MgO/CaO Nanocomposite Facilitates Economical Production of d-Fructose and d-Allulose Using Glucose and Its Response Prediction Using a DNN Model

Abstract

This study presents a method for the economical production of fructose and allulose (a valuable byproduct) directly from glucose over a MgO/CaO nanocomposite under an aqueous condition. The catalyst containing MgO and CaO at equal proportions helped manipulate the inherent characteristics of CaO, particularly strong basicity and surface properties. The analytical characterizations revealed that the structural assembly is such that MgO settles at the surface to initiate the isomerization reaction by providing a higher number of weak/medium base sites. The CaO present beneath undertakes the sequential conversion of the enolintermediate to ultimate fructose and byproducts (mannose and allulose). Thus, the catalyst accelerated the glucose interconversion to obtain a fructose yield as high as 33 wt % with 80% selectivity within 15 min. At the same time, it also initiated the C-3 fructose epimerization to yield allulose (a low-calorie sugar molecule). Moreover, the adopted deep neural network modeling well predicted the catalytic response with the MAE <5%. The technoeconomic analysis estimated the minimum selling price of different products to be US $ ∼4/kg (fructose), $ ∼4/kg (mannose), and $ ∼10/kg (allulose).

Thermodynamic Insights into MgBr2-Mediated Glucose Interconversion to Fructose Undertaking Multiple Reaction Pathways by Applying the Macro- and Micro-Kinetic Principles

“…While comparing the results with the reports, the MgBr 2 system has exhibited an average output, despite admirable features, including weak ion-dipole, which can enable a better interaction of the cation with sugar, attributed to a comparable ionic radius of Mg 2+ with Li + . This can be interpreted as follows: (i) possibly the scattered ion species in a large volume of water might have had the least chance of interaction with the glucose molecules; this is consistent with the result of x w = 0.13, which attained a reduced yield (up to 25.6%) and selectivity (55.7%), enabled by the dominant Br – ions; (ii) a typical sugar degradation to unwanted byproducts, including HMF and LA of ∼3% (excluding humin), which is influenced by the in situ-generated acidic species (which can behave as a Brønsted acid , ), consistent with the carbon balance (Figure a and Table S1); (iii) the thermodynamic equilibrium characteristics of glucose and fructose; and (iv) the parallelly progressing fructose (product) epimerization to allulose (∼1% wt) and isomerization to mannose (∼2% wt) under the prevailing conditions, attributed to the relatively higher reactive characteristics of fructose than glucose . In this way, the system could develop an equilibrium sugar network with byproducts, as proposed in Scheme , by obeying the Lobry de Bruyn and Alberda van Ekenstein (LdB–AvE) principle to form the enediol intermediate (via a proton transfer mechanism) and hydride shift mechanism over Br – and Mg 2+ , respectively. , For instance, Nguyen et al substantiated the influence of the cation of various metal chlorides (CrCl 3 and AlCl 3 ), specifically on the interconversion of glucose to mannose via a C2–C1 carbon shift mechanism (or the Bílik mechanism).…”

“…When the forward glucose to fructose reaction is assumed to be enabled by the counter ions at an equal proportion, obviously, the reverse reactions using fructose and mannose might have experienced a similar effect in forming the respective products, such as glucose and fructose (to an extent), respectively, via epimerization and isomerization reactions. Besides, a considerable formation of allulose was attained, especially when using fructose, which can be interpreted as the active participation of Br – in extending the fructose C3-epimerization. , Since these reverse reactions are reported to be possible via the acidic or basic pathway, determination of the proportion of active participation of cations and anions is a challenge. While interpreting the results, the fructose conversion was found to be relatively higher (relatively 10%) than that of glucose (as a substrate), likely caused by an accelerated degradation of the rest of the 26% fructose to a variety of unwanted products, including HMF, LA, and humin, accredited to its reactivity .…”

“…Besides, a considerable formation of allulose was attained, especially when using fructose, which can be interpreted as the active participation of Br − in extending the fructose C3-epimerization. 9,35 Since these reverse reactions are reported to be possible via the acidic or basic pathway, determination of the proportion of active participation of cations and anions is a challenge. While interpreting the results, the fructose conversion was found to be relatively higher (relatively 10%) than that of glucose (as a substrate), likely caused by an accelerated degradation of the rest of the 26% fructose to a variety of unwanted products, including HMF, LA, and humin, accredited to its reactivity.…”

“…In recent years, dedicated efforts have been made widely to produce fructose via a chemical approach by employing homogeneous and heterogeneous methods; through this, fructose can be rapidly obtained at a cheap cost, which is attributed to the recyclability of the solid catalysts . However, the chemical systems are able to produce only 30% wt fructose and 60% selectivity (an average). , This medium-range productivity by the chemical catalysts is caused by an unwanted sugar degradation to byproducts (including mannose, allulose, and unstructured humin) via side reactions. ,, The extent of these undesired reactions and the type of byproduct formation is dependent on the catalyst’s characteristics (acidic or basic). For instance, mechanistically, the acidic catalyst promotes glucose conversion via the 1,2-hydride shift pathway, yielding mannose and humin compounds predominantly.…”

“…4,7 This medium-range productivity by the chemical catalysts is caused by an unwanted sugar degradation to byproducts (including mannose, allulose, and unstructured humin) via side reactions. 4,8,9 The extent of these undesired reactions and the type of byproduct formation is dependent on the catalyst's characteristics (acidic or basic). For instance, mechanistically, the acidic catalyst promotes glucose conversion via the 1,2hydride shift pathway, yielding mannose and humin compounds predominantly.…”