Simply typing "carbon dioxide recycling" into the scientific research search engine "Google Scholar" yields dozens of success stories in which researchers have succeeded in devising a range of technologies and methods aimed at reducing carbon emissions, creating sustainable pathways for its valuable resource use, and thus mitigating its impact on climate change.
While these technologies seem promising, scientists continue to explore more efficient and cost-effective solutions with economic benefits and industrial scalability. Chinese researchers claim they have found a method that meets these criteria.
In the study published by the "Chinese Journal of Catalyst," researchers from Zhejiang University in China described their method of converting carbon dioxide into "dimethyl ether," an industrially important substance described as an exceptional material.
The global market size for dimethyl ether reached 6.6 billion US dollars in 2023. The International Conference on Mining and Resources expects the market to grow to 14.2 billion US dollars by 2032, showing a growth rate of 8.5% over the period from 2024 to 2032. This is primarily due to its diverse uses, as it is involved in many industries, including:
- First: It is used in the manufacture of aerosol products such as hair sprays, deodorants, and spray paints.
- Second: It serves as a refrigerant in thermal pump systems and air conditioning units, particularly in countries where environmental regulations restrict the use of traditional refrigerants due to their high global warming potential.
- Third: It is used as a solvent in various industries, especially in extraction processes or as a cleaning agent because of its solvent properties.
- Fourth: It can be employed as a raw material in the production of various chemicals, including olefins and dimethyl sulfate, which are used in manufacturing plastics, resins, and other chemical products.
- Fifth: It can be mixed with liquefied petroleum gas (LPG) to improve combustion properties and reduce emissions.
- Sixth: It can be used as a hydrogen carrier in fuel cell applications, making it beneficial for hydrogen-powered vehicles.
Two popular manufacturing methods
Apart from carbon dioxide recycling, this exceptional material is traditionally produced through two main processes, which are:
- First – The conversion of methanol to dimethyl ether:
This method starts with the production of synthetic gas (a mixture of carbon monoxide and hydrogen) from natural gas, coal, biomass, or other hydrocarbon raw materials. Once synthetic gas is obtained, it is converted into methanol using copper-based catalysts. Methanol then undergoes further catalytic dehydration to produce dimethyl ether. - Second – The direct dehydration of methanol:
This method relies on directly producing dimethyl ether through dehydration and involves using acidic catalysts such as zeolite to remove a water molecule from methanol, leading to the formation of the desired compound.
The choice between these methods often depends on factors such as available raw materials, cost, process efficiency, and environmental considerations. The indirect method via synthetic gas is more common in large-scale industrial production due to its use of various raw materials, whereas the direct methanol dehydration process is less common.
A third method… an additional advantage
In the global quest to mitigate carbon dioxide emissions due to their negative impact on the climate, previous studies have described several experiments for converting it into the exceptional material "dimethyl ether," thus "hitting two birds with one stone" by disposing of harmful carbon emissions and producing a highly beneficial substance for various industries. Among these experiments:
- Direct hydrogenation: Scientists have experimented with direct hydrogenation processes that involve catalytic reaction of carbon dioxide with hydrogen to produce dimethyl ether, using various catalysts including copper-based ones and copper nanoparticles.
- Sequential catalysis: This involves a series of reactions where carbon dioxide is first converted into methanol, which then undergoes condensation to form dimethyl ether, using copper catalysts for the initial synthesis of methanol, followed by acidic catalysts like zeolite for methanol dehydration.
- Dual-functional catalysts: This method is based on catalysts combining acidic and metallic functions, exploring acidic oxide-supported copper nanoparticles to achieve carbon dioxide conversion to dimethyl ether.
These experiments faced several challenges, including:
- Challenges in achieving high selectivity for the desired material at increased carbon dioxide conversion rates, leading to decreased productivity and the formation of undesired by-products such as hydrocarbons.
- Sintering or agglomerating of nanoscale catalyst particles during reaction, leading to reduced catalyst stability and efficiency.
Converting carbon dioxide to dimethyl ether offers promising prospects for efficient carbon recycling (Shutterstock)
What did the Chinese do?
To address these challenges, the Chinese researchers, led by Professor Feng Shuo Xiao and Professor Liang Wang from Zhejiang University, announced a more efficient, cost-effective, economic, and industrially scalable method.
The researchers presented a streamlined version of their new method in a press release issued by the Chinese Academy of Sciences, acknowledging the efforts of their predecessors. Here are the highlights of their accomplishments:
- Identifying catalyst limitations: They studied the initial catalysts developed for the direct conversion of carbon dioxide to dimethyl ether and identified the challenges faced by researchers, including low productivity and increased undesired by-products.
- Developing the enhanced catalyst: They addressed these challenges by creating an improved catalyst based on copper nanoparticles, loading the copper nanoparticles onto hydrophobic silica supports modified with gallium.
- Acidity and dehydration: The gallium-modified silica provides moderate acidity, facilitating the dehydration of methanol to dimethyl ether while preventing excessive dehydration that leads to hydrocarbon formation.
- Preventing catalyst deactivation: The effectively hydrophobic catalyst surface prevents the problem of copper nanoparticle sintering, a common issue arising from water and methanol, thus maintaining catalyst stability and efficiency.
- Improved reaction conditions: Under specific reaction conditions (6 liters per hour of reaction materials using the catalyst at a temperature of 240 degrees Celsius and pressure of 3 megapascals), the catalyst achieved a carbon dioxide conversion rate of 9.7% with a high selectivity of 59.3% for the desired dimethyl ether, and a reduced proportion of undesirable by-products.
- Durability and longevity: During a continuous test lasting 100 hours, the catalyst showed consistent and sustainable performance without any signs of decline, surpassing the performance of traditional copper catalysts.
The researchers state in the press release that "these steps represent an innovative approach to developing an effective and durable catalyst for converting carbon dioxide into dimethyl ether, providing promising prospects for efficient carbon recycling."
Predictions anticipate the global market for dimethyl ether to exceed 9 million dollars annually (Shutterstock)
Laboratory effort awaits real-world scalability testing
These promising recycling prospects need additional effort to prove their scalability and real-world applicability, according to Dr. Mahmoud Abdel Hafiz, Professor of Chemical Engineering at the New Valley University in Egypt.
Speaking with Al Jazeera Net, Dr. Abdel Hafiz says, "The laboratory experiments, as shown in the study, are very encouraging, but the important challenge is the feasibility of producing the new catalyst on an industrial scale for widespread use in converting carbon dioxide to dimethyl ether."
He explains that scaling up also requires further improvement to minimize by-products such as carbon dioxide and hydrocarbons. Although a selectivity rate of 59.3% for the desired dimethyl ether has been achieved, by-products still represent 40%, and it is preferable to reduce this rate.
He adds, "Safety issues must also be addressed, which requires answering the question: Are there any safety concerns during the scaled-up production of dimethyl ether from carbon dioxide."
