Christopher BradleyDr. Keith Hohn

Investigating the Use of Acid-Functionalized Iron Nano-Particles as a Catalyst for Sucrose Hydrolysis

AbstractThis report describes the potential use of acid-functionalized iron nano-particles as a catalyst for sucrose hydrolysis. These nano particles, due to their magnetic properties, might be easier to recover from solution after hydrolysis than conventional catalysts such as sulfuric acid. This research follows closely the experimental procedures of Ikenberry et. al. Of particular interest was the investigation of how different acid loadings on the nano-particles affected sucrose conversion. It would be preferable to not load the catalyst with more acid than necessary if there is a limiting sucrose conversion with respect to acid loading, or if the nano particles have a maximum loading. Prior study by Ikenberry et. al. showed that in some cases the ligands could become detached leading to a lowering of catalyst activity over time. This could be due to increased interaction between the ligands as the acid loading increases. The study of how different acid loadings affect the sucrose conversion might provide helpful results in determining if this is the case or not.

IntroductionThis report describes the potential use of acid-functionalized iron nano-particles as a catalyst for starch hydrolysis. These nano particles, due to their magnetic properties, might be easier to recover from solution after hydrolysis than conventional catalysts such as sulfuric acid. Iron nanoparticles were first precipitated using iron chlorides and ammonium hydroxide and then functionalized with 11-sulfoundecanoic acid. Multiple sucrose hydrolysis reactions were then carried out and characterized using HPLC analysis.

Synthesis of 11-Sulfoundecanoic AcidAs described in Ikenberry et. al., 11-sulfoundecanoic acid was synthesized using 11-bromoundecanoic acid and sodium sulfite. The reaction took place in a 100 mL round-bottom boiling flask submerged in an oil bath on a hotplate. A temperature probe monitored the oil bath to maintain the reaction temperature. Before the reagents were added, 50 mL of deionized water was heated to 50C. The reagents were added in a 10:1 salt to acid molar ratio using 5 g of 11-bromoundecaonic acid. The acid was added first with care taken to ensure that the acid dispersed evenly throughout the water. To achieve this, the acid was added slowly and a stir bar set to 1500 rpm was used to stir the solution. Sodium sulfite was then added slowly to the flask.The reaction was allowed to take place for 1 hour at 50 C, then for 2 hours at 70 C, 6 hours at80C , and finally for 3 hours at 90 C. The reaction was monitored to ensure that the stir bar was adequately dispersing the reagents and that there was no settling. After reaction, the solution was run through a vacuum filtration system. The dried product was then centrifuged to remove excess salt. 5 mL of the dried product and 20 mL of water were added to each of six 30 mL centrifugation tubes and centrifuged for 10 minutes at 5000 rpm. To further purify the 11-sulfoundecanoic acid and further remove excess salt, the pH was lowered to 5 with HCl and then filtered using the vacuum filtration system. The dried product was then placed in a laboratory oven at 80 C for 5 days. The filtrate was centrifuged three more times in the same manner as before.

Nano-particle Synthesis and FunctionalizationThe Iron oxide nanoparticles were synthesized using the method described by Ikenberry et. al. Two batches of nanoparticles were prepared; one having a ligand loading of 0.5 g and the other with a loading of 1.0 g.Iron II chloride and Iron III chloride were precipitated in a nitrogen environment (in the absence of oxygen) to ensure that the iron chlorides were not oxidized. To further reduce the chances of oxidation, deoxygenated water was used during the precipitation. Both the iron chlorides and the deoxygenated water were stored in the glovebox where a nitrogen environment could be maintained. The iron II chloride and iron III chloride were then weighed out in the glovebox in a 1:2 molar ratio with 5 g of iron II chloride. Still in the glovebox, the iron chlorides were added to a 3-necked flask with 50 mL of the deoxygenated water (pictured below).

The flask containing the reagents was then placed in an oil bath maintained at 80 C. Nitrogen was constantly bubbled through the flask to ensure minimal oxidation of the iron chlorides. A condenser was placed in the middle septum of the flask to condense any vapor in order to maintain the liquid volume in the flask (pictured below). After 30 minutes of heating, 10 mL of 1 M ammonium hydroxide was injected into the flask. Heating was allowed to continue for 30 more minutes.

The precipitated iron nanoparticles were then sonicated for 10 minutes using a Sharpertek Model SH80-2L sonicator capable of an ultrasonic frequency of 40 kHz. This was done in the hopes of breaking up an larger agglomerations of particles.Two different functionalization batches were made. For the first, 1 g of the 11-sulfoundecanoic acid ligand was added to 1 g (dry weight) of the sonicated particles. The second was made by adding 0.5 g of the ligand to 1 g (dry weight) of the sonicated particles. The functionalization process outlined in Ikenberry et. al. was used. Each solution was heated to 95 C in an oil bath under constant stirring for 24 hours. Then the solution was allowed to cool at room temperature for 12 hours, reheated to 95 C for another 24 hours, and finally allowed to cool to room temperature again.In order to remove any unbound ligands, the solutions were then repeatedly subjected to magnetic washing. The solutions were held above a neodymium supermagnet of field strength 3661 Gauss for ten minutes, and then the supernatant was removed. This was repeated until the supernatant did not become clear and there was no longer any apparent separation. To further remove any unbound ligands, centrifugation was used. Each solution was centrifuged at 10,000 rpm at 4 C for 1 hour, the supernatant discarded and then centrifuged twice more with deionized water.Sucrose HydrolysisThree sucrose hydrolysis reactions were conducted with catalyst samples from each batch. The reaction was conducted in a sealed flask placed in an oil bath maintained at 80 C with 0.05 g (dry weight) of catalyst, 0.1 g of sucrose and 5 g of water. The reaction was allowed to proceed for 6 hours under constant stirring. The experimental set-up is pictured below.

Between each run, 5 g of water and fresh sucrose were added to the flask. After all reactions were complete, vials were prepared for HPLC analysisResultsPrior to HPLC analysis, a control solution of sucrose and glucose was prepared in order to create a standards curve for the HPLC machine to analyze against. Five different 100 mL standards were prepared and their concentrations are reported in the following table.Flask # (100 mL each)g sucroseg glucose

10.09990.0110

21.00060.0508

32.00050.1001

43.00020.1516

54.00050.2001

The HPLC machine used a RCM-Ca2+ monosaccharide column and a refractive index detector.The results from the HPLC analysis are summarized in the tables below.HPLC Results for 1 g acid-loadingReactionInitial sucrose (mg/mL)Final sucroseFinal glucoseFinal fructoseFinal xyloseSucrose conversion

124.9620.022.092.850.0019.79%

226.0122.671.421.920.0012.85%

331.5228.041.442.04011.03%

HPLC Results for 0.5 g acid-loadingReactionInitial sucrose (mg/mL)Final sucroseFinal glucoseFinal fructoseFinal xyloseSucrose conversion

110.469.970.4500.044.71%

215.9415.240.6600.044.40%

321.4920.590.8600.044.21%

The HPLC curves for the above reactions (in the order that they appear) are below.

Conclusions and DiscussionThe above results show that the 1 g acid-loading led to higher sucrose conversion. This means that if there is a maximum acid-loading, it is higher than or equal to 1 g because the 0.5 g loading showed a marked decrease in conversion. If the 0.5 g loading was the maximum loading, we would expect to see little to no increase in sucrose conversion with the increase to 1.0 g loading. The results also show that there is a decrease in catalyst activity over time meaning either that some of the catalyst is being wasted during the washing process or that some of the ligands are detaching during the reaction. Further research should be done to determine which of these is occurring. Also, more research needs to be done with different acid loadings to determine if there is a maximum loading. Another interesting result is that with the 0.5 g loading, instead of forming fructose, the hydrolysis reaction formed xylose. Further research should be done to determine the mechanism behind this shift.