Process For The Aromatization Of Alkanes In An Alkane-Containing Gas Stream (Shell)

CATEGORY: ALKANES
Process For The Aromatization Of Alkanes In An Alkane-Containing Gas Stream (Shell)
United States Patent Application 20160251280
Tanev; Peter Tanev ;   et al.   September 1, 2016
Assignee: Shell Oil Company
Abstract
A process for the aromatization of alkanes in an alkane-containing gas stream, which alkane-containing gas stream contains at least one alkane selected from the group consisting of ethane, propane or butane and contains essentially no methane, comprising contacting the alkane-containing gas stream in a reaction zone with a moving bed comprising an aromatization catalyst and a hydrogen acceptor under alkane aromatization conditions to produce a product stream comprising aromatics and hydrogen wherein at least a portion of the hydrogen is bound by the hydrogen acceptor in the reaction zone and removed from the product and the reaction zone.
FIELD OF THE INVENTION
[0001] This invention relates to a process for the aromatization of alkanes in a C.sub.2-C.sub.4 alkane-containing gas stream in a reactor containing both catalyst and hydrogen acceptor particles, wherein at least the hydrogen acceptor particles are in a moving bed state and the removal of hydrogen from the reaction zone is accomplished in-situ by the hydrogen acceptor.
BACKGROUND OF THE INVENTION
[0002] The aromatic hydrocarbons (specifically benzene, toluene and xylenes) are the main high-octane bearing components of the gasoline pool and important petrochemical building blocks used to produce high value chemicals and a variety of consumer products, for example, styrene, phenol, polymers, plastics, medicines, and others. Since the late 1930's, aromatics are primarily produced by upgrading of oil-derived feedstocks via catalytic reforming or cracking of heavy naphthas. However, occasional severe oil shortages and price spikes result in severe aromatics shortages and price spikes. Therefore, there is a need to develop new, independent from oil, commercial routes to produce high value aromatics from highly abundant and inexpensive hydrocarbon feedstocks such as natural gas liquids, LPG or associated gas, but also refinery or petrochemical streams including waste streams.
[0003] To meet this projected supply shortage, numerous catalysts and processes for on-purpose production of aromatics (including benzene) from alkanes containing six or less carbon atoms per molecule have been investigated. These catalysts are usually bifunctional, containing a zeolite or molecular sieve material to provide acidity and one or more metals such as Pt, Ga, Zn, Mo, etc. to provide dehydrogenation activity. For example, U.S. Pat. No. 4,350,835 describes a process for converting ethane-containing gaseous feeds to aromatics using a crystalline zeolite catalyst of the ZSM-5-type family containing a minor amount of Ga. As another example, U.S. Pat. No. 7,186,871 describes aromatization of C.sub.l-C.sub.4 alkanes using a catalyst containing Pt and ZSM-5.
[0004] Despite these efforts, a direct, non-oxidative alkane aromatization catalyst and process cannot yet be commercialized. Some important challenges that need to be overcome to commercialize this process include: (i) the low, as dictated by thermodynamic equilibrium, per pass conversion and benzene yield for example, ca. 48% wt and 42% wt for ethane dehydroaromatization to benzene at atmospheric pressure, 575.degree. C.); (ii) the fact that the reaction is favored by high temperature and low pressure; (iii) the need to separate the produced aromatics and hydrogen from unreacted hydrocarbon off gas and (iv) the rapid coke formation and deposition on the catalyst surface and corresponding relatively fast catalyst deactivation. Among these challenges, overcoming the thermodynamic equilibrium limitations and significantly improving the conversion and benzene yield per pass has the potential to enable the commercialization of an efficient, direct, non-oxidative alkane aromatization process.
[0005] Examples of C.sub.2-C.sub.4 alkane aromatization reactions include the following:
Pt/ZSM-5
3C.sub.2H.sub.6.revreaction.C.sub.6H.sub.6+6H.sub.2
2C.sub.3H.sub.8.revreaction.C.sub.6H.sub.6+5H.sub.2
C.sub.2H.sub.6+C.sub.4H.sub.10.revreaction.C.sub.6H.sub.6+5H.sub.2
[0006] According to the reactions, 2 to 3 alkane molecules are required to generate a molecule of benzene. It is also apparent that, the generation of a molecule of benzene is accompanied by the generation of 5 to 6 molecules of hydrogen. Simple thermodynamic calculations reveal that, for example, ethane dehydroaromatization at atmospheric pressure is equilibrium limited to about 48% ethane conversion at reaction temperature of 575.degree. C. In addition, the equilibrium benzene yield at these conditions is limited to about 42% wt if no side reactions take place. The generation of 6 molecules of hydrogen per molecule of benzene during the ethane dehydroaromatization reaction leads to significant volume expansion that suppresses the reaction to proceed to the right, i.e. it suppresses alkane conversion and formation of reaction products, i.e. benzene yield. The aforementioned low per pass conversions and benzene yields and/or high temperature requirement are not very attractive to provide an economic justification for scale-up and commercialization of alkane dehydroaromatization processes.
[0007] Therefore, there is a need to develop an improved direct, non-oxidative lower alkane aromatization process that provides for significantly higher (than these allowed by the thermodynamic equilibrium) conversion and benzene yields per pass by implementing an in-situ hydrogen removal from the reaction zone.
SUMMARY OF THE INVENTION
[0008] The invention provides a process for the aromatization of alkanes in an alkane-containing gas stream, which alkane-containing gas stream contains at least one alkane selected from the group consisting of ethane, propane or butane and contains essentially no methane, comprising: contacting the alkane-containing gas stream in a reaction zone with a moving bed comprising an aromatization catalyst and a hydrogen acceptor under alkane aromatization conditions to produce a product stream comprising aromatics and hydrogen wherein at least a portion of the hydrogen is bound by the hydrogen acceptor in the reaction zone and removed from the product and the reaction zone.
[0009] The invention further provides a novel process and reactor schemes that employ single or multiple catalyst and/or hydrogen acceptor moving beds as well as a reactor that contains multiple fixed and moving beds of catalyst and hydrogen acceptor particles.
[0010] The invention also provides several catalyst and/or hydrogen acceptor recycle and regeneration process schemes. According to these schemes, the catalyst and/or hydrogen acceptor particles are regenerated simultaneously or separately in single or in separate vessels and then returned back to the reactor for continuous (uninterrupted) production of aromatics and hydrogen. The aforementioned in-situ hydrogen removal in the moving bed state allows for overcoming of the thermodynamic equilibrium limitations and for shifting the reaction equilibrium to the right. This results in significantly higher and economically more attractive alkane conversion and benzene yields per pass relative to the case without hydrogen removal in the reaction zone.
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Conversion of alkanes to linear alkylsilanes using an iridium–iron-catalysed tandem dehydrogenation–isomerization–hydrosilylation

CATEGORY: ALKANES 
Conversion of alkanes to linear alkylsilanes using an iridium–iron-catalysed tandem dehydrogenation–isomerization–hydrosilylation

Type	Journal Article
Author	Xiangqing Jia
Author	Zheng Huang
URL	http://www.nature.com/nchem/journal/v8/n2/abs/nchem.2417.html#affil-auth
Volume	8
Issue	2
Pages	157-161
Publication	Nature Chemistry
Date	February 2016
Abstract	The conversion of inexpensive, saturated hydrocarbon feedstocks into value-added specialty chemicals using regiospecific, catalytic functionalization of alkanes is an important objective of organometallic chemistry. Linear alkylsilanes are one such specialty chemical. They possess a wide range of applications, including release coatings, silicone rubbers and molding products. Direct, selective, functionalization of alkanes at primary C–H bonds is difficult. There are no known methods for catalytically converting alkanes into linear alkylsilanes. Authors report a well-defined, dual-catalyst system for one-pot, two-step alkane silylations. The system is composed of a pincer-ligated Ir catalyst for alkane dehydrogenation and an Fe catalyst that effects a subsequent tandem olefin isomerization–hydrosilylation. This method exhibits exclusive regioselectivity for the production of terminally functionalized alkylsilanes. This dual-catalyst strategy has also been applied to regioselective alkane borylations to form linear alkylboronate esters.

New reaction classes in the kinetic modeling of low temperature oxidation of n-alkanes

CATEGORY: ALKANE 
New reaction classes in the kinetic modeling of low temperature oxidation of n-alkanes

Type	Journal Article
Author	Eliseo Ranzi
Author	Carlo Cavallotti
URL	http://www.sciencedirect.com/science/article/pii/S0010218014003848
Publication	Combustion and Flame
Abstract	Recent literature describes a large number of intermediate products from the low temperature oxidation of hydrocarbon fuels in jet stirred reactors. The new information focuses on systematic deviations between model predictions and experimental measurements, both in oxygenated species and in fuel conversion at very low temperatures. The discrepancies are largely reduced by including new reaction classes in the oxidation mechanism. Successive H-abstraction and molecular reactions of hydroperoxide species play a significant role at very low temperatures, in competition with the chain branching decomposition reactions. Several recombination and disproportionation reactions of peroxy radicals are interesting, as well, in explaining some intermediate oxygenated components. Authors review the ability of these novel reaction classes to explain the formation of oxygenated species, such as organic acids and dicarbonyl species. Rate constants were determined using similarity and analogy rules for consolidated reactions, while theoretical calculations were performed to determine preliminary estimates for reaction channels lacking a reference reaction. Detailed comparisons with several experimental data of propane and n-butane oxidation at low temperatures support these assumptions.

Processes and Systems for Recovery of Residual Halogenated Hydrocarbons in the Conversion of Natural Gas to Liquid Hydrocarbons (Marathon GTF Technology)

CATEGORY: NATURAL GAS
PATENT
Processes and Systems for Recovery of Residual Halogenated Hydrocarbons in the Conversion of Natural Gas to Liquid Hydrocarbons (Marathon GTF Technology)
United States Patent Application 20130046121
Inventors:
Kurukchi, Sabah A. (Houston, TX, US)
Liu, Yijun (Houston, TX, US)
Moodley, Anand (Houston, TX, US)
Application Number:
13/212291
Publication Date:
02/21/2013
Assignee:
Marathon GTF Technology, Ltd. (Houston, TX, US)
Abstract:
Process and systems for converting lower molecular weight alkanes to higher molecular weight hydrocarbons that include recovery of residual halogenated hydrocarbons (e.g., CH3Br) from higher molecular weight hydrocarbon products.
BACKGROUND
The present invention relates generally to processes and systems for converting lower molecular weight alkanes to higher molecular weight hydrocarbons and, more particularly, in one or more embodiments, to processes for converting lower molecular weight alkanes that include recovery of halogenated hydrocarbons from higher molecular weight hydrocarbon products.
Natural gas, which is primarily composed of methane and other light alkanes, has been discovered in large quantities throughout the world. In the United States, the latest proved natural gas reserves are 6,731 billion standard cubic meters (238 trillion standard cubic feet) in 2010, which makes the United States a top-five country in natural gas abundance. Natural gas is generally a cleaner energy source than crude oil. It is normally heavy sulfur-free and contains none or a minimum amount of heavy metals and non-reacting heavy hydrocarbons. For a given amount of heat energy, burning natural gas produces about half as much carbon dioxide as coal.
However, the transportation, storage and distribution of natural gas in a gaseous form are much less favorable than those of crude oil making it more difficult to be a substitute as the predominant energy source. Converting natural gas to higher molecular weight hydrocarbons, which, due to their higher density and value, are able to be more economically transported, can significantly aid the development of natural gas reserves, particularly the stranded remote natural gas reserves.
One technique for converting natural gas to higher molecular weight hydrocarbons is a bromine-based process. In general, the bromine-based process may include several basic steps, as listed below.
• ◦(1) Bromination: Reacting bromine with lower molecular weight alkanes to produce alkyl bromides and hydrogen bromide (HBr).
◦(2) Alkyl Bromides Conversion: Reacting the alkyl bromides over a suitable catalyst under sufficient conditions to produce HBr, methane (C1), light end hydrocarbons (C2-C4) and heavy end hydrocarbons (C5+).
◦(3) HBr Recovery: Recovering HBr produced in both steps (1) and (2) by one of several processes, e.g., absorbing HBr and neutralizing the resulting hydrobromic acid with an aqueous solution of partially oxidized metal bromide salts (as metal oxides/oxy-bromides/bromides) to produce metal bromide salt and water in an aqueous solution; reacting HBr with metal oxide; or absorbing HBr into water using a packed tower or other contacting device.
◦(4) Bromine Regeneration: Reacting the bromide recovered in step (3) with oxygen or air to yield bromine and treating it sufficiently for recycle to step (1).
◦(5) Product Recovery: Fractionating by distillation and cryogenic distillation (demethanizer) the hydrocarbon mixtures contained in the effluent from step (2) and then separated from HBr in step (3) into methane, light end hydrocarbons, and heavy end hydrocarbons. The methane can be compressed for recycle to step (1). The light end hydrocarbons (C2-C4) may be, for example, salable as a product or cracked to produce light olefins. The heavy end hydrocarbons (C5+) may be used, for example, for further petrochemical or fuel processing.
In alkyl bromides conversion, the exothermic coupling reaction may be carried out in a fixed-bed, fluidized-bed or other suitable reactor in the presence of suitable catalysts under sufficient conditions (e.g., 150-600° C., 1-80 bar). The catalyst may have to undergo decoking periodically or continuously to maintain adequate performance. In some instances, a fluidized-bed reactor may be considered to be advantageous for the coupling reaction, particularly for commercial scale of operation, as it should allow for continuous removal of coke and regeneration of the spent catalyst without requiring daily shutdowns and expensive cyclic operation. However, the nature of the fluidized-bed reactor may make it difficult to achieve complete conversion of mono-bromomethane (CH3Br), typically the primary reactant in the case of converting natural gas to liquid hydrocarbons. In some instances, wherein the catalyst deactivation rate is lowered by feeding none or a minimum amount of polybrominated alkanes to the alkyl bromides conversion step, the fixed-bed configuration may be preferred over the fluidized bed. In the latter case, the fixed-bed reactor is typically allowed to operate continuously over a period until the conversion of CH3Br drops to a predetermined threshold (e.g., about 90%). Furthermore, CH3Br conversion is also highly sensitive to the operating conditions of the reactor, e.g., reaction temperature, space velocity, time on stream, number of catalyst regeneration cycles, etc., which adds additional factors leading to an appreciable and fluctuating amount of unconverted CH3Br leaving the reactor with HBr and higher molecular weight hydrocarbons. The presence of alkyl bromides in the product streams can limit the use or sale of the higher molecular weight hydrocarbons for further petrochemical or fuel processing.
The removal of halogenated hydrocarbons from product or emission streams has also been of a concern in other industries, such as the production of plastics and herbicides. There have been efforts to develop efficient processes for dehalogenation. Most of the previously proposed methods typically involve the use of chemical destruction through incineration, catalytic decomposition, or catalytic hydrogenation in presence of a suitable hydrogen source and/or oxygen source. In one example, butane is used as a hydrogen source to debrominate more than 98% of CH3Br in the presence of oxygen over a noble metal-alumina catalyst at 500-550° C. and 1 atmosphere. Another example is high-temperature gas phase reductive dehalogenation of polyhalogenated hydrocarbons by direct reaction with molecular hydrogen over a 10% Ni on ZSM5 catalyst supported on alumina. In another example, metal oxide (e.g., MgO, ZrO2, Al2O3, or zeolite) reacts with CH3Br and water to yield HBr and methanol. Yet another example involves reacting halogenated hydrocarbons over a Pt on alumina catalyst in the presence of methanol or alkane solvents to yield dehalogenated hydrocarbons and acid halide. If a metal oxide catalyst such as MnO2 is used instead of Pt/Al2O3, halogenated hydrocarbons can be completely destructed to carbon dioxide at 300-400° C.
The aforementioned methods for dehalogenation have some drawbacks in a bromine-based process for converting natural gas to higher molecular weight hydrocarbons. First, the introduction and/or production of oxygen-containing species such as air, alcohol, water, and carbon dioxide is typically not desirable for the removal of CH3Br from the synthesis reactor effluent, as it would lead hydrocarbon loss to carbon dioxide and water and/or generate a highly corrosive aqueous/alcoholic HBr stream, thus complicating the process metallurgy. Second, a source of molecular hydrogen is not typically available as a byproduct of this process, requiring a thermal cracker or electronic cell to be built separately to produce H2 on site. Third, selective debromination catalyst is necessitated as the olefinic and aromatic hydrocarbon products contained in the synthesis reactor effluent are prone to saturation in presence of active hydrogen donors. Such saturation would be counterproductive. Fourth, essentially all of catalytic dehalogenation methods mentioned above suffer from difficulties such as incomplete dehalogenation, catalyst deactivation, the need of catalyst regeneration and/or replacement, expensive cyclic operation, and limited process reliability. Furthermore, a catalytic unit often has to be overdesigned by using a larger reactor and more catalyst to such a degree that it can have some flexibility to handle a wide range of CH3Br slippage from the synthesis reactor.
Thus, although progress has been made in the conversion of lower molecular weight alkanes to higher molecular weight hydrocarbons, there remains a need for processes that are more efficient, economic, and safe to operate.
SUMMARY
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, one embodiment of the present invention is a process that comprises reacting at least gaseous alkanes and a halogen to produce at least a halogenation product stream, wherein the halogenation product stream comprises alkyl halides, hydrogen halide, and unreacted alkanes. The process may further comprise reacting at least a portion of the alkyl halides from the halogenation product stream in the presence of a catalyst to produce at least a synthesis product stream, wherein the synthesis product stream comprises unreacted methyl halide, higher molecular weight hydrocarbons, and hydrogen halide. The process may further comprise separating the synthesis product stream into at least a first stream comprising hydrocarbons having five or more carbons, a second stream comprising unreacted methyl halide, and a third stream comprising hydrogen halide and hydrocarbons having one to four carbons.
Another embodiment of the present invention is a process that comprises reacting at least gaseous alkanes and bromine in a bromination reactor to produce at least a bromination product stream, wherein the bromination product stream comprises alkyl bromides, hydrogen bromide, and unreacted alkanes. The process may further comprise separating the bromination product stream into at least a gaseous stream and a liquid alkyl bromides stream, wherein the gaseous stream comprises hydrogen bromide and unreacted alkanes, and wherein the liquid alkyl bromides stream comprises alkyl bromides. The process may further comprise separating the liquid alkyl bromides stream into at least a monobromides stream and a polybromides stream, wherein the monobromides stream comprises monobrominated alkanes, and wherein the polybromides stream comprises polybrominated alkanes. The process may further comprise reacting at least a portion of the monobrominated alkanes from the monobromides stream in a synthesis reactor in the presence of a catalyst to produce at least a synthesis product stream, wherein the synthesis product stream comprises unreacted methyl bromide, higher molecular weight hydrocarbons, and hydrogen bromide. The process may further comprise separating the synthesis product stream into at least a first stream comprising hydrocarbons having five or more carbons, a second stream comprising unreacted methyl bromide, and a third stream comprising hydrogen bromide and hydrocarbons having one to four carbons.
Yet another embodiment of the present invention is a system that comprises a halogenation reactor configured for reaction of at least gaseous alkanes and a halogen to produce at least a halogenation product stream, wherein the halogenation product stream comprises alkyl halides, hydrogen halide, and unreacted alkanes. The system further may comprise a synthesis reactor in fluid communication with the halogenation reactor configured for reaction of at least a portion of the alkyl halides from the halogenation product stream in the presence of a catalyst to produce a synthesis product stream, wherein the synthesis product stream comprises methyl halide, higher molecular weight hydrocarbons, and hydrogen halide. The system further may comprise a dehalogenation system in fluid communication with the synthesis reactor configured for separation of for separating the synthesis product stream into at least a first stream comprising hydrocarbons having five or more carbons, a second stream comprising methyl halide, and a third stream comprising hydrogen halide and hydrocarbons having one to four carbons.
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