HF Alkylation and NExOCTANE Tech for Gasoline Production

HF Alkylation & NExOCTANE Technology

Table of Contents

1. Abstract……………………………………………………………………………………...1 1.1. Objectives

2. Gasoline Market Assessment…………………………………………………………….2 2.1. Gasoline Price Volatility and Elasticity of Demand for Gasoline

3. Literature Survey…………………………………………………………………………..5 3.1. HF composition for Alkylation 3.2. Evolution of a More Reliable Gasket for HF Alkylation Units 3.3. New process analysis tool for HF alkylation 3.4. Block Flow Diagram for HF Alkylation 3.5. Solid Acid Catalyst Alkylation Technology

4. Introduction to Alkylation………………………………………………………………….7 4.1. Alkylation Reaction

4.1.1. Alkylation using Sulphuric Acid as a Catalyst 4.1.2. Alkylation using Hydrofluoric Acid as a Catalyst

5. HF Alkylation……………………………………………………………………………….8 5.1. Introduction 5.2. Background 5.3. Significance 5.4. Process Chemistry 5.5. Alkylation Feed Stocks 5.6. Process Description………………………………………………………………….13 5.7. Process Variables 5.8. Alkylation Products

6. NExOCTANE Technology for Isooctane Production………………………………….18 6.1. Introduction to MTBE 6.2. Introduction to NExOCTANE 6.3. Process Chemistry 6.4. Cost-Effective Technology 6.5. NExOCTANE Process Description…………………………………………………21

7. Environmental Considerations…………………………………………………………..22 7.1. Effluent Treatment 7.2. Effluent Gases 7.3. Liquid Effluents 7.4. Solid Effluents

8. Safety Issues in Alkylation Units………………………………………………………...24 9. Modifications & Recommendations……………………………………………………..24

9.1. Aerosol Potential 9.2. Mitigation 9.3. HF Modifiers

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9.4. Advances in HF Alkylation Technology 10. Distillation Column P&ID………………………………………………………………..26

10.1. P&ID Description 11. Conclusions………………………………………………………………………………33 12. References………………………………………………………………………………..34

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List of Figures and Tables

FIGURE 2.2: Gasoline Production and Consumption in Pakistan

FIGURE 2.3: Gasoline Production and Consumption Worldwide

FIGURE 2.4: Pakistan Gasoline Imports by Year

FIGURE 2.5: Pakistan Gasoline Exports by Year

FIGURE 2.6: Pakistan Crude Oil Reserves

FIGURE 3.4: Block Flow Diagram for HF Alkylation

TABLE 3.1: Features of Solid Acid Catalyst Alkylation Technology

FIGURE 5.4.1: HF alkylation primary reactions

FIGURE 5.4.2: Initiation reactions

FIGURE 5.4.3: Propagation reactions

FIGURE 5.4.4: Isomerization

FIGURE 5.4.5: Other reactions

TABLE 5.5.1: Compositions of Alkylate from Pure-Olefin Feed stocks

FIGURE 5.6.1: Process Flow Diagram C4 of HF Alkylation Process with NExOCTANE

TABLE 5.7.1: Range of Operating Variables in HF Alkylation

TABLE 5.8.1: HF Alkylate Properties

FIGURE 6.3.1: Dimerization Reaction

FIGURE 6.3.2: Hydrogenation

FIGURE 6.5.1: Integration OF NExOCTANE in a Refinery

TABLE 6.5.2: Typical Utility Requirements

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1. Abstract:

In today’s world, the demand of gasoline is increasing day by day due to increase in the number of auto-mobiles on the roads. The gasoline obtained by the crude distillation is not enough to meet the current worldwide demand. So there is a need of a method so that the less useful products of crude distillation can be converted to gasoline in the refinery. Keeping in view the world’s gasoline demand alkylation process units were primarily introduced by UOP and Philips. The alkylation process uses the almost worthless olefins as raw materials from FCC (fluid catalytic cracking) units in the refinery and converts them into the much more useful and valuable products like gasoline and LPG. The emergence of catalytic reforming techniques gave a vital tool for the production of high-quality gasoline but the motor fuel produced in these operations is mainly aromatic based and is characterized by its high sensitivity. The production of low sensitivity gasoline components was required. A consequence of all these requirements was the expansion of these alkylation operations.

Furthermore, the phase-out of MTBE (Methyl-ter-butyl-ether) which is used as an anti-knock agent and oxygenate in gasoline (due to water pollution) has rendered the already existing MTBE processing units useless. Hence, a suitable process is required that can replace the MTBE and can give high octane number products. Isooctane has been recognized essentially as a cost-effective alternative to MTBE [7]. It utilizes same isobutylene feed that was used in MTBE production and it offers excellent blending value and production of isooctane can be obtained in a low-cost renovation of an existing plant of MTBE.

The NExOCTANE technology was developed for the isooctane production. This technology is cost effective and also replaces MTBE effectively. NExOCTANE process can be combined with HF Alkylation process to produce high quality gasoline which is free from MTBE.

1.1 Objective:

The aim of this report is to combine the Alkylation process and NExOCTANE technology to produce high octane gasoline which is free from environment threatening MTBE and is also cost-effective. Both Alkylation and NExOCTANE processes are explained in detail in this report along with modifications which would enhance the safety of the Alkylation process.

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2. Gasoline Market Assessment: Factors affecting gasoline retail price: The cost for the production, transportation, and selling gasoline to consumers includes:

Crude oil cost Refining costs and profits Distribution and marketing costs and profits Taxes

2.1 Gasoline Price Volatility and Elasticity of Demand for Gasoline: The volatility in Gasoline price impacts on consumers' price elasticity of gasoline demand. Results displayed that prices volatility decreases consumer demand for the gasoline in intermediate run. It is found that consumers seem to be less elastic in response to variations in gasoline price when gasoline price volatility is either medium or high, in contrast to when it is low. Likewise, it was found that when variance in econometric model is controlled, the gasoline price elasticity of demand is lesser in magnitude in the long run [1]. 2.2 Gasoline Production and Consumption in Pakistan:

Source: Ref 2

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HF Alkylation & NExOCTANE Technology 2.3 Gasoline Production and Consumption Worldwide:

Source: Ref 2

2.4 Pakistan Gasoline Imports by Year:

Source: Ref 2

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HF Alkylation & NExOCTANE Technology 2.5 Pakistan Gasoline Exports by Year

Source: Ref 2 2.6 Pakistan Crude Oil Reserves:

Source: Ref 2 2.7 Latest gasoline products prices in Pakistan [2]:

• Unleaded Premium PKR 116.74/L • Unleaded-Hi Octane PKR 137.72/L • E10 Gasoline PKR 110.26/L

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3. Literature Survey:

3.1 HF composition for Alkylation:

There is a requirement for safe means for storing and distributing hydrofluoric acid when it is used in alkylation as a catalyst. In this development, acid is absorbed in co-polymer of a polyacrylamide and a polyacrylate which is semi-solid or solid.

3.2 Evolution of a More Reliable Gasket for HF Alkylation Units:

The need to reduce flange face corrosion, overcome handling issues and enhance sealing performance has directed to the development of a new kind of gasket for using in Hydrofluoric (HF) Alkylation Units to substitute the standard spiral-wound type. Now, carbon steel flange face can be secured from aggressive HF acid corrosion and resulting scaling of iron fluoride, complemented by an increase in the reliability and fsealability of flange joints [13]. The advantages include a decrease in costly flange damage, possible leakage and the related unit shutdowns required for repairs. This particular feature highlights the stages in the growth of the new gasket design

3.3 New process analysis tool for HF alkylation: ABB Process Fourier Transform Infrared Analyzer for Hydrofluoric Acid Alkylation Process Unit Optimization mutually developed with ConocoPhillips [3], aids petroleum refineries to operate HF alkylation units more safely and efficiently, while making an important contribution to the operational and the environmental risk mitigation [14].

3.4 Block Flow Diagram for HF Alkylation:

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HF Alkylation & NExOCTANE Technology 3.5 Solid Acid Catalyst Alkylation Technology: Neste Oil, Lummus Technology and Albemarle Catalysts have established and demonstrated an alkylation technology that is now being offered for license. AlkyClean process employs robust zeolite catalyst formulation that is coupled with a novel reactor processing system to yield a product of high quality alkylates. Total installation cost of the facility is appreciably lower than the current liquid-acid processes. With no presence of chlorides or liquid acids in the system, no treatment of product or disposal of chlorides or acids is required. Lack of corrosive acids in system and mild operating conditions allow for the carbon steel construction of the equipments.

TABLE 3.1: Features of Solid Acid Catalyst Alkylation Technology Process Features Process benefits

Robust, true-solid-acid catalyst

• Eliminates corrosive liquid acid use and associated safety concerns.

• Tolerant to feedstock impurities, changes in feedstockolefin composition, and process upsets (e.g., water spikes)

Removes safety risks associated with liquid acids

• Lower maintenance and monitoring requirements, • Eliminates costs associated with mitigation (acid dump and

water spray systems), disposal of acids or chlorides, and vapor suppression additives

Low pressure, liquid phase operation in the temperature range of 50°C-90°C

• Eliminates costly refrigeration requirements associated with H2SO4 units.

• Carbon steel construction material results in lower costs.

Does not produce acid soluble oil by-product

• Improves alkylate yield. • No by-product disposal requirement.

No emissions to air, water, or ground

• Environmentally friendly process.

Source: Ref 5

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4. Introduction to Alkylation:

In petroleum refining industry the term alkylation is used for the reaction of an isoparaffin with lower molecular weight olefins to produce higher molecular weight isoparaffins [5].

The alkylation process that is of commercial importance involves low temperature for alkylation performed in the presence of hydrofluoric acid or either sulphuric acid.

4.1 Alkylation Reaction:

In the process of alkylation by using sulphuric acid or hydrofluoric acid as catalysts olefins react with only isoparaffines such as isopentane or isobutane (having tertiary carbon atoms).Commercially only isobutane is used because isopentane has high octane number and its vapor pressure is low.

The two processes used for alkyation are:

1. Alkylation using Sulphuric Acid as a catalyst 2. Alkylation using Hydroflouric Acid as a catalyst

4.1.1 Alkylation using Sulphuric Acid as a Catalyst:

• This process does not require additional equipment as needed in the case of hydrofluoric acid process for the recovery and neutralization of the hydrofluoric acid in different streams.

• Drying is advantageous but not necessary in sulphuric acid process. Free water that drops out of the chilled feed is removed by only feed coalesces.

• Safety and maintenance cost is less in comparison to hydrofluoric acid process. • Self-alkylation occurs at lesser extent in this process. • Less harmful for the environment.

4.1.2 Alkylation using Hydrofluoric Acid as a Catalyst:

• Less capital and total operating costs in comparison to sulphuric acid process. • Instead of refrigeration cooling water can be used. • For emulsions smaller settling devices are required. • Reactor designs are smaller and feasible. • Hydrofluoric acid is completely regenerated. • Disposal of spent acid is not necessarily required. • Less turbulence and agitation is required. • Operation is more flexible relative to external ratio of isobutene to olefin,

temperature, etc.

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5. HF Alkylation

5.1 Introduction:

HF Alkylation process for the production of motor fuel catalytically combines isobutane with light olefins, which are the mixtures of butylenes and propylenes to form a branched-chain paraffinic fuel. The alkylation reaction is carried out in the presence of Hydrofluoric acid under specific conditions which are selected to maximize yield and quality of alkylate. The alkylate product has excellent antiknocking properties and has high-octane because of high percentage of highly branched paraffins. Alkylate is a low sulphur, clean-burning, low RVP gasoline blending component and it does not have aromatic or compounds.

5.2 Background:

In the mid of 1950s, the development and acceptance of more-sophisticated and high-performance automotive engines placed a stress on the petroleum refiner in order to increase both gasoline production and to improve the quality of motor fuel. The emergence of catalytic reforming techniques gave a vital tool for the production of high-quality gasoline [7]. However, the motor fuel which is produced in these operations is mainly aromatic based and is characterized by its high sensitivity (that is, the spread between motor and research octane number). Due to the fact that automobile performance is more closely and completely related to road, rating of octane (approximately the average of motor and research octanes), the production of low sensitivity gasoline components was required. A consequence of all these requirements was the expansion of these alkylation operations. Refiners started broadening the olefin feeds range to both new and existing alkylation units to involve propylene and occasionally butylenes as well as amylenes. In the beginning of 1960s, the HF Alkylation process had virtually replaced motor fuel polymerization units for the new installations of plants.

HF Alkylation process has got more importance in the refining situation of the 2000s. Its importance is further increased due to the phase-out of MTBE and the increased emphasis on the low-sulfur gasoline. The alkylation process is critically important in the quality motor fuels production including many environmental gasoline blends. The process facilitates refiners with a handy tool of unmatched economy and good efficiency, one that will help refiners in strengthening and maintaining their position and status in the gasoline production and marketing. 5.3 Significance:

The HF alkylation process is of vital importance to the present day. It plays a very important role in production one of the most essential feeds to the final gasoline blend.

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HF Alkylation & NExOCTANE Technology With the increase in number of fluid catalytic cracking (FCC) units used in refineries its significance has increased [23].

The FCC is used to add value to the heavy products produced in crude distillation. In FCC heavy feeds are catalytically cracked into lighter products such as FCC gasoline and light cycle oil, which can either be used after hydrotreating or directly in final gasoline blending operations. The drawback of this FFC is that light olefins, like butene and propene, are produced in FCC operations. These are products basically worthless as feedstock. In the same way, in any crude distillation a large amount of light end products like butane can be produced that has very limited use. Normal-butane can easily be transformed into iso-butane, and in iso-butane form it can joins the C3 or C4 olefins (butene or propene) produced by FCC as the joint feeds to the HF alkylation process [23].

The HF alkylation performs the critical role of improvement of these byproducts to high-value product (alkylate), which is then used as a component of gasoline blending. This task of utilizing the C4 olefins produced from the FCC and the C4 iso-alkanes produced from the distillation of crude oil and changing them, through the process of catalytic HF alkylation (an altered Friedel-Crafts reaction), into iso-octanes, continues to has major importance in refining of petroleum.

5.4 Process Chemistry:

General: In this process of HF Alkylation, HF acid is the catalyst that stimulates the isoparaffin-olefin reaction. In this process, olefins react with only isoparaffins having tertiary carbon atoms, such as isopentane or isobutane. In practice, only isobutane is used due of the fact that isopentane has a high octane number and it also has a vapor pressure that has historically permitted it to be blended directly into the finished gasolines. However, where the environmental regulations have reduced the allowed gasoline vapor pressure, isopentane is being removed from the gasoline, and refiner concern in alkylation of this material with light olefins, particularly propylene, is increasing. The real reactions occuring in the alkylation reactor are several and are comparatively complex. In practice, the main product from a single olefin contains only a fraction of alkylate because of the number of concurrent reactions that are probable in the alkylation environment. Reaction Mechanism:

Alkylation is one of the definitive examples of a reaction or reactions continuing via carbenium ion mechanism. These reactions comprises of an initiation step followed by a propagation step and may comprise of an isomerization step. In addition, polymerization step and cracking steps may also be involved. Though, these side reactions are commonly not desirable. HF alkylation primary reactions are shown in Fig 5.4.1.

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HF Alkylation & NExOCTANE Technology Initiation: The initiation step produces the tertiary butyl cations that will then carry on the alkylation reaction. This step is shown in Fig 5.4.2. Propagation: Propagation reactions include the tertiary butyl cation reacting with olefin to form larger carbenium ion, which then extracts a hydride from the molecule of isobutane. The hydride extraction produces the isoparaffin along with a new tertiary butyl cation for carrying on the reaction chain. This step is shown in Fig 5.4.3.

FIGURE 5.4.1: HF alkylation primary reactions

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HF Alkylation & NExOCTANE Technology Isomerization: Isomerization is very important in the production of good octane quality from feed that is rich in 1-butene. The isomerization of 1-butene is preferred according to thermodynamic equilibrium. Allowing 1-butene to isomerize to 2-butene decreases the production of dimethylhexanes and enhances the production of trimethylpentanes. Several recent HF Alkylation units, particularly those processing only butylenes, have olefin isomerization units at upstream that isomerize the 1-butene to 2-butene. (Fig 5.4.4)

FIGURE 5.4.2: Initiation reactions

Other Reactions: The polymerization reaction results in heavier paraffins production, which are undesirable because they decrease alkylate octane and they increase endpoint of alkylate. Minimization of this reaction is accomplished by right choice of reaction conditions. (Fig 5.4.5)

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FIGURE 5.4.3: Propagation reactions

FIGURE 5.4.4: Isomerization

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FIGURE 5.4.5: Other reactions

Hydrogen Transfer: The hydrogen transfer reaction is most noticeable with propylene feed. This reaction initiates via the carbenium ion mechanism. In the first reaction isobutane reacts with propylene to produce propane and butylene. After that the butylene is alkylated with isobutane to produce trimethylpentane. From octane’s view point, this reaction can be a desirable one because trimethylpentane has considerably higher octane than the dimethylpentane usually formed from propylene. Though, two molecules of isobutane are needed for each alkylate molecule, so from economics point of view this reaction may be undesirable.

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HF Alkylation & NExOCTANE Technology 5.5 Alkylation Feed Stocks:

Iso-butane and oelifins are used feedstocks in the alkylation unit. The sources of olefins mainly are coking operations and catalytic cracking. Propene and butenes are the most commonly used olefins, but pentenes (amylenes) are also used in some units. Some refineries also use pentenes feed to decrease the vapor pressure of FCC (fluid catalytic cracking) gasoline and as the result the bromine number in the final blend of gasoline is reduced. Alkylation of pentenes is also used to decrease the C5 olefin content of final gasoline blend and it also decreases the effect of C5 olefin on ozone depletion and causes less visual pollution in the environment.

Dehydrogenation of paraffins can yield olefins and isobutane provided to alkylation feed unit is produced by commercial cracking of heavy paraffins. Catalytic crackers and hydrocrackers produce a large amount of the isobutene that is provided in alkylation unit but it can also be obtained from crude distillation, natural gas processing, and catalytic reformers. Normal butane can be isomerized in some cases to provide additional isobutane to the feed of alkylation unit.

TABLE 5.5.1: Compositions of Alkylate from Pure-Olefin Feed stocks

Source: Ref 7

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HF Alkylation & NExOCTANE Technology 5.6 Process Description:

The HF alkylation of olefins with iso-butane is complicated because it consists of many simple addition reactions as well as various side reactions. Products of primary reaction are the isomeric paraffins which contain carbon atoms that are the sum of carbon atoms of isobutane and carbon atoms of the corresponding olefin. Though, secondary reactions such as isomerization, destructive alkylation, hydrogen transfer, and polymerization also occur, which result in the formation of secondary products which can be lighter or heavier than the primary products of alkylation. The factors which promote the primary and secondary reaction mechanisms are different, as well as the response of each reaction to any changes in operating conditions are different. Not every secondary reaction is undesired reaction; for example, they also make the formation of isooctane from amylenes or propylenes possible. In an ideal design and operation, primary reactions should dominate, but not to the complete elimination of secondary reaction. For the HF Alkylation, the optimal combinations of product yield, quality and plant economy are attained with the reactor system operates at cooling-water temperature and in the presence of excess of isoparaffin and with feedstocks free from contaminants and a vigorous, intimate acid-hydrocarbon contact. To ensure good alkylate quality and minimize acid consumption, the feeds to the alkylation unit are dried first and are of low sulfur content. Generally, a simple desiccant-drying system is provided in the unit.

Reactor Section: Dried and treated olefin feed along with makeup and recycle isobutene is charged to the reactor section of the plant. This combined feed enters the shell of the reactor through several nozzles placed to maintain a uniform temperature in the entire reactor. The removal of heat of reaction is done by a heat exchange with a large amount of coolant which flows through the tubes that have a little rise in temperature. If cooling water is used, then it is available for further use somewhere in the unit. The effluent coming from the reactor then enters into the settler, and the settled acid is recycled back to the reactor. Distillation Section:

The hydrocarbon phase, also containing the dissolved HF acid, flows out from the settler and it is preheated and then charged to the isostripper. Dried saturate field butane feed is also fed to the isostripper. The alkylate product is recovered from bottom of the column. Any normal butane that may enter the unit is withdrawn as a sidecut. The isobutane which does not react is also recovered as a sidecut and recycled to the reactor. The overhead of isostripper consists mainly of propane, HF acid, and isobutane. A drag stream of the overhead material is sent to the HF stripper to strip the acid. From the HF stripper the overhead is recycled to the isostripper overhead system to recover isobutane and the HF acid. A portion of the HF stripper bottom stream is used as material for flushing. A net bottom stream from the isostripper is withdrawn and then defluorinated.

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Dried Oeilfin Feed

iC4

Recycle

Dried iC4

Makeup

Cooling Water

in

Cooling Water

out

Dried Saturate C4's

Alkylate

nC4

Propane

Settled Acid

nC4

Unreacted iC4

Acid Recycle

Acid Return

R

S2

S1

I

AR

KT

KT

KT

AT

HS

Polymer & CBM to

Neutralization

HF Acid

Isobutylene Feed

iC4

Raffinate

H2

Iso-Octane

Iso-Octene

iC4 to Akylation

LEGENDR= ReactorS1 & S2= SettlersI= IsostripperAR= Acid RegeneratorHS= HF StripperAT= Aluminia TreaterKT= KOH Treater

LEGENDADR= Adiabetic ReactorPR= Product RecoveryTBR= Trickle Bed Reactor

ADR

TBR

PR

= Rector Section

= Distillation Section

= Acid Regeneration Section

= Neutralization Section

= Dimerization Section

= Product Recovery Section

= Hydrogenation Section

FIGURE 5.6.1: Process Flow Diagram C4 of HF Alkylation Process with NExOCTANE Technology

HF Alkylation & NExOCTANE Technology Acid Regeneration Section:

A slipstream of some circulating HF acid is regenerated internally so a desired level of acid purity is maintained. This method significantly reduces overall acid consumption. An acid regenerator column is also present for start-ups after changes or in the event of a process upset or contamination of feed. Neutralization Section:

When the normal butane or propane from the HF unit is used as liquefied petroleum gas, defluorination is suggested because of the potential breakdown of combined fluorides during the process of combustion which results in potential corrosion of burners. Defluorination is also essential when the butane is to be charged to an isomerization unit. After defluorination, the butane and propane products are treated with potassium hydroxide (KOH) for the removal of any free HF acid. Scrubbing and auxiliary neutralizing equipment is included in plant design to ensure that all materials exiting the unit during normal and emergency operations are acid-free. 5.7 Process Variables: The most significant process variables are: Reaction temperature Acid strength Isobutane concentration Olefin space velocity. Any change in these variables affects both product yield and quality. Typical HF alkylation operating conditions are shown in Table 5.7.1. Reaction Temperature: Reaction temperature has lesser effect using hydrofluoric

acid. In hydrofluoric acid alkylation increase in the temperature of the reactor from 60 to 125°F degrades the quality of alkylate up to three octane numbers In hydrofluoric acid alkylation, temperature is less important and reactor temperatures are generally in the range of 70 to 100°F [6].

Acid Strength: Acid strength has variable effects on the quality of alkylate depending on the effectiveness of the mixing in the reactor and the water content present in the acid. In hydrofluoric acid alkylation the alkylate having the highest octane number is obtained in the acidity range of 86 to 90%. Commercial operations generally have concentrations of acid between 83 and 92% hydrofluoric acid and contain water less than 1% [6].

Isobutane Concentration: Isobutane concentration is usually expressed in terms of the isobutane/olefin ratio. High ratios of isobutane/olefin increase the octane number and the yield, and decrease side reactions and consumption of acid. In industrial practice the ratio of isobutane/olefin on the reactor charge varies from 5:1 to 15: 1. In reactors having internal circulation to enhance the reactor feed ratio, internal ratios are from 100:1 to 1000:1.

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HF Alkylation & NExOCTANE Technology Olefin Space Velocity: Olefin space velocity is stated as the volume of olefin that is

charged per hour to the acid volume in the reactor. Decreasing the olefin space velocity decreases the quantity of high-boiling hydrocarbons formed, increases the octane of the product, and reduces acid consumption. Olefin space velocity is one technique of stating reaction time

TABLE 5.7.1: Range of Operating Variables in HF Alkylation

Source: Ref 8

5.8 Alkylation Products: The products exiting the alkylation unit also include the normal butane and propane in addition to the alkylate stream that may enter with the unsaturated and saturated feed streams as well as a small fraction of tar that is formed by polymerization reactions. The product streams leaving the HF alkylation unit are:

1. C5 + alkylate (See Table 5.3) 2. LPG grade propane liquid 3. Tar 4. Normal butane liquid

Merely about 0.1% by volume of the olefin feed is converted into the undesirable tar. This is not truly a tar rather it is thick dark brownish oil comprising of complex mixtures of conjugated cyclopentadienes with side chains.

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TABLE 5.8.1: HF Alkylate Properties [9]

6. NExOCTANE Technology for Isooctane Production 6.1 Introduction to MTBE: MTBE (methyl-t-butyl ether) belongs to a group of chemicals that are commonly known as fuel oxygenates. Oxygenates are added to fuel so that oxygen content the fuel can be increased. MTBE is also used in gasoline to somewhat lessen ozone levels and carbon monoxide caused by automobile emissions. MTBE substitutes the use of lead as an anti-knock agent and octane enhancer [11]. MTBE gives water an unpleasant taste even at very little concentrations, and hence it can pollute large amount of groundwater even at a concentration of 5 – 15 µg/l [10]. MTBE is often introduced into the water-supply aquifers by gasoline having MTBE spilled onto the ground or by underground leakage of storage tanks at gasoline stations. Its higher persistence and water solubility cause it to travel rapidly than many other constituents of gasoline when released into water storage. 6.2 Introduction to NExOCTANE: Issues regarding environment are threatening the use of MTBE in gasoline in the United States in future. Since the late 1990s, concern related to have ground and drinking water contamination have aroused with MTBE usage due to gasoline leakage from underground storage tanks and from two-cycle engine’s exhaust. In California numerous cases of drinking water pollution with MTBE have been reported. So, the elimination of MTBE in gasoline was mandated in California. The U.S. Senate had similar law, which eliminated MTBE in the 2006 to 2010 time frame [9].

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HF Alkylation & NExOCTANE Technology With MTBE phase-out imminent, U.S. refiners faced the challenge of replacing the lost octane value and the lost volume of MTBE in gasoline pool. Also, the utilization of idled MTBE facilities and isobutylene feedstock resulted in persistent problems of unrecovered and underutilized capital for the producers of MTBE. Isooctane has been recognized essentially as a cost-effective alternative to MTBE. It utilizes same isobutylene feed that was used in MTBE production and it offers excellent blending value. Furthermore, production of isooctane can be obtained in a low-cost renovation of an existing plant of MTBE. The NExOCTANE technology was developed for the isooctane production. In this process, isooctane is produced by the dimerization of isobutylene, which can be hydrogenated for isooctane production. Both products are remarkable gasoline blend stocks with ominously higher product value than polymerization or alkylate gasoline. 6.3 Process Chemistry: The main reaction in the NExOCTANE process for the production of isooctane is the dimerization of isobutylene over the acidic ion-exchange resin catalyst. The dimerization reaction produces two isomers of isooctane or trimethylpentene (TMP), specifically, 2, 4, 4-TMP-1 and 2, 4, 4-TMP-2; reactions are shown in Fig 6.3.1.

FIGURE 6.3.1: Dimerization Reaction

TMP also reacts with isobutylene to produce trimmers and tetramers; etc. Production of these oligomers is suppressed by polar components containing oxygen in the reaction mixture.

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HF Alkylation & NExOCTANE Technology NExOCTANE process uses alcohol and water as retarders. Acidic sites on the ion-exchange resin are blocked by these polar components (alcohol and water), thereby increasing the selectivity and controlling the catalyst activity to the formation of dimers. The conditions of the process in the dimerization reactions are adjusted to maximize high-quality isooctane product yield. A little amount of C7 and C9 components along with other C8 isomers will be produced when additional olefin components such as propylene, isoamylene and n-butenes that exist in the reaction mixture. In the process of NExOCTANE, these reactions are very slow in comparison to the dimerization reaction of isobutylene and therefore only a small percentage of these Isooctene can be hydrogenated resulting in the formation of isooctane, according to the following reaction:

FIGURE 6.3.2: Hydrogenation

6.4 Cost-Effective Technology: Iso-octene is formed by the dimerization of the oelifin isobutylene feedstock by a relatively low cost renovation of the existing MTBE production unit; hence the technology is cost effective and also replaces MTBE in an effective manner. In a hydrogenation unit, iso-octene can be further processed to produce saturated iso-octane [24]. The main features of NExOCTANE process are: Long-Life Dimerization Catalyst: The catalyst gives substantially longer run

lengths and superior performance than standard resins to decrease the operating costs. Dimerization catalyst system is based on acidic ion-exchange resin that is specifically designed for the dimerization of isobutylene and is exclusively available for the NExOCTANE process.

State-of-the-Art Hydrogenation Technology: Hydrogenation technology that is low cost and features trickle bed design based on catalysts commercially available, using once-through hydrogen operation, which removes the cost of a hydrogen recycle compressor.

Low-Cost Plant Design: Dimerization reactors are fixed bed and liquid phase reactions take place. Recovery of product in already existing MTBE unit distillation equipment reduces the capital investment.

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HF Alkylation & NExOCTANE Technology 6.5 NExOCTANE Process Description:

The NExOCTANE process unit consists of two independent sections: dimerization section and hydrogenation section. Isooctene is formed as the result of dimerization of isobutylene which occurs in the dimerization section, and then, the isooctane can be produced by hydrogenation of isooctane which occurs in the hydrogenation section. Hydrogenation and dimerization are independently functioning sections.

The integration of this process into the refinery is same as that of the MTBE processing unit. Furthermore, NExOCTANE process selectively reacts with isobutylene and a C4 raffinate is formed which is used for direct processing in an alkylation unit.

FIGURE 6.5.1: Integration OF NExOCTANE in a Refinery

Dimerization Section:

The dimerization of isobutylene occurs in adiabatic reactors dimerization over fixed beds of acidic ion-exchange resin catalyst. The quality of product, specifically the fractions of oligomers and dimers, is controlled by the recirculation of alcohol from the recovery of product section to the reactors. In the dimerization reactors, alcohol is produced through the reaction of a small quantity of water present in the olefin feed although make water may also be added. In the reactor feed the alcohol content is kept at a sufficient level typically so that the isooctene product contains fewer than 10% oligomers.

Product Recovery Section:

In the dimerization product recovery step the isooctene product is separated from the unreacted portion of the feed which is C4 raffinate and also produces a concentrated stream of alcohol for recirculation to the dimerization section. The C4 raffinate is free from oxygenates and is further suitable for processing in an HF alkylation unit.

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HF Alkylation & NExOCTANE Technology Hydrogenation Section:

In the dimerization section the isooctene formed is further processed to produce the saturated isooctane product in a hydrogenation unit. This unit can also be designed to minimize sulfur content in the product in addition to saturating the olefins. This section consists of a product stabilizer and trickle-bed hydrogenation reactor(s). The purpose of the product stabilizer is to eradicate lighter components and unreacted hydrogen in order to produce a product with a specified vapor pressure.

The utilities required for the NExOCTANE process are summarized as follows:

TABLE 6.5.2: Typical Utility Requirements

Source: Ref 7

7. Environmental Considerations:

7.1 Effluent Treatment:

In Alkylation unit’s system of effluent-treatment, large amount of the neutralized HF acid must ultimately leave the system as alkali metal fluoride. Due to its very low solubility in water, CaF2 is the desired final product. Effluent having HF acid can be treated with lime [CaO-Ca(OH)2] slurry or solution, or it can be indirectly neutralized in a KOH system to form the required CaF2 product.

KOH neutralization system presently used involves two-stage process. Since HF acid is neutralized by the aqueous KOH, soluble potassium fluoride (KF) is formed, and the KOH is progressively depleted. Periodically, some amount of KF containing the neutralizing solution is withdrawn to KOH regenerator. In this particular vessel, lime slurry reacts with KF to form insoluble CaF2 and thus regenerates KF to KOH. Regenerated KOH is returned to the system, and solid CaF2 is routed to neutralizing basin [7].

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HF Alkylation & NExOCTANE Technology 7.2 Effluent Gases: HF Alkylation unit utilizes two separate gas vent lines for maintaining acidic gases separation from non-acidic gases until acidic gases can be scrubbed free of the acid. Acidic Hydrocarbon Gases: The acidic hydrocarbon gases are originated from those sections of the unit where HF acid exists. These gases may possibly evolve during upset of unit, particularly during a shutdown, or during maintenance period in which all these acidic gases are fractionally or completely removed from process vessels or equipment. Gases from acid vents and also from acid pressure relief valves are piped to separate closed relief system for neutralization of acid contained in gas. The acid free gases are afterwards routed from this section of acid-scrubbing to refinery non-acid flare system, where these gases are disposed of correctly by burning. Non-Acidic Hydrocarbon Gases: These gases are produced from the sections of unit in which HF acid is not present. Non-acidic gases from the process vents and relief valves are made to discharge into refinery non-acid flare system, where these non-acidic gases are disposed of by burning. Material that is released to flare is mostly hydrocarbon in nature. Possibly, small amount of the inert gases are also included. Obnoxious Odours and Fumes: The only particular area from which all these potentially objectionable fumes can originate is unit’s neutralizing basins. In order to stop discharge of these odorous gases to surroundings, neutralizing basins are covered tightly and are equipped with a gas scrubber to get rid of any offensive odours. Gas scrubber use either activated charcoal or water as scrubbing agent. However, in aforementioned system of neutralization, the odours from basin are basically non-existent because main cause of these odours is handled in separately closed vessels. 7.3 Liquid Effluents: To ensure the segregation of the non-acid from the possibly acid-containing water streams, the HF Alkylation unit is equipped with two separate sewer systems. Acidic Waters: Any possible HF which contains water streams (rainwater runoff which is in wash water and acid area), the heavy hydrocarbons, and also possibly spent neutralizing media are then directed through acid sewer system to neutralizing basins for neutralizing any acidic material. In basins, lime is used in converting the incoming soluble fluorides to CaF2. Liquid Process Effluents (Hydrocarbon and Acid): Acid effluents and hydrocarbons originate from minor undesirable process side reactions and also from any other feed contaminants that are introduced to unit. The undesirable by-products produced in this way are finally rejected from Alkylation unit in acid regeneration column as bottom stream. 7.4 Solid Effluents: Neutralization Basin Solids: Neutralization basin solids largely consist of CaF2 and the unreacted lime. All of the HF-containing liquids that are directed to neutralizing basins having ultimately any contained soluble fluorides are converted to insoluble CaF2. Disposal of all of this solid material is done on batch basis. Vacuum truck is usually used to remove fluoride-lime sludge from pit. This sludge has conventionally been disposed of in landfill after analysis to assure that appropriate properties are met.

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HF Alkylation & NExOCTANE Technology Product-Treating Solids: Product treating solids are originated when LPG products are defluorinated over the activated alumina. Over the time, alumina loses ability to defluorinate LPG product streams. At this moment, alumina is considered as spent, and it is replaced with fresh alumina. The spent alumina must be disposed of in agreement with applicable regulations or it must be sent to alumina vendor for recovery. Miscellaneous Solids: The porous material such as wood, wiping cloths, pipe coverings, and the packings that are alleged of coming into contact with the HF acid are placed in specifically provided disposal cans for the removal and are then periodically burned. During normal unit operations these solids may originate or during maintenance period. Staging of wood and other use of wood in area are kept to a minimum level. Before being removed from the acid area the metal staging must be neutralized.

8. Safety Issues in Alkylation Units:

The alkylation unit consists of two main process hazards:

1) Light hydrocarbons in large volumes which are extremely flammable and possibly explosive if released.

2) Toxic and corrosive acid catalyst.

Both hydrofluoric acid and sulphuric acid alkylation units have same volumes of hydrocarbon with similar risks, but the risks accompanying each acid are different. From the aerosol tendencies to mitigating the effects of leakage to personal protective equipment, HF alkylation needs much stricter precautions because of its greater potential to cause damage.

9. Modifications & Recommendations:

9.1 Aerosol Potential:

HF has a boiling point of 66.92oF (19.4°C) at atmospheric pressure and it vaporizes in the incident of a leak to the atmosphere. The scientific HF release tests accompanied in 1986 in the Nevada desert astonished the researchers when 100% liquid HF that was released led to the formation of a white, dense and rolling cloud of toxic gas. This cloud rapidly expanded and concentrations toxic gas was measured at distances of about five to ten kilometers downwind of the release point. Therefore, unless mitigated, release of HF in a refinery will place the refinery workers and the surroundings in severe danger. Several HF accidents have occurred in recent years. The most prominent was in 1987 that occurred at Marathon Oil Company refinery situated in Texas City, Texas. This incident needed a 50 square block area nearby the refinery to be exiled with over 900 people needing medical treatment for injuries caused by the accident. Luckily there were no fatalities, since this was a minor release of HF vapor only.

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HF Alkylation & NExOCTANE Technology 9.2 Mitigation:

Due to its tendency to form aerosol, HF spills and leaks carry a greater potential for causing harm as the vapor resulting from a release cannot be contained easily. Furthermore, the possibility for an HF leakage exists throughout the unit. API RP 751 calls for the installation of various protective systems for mitigating the effects of a potential release of HF acid. Reliable instruments that speedily detect the release of HF are recommended. These may comprise of closed-circuit TV and point sensors [12]. Water sprays of high volume capable of "knocking down" the cloud of HF acid are also recommended. For mitigating 90% of an HF release, a 40:1 ratio of water to HF is required. Provisions must be ensured for the potential of handling a large amount of HF-contaminated runoff water. This system should be completely tested. Low HF inventory should be maintained, requiring close scheduling with the HF suppliers. Finally, a quick acid deinventory system is recommended. This would displace acid from the leaking section of the HF alkylation unit to a safe location, reducing the time the HF is allowed to leak.

9.3 HF Modifiers:

As HF mitigation systems are activated only once a leakage has taken place and aerosol has been released, research on HF modifiers shows that would itself decrease the aerosoling tendency of the HF has been ongoing. There are two technologies that are close to commercialization. Each technology claims that, when combined with a 40:1 water spray system of mitigation, the overall decrease in aerosol potential should be about 95-97%. Additionally, some of the tests have revealed octane increases in the alkylate product when additives are used. The HF modifier technologies applied needs the installation of an additive recovery system and additive separation additive recovery system, alkylate treating section, storage and supply facilities of the additive. Capital costs are projected to be around U.S $3.6 - 7.0 million. Furthermore, increase in operating costs is expected [15]. 9.4 Advances in HF Alkylation Technology: UOP has disclosed a new design for enhanced conventional HF alkylation processes. The new process uses split feed series recycle (SFSR) reactor sections for removing process heat. It also offers minimized operating cost and octane maximization. The Alkad process incorporates a vapor suppression additive into the cost-effective HF alkylation unit, where the additive reduces HF aerosol emissions by 90% using other mitigation techniques and hardware [15]. The additive does not give off sulfur to the alkylate product as the Alkad process is claimed to be very tolerant of high sulfur oils without contaminating the alkylate product. The additive does not adversely affect nor degrade wastewater treating, and separates cleanly from hydrocarbons. It can also be easily recovered and recycled into the alkylation unit.

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10. Distillation Column P&ID

Figure 1

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HF Alkylation & NExOCTANE Technology 10.1 P&ID Description:

Figure 2

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Figure 3

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HF Alkylation & NExOCTANE Technology Designer now starts thinking about proper orientation of the nozzles and the

provisions for accessing the points of operation and maintenance. Considerations of pipeline leaving tower area and adjacent piping shall be

visualized. First step is to orient manholes possibly all in the same directions. Levels of the platforms are decided on elevation view based on manholes and

access to the relief valves. All of the platform levels in proper segments of tower with a ladder location must be

drawn on a plan view. Manhole shall be displayed in proper segment with angle of orientation, and space for swing of manhole cover’s taking davit hinge as the center.

The layout should be initiated from top of column with designer visualizing layout as a whole. There shall be no trouble in dropping the large overhead line straight down on the side of column, and leaves column at high level and crosses directly to condenser. It clears the segment at lesser elevations for the piping or for the ladder from the grade level to first platform.

The flexibility and the thermal load connected with large-dia of overhead lines to condenser at grade level or at higher level should be considered. Relief valve protecting tower is generally connected to overhead line. Relief valve discharging to the atmosphere should be located on highest tower platform.

In closed system of relief-line, Relief-valve must be located on lowest tower platform above relief -system header. This will ensure shortest relief-valve discharge to flare header. Entire system of relief-line should be self-draining.

It is better to space platform brackets on tower equally and aligning brackets over one another for entire length of tower. This will reduce interferences between structural members and pipings.

Piping and nozzles must meet requirement of process while the platforms must satisfy the maintenance and the operating needs. Tower piping access, instruments and valves influence ladder’s placement.

The condenser and the reboiler lines are available between both sides of manhole and ladders.

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Figure 4

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Figure 5

See Fig.4 or 5 for the overall orientation of distillation column. The line approaching yard or piperack can be turn left or right on the basis of overall

arrangement of plant. Respective segments of all these lines are between ladders and 180°. Segment at 180° is suitable for lines without instruments and valves, this is that point which is farthest from the manhole platforms.

Sequence of the lines around tower is influenced by the conditions at a grade level. The piping provisions without the lines crossing over one another gives neat appearance and generally a more appropriate installation.

Correct relationship between tower internals and process nozzles is very vital. Angle is generally chosen between radial centreline of the internals and the tower-shell centrelines.

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HF Alkylation & NExOCTANE Technology By the proper choice of angle (generally 45° or 90° to piperack) many hours of the

work and the future problems can be saved. Providing clearance for lifting tackle to all points from which handling is needed, and

good access must be provided. Interpretation of the process requirements inside tower is generally more exact than

for the exterior piping design. Internal or external access is very significant. This includes the accessibility of the

connections from platforms and ladders and the internal accessibility through the shell manholes, the handholes or the removable sections of trays. Opening of manhole must not be obstructed by internal piping.

The reboiler-line elevations are to be determined by draw off and the return nozzles and orientation is influenced by the thermal flexibility considerations. The reboiler lines and overhead lines should be simple and direct.

The Fig (6) shows segments of the tower circumference allotted to the piping, manholes, nozzles and platform brackets and the ladders as generally recommended for developing a well-designed layout.

Figure 6

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11. Conclusions: The HF alkylation process is of vital importance to the present day. It plays a very

important role in production one of the mostessential feeds to the final gasoline blend. With the increase in number of fluid catalytic cracking (FCC) units used in refineries its significance has increased.

The HF alkylation performs the critical role of improvement of the byproducts from FCC (Fluid Catalytic Cracking) to high-value product (alkylate), which is then used as a component of gasoline blending.

With MTBE phase-out imminent, U.S. refiners faced the challenge of replacing the lost octane value and the lost volume of MTBE in gasoline pool. Also, the utilization of idled MTBE facilities and isobutylene feedstock resulted in persistent problems of unrecovered and underutilized capital for the producers of MTBE.

Isooctane has been recognized essentially as a cost-effective alternative to MTBE. It utilizes same isobutylene feed that was used in MTBE production and it offers excellent blending value. Furthermore, production of isooctane can be obtained in a low-cost renovation of an existing plant of MTBE. The NExOCTANE technology was developed for the isooctane production which is a cost-effective revamp of existing MTBE processing units. The product of NExOCTANE process is 2, 2, 4 trimethylpentane which has the highest octane number of 100 among all hydrocarbons so it can blended to give a very high quality gasoline.

The aim of this report was the production of high octane gasoline which is free from environment threatening MTBE hence HF Alkylation process and NExOCTANE technology were combined for this purpose.

For the installation of a new alkylation unit, H2SO4 Alkylation is preferred these days because it has less safety problems in case of leakages. So, for already existing HF alkylation plants modifications were proposed to reduce the process hazards and enhance its safety.

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References

1. Gasoline price volatility and the elasticity of demand for gasoline, C.-Y. Cynthia Lin, Lea Prince, United States.

2. www.indexmundi.com/ 3. The 12th Worldwide Alkylation Symposium, 4–9 June 2006, Orlando, FL, USA. 4. Hydrocarbon Processing, Jun 2003, 82 (6), 32 5. V. N. Ipatieff and L. Schmerling, Advances in Catalysis, vol. I (Academic Press, New

York, 1948), pp. 27–63. 6. R. E. Payne, Petrol. Refiner. 37(9), 316–329. 7. Robert A. Meyers, Handbook of Petroleum Refining Processes, Third Edition,

(McGraw-Hill Book Company, New York, 1960). 8. Petrol. Refiner. 31(9), 156–164 (1952). 9. Michael B. Simpson, Michael Kester 10. James H. Gary, Glenn E. Handwerk, Mark J. Kaiser, Petroleum Refining:

Technology and Economics, Fifth Edition. 11. http://en.wikipedia.org/wiki/Methyl_tert-butyl_ether 12. http://water.epa.gov/drink/contaminants/unregulated/mtbe.cfm 13. Conference, 23–27 July 2006, Vancouver, BC, Canada. Contact: ASME

International, Three Park Avenue, New York, NY 10016-5990. 14. “Volume 2006, Issue 11, November 2006”. 15. US 8,153,096, Honeywell International Inc, Morristown, NJ, USA, 10 Apr 2012 16. W. A. Gruse and D. R. Stevens, Chemical Technology of Petroleum, 3rd ed.

(McGraw-Hill Book Company, New York, 1960), pp. 153–163. 17. R. J. Hengstebeck, Petroleum Processing (McGraw-Hill Book Company, New York,

(1959), pp. 218–233. 18. Hydrocarbon Process. 49(9), 198–203 (1970). 19. V. N. Ipatieff and L. Schmerling, Advances in Catalysis, vol. I (Academic Press, New

York, 1948), pp. 27–63. 20. H. Lerner and V. A. Citarella, Hydrocarbon Process. 70(11), 89–94 (1991). 21. A. V. Mrstik, K. A. Smith, and R. D. Pinkerton, Advan. Chem. Ser. 5(97), (1951). 22. http://stratfordengineering.com/articles/safety-issues-in-alkylation-units 23. Hydrofluoric Acid Alkylation, ABB and ConocoPhillips develop a critical new process

analysis tool 24. NExOCTANE, Petrochemicals, KBR Technologies

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http://www.indexmundi.com/

http://en.wikipedia.org/wiki/Methyl_tert-butyl_ether

http://water.epa.gov/drink/contaminants/unregulated/mtbe.cfm

http://stratfordengineering.com/articles/safety-issues-in-alkylation-units


Source: Robert A. Meyers, Handbook of Petroleum Refining Processes, Third Edition, (McGraw-Hill Book Company, New York, 1960)

Source: James H. Gary, Glenn E. Handwerk, Mark J. Kaiser, Petroleum Refining: Technology and Economics, Fifth Edition.

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Source: Robert A. Meyers, Handbook of Petroleum Refining Processes, Third Edition, (McGraw-Hill Book Company, New York, 1960)

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HF Alkylation and NExOCTANE Tech for Gasoline Production