Next Article in Journal
Design of Experiment (DoE) for Optimization of HPLC Conditions for the Simultaneous Fractionation of Seven α-Amylase/Trypsin Inhibitors from Wheat (Triticum aestivum L.)
Next Article in Special Issue
Production of Oil and Phenolic-Rich Extracts from Mauritia flexuosa L.f. Using Sequential Supercritical and Conventional Solvent Extraction: Experimental and Economic Evaluation
Previous Article in Journal
Damage Model and Experimental Study of a Sand Grouting-Reinforced Body under Seepage
Previous Article in Special Issue
Fractional Factorial Design Study for the Extraction of Cannabinoids from CBD-Dominant Cannabis Flowers by Supercritical Carbon Dioxide
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Supercritical Technology-Based Date Sugar Powder Production: Process Modeling and Simulation

Department of Chemical Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates
Tata Consultancy Services, Bletchley, Milton Keynes, Buckinghamshire MK3 5JL, UK
Research and Innovation Center on CO2 and Hydrogen (RICH Center), Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates
Center for Membranes and Advanced Water Technology (CMAT), Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates
Zoology Department, King Saud University, Riyadh 11451, Saudi Arabia
Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
Authors to whom correspondence should be addressed.
Processes 2022, 10(2), 257;
Submission received: 5 January 2022 / Revised: 14 January 2022 / Accepted: 18 January 2022 / Published: 27 January 2022


Date palm fruits (Phoenix dactylifera) contain high levels of fructose and glucose sugars. These natural sugar forms are healthy, nutritional and easily assimilate into human metabolism. The successful production of soluble date sugar powder from nutritious date fruits would result in a new food product that could replace the commercial refined sugar. In this work, a novel process technology based on the supercritical extraction of sugar components from date pulp was modeled and simulated using Aspen Plus software. The process model consisted of three main steps that were individually simulated for their optimal working conditions as follows: (a) freeze-drying of the date pulp at −42 °C and 0.0001 bar; (b) supercritical extraction of the sugar components using a 6.77 wt.% water mixed CO2 solvent system at a pressure of 308 bar, temperature of 65 °C, and CO2 flow rate of 31,000 kg/h; and (c) spray-drying of the extract using 40 wt.% Gum Arabic as the carrier agent and air as drying medium at 150 °C. The overall production yield of the process showed an extraction efficiency of 99.1% for the recovery of total reducing sugars from the date fruit. The solubility of the as-produced date sugar powder was improved by the process selectivity, elimination of insoluble fiber contents, and the addition of Gum Arabic. The solubility of the final date sugar product was estimated as 0.89 g/g water.

Graphical Abstract

1. Introduction

Recently, the increasing awareness of the health effects of refined sugar has shifted consumers’ focus towards natural and organic sugars. This has provided a tremendous scope for the global organic sugar market, which is expected to grow by 14% between 2019 and 2027 for a net worth of USD 4500 million by 2027 [1]. To meet the growing demands for organic sugar, a wide variety of plant sources and their products are being analyzed for the development of natural fruit-sugar products that benefit human health. Among them, date palm (Phoenix dactylifera) is a promising plant widely cultivated in the arid regions of the Persian Gulf and North Africa [2]. Date palm fruits contain high amounts of fructose and glucose sugars with very little sucrose content [3]. These natural sugar forms are simple, healthy, and assimilate easily into human metabolism. The fruit contains numerous health benefits, including nutritional, functional, and therapeutic values [4]. Date sugar is commercially produced in syrup form through a hot water extraction method. However, there are various drawbacks associated with this method, such as low extraction performance, high energy input, and degradation of thermolabile compounds [5].
Recovery of sugar components from the date fruit biomatrix is mainly hindered by the tough skin and gummy consistency of the fruit pulp. Moreover, the rigid cell membrane layers of the biomatrix retard the movement of solvent in and out of the plant cells. As a result, most of the valuable sugar components are lost with spent biomass in the conventional hot water extraction process, decreasing the extraction efficiency [6]. Thus, an innovative process technology is required to overcome these limitations and efficiently recover the sugar components from date fruits. Non-conventional techniques such as microwave-, ultrasonic-, supercritical-, enzymatic-, and magnetic-/electrical- assisted extraction are widely explored for the effective extraction of various bioactive compounds from different plants and their parts [7]. These advanced approaches are advantageous because they are less costly to operate, require a shorter treatment time, consume low amounts of energy, and do not produce any toxic byproducts.
Compared to other non-conventional extraction techniques, supercritical CO2 (Sc-CO2) extraction has gained increased popularity due to its sustainability, versatility, and absence of solvent contamination [8]. Due to the properties that can be readily modified with changes in pressure and temperature, supercritical fluids have a wide range of applications. Indeed, the properties of both liquid and gaseous matter are combined in the supercritical phase [9]. One of the notable benefits of supercritical solvent-based extraction is that the solvent can be fully separated from the desired solutes, thus ensuring product purity. Various studies have investigated the extraction of high-value components from fruits and vegetable tissues using supercritical fluids, specifically Sc-CO2 [9,10,11,12]. However, usage of Sc-CO2 for plant carbohydrates extraction is partly hampered by its low polarity, which limits the solubilization of the targeted compounds into Sc-CO2. To overcome this problem, high-density polar solvents are used as a co-solvent to enhance the solubility of polar sugars in Sc-CO2. Studies on carbohydrate solubility in Sc-CO2 have shown that using polar co-solvents such as water significantly improves the solubility and separation of carbohydrates from mixtures at an optimal concentration of the co-solvent [13].
Further, a pre-drying step of the date pulp (prior to supercritical extraction) is essential for the maximum recovery of sugars and other nutritive analytes from the fruit matrix. Among the different pre-drying methods that could be applied to produce dehydrated food, freeze-drying is recognized as one of the best drying techniques to preserve food quality [14,15,16]. Freeze-drying, also known as lyophilization, is the process of removing water from the food by an initial freezing phase followed by a sublimation phase to remove the ice as vapor. The removal of water from food by sublimation protects the food product against the loss of essential components and damage caused by chemical reactions associated with the withdrawal or vaporization of liquid water [17].
A post-drying stage of the extract (obtained from the Sc-CO2 extraction) to a solid powder form ensures product stability and longevity of the sugar. The surface area of the final date sugar product plays a vital role in determining its dissolution rate. Spray-drying is one of the most widely used solvent evaporation techniques in the food industry to obtain products with a large surface area [18,19]. However, the rubbery nature of the low molecular weight sugars in the extract (owing to their lower transition temperature) causes product instability and particle agglomeration during the drying process. Hence, a carrier agent is highly required in the post-drying step to overcome these limitations. Gum Arabic (GA) is a widely studied carrier agent due to its low viscosity and high solubility [18]. It is a natural prebiotic and is considered natural, edible, and a safe source of dietary fiber [20]. GA is a complex polysaccharide that benefits gut health, digestion, and cardiovascular health.
A careful evaluation of the scientific literature shows that freeze-drying and spray-drying are the best drying techniques for the pre- and post-drying stages of the main extraction [14,21]. Hence, the same methods were adopted in this study to develop a novel process technology based on Sc-CO2 extraction for the enhanced recovery and production of soluble date sugar powder from the date fruit. Based on these literature findings, an Integrated Date Sugar Production Process (IDSPP) involving three main stages is conceptualized as follows: (i) Freeze-drying of date pulp, (ii) Sc-CO2-assisted extraction of date syrup with water as a co-solvent [8], and (iii) spray-drying of the extract for the production of soluble powder date sugar.
This study focuses on the modeling and simulation of the IDSPP process using Aspen Steady-State Modeler software to establish the feasibility of the process and determine the optimum working conditions for the process to maximize the sugar yield of date fruits. The simulation results would provide the necessary process data for the new technology and the recommended values for various critical process parameters for the experimental development and realization of the IDSPP process. Continuous-model simulation was performed for each stage of the process as a discrete block to determine the optimal values of the critical operating parameters for the respective stage of the IDSPP plant.

2. Materials and Methods

2.1. IDSPP Flowsheet

The process flowsheet for the as-proposed IDSPP technology is shown in Figure 1. Freeze-drying, supercritical extraction, and spray-drying are the major unit operations in the process. Operating pressure, freezing temperature, and drying temperature are the main parameters examined for the freeze-drying (FD) stage to minimize the moisture content in the fruit. Regarding the supercritical extraction (SCE) stage, variables such as operating pressure, temperature, and solvent:co-solvent ratio were considered to optimize the extraction efficiency. For the final spray-drying (SD) stage, the mass flow rate and temperature of air (drying medium), and feed flow rate were studied to understand their effects on the size and solubility of the final date sugar product.

2.2. Materials

The lack of experimental data for the IDSPP at its design stage creates greater reliability on numerical simulation to provide useful information for the process. Commercial process simulation software, Aspen Plus V10 (2019), was used to solve the flowsheets encountered in this work. The software was used to understand the compositions of various phases and streams involved in each stage of the IDSPP. The simulations were run on a standalone personal computer (PC) using a Microsoft Windows 10 (2020) operating system.

2.3. Data

The essential properties and data for the Barhe variant of the date palm fruits were obtained from a study conducted by Rambabu et al., [2]. The properties (Table S1, Supplementary Materials) and structure of the GA (Figure S1, Supplementary Materials) were included in the Aspen database through the user interface [22]. The necessary user-defined functions (UDFs) pertaining to the solubility behavior of the analytes into the Sc-CO2/water system (for the extraction stage) were developed using Phyton (V 3.9.9) scripting and patched to Aspen software.

2.4. Method

The simulation was performed through a model-based representation of chemical, physical, biological, and technical processes and unit operations in the software. The simulation prerequisites involved a detailed understanding of the chemical and physical properties of pure components and mixtures of various streams, as well as mathematical models that allowed stoichiometry-based process calculations. The simulator described processes in flow diagrams where the unit operations are positioned and connected by streams. The solver computed the necessary mass and energy balances for each node to find a stable operating point. The thermodynamic model suitable to present the behavior of each participating phase was selected after careful analysis of a wide range of scientific literature.
For the modeling, a basis of 100 kg/h of date fruit pulp, including the moisture content, was selected. All necessary components were found and defined in the Aspen database except for the date fruit, that was specified as a non-conventional solid. The date fruit was specified using the HCOALGEN enthalpy model and the DCHARIGT density model. Electrolyte Wizard was selected for the ice formation and drying of water, and the ice formation reaction was chosen and added to the chemistry profile to be used as an input to the units involving water phase change [23]. The Particle Size Distribution (PSD) was defined to describe the appearance of the non-conventional substream. A log-normal distribution function was used to describe the PSD with a geometric mean deviation of 27.5 mm, and a mass median diameter (D50) value of 27.5 mm. The IDEAL property method was selected that accommodates both Raoult’s law and Henry’s law and is recommended for vaccum systems where gas is assumed to behave ideally.
The FD process was modeled using a Gibbs reactor which uses Gibbs free energy minimization with phase splitting to calculate the chemical equilibrium between any number of solid components and the fluid phases. The amount of sublimated water was calculated using a UDF that was developed using the results of İzli [14]. Accordingly, the Two Term model (as shown in Equation (1)) that best described the FD behavior was used for the freeze-dryer simulation.
M R = a F D e x p k 0 t + b F D   e x p k 1 t
where MR is the moisture ratio (Mt/M0), Mt represents the moisture at a specific time, t (g water/g dry solid); M0 represents the initial moisture content (g water/g dry solid); k0 and k1 are the drying constants with values 0.002291 min−1 and 0.4768 min−1, respectively; aFD and bFD are FD coefficients with values 0.835 and 0.4768, respectively. These values were experimentally estimated using various thin-layer drying models for the freeze-drying of dates [14].
For SCE stage modeling, the frozen dates were demonstrated as a mixture of specific components to simulate the extraction process and evaluate the exact yield of these components from the overall fruit matrix. Among the various represented components, glucose and fructose were highlighted as the targeted entities for the extraction by Sc-CO2. The non-polar portion of the date fruit matrix was represented by fatty acids such as linoleic, palmitic, and oleic acids. The non-extractable material of the biomatrix was represented as cellulose due to its negligible solubility in Sc-CO2 [12]. The phase equilibrium behavior of the glucose–fructose, Sc-CO2, and water mixture was thermodynamically developed. The process simulation was based on the concept of stages in the extraction. Each stage was assumed as a component separator module at fixed temperature and pressure. The Soave-Redlich-Kwong (SRK) equation of state was used to calculate the thermodynamic properties. The SRK model is suitable for high-temperature and high-pressure extractions, such as supercritical conditioning [24]. Separation unit modules were used to manipulate the separation process of CO2–water–glucose–fructose based on the solubility values at a given temperature and pressure. The separation was based on an empirical solubility equation (Equation (2)) proposed by Stahl and Schilz that was fed to manipulator block modules [25].
l o g y gf = A + B P + C P 2
where ygf is the solubility of the glucose/fructose in the Sc-CO2 (mol solute/mol CO2); P is the total pressure of the system (bar); and A, B, C, are the empirical constants with values −4.3855, −6.2459 × 10−3, and 2.0307 × 10−5 for glucose, and 4.5455, −1.2617 × 10−3, and 1.1561 × 10−5 for fructose, respectively [25]. The solubilities of glucose and fructose in water were calculated according to the work of Saldaña et al., [26]. Additionally, Chrastil’s equation [27] was used to model the solubility of the palmitic, oleic, and linoleic acids into Sc-CO2. Equation (3) presents this model, which is based on the formation of acid–complex upon association of the solute and solvent molecules.
l n S = k × l n   ρ s + a T + b  
where S is the solubility of the solute in the supercritical solvent (g/L); ρs is the density of the pure solvent (g/L); and k, a, and b are empirical constants. Further, the solubility of water in CO2 was obtained through regression of experimental literature data [28] and is represented by Equation (4).
S w = 1.66 × 10 9 + 7.36 × 10 8 × T + 4.54 × 10 8 P + 1.22 × 10 6 × P × T
where Sw is the solubility of water in CO2 (kg H2O/kg CO2), and T is the temperature (°C).
Modeling and simulation of the SD stage were performed through the built-in spray-dryer unit block model available in Aspen Plus. The necessary parameters for the spray-dryer model were specified for the drying process based on the IDEAL property method [29]. The properties for water, air, glucose, and fructose were defined with the conventional values available in the Aspen database. The properties of GA were explicitly included in the software. A rotary atomizer was chosen and modeled with a wheel diameter of 10 cm, four droplet intervals, four 30 mm blades, and a wheel speed of 18,000 rpm [19]. The characteristic droplet size distribution and nozzle exit velocity were calculated based on the geometry of the nozzle. The median droplet size (d50, in μm) was calculated according to the model (Equation (5)) described by Masters [30].
d 50 = K × m ˙ l i q p N q × D R r × n h s × 10 4
where n is the number of blades; mliq is the mass flow rate of the feed (kg/h); N is the rotational speed (rpm); DR is the diameter of the atomizer (m); and h is the height of the vanes (m). The constant K and exponents p, q, r, s were determined from the correlations for the vane liquid loading [30]. Subsequently, the mass flow ratio/vane (Ms) to the height of the vanes was determined as 3587.1 kg/h m. The validity limits were expressed in terms of the speed of the circumference of the disc (U) using Equation (6).
U = π × N 60 × D R
Thus, the speed of the circumference of the disc was evaluated as 94.25 m/s. As the values of the Ms and U values were in the same category, the design was considerably adequate according to the validity table [30]. The values of the constants and exponents were obtained from the same category. Based on these calculations and validations, the median droplet size (d50) was estimated as 50.3 μm. Additionally, the critical moisture content for the drying process was evaluated as 2.67 kg water/kg dry solid (Equation (1)). The equilibrium moisture content was taken as 0.03 kg water/kg dry solid.
Table 1 summarizes the values for various parameters used for the simulation of each stage. The sensitivity analysis tool of the software was used to study the effect of different critical parameters on the final extracted amount of glucose and fructose.

3. Results and Discussions

Steady-state modeling and simulation of the IDSPP were conducted successfully using Aspen-Plus Software. Each sub-process was modeled and simulated separately. In addition, sensitivity analysis was performed for each block to identify the optimum operating conditions of the critical parameters for the respective stage.

3.1. Freeze-Drying

In the FD method, the biological qualities of the components, flavors, and colors of the food are usually preserved well [31]. For the analysis of IDSPP, vacuum-based FD was considered for the effective removal of moisture at a minimal drying time. The FD model accounted for the phase changes and water vapor diffusion within the date pulp. Modeling for the non-condensable species was accounted through the species transport model [32]. Technically, the feed sample was categorized into four layers, namely frozen front, vapor–ice interface, dry zone, and gas phase. A source term was used to adjust the distribution of gas-phase species due to water vapor generation [33].
Figure 2 depicts the process flow diagram of the FD process. Based on the simulation results, it was observed that the moisture content of the date pulp was reduced from 19.62% to 0.26%, calculated on a dry weight basis. The mass density of the freeze-dried dates was estimated as 1,639.05 kg/m3. This relatively low-density value of the freeze-dried date pulp signified higher porosity and thus a potential for improved cell rupture in the SCE stage [32]. Further, sensitivity analysis was performed by varying the temperature and pressure for the FD to examine the effect on the moisture content and duty consumption. The results for the optimization studies of FD are displayed in Figure S2 (Supplementary Materials). A minimum heat duty of 13.23 kW at a temperature of −42 °C and pressure of 0.0001 bar was computed for the FD required for maximum moisture removal.

3.2. Supercritical Extraction

An Aspen flowsheet for the SCE process is illustrated in Figure 3. For the proper design of the SCE stage, it was essential to employ appropriate mathematical representations. The SCE stage involved extraction from various solid natural matrices that were thermodynamically represented through solubility control, external mass transfer control, and/or internal mass transfer conventional models. Notably, three manipulators were used in the modeling of the SCE stage. The first one, “EXTRCALC” was used to estimate the quantity of the analytes to be extracted by the Sc-CO2/water solvent system based on the UDF patched to the software. The UDF contained the necessary data and equations for the solubility behavior of glucose, fructose, and other essential components of date fruit into the solvent mixture. The second one, “CO2OUTCA” calculated the amount of CO2 lost due to the opening of the extraction cell to fix the overall mass balance of the system. The third manipulator, “SEPARATO” was used to estimate the extracted mass lost with the exhaust stream of CO2 gas.

3.2.1. Operating Pressure

The extraction pressure of the SCE process is an important parameter that impacts the overall extraction efficiency [34]. Figure 4 shows the pressure effects on the extraction of reducing sugars from the freeze-dried date pulp. Simulation studies revealed that the extraction pressure had varying effects on the recovery of glucose and fructose sugars. For fructose sugar, the recovery efficiency decreased with incremental values in the operating pressure (Figure 4a). On the contrary, the extraction yield increased for glucose sugar with an increase in the operating pressure (Figure 4b). This opposing behavior can be ascribed to the different signs of the empirical coefficients in Equation (2) for glucose and fructose solubility in Sc-CO2. Consequently, the trade-off optimization tool of Aspen software was utilized to estimate the optimum pressure required for the maximum extraction of the total reducing sugars. Results showed a maximum product flow (glucose + fructose) of 73.70 kg/h was achieved at an operating pressure of 308 bar.

3.2.2. Extraction Temperature

Similar to pressure, the operating temperature of the SCE process is an imperative parameter that influences the efficiency of the separation process. Simulation studies showed that an increase in the extraction temperature had no significant effects on the recovery of reducing sugars from the fruit pulp. This insignificant temperature effect was anticipated as the solubility equation (Equation (2)) for the monosaccharide sugar molecules into Sc-CO2 did not involve any temperature effects. However, the extraction of non-polar analytes such as linoleic acid, palmitic acid, and oleic acid by the solvent showed a significant increase with temperature for T > 70 °C (Figure S3, Supplementary Materials). The increase in the temperature enhanced the kinetic energy of the Sc-CO2 fluid, which in turn improved the solvent diffusion and bioactive compound recovery [35]. However, it is worthy of specifying that higher extraction temperatures would cause the thermal degradation of the recovered sugar molecules, reducing the overall yield [36]. Based on the simulation results, an extraction temperature of 65 °C was recommended for the SCE stage.

3.2.3. Solvent Flow Rate and Composition

Results on the sensitivity analysis for the solvent:co-solvent ratio showed that a co-solvent concentration of 6.77 wt.% produced the maximum recovery of reducing sugars from the date pulp biomatrix. The simulation run resulted in an overall extraction yield of 99.1% for the reducing sugars with flow rates of 34.14 kg/h and 39.13 kg/h for glucose and fructose, respectively. Moreover, the sensitivity analysis showed that the total extracted quantity of glucose and fructose increased with the flow rate of Sc-CO2, as shown in Figure 5. Almost all of the reducing sugars were extracted into the solvent system for an Sc-CO2 flow rate of 31,000 kg/h. Further increases in the Sc-CO2 flow rate had no significant effects on the sugar extraction. This quantity of Sc-CO2 defines the solvent limit required for the maximum removal of targeted sugar components from the date palm fruit. Based on the optimization studies for the solvent:co-solvent ratio and the Sc-CO2 flow rate, the optimum flow rate of water was estimated as 2100 kg/h for the maximum recovery of glucose and fructose components. Figure 6 shows the effect of the water flow rate on the extraction of reducing sugars from the fruit biomatrix. Similar to Sc-CO2, the extraction yield increased with incremental levels of water flow rate. The improvement in the extraction of monosaccharides was due to the enhanced permeability and polarity of water molecules at the extraction conditions.
In general, the mass transfer mechanism for the recovery of plant bioactive compounds using supercritical technology involves four major steps [37]. Firstly, the analytes are desorbed from the biomatrix into the solvent film. Second, the analytes diffuse into the solvent, while in the third, the analytes dissolve into the solvent. The final step involves the bulk mass transfer of the solvent from the biomatrix to the external. Based on this mechanism, the increase in the extract yield with the flow rate of the solvent system signified that the external film transfer diffusion (second step) quantified by a diffusion coefficient, and the dissolution potential of sugars into the Sc-CO2/water system (third step) quantified by a partitioning coefficient, played the limiting roles for the recovery of the targeted analytes [38].

3.3. Spray-Drying

In general, beneficial features such as high drying rate, shorter drying time, and broad working temperature make SD an ideal choice for drying of food products to powder form [32]. The complicated three-dimensional nature of spray-dryers often makes it difficult to describe their exact behavior using empirical models. In this work, Aspen’s built-in simulator was used to characterize the SD process of the SCE extract (glucose and fructose solution) mixed with GA as the carrying agent. The model employed an Eulerian–Lagrangian approach to compute the particle motion paths, and heat and mass transfer phenomena occurring between the drying medium and the feed particles [32]. The choice of GA was to overcome the stickiness effect and increase the glass transition temperature of the mixture. Based on the previously reported experimental studies of SD for date fruit powder, the mass ratio of GA to SCE extract was fixed as 0.4 [18]. Figure 7 represents the process flow diagram for the SD stage of the IDSPP technology.
Sensitivity analysis of the SD stage involved the study of the effect of different parameters on the final moisture content of the sugar powder. Results showed that the final moisture content of the powdered product decreased with an increase in the mass flow rate of the drying air (Figure S4, Supplementary Materials). Complete removal of excess moisture was observed at an airflow rate of 8000 kg/h resulting in powdered sugar with the equilibrium moisture content. High flow rates of the drying air reduced the droplet size due to their improved atomizing effect. This resulted in a finer particle size of the product with a larger surface area that facilitated the rapid and higher drying rate of the product with complete removal of moisture [30]. It is worth specifying that the blank simulation without GA addition resulted in low drying efficiency. This can be attributed to the possible stickiness of the feed extract, as reported in several other related experimental works [39].
Figure 8a shows the effect of the inlet air temperature on the moisture removal from the feed solution for the powdered product formation. It was observed that an increase in the air temperature resulted in improved moisture elimination. This was clearly due to the improved heat and mass transfer processes between the air and feed particles owing to the greater driving force for moisture evaporation [40]. Moreover, higher operating temperatures would eliminate insufficient drying of the particles, thereby reducing the probability of semi-wet/sticky solids formation that would typically stick to the wall and thus result in higher yield [39]. Simulation results showed the attainment of equilibrium moisture content at a minimum air inlet temperature of 150 °C for the formation of dry powdered products of date sugar. Further, the results for the dependency of product moisture content on the feed flow rate are shown in Figure 8b. It was evident that lower feed flow rates resulted in a relatively drier product than higher flow rates. In the SD stage, a higher feed rate may result in slower heat and mass transfer processes. An increase in feed flow rate reduces the contact time between the drying medium and the atomized particles leading to low heat transfer rates resulting in low moisture removal. In general, feed flow rate not only affects the moisture content and yield of the product but also significantly influences the product solubility and water activity [41]. Based on the simulation results, a feed flow rate of 435 kg/h was recommended for the SD stage of the IDSPP.

3.4. Product Solubility

Product solubility is a critical benchmark for food products, especially food-grade sugars, to be used as an additive in food and beverages. In general, several parameters of the product, such as composition, water activity, morphology, equilibrium moisture content, etc., affect the product solubility [42]. The solubility of the product (glucose and fructose mixture) in an aqueous medium was simulated over a temperature range from 0 to 100 °C and at a pressure of 1 bar based on the UNIQUAC (universal quasichemical) thermodynamic model. The solid–liquid phase equilibrium of the powdered date sugar in pure water was simulated using activity coefficients [43]. The solubility of the sugar product at a temperature of 25 °C and 1 bar was estimated as 0.89 g/g water. Comparing this value with the solubility of the table sugar (2.1 g/g water), it was observed that sucrose (in table sugar) had a higher solubility than the extracted date sugar. However, it is expected that experimental validation would result in higher solubility of the date sugar powder due to the good emulsification properties and high solubility of GA in aqueous solutions [22]. Figure 9 depicts the PSD for the final powder product obtained for the optimal operating conditions of the SD step. The mean particle size and density were estimated as 504 µm and 0.0023 kg/m3, respectively, demonstrating the presence of significant levels of bioactive compounds in the product [42]. In addition, powders obtained using lower drying temperatures tend to possess a high percentage of smaller particles in the micro-range.
Experimental validation of IDSPP technology, with extensive analysis of extracts (including other vital analytes such as fibers, minerals, amino acids, etc.), determination of the extraction equilibrium and kinetics [44,45,46,47], and establishment of the necessary economics for production along with regulatory waste management approaches [48,49,50] would potentially realize effective production of date sugar that could ideally replace refined sugar.

4. Conclusions

In summary, this work conceptualized a novel IDSPP technology comprising of three main stages, namely freeze-drying, supercritical extraction, and spray-drying to process 100 kg/h of date fruit pulp to produce a soluble date sugar product. Stage-wise modeling and simulation studies were performed using Aspen Plus software with the sensitivity analysis to identify the optimum values of critical parameters for each stage. Freeze-drying studies revealed a minimum duty requirement of 13.23 kW at a temperature of −42 °C and pressure of 0.0001 bar to reduce the moisture content of the fruit pulp from 19.62% to 0.26%. The Sc-CO2 assisted extraction resulted in a total sugar recovery of 99.1% with flow rates of 34.14 kg/h and 39.13 kg/h for glucose and fructose sugars, respectively. Optimization studies showed that a pressure of 308 bar, temperature of 65 °C, Sc-CO2 flow rate of 31,000 kg/h, and Sc-CO2: water ratio of 0.07 resulted in the maximum extraction efficiency. Further, spray-drying simulation of the date extract into a powdered product using Gum Arabic as the carrier agent showed a mean particle size of 50.4 µm for the date sugar powder with a solubility of 0.89 g/g water (at 25 and 1 bar) and density of 0.0023 kg/m3. Sensitivity analysis revealed that the extraction pressure and solvent flow rates were the significant parameters for the extraction step while operating temperature had no salient effects on the recovery of the sugar. For the spray-drying process, drying air flow rate and its inlet temperature had positive effects, while feed flow rate negatively impacted moisture removal. Results showed that a mass flow rate of 8000 kg/h and an inlet temperature of 150 °C for the drying air was optimal to dry a feed stream mixture of date extract and Gum Arabic flowing at 435 kg/h containing 40 wt.% of Gum Arabic. Thus, this work confirmed the technical feasibility of IDSPP for the production of soluble date sugar powder and provided the necessary data with optimum operating conditions required for the process. Experimental validations and detailed characterizations of the product are further required to realize the outcomes of this study.

Supplementary Materials

The following supporting information can be downloaded at:, Figure S1: Chemical structure of Gum Arabic, Figure S2: Sensitivity analysis for FD: Temperature and pressure effects on the final moisture content and the net heat duty, Figure S3: Effect of temperature on the recovery of non-polar analytes of date fruit pulp, Figure S4: Effect of drying air flow rate on the moisture content of the date sugar powder product, Table S1: Properties of Gum Arabic used for the ASPEN simulation.

Author Contributions

Conceptualization, R.K. and F.B.; Data curation, H.B. and N.A.; Formal analysis, H.B., R.K. and S.W.H.; Investigation, H.B.; Methodology, R.K. and M.A.-Z.; Project administration, F.B.; Resources, S.W.H. and H.T.; Software, H.B. and R.K.; Supervision, F.B.; Validation, M.A.-Z., S.W.H., S.Y.A. and F.B.; Visualization, H.T.; Writing—original draft, H.B. and R.K.; Writing—review & editing, M.A.-Z., S.Y.A., N.A. and F.B. All authors have read and agreed to the published version of the manuscript.


This work was entirely funded and supported by the project grant CIRA-2019-028 under the Competitive Internal Research Award scheme of Khalifa University, UAE. The article processing charges were funded by grant RSP-2021/35, King Saud University, Riyadh, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.


This work was entirely funded and supported by the project grant CIRA-2019-028 under the Competitive Internal Research Award scheme of Khalifa University, UAE. This project was supported by the Researchers Supporting Project Number (RSP-2021/35), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflict of interest.


aEmpirical constant
AEmpirical constant
aFDFreeze Drying experimental coefficient
BEmpirical constant
bEmpirical constant
bFDFreeze Drying experimental coefficient
CEmpirical constant
D5Mass Median Diameter, mm
d50Median droplet size (μm)
DRDiameter of the atomizer (m)
FDFreeze Drying
GAGum Arabic
hHeight of the vanes (m)
IDSPPIntegrated Date Sugar Production Process
kEmpirical constant; k0–Drying constant (min−1);
k0Drying constant (min−1)
k1Drying constant (min−1)
M0Initial moisture content (g water/g dry solid)
mliqMass flow rate of the feed (kg/h)
MRMoisture ratio
MsMass flow ratio/vane (kg/h)
MtMoisture at a specific time (g water/g dry solid)
nNumber of blades
NRotational speed (rpm)
PTotal pressure of the system (bar)
pVane liquid loading correlation
PSDParticle Size Distribution
qVane liquid loading correlation
rVane liquid loading correlation
SSolubility of the solute in the supercritical solvent (g/L)
sVane liquid loading correlation
ScCO2–Supercritical Carbon dioxide
SCESupercritical Extraction
SDSpray Drying
SwSolubility of the water in CO2 (kg H2O/kg CO2)
TTemperature (°C)
USpeed of the circumference of the disc (m/s)
UDFUser Defined Function
ygfSolubility of the glucose/fructose in the supercritical carbon dioxide (mol solute/mol CO2)
ρsDensity of the pure solvent (g/L)


  1. Voora, V.; Bermúdez, S.; Larrea, C. Global Market Report: Sugar; International Institute for Sustainable Development: Geneva, Switzerland, 2020. [Google Scholar]
  2. Rambabu, K.; Bharath, G.; Hai, A.; Banat, F.; Hasan, S.W.; Taher, H.; Zaid, H.F.M. Nutritional Quality and Physico-Chemical Characteristics of Selected Date Fruit Varieties of the United Arab Emirates. Processes 2020, 8, 256. [Google Scholar] [CrossRef] [Green Version]
  3. Ahmed, I.A.; Ahmed, A.W.K.; Robinson, R.K. Chemical composition of date varieties as influenced by the stage of ripening. Food Chem. 1995, 54, 305–309. [Google Scholar] [CrossRef]
  4. Alharbi, K.L.; Raman, J.; Shin, H.-J. Date Fruit and Seed in Nutricosmetics. Cosmetics 2021, 8, 59. [Google Scholar] [CrossRef]
  5. Ameer, K.; Shahbaz, H.M.; Kwon, J.H. Green Extraction Methods for Polyphenols from Plant Matrices and Their Byproducts: A Review. Compr. Rev. Food Sci. Food Saf. 2017, 16, 295–315. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  6. Rambabu, K.; Edathil, A.A.; Nirmala, G.S.; Hasan, S.W.; Yousef, A.F.; Show, P.L.; Banat, F. Date-fruit syrup waste extract as a natural additive for soap production with enhanced antioxidant and antibacterial activity. Environ. Technol. Innov. 2020, 20, 101153. [Google Scholar] [CrossRef]
  7. Vallejo-Domínguez, D.; Rubio-Rosas, E.; Aguila-Almanza, E.; Hernández-Cocoletzi, H.; Ramos-Cassellis, M.E.; Luna-Guevara, M.L.; Rambabu, K.; Manickam, S.; Munawaroh, H.S.H.; Show, P.L. Ultrasound in the deproteinization process for chitin and chitosan production. Ultrason. Sonochem. 2021, 72, 105417. [Google Scholar] [CrossRef] [PubMed]
  8. Arumugham, T.; Rambabu, K.; Hasan, S.W.; Show, P.L.; Rinklebe, J.; Banat, F. Supercritical carbon dioxide extraction of plant phytochemicals for biological and environmental applications—A review. Chemosphere 2021, 271, 129525. [Google Scholar] [CrossRef] [PubMed]
  9. Al-Suod, H.; Ratiu, I.A.; Krakowska-Sieprawska, A.; Lahuta, L.; Górecki, R.; Buszewski, B. Supercritical fluid extraction in isolation of cyclitols and sugars from chamomile flowers. J. Sep. Sci. 2019, 42, 3243–3252. [Google Scholar] [CrossRef] [PubMed]
  10. Ratiu, I.-A.; Al-Suod, H.; Ligor, M.; Ligor, T.; Railean-Plugaru, V.; Buszewski, B. Complex investigation of extraction techniques applied for cyclitols and sugars isolation from different species of Solidago genus. Electrophoresis 2018, 39, 1966–1974. [Google Scholar] [CrossRef]
  11. Cavalcanti, R.N.; Albuquerque, C.L.C.; Meireles, M.A.A. Supercritical CO2 extraction of cupuassu butter from defatted seed residue: Experimental data, mathematical modeling and cost of manufacturing. Food Bioprod. Process. 2016, 97, 48–62. [Google Scholar] [CrossRef]
  12. Mirofci, S. A supercritical fluid extraction process to obtain valuable compounds from Eruca sativa leaves. Masters Thesis, University of Padova, Padua, Italy, 2014. [Google Scholar]
  13. Dohrn, R.; Buenz, A.P. Solubility enhancement of carbohydrates in carbon dioxide (Part 1 and 2). Int. Z. Lebensm. 1995, 46, 30–31. [Google Scholar]
  14. İZLİ, G. Total phenolics, antioxidant capacity, colour and drying characteristics of date fruit dried with different methods. Food Sci. Technol. 2016, 37, 139–147. [Google Scholar] [CrossRef] [Green Version]
  15. Seerangurayar, T.; Manickavasagan, A.; Al-Ismaili, A.M.; Al-Mulla, Y.A. Effect of carrier agents on flowability and microstructural properties of foam-mat freeze dried date powder. J. Food Eng. 2017, 215, 33–43. [Google Scholar] [CrossRef]
  16. Franceschinis, L.; Salvatori, D.M.; Sosa, N.; Schebor, C. Physical and functional properties of blackberry freeze-and spray-dried powders. Dry. Technol. 2014, 32, 197–207. [Google Scholar] [CrossRef]
  17. Shishehgarha, F.; Makhlouf, J.; Ratti, C. Freeze-drying characteristics of strawberries. Dry. Technol. 2002, 20, 131–145. [Google Scholar] [CrossRef]
  18. Manickavasagan, A.; Thangavel, K.; Dev, S.R.S.; Delfiya, D.S.A.; Nambi, E.; Orsat, V.; Raghavan, G.S.V. Physicochemical characteristics of date powder produced in a pilot-scale spray dryer. Dry. Technol. 2015, 33, 1114–1123. [Google Scholar] [CrossRef]
  19. Minh, N.P.; Vo, T.T.; Tu, T.T.C.; Vi, M.N.T.; Diem, N.T.N.; Thanh, H.T.T. Spray Drying Parameters Affecting to Dried Powder from Palmyra Palm (Borassus flabellifer) Juice. J. Pharm. Sci. Res. 2019, 11, 1382–1387. [Google Scholar]
  20. Anderson, D.M.W. Evidence for the safety of gum arabic (Acacia senegal (L.) Willd.) as a food additive—A brief review. Food Addit. Contam. 1986, 3, 225–230. [Google Scholar] [CrossRef]
  21. Georgetti, S.R.; Casagrande, R.; Souza, C.R.F.; Oliveira, W.P.; Fonseca, M.J.V. Spray drying of the soybean extract: Effects on chemical properties and antioxidant activity. LWT-Food Sci. Technol. 2008, 41, 1521–1527. [Google Scholar] [CrossRef]
  22. Glicksman, M. Gum arabic (Gum acacia). In Food Hydrocolloids; CRC Press: Boca Raton, FL, USA, 2019; pp. 7–29. [Google Scholar]
  23. Rockstraw, D.A. ASPEN Plus in the Chemical Engineering Curriculum: Suitable Course Content and Teaching Methodology. Chem. Eng. Educ. 2005, 39, 68–75. [Google Scholar]
  24. Rostamian, H.; Lotfollahi, M.N. New functionality for energy parameter of Redlich-Kwong equation of state for density calculation of pure carbon dioxide and ethane in liquid, vapor and supercritical phases. Period. Polytech. Chem. Eng. 2016, 60, 93–97. [Google Scholar] [CrossRef] [Green Version]
  25. Stahl, E.; Schilz, W.; Schütz, E.; Willing, E. A quick method for the microanalytical evaluation of the dissolving power of supercritical gases. Angew. Chem. Int. Ed. Engl. 1978, 17, 731–738. [Google Scholar] [CrossRef]
  26. Saldaña, M.D.A.; Alvarez, V.H.; Haldar, A. Solubility and physical properties of sugars in pressurized water. J. Chem. Thermodyn. 2012, 55, 115–123. [Google Scholar] [CrossRef]
  27. Chrastil, J. Solubility of solids and liquids in supercritical gases. J. Phys. Chem. 1982, 86, 3016–3021. [Google Scholar] [CrossRef]
  28. King, A.D., Jr.; Coan, C.R. Solubility of water in compressed carbon dioxide, nitrous oxide, and ethane. Evidence for hydration of carbon dioxide and nitrous oxide in the gas phase. J. Am. Chem. Soc. 1971, 93, 1857–1862. [Google Scholar] [CrossRef]
  29. Petersen, L.N.; Poulsen, N.K.; Niemann, H.H.; Utzen, C.; Jørgensen, J.B. An experimentally validated simulation model for a four-stage spray dryer. J. Process Control 2017, 57, 50–65. [Google Scholar] [CrossRef] [Green Version]
  30. Masters, K. Spray Drying Handbook; Halstead Press: New York, NY, USA, 1985. [Google Scholar]
  31. Nakagawa, K.; Ochiai, T. A mathematical model of multi-dimensional freeze-drying for food products. J. Food Eng. 2015, 161, 55–67. [Google Scholar] [CrossRef]
  32. Malekjani, N.; Jafari, S.M. Simulation of food drying processes by Computational Fluid Dynamics (CFD); recent advances and approaches. Trends Food Sci. Technol. 2018, 78, 206–223. [Google Scholar] [CrossRef]
  33. Li, S.; Stawczyk, J.; Zbicinski, I. CFD model of apple atmospheric freeze drying at low temperature. Dry. Technol. 2007, 25, 1331–1339. [Google Scholar] [CrossRef]
  34. Malaman, F.S.; Moraes, L.A.B.; West, C.; Ferreira, N.J.; Oliveira, A.L. Supercritical fluid extracts from the Brazilian cherry (Eugenia uniflora L.): Relationship between the extracted compounds and the characteristic flavour intensity of the fruit. Food Chem. 2011, 124, 85–92. [Google Scholar] [CrossRef]
  35. Zhang, Q.; Zhao, M.; Xu, Q.; Ren, H.; Yin, J. Enhanced enzymatic hydrolysis of sorghum stalk by supercritical carbon dioxide and ultrasonic pretreatment. Appl. Biochem. Biotechnol. 2019, 188, 101–111. [Google Scholar] [CrossRef] [PubMed]
  36. Oladipupo Kareem, M.; Edathil, A.A.; Rambabu, K.; Bharath, G.; Banat, F.; Nirmala, G.S.S.; Sathiyanarayanan, K. Extraction, characterization and optimization of high quality bio-oil derived from waste date seeds. Chem. Eng. Commun. 2021, 208, 801–811. [Google Scholar] [CrossRef]
  37. Islam, M.N.; Jo, Y.-T.; Jung, S.-K.; Park, J.-H. Thermodynamic and kinetic study for subcritical water extraction of PAHs. J. Ind. Eng. Chem. 2013, 19, 129–136. [Google Scholar] [CrossRef]
  38. Khajenoori, M.; Asl, A.H.; Hormozi, F. Proposed models for subcritical water extraction of essential oils. Chin. J. Chem. Eng. 2009, 17, 359–365. [Google Scholar] [CrossRef]
  39. Fazaeli, M.; Emam-Djomeh, Z.; Ashtari, A.K.; Omid, M. Effect of spray drying conditions and feed composition on the physical properties of black mulberry juice powder. Food Bioprod. Process. 2012, 90, 667–675. [Google Scholar] [CrossRef]
  40. Rambabu, K.; Muruganandam, L.; Velu, S. CFD simulation for separation of carbon dioxide-methane mixture by pressure swing adsorption. Int. J. Chem. Eng. 2014, 2014, 402756. [Google Scholar] [CrossRef]
  41. Cortés-Rojas, D.F.; Souza, C.R.F.; Oliveira, W.P. Optimization of spray drying conditions for production of Bidens pilosa L. dried extract. Chem. Eng. Res. Des. 2015, 93, 366–376. [Google Scholar] [CrossRef]
  42. Lourenço, S.C.; Moldão-Martins, M.; Alves, V.D. Microencapsulation of pineapple peel extract by spray drying using maltodextrin, inulin, and arabic gum as wall matrices. Foods 2020, 9, 718. [Google Scholar] [CrossRef]
  43. Zhao, H.; Li, J.; Wang, L.; Li, C.; Li, P. Thermodynamic investigation of 1,3,5-trioxane, methyl acrylate, methyl acetate, and water mixtures, in terms of NRTL and UNIQUAC models. Ind. Eng. Chem. Res. 2019, 58, 18378–18386. [Google Scholar] [CrossRef]
  44. Ramu, A.G.; Telmenbayar, L.; Theerthagiri, J.; Yang, D.; Song, M.; Choi, D. Synthesis of a hierarchically structured Fe3O4—PEI nanocomposite for the highly sensitive electrochemical determination of bisphenol A in real samples. New J. Chem. 2020, 44, 18633–18645. [Google Scholar] [CrossRef]
  45. Theerthagiri, J.; Lee, S.J.; Murthy, A.P.; Madhavan, J.; Choi, M.Y. Fundamental aspects and recent advances in transition metal nitrides as electrocatalysts for hydrogen evolution reaction: A review. Curr. Opin. Solid State Mater. Sci. 2020, 24, 100805. [Google Scholar] [CrossRef]
  46. Madhavan, J.; Theerthagiri, J.; Balaji, D.; Sunitha, S.; Choi, M.Y.; Ashokkumar, M. Hybrid advanced oxidation processes involving ultrasound: An overview. Molecules 2019, 24, 3341. [Google Scholar] [CrossRef] [Green Version]
  47. Senthil, R.A.; Priya, A.; Theerthagiri, J.; Selvi, A.; Nithyadharseni, P.; Madhavan, J. Facile synthesis of α-Fe2O3/WO3 composite with an enhanced photocatalytic and photo-electrochemical performance. Ionics 2018, 24, 3673–3684. [Google Scholar] [CrossRef]
  48. Theerthagiri, J.; Senthil, R.A.; Priya, A.; Madhavan, J.; Michael, R.J.V.; Ashokkumar, M. Photocatalytic and photoelectrochemical studies of visible-light active α-Fe2O3—gC3N4 nanocomposites. Rsc Adv. 2014, 4, 38222–38229. [Google Scholar] [CrossRef]
  49. Theerthagiri, J.; Senthil, R.A.; Senthilkumar, B.; Polu, A.R.; Madhavan, J.; Ashokkumar, M. Recent advances in MoS2 nanostructured materials for energy and environmental applications—A review. J. Solid State Chem. 2017, 252, 43–71. [Google Scholar] [CrossRef]
  50. Theerthagiri, J.; Salla, S.; Senthil, R.A.; Nithyadharseni, P.; Madankumar, A.; Arunachalam, P.; Maiyalagan, T.; Kim, H.-S. A review on ZnO nanostructured materials: Energy, environmental and biological applications. Nanotechnology 2019, 30, 392001. [Google Scholar] [CrossRef]
Figure 1. Integrated Date Sugar Production Process (IDSPP) flow diagram.
Figure 1. Integrated Date Sugar Production Process (IDSPP) flow diagram.
Processes 10 00257 g001
Figure 2. Freeze-drying process flow diagram.
Figure 2. Freeze-drying process flow diagram.
Processes 10 00257 g002
Figure 3. Aspen Plus Supercritical Extraction process flow diagram.
Figure 3. Aspen Plus Supercritical Extraction process flow diagram.
Processes 10 00257 g003
Figure 4. Effect of operating pressure on recovery of fruit sugars—(a) Fructose and (b) Glucose.
Figure 4. Effect of operating pressure on recovery of fruit sugars—(a) Fructose and (b) Glucose.
Processes 10 00257 g004
Figure 5. Effect of Sc-CO2 flow rate on glucose and fructose recovery from date pulp.
Figure 5. Effect of Sc-CO2 flow rate on glucose and fructose recovery from date pulp.
Processes 10 00257 g005
Figure 6. Effect of water flow rate on glucose and fructose recovery from date pulp.
Figure 6. Effect of water flow rate on glucose and fructose recovery from date pulp.
Processes 10 00257 g006
Figure 7. Aspen Plus Spray Drying process flow diagram.
Figure 7. Aspen Plus Spray Drying process flow diagram.
Processes 10 00257 g007
Figure 8. Effect of (a) inlet air temperature and (b) feed flow rate on the moisture content of the date sugar powder product.
Figure 8. Effect of (a) inlet air temperature and (b) feed flow rate on the moisture content of the date sugar powder product.
Processes 10 00257 g008
Figure 9. Particle size distribution of the spray-dried date sugar powder.
Figure 9. Particle size distribution of the spray-dried date sugar powder.
Processes 10 00257 g009
Table 1. Temperature and pressure of each unit block used in the simulation model.
Table 1. Temperature and pressure of each unit block used in the simulation model.
UnitTemperature (°C)Pressure (bar)
V1 VALVE31.372
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Bushnaq, H.; Krishnamoorthy, R.; Abu-Zahra, M.; Hasan, S.W.; Taher, H.; Alomar, S.Y.; Ahmad, N.; Banat, F. Supercritical Technology-Based Date Sugar Powder Production: Process Modeling and Simulation. Processes 2022, 10, 257.

AMA Style

Bushnaq H, Krishnamoorthy R, Abu-Zahra M, Hasan SW, Taher H, Alomar SY, Ahmad N, Banat F. Supercritical Technology-Based Date Sugar Powder Production: Process Modeling and Simulation. Processes. 2022; 10(2):257.

Chicago/Turabian Style

Bushnaq, Hooralain, Rambabu Krishnamoorthy, Mohammad Abu-Zahra, Shadi W. Hasan, Hanifa Taher, Suliman Yousef Alomar, Naushad Ahmad, and Fawzi Banat. 2022. "Supercritical Technology-Based Date Sugar Powder Production: Process Modeling and Simulation" Processes 10, no. 2: 257.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop