Role of Catalytic Reformers and Steam Crackers on the Integration of Aromatic Streams
We have outlined how different olefins enhancement process supplement the gaps from steam crackers; however, some of these processes may have an impact on the overall yields of aromatics; therefore, it is important to consider the role of other sources of aromatics and their potential interfaces with steam crackers and alternative olefin technologies.
The FCC process is one of the main sources of olefins, but also it represents an important catalytic route for the reforming of naphthas, contributing in the supply of aromatics, which is supplemented by the aromatic production from the steam cracking. This is opposite to the production of the olefins where the steam cracker is the main source supplemented by other catalytic processes.
The reforming process involves the conversion of paraffins into iso-paraffins and naphthenes with further dehydrogenation to produce aromatic components. This is a well-developed and mature technology with several licensors available in the market like UOP with the CCR Platforming, Axens with the CCR Aromizing or a more recent incorporation from the Chinese Sinopec. But in general, all of them follow a similar process sequence based on a set of highly endothermic reactors operating at very low pressures with a considerable amount of hydrogen (yields close to ~5%).
Catalytic reforming units are a key piece for integration of different streams since these can receive feedstock directly from crude distillation units, or indirectly from hydrocracking or FCC (or FCC type) units processing heavy feedstocks such as vacuum gasoil or light cycle oil to produce heavy naphtha to reform into aromatics. This connection is critical and provides a great degree of flexibility allowing a more open integration scheme.
On the other hand, catalytic reforming units are also an important contributor of blend material to the gasoline pool; therefore, there is a competition between aromatic derivatives and high octane gasoline. One of the main differences in the operational modes is the need of removal of C6 components in the feed when gasoline is the preferred product, because this will yield to benzene that is an undesired component in the gasoline, while in aromatics mode, this requirement needs to be switched. Over the time, an increase and sustained demand of aromatics is expected; therefore, a transitional period is expected where the demand of fuels and aromatics will coexist pushing the design of catalytic reformers to provide enough flexibility to handle different operational modes imposed by the seasonal demand of fuels.
The pygas recovered from the steam crackers has a considerable amount of aromatics; however, it also comes with olefinic components and some amount of contaminants (i.e., sulfur and nitrogen). These need to be removed before the aromatics stream is sent to fractionation. These components are removed in a two-stage hydrotreating process.
Impact of New Developments in Technologies
Petrochemical and refining industries are based on very well-developed technologies; however, in order to respond to different limitations and external restrictions (i.e., environmental, commercial, etc.), there is still a continuous research in the field of new alternative processes, some of them more promising than others; but at some point, their incorporation as a commercial technology will have an impact (either negative or positive) on current integration schemes. Some of these potential technologies are summarized in this section.
The dehydrogenation of olefins has been explored extensively especially for the production of propylene as an option of on-purpose generation of this product. The main driver to explore this option is the fact of having substantial amount of natural gas available (and the corresponding associate liquids) as in the case of the USA where the abundance of shale gas makes ethane and propane attractive feedstocks to justify the use of these components to produce olefins. But the dehydrogenation reaction, similarly to the steam cracking, is an endothermic process and conducted over catalytic conditions; this process is very demanding in terms of energy, especially for ethane where temperatures over 800 °C are required.
However, the oxidative dehydrogenation is on the contrary an exothermic process that can be carried out at lower temperatures, with a considerable reduction to the energy consumption in the order of 30% compared to the energy required in the steam cracking process, and therefore would apply as an ideal candidate to improve the operational cost in the production of olefins. Also as a secondary advantage, the coking is substantially reduced due to the presence of oxygen which promotes its conversion into carbon dioxide, improving the on-stream times.
However, the use of oxygen in the process, has a negative effect in the production of carbon dioxide not only produced from de-coking but also from the reaction itself. Therefore carbon monoxide (instead of oxygen) has been proposed as oxidant introducing a double benefit, the carbon monoxide required in the process can be collected from the capture in another neighbor unit but also since the by-product is now carbon monoxide, it opens a potential integration with a syngas user in another facility (i.e., a hydrogen unit).
This technology is in early stages of development for ethane but available with some maturity in propane; nevertheless, the availability of ethane and propane from shale gas represents a great incentive to further explore this technology.
As described in Section 4.1, biomass represents an option for decarbonization and a potential alternative to replace fossil fuels; however, the incentives to implement these technologies are in a very early stage and at this point depend on the alignment of several conditions such as more stringent environmental restrictions, very high crude oil prices, and development of other alternative technologies (i.e., methanol to olefins or gasoline).
However, a considerable progress has been made to define the possible routes for its implementation; in general, four lines of development can be identified:
This route is focused on the production of syngas from biomass which can further be transformed into fuels through the Fischer-Tropsch process, or into methanol or ethanol using a catalytic process, and then, the alcohols can be converted into olefins by dehydration.
• Catalytic Pyrolysis
This option involves the hydro-deoxygenation of the biomass under catalytic conditions with further hydrotreating, and a successful example of this implementation was developed by the Gas Technology Institute now' in collaboration with Shell to produce fuels.
• Hydrogenation and Reforming
In this process, the target is to deoxygenate the feedstock by hydrogen enrichment wdth a subsequent reforming process in aqueous phase that produces fuels and aromatic components, and such process has been referred to in Section 4.1. The process has proved to achieve similar yields compared to the conventional catalytic reforming process to produce aromatics but wdth considerable lower cost of the feedstocks and a huge reduction in the carbon footprint. Hence, one of the main interested parties is the PET industry; therefore, in the long term if this process is successfully implemented in large scale, it may become a risk for the producers of paraxylene, especially if the demand of fuels is reduced over the following decades.
• Hydrolysis and Fermentation
Alternative routes have been explored aiming for the fermentation of the biomass feedstock to further produce alcohols with a specific number of carbon atoms which can be dehydrated to produce the corresponding olefines (i.e., ethanol, propanol, butanols, butanediols).
Dehydrocyclodimerization of LPG
This process is very well known and was designed for its implementation in regions where the availability of naphtha is limited for its conversion into aromatic products. This route achieves almost full conversion of the paraffins; therefore, the separation of reactor effluent is less challenging (i.e., no extractive distillation is required) and contributes to the generation of hydrogen with yields slightly higher than catalytic reforming. However, nowadays the main competitor of this technology is the generation of propylene from propane (i.e., PDH or steam cracking).
Shock Wave Pyrolysis
This is one of the most sophisticated methods to produce olefines, and the technology consists of a so-called shock wave reactor which uses a standing shock wave in a supersonic flow of steam to provide the required energy to achieve a temperature pulse tailored to maximize the yield of desired products. This alternative claimed to achieve higher yields of ethylene with a lower energetic consumption and a considerable reduction in coking compared to the conventional steam cracking; however, the steam consumption was up to ten times higher than the typical requirement in a steam cracker; therefore, no further development was attempted.
Methanol to Aromatics
This technology is an extension of the methanol to olefin process described in Chapter 2, where the olefins can further be transformed into aromatics using the same zeolite-based catalysts, and similar developments have been explored to produce gasoline from methanol; therefore, the improvements in catalysts to reduce coking and maximize the conversion can at some point be implemented for aromatic production. The commercial implementation of this alternative w'ould open the door for further developments with a positive environmental impact such as the biomass processes described above or even the destruction of carbon monoxide from another sources which can be transformed to methanol through a catalytic process using hydrogen also available from neighbor integrated facilities.
Capital Cost of Integrated Schemes
The capital expense (CapEx) of building or revamping integrated petrochemical- refining facilities will depend on the region, level of integration, and of course capacity of each specific unit. In order to understand the impact of each of these variables, the CapEx can be analyzed based on each of its components according to the following typical breakdown:
- • Direct cost materials
- • ISBL
- • Off-sites and utilities
- • Other infrastructure
- • Direct cost of labor
- • Indirect cost
- • Feasibility studies
- • Engineering design
- • Procurement
- • Project management
- • Permitting
- • Construction cost
- - Temporary facilities
- - Supervision and management staff
- - Construction equipment
- - Insurance and bonds
- • Commissioning cost
- • Contingency and escalation.
An important point to highlight related to infrastructure is the amount of capex required for the Outside Battery Limits (OSBL); in a typical refinery or petrochemical complex the capex required for the OSBL assets (i.e., storage, handling, utilities, buildings, etc.) can exceed more than 50%-60% of the total capex. This is one of the opportunities for an integrated system to provide value since the integration can have a positive impact (reduction of utilities requirements, shared handling facilities, etc.); however, the overall value will depend also on the location of existing infrastructure in relation to the main processing units (i.e., if the integration is proposed between two sites several miles apart this opportunity may lose some value).
The breakdown shown above includes several items related to indirect cost (i.e., preliminary studies, design, permitting, commissioning, etc.) that may represent a considerable fraction of the capex. This is of importance for an integrated facility, since a considerable amount of effort needs to be invested to ensure that the facilities are designed with enough flexibility to respond to two different market needs sometimes competing with, but sometimes complementing each other.
Another important variable to keep in consideration is the capacity of the proposed units, and most of technologies available are designed to work independently and to perform in competitive scale economy if as a result of an integrated optimization the conclusion is to require units with small capacities (i.e., if enough propylene can be recovered from crackers and FCC units, an on-purpose propylene unit may be needed but at a reduced capacity), such unit may not be able to work efficiently with a consequent impact on the operational cost (i.e., shorter runs between catalyst regeneration for fixed bed processes).
In terms of location, there is no single answer to the impact on capital cost. Normally, these facilities are located in industrial hubs with access to both crude and natural gas pipelines as well as import/export facilities. However, not all these hubs around the world have the same availability of skilled personnel and equipment manufacturing facilities. Therefore, both direct and indirect cost will be completely different for an exact same scheme in the Gulf Coast compared to the West Coast or South Asia, and the impact is so high that interconnection of streams even in long distance may be preferred rather than building an asset in an unfavorable location.
Finally, an important element to consider is the risk, and these schemes may be considered as new developments form the commercial point of view and will require a deep analysis to support a strategy decision at different stages of the project from their construction, commissioning, and operation. Therefore, an increased contingency cost or at least the imposition of several conditions (shorter recovery times, higher insurance costs, etc.) either to execute or to finance the projects may disincen- tivize these investments to approve their implementation.