A Review of Recent Progress of Carbon Capture, Utilization, and Storage (CCUS) in China

Abstract

The continuous temperature rise has raised global concerns about CO₂ emissions. As the country with the largest CO₂ emissions, China is facing the challenge of achieving large CO₂ emission reductions (or even net-zero CO₂ emissions) in a short period. With the strong support and encouragement of the Chinese government, technological breakthroughs and practical applications of carbon capture, utilization, and storage (CCUS) are being aggressively pursued, and some outstanding accomplishments have been realized. Based on the numerous information from a wide variety of sources including publications and news reports only available in Chinese, this paper highlights the latest CCUS progress in China after 2019 by providing an overview of known technologies and typical projects, aiming to provide theoretical and practical guidance for achieving net-zero CO₂ emissions in the future.

1. Introduction

Global climate change has become a critical challenge facing humanity on a global scale [1,2,3,4,5,6,7,8,9,10]. Growing evidence indicates that global climate change is caused by greenhouse gas emissions from human activities [6,11,12]. The main greenhouse gas in the atmosphere has been proven to be carbon dioxide (CO₂), which contributes to approximately 66% of global warming [2]. The Global Carbon Project [1] has estimated that the annual anthropogenic CO₂ emissions averaged around 38.9 billion tonnes worldwide between 2011 and 2020, with energy consumption and land use change contributing 89% and 11% of the total emissions [2,13], respectively. Carbon emissions from energy consumption, especially CO₂ emissions from burning fossil fuels for power, heat, and transportation, are thought to be the dominant source of greenhouse gas emissions from human activities [14,15,16,17,18,19]. Global climate change driven by increased man-made emissions of heat-trapping greenhouse gas is already showing widespread effects on the environment, such as accelerated sea level rise [20,21,22], sea ice loss [23,24], melting glaciers and ice sheets [25,26], more intense heat waves [27,28], and plant and animal geographic ranges shifts [29,30,31,32,33]. The effects of human-caused global climate change are irreversible and will worsen in the decades to come.

Global greenhouse gas emissions have already reached the highest levels ever recorded in human history after the year 2010. To deal with the serious situation, at the 21st United Nations Climate Change Conference, the Paris Agreement was approved as the second binding climate agreement following the Kyoto Protocol. The Paris Agreement set a limit on global average temperature control of 2 °C below pre-industrial levels. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) proposed requirements for both greenhouse gas emission peaks and emission reductions. Global greenhouse gas emissions must peak before 2025 and a 43% emission reduction must occur by 2030 to limit warming to 1.5 °C, while emissions must peak before 2025 and a 25% emission must be lowered by 2030 to limit warming to 2 °C [1]. In terms of total annual CO₂ emissions, China, as a major representative of the Asia-Pacific Economic Cooperation (APEC), is now ranked first, followed by the United States, the core and dominant country in North American Free Trade Area (NAFTA). To achieve its goals of carbon peak and carbon neutrality, China has implemented a variety of initiatives to generate a coordinated development plan of decarbonization and carbon reduction, emission reduction and pollution reduction, green growth and sink increase, and sustainable growth [2,34,35,36], endeavoring to gradually realize net-zero CO₂ emissions [37].

At present, the world’s high energy consumption industries are shifting to developing countries [38,39,40], which results in the rising phase of CO₂ emissions in developing countries. The CO₂ emission reduction at the expense of reducing the amount of industrial activity harms economic development [41,42,43,44,45], generating two competing demands to keep both economic growth and substantial CO₂ emission reduction for developing countries, especially for China, the major developing country in the world. China has conducted numerous studies on carbon capture, utilization, and storage (CCUS) in an effort to find a solution to the issue of balancing economic expansion and CO₂ emissions. The concept of CCUS was first proposed in China [45], emphasizing the close integration of CO₂ emission reduction and CO₂ utilization to achieve maximum resource utilization. With the deepening understanding of CCUS as well as the continuous development of CCUS technologies, CCUS has gained international recognition recently.

The Chinese government clarified the low-carbon development goals in the “13th Five-Year Plan” and provided strong economic and policy support to China’s CCUS projects. After several years of preliminary preparation and construction, China’s CCUS projects have made significant progress after 2019, showing outstanding achievements in fundamental research [46,47], technology development [48], and engineering demonstrations [49]. Approximately 40 CCUS demonstration projects with a 3 million tonnes/year capture capacity are operating or under construction in China by 2021 [50]. Remarkable progress has been made in CCUS-enhanced oil recovery (CCUS-EOR) [51], CCUS-enhanced natural gas recovery (CCUS-EGR) [52], and CCUS-enhanced coalbed methane (CCUS-ECBM) [53]. CO₂ storage in China is dominated by deep saline aquifers, with the well-developed required technology and equipment. In addition, China’s first off-shore CO₂ storage demonstration project was also constructed and completed in July 2022 [54], aiming to achieve net-zero CO₂ emission and green low-carbon development of off-shore oil fields.

This study provides a comprehensive review of the latest progress of CCUS development in China through the steps of information collection, classification, analysis and summary. Targeted journal publications were collected from both English and Chinese bibliographic sources, including the Web of Science (WoS) in English and the China Integrated Knowledge Resources System in Chinese. In addition, news reports on CCUS development released by Chinese media were also collected to comprehend pertinent national policies and relevant advancements that have not yet been published in paper form. The collected information was classified according to CO₂ capture and transport, CO₂ utilization and CO₂ storage for detailed analysis and summary for each technology. Based on information from a wide variety of sources, an overview of known technologies and representative projects of CCUS in China is presented. Furthermore, the current challenges for CCUS development in China are clarified, and suggestions for future improvement are proposed.

2. Overview of CCUS in China

China’s energy system is large in scale and diverse in demand. China’s rapid economic development has resulted in an increase in CO₂ emissions. According to the total annual CO₂ emissions of some countries [55] from 1980 to 2020 as shown in Figure 1, China has risen to the top one in terms of annual CO₂ emissions in the world. To strike a balance between the carbon neutrality goal and energy security and economic development, China has been actively constructing a modern energy system that is dominated by renewable energy and complemented by nuclear and fossil energy. However, according to China’s actual national conditions, high-carbon-based fossil fuels continue to account for up to 85% of the country’s overall energy consumption. It is predicted that China’s energy consumption will still primarily depend on fossil fuels by 2060. Therefore, CCUS is the only technology option to achieve net-zero CO₂ emissions from fossil energy sources.

The Chinese government has consistently encouraged technical applications while prioritizing the development of CCUS technology. Research and development activities on CCUS have received substantial financial support and strong policy incentives from the government. In the mode of cooperation between industrial companies and universities or research institutes, China’s CCUS integrated technology has reached the stage of industrial demonstration. However, the demonstration scale is still limited due to the cost of the technology. With the continuous improvement and advancement of technology, China’s CCUS technology is expected to achieve low-cost large-scale demonstration applications in the near future [50].

2.1. Storage Potential in China

Despite the huge annual CO₂ emissions, China also possesses a considerable potential to store CO₂ compared with other countries in the world. Based on theoretical storage capacity [56] shown in

Table 1. CO₂ emissions and CCUS theoretical storage capacity in some countries [50,55,56].

Country	CO2 Emissions in 2020 (Million Tonnes)	CCUS Theoretical Storage Capacity (Ten Billion Tonnes)
China	10,667.89	121–413
United States	4712.77	230–2153
United Kingdom	329.58	7–7.8
Australia	391.89	22–41
India	2441.79	39–60
Japan	1030.78	14

, China’s CO₂ storage capacity is between 1.21 and 4.13 trillion tonnes [50]. Therein, CO₂-EOR and CO₂-EGR, with a storage capacity of 5.1 billion tonnes and 9 billion tonnes, respectively, are dominating in terms of CO₂ utilization. Deep saline aquifers can store up to 2420 billion tonnes of CO₂; it is followed by depleted oil and gas reservoirs, which can store 15.3 billion tonnes of CO₂ [50]. The major storage locations and their storage capacities in China are shown in

Table 2. Dominate CO₂ storage location and storage capacity in China [50].

CO2 Storage Location	CO2 Storage Capacity (Billion Tonnes)
Songliao Basin	694.5
Tarim Basin	552.8
Bohai Bay Basin	490.6
Subei Basin	435.7
Ordos Basin	335.6

.

2.2. CCUS Development Plan in China

China has approximately 40 CCUS demonstration projects in operation or under construction (Figure 2), with an annual CO₂ capture capacity of 3 million tonnes [50]. Most of these projects are small-scale CO₂ capture demonstrations in the electricity, coal, and petroleum industries. In China, every five years is set as one development period for CCUS, and a specific short-term development plan is designed for each development period. According to the “Overall CCUS Technology Development Roadmap in China” released in 2019, the four development periods from 2030 to 2050 are planned as follows. By 2030, the existing technologies are expected to move into the commercial stage to undergo industrialization; by 2035, certain new technologies are expected to be implemented at large scale; by 2040, breakthroughs in CCUS systemic integration and risk management technology are expected to be achieved; by 2050, the CCUS technology will be extensively deployed, and multiple industrial CCUS clusters will be completed.

3. Progress of CO₂ Capture and Transport in China

3.1. Development Status of CO₂ Capture in China

CO₂ capture is the process of capturing and separating CO₂ from the exhaust gases produced during the combustion of fossil fuels. The captured CO₂ is purified to provide a stream of high-purity high-concentrated CO₂ for subsequent transport, utilization and storage [57]. CO₂ capture technologies are classified into three categories [58], namely post-combustion capture, pre-combustion capture, and oxy-fuel combustion capture. Schematic flow diagrams of these three capture technologies are illustrated in Figure 3. In post-combustion capture, CO₂ is captured from flue gases after the combustion of the fuel [58]. In pre-combustion capture, fuel is pre-treated with steam and air (or oxygen) to generate syngas consisting mainly of CO and H₂, and then the syngas undergoes the water-gas shift reaction with steam to form CO₂ and more H₂. After CO₂ is separated, H₂ can be used as a carbon-free energy carrier to generate energy. In oxy-fuel combustion capture, the fuel is burned in pure oxygen instead of air, and the generated flue gases consist of mainly CO₂ and water vapor, the latter of which is easily removed through condensing, resulting in high-concentrated CO₂. The applicability, advantages and disadvantages of CO₂ capture technologies are summarized in

Table 3. Comparison of CO₂ capture technologies [57].

Technology	Appliance Object	Advantage	Disadvantage
Post-combustion	Pulverized coal (PC) power plant Natural gas combined cycle (NGCC) power plant Fossil-fuel power plant	Well understood Mature technology Applicable to existing plants Wide applicability Retrofit application	High energy consumption Generation inefficiency Low purity
Pre-combustion	Integrated gasification combined cycle (IGCC) power plant	High purity Mature technology High efficiency and easy separation	High investment cost Limited applicability
Oxy-fuel combustion	Pulverized coal (PC) power plant, Integrated gasification combined cycle (IGCC) power plant	High purity and concentration Simple procedures Retrofit and repowering option	Additional equipment required High investment cost High energy consumption

.

The CO₂ separation technology can be classified into two categories: physical method and chemical method [59], both of which can be further subdivided into absorption, adsorption, membrane separation, etc. Some comprehensive summaries of the principles, applicability, advantages and disadvantages of CO₂ separation technologies have been provided in detail by other literature [59,60,61].

The selection of capture technology mainly depends on appliance objects, and post-combustion capture is now the most developed and common technology of CO₂ capture in China. The Guohua Jinjie carbon capture demonstration project of China Energy Investment Group CO., Ltd. (CHN ENERGY), which was put into operation in June 2021, is currently the largest demonstration facility for CO₂ capture employing post-combustion capture technology, with a capture capacity of 150,000 tonnes/year [61,62]. By utilizing post-combustion capture technology, the advanced low-energy carbon capture engineering project of Huaneng Longdong Base with a carbon capacity of 1.5 million tonnes/year, which is about to start construction, will become the largest coal-fired power plant carbon capture project in China once it is put into operation in 2023 [62]. Compared with post-combustion capture, pre-combustion capture has a more complicated system. Currently, IGCC-based pre-combustion CO₂ capture technology is an important technology for large-scale carbon capture demonstration in the power industry [63]. The carbon capture plant of the Huaneng IGCC power plant is China’s first demonstration project with pre-combustion CO₂ capture technology, and it has a capture capacity of 100,000 tonnes/year after being put into operation in July 2016 [63,64]. In addition, oxy-fuel combustion capture technology, which has the benefit of high CO₂ concentration for effective capture, has made significant strides. In 2016, the first 10,000-tonne pilot system for oxy-fuel combustion capture was completed in China [59,65], and the construction of a 100,000-tonne oxy-fuel combustion industrial demonstration project has been planned [66,67]. CO₂ capture projects that are currently in operation are listed in

Table 4. CO₂ capture projects in China [50].

Project	Operation Start Year	Capture Technology	Capture Capacity (Tonnes/Year)
Huaneng Longdong Base low-energy carbon capture project	2023 (expected)	Post-combustion	1,500,000
CHN ENERGY Guohua Jinjie carbon capture demonstration project	2021	Post-combustion	150,000
Huaneng Shidongkou carbon capture project	2009	Post-combustion	120,000
China Resources Power Haifeng carbon capture test platform	2019	Post-combustion	20,000
Guodian Tianjin Beitang power plant carbon capture project	2012	Post-combustion	20,000
CPI Chongqing Shuanghuai power plant carbon capture demonstration project	2010	Post-combustion	10,000
Huaneng Changchun thermal power plant carbon capture project	2017	Post-combustion	1000
Huaneng IGCC power plant carbon capture demonstration project	2016	Pre-combustion	100,000
Anhui Conch Group’s carbon capture project	2018	Pre-combustion	50,000
Lishui 36-1 Gasfield CO2 separation project	2019	Pre-combustion	50,000
Huazhong University of Science and Technology 35mw oxy-fuel combustion carbon capture demonstration project	2016	Oxy-fuel combustion	10,000

.

While existing capture technologies are gradually being put into practical large-scale application, major advancements have been achieved in the study of CO₂ separation technology. In 2020, the first “phase-changing” carbon capture industrial facility with a capacity of 1000 tonnes/year, which was developed by China Huaneng Group (CHNG), successfully realized continuous and stable operation in Huaneng Changchun Thermal Power Plant. In this facility, a biphasic carbon separation technology used in the post-combustion capture process can address the issue of high energy consumption caused by the heating of the CO₂ absorption liquid in the traditional method, thus reducing the cost of CO₂ capture [68].

In addition, direct air capture (DAC), which can reduce the atmospheric level of CO₂, has also attracted attention in China. In contrast to the above-mentioned three traditional CO₂ capture technologies, which are primarily appropriate to capture CO₂ emissions from industrial stationary sources, DAC is primarily designed to capture less-concentrated CO₂ from distributed sources, such as small fossil combustion units and vehicles. It is regarded as a means of balancing difficult-to-avoid emissions as well as a remedy for legacy emissions [69,70]. The research focus in DAC technology is on the development and utilization of efficient and low-cost adsorption materials. Hydrogen-bonded Organic Frameworks (HOFs) [71], which are a type of solid adsorption material with an organic framework crystal structure, can achieve direct CO₂ capture from the air at atmospheric pressure of 25 °C. With the help of the permanent pores, selective adsorption of CO₂ can be accomplished with 1 tonne of adsorbent for 113 kg of CO₂ captured [59]. Given the promising application of HOFs materials for direct air capture of CO₂, Chinese research institutions and scholars have been improving the properties of HOFs materials in recent years. Hu et al. developed a type of HOFs material (HOF-TCBP) with high stability and a large specific surface area, which can be regenerated under the rotary evaporation method. The regenerated material has the same specific surface area as the original sample, so it can be repeatedly used for efficient CO₂ capture [72]. Huang et al. proposed a flexible HOFs material with large-scale void-regulated permanent pores. Its maximum porosity can reach 33.2% of the total unit volume, enabling a larger volume of CO₂ adsorption. These advancements in HOFs material development have laid the foundation for the future potential application of direct air capture of CO₂ [73].

3.2. Development Status of CO₂ Transport in China

Many of the power stations and industrial plants where CO₂ capture can be implemented are not located close to potential CO₂ utilization or storage sites, thus requiring significant CO₂ transport as a momentous link [74,75]. At present, the main CO₂ transport can be sorted into two categories. One is pipeline-based transport [76,77], which includes on-land and off-shore pipelines; the other is tank-based transport, which includes ship transport, rail train transport, and tanker truck transport. Pipeline-based transport has historically been the preferred means to transport CO₂ due to its low cost and large transport capacity for low-to-medium distances [74,78]. Tank-based CO₂ transport has recently garnered increased interest [79,80] due to the lower investment costs, flexibility, and shorter construction times compared to pipelines for modest amounts of long-distance transport. It is worth noting that tank-based transport only carries liquefied CO₂ with strict temperature and pressure restrictions whereas pipeline-based transport can transport CO₂ in various states, including gaseous, liquid, dense-phase, and supercritical states [75].

Due to the small scale of China’s current CCUS demonstration projects, tanker truck transport remains the primary mode of CO₂ transport [81], while certain oil and gas fields use ship transport [82]. On-land pipeline transport is still in the pilot stage, with only limited adoptions in the Jilin oilfield and Qilu Petrochemical projects [83]. Jilin Oilfield has built a 50 km of CO₂ gas-phase transport pipeline with a transport capacity of 50 × 10⁴ tonnes/year [83]. Up to now, off-shore pipeline transport of CO₂ is still in the research stage. Additionally, the supercritical CO₂ long-distance pipeline construction is another challenge for CO₂ transport, with no undertaken demonstration projects [81].

4. Progress of CO₂ Utilization in China

CO₂ can be utilized in a variety of ways, and CO₂ utilization has drawn interest from all over the world due to its ability to reduce CO₂ emissions and provide economic value [84,85,86,87,88]. As illustrated in Figure 4, CO₂ utilization is classified into chemical [89,90], biological [91,92] and geological categories [93,94] based on the various technologies. Valuable products generated by CO₂ utilization cover a wide range, including useful chemicals and materials [94], fuels [95], food, feed, and fertilizer [96].

4.1. Development Status of CO₂ Chemical Utilization in China

CO₂ chemical utilization refers to the efficient conversion of CO₂ into a variety of more valuable compounds through some complicated chemical processes such as catalyzed hydrogenation [98,99,100,101,102,103], photochemical [104,105], electrochemical [104,105,106], thermochemical [102,107,108], and hybrid methods.

China’s CO₂ chemical utilization technology has advanced in recent years, yielding considerable economic benefits. Currently, approximately 10 × 10⁴ tonnes of captured CO₂ are used for synthesizing energy fuels each year, with an output value of about 100 million yuan/year; about 10 × 10⁴ tonnes of captured CO₂ are used annually in the synthesis of high-value-added chemicals, with an output value of about 400 million yuan/year; about 5 × 10⁴ tonnes of captured CO₂ are used for synthetic materials, with an output value of 200 million yuan/year [67]. It is worth noting that the methanol [59,109] and carbonate syntheses [110] using captured CO₂ have realized industrialization, and the production of olefin and fuel [111,112] from CO₂ has also made significant strides. Meanwhile, industrial demonstration of syngas production from captured CO₂ has been accomplished [113]. CO₂ chemical utilization projects in China are listed in Table 5.

Methanol synthesis from CO₂. China’s first 1000-tonne liquid solar fuel synthesis demonstration project was successfully launched in January 2020 [114]. This project adopts the methanol synthesis from CO₂ hydrogenation technology developed by the Dalian Institute of Physical Chemistry, Chinese Academy of Sciences (CAS) [59]. In this project, methanol can be synthesized through three fundamental components, namely, solar photovoltaic power generation, electrolysis of water to produce hydrogen, and CO₂ hydrogenation. Solar energy can be converted into liquid fuel methanol with an efficiency of more than 14% [59]. The project is expected to produce 1440 tonnes of “liquid sunshine” methanol annually after being put into operation [115]. In addition, in September 2020, the world’s first 5000 tonnes/year CO₂ hydrogenation to methanol industrial pilot plant, which was developed by China National Offshore Oil Corporation (CNOOC), achieved stable operation and realized industrial demonstration [116].

Carbonate synthesis from CO₂. The energy required to synthesize carboxylic acids or carbonates from CO₂ is comparatively low, and the corresponding energy utilization efficiency and economy are relatively high. Therefore, the synthesis of carbonates from captured CO₂ is also a major chemical utilization of CO₂ in China. In addition to China’s first industrial production plant for polycarbonate degradable plastic synthesis from CO₂ built in 2004 [117], China’s first 100,000-tonne facility for carbonate synthesis from ionic liquid catalyzed CO₂ was put into operation in March 2021 and has achieved continuous and stable operation [118]. The produced carbonate (including ethylene carbonate and DMC) products meet electronic-grade standards, and the system energy consumption has been reduced by 37%, demonstrating the remarkable carbon reduction effect [110,113].

Olefin and fuel production from CO₂. The direct synthesis of low-carbon olefins, liquefied petroleum gas, aromatics, and other components from CO₂ hydrogenation can be achieved by using a bifunctional catalyst system and coupling multiple reaction mechanisms [119]. Shanghai Advanced Research Institute, CAS, achieved a highly selective synthesis of gasoline fractions with high isomeric hydrocarbons (C5–C11) by direct CO₂ hydrogenation in 2017 [120] and direct conversion of CO₂ hydrogenation to aviation fuel under milder conditions in 2021 [121]. In May 2022, Li et al. achieved the highly selective preparation of long-chain olefins by ambient-pressure hydrogenation of CO₂ [122]. In June 2022, the world’s first 10,000-tonne CO₂ hydrogenation to aromatics industrial pilot project jointly constructed by Tsinghua University and Jiutai Group started construction [123], further promoting the production process of high-end chemicals from CO₂.

Table 5. CO₂ chemical utilization projects in China [50,113,123].

Project	Operation Start Year	Technology	Productivity
Lanzhou liquid solar fuel synthesis demonstration project	2020	Methanol synthesis from CO2 hydrogenation technology	1440 tonnes/year
CNOOC methanol synthesis industrial pilot plant	2020	Methanol synthesis from CO2 hydrogenation technology	5000 tonnes/year
Guangdong Huizhou Daya Bay carbonate synthesis project	2021	Carbonate synthesis from ionic liquid catalyzed CO2	100,000 tonnes/year
Erdos aromatics industrial pilot project by Tsinghua University and Jiutai Group	2023 (expected)	Aromatics synthesis from CO2 hydrogenation	10,000 tonnes/year
Shanxi Lu’an CH4-CO2 dry reforming project	2021	Syngas production from CH4-CO2 reforming	10,000 m3/year

Table 5. CO₂ chemical utilization projects in China [50,113,123].

Project	Operation Start Year	Technology	Productivity
Lanzhou liquid solar fuel synthesis demonstration project	2020	Methanol synthesis from CO2 hydrogenation technology	1440 tonnes/year
CNOOC methanol synthesis industrial pilot plant	2020	Methanol synthesis from CO2 hydrogenation technology	5000 tonnes/year
Guangdong Huizhou Daya Bay carbonate synthesis project	2021	Carbonate synthesis from ionic liquid catalyzed CO2	100,000 tonnes/year
Erdos aromatics industrial pilot project by Tsinghua University and Jiutai Group	2023 (expected)	Aromatics synthesis from CO2 hydrogenation	10,000 tonnes/year
Shanxi Lu’an CH4-CO2 dry reforming project	2021	Syngas production from CH4-CO2 reforming	10,000 m3/year

Syngas production from CO₂. As the “cornerstone” of the synthesis industry, syngas has a huge market demand [113]. The efficient production of syngas can be achieved by employing recent technological advancements such as CH₄-CO₂ dry reforming [124,125], CH₄-CO₂-H₂O ternary reforming [126], and reverse water gas shift reaction (RWGS) [127]. Moreover, these technologies promote the effective utilization of natural gas while lowering CO₂ emissions. In August 2021, the world’s first 10,000-cubic-meter-level CH₄-CO₂ dry reforming facility for syngas production [128] was completed in Changzhi, Shanxi. After achieving stable operation, it realizes the daily conversion of CO₂ up to 60 tonnes [129]. In addition, this facility can realize the efficient utilization of CO₂ and the flexible adjustment of H₂/CO of the product syngas, and it is ready for industrial application promotion [130].

4.2. Development Status of CO₂ Biological Utilization in China

CO₂ biological utilization combines synthetic biology processes with CO₂ to produce valuable products, including food and feed, biofertilizers, chemicals, biofuels, and gas fertilizers [131]. Products generated by CO₂ biological utilization technology have high-added values and substantial economic benefits [132].

In China, the conversion of CO₂ to food and feed has been commercialized on a large scale, with a CO₂ utilization of 1000 tonnes/year and an output value of about 50 million yuan/year; about 50,000 tonnes of CO₂ are utilized annually to create biofertilizers, with an annual production value of 500 million yuan; about 10,000 tonnes of CO₂ are used annually for chemical conversion, with an annual production value of 20 million yuan; and roughly 10,000 tonnes of CO₂ are used to make gas fertilizer each year, with an annual production value of about 20 million yuan [67].

In addition to the existing CO₂ biological utilization technologies such as microalgae fixation [84,133] and gas fertilization [59], the research institutions and universities in China are dedicated to the development of more advantageous CO₂ biological utilization technologies, and some outstanding outcomes have been obtained. Tan et al. proposed an innovative method to produce high-performance biodegradable plastics by directly employing captured CO₂ in conjunction with cyanobacterial cell factories [134], which resolves the issues of plastic pollution and the replacement of non-grain raw materials in PLA production. Cai et al. realized the efficient cell-free chemoenzymatic starch synthesis from CO₂, bringing the opportunity to replace the traditional starch manufacturing factory. This technical route of synthesizing starch from CO₂ has achieved the first-time complete synthesis of CO₂ to starch from beginning to end in the laboratory, which is a major disruptive and original breakthrough in the field of artificial starch synthesis [135]. Yu et al. constructed a biosynthetic pathway of CO₂ to organic matter by using Rhodobacter sphaeroides strains [136]. Wei et al. proposed a new “genomic scalpel” that can quickly prune and knock out the genome of microalgae named “Nannochloropsis oceanica” to form an efficient cell factory, which can be combined with available CO₂ and sunlight to customize the production of biomolecules such as biofuels or bioplastics [137]. The continuous development of CO₂ biological utilization technology lowers the price of processing raw materials while simultaneously improving environmental friendliness, which is consistent with the concept of green ecology and accelerates the transition toward carbon neutrality.

4.3. Development Status of CO₂ Geological Utilization in China

The process of injecting massive volumes of CO₂ into the ground to achieve the purpose of production and enhancement of fossil fuels is known as the geological utilization of CO₂. The notable advantage of this technology is its capacity to dramatically enhance energy output while fulfilling the target of reducing CO₂ emissions. Therefore, it is now viewed as the most economically efficient approach for CO₂ utilization.

4.3.1. CO₂-Enhanced Oil Recovery (CO₂-EOR) in China

CO₂-EOR is injecting CO₂ into the reservoir to modify the flow characteristics of the multiphase fluid in porous media, including interfacial tension reduction, oil viscosity reduction and oil permeability improvement, thereby enhancing oil recovery [113]. CO₂-EOR is applicable to both conventional and unconventional reservoirs with low or ultra-low permeability.

China’s CO₂-EOR technologies and apparatus are extremely advanced because CO₂ flooding research and applications have been carried out in China since the 1960s [97]. Currently, China’s CO₂-EOR has already progressed to the stage of industrial demonstration. The annual CO₂ utilization scale for EOR is approximately 1.54 million tonnes, and the cumulative CO₂ storage has exceeded more than 660 × 10⁴ tonnes [83], still demonstrating considerable potential.

The distribution of CO₂ emission sources and the geological characteristics need to be considered when selecting the location for CO₂-EOR projects. China’s iron and steel enterprises are mainly distributed in the east and north, and the large amount of CO₂ emissions produced during the steel production process can serve as the CO₂ source for CO₂-EOR projects. For the basins that are also located in the east and north of China, such as the Ordos Basin, Songliao Basin, and Bohai Bay Basin, there is a shorter CO₂ transport distance between the CO₂ emission sources and these basins, namely, good spatial matching. Therefore, these basins are regarded as priority areas for China’s CO₂-EOR project implementation [50] due to the substantial advantage of good spatial matching. For the Tarim Basin and Junggar Basin situated in the northwest of China, although there are fewer CO₂ emission sources nearby, they are still considered to be appropriate areas for CO₂-EOR projects due to their favorable geological characteristics and high geological storage capacities.

Due to the close integration of CO₂ with oil production in CO₂-EOR, most of the CO₂-EOR projects in China are undertaken by oil companies, including CNPC, Sinopec, and Shaanxi Yanchang Petroleum. By 2021, there are nine major CO₂-EOR projects in operation. The CNPC Jilin oilfield CO₂-EOR project is currently the largest CCUS project in Asia, and it is also the only project in China among the 21 large CCUS projects currently operating across the world. It adopts pre-combustion capture combined with associated gas separation technology and pipeline transport, with a CO₂ injection capacity of 60 × 10⁴ tonnes/year [50] and an oil production capacity of approximately 10 × 10⁴ tonnes/year [83]. The cumulative CO₂ storage has reached 2.12 million tonnes since it was put into operation in 2008 [83]. Another representative national demonstration project in China is the Daqing Oilfield CO₂-EOR project. It adopts the pre-combustion method to capture CO₂ generated from natural gas processing and uses a combination of tanker truck and pipeline for CO₂ transport, realizing CO₂ injection of 30 × 10⁴ tonnes/year and oil production of 10 × 10⁴ tonnes/year [83]. The current CO₂-EOR projects in China are listed in

Table 6. CO₂-EOR projects in China [50,83].

Project	Capture Technology	Operation Start Year	Transport	CO2 Injection Capacity (Tonnes/Year)	Oil Production Capacity (Tonnes/Year)
Jilin Oilfield CO2-EOR project	Pre-combustion	2008	Pipeline	600,000	100,000
Daqing Oilfield CO2-EOR project	Pre-combustion	2003	Tanker truck and pipeline	300,000	100,000
Zhongyuan Oilfield CO2-EOR project	Pre-combustion	2015	Tanker truck	100,000	N/A
East China Oil&Gas CCUS full-process demonstration project	Pre-combustion	2005	Tanker truck and ship	100,000	N/A
Xinjiang Oilfield CO2-EOR project	Pre-combustion	2015	Tanker truck	(5–10) × 104	(1.4–3.9) × 104
Changqing Oilfield CO2-EOR project	Pre-combustion	2017	Tanker truck	50,000	N/A
Shaanxi Yanchang Petroleum CO2-EOR project	Pre-combustion	2013	Tanker truck	50,000	N/A
Shengli Oilfield CO2-EOR project	Post-combustion	2010	Tanker truck	40,000	N/A
Qilu Petrochemical and Shengli Oilfield CO2-EOR project	Rectisol wash	2022	Tanker truck	1,000,000 (expected)	300,000 (expected)

. According to the results of CO₂-EOR in Jilin and Daqing oilfields, oil recovery can be enhanced by 10–25% through CO₂-EOR, that is, approximately 1.0 tonnes of oil increment for every 2.0–3.0 tonnes of CO₂ injection, indicating obvious advantages in oil increment and CO₂ storage [83].

In addition, Sinopec Shengli Oilfield and Qilu Petrochemical cooperate to carry out China’s first million-tonne CO₂-EOR project, which was officially completed and put into production in August 2022 [83,138]. In this project, Qilu Petrochemical is responsible for CO₂ capture and transport, while Shengli Oilfield is in charge of CO₂ injection into oil reservoirs for oil production. CO₂ produced in the coal gasification process of the fertilizer plant is captured and transported by tanker truck; 73 injection wells and 166 production wells are deployed; and CO₂ is injected into the ultra-low permeability reservoirs of Shengli Oilfield. It is expected to inject a cumulative amount of more than 10 million tonnes of CO₂ over the course of 15 years [138], to achieve the purpose of increasing oil production by 3 million tonnes [83] and enhancing oil recovery by 12% [139].

4.3.2. CO₂-Enhanced Natural/Shale Gas Recovery (CO₂-EGR) in China

Natural gas mainly exists in a free state under natural conditions, and it is stored in underground porous formations, primarily in oil and natural gas fields. Natural gas is easy to produce in large amounts due to its free state. Although shale gas has the same composition as natural gas, it is trapped within the microcracks of shale rock. The characteristics of shale, such as the low pore pressure, porosity, and permeability, make shale gas production much more difficult. Therefore, shale gas is considered as unconventional natural gas. The utilization of CO₂ has a considerable positive impact on the production of both natural gas and shale gas. The primary premise of CO₂-enhanced natural gas recovery is to leverage the physical differences between the supercritical-state CO₂ and the free-state natural gas to accomplish natural gas displacement by CO₂ in natural gas reservoirs [140], while the CO₂-enhanced shale gas recovery process mainly relies on distinctions in the adsorption characteristics of shale for CO₂ and CH₄. Because shale preferentially absorbs CO₂ over CH₄, shale gas recovery can be enhanced by replacing CH₄ in the shale formation with CO₂ injection [141].

The proven reserves of gas in China have rebounded since 2018 [142]. In 2019, new proven natural gas reserves of over 100 billion m³ were discovered in three gas fields, including two gas fields in the Ordos Basin and one in the Sichuan Basin [138]; the Sichuan Basin added 124.7 billion m³ of proven shale gas fields [143], and Guizhou added 642.4 billion m³ of predicted shale gas geological reserves [144]. Theoretically, China’s CO₂-EGR has approximately 9 billion tonnes of CO₂ storage potential, while China’s CO₂-EGR technologies currently are still in the basic research stage [50].

Both natural gas and shale gas in China show great development potential [145]. The geological conditions of some gas reservoirs limit their development efficiency, especially shale gas reservoirs. China’s continental shale gas enrichment areas have typical characteristics of low porosity, low permeability, high adsorption, high clay content, and high depth. These characteristics lead to huge water consumption and clay hydration swelling by hydraulic fracturing during the shale gas production process, further causing fracture blockage and low gas recovery [146]. Given the above-mentioned characteristics of shale gas reservoirs and the difficulties in exploitation, Chinese experts and scholars have launched a series of research on CO₂ utilization to enhance shale gas recovery, covering the microscopic behavior of gas molecules in shale nanopores [147] as well as the macroscopic parameter optimization and technical improvements in the production process [146,148]. Sun et al. investigated the microscopic states and behaviors of CH₄ and CO₂ in typical shale nanopores using molecular dynamics (MD), grand canonical Monte Carlo (GCMC) simulations, and density functional theory (DFT). The result revealed the prevalence of competitive adsorption of CO₂ and CH₄ in nanopores of different compositions, that is, CO₂ adsorption ability is greater than CH₄ while its self-diffusion is usually weaker than CH₄ in the nanopores of kerogen, quartz, montmorillonite, calcite, and mixed components [147]. Shi et al. determined the appropriate CO₂ injection parameters into shale oil reservoirs by employing numerical simulation, providing theoretical guidance for CO₂ injection to enhance shale gas recovery [146]. Lu et al. proposed an integrated technology for the efficient development of shale gas and the geological storage of supercritical CO₂ [148]. With this technology, the shale was first fractured with supercritical CO₂ to promote the development of a more complex fracture grid, and then CO₂ was continuously injected to replace CH₄ in the reservoir to maximize shale gas recovery and geological storage of CO₂. Unlike the traditional shale gas production process that requires hydraulic fracturing to increase the porosity and permeability of shales, this approach’s innovation lies in utilizing supercritical CO₂ instead of water for fracturing. According to the pilot test result of this technology in Yanchang Petroleum National Continental Shale Gas Demonstration Area, a 2.5-time increase in the daily average production from a single well was achieved, demonstrating a considerable rise in shale gas production. This innovative technology offers a new alternative for massive CO₂ storage while enhancing shale gas recovery and reducing water waste from the hydraulic fracturing of shales [149].

4.3.3. CO₂-Enhanced Coalbed Methane Recovery (CO₂-ECBM) in China

A large amount of coalbed methane in coal seams is formed and stored in the process of coalification. Unlike free-state natural gas in reservoirs, coalbed methane resides in the adsorbed state within coal seams. Different storage forms result in various production mechanisms and processes. In general, the production of coalbed methane is more complicated than that of conventional natural gas. Due to the lower permeability of coal seams, stimulation measures such as hydraulic fracturing and CO₂ injection, are required during coalbed methane production [150]. The kinetic process of CO₂ adsorption and displacement of CH₄ is the key mechanism of CO₂-ECBM. By injecting CO₂ into the coal seam, the partial pressure of CH₄ is reduced, which speeds up the desorption of CH₄ adsorbed on the surface of coal particles. Meanwhile, when CO₂ and CH₄ are present in the coal seam at the same time, they compete for adsorption. Due to the higher adsorption energy of CO₂ [151], the injected free-state CO₂ can take over the initial adsorption position of CH₄ in the coal seam so that the adsorbed-state CH₄ can be converted into the free state, facilitating CH₄ production and achieving coalbed methane enhancement by CO₂.

China’s CO₂-ECBM project has completed the pilot phase study. Although China has abundant coalbed methane resources, the development of coalbed methane is constrained by the “three lows and one high” properties of coalbed methane reservoirs, namely low pressure, low saturation, low permeability, and high adsorption [152]. Therefore, a series of studies have been conducted in China to address this situation. Fan et al. established a thermos-hydro-mechanical-chemical (THMC) coupled model to simulate the displacement of coalbed methane by CO₂, providing insights into key processes controlling key factors [153]. Bai et al. analyzed the impact of CO₂ injection on some key parameters in coal seams through experiments and summarized the changes in gas outflow rate, gas components, coal seam temperature, CH₄ desorption rate and other displacement parameters during this process, establishing a crucial theoretical basis for the CO₂ storage effect in coal seams and the enhanced development of coalbed methane [154]. Li et al. investigated the microstructure changes of coal samples after the injection of supercritical CO₂ and confirmed that the injected supercritical CO₂ could enlarge the pores and fractures in coal samples by dissolving the coal minerals, thus enhancing coalbed methane recovery [155]. Zhang et al. focused on the geochemical reactions that occurred after CO₂ injection into coal seams and put forward the insight that anthracite may be a potential geological body for CO₂ storage [156].

In addition to the above studies, there are currently two CO₂-ECBM projects in operation in China, both of which are under the responsibility of China United Coalbed Methane Corp., Ltd. (CUCMC). Both the Shizhuang CO₂-ECBM project and the Liulin CO₂-ECBM project have a CO₂ injection capacity of 1000 tonnes/year [50], as shown in

Table 7. CO₂-ECBM projects in China [50].

Project	Project Location	Operation Start Year	Transport	CO2 Injection Capacity (Tonnes/Year)
CUCMC Shizhuang CO2-ECBM project	Shizhuang Block of Qinshui Basin in Shanxi	2004	Tanker truck	1000
CUCMC Liulin CO2-ECBM project	Liulin Block of Ordos Basin in Shanxi	2012	Tanker truck	1000

.

4.3.4. CO₂ for In-Situ Leach Uranium Mining in China

Uranium resources are not only a strategic national resource and an important energy resource, but also an important raw material for the nuclear military industry and nuclear power [157]. Sandstone-type uranium resources contribute 41.57% of all the proven uranium resources in China. More than 70% of these complex sandstone-type uranium resources have high salinity, high carbonate, low permeability and low grade, making them difficult to mine using the traditional acid or alkali in situ leach method. In response to this actual situation, the Beijing Research Institute of Chemical Engineering and Metallurgy of China National Nuclear Corporation (CNNC) has carried out a series of theoretical research and technological innovations since 2002. China has successfully mastered and industrialized the technology of CO₂ and O₂ in-situ leach uranium mining through three generations of improvement in mining and metallurgical technology, becoming the second nation after the United States to accomplish this advancement in the world.

In this technology, CO₂ and O₂ are added to the groundwater to form a leaching agent, which is then introduced into the uranium ore. In the reaction between the leaching agent and uranium ore, O₂ oxidizes tetravalent uranium into hexavalent uranium, while CO₂ reacts with groundwater to form bicarbonate ions. Then, bicarbonate and hexavalent uranium combine to form uranyl ions, which are dissolved in the solution and potently inhibit the precipitation of calcium ions. Finally, the uranium solution is lifted to the ground with a submersible pump for processing, and primary products of uranium can be obtained. The tail solution serves as the leaching agent for cycle use [158].

Low permeability now has become a major barrier restricting uranium mining in China. The permeability of sandstone-type uranium deposits gradually decreases with increasing mining depth. Therefore, based on the mature technology of CO₂ and O₂ in-situ leach uranium mining, Niu et al. proposed a method of combining CO₂ blasting and CO₂ in-situ leach uranium mining, where CO₂ blasting can create a three-dimensional fracture grid inside the uranium deposit to improve its overall permeability, thereby improving the efficiency of subsequent CO₂ in-situ leach uranium mining [159,160]. Chang et al. put forward a simulation test system for in-situ leach uranium mining in horizontal wells, where horizontal wells are used for liquid injection while vertical wells are used for liquid extraction, to investigate and enhance recovery of CO₂ in-situ leach uranium mining [161].

At present, there is one CO₂ and O₂ in-situ leach uranium mining project in China, which is operated by CNNC. The improvement of CO₂ and O₂ in-situ leach uranium mining makes “dead ore” a lucrative resource that can be economically mined by resolving the technical challenges of excessive acid consumption and easy blockage in the in-situ leach uranium mining of sandstone-type ore. While addressing the issue of CO₂ emissions, it greatly enhances the usage of sandstone-type uranium resources and effectively solves the problem of difficult groundwater pollution treatment [162].

5. Progress of CO₂ Storage in China

CO₂ storage occurs when captured CO₂ is pumped into deep reservoirs employing engineering technologies to establish long-term separation of CO₂ from the environment. CO₂ storage is categorized into two forms based on its location: geological storage and ocean storage. Figure 5 shows CO₂ storage classifications. The Summary of advantages and disadvantages of the various CO₂ storage methods based on other literature [58,94,163,164,165,166,167,168,169] is listed in

Table 8. Advantages and disadvantages of CO₂ storage methods [58,94,163,164,165,166,167,168,169].

Storage Type		Advantage	Disadvantage
Geologicalstorage	Deep saline aquifers	Widely distributed Large storage potential	Uncertain sealing groundwater resources pollution
	Depleted oil and gas reservoirs	Good storage condition Infrastructure facilities Experienced storage	Large, depleted field is required
	Un-mineable coal seams	No more investment cost	Specific geological structures with lateral connection and vertical isolation with surrounding strata are required
	Salt caverns	Low cost Widely distributed	Suitable rock salt structure is required for salt cavern construction
	Mineralogical carbon storage	Permanent storage Negligible leakage risk Environmentally safe	Slow reaction kinetics
Ocean storage		Huge storage potential	Seawater’s pH value variation, Marine ecological destruction

.

5.1. Development Status of CO₂ Geological Storage in China

Currently, geological storage is still the dominant method of CO₂ storage [167]. The principle of CO₂ geological storage is an imitation of the mechanism of fossil fuel storage in nature. The geological storage of CO₂ can be achieved by transporting CO₂ to an appropriate location through pipelines or vehicles and injecting it into the ground with specific geological conditions [94,170] and specific depths [170,171]. Currently, the available geological storage of CO₂ includes deep saline aquifers, depleted oil and gas reservoirs, un-mineable coal seams, salt caverns, and mineralogical carbon storage.

5.1.1. CO₂ Storage in Deep Saline Aquifers in China

In China, the widespread distribution of trap structures in saline aquifers matches well with high-concentration CO₂ emission sources, which can reduce transport and comprehensive costs. Meanwhile, deep saline aquifers in China have a huge storage potential, with a theoretical storage capacity of up to 2417 billion tonnes [50]. Therefore, saline aquifers are currently the most widely used CO₂ storage method in China. China’s current technology and equipment required for storing CO₂ in saline aquifers can completely meet the demands of practical applications.

Saline aquifers located in the Ordos Basin, Bohai Bay Basin, Qaidam Basin, Tarim Basin, Junggar Basin and Songliao Basin are considered to be the most ideal areas for storing CO₂ due to their excellent storage capacities and geological conditions [50]. The Ordos Basin was selected as the site for the first demonstration project of full-process CO₂ capture and deep saline aquifer storage in China. The CO₂ injection experiment was implemented in May 2011, and the injection was stopped in 2015. The target of 30 × 10⁴ tonnes of CO₂ injection was completed, and then the monitoring period has begun. The CO₂ source of this demonstration project came from the tail gas of the conversion unit of the coal-to-hydrogen plant, and the CO₂ with a purity of 88.8% was purified to over 99.99% through gas-liquid separation, oil removal, desulfurization, purification, and distillation processes. Then the CO₂ was transported to the storage area by cryogenic tanker truck, firstly into the buffer tank, and later injected into the ground after pressurization and heating. Monitoring data such as buffer tanks, injection wells, monitoring wells, pressure, and temperature could be transmitted to monitoring staff in real-time [172]. Monitoring data for the past nine years show that the groundwater quality, pressure, temperature, land subsidence, surface CO₂ concentration, and other indicators in the storage area have not changed significantly, and no CO₂ leakage has been monitored using tracer technology [173]. Another demonstration project of full-process CO₂ capture and deep saline aquifer storage, operated by CHN ENERGY, began construction in 2019 and is currently in progress. It will be utilized for CO₂ storage in saline aquifers after completion with an estimated annual CO₂ storage capacity of 15 × 10⁴ tonnes [174]. China’s CO₂ storage projects in deep saline aquifers are listed in

Table 9. CO₂ storage projects in deep saline aquifers in China [50].

Project	Operation Start Year	Capture Technology	Transport	CO2 Storage Capacity (Tonnes/Year)
CHN ENERGY Ordos deep saline aquifer project	2011	Pre-combustion	Tanker truck	100,000
CHN ENERGY Guohua Jinjie CCUS full-process demonstration project	2020	Post-combustion	N/A	150,000 (expected)

.

5.1.2. CO₂ Storage in Depleted Oil and Gas Fields in China

Depleted oil and gas reservoirs have ideal geological characteristics to retain hydrocarbons and prevent their leakage for millions of years, so they are regarded as another promising site for CO₂ storage [175]. Additionally, since these reservoirs have gone through the production stage, a variety of historical data such as logging data, drilling and completion data, formation parameters, and production history, is sufficient to provide a detailed basis for assessing the suitability of CO₂ storage [175].

Oil and gas fields in the eastern and northern areas of China that have reached late production phases and are no longer economically feasible for production are expected to be excellent depleted oil and gas field sites for CO₂ storage. It is anticipated that the overall CO₂ storage capacity of these areas can reach 30% of the total demand for CCUS. The obvious benefits of CO₂ storage in depleted oil and gas fields include less additional costs to implement, mature technical processes and ease of management. However, it is worth noting that the leakage of stored CO₂ may occur due to fractures created by the design and production of oil and gas fields [176]. Up to now, there are still only a few large-scale projects worldwide using depleted oil and gas fields to store CO₂ [177]. Although China possesses the required advanced technology, there is currently no demonstration project for storing CO₂ in depleted oil and gas fields since such projects are often launched after the completion of CO₂-EOR and CO₂-EGR projects.

5.1.3. CO₂ Storage in Um-Mineable Coal Seams in China

When a coal mine reaches the late stage of mining and the coalbed methane content is too low to be easily produced, the mine may be considered un-mineable. Although such coal mines are no longer suitable for coalbed methane mining for economic reasons, the capability of coal seams to absorb CO₂ enables this type of un-mineable coal seams to function as appropriate sites for CO₂ storage.

China is relatively rich in coal resources. Currently, there are few un-mineable coal mines, so China has not yet carried out any CO₂ storage projects in un-mineable coal seams. However, some studies on technologies and methods of CO₂ storage in um-mineable coal seams and coal mine goafs have been conducted, and the research patent has been released [178], which introduces the key technologies and precautions of the implementation process in detail, laying the foundation for future CO₂ storage in un-mineable coal seams in China.

5.1.4. CO₂ Storage in Salt Caverns in China

Salt caverns are artificial cavities constructed by dissolving salt deposits using water in deep underground salt formations [168]. The low permeability and visco-plastic properties of rock salt [179] allow salt caverns for the safe containment and storage of large volumes of liquids and gases under high pressure. Therefore, salt caverns have been widely used to store natural gas [180] and hydrogen [181]. The extensive successful track records of salt caverns for natural gas storage suggest that they may serve as a potential option for CO₂ geological storage [182].

China’s rock salt has a bedded structure with thin salt layers and interlayers [180], and this brings great challenges for salt cavern construction. Currently, CO₂ storage in salt caverns in China is still in the research stage. Zhang et al. carried out the safety and applicability evaluation of CO₂ storage in typical bedded rock salt caverns of China [179] by using numerical simulation to preliminary determine the appropriate cavern pressure, volume variation, displacement and other parameters, so as to provide theoretical support for subsequent practical applications.

5.1.5. Mineralogical Carbon Storage in China

Mineralogical carbon storage, also known as carbon mineralization or mineral carbonation, is a process, in which injected CO₂ reacts with geological rocks or soil containing high concentrations of divalent cations to form stable carbonate minerals [169,183]. It results in carbon permanently stored with a negligible risk of returning to the atmosphere while generating carbonate products [184,185] that can be beneficially utilized. Therefore, it is considered to be a reliable technology with excellent potential for CO₂ storage [185].

Currently, mineralogical carbon storage is still in the stage of laboratory-based and field-based experiments and has not yet been implemented on a large scale throughout the world [169]. The requirement for a significant quantity of fresh water for CO₂ dissolution to accelerate the carbonation reaction is one of the primary reasons preventing the large-scale implementation of this technology. Because of this, the research focus of this technology in China is mainly on increasing carbonation reaction speed. The results show that carbonation reactions can be accelerated by optimizing reaction conditions [186,187,188], such as pressure, temperature and solid–liquid ratio, and employing pretreatments [189,190], such as heat treatment and mechanical activation. China has abundant mineral resources of wollastonite [183] and serpentine [191], which are favorable raw materials for carbonation reactions. Therefore, mineralogical carbon storage theoretically has a huge potential for CO₂ storage in China.

5.2. Development Status of CO₂ Ocean Storage in China

The ocean, which makes up over 71% of the planet’s surface, has the largest potential capacity to store CO₂. However, CO₂ ocean storage is still subject to some uncertainties, such as the isolation prediction of CO₂ emitted to the seafloor, the risk of CO₂ leakage during storage in marine sedimentary strata, and the influence of CO₂ on pH value change of the seawater, which have limited the deployment of CO₂ ocean storage [94,163]. Therefore, no CO₂ ocean storage project has been implemented in China before 2021.

In recent years, China has strengthened the progressive exploration of marine geological conditions and continuously improved the CO₂ ocean storage technology. China’s first off-shore large-scale CO₂ storage demonstration project has all manufacturing and installation completed in June 2022 [54] and began to officially launch [192]. Since 2021, CNOOC has been conducting research on critical technologies for the integration of geological reservoirs, drilling and completion, and engineering appropriate for CO₂ ocean storage, and has successfully developed a complete set of technology and equipment systems for CO₂ capture, treatment, injection, storage, and monitoring on off-shore platforms, filling the gap in China’s CO₂ ocean storage technology [193]. The project is situated in the Enping 15-1 oilfield group in the Pearl River Estuary Basin. It is planned to permanently store 1.46 million tonnes of CO₂ in total at an injection rate of about 30 × 10⁴ tonnes/year [194]. In the project, the CO₂ associated with the oil field development is injected into the saline aquifer at a depth of 800 m on the seabed. CO₂ can be retained effectively and gas leakage can be prevented by making use of the saline aquifer’s dome structure in conjunction with the muddy protective layer of sufficient thickness [194]. The successful implementation of this project will create new industries and new formats of CO₂ storage in China, showing important demonstration significance for the environmentally friendly development of offshore oil and gas resources [194].

6. Challenges and Suggestions for Future Development of CCUS in China

Although significant progress has been made in China’s CCUS projects, there are still issues and challenges that limit the large-scale implementation of China’s CCUS projects.

Currently, post-combustion capture, pre-combustion capture and oxy-fuel combustion as traditional CO₂ capture technologies have achieved mature development. However, their large-scale demonstration applications have been constrained due to the enormous energy consumption caused by CO₂ capture devices [57,58] as well as the high economic cost of CO₂ compression [57,58] during the capture process. Therefore, the reduction of energy consumption and cost is the primary research focus of traditional CO₂ capture technologies in the future.

In addition, future research on capture technology should concentrate on negative emission technologies, such as direct air carbon capture and storage (DACCS) and bioenergy with carbon capture and storage (BECCS). The development of adsorption materials appropriate for DAC technology has advanced significantly in recent years, and the constant enhancement of the properties of adsorption materials has improved the adsorption efficiency of DAC [71,72,73]. However, the high price of existing adsorption materials and the low concentration of CO₂ in the air lead to the high application cost of DAC, making its implementation difficult despite its potential for negative emission [195]. Therefore, accelerating the development of cost-effective adsorption materials should be the research focus of DAC.

BECCS is a greenhouse gas reduction technology that combines carbon capture and storage with the use of biomass to create negative carbon emissions. The basic principle of BECCS is using biomass (CO₂-absorbing plants) to generate energy while capturing and storing the resulting CO₂ during biomass combustion [196,197]. The most obvious advantage of BECCS is that biomass serves as a renewable energy source to generate bioenergy, and it also acts as a carbon sink by absorbing CO₂ during the growth process through photosynthesis [195,198,199]. However, there are several challenges to implementing BECCS in China. One major challenge is the high cost [197,198,199,200,201,202,203] of technology development and implementation. Additionally, there are some environmental challenges [203], such as the waste of land caused by growing biomass plants instead of food, and the drinking water contamination caused by the large-scale growth of biomass, especially algae. Despite these challenges, BECCS has the potential to play a significant role in CO₂ reduction in China. To fully realize this potential, it is important to continue investing in research and development, as well as working to address the challenges associated with the technology.

In terms of CO₂ transport technology, tank-based transport is the primary method of CO₂ transport in China. Although pipeline-based transport is still in the research and pilot stage, it will be the most promising and economical technology for CO₂ transport in future large-scale CCUS demonstration projects due to its outstanding advantages and the gradual expansion of CCUS projects. Currently, the implementation of CO₂ pipeline transport is constrained by many challenges. One major challenge is that pipeline facilities are usually large and influenced by geographical conditions, which leads to long construction times and high investment costs for pipelines. In addition, pipeline design is affected by the transport states of CO₂. There are different requirements [75] for CO₂ transport in different states. For example, less than critical pressure is required for gaseous CO₂ transport; temperature control is required for liquid CO₂ transport; both temperature control and fixed pressure range are required for dense-phase CO₂ transport; and above critical temperature and pressure are required for supercritical state CO₂ transport. Therefore, it is necessary to comprehensively consider these influencing factors in the pipeline design. The potential improvements in future research should focus on optimizing the pipeline design, developing precise design specifications, and using suitable construction materials for pipelines, so as to achieve the cost-effective and safe transport of CO₂ in the pipeline.

The potential for CO₂ leakages is another challenge for CO₂ transport and subsequent utilization and storage in China. Generally, CO₂ leakages are less likely to occur in tank-based transport, because tanker trucks are equipped with reliable safety features to minimize the risk of spills, but CO₂ leakages may still occur due to the accident of the truck or the failure of the equipment. CO₂ leakages during transport by pipeline are usually caused by CO₂ corrosion [204,205] or mechanical damage to pipelines [206,207]. Therefore, it is essential to employ high-quality equipment and advanced materials [208,209] for the transport system to avoid or minimize the potential risk of CO₂ leakages during transport. Meanwhile, it is necessary to implement monitoring and leakage detection systems [210,211] to rapidly identify and address any leakages.

The potential reasons for leakages in CO₂ utilization and storage may include unstable underground reservoir conditions and inappropriate injection equipment. Therefore, a comprehensive evaluation of geological conditions is required in the site selection for CO₂ utilization and storage, and high-quality corrosion-resistant injection equipment is necessary. In addition, the implementation of reliable monitoring and leakage detection systems is also crucial. However, immature technologies of monitoring, leakage prevention and control, and corrosion prevention for post-CO₂ injection are the main problems [50] faced by existing CO₂-EOR projects in China. Furthermore, the challenge of accurate monitoring is even more prominent in China’s CO₂-ECBM projects since accurate monitoring of the movement of one gas is more difficult in a gas-gas system than in a gas-liquid system. Therefore, future research on CO₂ utilization and storage in China should focus on improving accurate monitoring and leakage detection technologies, leakage prevention and control technology, and anti-corrosion technology, to achieve effective utilization and safe storage of CO₂.

7. Conclusions

Based on a large number of literature, this study demonstrates the latest progress of CCUS development in China after 2019. As a major member of developing countries, China has placed a high priority on the issue of CO₂ emissions. With the great support of the Chinese government, a series of scientific research and demonstration projects have been conducted and some remarkable results have been obtained.

Currently, post-combustion capture is the dominant technology for CO₂ capture in China, while pre-combustion capture and oxy-fuel combustion are being improved and gradually promoted. Additionally, direct air capture, as a negative carbon emission technology, has attracted more attention. The development of cost-effective adsorption materials used in this technology is becoming a new research focus of capture technology in China.

Tanker truck transport remains the primary mode of CO₂ transport due to the limited scale of China’s current CCUS projects. Long-distance pipeline construction is a challenge for CO₂ transport, which requires more technical improvement.

China’s CO₂ utilization technology has advanced significantly in recent years, yielding considerable benefits. CO₂ chemical utilization has realized industrial demonstration, while CO₂ biological utilization has achieved significant technological innovations. China’s CO₂-EOR has reached the commercial application stage, realizing the obvious enhancement in oil recovery with remarkable economic benefits. CO₂ in-situ leach uranium mining is another CO₂ utilization technology that is ready for commercial application in China, and it is going to serve as the cornerstone for China’s military development. Deep saline aquifers are the dominant site for CO₂ storage, while China’s first off-shore large-scale CO₂ storage demonstration project in the Enping oilfield also demonstrates promising prospects of CO₂ ocean storage in China.