisting of K, Na, Ca, Mg, Sn, Al, La, Si, C, Fe, Co, V, Pr, Ce, Yb, Cu, Ag, Ti, Zr and combinations thereof.

15. The catalyst of claim 13, wherein the second metal is La or Pr.

16. The catalyst of claim 13, 14 or 15, further comprising a support, wherein zinc oxide and the oxide of the second metal are supported on the support.

17. A process, comprising:

contacting the catalyst of claim 1, or 13 with a reaction, the catalyst catalyzing the reaction.

18. The process of claim 17, wherein the reaction is an esterification reaction.

19. The process of claim 17, wherein the reaction is a transesterification reaction.

20. The process of claim 17, wherein the reaction comprises both an esterification reaction and a transesterification reaction, and the catalyst catalyzes both the esterification reaction and the transesterification reaction.

21. A process, the process comprising: contacting a material that comprises a glyceride with an alcohol in the presence of the catalyst of claim 1, or 13 such that at least some of the glyceride is converted into the corresponding alcoholic ester of the glyceride.

22. The process of claim 21, wherein the alcohol is methanol.

23. The process of claim 21 or 22, wherein the catalyst catalyzes the alcoholic ester formation.

24. The process of claim 21 or 22, wherein the material further comprises a free fatty acid, and wherein at least some of the free fatty acid is converted into the corresponding alcoholic ester of the free fatty acid in the presence of the catalyst.

25. The process of claim 24, wherein the catalyst catalyzes the formation of the alcoholic ester of the free fatty acid.

26. The process of claim 24, wherein the catalyst simultaneously catalyzes the transesterification reaction of the glyceride and the esterification reaction of the free fatty acid.

27. The process of claim 21 or 22, wherein the glyceride comprises a triglyceride.

28. The process of claim 21 or 22, wherein the glyceride comprises a diglyceride.

29. The process of claim 21 or 22, wherein the material is a non-refined oil.

30. The process of claim 21 or 22, wherein the material is selected from the group consisting of a crude oil, a waste oil, an animal fat, and combinations thereof.

31. The process of claim 21 or 22, wherein the material further comprises water, and wherein the water content in the material is more than about 0.15 weight %.

32. The process of claim 31, wherein the water content in the material is more than about 5 weight %.

33. The process of claim 32, wherein the water content in the material is more than about 10 weight %.

34. The process of claim 21 or 22, wherein the material further comprises one or more free fatty acids, and wherein the free fatty acid content in the material is more than about 0.5 weight %.

35. The process of claim 34, wherein the free fatty acid content in the material is more than about 3.5 weight %.

36. The process of claim 34, wherein the free fatty acid content in the material is more than about 10 weight %.

37. A process, the process comprising:

contacting a material that comprises a free fatty acid with an alcohol in the presence of the catalyst of claim 1, or 13 such that at least some of the free fatty acid is converted into the corresponding alcoholic ester.