I. Introduction

1. Background

Propylene oxide (PO) is an important derivative of propylene and one of the 50 chemicals with the largest consumption in globe, which is mainly used to produce polyether, propylene glycol, widely applied in automobile, construction, food, medicine, cosmetics and other industries. Nearly 100 kinds of downstream products have been produced, in addition PO can also react with CO2 to produce polycarbonate and degradable plastics, which is of great significance for carbon emission reduction and carbon neutralization. China's consumption in 2020 is around 3.38 million tons, accounting for 34% of the global PO consumption, with a total growth rate of 814% from 2001 to 2020. In 2020, China also imports about 500 kilo-tons of PO and more than 1 million tons of PO downstream products.

SINOPEC has successfully developed a complete set of propylene hydrogen peroxide (HPPO) production technology with independent intellectual property rights. Using fixed bed reactor, hydrogen peroxide reacts with propylene to produce propylene oxide under the effect of surface silicon rich hollow titanium silicon molecular sieve under mild conditions, with water as sole side-product, and then propylene oxide product is obtained via separation and purification. The excess propylene is treated and recycled, the solvent methanol is recycled, and the waste water is recovered and discharged after treatment. Therefore, this process is quite clean and environment-friendly.

2. Process scheme

HPPO process is mainly divided into propylene epoxidation reaction unit, separation and the purification units of PO, and the refining, separation and recycling units of solvent methanol, the deoxygenation and impurity removal of excess propylene and the abstraction units of alcohols and ethers from effluent wastewater, as shown in Figure 1. The raw material propylene, hydrogen peroxide, solvent methanol and additives are mixed and injected to the fixed bed reactor, which is full of surface silicon rich hollow titanium silica molecular sieve based catalyst, under mild conditions and at a temperature of 30~60℃, with the formation of PO. The reaction equation is shown in Figure 2. After the separation of residual propylene, solvent methanol and water by distillation towers, the raw product is sent to the refining unit to obtain final PO product through combining extraction distillation and chemical impurity removal treatments. The aqueous solution of solvent methanol enters the refining unit, where oxides such as aldehydes and ketones are converted to easily separated components, and methanol is sent back to the reactor for reuse after separation and purification. The organic subtracts, including alcohols and ethers, are separated from wastewater, and the treated wastewater up to standard are discharged. Propylene is sent back to the reactor for recycling after removing oxygen, propane and other impurities.

3. Reaction conditions

•Reaction temperature: 30~60℃

•Reaction pressure: around 2 MPaG

II. Technology characteristics

1. Process feature

•Surface silicon rich hollow titanium silicate zeolite based HPO-1 epoxidation catalyst is of high activity, high conversion, high product selectivity, excellent stability and long life-time.

•The reaction takes place under mild reaction conditions, at 30-60 oC, with high yield of propylene oxide and low material consumption. The purity of propylene oxide product exceeds the national standard. It is used to produce high value-added polyurethane with good color and slight odor.

•The reaction process is optimized, the methanol double-effect distillation and heat integration technology is adopted, the heat energy is fully utilized, and hence the comprehensive energy consumption is very low.

•High quality of propylene oxide is obtained via the integration of low temperature separation, chemical impurity removal and extractive distillation technology.

•The device is operated easily, with stable reaction control and the long-term operation.

•The catalyst and reaction materials are totally incorrosive.

•The deactivated catalyst can be fully recovered via In-situ regeneration process, without using any special equipment.

•The process design ensures intrinsic safety in whole process.

•The production process is clean and environment-friendly, with less wastewater generation.

2. Feedstock adaptibility

This process can use propylene produced by catalytic cracking, steam cracking, coal to olefin, methanol to olefin and propane dehydrogenation, thus it is convenient to combine with the above processes.

3. Performance and economics

•Hydrogen peroxide conversion ≥98%

•PO selectivity ≥97%

The quality of PO product of HPPO process is listed in Table.1. It is obvious that the quality of PO product at SINOPEC is much better than that of premium grade PO of Chinese national standard (GB_T 14491-2015).

Table.1 Product quality of PO from HPPO process at SINOPEC

4. Running cycle

The single operation cycle of HPPO process is 3~4 years.

III. HPPO catalysts

Using surface silicon rich hollow titanium silicate molecular sieve as the active component, the low binder molding catalyst was developed. The catalyst shows high activity, good selectivity and long lifetime.

IV. Commercial Experience

Using the complete set of HPPO technology of SINOPEC, the first 100 kt/a industrial HPPO plant with independent intellectual property rights in China has been built, with smooth operation stability and remarkable economic and social benefits. The 300 kt/a process package design has been completed and it is currently under technology licensing.