Membrane Separation Injects Vigor into Petrochemicals Quality Enhancement
Year:2019 ISSUE:10
Click:186    DateTime:May.22,2019

MIAC (Membrane Industry Association of China)

China’s membrane industry has achieved great progress over the past 20 years. Membrane technology has found major applications in water resources, energy, and technological transformation of traditional industries. The development of membrane technology has played a significant role in promoting progress in energy conservation, emission reduction, and transformation of traditional industries. 

Applications of gas membranes in the petrochemical industry

   Successfully developed in the 1970s, gas membrane separation technology is a new-generation gas separation technology. Of the various types of gas membranes, hydrogen membranes, organic vapor membranes, air-separation nitrogen-rich, oxygen-rich membranes, and carbon dioxide separation membranes are all used in the petrochemical field for resource recycling and utilization as well as for energy saving and emission reduction.   

   Hydrogen membranes have been used in China since the late 1980s, when the country introduced for the first time the whole-set of membrane devices to recover hydrogen from the tail gas during fertilizer production. At present, more than 100 sets of hydrogen recovery units are operated at oil refining, fertilizer and methanol plants. China’s crude runs are currently at around 604 million tons, equivalent to hydrogen consumption of 5X108 Nm3, and around 150X108 Nm3 tail gas can be recovered.   

   Organic vapor membranes are mainly used for organic gas recovery in oil refining, ethylene production, and natural gas processing, as well as emitted oil and gas recovery during storage and transportation, including ethylene, propylene, organic oil, and gas recovery, volatile organic chemicals (VOCs) treatment, etc. China has nearly 200 sets of propylene recovery units.   Membrane air separation nitrogen production (oxygen reduction) and oxygen-enriched energy-saving combustion find applications in oil and gas fields and refining and chemical enterprises. Air separation nitrogen production (oxygen reduction) in particular has bright prospects in applications for oil fields’ tertiary recovery, to enhance oil recovery. Carbon dioxide membranes are mainly used for the removal and enrichment of carbon dioxide in natural gas and associated gas. This application remains in the trial promotion stage.

Application of membrane technology in wastewater treatment in the petrochemical industry

   1. Application in refining and chemical industry

   Microfiltration, ultrafiltration, nanofiltration, reverse osmosis (RO) membranes, and electrodialysis membranes are widely used in wastewater treatment of refinery and chemical companies. The “dual membrane process”, which is microfiltration and ultrafiltration membranes in combination, finds major applications in deep treatment of wastewater. In 2014, Sinopec Yanshan Petrochemical used the “dual membrane process” for wastewater treatment, with handling capacity at 1 800Nm3/h. At present, hundreds of such membrane units are used to treat wastewater in China’s refining and chemical sector. 

   Key problems to solve: 

   (1) Promotion of domestically-made membranes

   The dual membrane processes, especially the RO membrane, are heavily reliant on imports. More domestically-made products shall be used, as the quality has been greatly improved and the technology for making ultrafiltration membranes has reached the world advanced level.  

    (2) Enhance membrane’s anti-polluting performance and service life; develop the applications of inorganic ceramic membranes

   Improving the anti-pollution performance and service life of membranes can reduce the costs of wastewater treatment. For instance, RO membrane can be used for pollution control caused by microorganisms. At present, refining and chemical enterprises are carefully studying the membrane’s pollution control problems. The inorganic ceramic membrane boasts the advantages of acid and alkali resistance, high temperature resistance, high flux, long service life, etc. Hence, it is recommended to make proactive research and development in the application of flat ceramic membranes and large diameter pollution-resistant ceramic membranes in wastewater treatment.

   (3) RO concentrated water not allowed to discharge

   China has banned the discharge of high-salt RO concentrate water because of environmental concerns, which has put forward higher requirements for membrane separation technology. It is necessary to actively develop zero emission technology of RO concentrate water and other high-salt wastewater.  

   2. Applications in oil and gas fields

   Many oil fields in China have entered their late-development stage, which requires a large amount of water injection for oil recovery. The annual output of water is about 1.4 billion tons, of which around 700 million tons are extracted from low-permeability oil fields. Ultrafiltration membrane filtration is adopted to meet the high standard requirements for low-permeability water re-injection (oil content<5mg/L, suspension <1mg/L, median particle size <1mg/L). In the early 21st century, China's oilfields began to test and promote the application of biological pre-treatment + organic tubular ultrafiltration membranes. At present, there are more than a dozen units under operation at low-permeability oilfields. Ceramic membranes have been developed in recent years. Large-diameter and pollution-resistant ceramic membranes have been promoted for application. The diameter of a single ceramic membrane is 142mm, with 800-1 200 channels, boasting large membrane flux, high efficiency, low cost and high temperature resistance. It is also resistant to acid and alkali, oil pollution and low energy consumption. It has good application prospects for the treatment of water extracted from low-permeability oilfields.

   After treatment, high-temperature (90℃ water extracted from heavy oil can be used for steam boiler hydration. However, the water extracted from heavy oil has high temperature, high salinity, high silicon content and contains oil and suspended solids. Hence, the traditional treatment process needs a long flow, large dosage, and high operation costs. At present, the pretreatment + ceramic membrane combination treatment process using electrochemical degreasing and silicon removal and suspension is under experimentation and will soon be widely applied in water extraction from heavy oil.  

   High-salt water extracted during natural gas exploitation is mainly reinjected into the stratum. It needs to be treated and reused or discharged in the long run. The membrane combination technology test has been carried out, and large numbers of ultrafiltration membranes and RO membranes will be required for the discharge of such wastewater after treatment.

Development and application of membrane technology in the petrochemical production process

   The application of membrane technology in petrochemical production processes can improve production efficiency and product quality, and can reduce energy consumption. Sinopec Baling Petrochemical Company adopts inorganic ceramic membranes to remove catalyst particles in the cyclohexanone amine hydration process so as to enhance its product quality. Henan Fang Zhou Ceramics Co., Ltd. uses large-diameter ceramic membranes for hydrogen filtration in coal tar production and diesel processing, catalyst recovery during the desulfurization process, and filtration of the residual catalyst in finished diesel products. The company has completed experimentation and is conducting on-site tests. The inorganic molecular sieve membrane technology of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has been applied in the dehydration of organics. In addition, pervaporation membranes (PV) and vapor permeable membranes (VP) are a new membrane technology for the separation of liquid (gas) mixtures. The technology displays an outstanding advantage in that it can realize separation such as distillation, extraction and absorption with low energy consumption, which is hard for traditional methods to accomplish. It is especially suitable for the separation of organic mixture solutions at near-boiling points and constant-boiling points and the removal of water in the mixture. The technology is currently being tested and used in the refining chemical production process.