Economic propane dehydrogenation

Table 10.6 Economics of Propylene Production by Propane Dehydrogenation...

Steam cracker plants based on naphtha and/or gas-oil feedstocks are the major source of locally produced propylene in Europe and the Far East. In the United States approximately 90% of propylene comes from steam crackers and refinery operations. The balance comes from catalytic dehydrogenation units. The growth rate of propylene use is expected to be 3—4% worldwide. With the more conventional sources of propylene such as steam cracker operations and refinery operations, it is not possible to supply sufficient propylene for this growing demand. However, at the price levels of mid 1993 the economics of propane dehydrogenation are not very attractive. 

On behalf of KTI an experimental programme on these reactor concepts has been started at the University of Southern California (USC). Some of the experimental results, concerning the use of Knudsen diffusion membranes are available in the literature [32,40]. These data have been used to calculate the economics of an isothermal propane dehydrogenation membrane reactor concept and are compared with the commercial Oleflex and Catofin processes, based on an adiabatic concept. The experimental circumstances of these lab-scale experiments, especially residence time, pressures and gas composition are not the same as in commercial, large-scale processes. However, we do not expect these differences to have a great influence on the results of the work presented here. 

A sensitivity analysis of the ROI on both the feed costs and the product values is performed. For the Oleflex and CMRH case these results are siraima-rised in Figs. 14.6 and 14.7 which indicate that the ROI of such a propane dehydrogenation unit is not attractive when the price difference between propane and propylene is less than about 250-300 /tonne. At mid 1993, price levels of 330 /tonne propylene and 130 /tonne propane, the process is not economically viable. Historical price levels show that a price difference of 300... 

Application of ceramic membranes can improve the return on investment in the propane dehydrogenation process. Probably the only possibility for a technically and economically feasible propane dehydrogenation process, able to enhance the ROI enough to make the investment worthwhile, is the combination of a high driving force (sweep gas or low permeate pressure) and a very high selective membrane. The isothermal reactor concept shows better prospects than the adiabatic concept. At a price difference smaller than 300 /tonne between propylene and propane the propane dehydrogenation process based upon membranes will hardly be economically viable. 

Propylene demand will grow to the 11-billion lb level by 1973. Propylene from either heavier ethylene feed stocks or European imports will not alleviate the shortage completely. On the other handy it is not expected that price will exceed 3.1 cents/lb. In spite of decreasing propylene availability, refiners will consider release of alkylate stocks at this level. Development of an economic process for direct propylene production is in the future. Dehydrogenation or iodinative partial oxidation processes for propylene from propane are neither commercially proved nor have they been demonstrated to have economic promise. Dehydrogenation in the presence of sulfur may bypass propane dehydrogenation equilibrium limits, and preliminary experimental data are presented. 

The author thanks the Esso Research and Engineering Corp. for their support of propane dehydrogenation experimentation at Worcester Polytechnic Institute. The isobutane cracking study was funded by Chem Systems, Inc. the assistance and expertise obtained from Bronek Dutkiewicz, Bert Struth, and Martin Sherwin of Chem Systems and from John Johns on technical and economic points is deeply appreciated. 

Direct propane dehydrogenation is the most economical route to propylene, but the process is very complex. However, performing this reaction on a MSR offers the possibility to reach a propylene selectivity of 73-95%, with conversions between 31 and 24% (over calcium hydroxyapatite or Pt-Sn/Al-SAPO-34 catalyst, at 590 °C, respectively) [30,31]. On the other hand, Karinen et al. [32] performed the dehydrogenation of isobutane to isobutene over a chromia/alumina catalyst in a sandwich-type structured microreactor, at 570 °C under atmospheric pressure, showing good results despite its high endothermicity. 

Over Pt-based catalyst, coking and consequential deactivation of the catalyst during propane dehydrogenation is a well-known phenomenon (Webb et al., 1994). Regeneration of the catalyst is always needed, which lowers the process productivity and economics. In this section, the efforts about the modeling of coking reaction and deactivation behavior are reviewed. 

Zhu YC The technical and economic analysis of propane dehydrogenation to propylene (Chinese), Petrol Petrochem Today 20(8) 36—42, 2012. 

Dehydrogenation. The dehydrogenation of paraffins is equihbrium-limited and hence requites high temperatures. Using this approach and conventional separation methods, both Houdry and UOP have commercialized the dehydrogenation of propane to propylene (92). A similar concept is possible for ethane dehydrogenation, but an economically attractive commercial reactor has not been built. 

Methanol dehydrogenation to ethylene and propylene. In some remote ioca-tions, transportation costs become very important. Moving ethane is almost out of the question. Hauling propane for feed or ethylene itself in pressurized or supercooled vessels is expensive. Moving naphtha or gas oil as feed requires that an expensive olefins plant with unwanted by-products be built. So what s a company to do if they need an olefins-based industry at a remote site One solution that has been commercialized is the dehydrogenation of methanol to ethylene and propylene. While it may seem like paddling upstream, the transportation costs to get the feeds to the remote sites plus the capital costs of the plant make the economics of ethylene and its derivatives okay. 

Processes based on propane ammoxidation to manufacture acrylonitrile have also been developed,915 966 and BP has announced commercialization.966 Dehydrogenation at high reaction temperature (485-520°C), which is about 100°C higher than for propylene ammoxidation, results in the formation of propylene, which subsequently undergoes normal ammoxidation. Despite higher investments and the markedly lower selectivity (30-40%), the process can be economical because of the price difference between propylene and propane.966 Better selectivites can be achieved at lower (40-60%) conversions. 

Propylene is also obtained by dehydrogenating propane, which could open up a new product stream for the Middle East. Again, this technology needs to be improved before the process economics are competitive with recovery from steam crackers or refineries. 

The basis of the economic evaluation is the comparison of operating and investment costs for a membrane reactor with those for a conventional dehydrogenation plant. The return on investment (ROI) and the propylene production costs of the different processes have been calculated. The results are summarised in Table 14.6. Details of the calculations are reported in Ref. [33]. In the calculations a propane price of 130 /tonne and a propylene price of 330 /tonne has been assumed [33]. 

Propane and propylene prices are the main actors in the introduction of a dehydrogenation process in general, thus also for processes based upon membrane reactors. At a price difference (propylene-propane) of 300 /tonne or less membrane based dehydrogenation processes will hardly be economic feasible. 

Technical and economic evaluation study for the use of ceramic membrane reactors for the dehydrogenation of propane to propylene. Confidential NOVEM Report No. 33105/0090, by KTl, ECN and HlC, Jan. 1994. 

The world propylene production capacity based on the use of catalytic dehydrogenation of propane has increased steadily over the past lOyr and is expected to grow even further under the right economic conditions relative to the availability and pricing of pro-pane. On the other hand, environmental concerns on the use of methyl-/ r/-butyl ether (MTBE), an oxygenated gasoline additive, are expected to adversely impact the future expansion of isobutane dehydrogenation applications. 

They also evaluated isothermal MR concepts and compared them in performance with the adiabatic Catofin and Oleflex processes. They studied two different type processes using Knudsen diffusion membranes a process called CMRL, patterned after the commercial Oleflex process, with low propane conversion, and a process called CMRH, patterned after the commercial Catofin process with high propane conversion. They have calculated the return on investment (ROI) for all four processes. Though marginally better than the commercial processes, the ROI for all four processes evaluated is not very attractive. A sensitivity analysis indicates that for the ROI of the MR processes to be attractive a price difference between propane and propylene of more that 300/ton is required. Though published calculations have only been performed for the propane/propylene pair, it is not unreasonable to assume that similar conclusions apply to other alkane/alkene pairs. Similar conclusions about catalytic alkane dehydrogenation have also been reached in a technical/economic evaluation study by Amoco workers and their academic collaborators (Ward et al [6.3 ]). 

When one contemplates the shortage of propylene and the availability of propane, it is natural to postulate whether catalytic dehydrogenation of propane rather than pyrolysis of propane would be an inherently economic process. Unwanted side reactions are minimized in catalytic processes, and the reaction ... 

With respect to the catalytic reactions, there are well-established industrial reactions (as occurs in the case of n-butane to maleic anhydride), reactions in the preindustrial stage (such as the transformation of propane to acrylonitrile), very promising reactions (such as ethane oxidative dehydrogenation to ethylene), and potential reactions whose economical viability will depend on the prices of crude and natural gas in the future (such as propane selective oxidation to acrylic acid or methane transformation). 

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