In this article you are going to be presented to a propylene production process similar to Olefin Conversion Technology licensed by Lummus Technology.
Apart from a historical perspective of this process technology, operating plants, block flow diagram and process description you will have access to a detailed analysis of one of its process areas.
Extending the detailed analysis to the whole process we are able to evaluate its economic perfomance based on a historical chart which compares EBITDA margins and average chemical sector profitability.
Metathesis is a general term for a reversible reaction between two olefins, in which the double bonds are broken and then reformed to form new olefin products. In order to produce propylene by metathesis, a molecule of 2-butene and a molecule of ethylene are combined to form two molecules of propylene.
By the 1960s, Phillips Petroleum developed the first commercial process of olefin metathesis. The focus, at that time, was to convert propylene into ethylene and 2-butene. This technology was developed in an effort to increase ethylene and butene production from “low value” cracker-derived propylene to meet the growing market demand for polyethylene and polybutadiene.
The fact that metathesis is a reversible reaction, and that the demand for polymer grade (PG) propylene grew from the 1970s on, led to the use of the Phillips Triolefin process in a reverse way. This reverse process is known as Olefin Conversion Technology (OCT), and is now offered for license by Lummus Technology, a CB&I Company.
Click on the icons for further details on the plants presented. The map data is available for download at the bottom of the present page.
Note: This map is illustrative only. Location is not exact, It just indicates the city or province where the plant is located.
The raw materials for the production of propylene via metathesis reaction are ethylene and 2-butenes. Both components are mainly supplied from steam cracker units (olefins plants) or fluid catalytic cracking (FCC) units.
Steam cracker units are facilities in which a feedstock such as naphtha, liquefied petroleum gas (LPG), ethane, propane or butane is thermally cracked through the use of steam in a bank of pyrolysis furnaces to produce lighter hydrocarbons. The products obtained depend on the composition of the feed, the hydrocarbon-to-steam ratio, and on the cracking temperature and furnace residence time.
After the pyrolysis process, the olefins are separated from the other by-products by distillation.
Source: CB&I Lummus website, Intratec analysis
The process is separated into two different areas: the purification and reaction section; and the separation section.
Ethylene feed plus recycled ethylene are mixed with the butenes feed plus recycled butenes and heated prior to entering the fixed-bed metathesis reactor.
The catalyst promotes the reaction of ethylene and butane-2 to form propylene, and simultaneously isomerizes butene-1 to butene-2. A small amount of coke is formed on the catalyst, so the beds are periodically regenerated using nitrogen-diluted air. The ethylene-to-butene feed ratio to the reactor is controlled to minimize C5+ olefin by-products and maintain the per-pass butene conversion above 60%.
Typical butene conversions range between 60 to 75%, with about 90% selectivity to propylene.
The reactor product is cooled and fractionated to remove ethylene for recycle. A small portion of this recycle stream is purged to remove methane, ethane, and other light impurities from the process. The ethylene column bottom is fed to the propylene column where butenes are separated for recycle to the reactor, and some is purged to remove butanes, isobutylenes, and heavies from the process. The propylene column overhead is high-purity, PG propylene product.
This section will focus on describing in further details the separation area, providing a detailed flow diagram of the process area, its main streams material balance, the equipment list and utilities consumption, as well as a brief economic analysis. For a similar analysis on the complete process check the Propylene via Metathesis, one of Intratec's Publications.
This process area comprises the equipment used to purify the reactor stream in order to recover propylene and other byproducts.
This material balance presents the compositions and operating conditions for the main streams in the separation area.
In this section operational costs and the total fixed investment are calculated to evaluate the economic performance of the separation area. The economic analysis was based on the following assumptions:
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In this section the total fixed investment for the separation area is calculated. Direct costs are the total direct material and labor costs associated with the equipment (including installation bulks). Indirect costs are defined as the "costs which do not become a final part of the installation but which are required for the orderly completion of the installation."
Operational Expenditures are composed of two elements: a fixed and a variable cost. In this analysis only the variables costs associated to utilities production or consumption were considered.
The fixed cost assumptions Plant Overhead and General and Administrative (G and A) expenses were not considered since they can not be associated to a single process area.
Using a similar methodology as to that presented for the separation area, all other process areas were analysed so that the whole process could be evaluated. Comparing the process' EBITDA margins against Intratec's Profitability (IP) Index for the Chemical Sector it is possible to evaluate the economic performance of the technology under analysis.
This chemical process technology exhibited greater profitability than the average chemical sector profitability in different moments of the analysed years. Despite high fluctuations, the average EBITDA margins in the years 2008, 2009 and 2010 presented substantially increase in comparison to 2006 and 2007.