Description:PROCESS TO PREPARE MONOMERIC SUGARS FROM CARBOHYDRATES USING ENGINEERED CARBON CATALYSTS

FIELD OF THE INVENTION:

[1] The present invention is in the field of carbohydrates. Particularly, the present invention relates to a process to prepare monomeric sugars from carbohydrates using engineered carbon catalysts. More particularly, the present invention relates to a process to prepare valuable monomeric rare sugars from carbohydrates using activated carbon with halogen and carboxylic acid functionalities.

BACKGROUND OF THE INVENTION:

[2] In the field of sustainable chemistry, recent focus has been drawn on converting waste-derived feedstocks into value-added products.1 The global food industry faces significant challenges associated with food waste, which possess environmental, economic, and social concerns.2 However, this growing problem also presents an opportunity to transform waste streams or by-products into valuable resources.

[3] Among these by-products, whey protein has garnered substantial attention due to its extensive applications in industries such as food and beverages, sports nutrition, infant formula, and personal care. The global whey protein market, valued at approximately USD 6.45 billion in 2022, is projected to reach USD 14.32 billion by 2030, growing at a compound annual growth rate (CAGR) of 10.48%.3 Whey protein is a by-product of cheese production, with lactose as a secondary by-product. Depending on the type of whey (sweet or acid whey) and the production process, whey typically contains 4.5–5% lactose by weight.4

[4] Driven by whey protein demand, global lactose production is significant, exceeding 1.2 million metric tons annually, with widespread use in food, pharmaceuticals, and infant nutrition.4-6 Therefore, many strategies are coming up to utilize the waste lactose for the value-added chemical. Recent approaches have focused on the direct utilization of lactose in pharmaceutical7, food, and nutritional applications8, as well as its advanced conversion into high-value derivatives such as lactobionic acid7, lactulose, and lactitol.9

[5] One of the most promising advancements involves the depolymerization of lactose into its monomeric units, glucose and galactose. Galactose holds particular significance in the treatment and diagnosis of conditions such as hepatitis C, hepatic cancer, Wilson’s disease, diabetic macular edema, and focal segmental glomerulosclerosis.10 Glucose derived from waste lactose also has diverse applications, including its use as a green capping agent11, and in pharmaceuticals.12 Despite these potential applications, most lactose depolymerization processes rely on enzymatic catalysts.13,14

[6] Similarly, guar gum is another important raw material because of its wide availability for producing sugars like galactose and mannose. India accounts for 80% of the world’s guar gum production, with over one million tons produced annually worldwide.15 Guar gum, a water-soluble polysaccharide extracted from the seeds of the Cyamopsis tetragonolobus plant, consists of β-(1−4)-linked D-mannose on the backbone and α-(1−6)-linked galactose on the side chain.16 Guar gum is highly valued in the food and pharmaceutical industries due to its low cost and hydrogen-bonding capabilities.17 It is commonly used as an additive in syrups, tablet manufacturing (as a binder or disintegrating agent), drug microencapsulation, beverages, and baking products, primarily for its thickening and gelling properties.18 Additionally, guar gum plays a role in the treatment of hypercholesterolemia and hyperglycemia.19 It is also utilized as a hydraulic fracturing fluid in the oil and gas industry.20 Its monomeric sugar, mannose plays a significant role in the chemical industry, being used to treat polysaccharides-deficient glycoprotein syndrome type 1b, urinary tract infections, and other applications.21

[7] Further, xanthan gum is another important raw material for producing sugars like glucose and mannose. Xanthan gum is a polysaccharide with many industrial uses, including as a common food additive. It is an effective thickening agent and stabilizer that prevents ingredients from separating. It derives its name from the species of bacteria used, Xanthomonas campestris.

[8] Reference is made to the non-patent literature “Osama Ibrahim - A New Low Calorie Sweetener D-Tagatose from Lactose in Cheese Whey as a Nutraceutical Value-Added Product”, which discloses a new low calorie sweetener D-tagatose from lactose in cheese whey. The research results show progress in improving enzymes bioconversion rate, thermos ability in increasing the half-life of the immobilized enzyme, shorting enzyme reaction time and improving both bioconversion efficiency for the hydrolysis of lactose to lactose hydrolysate (D-glucose and D-galactose) and for isomerization of D-galactose to higher yield of D-tagatose.

[9] Reference is further made to US20190289867A1, which discloses acid-catalyzed lactose hydrolysis to afford glucose and galactose monomers at temperatures between about 120°C and about 160°C. The acid used in the method may be a solid acid or a mineral acid.

[10] Reference is further made to the non-patent literature “Jing Shen, et. al. - Sweet As Sugar-Efficient Conversion of Lactose into Sweet Sugars Using a Novel Whole-Cell Catalyst”, which discloses modification of Corynebacterium glutamicum (Gram-positive bacterium), to become a host for expressing the relevant enzymes needed for lactose hydrolysis and subsequent isomerization. The strain applied is able to ferment lactose and lacks lactate dehydrogenase. It has been demonstrated that this engineered C. glutamicum strain efficiently can convert whey permeate into a sweet syrup in a single-step process.

[11] Reference is further made to the non-patent literature “Wenli Zhang - Enzymatic Approaches to Rare Sugar Production”, which discloses the non-Izumoring enzymatic techniques to synthesize rare sugars.

[12] Reference is further made to the non-patent literature “Lin Fan - Biosynthesis of a Healthy Natural Sugar D-Tagatose: Advances And Opportunities”, which discloses the properties of D-tagatose, recent advances in the biosynthesis of D-tagatose from abundant feedstocks but excluding costly sugar alcohols, such as D-galactitol, highlight both key academic literature and industrial patents, as well as discuss the future challenges and opportunities.
[13] Reference is further made to “Nankai H et. al. - Microbial System for Polysaccharide Depolymerization: Enzymatic Route for Xanthan Depolymerization By Bacillus Sp. Strain GL1”, which discloses that in the past, xanthan gum has been depolymerized by the enzymatic methods by using Bacillus sp. Strain GL1 which discloses xanthan was depolymerized to constituent monosaccharides by two extracellular and three intracellular enzymes, including a novel unsaturated glucuronyl hydrolase. However, so far, no clear study has been reported for depolymerization of xanthan gum into monomers (glucose and mannose).

[14] Further, the above-mentioned references have disadvantages, for instance, conventional processes like enzymatic hydrolysis have issues of scalability, increase in the production cost, and almost impossible recyclability of catalysts. Further, the enzymatic hydrolysis is required to be performed under very sensitive conditions (certain temperature and pH). Other conventional methods like acid hydrolysis include harsh preparation, poor yield, and more solvent waste during the treatment process. Therefore, there is a need in the art to provide an alternate process to prepare high value monomeric sugars from the widely available carbohydrates.

[15] To date, no efficient heterogeneous catalytic processes for the depolymerization of the carbohydrates have been reported. The few advantages of the heterogeneous catalysts over enzymes and homogeneous catalysts are that they can be recycled, have a more affordable price, and are widely available.

[16] In order to address the above-mentioned issues, there exists a dire need in the state of art to provide a sustainable process for depolymerization of the carbohydrates to prepare monomeric sugars with improved conversion rate and selectivity. There is also a need in the art to provide such process which is recyclable and scalable.

OBJECT OF THE INVENTION:

[17] The principal object of the present invention is to provide a process for depolymerization of a wide range of carbohydrates to prepare monomeric sugars, more importantly, rare sugars, using the functional activated carbon heterogenous catalyst having binding sites (surface halogen) and active sites (acid functionalities) under optimized reaction conditions.

[18] Another object of the present invention is to provide a sustainable process for depolymerization of the carbohydrates into monomeric sugars using the activated carbon powder treated with aqua regia, with improved conversion rate and selectivity.

[19] Another object of the present invention is to provide a sustainable process for depolymerization of the carbohydrates into monomeric sugars using the activated carbon powder treated with aqua regia, which is recyclable and scalable.

[20] Another object of the present invention is to provide a process for depolymerization of lactose into glucose and galactose using the activated carbon powder treated with aqua regia.

[21] Another object of the present invention is to provide a process for depolymerization of guar gum into mannose and galactose using the activated carbon powder treated with aqua regia.

[22] Another object of the present invention is to provide a process for depolymerization of xanthan gum into glucose and mannose using the activated carbon powder treated with aqua regia.

[23] Another object of the present invention is to provide a process for the depolymerization of carbohydrates into monomeric sugars using the different biomass-derived activated carbon powder treated with aqua regia.

[24] Another object of the present invention is to provide a chlorine-functionalized activated carbon catalyst derived from agricultural waste, wherein the catalyst comprises surface-bound chlorine groups and carboxylic groups introduced via aqua regia treatment.

SUMMARY OF THE INVENTION:

[25] The current innovation relates to a process to prepare monomeric sugars from carbohydrates using the engineered carbon catalysts.

[26] In an aspect of the present invention, there is provided a process to prepare monomeric sugars from carbohydrates, comprising the steps of: (a) Treating activated carbon powder with a mixture of nitric acid and hydrochloric acid in a ratio of 1:3 by volume at temperature ranging from 55-85oC for time period ranging from 1.5-4.5 hours, to prepare functionalized carbon catalyst; and (b) Mixing the carbohydrates with the functionalized carbon catalyst at temperature ranging from 130-220oC for time period ranging from 0.5-2.5 hours.

[27] The present invention introduces a process, for the first time, where the inventors have performed chemo-catalytic depolymerization by using the heterogeneous catalyst and obtaining the maximum yield and conversion.

[28] The present invention demonstrates, for the first time, a non-enzymatic catalytic approach utilizing functionalized carbon catalysts. The catalyst, treated with aqua regia, was characterized by carboxylic groups as active sites and surface halogen as binding sites, enabling more than 99% conversion of lactose to glucose and galactose with a selectivity exceeding 98% as shown in Figure 1a and Figure 1b. The conversion was achieved under mild conditions, specifically at 150°C over 2 hours, highlighting the potential of this sustainable catalytic method for lactose valorization.

[29] Similarly, around 80% conversion of guar gum into galactose and mannose was observed at 200°C over 1.5 hours with around 90% selectivity as shown in Figure 3a and Figure 3b.

[30] Similarly, xanthan gum was successfully converted into glucose and mannose at 190°C over 1 hour with conversion and total selectivity of around 100% and 54%, respectively as shown in Figure 4a and Figure 4b.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

[31] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention, which are used to describe the principles of the present invention together with the description.

[32] Figure 1 illustrates the lactose depolymerization using the catalyst activated carbon treated with aqua regia at temperature of 60°C for 2 hours (AR/AC60@2). Reaction conditions: Lactose 40 mg, catalyst 20 mg, distilled water 5 mL, temperature varies, time varies, N2 = 10 bar; (a) under different reaction temperatures, time 1 hour; (b) under different reaction times, temperature 150℃.

[33] Figure 2 illustrates the lactose depolymerization using the catalyst AR/AC60@2, Reaction conditions: temperature 150℃, time 2 hours, N2 = 10 bar; (a) recyclability, lactose 40 mg, catalyst 20 mg, distilled water 5 mL; (b) scalability, level x, lactose 40*x mg, catalyst 20*x mg, distilled water 5*x mL.

[34] Figure 3 illustrates guar gum depolymerization using the catalyst AR/AC60@2, Reaction conditions: guar gum 500 mg, catalyst 100 mg, distilled water 30 mL, temperature varies, time varies, N2 = 10 bar; (a) under different reaction temperatures, time 2 hours; (b) under different reaction times, temperature 200℃; (c) under different ratios, temperature 200℃, time 1.5 hours; (d) recyclability.

[35] Figure 4 illustrates xanthan gum depolymerization using the catalyst AR/AC60@2, Reaction conditions: xanthan gum 40 mg, catalyst 20 mg, distilled water 5 mL, temperature varies, time varies, N2 = 10 bar; (a) under different reaction temperatures, time 0.5 hour; (b) under different reaction times, temperature 190℃.

[36] Figure 5 illustrates lactose depolymerization using the aqua regia-treated sugarcane bagasse-derived activated carbon, Reaction conditions: Lactose 40 mg, catalyst 20 mg, distilled water 5 mL, temperature varies, time 1 hour, N2 = 10 bar.

DETAILED DESCRIPTION OF THE INVENTION:

[37] While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.

[38] Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[39] Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs.

[40] The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[41] In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise.

[42] As used herein, the verb “to comprise” and its conjugations “comprises” or “comprising” are used in their non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

[43] The term “carbohydrates” denotes a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The term is predominantly used in biochemistry, functioning as a synonym for saccharide, a group that includes sugars, starch and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides, the smallest (lower molecular weight) carbohydrates, are commonly referred to as sugars.

[44] The term “monomeric sugar” denotes monosaccharides, also called simple sugars. They are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.

[45] The term “aqua regia” denotes a mixture of nitric acid and hydrochloric acid, in a molar ratio of 1:3.

[46] As discussed in the background section of the present invention, the existing knowledge reported in the references or literature regarding processes and/or methods to depolymerize carbohydrates into monomeric sugars rely on enzymatic catalysis or acid catalysis. However, they possess several disadvantages, for instance, conventional processes like enzymatic hydrolysis have issues of scalability, increase in the production cost, and almost impossible recyclability of catalysts. Further, the enzymatic hydrolysis is required to be performed under very sensitive conditions (certain temperature and pH). Other conventional methods like acid hydrolysis include harsh preparation, poor yield, and more solvent waste during the treatment process.

[47] Therefore, to overcome the existing problems in the art, the present invention aims to develop a heterogeneous catalyst for the selective depolymerization of carbohydrates into monomeric sugars.

[48] The present invention has significant utility in the food industry, particularly within the whey protein sector, where lactose, an abundant by-product, can be utilized for the production of monomeric sugars such as galactose and glucose. These sugars hold immense value due to their wide-ranging applications in the pharmaceutical industry and lactose-free food products.

[49] Currently, the market price of monomeric sugars is prohibitively high due to the complex and expensive production processes involved. The present invention offers a green and sustainable process to convert industrial by-products like lactose into monomeric sugars, effectively reducing production costs while addressing waste management challenges. The adoption of this technology has the potential to revolutionize the market by making monomeric sugars more affordable, expanding their accessibility for various industrial applications. Considering the growing demand for these sugars in the health and wellness sectors, the present innovation is poised to unlock substantial market potential.

[50] Further, along with the lactose, the sustainable and selective depolymerization of guar gum and xanthan gum into high-value sugars using functional carbon material as a heterogeneous catalyst in aqueous conditions has also been investigated.

[51] The depolymerization of glycosidic bonds, extensively studied for cellulose-to-glucose conversion, has shown promising results using functional carbon-based materials, zeolites, and metal oxides.22 Recently, the inventors have demonstrated that a functional carbon catalyst with chlorine as the binding site and carboxylic acid as the active site achieved efficient depolymerization of guar gum into its monomers, galactose, and mannose.23 Building on the said work, the inventors have explored the application of functional carbon catalysts for lactose and xanthan gum depolymerization.

[52] The activated carbon catalyst treated with aqua regia used in the process of the present invention comprises surface chlorine functionalities. These chlorine groups act as specific binding sites for catalysis, while the carboxylic groups serve as active sites for depolymerization. This dual functionality is absent in the prior art, which primarily utilizes homogeneous catalysts or conventional acid hydrolysis. The heterogeneous catalyst can be reused multiple times with minimal loss in activity, unlike enzyme-based or homogeneous acid catalysts. Further, the experimental data provided below demonstrates recyclability, scalability, which leads to economic viability. The catalyst has been tested across various carbohydrates (lactose, guar gum, xanthan gum), confirming its broad applicability and effectiveness, which further distinguishes it from existing solutions.

[53] The investigations revealed that functional carbon catalysts with surface chlorine as binding sites and carboxylic acid as active sites achieved remarkable efficiency. Under optimized reaction conditions, more than 99% conversion of lactose with over 98% selectivity for monomeric sugars was obtained within 2 hours of reaction time as shown in Figure 1a and Figure 1b. Further, around 80% conversion of guar gum with around 90% selectivity was obtained for monomeric sugars within 1.5 hours as shown in Figure 3a and Figure 3b. Furthermore, around 100% conversion of xanthan gum with around 54% selectivity was obtained for monomeric sugars within 1 hour as shown in Figure 4a and Figure 4b.

[54] In an embodiment, the present invention relates to a process to prepare monomeric sugars from carbohydrate, comprising the steps of:
(a) Treating activated carbon powder with a mixture of nitric acid and hydrochloric acid in a ratio of 1:3 by volume at temperature ranging from 55-85oC for time period ranging from 1.5-4.5 hours, to prepare functionalized carbon catalyst; and
(b) Mixing the carbohydrate with the functionalized carbon catalyst at temperature ranging from 130-220oC for time period ranging from 0.5-2.5 hours.

[55] The activated carbon may be obtained from commercial sources or may be obtained from agricultural waste, such as sugarcane bagasse, pistachio nut, coconut shell, sawdust, and corn cob.

[56] In another embodiment, the present invention provides the process as described herein, wherein the functionalized carbon catalyst comprises carboxylic acid as active sites and surface halogen as binding sites.

[57] In another embodiment, the present invention provides the process as described herein, wherein the functionalized carbon catalyst comprises fluorine, chlorine, bromine, and iodine as binding sites.

[58] In another embodiment, the present invention provides the process as described herein, wherein in step (a), the temperature is from 60-80oC and the time period is from 2-4 hours.

[59] In another embodiment, the present invention provides the process as described herein, wherein in step (a), the temperature is 80oC and the time period is 4 hours.

[60] In another embodiment, the present invention provides the process as described herein, wherein in step (a), the temperature is 60oC and the time period is 4 hours.

[61] In another embodiment, the present invention provides the process as described herein, wherein in step (a), the temperature is 60oC and the time period is 2 hours.

[62] In another embodiment, the present invention provides the process as described herein, wherein the functionalized carbon catalyst consists of 80% Carbon, 13% Oxygen, 1% Nitrogen, and 6% Chlorine.

[63] In another embodiment, the present invention provides the process as described herein, wherein the carbohydrate is lactose and the monomeric sugars are glucose and galactose.

[64] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is from 130-150oC, and the time period is from 1-2 hours.

[65] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is 150oC, and the time period is 2 hours.

[66] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio ranging from 2:1 to 1:2.

[67] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio of 2:1.

[68] In another embodiment, the present invention provides the process as described herein, wherein the carbohydrate is guar gum and the monomeric sugars are mannose and galactose.

[69] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is from 170-220oC, and the time period is from 1-2.5 hours.

[70] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is 200oC, and the time period is 1.5 hours.

[71] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio ranging from 1:5 to 3:3.

[72] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio of 2:4.

[73] In another embodiment, the present invention provides the process as described herein, wherein the carbohydrate is xanthan gum and the monomeric sugars are glucose and mannose.

[74] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is from 150-190oC, and the time period is from 0.5-1.5 hours.

[75] In another embodiment, the present invention provides the process as described herein, wherein in step (b), the temperature is 190oC, and the time period is 1 hour.

[76] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio ranging from 2:1 to 1:2.

[77] In another embodiment, the present invention provides the process as described herein, wherein carbohydrate and catalyst are in ratio of 2:1.

[78] In another embodiment, the present invention provides a chlorine-functionalized activated carbon catalyst derived from agricultural waste, wherein the catalyst comprises surface-bound chlorine groups and carboxylic groups introduced via aqua regia treatment.

[79] In another embodiment, the present invention provides the catalyst as described herein, wherein the agricultural waste comprises sugarcane bagasse, pistachio nut, coconut shell, sawdust, and corn cob.

[80] The present invention is illustrated hereunder in greater detail in relation to non-limiting exemplary embodiments as per the following examples:

EXAMPLES

[81] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and the description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all and only experiments performed. The methodology of preparing few of the preferred embodiments shall become clearer with working examples provided below.

Example 1: Preparation of functional carbon catalyst

[82] The activated carbon (AC) powder (purchased from Tokyo Chemical Industries) was treated with 20 mL with the aqua regia (HNO3 and HCl in a 1:3 ratio by volume), which was added dropwise. The slurry was stirred at room temperature of 60°C for 2 hours under consistent stirring (500 rpm). After completing the reaction, the material was cooled to room temperature. The slurry was then diluted in 2 L of distilled water and filtered until the pH was neutral (pH 7). Finally, the powder catalyst was dried in an oven at 80°C overnight. The catalyst is named aqua regia/AC (AR/AC60@2).

Example 2: Depolymerization of lactose into glucose and galactose

[83] Lactose (purchased from Tokyo Chemical Industries) was depolymerized in a batch reactor by mixing lactose (40 mg) with functionalized carbon catalyst AR/AC60@2 (20 mg) in 5 mL of distilled water at 110-150°C for 0.5–2 hours and 10 bar of N2 pressure. The batch reactor was immediately placed in an ice bath just after the completion of the reaction to quench the reaction. The yield of products was determined by filtering the reaction solution and injecting it into a high-performance liquid chromatograph equipped with a refractive index detector (RID-20A, Shimadzu) and a Bio-Rad Aminex HPX-87H Column maintaining the 0.6 mL/min flow at an oven temperature of 50°C. With respect to the standard sample calibration line, the yield was calculated.

Example 3: Functional carbon catalyzed depolymerization of lactose in water

[84] Table 1 presents the catalytic performance of various systems, evaluated under reaction conditions of 1 hour at 130°C. To investigate the role of catalysts in promoting depolymerization, an initial blank reaction was conducted in the absence of a catalyst (Table 1, Entry 1). As anticipated, no depolymerization products were detected, indicating that the thermal conditions alone were insufficient to drive lactose cleavage. A similar outcome was observed when activated carbon (AC) was employed as the catalyst (Table 1, Entry 2), with only a marginal increase in selectivity compared to the blank reaction. This limited activity underscores the intrinsic catalytic inefficiency of untreated AC under the specified conditions. Functionalization of AC using HCl, H₂SO₄, and HNO₃ (Table 1, Entries 3–5) resulted in modest improvements, with total sugar yields increasing by approximately 2–4%. These enhancements can be attributed to the introduction of acidic functional groups, which likely facilitated limited glycosidic bond cleavage, although insufficient for achieving high overall yields. The most notable improvement was observed with aqua regia-treated AC (Table 1, Entry 6), which significantly enhanced catalytic activity. This treatment yielded a total sugar production of 30%, with a selectivity of 91%. However, in all the cases, an equal amount of glucose and galactose yield was observed. This outcome is consistent with the molecular structure of lactose, a disaccharide composed of equal proportions of glucose and galactose monomer units linked by a glycosidic bond. To further enhance the total sugar yield, AC was treated with aqua regia under varying temperatures and treatment durations. The impact of different treatment temperatures was studied, while maintaining the duration of 4 hours. Among the tested conditions, AC treated with aqua regia at 60°C (AR/AC@60) demonstrated the highest efficiency, achieving the best total sugar yield of 50% (Table 1, Entry 7). Subsequently, at the optimized temperature of 60°C, the effect of varying treatment durations was investigated. It was observed that AC treated with aqua regia for 2 hours (AR/AC60@2) exhibited the highest total sugar yield of 64%, further optimizing the catalytic performance (Table 1, Entry 8). These results highlight the importance of fine-tuning treatment conditions to maximize the functionalization of AC and enhance its catalytic efficiency.

Table 1. Depolymerization of lactose in the presence of different functionalized carbon catalysts.

Entry Catalyst Conversion/% Yield/% Total sugar selectivity/% Mass balance/%
Glucose Galactose
1 Blank 12 <1 <1 5 89
2 AC 15 <1 <1 7 86
3 HCl/AC 17 1 1 12 85
4 H2SO4/AC 21 1.5 1.5 14 82
5 HNO3/AC 19 2 2 21 85
6 AR/ACa 33 15 15 91 97
7 AR/ACb 51 25 25 98 99
8 AR/ACc 65 32 32 98 99

Reaction conditions: Lactose 40 mg; catalyst 20 mg; distilled water 5 mL; temperature 130°C; time 1 hour, N2 = 10 bar, Mass balance = 100 × (total amount of products and remaining lactose)/initial amount of lactose; Catalyst preparation: aT = 80°C, t = 4 hours, bT = 60°C, t = 4 hours, cT = 60°C, t = 2 hours.

Example 4: Reaction optimization

[85] The reaction conditions for lactose depolymerization into its monomeric sugars, glucose and galactose, were optimized using the catalyst AR/AC60@2. Initially, the effect of reaction temperature was investigated by maintaining a constant reaction time of 1 hour. As illustrated in Figure 1a, the maximum total sugar yield of 78% was achieved at 150°C. Subsequently, the reaction time was optimized at the fixed temperature of 150°C, with experiments conducted over varying time intervals (Figure 1b). It was observed that nearly 100% conversion was achieved at 2 hours, yielding a total sugar yield of 98% with a selectivity of 98%. These findings confirm that the reaction conditions are fully optimized, achieving complete lactose depolymerization and maximizing the total sugar yield under the identified optimal conditions.

Example 5: Catalyst recyclability and scale-up

[86] The recyclability of the AR/AC60@2 catalyst was thoroughly investigated over four consecutive reaction cycles. After each reaction, the catalyst was carefully separated from the reaction mixture and extensively washed with deionized water to remove any residual contaminants or reaction by-products that might have adhered to its surface. The results (Figure 2a) demonstrated that the catalyst remained stable and efficient up to the second cycle, maintaining high catalytic activity. However, a slight decline in yield was observed in the third and fourth cycles. This gradual decrease in performance is attributed to the deposition of humins, a common by-product in biomass conversion reactions, on the surface of the catalyst. The accumulation of these humins likely blocks or deactivates some of the active sites, reducing overall catalytic efficiency.24 Despite this minor decline, Figure 2a highlights that the AR/AC60@2 catalyst retained substantial activity over four cycles, indicating its potential for reusability.

[87] A systematic scale-up was performed to evaluate the applicability of the reaction at an industrial scale. The reaction parameters were progressively increased across five levels while maintaining the catalyst-to-substrate ratio. At each level, both the catalyst loading and substrate loading were proportionally increased, along with the total reaction volume, to simulate larger-scale industrial conditions. In Level 1, all reaction parameters were kept at their original, unmodified values to serve as a baseline. For each subsequent level, the reaction parameters were incrementally adjusted to reflect the requirements of scaled-up processes. This stepwise approach ensured that the reaction conditions remained consistent with the demands of industrial scalability while maintaining optimal performance. As shown in Figure 2b, the results demonstrated that the reaction could be efficiently scaled up without any significant loss in catalytic activity or reaction yield. Even at the highest level tested, the reaction maintained its efficiency, indicating the strength of the reaction system under scaled-up conditions. These findings confirm that the reaction system is not only scalable but also suitable for industrial applications, providing a reliable pathway for larger-scale production processes.

Example 6: Depolymerization of guar gum into mannose and galactose

[88] The prepared AR/AC60@2 catalyst was also tested for guar gum depolymerization into galactose and mannose.

[89] Guar gum (purchased from Tokyo Chemical Industries) was depolymerized in a batch reactor by mixing guar gum (500 mg) with functionalized carbon catalyst AR/AC60@2 (100 mg) in 30 mL of distilled water at 140-220°C for 0.5–3.5 hours and 10 bar of N2 pressure. The batch reactor was immediately placed in an ice bath just after the completion of the reaction to quench the reaction. The yield of products was determined by filtering the reaction solution and injecting it into a high-performance liquid chromatograph equipped with a refractive index detector (RID-20A, Shimadzu) and a Bio-Rad Aminex HPX-87H Column maintaining the 0.6 mL/min flow at an oven temperature of 50°C. With respect to the standard sample calibration line, the yield was calculated.

[90] The reaction was maintained for 2 hours at different temperatures ranging from 140℃ to 220℃ to obtain the optimum conditions. It has been found that 200°C for 2 hours shows the best optimum result with a maximum yield and conversion of around 65% and 72%, respectively, with equal amounts of galactose and mannose yield, as shown in Figure 3a. After optimizing the temperature, the reaction was held at 200oC for time intervals ranging from 0.5 to 3.5 hours. At a time of 1.5 hours, the selectivity of galactose and mannose is higher, as shown in Figure 3b. Thus, the reaction condition at 200oC for 1.5 hours was found to be the best.

[91] Further, reactions were performed with different substrate and catalyst ratios. The yield obtained in a ratio of 2:4 was the maximum of around 77%, as shown in Figure 3c. To assess the stability of the catalyst, a recyclability test was conducted. After each cycle, the catalyst was washed with DI water and dried overnight at 80°C. The catalyst shows good stability up to the 4 cycles, as shown in Figure 3d. Hence, it can be concluded that catalysts can be reused.

These findings confirm that the reaction system is not only scalable but also suitable for industrial applications, providing a reliable pathway for larger-scale production processes.

Example 7: Depolymerization of xanthan gum into glucose and mannose

[92] The prepared AR/AC60@2 catalyst was also tested for xanthan gum depolymerization into glucose and mannose.

[93] Xanthan gum (purchased from Sisco Research Laboratories Pvt. Ltd.) was depolymerized in a batch reactor by mixing xanthan gum (40 mg) with functionalized carbon catalyst AR/AC60@2 (20 mg) in 5 mL of distilled water at 150-190°C for 0.5–2.5 hours and 10 bar of N2 pressure. The batch reactor was immediately placed in an ice bath just after the completion of the reaction to quench the reaction. The yield of products was determined by filtering the reaction solution and injecting it into a high-performance liquid chromatograph equipped with a refractive index detector (RID-20A, Shimadzu) and a Bio-Rad Aminex HPX-87H Column maintaining the 0.6 mL/min flow at an oven temperature of 50°C. With respect to the standard sample calibration line, the yield was calculated. The reaction was maintained for 0.5 hour at different temperatures ranging from 150℃ to 190℃ to obtain the optimum conditions. It has been found that 190°C for 0.5 hour shows the best optimum result with a maximum yield and conversion of around 52% and 100%, respectively, as shown in Figure 4a. After optimizing the temperature, the reaction was held at 190oC for time intervals ranging from 0.5 to 2.5 hours. At a time of 1 hour, the yield of glucose and mannose is higher with maximum yield of 54% and 100% conversion, as shown in Figure 4b. Thus, the reaction condition at 190oC for 1 hour was found to be the best.

[94] The above examples prove that the prepared catalyst can be used for lactose, guar gum and xanthan gum depolymerization and the production of highly valuable monomeric sugars.

Example 8: Preparation of functional carbon catalyst from sugarcane bagasse

[95] The sugarcane bagasse (SB) collected from Bengaluru, India, was washed thoroughly by heating it with water to remove the impurities. Thereafter, it was dried in the oven at 100℃ until it was fully dried. The obtained SB was ground into very fine particles and was treated with 9 M H2SO4 at 100℃ for 18 hours. The slurry was then diluted in 2 L of distilled water and filtered until the pH was neutral. The powdered carbon was dried in an oven at 80℃ overnight. The obtained powder was kept in a Tubular furnace at 650℃ for 3 hours under a N2 flow, and the activated carbon derived from SB is named as ASB. The ASB was treated with 20 mL of the aqua regia (HNO3 and HCl in a 1:3 ratio by volume), which was added dropwise. The slurry was stirred at a room temperature of 60°C for 2 hours under consistent stirring (500 rpm). After completing the reaction, the material was cooled to room temperature. The slurry was then diluted in 2 L of distilled water and filtered until the pH was neutral (pH 7). Finally, the powder catalyst was dried in an oven at 80°C overnight. The catalyst is named AR/ASB_60@2.

Example 9: Preparation of functional carbon catalyst from sugarcane bagasse with KOH treatment

[96] For the KOH treatment, sulfonated SB was mixed with KOH (1:3 wt. ratio) in 300 mL DI water, stirred at 100°C overnight, and evaporated to dryness. The sample was dried at 100°C, then carbonized in a muffle furnace at 450°C, 550°C, and 650°C (3 hours each). Post-carbonization, potassium residues were removed by stirring in 1 M HCl (1 hour, room temperature), followed by DI water washing (until neutral pH) and drying at 80°C. The porous carbon was further functionalized with aqua regia (as above) and labelled AR/ASB450_60@2, AR/ASB550_60@2, and AR/ASB650_60@2.

Example 10: Depolymerization of lactose under aqua regia-treated sugarcane bagasse-derived activated carbon

[97] Under optimized lactose depolymerization conditions (1 hour, variable temperatures), aqua regia-treated sugarcane bagasse-derived activated carbon (AR/ASB450_60@2) achieved near-complete conversion and yield (~100%) at 140°C (Figure 5). This demonstrates the excellent catalytic performance of the waste-derived catalyst, enabling energy-efficient depolymerization at reduced time and temperature while aligning with sustainable practices by repurposing agricultural waste (sugarcane bagasse) into high-value materials for depolymerization process.

Similar to the above, other carbohydrates can also be converted into the monomeric sugars.

ADVANTAGES OF THE PRESENT INVENTION:

[98] The present invention provides a process to prepare monomeric sugars from carbohydrate using the activated carbon powder treated with aqua regia under optimized reaction conditions. A few advantages of the present process are as follows:

• The present invention provides a process of conversion of carbohydrates into monomeric sugars using a heterogeneous catalyst, reported for the first time.

• The process conditions were optimized to achieve the complete conversion and maximum yield of monomeric sugars from the carbohydrates, with no detectable formation of by-products.

• The present invention utilizes a specifically designed catalyst with the presence of carboxylic acid groups as active sites and surface halogen as the binding sites that demonstrates high stability and recyclability across multiple reaction cycles without a significant drop in efficiency.

• The present invention provides a compatible reaction system with scalability, ensuring adaptability to various industrial setups.

• The present invention provides conversion of lactose into glucose and galactose, conversion of guar gum into mannose and galactose, and conversion of xanthan gum into glucose and mannose, using the heterogeneous catalyst, reported for the first time.

• The present invention provides the catalytic depolymerization of lactose, guar gum and xanthan gum in water under mild reaction conditions, enabling an eco-friendly and sustainable process.

• The present invention supports absence of additional solvents or harmful chemicals during the reaction, promoting a green and sustainable approach.

• The present invention provides a reproducible reaction, offering consistent product selectivity of monomeric sugars, suitable for food and pharmaceutical industries.

• The present invention provides process which is not only scalable but also suitable for industrial applications, providing a reliable pathway for larger-scale production processes.

REFERENCES:

(1) Al-Obadi, M.; Ayad, H.; Pokharel, S.; Ayari, M. A. Perspectives on Food Waste Management: Prevention and Social Innovations. Sustain. Prod. Consum. 2022, 31, 190–208. https://doi.org/10.1016/j.spc.2022.02.012.

(2) Andler, S. M.; Goddard, J. M. Transforming Food Waste: How Immobilized Enzymes Can Valorize Waste Streams into Revenue Streams. Npj Sci. Food 2018, 2 (1), 19. https://doi.org/10.1038/s41538-018-0028-2.

(3) Whey Protein Market Size, Share, Trends & Forecast. Verified Market Research. https://www.verifiedmarketresearch.com/product/whey-protein-market/ (accessed 2024-11-29).

(4) Limnaios, A.; Tsevdou, M.; Zafeiri, E.; Topakas, E.; Taoukis, P. Cheese and Yogurt By-Products as Valuable Ingredients for the Production of Prebiotic Oligosaccharides. Dairy 2024, 5 (1), 78–92. https://doi.org/10.3390/dairy5010007.

(5) Lactose Market Size, Share, Growth | Forecast Report [2032]. https://www.fortunebusinessinsights.com/industry-reports/lactose-market-101774 (accessed 2024-12-06).

(6) Global Dairy Market | Size, Share, Industry Report 2024-2032. https://www.imarcgroup.com/global-dairy-market (accessed 2024-12-06).

(7) Gutiérrez, L.-F.; Hamoudi, S.; Belkacemi, K. Lactobionic Acid: A High Value-Added Lactose Derivative for Food and Pharmaceutical Applications. Int. Dairy J. 2012, 26 (2), 103–111. https://doi.org/10.1016/j.idairyj.2012.05.003.

(8) Dominici, S.; Marescotti, F.; Sanmartin, C.; Macaluso, M.; Taglieri, I.; Venturi, F.; Zinnai, A.; Facioni, M. S. Lactose: Characteristics, Food and Drug-Related Applications, and Its Possible Substitutions in Meeting the Needs of People with Lactose Intolerance. Foods 2022, 11 (10), 1486. https://doi.org/10.3390/foods11101486.

(9) Saarela, M.; Hallamaa, K.; Mattila-Sandholm, T.; Mättö, J. The Effect of Lactose Derivatives Lactulose, Lactitol and Lactobionic Acid on the Functional and Technological Properties of Potentially Probiotic Lactobacillus Strains. Int. Dairy J. 2003, 13 (4), 291–302. https://doi.org/10.1016/S0958-6946(02)00158-9.

(10) Coelho, A. I.; Berry, G. T.; Rubio-Gozalbo, M. E. Galactose Metabolism and Health. Curr. Opin. Clin. Nutr. Metab. Care 2015, 18 (4), 422. https://doi.org/10.1097/MCO.0000000000000189.

(11) Tavakoli, F.; Salavati-Niasari, M.; Ghanbari, D.; Saberyan, K.; Hosseinpour-Mashkani, S. M. Application of Glucose as a Green Capping Agent and Reductant to Fabricate CuI Micro/Nanostructures. Mater. Res. Bull. 2014, 49, 14–20. https://doi.org/10.1016/j.materresbull.2013.08.037.

(12) Galant, A. L.; Kaufman, R. C.; Wilson, J. D. Glucose: Detection and Analysis. Food Chem. 2015, 188, 149–160. https://doi.org/10.1016/j.foodchem.2015.04.071.

(13) Amaretti, A.; Bernardi, T.; Tamburini, E.; Zanoni, S.; Lomma, M.; Matteuzzi, D.; Rossi, M. Kinetics and Metabolism of Bifidobacterium Adolescentis MB 239 Growing on Glucose, Galactose, Lactose, and Galactooligosaccharides. Appl. Environ. Microbiol. 2007, 73 (11), 3637–3644. https://doi.org/10.1128/AEM.02914-06.

(14) Zhang, W.; Poojary, M. M.; Rauh, V.; Ray, C. A.; Olsen, K.; Lund, M. N. Limitation of Maillard Reactions in Lactose-Reduced UHT Milk via Enzymatic Conversion of Lactose into Galactooligosaccharides during Production. J. Agric. Food Chem. 2020, 68 (11), 3568–3575. https://doi.org/10.1021/acs.jafc.9b07824.

(15) Indian guar gum market; https://www.researchnester.com/reports/india-guar-gum-market/4710 (accessed 2024−10−21).

(16) Ye, L.; Han, Y.; Wang, X.; Lu, X.; Qi, X.; Yu, H. Recent Progress in Furfural Production from Hemicellulose and Its Derivatives: Conversion Mechanism, Catalytic System, Solvent Selection. Mol. Catal. 2021, 515, 111899.

(17) Sharma, G.; Sharma, S.; Kumar, A.; Al-Muhtaseb, A. H.; Naushad, Mu.; Ghfar, A. A.; Mola, G. T.; Stadler, F. J. Guar Gum and Its Composites as Potential Materials for Diverse Applications: A Review. Carbohydr. Polym. 2018, 199, 534−545.

(18) Kaur, S.; Santra, S. Application of Guar Gum and Its Derivatives as Green Binder/Separator for Advanced Lithium-Ion Batteries. Chemistry Open 2022, 11 (2), No. e202100209.

(19) Butt, M. S.; Shahzadi, N.; Sharif, M. K.; Nasir, M. Guar Gum: A Miracle Therapy for Hypercholesterolemia, Hyperglycemia and Obesity. Crit. Rev. Food Sci. Nutr. 2007, 47 (4), 389−396.

(20) Hasan, A. M. A.; Abdel-Raouf, M. E. Applications of Guar Gum and Its Derivatives in Petroleum Industry: A Review. Egypt. J. Pet. 2018, 27 (4), 1043−1050.

(21) Kranjčec, B.; Papeš, D.; Altarac, S. D-Mannose Powder for Prophylaxis of Recurrent Urinary Tract Infections in Women: A Randomized Clinical Trial. World J. Urol. 2014, 32 (1), 79–84. https://doi.org/10.1007/s00345-013-1091-6.

(22) Shrotri, A.; Kobayashi, H.; Fukuoka, A. Cellulose Depolymerization over Heterogeneous Catalysts. Acc. Chem. Res. 2018, 51 (3), 761–768. https://doi.org/10.1021/acs.accounts.7b00614.

(23) Nayak, R. R.; Gupta, N. K. Tailoring Carbon Nanostructure for Selective Guar Gum Conversion: Unveiling the Interplay between Structure and Surface Functionalities in Galactose and Mannose Production. ACS Sustain. Chem. Eng. 2024. https://doi.org/10.1021/acssuschemeng.4c08126.

(24) Gupta, N. K.; Fukuoka, A.; Nakajima, K. Amorphous Nb2O5 as a Selective and Reusable Catalyst for Furfural Production from Xylose in Biphasic Water and Toluene. ACS Catal. 2017, 7 (4), 2430–2436. https://doi.org/10.1021/acscatal.6b03682.
, Claims:We Claim:
1. A process to prepare monomeric sugars from carbohydrate, comprising the steps of:
(a) Treating activated carbon powder with a mixture of nitric acid and hydrochloric acid in a ratio of 1:3 by volume at temperature ranging from 55-85oC for time period ranging from 1.5-4.5 hours, to prepare functionalized carbon catalyst; and
(b) Mixing the carbohydrate with the functionalized carbon catalyst at temperature ranging from 130-220oC for time period ranging from 0.5-2.5 hours.

2. The process as claimed in claim 1, wherein the functionalized carbon catalyst comprises carboxylic acid as active sites and surface halogen as binding sites.

3. The process as claimed in claim 1 or 2, wherein in step (a), the temperature is from 60-80oC and the time period is from 2-4 hours.

4. The process as claimed in claims 1-3, wherein in step (a), the temperature is 80oC and the time period is 4 hours.

5. The process as claimed in claims 1-3, wherein in step (a), the temperature is 60oC and the time period is 4 hours.

6. The process as claimed in claims 1-3, wherein in step (a), the temperature is 60oC and the time period is 2 hours.

7. The process as claimed in claim 1 or 6, wherein the functionalized carbon catalyst consists of 80% Carbon, 13% Oxygen, 1% Nitrogen, and 6% Chlorine.

8. The process as claimed in claims 1-7, wherein the carbohydrate is lactose and the monomeric sugars are glucose and galactose.

9. The process as claimed in claims 1-8, wherein in step (b), the temperature is from 130-150oC, and the time period is from 1-2 hours.

10. The process as claimed in claims 1-9, wherein in step (b), the temperature is 150oC, and the time period is 2 hours.

11. The process as claimed in claims 1-10, wherein carbohydrate and catalyst are in ratio ranging from 2:1 to 1:2.

12. The process as claimed in claims 1-11, wherein carbohydrate and catalyst are in ratio of 2:1.

13. The process as claimed in claims 1-7, wherein the carbohydrate is guar gum and the monomeric sugars are mannose and galactose.

14. The process as claimed in claims 1-7, and 13, wherein in step (b), the temperature is from 170-220oC, and the time period is from 1-2.5 hours.

15. The process as claimed in claims 1-7, and 13-14, wherein in step (b), the temperature is 200oC, and the time period is 1.5 hours.

16. The process as claimed in claims 1-7, and 13-15, wherein carbohydrate and catalyst are in ratio ranging from 1:5 to 3:3.

17. The process as claimed in claims 1-7, and 13-16, wherein carbohydrate and catalyst are in ratio of 2:4.

18. The process as claimed in claims 1-7, wherein the carbohydrate is xanthan gum and the monomeric sugars are glucose and mannose.

19. The process as claimed in claims 1-7, and 18, wherein in step (b), the temperature is from 150-190oC, and the time period is from 0.5-1.5 hours.

20. The process as claimed in claims 1-7, and 18-19, wherein in step (b), the temperature is 190oC, and the time period is 1 hour.

21. The process as claimed in claims 1-7, and 18-20, wherein carbohydrate and catalyst are in ratio ranging from 2:1 to 1:2.

22. The process as claimed in claims 1-7, and 18-21, wherein carbohydrate and catalyst are in ratio of 2:1.

23. A chlorine-functionalized activated carbon catalyst derived from agricultural waste, wherein the catalyst comprises surface-bound chlorine groups and carboxylic groups introduced via aqua regia treatment.

24. The catalyst as claimed in claim 23, wherein the agricultural waste comprises sugarcane bagasse, pistachio nut, coconut shell, sawdust, and corn cob.