This article is dedicated to Dr. Praveen Kumar Tandon, Professor (Former Head), Department
of Chemistry, University of Allahabad, on his 67th Birth Anniversary as a token of
respect for his remarkable contribution to the field of catalysis and chemical kinetics.
1
Introduction
In 2015, the 2030 Agenda for Sustainable Development was adopted by all the members
of the United Nations, which sketched a detailed outline and plan for prosperity and
peace for peoples and the earth not only for the present but also for the future.
This agenda includes a plan of action for people to maintain peace, prosperity, and
symbiotic partnerships on this planet to sustain the life with beauty of natural biodiversity
[1], [2]. Nature has a unique work culture, that is, material cyclization and resilience
to maintain its sustainability, and it is the source of inspiration behind many of
the innovative acts of human beings [3]. Humans observe and learn everything from nature by mimicking. Nature maintains
its sustainability through circular approaches [4]. Nature sustains all forms of life and its own resources from millions of years
by circular processes, that is,
biogeochemical cycles. Due to this unique feature, that is, true circularity, nature
produces no waste and continuously works on a zero-waste strategy. Zero-waste goal
(ZWG) is a global initiative to treat discarded materials (i.e., waste) as resources
that can be returned back to nature/marketplace to be reused again and again and thus
reduce waste production at its minimal level via reducing, reusing, and recycling
(3Rs) [5], [6], [7]. It is a key pillar of the movement for environmental justice. ZWG is the integral
paradigm toward the achievement of circular economy (CE). The CE is a model where
materials are kept in circulation via 3Rs for their optimal use. In recent years,
CE has become an emerging field of sustainability due to its capability to conserve
and regenerate natural resources [8], [9]. The Application of CE principles in chemistry and its
related practices are the only promising solutions to the environmental and sustainability-related
challenges of the chemical industry. Waste is an invention of humans and is now treated
as one most horrible challenges for the world. According to the recently published
United Nations Environment Programme (UNEP) report 2024, municipal solid waste (MSW)
production is expected to grow from 2.1 billion tonnes in 2023 to 3.8 billion tonnes
by 2050 [10]. The global direct expenditure of waste management was estimated at about 252 billion
USD in 2020. Total global cost is expected to rise up to 361 billion USD when other
hidden costs of pollution, climate change, health issues, etc. which are directly
or indirectly associated with improper waste management are included [10]. Without taking serious steps toward waste management, it is expected that the total
annual cost could be doubled by about 640.3 billion USD. Only by a
drastic reduction in waste production, proper waste management, and following concepts
of CE (i.e., way to use waste as a resource), we can secure an affordable, livable,
and sustainable future. Waste is the one of the main source of various hazardous chemicals,
that is, heavy metals (i.e., Pb, Cd, Hg, Ni, Zn, Cr, As, Cu, etc. are present in waste
obtained from pesticides, dyes, catalysts, electronic devices, medicines, paints,
printing materials, industrial sludge, and incineration of household wastes) [11], [12], volatile organic compounds (VOCs, i.e., benzene, toluene, ethylbenzene, xylenes,
etc. are organic pollutants affecting human health and atmospheric chemistry and are
released from wastes containing paints, solvents, cleaners, degreasers, dyes, varnishes,
refrigerants, household wastes, and also from plastics, e-wastes, and incineration
of wastes) [13], [14],
persistent organic pollutants (POPs, i.e., polychlorinated biphenyls, polychlorinated
dibenzo-p-dioxins, polychlorinated dibenzofurans, etc. are chemicals with minimum
degradation capability in the environment, high accumulation in animal/human tissues
and able to transmit through food chain), etc [15], [16]. Integration of circular approaches in chemical science and its related field of
research and development, that is, CE in design of new products [17], sustainable circular uses of chemicals [18], CE for chemicals in plastics [19], CE-based design for research and development in the field of chemical science [20], role of CE in a sustainability framework [21], and CE perspective of plastic value chain [22] have great potentials to solve the world’s chemical waste problems. By
replacing linear approaches (i.e., take-make-use-dispose) with circular approaches
(i.e., take-make-use-reuse-recycle-retake-…), waste generation, as well as pollution
[23], can be minimized. Thus, circular approaches like circular chemistry (CC) contribute
toward a circular economy—a system where material never becomes waste just similar
to nature like recyclable plastics in CE [24], degradable and chemically recyclable polymers [25], CE implications of recycled PET [26], sustainable chemistry by circular design [27], and circular model of recycling plasmix [28]. Thus, circular chemistry (CC) has great capability to solve the various challenges
related to the chemical industry. Although CC has gained the attention of researchers
worldwide [8], [18], [27],
[29], [30], [31], [32], still it requires more attention to popularize the concepts of circular chemistry
among nonfield specific researchers. In this context, the present article briefly
reviewed the fundamental aspects of CC with respect to ZWG and CE to overcome the
global challenges associated with chemistry as an enabler of CE to achieve the ZWG.
Humankind is facing various challenges regarding sustainability, that is, the ability
to sustain our environment, ecosystem, civilization, and humanity on this blue planet.
It is expected that rampant growth in the human population and related developmental
activities will intensify these challenges much more in the near future. The ways
to tackle these challenges should be cost-effective, simple, and sustainable. Therefore,
the development of circular processes (circular chemistry, CE, etc.) mimicking the
biological life
cycle is crucial to achieving a more sustainable future. To explore the role of circular
approaches in chemical processes to optimize the resources for their sustainable use.
This study can address the limitations of linear approaches and their environmental
impacts and is also able to explore the application of circular approaches in chemistry.
Thus, the scope of sustainability may be expanded to the entire lifecycle of chemical
materials.
1.1
Waste
Waste can be understood as an unwanted matter in place and time and first time described
in the 12th century [33]. There is no waste in nature. One organism’s waste is another’s resource in a natural
ecosystem. Waste is considered a precious resource in the natural ecosystem, while
in the anthropogenic ecosystem, waste (i.e., human invention) is considered one of
the world’s main ecociders. As a result of uncontrolled and rampant growth in the
world’s population, waste production has increased about tenfold, and it is expected
that it should double again by 2025 [34]. Annually, about 7–10 billion tonnes of anthropogenic waste are generated globally
[15], [35], including 300–500 million of tonnes waste labeled as municipal solid waste [36] and hazardous wastes [37], [38], that is, toxic, explosive,
flammable, corrosive, etc.
1.2
Zero-Waste Goals
ZWGs are defined as the conservation of natural resources by reasonable and responsible
production, use, reuse, and recycling of materials. United Nations declared 30 March
as International Day of Zero-Waste to explore the impact of ZWGs. The main aims of
ZWGs are the promotion of sustainable production and consumption which support the
societal move toward circular approaches and enhance the awareness about how zero-waste
goals contribute toward the 2030 Agenda for Sustainable Development. ZWGs are the
integral paradigm toward the achievement of CE or circularity throughout the world
[5], [6], [7]. To achieve ZWGs, actions are required at all levels, that is, (i) the product should
be designed to be durable and reusable with less environmental impact, (ii) resource-efficient
methods, (iii) sustainable and economic transportation, (iv) managed demand can enable
zero-waste throughout the life cycle
of a product, (v) consumer can play a pivotal role toward zero-waste by reuse and
repair of products as much as possible before proper disposal, and (vi) the government,
communities, and industries can play their role by improving waste management and
recovery system through better policymaking [39] ([Fig. 1]).
Figure 1 ZWGs: action is required at all levels.
1.3
Sustainable Development and Sustainability
Life on Earth is the epitome of resilience, adapting and changing to fit its context
over billions of years. Understand true sustainability from nature itself—not only
creating but also continuing to nourish and heal the systems that create conditions
conducive to life. Demand for basic amenities including food, shelter, health, and
energy resources increases continuously due to rampant growth in the world’s population
and the rise in living standards of human beings. The existing and more popular linear
approach/economy poses significant threats to human health and the environment through
resource depletion and waste production in huge amounts. To overcome all these global
challenges, the closed loop, restoring, and waste-free (zero-waste) concept, that
is, CE has gained worldwide acceptance to achieve the goal of sustainability. CE is
a part of emerging science, that is, industrial ecology, which is very crucial for
sustainable development. The CE is also known as
sustainable economy where economic growth is associated with reduction of resource
consumption and recirculation of natural resources [40], [41], [42], [43], [44]. The main goal of sustainability is to encourage and inspire people to explore a
new way of looking at themselves as well as the world. Thus, true sustainability comes
through circularity [23]. Circularity is at the core of eco-design, the production technology in which waste
is repurposed and environmental impacts such as raw material consumption are reduced
via 3R concepts: reduce, reuse, and recycling.
1.4
Linear and Circular Approach
The linear approach includes take-make-use-and-dispose, therefore generating a huge
amount of waste materials to contaminate the environment. Linear approaches are a
major cause of environmental degradation. It causes resource constraints and thus
affects economic growth. Circular approaches can overcome these disadvantages of linear
approaches. Circular approaches include take, make, use, recollect, repair, reuse,
and recycle the materials to create a close cyclic system to minimize the intake of
natural resources as well as the generation of wastes. Thus, circular approaches can
help to restore the regenerative capacity of an ecosystem to conserve resources. [Fig. 2] provides a schematic comparison between linear and circular approaches [23].
Figure 2 Linear versus circular approach.
1.5
Need for Circular Approach
Circular approaches are essential to solve the imminent challenges related to environmental
degradation and exhausting natural resources. Recently, CE has attracted a lot of
attention from research communities worldwide due to its significance and contribution
toward sustainable development goals [45]. The concept of CE has become more popular due to its applicability toward environmental
sustainability and ZWGs [46]. The functioning of CE is based on the principles, that is, rethink, reduce, reuse,
recover, recycle, redesign, repurposing, etc. to conserve natural resources [47]. CE is based on the concept of ‘zero-waste’ which can be achieved only by circular
approaches. Thus, circular approaches may play a very important role in the CE [18], [48]. There are various indicators or business activities that can be used to access
the transition to the
CE in terms of resource efficiency (i.e., reduction in ecological footprint in production
inputs/infrastructure, reduction in pollution product use/production process, reduction
in raw material use in production, optimization of warehouse concept to reduce storage
space, etc.), closing the resource loop (i.e., increase in reuse of production inputs/infrastructure,
facilitation for recycling, reuse of waste and residual materials inside or outside
the company, expansion of the facility to use sharing platforms, refunds on product
returns, resale/upgrade of returned products, etc.), and increasing product life (i.e.,
purchase of infrastructure with a long product life, increase the life span of infrastructure
by maintenance and repair, expansion of product life, facilitate the repair during
use, extend warranty and repair services, improve spare parts accessibility, etc.)
[49].
1.6
Methodologies To Assess the Circularity
Measurement of the circularity of the chemical industry involves the assessment of
its progress toward a CE. There are various tools and metrics that are more frequently
used in the measurement of circularity, that is, MCI (Material Circularity Index:
measures the production of recycled materials) [50], CEI (Circular Economy Index: assess waste reduction, recyclability, and resource
efficiency), LCA (Life Cycle Assessment: assessment of environmental impacts throughout
the value chain, MFA (Material Flow Analysis: measure material flows and stocks),
rate of recyclization, waste reduction rate, carbon footprint, circular use of water,
use of renewable energy, etc. [43], [51], [52] Various indicators like the ratio of recycled materials used at a production level,
the percent reduction in generation of hazardous/toxic waste, reduction in water consumption,
etc. are also used
to assess/measure the circularity of a process with a particular system. [53] Chemical industries can measure and improve their level of circularity by using
the above metrics/methodologies and indicators to contribute toward a more sustainable
future.
2
Circular Chemistry
CC is an emerging and innovative approach to make chemical practices more sustainable
and truly circular. CC aims to replace today’s linear approach with a new circular
approach for optimizing resource efficiency and preserving finite natural resources.
Thus, CC can play a very crucial role in achieving the ZWG, which ultimately contributes
to a CE (i.e., all activities of the 3Rs concept in manufacturing, supply, and consumption
of products). Chemistry can act as a proponent of sustainability via sustainable development
to provide ethical, sustainable, and practical solutions to global challenges by catalyzing
radical reforms in the chemical industry. Catalysis is one of the key principles of
green chemistry and can play a very important role in CC by enhancing the regeneration
and reuse of catalytic materials [23],[54], [55], [56], [57], [58], [59], [60]. Catalyzed processes are involved in the production of about 90% of products in
the chemical industry [61]. Catalyzed processes produce a huge amount of catalytic materials as waste after
their end-use. Regeneration and reuse of catalytic materials can increase the total
resource efficiency of catalysts and also enable a closed loop for circular use of
precious noble metals (as noble metals are precious and too costly). Thus, catalysts
play a pivotal role in our pursuit of CC [62].
2.1
Nature and Circularity
Nature has worked on zero-waste strategy for millions of millions of years. Nature
is regenerative as it reuses and recycles the nutrients to generate new raw materials;
thus, there is no waste in nature. [Fig. 3] schematically shows the true circularity of nature as a nutrient cycle (a vital
natural service)—the circulation of matter essential for life from the environment
(mostly from soil or water) through the biotic kingdom (living organism) back to the
environment [63]. [Fig. 3] explains a completely closed loop for cyclization of organic matters from biotic
to abiotic kingdom and vice versa. The nutrient cycles are real examples of the true
circularity of nature. Carbon, nitrogen, sulfur, phosphorous, and water are among
the essential elements that move through biotic, earth, and atmospheric systems via
biogeochemical cycles. Earth is the only known planet in our solar system that has
vital
conditions (i.e., air, water, soil, fire, and sky) for the survival of life. Maintenance
of these vital conditions requires a constant recycling of materials between abiotic
(nonliving) to biotic (living) components of ecosystems.
Figure 3 Nutrient cycle in nature: true circularity.
2.2
Chemistry and Global Challenges
Global demands for materials and energy increase continuously due to rampant growth
in the world’s population and people’s demand for high quality of life. Humans as
well as society could not survive sustainably without chemicals because chemicals
have become an integral part of modern society. A number of chemicals are essential
parts of our daily life needs and very crucial for economic and societal sectors also.
Many of these chemicals are hazardous in nature and have great potential to harm living
beings and environmental biodiversity. The chemical industry has serious negative
environmental, health, and safety impacts at every level of chemical production and
its uses [64], [65]. [Table 1] summarizes some selected hazardous chemicals and their impacts on human health [66].
Table 1
Some selected chemicals and their adverse effects on human health.
|
S. no.
|
Chemicals
|
Adverse health effects
|
|
a Secondhand smoke is a mixture of smoke exhaled by a smoker that is diluted by the
surrounding air (main stream smoke) and the smoke from the burning tip of a cigarette
or other smoked tobacco product (side stream smoke).
|
|
1
|
Lead
|
Neuro-disorders, intellectual disability, cardiovascular disease (IHD, ischemic heart
disease), stroke, etc.
|
|
2
|
Pesticides
|
Parkinson’s disease, the cause of suicide by self-poisoning of pesticides, etc.
|
|
3
|
Ambient air pollutants
PM (particulate matter), SO
x
(sulfur dioxides), NO
x
(nitrogen oxides), benzene, benzo[α-]pyrene, etc.
|
ALRI (acute lower respiratory infections, i.e., pneumonia, bronchitis, and bronchiolitis),
upper respiratory infections and otitis media (middle ear infection), IHD, adverse
pregnancy outcomes (i.e., low birth weight, prematurity, and stillbirths), COPD (chronic
obstructive pulmonary disease), asthma, lung cancer, stroke, etc.
|
|
4
|
Household air pollutants
CO (carbon monoxide), SO
x
, NO
x
, C6H6, HCHO, poly-aromatic hydrocarbons (PAHs), PM, etc.
|
COPD, cataracts (an important cause of blindness worldwide), ALRI, IHD, otitis, lung
cancer, stroke, etc.
|
|
5
|
Second-hand smokea
Nicotine, HCHO, CO, phenols, NO
x
, naphthalene, tar, nitrosamine, PAHs, vinyl chloride, metals, HCN, NH3, etc.
|
ALRI, IHD, otitis, lung cancer, stroke, etc.
|
|
6
|
Chemicals in occupational exposure
As, asbestos, Be, Cd, Cr, diesel exhaust, Ni, silica, C6H6, ethylene oxide, ionizing radiation, dust, fumes/gas, etc.
|
Leukemia (blood cancer), COPD, trachea, bronchus, lung cancer, etc.
|
Improper handling and management of chemicals and related wastes severely damaged
our life support systems, that is, air, water, and soil. As a result of these, chemicals
enter the food chain and affect living beings [67]. Chemistry has great potential to address the various human challenges related to
their sustainable survivability and plays a direct and dynamic role at the interface
of science, society, and policy. Thus, chemistry plays the role of central science.
It is crucial to understand life, environment, economy, society, technology, etc.
[68], [69] Global Chemicals Outlook II, which was electronically launched on April 29, 2019,
in Geneva, Switzerland, as a working document to give innovative solutions to minimize
the adverse environmental, health and safety effects of chemicals and its related
wastes and for implementation of 2030 agenda of sustainable development mandated by
UNEA
(United Nation Environmental Assembly), 2016. The report highlights that the global
goal to minimize the adverse effects of chemicals and wastes needs urgent attention
and more ambitious worldwide action by all stakeholders [65]. Global trends, that is, population growth, economic growth, and urbanization are
rapidly increasing the consumption of chemicals. By 2030, it is estimated that the
chemical industry's worth (market size) would have doubled its worth in 2017. Whether
this growth will show its positive or negative impact on the biotic kingdom, including
humanity, only depends on how chemicals and their related challenges are managed.
Toxic and hazardous chemicals continuously pass into the surroundings (environment),
contaminating food cycles and finally entering living beings where they cause severe
damage. Recently, the World Health Organization (WHO) estimated that about 2 billion
lives and 53 billion disability-adjusted life-years
were lost in the year 2019 due to exposure to selected toxic/hazardous chemicals [66]. [Fig. 4] explains the merits and demerits of the chemical industry and possible solutions
to reduce its adverse effects on the ecosystem.
Figure 4 Economical and environmental perspectives of the chemical industry.
2.3
Concepts of CC
The application of circular approaches in chemistry by which materials/chemicals are
continuously cycled back through the value chain for reuse, thereby optimizing resource
efficiency and preserving finite natural resources is known as CC. Thus, the scope
of sustainability may be expanded to the entire lifecycle of chemicals. CC can optimize
resource efficiency and enable a closed loop for an environmentally benign chemical
industry [23]. CC can solve various challenges associated with the chemical industry from an environmental
perspective. Twelve basic principles of CC and their sustainability aspects are briefly
presented in [Table 2], [29], [32].
Table 2
The 12 principles of CC and their sustainability aspects.
|
S. no.
|
Principles of circular chemistry
|
Brief explanation
|
Sustainability aspects
|
|
1
|
Collect and reuse the waste
|
Reusing waste as a resource is a necessary prerequisite for enabling circularity of
elements, molecules, and materials
|
An economic and environmental perspective of sustainability is directly linked to
the way in which we extract, process and consume the earth’s finite natural resources.
This can include conservation of natural resources, making sustainable products by
adopting circular approaches (mainly recyclability) in product design, changing consumption
behavior, and incorporating more sustainable business models to favor the circular
economy (CE). The circular economy is a key enabler to achieving the objectives of
UN SDGs, i.e., reducing inequality, improving health and education, peace and prosperity
for all, protecting environment, etc. Proper management of chemicals and related waste
is a specific target 12.4 under SDG 12. It is also referred to under good health and
well-being (SDG 3), clean water and sanitation (SDG 6), industry innovation and infrastructure
(SDG 9), climate change (SDG 13), life below water (SDG 14), and life on land (SDG
15) Reuse is
the second important strategy of 3Rs concept for waste management after the waste
reduction. It is the process of using a material over and over period of time. It
preserves energy and material both. Thus, it favors SDG 12, i.e., responsible consumption
and production, and targets 12.2 & 12.5
|
|
2
|
Maximize atom circulation
|
Truly circular chemical process platforms should maximize every atom in existing molecules
|
|
3
|
Optimize resource efficiency
|
Resource conservation should be targeted, promoting reuse, and preserving finite feedstocks
|
|
4
|
Strive for energy persistence
|
Energy efficiency should be maximized
|
|
5
|
Enhance process efficiency
|
Continuous innovations are required to promote the reuse and recycle of materials
during the process (in-process) and repurposing of used materials (post-process) preferably
on the site by reducing the consumption of raw materials and by optimizing resource
production.
|
|
6
|
No out-of-plant toxicity
|
Chemical processes should not release any toxic compounds into the environment
|
|
7
|
Target optimal design
|
Design should be based on the highest end-of-life options, accounting for separation,
purification, and degradation
|
|
8
|
Assess sustainability
|
Environmental assessment (by life cycle assessment) should become prevalent to identify
inefficiencies in chemical processes
|
|
9
|
Apply ladder of circularity
|
The end-of-life options for a product should strive for the highest possibilities
on the ladder of circularity
|
|
10
|
Sell service rather than product
|
Producers should employ service-based business models such as chemical leasing, promoting
efficiency over production rate
|
|
11
|
Reject lock-in
|
The business and regulatory environment should be flexible to allow the implementation
of innovations
|
|
12
|
Unify industry and provide coherent policy framework
|
The industry and policy should be unified to create an optimal environment to enable
circularity in chemical industry
|
The principles of green chemistry were introduced by Paul Anastas and N. Eghbali in
the year 2010 to make chemical processes/products greener or more environmentally
friendly [70]. The principles were mainly developed to prevent the production of pollutants at
their source by minimizing the use of hazardous chemicals. In the year 2003, Anastas
and Zimmerman published 12 principles of green engineering mainly focusing on how
to achieve sustainability through science and technology [71]. The main objective of these principles of green engineering was to provide new
human, health, and environment benign materials/products/processes through the synergetic
engagement of scientists and engineers. In 2019, Chris Slootweg published a commentary
in ‘Nature Chemistry’ and introduced a new concept: CC by presenting 12 principles
of CC for a far-reaching reform (revolution) in the practices of chemistry to solve
the socioeconomic
and environmental challenges of the future [32]. According to Slootweg, “the concept of circular chemistry expands the scope of
sustainability to the entire life of chemical products.” CC requires clear objectives
at molecular, method, product, and system levels. [Table 3] lists the comparative aspects of the 12 principles of CC, green chemistry, and green
engineering [72], [73], [74].
Table 3
Principles of CC, green chemistry, and green engineering.
|
S. no.
|
Principles of circular chemistry
|
Principles of green chemistry
|
Principles of green engineering
|
|
1
|
Collect and use waste
|
Prevention
|
Inherent rather than circumstantial
|
|
2
|
Maximize atom circulation
|
Atom economy
|
Prevention instead of treatment
|
|
3
|
Optimize resource efficiency
|
Less hazardous chemical syntheses
|
Design for separation
|
|
4
|
Strive for energy persistence
|
Designing safer chemicals
|
Maximize efficiency
|
|
5
|
Enhance process efficiency
|
Safer solvents and auxiliaries
|
Output-pulled versus input-pushed
|
|
6
|
No out-of-plant toxicity
|
Design for energy efficiency
|
Conserve complexity
|
|
7
|
Target optimal design
|
Use of renewable feedstocks
|
Durability rather than immortality
|
|
8
|
Assess sustainability
|
Reduce derivatives
|
Meet need, minimize excess
|
|
9
|
Apply ladder of circularity
|
Catalysis
|
Minimize material diversity
|
|
10
|
Sell service, not product
|
Design for degradation
|
Integrate material and energy flows
|
|
11
|
Reject lock-in
|
Real-time analysis for pollution prevention
|
Design for commercial ‘Afterlife’
|
|
12
|
Unify the industry and provide policy
|
Inherently safer chemistry for accident prevention
|
Renewable Rather than Depleting
|
[Table 3] listed the 12 principles of CC, green chemistry, and green engineering.
