How did “gutter oil” become aviation fuel for domestic large aircraft?

At noon on June 5, the domestically-produced large aircraft C919 and the domestically-produced regional aircraft ARJ21 successfully completed their first demonstration flight missions fueled with sustainable aviation fuel ( SAF ) in Dongying and Shanghai respectively.

Source: Sinopec News

Cao Dongxue, chief expert of Sinopec, said that the aviation fuel used in this test flight adopted the bio-jet fuel production technology independently developed by Sinopec. The raw material is waste cooking oil , which is what we usually call "gutter oil" , and is blended with ordinary aviation fuel at a ratio of 40%.

It's amazing! The "gutter oil" that we usually dislike has been transformed into aviation fuel that helps large aircraft soar. How is this achieved? Let's first understand -

01

The history of aviation fuel

The sustainable aviation fuel (SAF) used in this demonstration flight is an advanced alternative aviation fuel that shows revolutionary prospects and marks the arrival of the green aviation fuel era.

02

What are the advantages of sustainable aviation fuel compared to traditional aviation fuel ?

Sustainable aviation fuel (SAF) is a liquid alternative aviation fuel made from renewable raw materials . The raw materials mainly include vegetable oils such as coconut oil, palm oil, jatropha oil, linseed oil, as well as microalgae oil, waste cooking oil, animal fat, etc.

Compared with traditional aviation fuel, it can reduce carbon emissions by up to 80% over its entire life cycle, and can even achieve negative carbon emissions over its entire life cycle through carbon sequestration.

Carbon capture, utilization and storage technology | Source: Reference 1

The SAF production processes that have been certified mainly include the following. Among them, the ester and fatty acid hydrogenation process (HEFA) is used to refine "gutter oil" into aviation kerosene.

03

How does “ gutter oil ” become aviation fuel through the HEFA process ?

The ester and fatty acid hydrogenation process (HEFA) is a process of hydrogenating triglycerides, saturated and unsaturated fatty acids in vegetable oils, waste cooking oils and animal fats . The process is generally divided into three steps:

The first step: unsaturated fatty acids and triglycerides are converted into saturated fatty acids by catalytic hydrogenation , wherein triglycerides are converted into fatty acids by β-hydrogen elimination reaction.

Step 2: Saturated fatty acids are converted into C15-C18 straight-chain alkanes through hydrodeoxygenation and decarboxylation . In the early days, this step mainly used zeolite or oxide-supported precious metal catalysts, but these catalysts are easily poisoned and deactivated, easily generate cracking products, and are expensive. Later, they were gradually replaced by transition metals such as Ni, Mo, Co or their supported bimetallic catalysts.

The third step: cracking and isomerization reaction , the deoxygenated straight-chain alkanes are further selectively hydrocracking and deeply isomerized to produce highly branched alkanes . The commonly used catalysts in this step are Pt-loaded Al2O3, zeolite molecular sieves, etc.

Finally, the mixed liquid fuel is separated into light gas, naphtha and biojet fuel through a distillation process.

China is the first country in Asia and the fourth in the world to have independently developed bio-jet fuel technology. At present, China has initially formed a bio-jet fuel production, certification and application system. China's first bio-jet fuel plant with an annual output of 100,000 tons has successfully carried out large-scale production at Zhenhai Refining and Chemical.

A tanker truck loaded with Sinopec No. 1 bio-jet fuel leaves Zhenhai Refinery

Image source: China National Radio The sustainable aviation fuel that helps domestic large aircraft soar is produced by Zhenhai Refining and Chemical. It is produced using Sinopec's independently developed technology, and its quality indicators meet national standards. It has obtained Asia's first global RSB biomass aviation fuel certification . RSB certification is one of the highest sustainable standards in the industry.

Comparison of food waste oil before refining and aviation fuel produced by Zhenhai Refining and Chemical

Image source: Beijing Daily

04

Is it cost-effective to produce biofuel using “ gutter oil ” ?

In fact, the cost of converting waste cooking oil into bio-jet fuel is not low, about three times that of ordinary aviation fuel, but carbon emissions can be reduced by more than half .

For example, if all of China's aviation fuel consumption last year was replaced by biofuel, it is estimated that emissions could be reduced by 55 million tons per year, which is equivalent to planting nearly 500 million trees . From this perspective, this "ecological account" is still very worthwhile.

Image source: iStock

China has sufficient potential sustainable aviation fuel raw material resources, including 3.4 million tons of waste edible oils and fats per year, 207 million tons of agricultural waste per year, 195 million tons of forestry waste per year, 23.5 million tons of urban organic solid waste per year, and 5 million tons of ethanol produced from industrial waste per year. The total SAF production capacity corresponding to these raw materials can reach 46.41 million tons per year .

According to statistics, China has built a SAF production capacity of 200,000 tons per year and has announced a planned sustainable aviation fuel production capacity of more than 3 million tons per year. The aviation industry accounts for about 2% of global carbon emissions . The construction of the entire bio-aviation fuel industry chain is crucial to reducing emissions in the aviation industry. At present, major global aviation industry chain companies including Airbus and Boeing are actively promoting green transformation. China is playing an increasingly important role in building a green and economic aviation industry.

References

[1] Chang Zhonghong. The past and present of aviation fuel[J]. Large Aircraft, 2023, (09): 8-13.

[2] Zhou Dan. Current status of sustainable aviation fuel development in my country[J]. China and Foreign Energy, 2024, 29(05): 10.

[3] Yan Feng, Su Shuai. A brief discussion on the development status and application of sustainable aviation fuels[J]. Journal of Civil Aviation, 2024, 8 (01): 112-115.

[4] Wang Sheng, Yang He, Yan Rui, et al. Current status of bio-jet fuel production technology[J]. Chinese Journal of Biotechnology, 2022, 38 (07): 2477-2488.

Author: Guo Weihong, PhD, Senior Engineer, University of Chinese Academy of Sciences

Planning & Editing: Little Dandelion

Scientific review: Wu Yang, Associate Professor, School of Environmental and Chemical Engineering, Shanghai University