1. Introduction

1.1 Technical background

Waste oil, including waste cooking oil, expired edible oil, acid oil and inedible adipose, is a kind of oil resource generated in edible oil or meat production and consumption. These waste oils may cause serious environmental problems if they are improperly disposed. The SRCA biodiesel process developed by SINOPEC is applicable to a wide range of feedstocks including crude plant oil, refined oil, animal fat and waste oil, and especially suitable for waste oil with high acid value. When the biodiesel produced from waste oil via SRCA process is used in diesel vehicle, the emission will be greatly improved, especially for particulate emission.

1.2 Process flow

The SRCA biodiesel process includes:

Storage and handling system: consisting of storage, transportation and loading facilities for feedstocks (oil and methanol), products (biodiesel and glycerin) and fuel oil; all storage tanks are accompanied with protective nitrogen pipe and hot water heating pipe.

Reaction system: reaction materials (oil and methanol) are mixed, pressurized and heated, and then react in the reactor. The crude products obtained will be treated in the refining system.

Methyl ester refining system: consisting of methanol recover and recycle units, glycerin separation unit, light component removal unit and vacuum distillation unit. The biodiesel product is obtained in this system and the separated glycerin will be sent to glycerin refining system.

Glycerin refining system: methanol in glycerin is separated and glycerin is concentrated via triple-effect evaporation to obtain crude glycerin product.

Utilities system: including the facilities used for tail gas treatment, returned liquid storage, the high temperature heat conducting oil circulation, hot water circulation, compressed air supplying and nitrogen supplying.

1.3 The main process parameters

2.Characteristics and features of SRCA process

2.1 Technical characteristics

Technical features of SRCA biodiesel process are as follows：

（1）The reaction of free fatty acid with methanol, namely esterification, and the reaction of triglyceride with methanol, namely transesterification, occur simultaneously at high conversion rate when the oil react with sub/supercritical methanol. The yield of biodiesel product for SRCA is not less than 95%.

（2）SRCA process shows good adaptability of feed oil materials. It is not necessary to reduce the free fatty acid content and oil soluble unsaponifiable impurities of raw material before used. All kinds of feed oil materials can be used in SRCA process on condition that the solid impurity is separated.

（3）The super separation technology is adopted to ensure the quality of biodiesel product by separating product from heavy components such as oil soluble unsaponifiable impurities, et al. The separated heavy components can be used as fuel oil.

（4）No catalyst is used in SRCA process. It is not only helpful to reduce auxiliary chemicals but also helpful to avoid equipment corrosion and waste discharges caused by acid & base catalyst. The SRCA biodiesel process is, therefore, a clean process.

（5）Besides biodiesel, SRCA unit can also produce feedstock for high value-added fine chemicals and the turndown ratio typically is 70%~110%.

2.2  Performance

Biodiesel product meeting the following specification or other country or region’s product specifications can be produced by SRCA process.

2.3  Operation run length of SRCA unit is not less than one year.

3.Industrial applications of SRCA process

One commercial unit with a biodiesel production capacity of 60kta was constructed and put into operation in 2009 and the feedstock includes mainly waste cooking oil and palm acid oil.