Methacrylic acid production method

Abstract

A method of producing methacrylic acid using a hydrotalcite catalyst and subcritical water is described.

Claims

1. A method of producing methacrylic acid comprising reacting a substrate with a palladium nitrate catalyst comprising a hydrotalcite under conditions sufficient to produce methacrylic acid in a single step, wherein the substrate is selected from the group consisting of 2-hydroxyisobutyric acid or salts thereof, itaconic acid or salts thereof, citric acid or salts thereof, citramalic acid or salts thereof, and combinations thereof.

2. The method of claim 1, wherein the hydrotalcite is a solid form of hydrotalcite.

3. The method of claim 2, wherein the solid form of hydrotalcite is porous.

4. The method of claim 1, further comprising reacting in the presence of an inert gas.

5. The method of claim 1, further comprising reacting in the presence of subcritical water or supercritical water.

6. The method of claim 1, wherein a temperature of reacting is from about ambient temperature to about 700 C.

7. The method of claim 1, wherein a pressure of reacting is from about ambient pressure to about 1000 pounds per square inch.

8. The method according to claim 1, wherein a residence time of the reacting is from about 0.5 minutes to about 60 minutes.

9. The method of claim 1, wherein a catalyst turnover number is from about 10 to about 10.sup.6.

10. The method of claim 1, wherein a temperature of the reacting is from about 200 C. to about 250 C.; and a pressure of the reacting is about 500 pounds per square inch, and the reacting takes place in the presence of helium; and from about 1 to about 30 minutes, wherein the substrate is at a concentration of from about 5 to about 20 grams per liter; and wherein the catalyst weight is from about 0.125 g to about 2 grams.

11. A method of producing methacrylic acid comprising reacting a substrate with a catalyst comprising a hydrotalcite under conditions sufficient to produce methacrylic acid in a single step, wherein the substrate is selected from the group consisting of 2-hydroxyisobutyric acid or salts thereof, itaconic acid or salts thereof, citric acid or salts thereof, citramalic acid or salts thereof, and combinations thereof, and wherein the hydrotalcite is both solid and porous.

12. The method of claim 11, further comprising reacting in the presence of subcritical water or supercritical water.

13. The method of claim 11, wherein the catalyst comprises a transition metal or a salt thereof, wherein the transition metal is selected from the group consisting of palladium, platinum, and rhodium.

14. The method of claim 11, wherein a catalyst turnover number is from about 10 to about 10.sup.6.

15. A method of producing methacrylic acid comprising reacting a substrate with a catalyst comprising a hydrotalcite under conditions sufficient to produce methacrylic acid in a single step; wherein the substrate is selected from the group consisting of 2-hydroxyisobutyric acid or salts thereof, itaconic acid or salts thereof, citric acid or salts thereof, citramalic acid or salts thereof, and combinations thereof; and further comprising reacting in the presence of subcritical water or supercritical water.

16. The method of claim 15, wherein the catalyst comprises a transition metal or a salt thereof, wherein the transition metal is selected from the group consisting of palladium, platinum, and rhodium.

17. The method of claim 15, wherein the hydrotalcite is a solid form of hydrotalcite, wherein the solid form of hydrotalcite is porous.

18. The method of claim 15, wherein a catalyst turnover number is from about 10 to about 10.sup.6.

19. A method of producing methacrylic acid comprising reacting a substrate with a catalyst comprising a hydrotalcite under conditions sufficient to produce methacrylic acid in a single step; wherein the substrate is selected from the group consisting of 2-hydroxyisobutyric acid or salts thereof, itaconic acid or salts thereof, citric acid or salts thereof, citramalic acid or salts thereof, and combinations thereof; and wherein a catalyst turnover number is from about 10 to about 10.sup.6.

20. The method of claim 19, wherein the catalyst comprises a transition metal or a salt thereof, wherein the transition metal is selected from the group consisting of palladium, platinum, and rhodium.

21. The method of claim 19, further comprising reacting in the presence of subcritical water or supercritical water.

22. The method of claim 19, wherein the hydrotalcite is a solid form of hydrotalcite, wherein the solid form of hydrotalcite is porous.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 describes C.sub.2 carbonylation technologies in methacrylic and methyl methacrylate production as described by Spivey et al., 1997

(2) FIG. 2 describes pathways for decomposition of citric acid in hot liquid water as described by Carlsson et al., 1994.

(3) FIG. 3 describes a Pd-catalysed itaconic acid decarboxylation with different amounts of NaOH wherein the reaction conditions are 0.15M itaconic acid, 250 C., 1 hr residence time as described by Le Ntre et al., 2014.

(4) FIG. 4 shows a scheme describing a biosynthesis pathway of itaconate and its compartmentalization between cytosol and mitochondrion in the A. terreus cell; note: cis-aconitate transport is speculative as described by Steiger et al., 2013.

(5) FIG. 5 is a schematic diagram showing a manner of converting renewable sugars to biobased methacrylic acid.

(6) FIG. 6 shows a picture of a PARR 5000 Multiple Reactor System.

(7) FIG. 7 is a graph of MAA yield at 200 C. under reaction conditions of 20 gr/lit citric acid+0.15 M NaOH, 1 g catalyst for 1 hr

(8) FIG. 8 is a graph of MAA yield at 225 C. under reaction conditions of 20 g/lit citric acid+0.15 M NaOH, 1 g catalyst for 1 hr.

(9) FIG. 9 is a graph of MAA yield at 250 C. under reaction conditions of 20 g/lit citric acid+0.15 M NaOH, 1 g catalyst for 1 hr.

(10) FIG. 10 is a graph of MAA yield at 250 C. (Substrate: 20 g/lit citric acid+No base).

(11) FIG. 11 is a graph of a comparison between blank reactions with and without sodium hydroxide (250 C. with 0.15M NaOH and 20 g/lit citric acid.

(12) FIG. 12 is a graph of MAA yield at 250 C. (Substrate: 20 g/lit itaconic acid+No base)

(13) FIG. 13 is a graph of a comparison between blank reactions with and without NaOH (250 C. 0.15M NaOH-20 g/lit itaconic acid)

(14) FIG. 14A and FIG. 14B are a set of graphs showing catalyst reuse results (1 g fresh hydrotalcite-0.92 g recovered hydrotalcite-250 C.-20 g/lit itaconic acid-15 minutes).

(15) FIG. 14C and FIG. 14D are a set of graphs showing catalyst reuse results (1 g fresh hydrotalcite0.70 g recoverd hydrotalcite250 C.-20 g/lit citric acid-5 minutes)wherein the abbreviations have the following meanings: MA is methacrylic acid, MS is mesaconic, CC is citraconic, IT is itaconic, and AA acetic acid.

(16) FIG. 15 is a graph showing the effect of itaconic acid concentration on MAA yield (1 g hydrotalcite-250 C.)

(17) FIG. 16 is a graph showing the effect of adding HTC on lower concentrations of itaconic acid (1 g hydrotalcite-250 C.-15 minutes residence time)

(18) FIG. 17A and FIG. 17B are graphs showing the conversion of 2-hydroxyisobutryic acid to methacrylic acid using subcritical water at 250 C. wherein HIBA is 2-Hydroxyisobutyric acid and HTC is hydrotalcite.

DETAILED DESCRIPTION

(19) In the description and claims of the present application, each of the verbs, comprise, include and have, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements, or parts of the subject or subjects of the verb.

(20) The production method may be carried out in an inert gas, for example, nitrogen, helium, or argon. The method may be carried out in subcritical water or in supercritical water. The production method may be carried out in anhydrous conditions in an appropriate organic solvent.

(21) The production method may carried out at a temperature of from about ambient temperature to about 700 C., or from about 50 C. to about 500 C., or from about 100 C. to about 400 C. or from about 200 C. to about 300 C.

(22) The production method may be carried out at a pressure of from about ambient pressure to about 1000 psi (pounds per square inch), or from about 100 psi to about 1000 psi, or from about 200 psi to about 700 psi, or from about 250 psi to about 500 psi.

(23) The production method may be carried out in a batch or continuous mode.

(24) The production method may be carried out with residence time i.e, a time a reaction mixture is in contact with the catalyst, is from about 0.5 min to about 60 min, or from about 1 min to about 45 min, or from about 1 min to about 30 min, or from about 1 min to about 15 min, or from about 15 min to about 30 min.

(25) The concentration of acid precursor in a reaction vessel may be from about 1 to about 100 g/L or from about 2 to about 50 g/L, or from about 3 to about 50 g/L, or from about 5 to about 20 g/L, or from about 5 to about 10 g/L, or from about 10 to about 20 g/L.

(26) The amount of catalyst that may be utilized may range from about 0.1 g to about 1 g using the concentrations of acid precursor and may depend on whether the reaction is run as a batch or as a continuous process.

(27) The catalyst turnover number (moles of acid converted per mole of catalyst) may be from about 10 to about 10.sup.6, or from about 10 to about 10.sup.6, or from about 100 to about 10.sup.5 or from about 100 to about 10.sup.4.

(28) In order to determine the kinetics of methacrylic acid formation over a solid base catalyst, hydrotalcite (clay mineral) will be employed as reaction catalyst. Hydrotalcite impregnated with palladium catalyst will be also synthesized, since the use of both transition-metal catalysts and base catalysts in decarboxylation of itaconic acid to methacrylic acid is discussed in literature review analysis. Each catalyst will be used to catalyze the decarboxylation of itaconic acid and citric acid and citramalic acid. These substrates are used in order to have an organic decarboxylation reaction since itaconic acid only needs one decarboxylation step to produce methacrylic acid and citric acid requires one step dehydration followed by two step decarboxylation and citramalic acid requires one step decarboxylation followed by one step dehydration. A kinetic study of decarboxylation reaction over different amounts of catalysts, concentrations of substrate and residence times will be performed in a series of batch reactors. Yield, conversion and selectivity achieved by each catalyst will be determined. Hence, the results of each experiment will help us to find an optimum temperature, substrate concentration and residence time point for the highest methacrylic acid selectivity and yield. Table 3 shows different reaction conditions that are going to be tested.

(29) TABLE-US-00003 TABLE 3 Reaction Variables Temperature 200-250 C. Pressure 500 psi Inert Gas Helium Residence Times 1-15-30 min Carboxylic Acid 5-10-20 gr/lit Concentrations Catalyst Weight 0.125-0.25-0.5-1-2 gr

(30) Production of methacrylic acid is performed in the 75 mL vessel of a PARR 5000 Multiple Reactor System. The vessel is loaded with 40 mL of substrate solution in deonized water and catalyst that are mixed using a magnetic stir bar, inside the vessel. The vessel is sealed using the vessel cap with six screws. The mixture is stirred with a magnetic bar stirrer at 750 rpm. The headspace of the vessel is charged with 500 psi of helium through a needle valve. The vessel is heated using a heating well at an average heating rate of 9 C./min. The temperature is measured by a thermocouple in an alloy thermowell (FIG. 5). Once the reaction is completed, the vessel is cooled down using a water bath at room temperature. The stirrer bar is allowed to agitate during heat-up. After taking gas sample (using 1 liter Tedlar bag), the headspace pressure is released through a second needle valve. The catalyst is removed from the liquid product using filter paper.

(31) Methacrylic acid and byproducts concentrations (liquid sample) are determined using High Performance Liquid Chromatography (HPLC). HPLC (Shimadzu LC-20 AT) is performed by using an autosampler and pump with 7 mN H.sub.2SO.sub.4 eluent and 0.6 mL/min flow at 60 C. Methacrylic acid peak is verified with UV detection at 210 nm. The sample injection volume and run time are 5 microliter and 30 minutes, respectively. Coregal 64-H transgenomic column (7.8300 mm) is used in this instrument. Gas ChromatographyThermal Conductivity Detection (GC-TC Hewlett Packard 5890 Series II) is performed for gas analysis with the inlet temperature of 100 C., initial oven temperature of 35 C. and detector temperature of 140 C. The initial 5 minutes holding time, followed by a ramp of 20 C./min for 8.25 minutes and final holding time of 5.75 minutes at 200 C. is used as the method for gas analysis. The volume of each injection is 50 microliter. The concentration of each compound is determined with standard curves on HPLC and GC-TCD. Since the main reaction is decarboxylation, CO.sub.2 and propene (result of methacrylic acid degradation) are expected in gas samples. The standard curve for CO.sub.2 was performed using nitrogen as the balance gas. 5, 10, 25, 50 and 75 percent by volume CO.sub.2 (run in triplicate) was used to make the standard curve on GC-TCD. Methacrylic acid, mesaconic acid, citraconic acid, acetone, acetic acid, pyruvic acid, citric acid and itaconic acid standard curves were made using deionized water as the solvent. 5 different concentrations of each compound based on g/lit were used to make the standard curve on HPLC.

(32) Methacrylic acid and byproducts concentrations (g/lit) are determined using High Performance Liquid Chromatography (HPLC). Considering that the volume of reaction is 40 ml, moles of each compound are calculated through molar weight. In order to calculate yield and selectivity of each compound and conversion of reaction substrate the following equations are used.

(33) $\begin{array}{cc}\%\mathrm{Yield}\mathrm{of}\mathrm{Compound}i=\frac{\mathrm{Moles}\mathrm{of}\mathrm{Compound}i\mathrm{Generated}}{\mathrm{Moles}\mathrm{of}\mathrm{Substrate}\mathrm{Charged}}*100& \mathrm{Eq}.\left(1\right)\\ \mathrm{Conversion}\mathrm{of}\mathrm{Substrate}\left(X\right)=\frac{\mathrm{Moles}\mathrm{of}\mathrm{Substrate}\mathrm{Reacted}}{\mathrm{Moles}\mathrm{of}\mathrm{Substrate}\mathrm{Charged}}& \mathrm{Eq}.\left(2\right)\\ \%\mathrm{Selectivity}\mathrm{of}\mathrm{Methacrylic}\mathrm{Acid}=\frac{\mathrm{Moles}\mathrm{of}\mathrm{Methacrylic}\mathrm{Acid}\mathrm{Generated}}{\mathrm{Total}\mathrm{Moles}\mathrm{of}\mathrm{Undesired}\mathrm{Byproducts}}*100& \mathrm{Eq}.\left(3\right)\end{array}$

(34) Gas ChromatographyThermal Conductivity Detection (GC-TC) is performed for gas analysis. Gas samples are taken after the reactor is cooled down at room temperature. 50 microliter of each gas sample is injected on GC-TCD. Percent CO.sub.2 (by volume) of each sample is calculated using the peak area and standard curve of CO.sub.2. In order to calculate the number of carbon dioxide moles, total moles of gas in the reactor is calculated using ideal gas law. The total moles of gas multiplied by percent CO.sub.2 will give the number of CO.sub.2 moles:

(35) $\begin{array}{cc}{n}_{\mathrm{CO}2}=\frac{\mathrm{PV}}{\mathrm{RT}}*\%\mathrm{CO}2& \mathrm{Eq}.\left(4\right)\end{array}$
P=Reactor Pressure
V=Reactor Headspace Volume
R=Universal Gas Constant 8.314 J/K.Math.mol
T=Temperature of The Gas after cool-down

EXAMPLES

Example 1: Hydrotalcite and Pd/Hydrotalcite Synthesis

(36) The raw hydrotalcite (HTC) powder with MgO/Al.sub.2O.sub.3 ratio=4.0-5.0 (purchased from Sigma-Aldrich) was calcined at 400 C. overnight and then allowed to cool. It was stirred in deionized water to make a paste, and the paste was placed in a 105 C. degree drying oven over night. Then the dried hydrotalcite was smashed and sieved to a particle size between 1 mm and 0.5 mm.

Example 2: Palladium on Hydrotalcite Preparation

(37) Literature review analysis indicates use of transition-metal catalysts such as palladium and platinum in production of methacrylic acid from itaconic acid. The importance of reaction medium basicity in decarboxylation of itaconic acid to methacrylic acid was also discussed in the background and literature analysis chapter. Therefore a solid-base catalyst impregnated with a transition metal will be synthesized with the purpose of increasing methacrylic acid yield in decarboxylation of carboxylic acids such as itaconic acid. Pd/HTC will be prepared using incipient wetness impregnation (Nikolopoulos et al., 2005). Incipient wetness impregnation is a technique for the synthesis of heterogeneous catalysts. The active metal precursor is dissolved in aqueous solution. Then the metal containing solution is added to the catalyst support containing the same pore volume as the volume of the solution that was added. Capillary action draws the solution into the pores. In our case, a 5 wt. % palladium (II) nitrate dihyrate (40% Pd basis, Sigma-Aldrich) solution in deionized water will be prepared. Nikolopoulos et al. 2005 used palladium chloride salt for impregnating hydrotalcite catalyst. Since chloride can have a poisoning effect, the nitrate salt is used in our study. After adding the solution to the hydrotalcite powder (containing the same pore volume as the volume of the solution that is added), The catalyst will be dried at 120 C. for two hours, calcined at 400 C. for two hours and then crushed and sieved to the desired particle size. Total pore volume of the catalyst is measured using nitrogen desorption curves with BJH analysis. Prior to reaction the sample will be reduced at 450 C. for 8 hours in flowing 100% hydrogen (Nikolopoulos et al., 2005).

Example 3: Decarboxylation of Citric Acid

(38) Decarboxylation process is also applicable to citric acid, a more widely available bio-based substrate. Citric acid requires one dehydration step, followed by two decarboxylation steps to result methacrylic acid. The kinetics of methacrylic acid formation from citric acid over varying temperatures, and catalysts were studied. The reactions were performed at temperatures of 200, 225, 250 C. and for one hour residence time. The feedstock solution contains 20 g/lit citric acid and 0.15 mol/lit NaOH. The effect of adding NaOH in experiments is due to a change in pH. pH of the medium effects on methacrylic acid selectivity. At low base concentrations, methacrylic acid degradation can also occur due to acid-catalysed addition of water molecules across the double bonds. The initial series of experiments were performed with hydrotalcite, Pd/C (5 wt. %-Alfa Aesar) and synthesized iron oxide/C catalysts.

Example 4: Deposition of Iron Oxide Nanoparticles in Activated Carbon

(39) Using iron containing catalysts in catalytic decarboxylation has been reported. Zhang et al. reported catalytic decarboxylation of fatty acids by iron-containing minerals. For the purpose of decarboxylation reaction, iron oxide catalyst was prepared using the following procedure: 150 ml of Fe(NO3)3.9H2O (SIGMA-ALDRICH, ACS reagent of minimum purity 98 wt. %) Solution (0.5 M) was made with deionized water. 30.3 g activated carbon (SIGMA-ALDRICH, Norit RO 0.8) pellets were allowed to soak in the solution. The solution was subjected to sonication treatment for 45 minutes at room temperature. After five days of soaking, the mixture was divided into three batches (each 10.1 grams of activated carbon and 50 ml of the solution). Each batch was treated under helium gas in the high pressure micro reactor system. Starting pressure was 750 psi to the final pressure of 4050 psi. Starting temperature was 17 C. and final temperature was 355. The mixture was maintained at 355 C. for 90 minutes. Finally the reactor was cooled down to 33 C. The activated carbon pellets were separated from the mixture and washed several times with deionized water and dried overnight in the oven (Xu and Teja, 2006).

(40) FIG. 7 shows that at 200 C. methacrylic acid yield, in presence of hydrotalcite, is zero. Results of control experiments indicate higher yields of methacrylic acid in comparison with catalytic experiments at 200 C. FIG. 7 and FIG. 8 also suggest the same trend for methacrylic acid formation from citric acid at higher temperatures. The results verify that methacrylic acid yield increases with increasing the temperature in both blank and catalytic experiments.

(41) Unfortunately, we were not able to repeat Le Ntre et al., 2014 results (65% MAA yield) with palladium on carbon catalyst and none of the other catalysts worked in the decarboxylation process of citric acid in presence of sodium hydroxide.

(42) Since hydrotalcite is a solid-base catalyst, a set of experiments with no base in reaction medium at different residence times using different amounts of hydrotalcite were also performed on citric acid. The results, shown in FIG. 10, indicate that methacrylic acid yield increases with decreasing the amount of catalyst in the reaction medium. The highest and the lowest methacrylic acid yield were achieved at 0.125 g and 1 g amount of hydrotalcite, respectively. It is notable that blank reactions had lower methacrylic acid yields than almost all of the catalytic reactions except for 1 gram hydrotalcite runs. From FIG. 9 and FIG. 10, it is obvious that adding both homogeneous and heterogeneous catalysts increases the methacrylic acid yield. The 1 minute residence time experiments show promising results for production of methacrylic acid continuously.

Example 5: Decarboxylation of Itaconic Acid

(43) Formation of methacrylic acid from citric acid requires one dehydration step followed by two decarboxylation steps (FIG. 2). Itaconic acid can form methacrylic acid with only one decarboxylation step. Hence a set of experiments with no base in reaction medium at different residence times using different amounts of hydrotalcite were also performed on itaconic acid.

(44) Methacrylic acid yield also increases with decreasing amounts of catalyst using itaconic acid as the reaction substrate. The highest methacrylic acid yield was achieved at 0.125 g catalyst (the same trend as citric acid reactions). The results of both citric acid and itaconic acid experiments suggest an optimum amount of solid-base catalyst for the highest methacrylic acid yield. In order to compare methacrylic acid yield in blank reactions and reactions with homogeneous base catalysts, 0.15 M sodium hydroxide was added to the reaction medium. Adding sodium hydroxide to the reaction medium also caused an increase in methacrylic acid yield (FIG. 12 and FIG. 13).

Example 6: Catalyst Reuse

(45) In order to study the reusability of catalysts, the catalysts were recovered after the reactions and washed with deionized water and dried at 105 C. in oven for one hour. After drying the catalyst and performing catalyst characterization using BET/BJH analysis, the recovered catalyst was reused in the same reaction condition as the fresh catalyst was used. FIG. 14 shows that the same itaconic acid conversion was achieved with both fresh and reused hydrotalcite. FIG. 14 also shows that methacrylic acid yield increased (1.65 factor increase in yield) and is higher in the reused hydrotalcite run. Further catalyst characterization is required in order to determine the reason for increasing activity of hydrotalcite after it is reacted. Similar results were obtained using citric acid (FIG. 14, a 2.55 factor increase in MA yield when the catalyst was recovered and reused).

(46) Surface area, total pore volume and average pore size of hydrotalcite was measured with BET and BJH analysis (Table 4). Surface area is determined using nitrogen adsorption in a Quantachrome Austosorb-1C with BET analysis. Total pore volume and average pore size are determined using nitrogen desorption curves with BJH analysis. The surface area, average pore size and total pore volume of the reacted hydrotalcite decreased after the first reaction as expected. Interestingly, the catalyst characterization for the reused hydrotalcite indicates an increase in surface area and total pore volume. The increased surface area and pore volume of reused hydrotalcite might be attributed to the removal of interlayer water molecules and carbon dioxide from the carbonate anion present in the brucite layer (Onda et al., 2008).

Example 7: Effect of Substrate Concentration on Methacrylic Acid Yield

(47) In order to study the effect of itaconic acid concentration on methacrylic acid yield, a series of experiments with varying substrate concentration were performed at 250 C. with 1 gram hydrotalcite. In all three residence times, the highest methacrylic acid was achieved in 20 g/lit itaconic acid concentrations (FIG. 15) and methacrylic acid yield did not show a remarkable increase or decrease with increasing residence time in each concentration. The 1 minute residence time experiments on both citric acid and itaconic acid show promising results for production of methacrylic acid continuously. Blank runs were also performed on 5, 10, 20 g/lit concentrations of itaconic acid. At 5 and 10 g/lit itaconic acid concentration, methacrylic acid yield was higher in blank runs in comparison to runs with one gram hydrotalcite which means that hydrotalcite has an inhibition effect on the decarboxylation reaction in lower concentrations of itaconic acid (FIG. 16).

Example 8: Production of Methacrylic Acid in Continuous Packed Bed Reactor System

(48) Preliminary results from studying the effect of itaconic acid residence time on methacrylic acid yield in presence of hydrotalcite verify that methacrylic acid yield rises rapidly to almost a steady state value. The methacrylic acid yield value in shorter residence times is approximately equal to the methacrylic acid yield value in longer residence times. These promising results lead us to design a process in order to produce methacrylic acid continuously using solid base catalysts. With this purpose, decarboxylation reactions will be performed in a continuous packed bed reactor system (Parr Instrument Company). The catalysts are loaded into the stainless steel tube reactor with inner diameter of 2.4 cm and length of 38 cm. Since our best results occur at 250 C. in the batch reactor system, this temperature will be used as the operating temperature in the continuous packed bed reactor system. In order to keep the substrate (carboxylic acid in water solution) in liquid phase during the reaction, the starting reaction pressure will be higher than the vapor pressure of water at 250 C. (600 psig). The

(49) $\frac{\mathrm{Concentration}\mathrm{of}\mathrm{Substrate}}{\mathrm{Mass}\mathrm{of}\mathrm{Catalyst}}$
ratio for the best results in the batch reactor system will help us design the process in the continuous reactor system. Residence time in packed bed reactors is equal to volume of bed/flow rate. Therefore measuring the bulk density of the catalyst and knowing the optimized mass of catalyst, we will be able to calculate the volume of catalyst bed. Therefore, with changing flowrate, liquid residence time will change. 50 grams of liquid feedstock will be used for each reaction, resulting in a total reaction time 100 minutes. Nitrogen is used as a carrier gas to the reactor at a rate of 100 mL/min.

Example 9: Production of Methacrylic Acid from 2-Hydroxyisobutyric Acid (HIB or HIBA)

(50) As described supra, 2-hydroxyisobutyric acid was reacted in subcritical water at 250 C. for different residence times. The reactions were performed in subcritical water alone and in the presence of hydrotalcite. 2-Hydroxyisobutyric acid (HIBA) can be produced via fermentation using genetically engineered microbial strains. As noted in FIG. 17, HIBA conversion approaches 80% in 15 minutes and achieves 66% yield, using subcritical water at 250 C. Since subcritical water can act as an acid under these conditions we theorize that an acid catalyzed reaction is occurring under these conditions leading to dehydration of HIBA to form methacrylic acid.

(51) ##STR00002##

(52) The results of preliminary studies using hydrotalcite indicate that using this solid base catalyst increases the methacrylic acid yield in decarboxylation reaction of itaconic acid and citric acid. High methacrylic acid yields in low residence times lead us to design a process in order to produce methacrylic acid continuously (in packed bed reactor system). Literature review analysis indicates the use of transition-metal catalysts such as palladium and platinum in production of methacrylic acid from itaconic acid and citric acid. However, we were not able to reach high methacrylic acid yields with Pd/C catalyst. We expect that synthesizing a solid base catalyst with acid sites and impregnated with a transition metal catalyst will be effective on increasing the methacrylic acid yield in decarboxylation reaction of carboxylic acids. Our results clearly indicate that there is an optimum substrate concentration to catalyst mass ratio in decarboxylation of citric acid and itaconic acid to methacrylic acid. Therefore we expect the same trend for decarboxylation of citramalic acid to methacrylic acid in presence of solid base catalysts. The reacted hydrotalcite showed higher activity in comparison to the fresh hydrotalcite. These promising results about the reusability of catalyst also confirm that this solid base catalyst can be a proper substitute for homogeneous base catalysts which are difficult to recycle and separation.

(53) The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art.

(54) It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above.

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