Sample of high-grade fuel for internal-combustion engine from biomass. (left: low boiling-point fuel: right: high boiling-point fuel.)

To address the current energy crisis, people are exploring ways of synthesizing fuels with biomass. As biomass contains nearly 50% of oxygen in addition to hydrogen and carbon in its composition, the key to turning it into high-grade fuel for an internal-combustion engine lies in the technology that could liquefy biomass via deoxidation by making the best use of its hydrogen and carbon without adding any additional hydrogen or generating any water.

Recently, CAS researchers have made breakthrough progress in their attempts in the regard. With the technology and equipment they have developed, Prof. YANG Zhengyu and colleagues from the CAS Technical Institute of Physics & Chemistry have succeeded in their pilot study of a manufacturing facility that could annually synthesize 50 tons of high-quality fuel from biomass.

With the support of the National High-tech Development Program (dubbed "863 Program") and the CAS Knowledge Innovation Program, the team led by Yang completed bench tests and pilot studies, making a series of technological breakthroughs. Experiments show that many parameters of the synthesized fuel excel those from small-scale lab tests. Its biomass conversion rate is up to 80% of the theoretical value while the productivity reaches 12-16%. Its chemical composition is similar to that of the standard mineral diesel and its calorific value is on a par with that of standard diesel products (about 45 billion joules per liter). Its contents of oxygen and sulfur are less than 0.5% and 0.001% respectively.

The scientists have realized the direct deoxidation of biomass, recombination of carbon, hydrogen, one-step synthesis and separation of products in solid, liquid and gaseous states, the temperature of the reaction is lower than 380ºC, and the reaction pressure is less than 2.6 mega-pascal. The energy consumption for the production is less than one fifth of its energy output while the solid residue is less than 10% of the intake of the raw material in weight.

The residue has no toxic substance in composition and may be returned to the field as manure or used as a construction material. The technology features a simple circuit with easy maneuverability. The raw material includes the straw and stem of 15 crop plants such as those withdrawn or processed from rice, wheat, soy bean, maize, peanut, sweet potato, oil-rich plants, wood bits, fruit shells etc. An initial analysis of the scale-up tests shows that the process is feasible viewed from an economic angle.

According to statistics, the waste discarded each year from farming practice and wood-processing industry in this country reaches 1.5 billion tons, including 720 million tons in the form of straw and stems. In addition, there is up to 100 million hectares of land which is unfavorable for grain and oil crops but could be used to grow fat-rich plants. This is a huge trove of biomass exploitable for reusable energy source. It not only can provide a new way for producing diesel, but also can mitigate the pollution caused by our farming production in the vast countryside.