1. Introduction
Materials and energy are fundamental carriers and drivers for the evolution of life and human civilization. The transition of energy supply from wood to coal, and subsequently to petroleum, especially with the widespread application of electricity, has promoted the productivity of society. Energy revolutions have laid almost every significant milestone of technological advancements in industrial sectors. In the 20th century, the demand for fossil fuels (coal, oil, and natural gas) continued to increase. In 2022, fossil fuels accounted for 82.3% of global energy consumption, rendering them primary components of human energy supply. With the development of the synthetic materials industry, the proportion as resource essence of fossil fuels has increased. Chemical products that originate from fossil fuels, especially petroleum, have provided vast amounts of raw materials for clothing, food, housing, and transportation, thereby creating an important material foundation for humans [
1], [
2].
However, in the process of obtaining energy from fossil fuels, CO
2 emissions have increased markedly and have caused prominent and serious environmental issues [
3]. In 2022, the global CO
2 emission from fossil fuels was approximately 3.66 × 10
10 t for power generation, heating, and transportation accounting for 69% of the total [
4].
Fig. 1 [
5] shows the trend of global primary energy consumption predicted by the International Energy Agency (IEA). To accomplish the net zero emission (NZE) scenario, energy supplies will have to undergo significant changes, which would inevitably decrease the contribution made by fossil fuels. The proportion of green energy such as renewable and nuclear energies in the primary energy structure is predicted to reach over 60% around 2050. At that time, using petroleum as a source of energy should decrease, and the role of petroleum as a resource for materials will be highlighted. Thus, the foundation of the petrochemical industry will undergo significant changes, for example, present petrochemical processes will need to be restructured [
6], [
7].
This review aims to scrutinize the history and evolution of the petrochemical industry with contemporary hindsight, to examine the trends, identify possible problems in the context of the NZE scenario, and propose a simplified and green reconstruction of the petrochemical industry. These proposals could enhance comprehensive reconsideration of the past, current, and future petrochemical industry to provide insight into possible research directions.
2. Why did the petrochemical industry become complicated?
2.1. How did the petrochemical industry evolve?
Over the course of the 19th century, the development of the petrochemical technology, which is closely related to the necessities of human life (food, clothing, housing, and transportation), has had a huge impact on human society and civilization. An estimation from Organization of the Petroleum Exporting Countries (OPEC), indicates that the global consumption of crude oil will reach a record high of 106.1 million barrels per day (1 barrel = 158.98 L) in 2025 [
8].
The evolution and development of the petrochemical industry are closely related to the material needs of humans, which have also driven developments in the petrochemical industry. Distillation is the earliest technology that was used in the petroleum industry to meet the demand for household kerosene [
9]. At the beginning of the 20th century, thermal cracking technology emerged with the development of the automotive industry. In the 1940s, catalytic cracking technology became the predominant process for gasoline production. In the 1950s, platinum reforming technology was developed to satisfy the requirements for the anti-knock performance of gasoline. In the 1960s, the large-scale use of zeolites in refineries was a milestone in catalytic cracking technology. In the 1980s, hydro-fining and hydro-cracking as typical hydrogenation technologies were commercialized on a large-scale along with the increasingly stricter requirements on environmental protection. Additionally, technologies such as steam cracking, catalytic cracking, and aromatization were developed to produce more olefins and aromatics as the demands for bulk chemicals increased [
9], [
10], [
11], [
12]. At this point, the petrochemical industry has evolved into a highly complicated, but rationally integrated system (a typical petrochemical process is shown in
Fig. 2).
2.2. How did the petroleum industry form?
Given the history and evolution of the petrochemical industry, it is apparent that the driving force for technological development is to produce more value-added products from crude oil in a more efficient and economical manner. A central unanswered question is why the petrochemical industry became so complicated. We consider that the evolution of the petrochemical engineering is closely related to the general needs of humans, availability of raw materials, advancement of science and technology, and path dependence. The following factors have contributed to the development of the petroleum industry in its current form.
(1)
Complexity of crude oil. Crude oil is a complex mixture of molecules containing C, H, O, N, S, and trace metal atoms (Ni, V, Fe, etc.), and usually comprises alkanes, cycloalkanes, aromatics, and/or their mixtures. The numbers of C atoms in these compounds vary greatly, with relative molecular weights ranging from tens to thousands; furthermore, the boiling points range from room temperature to ≥ 500 °C; these wide ranges imply that crude oil in the unrefined state is of limited valued and of limited use [
9]. Therefore, refineries transform crude oil to different degrees using the most common form of separation, refining, to obtain fuels and other chemicals.
(2)Low requirements on power fuels. Combustion is a high-temperature exothermic oxidation chemical reaction between fuels and oxidants, usually O2, involving rapid lighting and heating, and is the predominant manner of utilizing fossil fuels. Power fuels comprise mixtures of hydrocarbons to satisfy thermal and emission requirements. Fuels combine molecules with different compositions and structures, thereby balancing energy requirements, complexity of the crude oil and level of technology. Even widely distributed compositions of gasoline and diesel can meet requirements on combustion. Hence the molecular composition of fuels produced by each refinery varies significantly. In other words, the fuel has become a pool for imprecise processing in the petrochemical industry.
(3)Limitations of technology. Science and technology play a vital role in the development of the petrochemical industry, and they determine and limit the choice of process routes. For instance, the breakage of C-C bonds is the most fundamental reaction in petrochemical processing. However, due to its endothermic nature, excessive breakage usually requires extra energy input. Petrochemical processes, especially those that focus on producing fuels, generally follow the principle of maximizing the preservation of the original molecular structure, which limits the development of processing routes to an extent. Despite the intensive energy input, most separation processes still rely on differences in boiling points due to limitations in technology that is based on molecular sizes, adsorption energy, binding energy and others.
(4)
Path dependence. The progress of technology can restrict creativity which limits further developments; petrochemical technology is a typical example. This path dependence is similar to inertia in physics [
13]. Using distillation as the basic technology, a processing path has gradually developed that uses the original molecular structure as the core and cracking and isomerization as the main chemical reactions [
14]. This phenomenon of the path dependence of technology drives strengthens processing schemes many times over; hence, petroleum processing has become more complicated.
2.3. What are the limitations?
From the perspectives of economy, CO2 emissions, material and energy demands, current petrochemical technologies can meet the needs of society. However, as the NZE target approaches and with the continuous increase in demand for raw materials, current solutions will not meet the overall needs. In the future the problems listed below will gradually emerge.
(1)
High dependence on raw materials. Due to the limitations of units, processing, and product distribution, enterprises have specific requirements for the sulfur and wax content, and fraction composition of crude oil. Those industries that use base oil and solvent oil, among others, as products, have very high requirements for a specific composition and cannot tolerate significant adjustments in the composition of crude oil. Factors such as the yield of light oil should be considered comprehensively during the design of plants for the production of aromatics and olefins. Importantly, coal, biomass, natural gas, and CO
2 cannot be used as raw materials for the plants currently in operation [
15]. When it becomes necessary to switch raw materials owing to environmental factors or other reasons, the enterprises cannot manage the transformation of through equipment within a short period.
(2) Low utilization efficiency of C atoms. Conversion and separation are the most important processes in the petrochemical industry. To obtain products containing the ideal components, complicated reactions and separations are sometimes needed. However, many reactions occur via multiple steps owing to thermodynamic and kinetic limitations, leading to extremely complex processes. Additionally, the yields of target chemicals are influenced by the nature of the feedstocks, and is not optimal. For example, in the production process of aromatics, the yield is affected by the feedstock, typically with the aromaticity value at 45%-50%, implying that more than 50% of the molecules are not easily converted into aromatics. A significant portion of molecules in petrochemical processing undergo catalysis, heat transfer, and separation processes without effectively participating in the reforming process, which causes lower utilization efficiency of C atoms with more energy loss.
(3)
Higher energy consumption. Energy is an important factor for petrochemical production processes, and plays a role in driving the flow of fluid materials, separation of process media and promoting the reaction. The form and amount of energy used are determined by the process characteristics. As a result, many problems, such as a wide variety of energy and conversion and energy use forms still need to be solved in the petrochemical industry. Energy efficiency became more important in those processes whose products are chemicals. In a typical case, the energy consumption of petroleum refining is approximately 2.47 × 10
6 kJ for one metric ton product [
16]. Moreover, more than 2.68 × 10
7 kJ of energy was consumed to produce one metric ton of ethylene via naphtha steam cracking; the separation processes account for 31% of the total [
17], [
18].
(4) Inadequate standardization of equipment. The poor standardization of equipment and processing has always been regarded as hindering improvements to the petrochemical industry. For example, during the design and construction of units, factors, such as raw materials, scale, flow, products, location, must be considered. Therefore, each enterprise has its unique characteristics and requires the customized design of equipment. Consequently, the problem of the lack of equipment versatility is commonly encountered. The construction of petrochemical processes still relies on on-site fabrication and assembly with complicated operations, intensive labor and cost, with increased concerns regarding quality management. Devices such as reactors and pipe racks are difficult to manufacture in a standardized and streamlined manner, and prominent issues such as long processing cycles, intensive labor input, and transportation difficulties abound. Additionally, scale manufacturing advantages cannot be leveraged.
(5) Limitation of current processes. The petrochemical industry has developed a systematic technology based on raw material molecule selection and transformation determined by product molecules. The fundamental principle underpinning petrochemical processing involves obtaining ideal molecules from complicated mixtures with non-ideal structures via reconstruction and other chemical or physical pathways. Given the higher quality requirements for products, traditional technology will not suffice. Therefore, process intensification, fine separation, and other operations will need to increase, leading to additional energy consumption and CO2 emissions; however, it is difficult to overcome the limitations of the thermodynamic and kinetic equilibrium of the reaction process itself, which prevents further improvement in product yield and quality. Thus, the interplay between demand and efficiency will become more pronounced.
3. Reconstruction approaching
3.1. New round industrial revolution
(1)
The rise of renewable energy. In the past 20 years, human demand for energy has continued to increase. The share of electricity in the global final energy consumption is rising, from 20% in 2022, to 52% in 2050 with a huge overall increase in demand of 150% predicted in the NZE scenario [
19]. As shown in
Fig. 3 [
20], in the global newly built electricity plants, the proportion of renewable energy generation in 2002 was only 15%, while fossil fuel generation accounted for 85%. In 2014, renewable energy generation accounted for 50%. In 2022, global renewable energy generation increased by 295 GW, accounting for 83%, while the proportion of fossil fuel generation decreased to 17%. To achieve the 1.5 °C scenario, the share of renewable energy in final global energy consumption would reach 83%, and the share in electricity generation could reach 91% with a new renewable power capacity addition of 1066 GW [
20]. In China, the newly installed capacity of wind and solar power generation in 2022 exceeded 120 GW with the newly installed capacity of renewable energy being 152 GW [
21], [
22]. Green electricity and electrification are absolutely central to meet the requirements of NZE. Therefore, fossil energy will gradually shift from the primary to supplementary roles, with renewable energy as the dominant source of energy supply.
(2)
Reshaping industry by green hydrogen. As the material and energy vector in our societies, green hydrogen presents advantages such as being environmentally benign and producing a minimal CO
2 footprint. Additionally, the flexibility of green hydrogen production ensures convenience owing to the power transmission network. Despite the hydrogen energy industry being nascent, with disadvantages such as immature technology, high investment, and incomplete facility construction, the development of green hydrogen will quickly enter into a growth period with the accelerated global layout of renewable electricity. The US government predicted that the manufacturing cost of green hydrogen would decrease to 1 USD·kg
−1 by 2030, close to that of gray hydrogen [
23]. At that time, green hydrogen, as the main source material, will significantly change the concept of the current petrochemical industry.
3.2. Enlightenment from other fields
3.2.1. Electric vehicles
The first electric vehicle was invented in 1837. In the early 20th century, the sales of electric vehicles reached the first peak with 38% of cars in the United States powered by electricity, and 22% being powered by liquid fuels [
24]. In the 20th century, the global petroleum industry and the automotive internal combustion engines experienced significant development, thus electric vehicles were gradually displaced. In 2016, the rise of Tesla electric vehicles promoted by the rapid innovation in battery production and other technologies, led to the rapid expansion of electric vehicles. In 2023, global electric car markets are experiencing exponential growth as sales exceed 14 million, and the market share increased from 2% in 2018 to 18% in 2023 [
25].
The efficiency of energy is paramount in the competition between electric and fuel vehicles. First, electric vehicles convert electricity into mechanical energy from batteries, while engines convert chemical energy into mechanical energy by burning fuels. In terms of efficiency from on-board energy storage devices to wheels, the energy efficiency of electric vehicles is usually between 80%-90% without considering the origins of electricity, while the efficiency of fuel vehicles is usually only between 16%-32% and is limited by the Carnot cycle [
26]. Second, the process of replacing fuel engines with electric motors greatly simplifies the car manufacturing process with significantly reduced spare parts. Third, some characteristics are unique to electric vehicles, such as autonomous driving, ultra-high acceleration, independent four-wheel drive, and so on, which are attributed to the simplified operation of the electronic system. The improvements in energy conversion efficiency and the simplification processes promote the choice of electric vehicles over automotive vehicles again after 100 years.
3.2.2. Lab-grown meat
The history of human development is a history of transforming food. Approximately 11 000 years ago, humans began intentionally cultivating plants and domestic animals, allowing a series of occasional genetic mutations to be passed down through the generations. This advancement enables humans to create various meats and foods. With the global population more than 8.1 billion, meat consumption reached approximately 3.7 × 10
8 t in 2023 [
27]. Inadequate feeding began limiting the growth of meat production. In the recent past 100 years, extensive efforts have been made to improve the growth rate, production efficiency, and protein content of meat-producing animals through agricultural, medical, and biotechnological advancements. Nonetheless, we are still unable to enhance the efficiency of meat production fundamentally. In addition, the moral dilemma and ethical issues associated with meat consumption are continuously raised.
Fortunately, it has been proven that lab-grown meat will significantly change the history of human food production [
28]. The principle of lab-grown meat is to utilize modern bioengineering techniques to scale up the cultivation of animal cells or extract plant-based proteins, that is, the preparation of various types of meat products with distinctive textures through efficient and targeted cellular cultivation/extraction. As a result, significantly reduced material and energy consumption can be achieved. For instance, the energy conversion efficiency could reach 47%. The protein feed conversion of protein reached 72% as animal breeding was eliminated [
29], however, the land occupation, water use, and CO
2 emissions decreased by 99%, 82%-96%, and 78%-96%, respectively [
29].
The development of lab-grown meat illustrates that technological progresses can trigger leapfrog transformations to improve production efficiency through targeted cultivation and recombination based on simplified units. Leapfrog transformations remind us to breach the boundaries of current knowledge, revert to the innate nature of matter, and to start from the most fundamental elements of matter (such as atoms, molecules, and cells), and to address our most essential needs.
4. Ideas for the future
4.1. Engineering mindset
Engineering is a discipline that applies theories to solve problems, and promotes industrial revolutions, economic development, and social progress. The engineering mindset was initially formed in the Stone Age, gradually gained momentum during the Agricultural Age, and matured in the Industrial Age [
30]. The engineering mindset has evolved from simplicity to complexity. Recently, with the advance of automation and intelligentization, the engineering mindset has begun reverting to simplification. For example, the precise design of product, processing, and assembly could be efficiently accomplished with advanced design software, precision machine tools, 3D printing, artificial intelligence, and other technologies. Through modular designs, rapid replacement and adjustment can be realized to improve the flexibility of production and speed of market response.
The simplified engineering mindset has begun to emerge in various fields. For instance, in automotive engineering, the use of integrated body die-casting significantly enhanced the production efficiency of car bodies. Additionally, modular design enables sharing car components among different car models to reduce repetition of design, and has significantly simplified the management of supply chains. However, these approaches have become vital for cost control. In construction engineering, utilizing prefabricated components and modular design has enhanced building quality and construction efficiency, reduced the formation of waste building raw materials, and has been more conducive to secondary recycling. In software engineering, the concept that begins from systematic design to modular overlay reduces the complexity of software design, simplifies software development, and improves efficiency and maintainability.
Chemical engineering is a discipline that explores the principles of chemical processes and reaction engineering. Production processes are designed and improved by optimizing feedstocks, momentum transfer, heat transfer, mass transfer, and chemical reaction engineering. Recently, chemical engineering has also begun reverting to simplification. The highly regarded crude oil direct cracking technology, which is innovatively designed to achieve low energy consumption and high yield through a shortened process, has the advantages of a simple process, low investment requirement, low energy consumption, and high chemical yields. The technology is considered a disruptive technological transformation of the traditional refining industry [
31]. ExxonMobil has built a 1 Mt·a
−1 crude oil direct cracking unit in Singapore. This process involves the separation of crude oil via flash distillation to form light and heavy fractions. The light fraction (∼76%) enters the steam cracking unit, and the heavy fraction (∼24%) enters refining units for deep processing. The yield of chemicals could reach 40%-50% [
32]. Based on the scientific principle of different cracking temperatures required for light and heavy fractions, the SINOPEC Research Institute of Petroleum Processing (RIPP) designed a dual riser catalytic cracking reactor to construct two catalytic cracking reaction zones at 560-620 and 640-670 °C, respectively, which achieved a total yield of over 50% for ethylene, propylene, and light aromatics [
33]. This innovative approach has been scaled up to industrial scale in Yangzhou, China.
The direct cracking of crude oil is an effective step toward simplified reconstruction of petrochemical processes [
31]. However, it is still based upon the concept of distillate refining with low utilization efficiency of C atoms, strong dependence on light crude oil, and high yield of low-value products such as coke and dry gas (> 34.84%) [
34]. From the perspective of simplified engineering, high-quality development can be achieved with reduced units and separation intensity only by stepping away from the concept of distillate refining and starting from efficient atomic assembly.
4.2. Scientific perspective
4.2.1. Nature of a chemical reaction
The core aim of petrochemical processes is the conversion of crude oil molecules into useful or valuable chemicals via a series of reactions. Chemical reactions involve the breaking of chemical bonds in reactants and formation of chemical bonds in products, as well as the generation of new substances and transformation of energy, which strictly follows the principles of mass and energy balances [
35]. Fossil fuels mainly consist of C, H, and O atoms. C atoms are the main component forming a major part of the molecular skeletons and H and O atoms occur in different proportions (
Fig. 4). C, CO, H
2, C
nH
x, and C
nH
xO
y form the material basis for fossil energy to participate in combustion reactions. CO
2 and H
2O are the final products after the release of energy from fossil fuels, which is the material basis for recycling in nature through photosynthesis. An energy balance means that energy undergoes mutual transformation or transfer from one substance to another in different forms with the total amount of energy remaining unchanged. Energy conversion includes mechanical, electrical, and thermal energy conversion via fossil fuel combustion and potential energy and photoelectric conversion, among others; in addition, the transfer of chemical and internal energy occurs in the molecular reconstruction process caused by the participation of chemical energy.
Petrochemical engineering is a dual management process of both material and energy. C and H atoms in fossil fuel molecules are used as the material base, and the combustion of fossil fuels such as coal, oil, and natural gas is the energy base used for reconstruction to enhance the utilization of the original molecules. Typical chemical reactions include cracking, hydrogenation, dehydrogenation, and isomerization, as shown in
Fig. 5.Petrochemical engineering in its current form has established the processing method based on the concept of petroleum fractions, in which the boiling point and C atom number are used as the main basis for separation. Nonetheless, the reactivity of different isomers varies greatly. For example, the C-C bond energy of long-chain alkanes is approximately 365 kJ·mol
−1, that of cycloalkanes is approximately 407.3 kJ·mol
−1, and that of aromatic hydrocarbons is as high as 580.6 kJ·mol
−1 [
36]. Moreover, even if the structure is similar, the difference in the number of C atoms ensure a wide variation in the properties; using the activity of
n-alkanes as an example, in which,
n-C16(42.3) >
n-C14(19) >
n-C12(4.5) >
n-C10(1) >
n-C8(0.23), 350 °C, over Y zeolite [
37]. Therefore, it is difficult for molecules with different structures and C atoms to react simultaneously. Molecules that do not participate in reactions often reduce the efficiency and energy consumption of processing methods.
In the past two decades, the concept of component molecular refining has been proposed and is currently being into practice. Molecular refining refers to the understanding and utilization of fossil fuels at the molecular level, which involves using every molecule in its most efficient state. However, given the C, H, and O ternary system, current molecular refining is limited to dealing with mixtures of molecules with similar structures, instead of accurate combinations of atoms. To fundamentally improve atom utilization, traditional petroleum processing will have to be substantially overhauled. In doing so, the concept of the precise control of reaction chemistry can be used to accomplish the evolution of petrochemical processes from complexity to simplicity. Thus, leapfrog progresses in the petrochemical system can be ultimately realized.
4.2.2. Proposed optimal scheme
C1 chemistry is the organic chemistry and process of synthesizing chemicals or liquid fuels from compounds containing one C atom such as CH
4, CO, and CO
2 [
38]. CH
4 is the main component of natural gas, with a high C-H bond energy (bond dissociation energy (BDE) = 439.3 kJ·mol
−1), low polarity, and electron affinity with extremely stable chemical properties [
39]. Methane is an important energy carrier, and humans have obtained heat via the combustion of CH
4 for a long time. CO, is a heteronuclear diatomic molecule and contains a total of ten valence electrons. Those electrons are distributed as defined by the octet rule, in which four shared electrons originate from the O atom and two from the C atom. The resulting triple bond comprises 2π-bonds and 1σ bond with a length of 112.82 pm and bond association energy of 1070 kJ·mol
−1. Two electrons from the O atom in one of the bonding orbitals form a dipolar bond, resulting in polarization within the molecule. Moreover, the difference in electronegativity between the C and O atom, which are 2.55 and 3.44, respectively, on the Pauling scale, leads to an unequal charge distribution within the molecule [
40]. These two characteristics and the asymmetric geometrical nature of the CO molecule, together, give rise to a relatively small electric dipole moment. The electrons of the C atom are easily lost and C is easily oxidized. CO is the most commonly used synthetic gas fuel and is the main component of syngas (a mixture of H
2 and CO), which can be used as an intermediate to synthesize a series of basic chemicals. CO
2 is a linear molecule composed of a C atom and two O atoms [
41]. CO
2 has a strong C=O bond energy (∼799 kJ·mol
−1), resulting in high thermodynamic stability [
42]. CO
2 is the iconic greenhouse gas and the major factor driving global climate change, and is also the material basis for natural recycling through pathways such as photosynthesis [
43], [
44]. As shown in
Fig. 6, almost all basic chemicals can be produced starting from CH
4, CO, and CO
2 [
45].
CO is one of most widely used C1 molecules because of its relatively high activity and easy availability. For example, syngas obtained through coal gasification, can be utilized as the raw material to produce CH
4, methanol, fuels, and light olefins, which have been commercially available. Using C1 chemistry, the energy supply may be diversified fossil fuels can be efficiently utilized. By using the approach of energy, materials, and CO
2 emissions, the scientific nature of the C1 chemical industry can become consistent with the concept of simplified engineering, as C1 chemistry refocuses on the basis and innate characteristics of materials. Furthermore, by further optimizing science, technology, and engineering, using the basics of C1 chemistry, C1 chemistry can become an important path for more efficient use of petroleum resources; additionally, C1 chemistry could lay the chemical foundation for the clean and efficient use of biomass, CO
2, and waste plastics [
46].
However, current C1 chemistry has drawbacks, including, complicated multi-step reaction systems, high energy consumption, and high CO
2 emissions despite successful commercialization of methanol-to-olefins (MTO), methanol-to-propylene (MTP) and Fischer-Tropsch (FT) synthesis [
47]. In the current coal chemical industry, coal may be used in three predominant ways. The first is as a provider of energy. In a typical coal gasification stage, approximately 25%-30% of C atoms are converted into CO
2 after releasing energy through oxidation to meet the requirements of high-temperature conditions. The second is to serve as the transfer vector for generation of H
2. The CO:H
2 ratio in coal-based syngas, however, is approximately 1.0:0.8 owing to the high C:H ratio of coal. For the production of methanol, fuel, and ethylene glycol, the CO:H
2 of syngas should be adjusted to 1:2 via the water gas shift reaction, during which more than 30% of CO is converted into CO
2. The third is to serve as the material basis for C chains in chemicals. In the synthesis stage, C atoms in CO molecules participate in molecular recombination to form C-C chains. Nonetheless, the high consumption of C atoms during energy and hydrogen production results in a low proportion of C atoms into the final products [
48]. For a typical MTO process, less than 35% of C atoms are transformed into methanol while with more than 60% of C atoms are converted into CO
2.
Novel solutions are required to solve long existing problems that have been classically approached and cannot be completely or satisfactorily solved [
49]. A gap remains between the process efficiency and economy of C1 chemistry and the petrochemical industry at present, and the issue of CO
2 emission is particularly prominent. Eventually, when significant changes occur in the production of renewable energy and H
2, the C, H, and O ternary system in industry will be reconstructed, as shown in
Fig. 7. From the perspective of materials, originated will be sourced from H
2O molecules through electrolysis of water and partly from C-based materials via gasification, which would significantly reduce dependence on fossil fuels. The sources of C atoms will be more extensive, including but not limited to crude oil and coal. Biomass, CO
2, and waste plastics will predominantly provide C atoms. O atoms from air and H
2O molecules could be directly or indirectly transferred into final products [
50]. From the perspective of energy, the dependence on the combustion of fossil fuels will be markedly reduced with solar, wind, and nuclear being the primary energy suppliers [
51]. Furthermore, the recombination of C atoms will be a vitally important step in the chemical process, and H atoms will lose their dominance. The material and energy structure will undergo significant changes in the future with more precise management of C atoms. Therefore, C1 chemistry will become the key strategy in the simplified reconstruction of petrochemical engineering.
4.3. Toward simplification
The evolution of chemistry is a process that considers the mutual influence of science, technology, and social requirements. From the earliest use of fire to the brilliant accomplishments of modern chemistry, chemistry has driven the progress of society. The research focus of chemistry and chemical technology evolved from activity to selectivity, then to an atom economy. With the implementation of the net zero target, the phenomenon of CO2 emissions will become critical, and the renewability of carbon resources will gradually become an important consideration.
Any change is not overnight, it needs to be affected by the level of science and technology, social needs and so on. The reconstruction of the petrochemical process will be accomplished in different stages based upon developments in the maturity of the current petrochemical processes, utilization level of equipment, and availability of green energy, which will evolve according to the short to medium and long terms, as shown in
Fig. 8.In the short to medium term, the maturity and scale effects of green hydrogen and electricity technology will gradually emerge. The CO2 emissions from the C1 chemistry process will therefore be significantly reduced owing to green hydrogen and green electricity replacing gray hydrogen and fuel. The olefins and aromatics produced via C1 chemistry will be cost effective. At this stage, on the basis of current petroleum processes, simplified procedures for heavy fractions (e.g., heavy and residual oils) could be realized. Similar to current petrochemical processes, crude oil is pre-treated and then separated into distillation units. The naphtha fraction generally follows the existing processing flow. While the heavy fractions would preferably enter the gasification unit in the liquid form to form the target product (i.e., syngas), instead of being processed via traditional processing units such as hydrogenation, cracking, coking, and extraction. Subsequently syngas will be purified via desulfurization, denitrification, and dechlorination, among other treatments, and mixed with green hydrogen in proportions determined by different requirements, without the water gas shift reaction. Thus, the syngas will participate in the process of the growth of the carbon length to selectively generate olefins, aromatics, oxides, liquid fuels, and other products.
In the medium to long term, once transportation fuels have been replaced by power batteries, the global crude oil consumption will be significantly decreased. At this time, the relationship between the supply and demand of petroleum will be reshaped; the C atom price of crude oil and coal will be unified, and the comprehensive cost of gasification will be similar. Simultaneously, the efficiency of C1 chemistry will be significantly enhanced with high selectivity being the most prominent characteristic. Thus, the petrochemical processes will undergo a complete reconstruction through combination with C1 chemistry, as shown in
Fig. 9. Gasification will become the key unit to produce high purity CO, in which crude oil is processed on a large scale and biomass will be processed on the small and medium scales [
51]. The reconstruction of C atoms will be accomplished in efficient synthetic units via the combination of CO and green hydrogen, and the catalysts and process parameters will be optimized to furnish different target products. In addition, syngas derived from the gasification of biomass will enter a skid-mounted and modular synthesis device to form sustainable aviation fuels and other carbon neutral products. Simultaneously, CO
2 generated in industries would be captured economically and converted into CO or chemicals via electrocatalysis, photocatalysis, and direct hydrogenation processing.
4.4. Advantages
The simplified development pathway proposed in this article is the preferred pathway to improve the efficiency of the petrochemical process, and the efficient utilization of C atoms with minimal CO2 emissions; the pathway exhibits notable advantages such as, a lower dependence on raw material, process sustainability, and better construction standards.
(1)
Lower dependence on raw materials. As a highly versatile process, gasification with CO as the target product will significantly reduce dependence on fossil fuels, and is similar to the lab-grown meat process which displays reduced dependence on animals (
Fig. 10). The raw materials for gasification can be expanded to all carbon-based materials such as natural gas, crude oil, biomass, and waste plastics. It should be noted that the main characteristic of the new gasification processes is that CO is the target product and H
2 is the byproduct, which is different to current gasification. Thus, there it will not be necessary to sacrifice the efficiency of C atoms to adjust the H
2:CO ratio. In particular, with a high C and O, and low H content, biomass will be partially oxidized, resulting in it being a less energy dense fuel. However, the direct gasification of biomass can efficiently produce syngas with CO as the primary product, which will be a vital strategy to overcome the drawback of low energy density [
52], [
53].
(2)Greater utilization efficiency of C atoms. In the future, simplified synthesis and separation will be vital for minimizing CO2 emissions and the economy of the entire process. By replacing gray with green hydrogen, CO2 emissions will be reduced by more than 30%, and the gasification scale will be reduced by more than 50%. However, with the continuous evolution of science and technology, processing units based on native or quasi-native structures in the current petrochemical process will be replaced by the efficient recombination of C atoms. Therefore, the efficient utilization of C atoms will break the limitation of the composition of the raw material to significantly reduce silent molecules. It is beyond doubt that utilizing C atoms more efficiently will result in a substantial increase in atom efficiency, greatly simplifying the reaction and separation process, and significantly reducing the overall energy consumption.
(3)Higher energy efficiency. Gasification has always been considered as being energy intensive. However, energy is expended to obtain CO and H2 through combining C atoms with O atoms from CO2 and H2O at high temperature during the gasification phase, while a large amount of energy is released when C atoms further dissociate from O atoms to rebuild the C-C bond in the reconstruction phase. In this case, the energy can be relatively balanced. Simultaneously, given a relatively simple process, the form of energy required and its utilization will be simplified, resulting in an improvement in the recovery of energy. The continuous progress of energy recovery technology and input of zero-carbon energy, will be conducive to accomplishing a comprehensive balance of energy and CO2 emissions.
(4)Better construction standards. Owing to the relatively simple nature of the reaction processes, the units of gasification and C1 chemistry will gradually transform from those of specialization to those of standardization and modularization. Thus, construction areas will be moved from on-site construction to assembly workshops, which is more conducive for using advanced tools such as industrial robots. Hence, the effects of human factors on manufacturing will be reduced, leading to an improved quality of equipment, reduced failure rate, and controlled safety risk. Standardization can also improve the interchangeability of equipment and efficiency of maintenance. In particular, upgrading can be accomplished by adding or replacing different modules without shutdown, which would enhance the efficiency and avoid production stagnation and risks caused by the shutdown of units.
(5)Larger space for development. The key to simplified development is the C atom reconfiguration process driven by the CO2 emissions of the process and products. Through gasification of the raw material into the smallest unit, followed by precise combination, the limitations of internal thermodynamics and dynamic balance in traditional refining will be overcome, creating space for more efficient, accurate, and characteristic synthesis. In terms of science, the task of research will be more focused on efficient gasification and targeted synthesis, indicating the directions for rapid iterative advances in technology. Simultaneously, the simple path uses CO and H2 as the most basic material units and electric energy as the basic energy unit, which is more conducive to the inclusion of green energy. With the large-scale input of green energy and hydrogen, this path will have the opportunity to provide a broader space for the green, low-carbon, or even net-zero development of petrochemical industry.
5. Issues to be resolved
Petrochemical engineering is a complicated and comprehensive system involving multiple disciplines. A simplified process focuses on the integrated revolution of energy, resource, and CO2 emissions, instead of partial progress. However, the theoretical potential will encounter huge practical challenges. The deficiency of science and technology is a key factor affecting the reconstruction, while reliance on traditional petrochemical processing would also begin limiting progress.
5.1. Science and technology for the future
5.1.1. Gasification
The traditional process of gasification involves the reaction between coal and gasification agents (O
2, H
2O, or CO
2) at a high temperature via a series of physical processes and chemical reactions [
54]. C and H atoms in coal are partially oxidized and converted into syngas. Over the last century, gasification has been widely applied in the coal chemical industry owing to its strong compatibility with feed stocks, versatile application scenarios, and various downstream industrial chains. Moreover, heavy oil, coke, and biomass have been utilized as feed for gasification, which has become a fundamental and leading technology in many chemical industries [
55].
Coal is more complicated and contains various impurities; it is distinct from oil and natural gas. The properties of syngas are often affected by the quality of coal, such as moisture, volatile matter, adhesion, activity, slurry ability, ash melting point, and mechanical strength. Owing to the inherent complexity of coal, gasification technologies still have shortcomings that are difficult to completely eradicate. For fixed-bed gasification technology, several problems exist, including the high requirement of mechanical strength, adhesion, slagging and thermal stability of raw coal, and the ease of formation of tar and phenolamine wastewater. For fluidized bed technology, the high coal activity and low carbon conversion rate need to be resolved. For gas-fluidized beds, problems such as burner ablation, water wall burning loss, short life of refractory lining, gasifier slagging, must be resolved. With the chilling process, obvious energy loss occurs at high temperatures. In the waste pot process, ash accumulation and clogging in the system emerge as drawbacks to be overcome [
56], [
57]. The development of coal gasification technology has been an iterative evolution process, with the main focus involving overcoming the complexity of coal.
Nonetheless, gasification should play a crucial role as the platform technology in the development of the simplified petrochemical industry. Using more diverse and abundant feed stocks as carbon sources enables the shift in the function of carbon-containing organics from that of energy unit to resource unit; this shift would maximize atom economy value and minimize CO2 footprints to the greatest extent.
In the short term, gasification technologies must be developed with carbon-containing resources such as crude oil and coal as raw materials, with CO as primary product, H
2 as the secondary product, and CO
2 as the byproduct [
58]. Most noteworthy, petroleum in the liquid form, with a high hydrogen content, and low impurity, would exhibit significant advantages in the gasification stage. Thus, the key focus lies in the design of petroleum gasification technologies, with the necessity of improving the compatibility of raw materials, increasing CO selectivity with reduced CO
2 selectivity and energy consumption. Simultaneously, research and application demonstration must be promoted in the relevant application scenarios of raw material diversification and low carbonization, especially the integrated development of gasification, new energy, and integrated utilization of gasification and CO
2. In terms of basic research, the gasification reaction law, gasification process control mechanism, and new catalysts must be continuously studied. In the medium to long term, biomass, as organic compounds primarily composed of C, H, O, N, and minerals, is considered an ideal renewable resource owing to its abundance (approximately 2.2 × 10
11 t of biomass available globally each year), low sulfur content, and its carbon neutrality [
59], [
60]. Utilization of biomass enables the complete lifecycle of C atoms, which will be the most valuable pathway in the future. Nonetheless in terms of technology, further exploration on biomass coke regulation, catalytic processes, and gas purification, among others are still needed [
61], [
62].
5.1.2. Chemicals from syngas
Olefins and aromatics are vital chemicals closely related to human life and industry. Recently, with the development of the coal chemical industry, both MTO and MTP processes have been successfully commercialized [
63]. Methanol-to-aromatics (MTA) has been demonstrated on an industrial scale. The diagram of olefin and aromatic synthesis paths using syngas as raw materials is shown in
Fig. 11. From the perspective of the simplified engineering mindset, the direct synthesis of hydrocarbons without the formation of methanol becomes feasible and potentially economical.
The direct transformation of syngas to hydrocarbons is based on FT synthesis and the synergistic catalytic mechanism. The FT synthesis process occurs via the mechanism of surface polymerization with the carbon number distribution of products approximately following the Anderson-Schulz-Flory (ASF) distribution [
64]. By optimizing the catalysts, the distribution can be limited within a specific range; however, it is challenging to go beyond the constraints of ASF limits, such as maximum C
2=-C
4= selectivity at 58% and aromatic selectivity at 15% on an industrial scale [
65], [
66].
Synergistic catalysis can couple multiple catalytic reactions, in which the products of one reaction are utilized as substrates for subsequent reactions. By coupling FT synthesis and cracking, a simultaneous advancement in FT synthesis and the acid catalyzed reaction can be realized to increase the selectivity toward desired products, during which products such as C
2=-C
4= could be formed by cracking long-chain hydrocarbon products [
67]. Furthermore, by coupling FT synthesis and aromatization, the formation of aromatics can be enhanced, but the aromatic selectivity still cannot be greater than 57% because of the high conversion to CH
4. Other synergistic catalysts (oxide-zeolite, OXZEO) composed of oxides having CO hydrogenation activity and zeolites with cracking activity exhibited excellent catalytic performance for the transformation from syngas to light olefins and aromatics [
68], [
69]. In such a system, the intermediate products such as methanol, dimethyl ether (DME), and vinyl ketones are formed on the oxide surface, and subsequently transform to olefins and aromatics selectively within the confined environment of the zeolitic channels. Owing to the combination of C-O bond activation and C-C chain growth in this process, the OXZEO system display advantages, such as, the control of product distribution [
70], [
71], [
72].
Recently, through combining efforts in fundamental theory on synergistic catalysis, catalysts such as Zn-ZrO
2/ZSM-5 and Zn-CrO
x/ZSM-5 have been prepared to accomplish the direct conversion of syngas to aromatics, with CO conversion at 20% and 16%, and aromatics selectivity at 80% and 73.9%, respectively [
73], [
74]. Ethylene selectivity of 73% and 65% has been obtained over ZnCrO
x/MOR and ZnAl
2O
4/MOR, respectively, by the selective poisoning of acids located in the 12 membered-ring channels of MOR zeolites and design of methanol carbonylation pathways [
71], [
75], [
76]. Additionally, through incorporating germanium-substituted AlPO-18 within the framework of the OXZEO catalyst concept, and disentangling the target reaction from the secondary reactions, an unprecedented light olefin yield of 48% has been realized under optimal conditions [
75]. With an increase in the density of acid sites, a single-pass conversion of CO of 85% has been achieved with light olefin selectivity over 80%; this was ascribed to the C-C coupling of vinyl ketones and olefins while inhibiting secondary reactions that consume the olefins [
77].
Synergistic catalysis provides valuable solutions to obtain more light olefins and aromatics beyond the ASF distribution obtained through FT synthesis. Researchers are still exploring the classic FT synthesis, and challenges regarding activity, selectivity, and stability on an industrial scale must still be overcome [
78]. Needless to say, it is of great significance for the direct conversion of syngas to chemicals that the structure of energy resources be adjusted and the strategy of the NZE target be supported. Commercialization of the direct conversion of syngas to chemicals could be successfully realized via the development of high-performance catalysts in the near future.
5.1.3. Electrocatalytic reduction of CO2
As a major greenhouse gas, CO
2 is the ultimate product formed from the oxidation of organic compounds. Through reduction and hydrogenation, CO
2 can be converted into valuable fuels and chemicals, such as CO, CH
4, CH
3OH, DME, and olefins, through which CO
2 can be used as the material foundation and storage of energy for efficient recycling [
79], [
80]. However, the engineering processes and the reaction chemistry of CO
2 reduction can be difficult to realize as the CO
2 molecule is quite stable and its Gibbs free energy (△
G0 = −394 kJ·mol
−1) is much lower than those of the products (CO: 137.2 kJ·mol
−1, CH
4: −51 kJ·mol
−1, CH
3OH: −166.4 kJ·mol
−1, HCOOH: −361.4 kJ·mol
−1l, HCHO: −109.9 kJ·mol
−1, (NH
2)
2CO: −197.5 kJ·mol
−1) [
81].
With a low empty orbital (2πu) and high electron affinity (38 eV), CO
2 tends to accept electrons from other molecules, through which the CO
2 molecules can be activated thereby accomplishing energy input to overcome the energy barrier of CO
2 reduction [
82]. The electrocatalytic reduction of CO
2 refers to the use of electrical energy in an electrolysis cell to convert CO
2 into fuels and chemicals (
Fig. 12(a)) [
83]. During the electrocatalytic reduction of CO
2, H
2O molecules undergo oxidation at the anode to produce O
2 and electrons/protons (e
−/H
+). Simultaneously, CO
2 molecules are reduced at the cathode to yield various carbon-containing compounds, such as CO, CH
4, HCOOH, CH
3OH, HCHO, CH
3CH
2OH, and C
2H
4. The electrocatalytic reduction of CO
2 is a complicated process involving multiple steps of electron transfer and reactions with different quantities of electrons, such as the two-electron reduction of CO and HCOOH, six-electron reduction of CH
3OH, C
2H
4, and CH
3CH
2OH, and eight-electron reduction of CH
4 (
Fig. 12(b)) [
84], [
85]. Distinct from photocatalysis, thermal catalysis, and biocatalysis, electrocatalysis is characterized by being environmentally benign with controllable selectivity, is performed under relatively mild conditions in compact devices and can be easily scaled up using modular systems. Additionally, thermodynamic limitations can be overcome by using H
2O as a source of hydrogen [
86].
Predictably, electrocatalysis would play a crucial role in energy storage and CO
2 conversion, which will be an ideal pathway for closing the anthropogenic carbon cycle and storing intermittent renewable electricity potentially. However, there are numerous challenges on the path to commercialization, such as catalytic activity, selectivity, stability, cost, and the stability of ion exchange membranes, ion conductivity, and selection of new types of electrolytes [
87], [
88]. In particular, the complex generation steps of C2+ hydrocarbons and oxygen-containing compounds require more electron transfers (> 12e
−), resulting in relatively low Faradaic efficiencies (FEs) [
89]. For example, the FEs for the electrocatalytic reduction of CO
2 to ethylene and ethanol are only approximately 60% and 40%, respectively, while FEs for other C2+ products are even lower (
Fig. 13(a) [
90]). Consequently, low FEs result in additional energy, and low selectivity increases the cost of product separation, both of which become the primary barrier to industrialization. Fortunately, the electrocatalytic reduction of CO
2 to CO demonstrates promising industrialization. For instance, the FEs for syngas can approach 100%, with an overall CO energy efficiency of 40%-50% and a minimum cost of 130 USD·t
−1 at a current density of 300 mA·cm
−2. The cost of ethylene synthesized using CO is 40% lower than that of one-step electrocatalytic reduction (780 USD·t
−1) [
91]. Fusing existing technologies, in this case, through the electrocatalytic reduction of CO
2 to CO, and further conversion to ethylene becomes economically feasible.
Recently, the concept of “electricity refinery” has been proposed (
Fig. 13(b) [
90]). Electricity refinery refers to the conversion of renewable energy into transportable fuels (e.g., ammonia and ethanol), chemicals (e.g., CO, ethylene, methanol, and formic acid), and renewable specialty chemicals, via various electrocatalytic processes. Distinct from fossil-based refineries, an electricity refinery is sustainable and carbon neutral and easily modulated and decentralized in scale [
91], [
92]. Furthermore, the driving force of electrocatalytic reactions can be controlled directly by varying the bias potentials, which is inherently safer and flexible for selectivity tuning; thus rendering more opportunities for optimizing partial oxidation and reduction conversions [
86], [
93]. As estimated, with EFs > 60% and renewable electricity price < 0.04 USD·(kW·h)
−1, the electrocatalytic reduction of CO
2 will become more economically feasible than the traditional fossil route [
90].
5.1.4. Green electricity and hydrogen
Green electricity and hydrogen are a vital energy and material basis, respectively, for the green transformation and development of petrochemical industry. High-temperature heat pumps, electrode boilers, and high-temperature nuclear heat and other technologies will become the main path of energy transformation in the chemical process that replaces fossil combustion. Green hydrogen, as a widely available low-carbon secondary energy source, provides effective solutions for the transformation of material and energy, and serves as a crucial facilitator for sustainable development of industry. After rapid development, green electricity has become a crucial part of the global energy supply [
94]. A number of green hydrogen projects have been in operation or construction in the fields of electrical power, petrochemical, coal chemical, and metallurgy to support carbon reduction and sustainable reform [
95].
It is noteworthy that nuclear energy, a stable and controllable green energy, will probably play a crucial role in the production of green hydrogen. In particular, nuclear energy-originated thermo chemical water splitting technologies, such as nuclear energy electrolysis and the iodine-sulfur (IS) cycle, show promising results among many thermochemical cycles offered so far [
96], [
97], [
98]. For example, the coupled electrolysis of water with a high-temperature gas-cooled reactor (HTGR) using helium as a coolant can accomplish hydrogen production efficiency over 50%, at a cost of 1.5 USD·kg
−1 [
98].
Green hydrogen should play a vital role in the transformation of energy and commodity materials production (
Fig. 14). Because science and technology improve continuously, the cost advantage associated with large-scale manufacturing will be more obvious. Solar, wind power generation, and electrolytic cell manufacturing costs will continue to decrease, and there is still a very large cost reduction space for hydrogen production from electrolytic water. However, in particular, the current electric-hydrogen conversion rate is still low (50%-68%) [
99], and crucial equipment, components, and integration systems have not proven their long-term feasibility. In addition, the coupling of renewable energy and electricity net need further investigation owing to the unstable large-scale production of hydrogen from wind and solar power [
100].
5.2. Thinking beyond traditional views
Innovation is the fundamental driving force behind technological change, however, it is not the only source of technological developments. Thinking is also crucial to developments in technology. Advanced thinking can accelerate technological evolution, however rigid thinking can inhibit technological changes. Throughout the history of industrial developments, every transformation has been accompanied by a process of mindset change. Only by breaking the constraints of conventional views can transformative technologies have the opportunity to reconstruct industrial schemes. Below are two examples.
5.2.1. Revolution of monomers
Molecules of material monomers are mostly derived from the basic structure of petroleum molecules. The synthesis of these materials involves processes such as cracking and dehydrogenation of hydrocarbons to form olefins, aromatics, and other basic chemicals, which are then directly polymerized to produce polyethylene (PE), polypropylene (PP), and polybutylene (PB). In addition, by introducing O and N atoms to the above bulk chemicals, O and N containing monomers can be synthesized, which can be transformed into synthetic fibers via acid-alcohol or acid-amine copolymerization. Over a century, the synthetic material system based on core monomers such as ethylene, propylene, butene, phthalic acid, styrene, and acrylic acid has been established.
Petroleum provides the key raw materials for synthetic materials, and polymer structures are limited by the petroleum ecosystem. The design of polymers based on molecular configuration is still determined by multiple factors such as the availability and economic feasibility of raw materials. Most importantly, conventional thinking has always been one of influential obstacles hindering the selection of monomers. However, would the scope of monomer selection extend infinitely if C1-based synthetic chemistry is fully practiced? Is it possible for the structural-property relationship of materials to break the constraints of raw materials? Can the performance and cost of synthetic materials be the determining driving force of technology and development? These questions can all be addressed by future synthetic chemistry.
5.2.2. Rethinking on scale
The large-scale upgrade of individual units is vital to control costs, energy consumption, and efficiency in production, however there are also limitations on mass, heat transfer, and other related aspects. With C1 chemistry as the typical exothermic reaction, mass and heat transfer can be enhanced with standardized, modular, and integrated equipment, which can enhance activity and selectivity. Additionally, the inherent safety of the equipment can be significantly improved. Moreover, the implementation of modular equipment enables the utilization of more efficient technologies (e.g. electrification devices, membrane separation, and adsorption separation), resulting in reduced energy consumption and cost in separation processes. Obvious advantages in terms of equipment standardization, enhanced inherent safety, and advanced intelligent regulation can be demonstrated via a combination of standardized assembly, workshop installation, and other modern assembly methods [
101].
A few questions arise based upon the above analysis. Will the new C1 chemical engineering be able to reshape trends of large-scale development in the petrochemical process? Can equipment upgrading through plug-in modular expansion overcome the limitations and risks of traditional upgrading through shutdowns and disassembly? Is it feasible to achieve adjustments in product distribution and variety through flexible control on modular devices? The realization of these concepts will require further effort from relevant practitioners.
6. Outlook
Petroleum has played a key role as the major supplier of materials and energy for humans from agricultural civilization to industrial civilization, and subsequently to information and artificial intelligence civilization. Until now, the petrochemical industry has also become intelligence and technology intensive with long supply chains and has a big impact on society. However, by replacing transportation fuels with electricity for the most part, global crude oil consumption will be significantly lower than that today with the loss of the associated political overtones. Thus, a glut of supply will develop and the price and value of crude oil will balance out. By then, the price of C atoms will be unified in crude oil and coal, both of which can be defined as fossil-derived C atoms. The science, technology, and engineering thinking of energy chemistry is being reconstructed with the change of human needs.
There is no doubt that the current petrochemical system has become highly integrated and mature after almost one century of development. Many significant breakthroughs in theory and technologies have emerged in the petrochemical industry, and a complete production process, equipment system, and huge and complicated industrial ecosystem has arisen. However, has inertia dependence become an obstacle restricting the development of the petrochemical industry? We could even compare the current petrochemical industry to the “Stone Age,” and even further to the “Bronze Age.” Similar to the Stone Age, the petrochemical industry is still based on the original structure of fossil molecules, however future petrochemical processes can be reconstructed similar to bronze metallurgy in which the core component-copper atoms are enriched and then cast as required. Admittedly, the development of green hydrogen in the world is still nascent, and the competitive advantage has not yet manifested. In C1 chemistry, problems such as high energy consumption and ultra-high CO2 emissions exist; furthermore, many scientific challenges such as low conversion efficiency and insufficient selectivity exist in the electrocatalytic/photocatalytic reduction of CO2, which are the key factors restricting the development of the petrochemical process to simplicity.
At this moment, it is important to systemically scrutinize and interpret the history and evolution of petrochemical processes from the perspective of the future; the innate nature of energy, carbon resources, and CO
2 emissions must be analyzed from the past to the future, because they might differ from contemporary perceptions. Although it is commonly acknowledged that technology is an engine to both solve old and create new problems— we perversely turn to even newer technologies for potential solutions [
12]. As for energy transformation, only by continuously addressing these problems can we accomplish technological leaps or breakthroughs. Only by going beyond mental constraints can we reconstruct the modern industrial system to truly accomplish the simplified and green development of petrochemical engineering.
Overall, the perspective here does not discuss the overhaul of the current petrochemical industry, instead supplementing and optimizing the current industry via the introduction of simplified engineering is advocated. In other words, by integrating local reconstruction into the current highly matured petrochemical industry, the CO2 emission issue imposed by the implementation of the net zero emission goal might be partially settled. Gradual accumulation of quantitative changes results in the breakthrough of a qualitative change with the petrochemical industry as one of the examples. In the longer term, it is not difficult to predict that the petrochemical industry will gradually evolve through continuous local reconstruction and eventually achieve qualitative changes. This viewpoint should cause people to re-think the past and future of the petrochemical industry in a systematic and comprehensive manner, and also inspire the future research work of science and engineering.
Compliance with ethics guidelines
Yao Zhang, Enhui Xing, Wei Han, Panfeng Yang, Song Zhang, Su Liu, Dongxue Cao, and Mingfeng Li declare that they have no conflict of interest or financial conflicts to disclose.
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