|Ethylene and propylene the two basic olefin feedstocks are generally coproduced in steam crackers or in refineries. Typically, a steam cracker produces more of ethylene compared to propylene. Similarly, ethane based gas crackers predominantly produce ethylene. Only fluid catalytic cracking (FCC) can produce more of propylene compared to ethylene. The propylene production distribution in 2009 was 70% from steam cracking at 52 mln tons, 25% from FCC conversion at 19 mln tons and 5% from other methods (about 4 mln tpa).
Ethylene demand forecast for the next decade is 3% pa while propylene is forecast to grow at 4-5%, mainly due to its major derivative PP growing exceptionally well. Propylene and is expected to grow at more than 5% in the next decade. As per Chemsystems, ethylene consumption in 2009 was about 110 mln tpa. Additional ethylene required at 3% growth will be just about 3-3.5 MMT while additional propylene required at 4.5% growth would be just about the same. The present production distribution therefore cannot fulfill the increasing demand of propylene. The new massive crackers coming up in the Middle Eastern region are predominantly based on ethane rich gas. Hence the newer capacity additions will be unable to fulfill the additional demand of propylene. Therefore special investments are being made in other dedicated manufacturing processes for propylene. There are essentially two dedicated propylene manufacturing routes that are well known and established. They are:
• Propane dehydrogenation (PDH) and metathesis
• Methanol to propylene (MTP) technologies
PDH, which involves catalytic removal of hydrogen from propane to yield the olefins, is clearly the most important 'on-purpose' route now. A small amount is also produced by olefin metathesis, in the double bonds of olefins (say, C2 and C4 mixtures) are broken and different olefins (C3, in this case) are formed. An even smaller amount comes from cracking of C4/ C5 olefins, which technology is similar to metathesis in that low value hydrocarbon streams are converted to higher value olefins (however, their chemistry is a combination of olefin oligomerization, cracking, disproportionation and hydrogen transfer). MTO and MTP technologies are not yet commercial. There is increasing interest in these technologies, especially in China, which is looking to utilize its large coal reserves for chemicals production through methanol. The world's first MTO plant looks likely to be coming up at Shenhua in China in 2011. Both theses dedicated production routes are expensive. The cost economics therefore do not favour these alternate manufacturing processes. However, the increasing demand of propylene would compel the industry to consider PDH process. It seems that PDH manufacturing could increase in the near future particularly in the Middle Eastern region to meet the faster growing demand of PP.
As per ICIS, the two main sources of propylene are as a byproduct from the steam cracking of liquid feedstocks such as naphtha as well as LPGs, and from off-gases produced in fluid catalytic cracking (FCC) units in refineries. The remainder of propylene is produced using on-purpose technologies such as propane dehydrogenation (PDH) and metathesis. The primary source of propylene is from cracking naphtha and other liquids such as gas oil and condensates to produce ethylene. By altering the cracking severity and the feedstock slate, the propylene : ethylene ratio can vary from 0.4:1 to 0.75:1. Smaller amounts of propylene can be obtained from cracking propane and butane. The cracking of liquid feedstocks is carried out predominately in Europe and Asia but less so in the Middle East and North America. A growing source of propylene, particularly in the US, is from refineries where splitters recover the propylene from the off-gases produced by FCCs. However, refinery propylene needs to be purified for chemical and polymer use. New catalysts are now available that increase propylene output from the FCCs. With propylene demand growing faster than ethylene, combined with the building of more ethane crackers (which produce no propylene) rather than naphtha crackers, on-purpose technologies are being employed increasingly to make propylene. The main on-purpose process used is propane dehydrogenation (PDH) but it is only economically viable in cases where low-cost LPGs are available. Propane is converted to propylene at 500-700°C in a reactor containing a nobel metal catalyst. Although PDH technology is reasonably well established, the main criticisms of this route are relatively high capital costs and the need for a long-term, low-cost supply of propane such as available in the Middle East. New processes are being developed that claim to lower both capital and operating costs. Much effort is being put into increasing propylene output from liquid steam crackers and FCC units.
For example, the BASF-Fina cracker at Port Arthur, Texas, employs a metathesis unit to boost propylene output. Metathesis is the catalytic conversion of ethylene and butene-2 into propylene. However, these units need access to large C4 streams that are free of isobutylene and butadiene. The Superflex process, originally developed by Arco Chemical and licensed by Kellogg Brown & Root, converts light hydrocarbons in the C4 to C8 range into a propylene-rich stream. Deep catalytic cracking (DCC), developed by China's Sinopec and offered by Stone & Webster, produces light olefins from heavy vacuum gas oils and de-asphalted oils. ExxonMobil has developed an olefins interconversion (MOI) technology that uses the ZSM-5 zeolite catalyst to convert C4s, light pygas and light naphtha into propylene and ethylene using a fluidised bed. By contrast, Lurgi employs a fixed bed catalytic reactor that converts C4 and C5 olefins into propylene and ethylene. While the methanol-to-olefins (MTO) process is normally seen as a way of boosting ethylene output, the flexibility of the process allows for propylene production to increase to 45% of total output. Total in conjunction with UOP has further boosted propylene output by developing an olefin cracking process (OCP) which takes the heavier olefins from the MTO unit and converts them into lighter olefins, in particular propylene. The integrated MTO/OCP process, which is being tested in a pilot plant in Feluy,Belgium, produces significantly more propylene than ethylene. Lurgi is developing a process that converts methanol to propylene (MTP) and, in conjunction with Statoil, operates a pilot plant in Norway. The MTP process is expected to be used in China converting methanol produced from coal into propylene and in Trinidad where the methanol will ultimately be used to make polypropylene.
The UOP Oleflex™ Process for the catalytic dehydrogenation of propane provides a dedicated, reliable, independent source of high-quality propylene to give you more control over propylene feedstock costs. As the leading on-purpose polymer grade propylene production technology in the world, Oleflex provides the lowest cash cost of production and highest return on investment when compared to competing PDH processes via:
• Lowest operating cost enabled by low feedstock consumption and low energy usage
• Lowest capital cost enabled by the industry�s only continuous process and operation with a highly active and stable catalyst at positive pressure utilizing only 4 reactors.
• Highest reliability enabled by recent design enhancements and the ability to change catalyst on-the-fly without stopping propylene production.
The Oleflex process leverages industry leading UOP heat and mass transfer equipment, process equipment and control systems. Today there are nine C3 Oleflex units in operation, which is more than twice the number of operating units of the nearest competitor. The same proprietary design is used in the catalytic dehydrogenation of isobutane to isobutylene. The UOP Advanced MTO Process, which combines the UOP/Hydro MTO Methanol to Olefins Process with the UOP/Total Petrochemicals Olefin Cracking Process (OCP), converts cost advantaged alternative feedstocks such as coal, natural gas and petcoke to light olefins. The process offers a number of benefits:
• Lower light olefin cost of production than conventional routes
• The highest propylene and ethylene yields when compared to competing MTO technologies
• Minimal by-product formation
• A wide range of ethylene and propylene production
The Advanced MTO process has been fully demonstrated at the semi-commercial scale by Total Petrochemicals in Feluy, Belgium. To date, the site has successfully produced both polypropylene and polyethylene. In addition to its role upgrading C4+ by-product streams into propylene and ethylene in the Advanced MTO process, OCP can be used for by-product upgrading in steam crackers, FCC units and Delayed Cokers. The UOP Propylene Recovery Unit is the most economic method to separate propylene from propane. It brings together three proven technologies - UOP�s MD distillation trays, High Flux tubing and heat pump compressor system to produce chemical or polymer-grade propylene from refinery by-product streams. Multiple UOP-designed propylene recovery units are in operation around the world, and more than 170 propane-propylene splitters with MD trays are in operation or under construction today.
SK Corporation and KBR have developed a new and innovative catalytic cracking technology called the Advanced Catalytic Olefins (ACO) process to produce ethylene and propylene from predominantly paraffinic streams, such as straight run naphtha. This technology holds promise for replacing the conventional hot ends area of liquid crackers. Moreover, ACO can produce a propylene/ethylene ratio of about 1/1, thereby filling the regional propylene gap with a commonly available feedstock.
Steam crackers using feeds other than ethane generally also produce propylene as a byproduct (among other byproducts). Indeed, as the ethylene market grew, so did the propylene market. In recent years, the growth in propylene exceeded the growth in ethylene, opening up other technology opportunities focused primarily on propylene. These �propylene-on-purpose� technologies have and will fill a niche need in the propylene market. However, most of these technologies depend on the availability of certain niche feeds, which may not be generally be the case. As such, there is a need for a new technology that can address any propylene gap or shortage in the future, but with more commonly available feeds. This paper discusses the olefins market and trends, with an emphasis on propylene. It also covers briefly available technologies for �propylene-on-purpose�, but also addresses a new technology developed jointly by KBR and SK Corporation called the Advanced Catalytic Olefins (ACOTM) process. Unlike steam crackers which predominately make ethylene or �propylene-on-purpose� technologies which make propylene, the ACO process produces about equal amounts of ethylene and propylene.