1. Introduction
Evaluating the environmental sustainability of newly developed product systems is vital to foresee potential issues and direct future research endeavors. The industrial extraction of cellulose from biomass is presently progressing rapidly, driven by growing demand for sustainable and renewable materials. Numerous chemical methods [1,2] have been used to extract cellulose from a variety of biomass sources. The extraction of cellulose from biomass is significant for numerous reasons. Firstly, cellulose is a plentiful and renewable biopolymer, rendering it a sustainable alternative to fossil-fuel-based materials. Extracting cellulose from biomass, such as agricultural waste, not only adds value to otherwise disposed-of by-products but also facilitates waste management and ameliorates environmental pollution [3].
The LCA is a widely utilized technique for quantifying the environmental impact of objects and processes throughout their life cycles based on selected scopes and boundaries. Several LCA techniques have been developed and applied to the extraction of cellulose from biomass to reduce the environmental impact by guiding the decision-making process towards more sustainable alternatives. LCA research on cellulosic materials has mostly focused on the material’s impact on eutrophication, human toxicity, water depletion, energy consumption and climate change [1]. Wibowo and co-researchers [2] used sugar cane waste to obtain a cellulose purity of 95.42% and subsequently conducted its LCA analysis. The findings indicated that the production of nanocrystalline cellulose has the greatest environmental impact due to the electricity consumption during freeze-drying. Piccinno and co-researchers [3] developed a novel method for converting vegetable food waste into cellulose nanofibers and performed a laboratory-scale LCA. The findings indicate that electrospinning has a more significant environmental impact compared to wet-spinning.
Arvidsson and co-workers [4] evaluated the LCA of three methods (enzymatic production route, carboxymethylation route and no pretreatment route) for generating cellulose nanofibrils from wood pulp. The findings indicate that the production of cellulose nanofibrils using carboxymethylation has the greatest environmental impact due to the high use of solvents derived from crude oil. In contrast, the enzymatic and no-pretreatment routes have a lower environmental impact. de Figueirêdo and co-workers [5] evaluated the LCA of cellulose nano-whiskers extracted from white cotton (EC system) and unripe coconut fibers (EUC system). The results showed that nano-whiskers produced in the EC system consumed less energy and water, discharged fewer pollutants and had a lower impact on eutrophication, human toxicity and climate change compared to those obtained from the EUC system. Zhang and co-researchers [6] investigated the LCA for the sulfuric acid hydrolysis-based synthesis of cellulose nanocrystals from cotton. The study employed three acid–cellulose nanocrystal separation methods: microfiltration, gravity settling and centrifugation. The results showed that the microfiltration technique was the most effective method for separating acidic–cellulose nanocrystals. In addition, according to the LCA results, the application of microfiltration in the separation of acidic cellulose nanocrystals reduced aquatic ecotoxicity by 33.4%, aquatic acidification by 47.9%, aquatic eutrophication by 55.8%, terrestrial ecotoxicity by 38.1%, potential global warming by 40.0% and non-renewable energy consumption by 47.8%.
In Saudi Arabia, date palm biomass is available in large quantities but has remarkable potential as a resource for numerous applications. The country is one of the largest date producers in the world and produces significant amounts of biomass in the form of date palm leaves, trunks and fruit residues. Saudi Arabia produces a total of 345,000 tons of date palm waste per year [7]. Conventionally, this biomass has been underutilized and often disposed of as agricultural waste [7] or used for low-value applications such as animal feed or fuel. However, there is a rising interest in valorizing date palm biomass for higher-value applications. Research and development initiatives are concentrating on transforming this biomass into useful products such as biofuels, biochar and cellulose-based materials. This focus aligns with the broader goals of Saudi Arabia’s Vision 2030 initiative, which targets to diversify the economy and encourage sustainable development. The application of date palm biomass not only supports waste management and environmental sustainability but also opens up new economic opportunities in the bio-based industries. In the present study, we conducted LCA to quantify the environmental impacts attributed to the extraction of cellulose from date palm biomass using a NaDES integrated with a microwave-assisted process. To the best of our knowledge, there is no prior LCA study carried out on a date palm cellulosic extraction using NaDES incorporated with microwave capability.
2. Methodology
2.1. Extraction of Cellulose via (NaDES) and Microwave-Assisted Process
The following method of cellulose extraction was adopted from our previous study [8]. Empty fruit bunch date palms were transported from a compound within the vicinity of King Saud University in Riyadh, Saudi Arabia. The biomass was washed several times with tap water and then dried for 48 h at 80 °C in a laboratory dryer. The biomass was then ground with a cutting mill and sieved into powder form. The time required to obtain 1 kg of the material having a particle size of 0.25 mm was approximately 1 h. To process the biomass, 1 g was mixed with 30 mL of an alkali reagent (NaOH, 5% w/v) in a TANK eco microwave extraction system (SINEO, Shanghai, China) for 10 min at 90 °C. After irradiation, the solution was allowed to cool to room temperature (24 °C) for about 30 min before centrifugation. The dark liquid from microwave extraction was separated using a high-speed centrifuge for 10 min. Successive washings with deionized water and ethanol by centrifugation were performed to adjust the pH neutral (pH 7), as shown in Figure 1, and to remove unwanted residuals. After washing, the sample was dried for 8 h at 85 °C.
A chlorine-free, environmentally safe bleaching reagent, 30% H2O2 v/v (pH 5.9), was subsequently mixed with the alkali-treated dry biomass in a microwave reactor for 10 min at 65 °C. The bleached sample was then spun in a centrifuge and rinsed with deionized water and 96% v/v ethanol to remove any remaining excess reagents and non-cellulosic components until a neutral pH was achieved. The sample was dried again for 8 h at 85 °C. Following this, 15 mL of 1 M H2SO4 and 6.5 g of NaDES (in a 1:1 molar ratio of choline chloride-to-citric acid anhydrate) were added, serving as a hydrolytic medium. The dried, bleached solid was further mixed and placed in a microwave reactor with NaDES and H2SO4 at 90 °C for 10 min. Subsequent washing of the resulting solid was performed with deionized water and 96% v/v ethanol using a high-speed centrifuge. The DES-treated sample was dried for 8 h at 85 °C. The dried solid product was collected from the dryer and then manually ground into a fine powder using a ceramic or glass mortar. Finally, the extracted microcellulose powder was stored in a well-sealed container in a dry place for further characterization. The surface and morphological analysis of the synthesized cellulose samples was conducted under vacuum conditions using a scanning electron microscopy (SEM) Model VEGA II LSU (Tescan, Brno-Kohoutovice, Czech Republic).
2.2. Life Cycle Assessment Method
2.2.1. Goal and Scope Definition
The ISO 14040 standard [9] was employed as a structure for developing the LCA for the present study consisting of four prominent stages. This includes goal and scope definition, life cycle inventory analysis (LCI), life cycle impact assessment (LCIA) and subsequent interpretation. The chosen functional unit for the present LCA research is 1 g of data palm biomass. The boundary delineated for this study is for a gate-to-gate process with systematic exclusion of the upstream transportation supply chain. Our work is, therefore, confined to a lab setting with consideration of energy and water consumption necessary to extract the cellulose. Therefore, our research scope includes the research commencing from the collection of raw data on palm biomass to the ultimate extraction of microcellulose powder in its final form. Figure 1 shows the process flow diagram of the extraction process from raw date palm biomass with relevant input and output components.
2.2.2. Assumptions
There are various assumptions employed to facilitate the LCA study. Water evaporation attributed to the drying unit operation was construed to be insignificant compared to water consumption from washing. The first part of the process entailed the preparation of bulky date palm biomass (in kg) and turning it into powder form. To streamline the LCA process, we have normalized the functional unit to 1 g for the first unit so that it is consistent with the functional unit for the second unit of the process. In the same vein, the electricity used for the three drying stages in the second unit of the process has been normalized and optimized in terms of the maximum amount of biomass that can be dried for a particular run. We presumed that the embodied energy of utilized technologies was negligible based on the reported study by Výtisk and co-researchers [10] since such systems had very low embodied energy compared to NaDES process operational energy use. The source of water resources was specified to be “in ground” and assigned to the Gulf Cooperation Council as Saudi Arabia has many arid regions and significantly relies on groundwater for water supply. In regard to energy consumption, we used a % mix of natural gas and oil of 61% and 39% to characterize energy use—this % mix was extracted from a 2021 study reported by Ember (
2.2.3. Life Cycle Inventory (LCI) Analysis
The life cycle inventory (LCI) analysis stage requires the collection of data and subsequent development of an inventory consisting of inputs (utilities, energy, etc.) and outputs (emissions, waste, etc.) in regard to the entire (NaDES) and microwave-assisted process restricted within a gate-to-gate scope. This includes data pertaining to the unit operations shown in Figure 1. To facilitate the creation of an LCA database, the openLCA software (version 2.1.1) was employed in the present study. The European Life Cycle Database 3.2 (ELCD 3.2) was obtained from the openLCA website and duly integrated into the software. The ELCD 3.2 database was selected because it contained a wide variety of impact assessment methods which were applied to our case and ultimately compared.
2.2.4. Life Cycle Impact Assessment (LCIA)
The life cycle impact assessment (LCIA) stage is a prominent stage where the potential environmental impacts of a process are evaluated. This stage involves projecting the inventory data, which includes all the inputs and outputs collected during the LCI stage, into environmental impact categories. In the current study, two impact assessment methods were utilized, namely, the ReCiPe Midpoint (H) 2016 and ILCD 2011 Midpoint Methods. The ReCiPe Midpoint (H) 2016 method is a popular LCIA methodology that includes 18 impact categories employed to render water and energy consumption into environmental impacts [11,12]. The Midpoint characteristic for both methods was selected over the Endpoint method as the former provides more depth of information (rather than breath) with lesser statistical uncertainties. The ILCD 2011 Midpoint Method is a standardized approach within the International Reference Life Cycle Data System (ILCD) framework for evaluating environmental impacts at Midpoint levels. The ILCD builds on ISO 14040 and 14044 standards [9,13] which affords a general basis for reliable and robust life cycle data [14]. Our selection of both the ReCiPe and ILCD methods was intended to be complementary. The ReCiPe method predominantly focuses on assessing potential impacts in a limited number of environmental categories, but it affords a thorough analysis of specific environmental factors.
2.2.5. Life Cycle Interpretation
The Life Cycle Interpretation stage following the LCIA for a gate-to-gate lab scale process of cellulose extraction from date palm biomass necessitates analysis of the results to draw meaningful conclusions and afford actionable recommendations. This stage identifies substantial environmental impacts and their sources, assesses data quality and consistency and ensures that the findings align with the goals and scope of the study. By assessing uncertainties, this stage facilitates understanding of the trade-offs and potential environmental benefits of the extraction process. The interpretation identifies main areas for improvement, optimizing resource use and reducing environmental burdens, thereby guiding decision-makers towards more sustainable practices in cellulose extraction.
2.2.6. Normalization and Weighting
The normalization and weighting stage in our study involves adjusting the impact assessment results to enable consistent comparisons and prioritization. During normalization, the impacts are scaled relative to a reference value (e.g., total environmental load of a region or the world), rendering it simpler to comprehend the significance of each impact category. Weighting further refines this by assigning relative importance to different impact categories based on specific preferences. This stage assists in stressing the most significant environmental impacts, hence guiding focused efforts on areas that necessitate urgent attention, ultimately assisting the development of more sustainable and effectual cellulose extraction processes. The ReCiPe Midpoint (H) 2016 method employed an in-built world (2010) H global database, while for the ILCD 2011 Midpoint Method, we incorporated the European Commission’s Joint Research Centre (EC-JRC) Global normalization and weighting set.
3. Results and Discussion
3.1. Surface Morphology of Extracted Cellulose
Figure 2 shows the scanning electron micrograph of cellulose extracted from date palm biomass using NaDES and a microwave-assisted process. Interestingly, the cellulosic fibers show splintered fibril-like morphology in the size range between 50 and 100 (diameter), which could be attributed to the elimination of hemicellulose and lignin components [15]. Indeed, it is a well-known observation that NaDES are very efficient in dissolving lignocellulosic biomass by breaking the hydrogen bonds within the cellulose structure. This, coupled with microwave applications, affords fast and uniform heating, which enhances the penetration and reaction effectiveness of NaDES within the biomass. Our experimental analysis indicated that the NaDES-based method attained a high yield of up to 89% based on the weight of extracted cellulose obtained from the weight of the raw biomass. In terms of crystallinity, the cellulose’s crystallinity index, as calculated via the Segal equation through X-ray diffractometry analysis, was 69.94, indicating a good level of crystallinity, as detailed in our previous study [8].
3.2. Life Cycle Assessment Results
Impact scores established in the LCIA stage represented the quantified potential environmental impacts of the cellulosic extraction process. They were derived from the LCI data and subsequently categorized into specific (and identified) environmental impact categories. By employing characterization factors, the raw data from the LCI stage are converted into these impact scores, which reflect the magnitude of potential environmental burdens associated with each category.
Table 1 lists the impact scores for the entire cellulose extraction process in the current study. The impact categories identified using the ReCiPe method are fossil resource scarcity, terrestrial ecotoxicity, freshwater ecotoxicity, water consumption, human carcinogenic toxicity and marine ecotoxicity, while categories identified using the ILCD method are freshwater ecotoxicity, water resource depletion, mineral, fossil and resource depletion, human toxicity and cancer effects. The differences in identified impact categories for both ILCD and ReCiPe arise from their distinctive methodological frameworks. The ILCD method, developed by the European Commission, is created to provide comprehensive impact assessment categories that align with European regulatory contexts, while the ReCiPe method emphasizes incorporating impact categories to complement scientific robustness with practical applicability. It is our opinion that their methodological differences are manifested in ILCD, identifying more on specific impact categories, while ReCiPe exhibits a more consolidated set and possibly overlooks some specific impacts highlighted by ILCD. Consequently, the difference in identified impact categories reflects the diverse objectives, local considerations and aggregation levels innate in each Midpoint assessment method.
It can be observed that fossil resource scarcity from the ReCiPe method shows the highest impact in the cellulose extraction process, as indicated by its raw impact score of 0.21367 kg oil eq., though the comparison between categories at this stage is moot given that their scores are not normalized. The numerous identified toxicity and ecotoxicity categories are unsurprising, given the amount of wastewater and residual chemicals emitted from the cellulosic extraction process. It can be argued that, however, the use of NaDES-based chemicals mitigates the toxicity impact as they are reported to exhibit low toxicity [16,17]. It can be seen that the category of global warming is conspicuously missing from the table; this is expected as energy is being consumed from an external source (energy generator) rather than being generated from on-site fossil fuel combustion (i.e., non-Scope 1 emission according to GHG protocol) [18].
The normalization stage serves the purpose of affording context and comparative significance to the impact category scores obtained from the ILCD and ReCiPe methods. In essence, the normalization process compares the impact category scores to reference values that characterize the average environmental impacts caused by activities associated with the cellulosic extraction process within a specific region (in this case, Saudi Arabia). This comparison facilitates the evaluation of the significance of the impacts in relation to broader environmental burdens. On a broader scale, normalization allows stakeholders to recognize that the environmental issues associated with the NaDES–microwave extraction of cellulose from biomass process are comparatively more or less important compared to other process activities. By affording a relative scale, normalization assists in decision-making and prioritization of environmental improvement strategies.
Figure 3 shows comparative normalized impact category scores by using ReCiPe 2016 Midpoint (H) and ILCD 2011 Midpoint assessment methods for the cellulosic extraction process. Perhaps unsurprisingly, the general trend of normalized scores does not seem to mirror their corresponding impact scores. For ReCiPe, after normalization, it appears that fossil resource scarcity exhibits a far lower relative score in comparison with freshwater ecotoxicity, indicating that the latter category imparts a more significant impact than the former. Indeed, the impact exhibited by fossil resource scarcity is not substantially higher than even human carcinogenic toxicity and marine ecotoxicity. On the other hand, the impacts exerted by both terrestrial ecotoxicity and water consumption can be construed as negligible in the grand scheme of things. The normalization results of ReCiPe are echoed by ILCD, in which freshwater ecotoxicity exhibits the most significant impact by far, followed by human toxicity and cancer effects.
Figure 4 shows the comparative weighted impact category scores by using the ILCD 2011 Midpoint impact assessment method for the cellulosic extraction process. Likewise, the general trend of weighted scores qualitatively mirrors their corresponding normalized scores in which freshwater ecotoxicity exhibits the most substantial impact. In the context of NaDES–microwave cellulosic extraction, qualitative similarity for both normalization and weighting is perhaps due to the ILCD method’s structured approach to evaluating environmental impacts comprehensively. This alignment highlights the method’s capacity to provide a sensible evaluation of environmental performance, guiding extraction scientists toward sustainable practices and emphasizing areas for improvement in the cellulose extraction process. In our extraction process, the emission of lignocellulose-based wastewater represents an environmental issue, as reflected in our LCA results. Such lignocellulose residues would be infused into the sediment systems in water bodies, causing copious concentrations of toxic organic waste to accumulate at the bottoms of rivers and lakes [19]. These polluted sediments are contaminated with assortments of organic and inorganic pollutants, posing a severe threat to both public and ecological health. To mitigate this issue, lignocellulose residues could be extracted from wastewater streams and treated via a myriad of physico-chemical or even biological treatment techniques [20].
At this juncture, it should be noted that when scaling up LCA parameters from small functional units, such as 1 g of biomass, to greater quantities, linear scaling is frequently assumed at first. Nonetheless, larger scales may lead to enhanced energy efficiency and process optimization, decreasing environmental impacts per unit of biomass due to economies of scale. Conversely, large-scale operations may add infrastructure needs, transportation and supply chain impacts and probable inefficiencies that are nonexistent at smaller scales. To address this, practitioners may use pilot-scale findings, process modeling or scaling factors to ensure accurate evaluation at larger scales.
4. Conclusions
A holistic LCA study of cellulose extraction from date palm biomass using natural deep eutectic solvent (NaDES) integrated with a microwave-assisted process was presented. Our findings highlight substantial insights into the environmental impacts associated with the cellulose extraction process. Notably, the normalized scores show that freshwater ecotoxicity imparts the most significant impact in both ReCiPe and ILCD assessment methods, surpassing other categories such as fossil resource scarcity. This underlines the critical need to address freshwater ecotoxicity in the development and optimization of the cellulosic extraction process. The incorporation of NaDES with microwave-assisted extraction offers favorable potential for sustainable date palm biomass applications. The process shows a reduced dependency on fossil resources, aligning with the United Nations Sustainability Development Goal (No 7). However, the prominent impact on freshwater ecotoxicity calls for further fine-tuning in solvent selection and process optimization to alleviate environmental burdens associated with clean water aspirations outlined in the United Nations Sustainability Development Goal (No 6). In conclusion, this study shows the significant environmental implications of applying NaDES and microwave-assisted processes for cellulose extraction from date palm biomass. The use of rigorous LCA methodologies affords a cohesive framework for evaluating and improving the environmental sustainability of bioprocesses. Future research should focus on improving the environmental performance of this extraction method, potentially expanding its application to other waste biomass in the Gulf region. This study adds to the growing body of knowledge in sustainable material science and waste management, offering crucial insights for scientific researchers, LCA practitioners, industry stakeholders and policymakers aiming to advance environmentally friendly technologies.
Y.M.A.: funding acquisition, visualization, writing—original draft. C.-Y.Y.: conceptualization, methodology, data curation, software, validation, writing—review. A.A.R.: conceptualization, methodology, writing—original draft and editing and review. M.E.-H.: formal analysis, visualization, methodology, manuscript writing, editing and review, supervision and project administration. M.S.: formal analysis, methodology, manuscript writing, editing and review. All authors have read and agreed to the published version of the manuscript.
Not applicable.
Not applicable.
The data presented in this study are available on request from the corresponding author (accurately indicate status).
Author Chun-Yang Yin was employed by the company Cypress Sustainability Pte Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Footnotes
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Enlarge this image.Figure 1. Process flow diagram of the extraction process from raw date palm biomass.
Enlarge this image.Figure 2. Scanning electron micrograph of cellulose extracted from date palm biomass using NaDES and microwave-assisted process.
Enlarge this image.Figure 3. Comparative normalized impact category scores by using (a) ReCiPe 2016 Midpoint (H) and (b) ILCD 2011 Midpoint assessment methods for the cellulosic extraction process.
Enlarge this image.Figure 4. Comparative weighted impact category scores by using ILCD 2011 Midpoint impact assessment method for the cellulosic extraction process.
Impact scores for the entire cellulose extraction process in the current study.
| Impact Category | Impact Assessment Method | Score |
|---|---|---|
| Fossil resource scarcity | ReCiPe Midpoint (H) 2016 | 0.21367 kg oil eq. |
| Terrestrial ecotoxicity | ReCiPe Midpoint (H) 2016 | 0.00435 kg 1,4-DCB |
| Freshwater ecotoxicity | ReCiPe Midpoint (H) 2016 | 0.00110 kg 1,4-DCB |
| Water consumption | ReCiPe Midpoint (H) 2016 | 0.00033 m3 |
| Human carcinogenic toxicity | ReCiPe Midpoint (H) 2016 | 0.00020 kg 1,4-DCB |
| Marine ecotoxicity | ReCiPe Midpoint (H) 2016 | 3.8 × 10−5 kg 1,4-DCB |
| Freshwater ecotoxicity | ILCD 2011 Midpoint | 0.54024 CTUe * |
| Water resource depletion | ILCD 2011 Midpoint | 5.4 × 10−5 m3 |
| Mineral, fossil and resource depletion | ILCD 2011 Midpoint | 7.6 × 10−8 kg Sb eq. |
| Human toxicity, cancer effects | ILCD 2011 Midpoint | 4.2 × 10−10 CTUh * |
* CTUe and CTUh denote comparative toxic units for the ecosystem and comparative toxic units for humans, respectively.
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Details
; El-Harbawi, Mohanad 1 ; Magaret Sivapragasam 3 1 Department of Chemical Engineering, King Saud University, Riyadh 11421, Saudi Arabia;
2 SIT Building @ Ngee Ann Polytechnic, Newcastle University in Singapore, 537 Clementi Road #06-01, Singapore 599493, Singapore; Cypress Sustainability Pte Ltd., Singapore 409015, Singapore
3 Science Communication Unit, School of Applied Sciences, College of Health, Science and Society, University of the West of England (UWE Bristol), Coldharbour Lane, Stoke Gifford, Bristol BS16 1QY, UK;