JP3836499B2 - Low sulfur reforming method - Google Patents

Abstract

There is disclosed a catalytic reforming method in which hydrocarbons are treated in a reactor system to produce an aromatics enriched product, said reactor system comprising: (a) a series of reactors (10,20,30), containing a catalyst bed comprising a sulfur sensitive zeolite reforming catalyst, and each being associated with (b) a respective furnace (11,21,31) each comprising a plurality of furnace tubes for heating hydrocarbons to an elevated temperature in the range of from 850 to 1025 F suitable for reforming, (c) a heat exchanger (12); and (d) a separator (13) for separating an aromatics enriched product from effluent gas; said method comprising passing hydrocarbons through said reactor system to contact the hydrocarbons with the reforming catalyst in said reactors and separating said aromatics enriched product from said effluent gas; wherein: (i) hydrocarbons are reformed in each of said reactors under low sulfur reforming conditions of less than 50ppb sulfur; and (ii) at least the furnace tubes of the reactor system are protected from carburization and metal dusting. Apparatus for carrying out the process is also described. <IMAGE>

Description

内に吊した熱電対を用いて1200°Ｆの適用温度で幾つかの実験を行なった。内部熱電対により、外部熱電対よりも０〜10°Ｆ低い温度が一定して測定された。
軟鋼（Ｃ鋼及び２¹/₄Ｃｒ）の試料及び300系列のステンレス鋼の試料を、1100°Ｆ、1150°Ｆ及び1200°Ｆで24時間試験し、1100°Ｆで90時間、低硫黄改質条件下で材料を露出させるのに類似させた条件下で試験した。種々の材料の試料を、炉管の高熱領域内の開放石英ボート中に入れた。それらボートは長さ１in、幅1/2inで、管の２inの高熱領域内によく適合するものであった。それらボートは、シリカガラス棒に取付けて夫々の出し入れを行なった。ボートが管の内部に入れられた時には、内部熱電対は用いなかった。
開始前に、管を数分間窒素でフラッシュした。水素中に７％のプロパンを入れた市販容器入り混合物である炭素化用ガスを、室温でトルエンの１ｌフラスコに気泡として通すことにより供給物ガス混合物中に約１％のトルエンを導入した。装置中、25〜30cc／分のガス流及び大気圧を維持した。試料を144°Ｆ／分の速度で操作温度へ持っていった。
希望の温度で希望の時間、材料を炭素化用ガスに曝した後、装置を管の外側に適用した空気流で急冷した。装置が充分冷たくなった時、炭化水素を窒素で追い出し、ボートを取り出して検査分析した。
開始前に、試験材料をそのまま肉眼観察するのに適した大きさ及び形に切断した。清浄化又は焙焼の如き前処理を行なった後、試料を秤量した。殆どの試料は300mgよりも少なかった。典型的には、各実験をボートの中に３〜５個の試料を入れて行なった。347ステンレス鋼の試料を各実験で内部標準として存在させた。
各実験が終わった時、ボート及び各材料の状態を注意深く観察した。典型的には、ボートの写真を取った。次に各試料を、適当な基体材料でコークス付着物を維持するように注意しながら秤量し、変化を決定した。次に試料をエポキシ樹脂に取付け、研磨して岩石学的分析及び走査電子顕微鏡分析のための試料を作り、各材料のコークス化、金属顆粒化、及び炭素化に対する変化を決定した。
必要に応じ、これらの試験で用いた炭素化用ガスの滞留時間を、典型的な商業的操作の場合よりもかなり長くした。従って、実験条件は商業的条件よりも厳しいものであったと考えられる。これらの試験で不良になった材料の幾つかは、実際には商業的には信頼性を持つものとされている。それにも拘わらず、この試験は材料のコークス化、炭素化及び金属顆粒化に対する相対的抵抗性を示す信頼性のある示標を与えている。
結果を下の表に記載する。

勿論、上記結果は定量的であり、表面形態、即ち、金属の微視的粗さに依存する。炭素重量増加は、自触的である表面コークス化の示標になる。
実施例３
上で用いたのと同じ方法を再び用いて、1200°Ｆの温度で16時間材料の広範な分類選抜試験を行なった。結果を下に示す。各群は、同様な条件下で単一のボート中に並べて比較したものを示す。

実施例４
実施例２に記載した方法を再び用いて（別に記述しない限り）更に別の材料を試験した。
446ステンレス鋼及び347ステンレス鋼の試料を試料ボートに入れ、1100°Ｆの炭素化装置で合計２週間同時に試験した。446ステンレス鋼は薄いコークス被覆を持っていたが、他の変化は検出されなかった。一方347ステンレス鋼は、大きな局部的コークス付着物を持ち、４ミルより深い孔を有し、そこからコークス及び金属顆粒が噴き出していた。
錫、銀、銅、及びクロムを電気メッキした炭素鋼網の試料を試験した。試料は約0.5ミルの被覆を持っていた。1200°Ｆで16時間炭素化スクリーニング試験を行なった後、錫メッキ網及び及びクロムメッキ網にはコークスは形成されていなかった。銀メッキ網及び銅メッキ網にはコークスが形成されていたが、メッキが剥がれた所だけであった。メッキした網と同時に試験したメッキしていない炭素鋼網は、ひどいコークス化、炭素化及び金属顆粒化を示していた。304ステンレス鋼網の試料を試験した。各試料には錫、銀、銅、及びクロムの一種類を電気メッキした。それら試料は約0.5ミルの厚さの被覆を持っていた。1200°Ｆで16時間炭素化スクリーニング試験を行なった後、メッキした網のいずれにも、銅メッキ網のメッキが泡立って剥がれた局部的部分を除き、コークスは形成されていなかった。メッキした網と同時に試験した304ステンレス鋼のメッキしていない試料には薄いコークスの被覆が観察された。
304ステンレス鋼網の試料を試験した。各試料には錫及びクロムの一方を電着した。これらの試料は446ステンレス鋼の試料と共に1100°Ｆの炭素化試験で試験した。試料は５週間露出した。各週毎に、試料を室温に冷却し、観察及び写真撮影の記録を行なった。次にそれらを1100°Ｆに再び加熱した。錫メッキした網はコークスを持たなかった。クロムをメッキした網も、クロムメッキが剥がれた局部的部分を除き、コークスを持たなかった。446ステンレス鋼片はコークスで均一に被覆されていた。
未被覆インコネル600（75％Ｎi）及び錫被覆（電着）インコネル600（75％Ｎi）の試料を1200°Ｆで16時間試験した。錫メッキした試料はコークス化及び顆粒化を起こしたが、未被覆試料程ではなかった。
実施例５
低硫黄条件下で改質している間にコークスボールの形成及び燃焼により発生する発熱メタン化反応を研究するため、次の実験を行なった。更にメタン形成を減少させるための添加物として錫を研究した。
低硫黄改質反応器装置で、鉄の溶融粒子を含むコークス付着物が見出されている。900〜1200°Ｆの温度で改質している間に起きるこの溶融鉄の形成は、改質中に起きる非常に発熱的な反応によるものと考えられる。そのような温度を発生させる唯一の経路は非常に発熱的なメタン形成によるものと思われる。その高い温度は特に意外なものである。なぜなら、改質は一般に吸熱的性質を持ち、実際に反応器装置を冷却する傾向を持つからである。それらの高温は充分絶縁されたコークスボール内部で、内部触媒鉄粉末部位に水素が拡散し、そこでそれらがコークス及び水素からのメタン形成に触媒作用を及ぼすことにより発生する。
この実験では、微小パイロットプラントでメタン形成を研究するために鋼ウールを用いた。1/4inのステンレス鋼管に、0.14gの鋼ウールを充填し、1175°Ｆの管中に入れた。ヘキサンと水素をその鉄の上に送り、出てきた流れを供給物及び生成物について分析した。鋼ウールはヘキサンを導入する前に24時間水素中で予め処理した。次にヘキサンを反応器中に25μｌ／分の流量で導入し、水素の流量を約25cc／分とした。
最初はメタンの形成は低くかったが、実験が進むにつれて上昇し続け、最後に4.5％に到達した。次に２ccのヘキサンにテトラブチル錫0.1ccを溶解したものを鉄の前の純粋供給物流中に注入した。メタン形成は約１％に減少し、次の３時間で１％に留まり続けた。データーを下の表に要約する。

上記結果から、鋼ウールに錫を添加するとメタン形成の促進が止まり、それを生成物中許容出来る水準まで低下することが分かる。
実施例６
予めテトラブチル錫を被覆した鋼ウールを用いて更に別の試験を行なった。特に、実施例５の場合のように、２ccのヘキサンに0.1ccのテトラブチル錫を溶解したものを、0.15gの鋼ウールの入った1/4inのステンレス鋼管中に３回注入した。溶液は900°Ｆの水素流中に入れて鋼ウールの上へ運んだ。
次に炭化水素供給物を25μｌ／分の炭化水素流量で1175°Ｆで導入し、水素の流量は約25cc／分にした。出てくるガスをメタンについて分析し、24時間１％より低く留まっていた。次に反応器を停止し、反応器管を切り開き、検査した。鋼ウールには非常に僅かな炭素化が起きていた。
これとは対照的にテトラブチル錫による前処理を行わない対照実験を行なった。それは上に記載したのと同じ条件下で１日間行なった。24時間後、管出口で検出された水素又は供給物はなかった。導入圧力は最初の50 lbから300 lbに上昇した。反応器管を切り開いて検査すると、コークスが完全に管に詰まっていたことが判明した。
従って、有機錫化合物は改質条件下で鋼ウールの炭素化を防ぐことができることが分かる。
実施例７
金メッキした反応器管中に錫を蒸着被覆したステンレス鋼ワイヤーに対する炭素化条件の影響を調べるため、実施例１の対照実験と同様な実験を更に行なった。その対照実験との唯一の相違点は、100ml／分の一層大きな水素流量を用いたことである。
実験は８時間行われたが閉塞又は過度のメタン形成は起きなかった。管を開いて分析すると、閉塞又は炭素の帯は観察されなかった。１本のワイヤーにただ一つの黒色の炭素の筋が見られただけである。これは恐らく不適切な被覆によるものである。
この実験は、錫が硫黄と同様なやり方でステンレス鋼を炭素から保護することができることを示している。しかし、硫黄とは違ってそれは供給物中に連続的に注入する必要はない。硫黄は、鋼上に硫化物表面を維持するのに充分な量で系中に硫化水素の分圧を維持するため、供給物中に連続的に注入しなければならない。供給原料から硫黄を除去すると、硫黄が反応器装置から追い出された後、炭素化の開始が起きる。これは通常硫黄停止後10時間以内に起きる。
本発明を好ましい態様に関して上で記述してきたが、当業者には認められるように、種々の変更及び修正を行うことができることは理解されるべきである。例えば、反応器装置中の鋼の部分をニオブ、ジルコニウム、シリカ、セラミック、タングステン或はクロム（クロム化）によって被覆することができるが、これらの技術は極めて実施或は使用しにくく、高価になり過ぎて利用できないであろう。或は、炭化水素を反応温度へ加熱するために使用する熱交換器をできるだけ少なくすることができる。熱は過熱した水素によって与えることもできる。或は加熱表面の炭化水素への露出を一層大きな管直径及び一層大きな管速度を用いることにより減少させることができる。従って、上記好ましい態様に対する多くの変更或は修正があり、それらは当業者によって容易に分かることであり、次の請求の範囲によって規定された本発明の範囲内に入るものと考えるべきである。 Background of the invention
The present invention is based on U.S. Patent Application No. No. 07 / 666,696 (the contents of which are hereby incorporated by reference) and corresponds to the CIP application filed at the same time. 802,821 [Attorney's Docket No. 005950-316] and US patent application no. 803,215 [Attorney's Docket No. 005950-333] (the contents of which are here for reference).
The present invention relates to an improved catalytic reforming method, particularly a low sulfur condition and a catalytic reforming method under low sulfur and low water content conditions. Specifically, the present invention relates to the discovery and suppression of particularly severe problems for low sulfur and low sulfur / low water content reforming processes.
Catalytic reforming is well known in the petroleum industry and involves treating a naphtha fraction to improve the octane number by the formation of aromatics. The more important hydrocarbon reactions that occur during the reforming operations include dehydrogenation of cyclohexane to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, and dehydration of acyclic hydrocarbons to aromatics. Includes cyclization. Numerous other reactions also occur, including dealkylation of alkylbenzenes, isomerization of paraffins, and hydrocracking reactions to produce light gaseous hydrocarbons such as methane, ethane, propane and butane. It is important to minimize the hydrocracking reaction during reforming. Because they reduce the yield of gasoline boiling products and hydrogen.
Since high octane gasoline is required, a great deal of research has been done to develop improved reforming catalysts and catalytic reforming processes. The catalyst that makes the reforming process successful must have good selectivity. That is, they should be effective in producing high yields of liquid products in the gasoline boiling range containing high concentrations of high octane aromatic hydrocarbons. Similarly, the yield of light gasoline hydrocarbons should be low. The catalyst should have good activity that minimizes excessively high temperatures to produce a certain amount of product. In addition, the catalyst has good stability so that the activity and selectivity characteristics can be maintained over a long period of operation, or it can be fully regenerated so that it can often be regenerated without degrading performance. It is necessary to be.
Catalytic reforming is also an important method in the chemical industry. Various chemicals such as synthetic fibers, insecticides, adhesives, detergents, plastics, synthetic rubbers, pharmaceuticals, high octane gasoline, fragrances, drying oils, ion exchange resins, and various other products well known to those skilled in the art There is an increasing demand for aromatic hydrocarbons to produce products.
Significant technological advances have recently emerged in catalytic reforming processes, including the use of air-pore zeolite catalysts. These catalysts are further characterized by the presence of alkali or alkaline earth metals, to which one or more Group VIII metals have been added. This type of catalyst has been found to have the advantage of providing greater selectivity and longer catalyst life than previously used.
With the discovery of selective catalysts with acceptable repeat life, successful commercialization seemed inevitable. Unfortunately, it has since been discovered that highly selective atmospheric pore zeolite catalysts containing Group VIII metals are unusually susceptible to sulfur poisoning. See U.S. Pat. No. 4,456,527. Ultimately, in order to effectively address this problem, in order to obtain acceptable stability and activity for the catalyst, the sulfur in the hydrocarbon feed is extremely low, preferably less than 100 ppb, It has been found that more preferably it should be lower than 50 ppb.
After recognizing the sensitivity to sulfur associated with these new catalysts and determining the necessary and acceptable levels of process sulfur, the prospect of successful commercialization began to reappear. However, it eventually disappeared due to another incident. It has been found that certain pore pore zeolite catalysts are adversely affected by the presence of water under typical reaction conditions. In particular, water has been found to significantly increase the catalyst deactivation rate.
Sensitivity to water has been found to be a significant drawback that makes it difficult to deal with effectively. Water is produced at the beginning of each reaction step when the catalyst is reduced by hydrogen. Also, water may be generated during process abnormalities when water leaks into the reformer feed or when the feed becomes contaminated with oxygen-containing compounds. Eventually, a method for protecting the catalyst from water was also developed.
The development of various low sulfur, low water content devices for catalytic reforming using highly selective atmospheric pore zeolite catalysts with long catalyst life seemed to make commercialization again practical. Low sulfur and low water content devices are initially effective, but it has been discovered that reactor equipment must be shut down in just a few weeks. The reactor equipment of one test plant has become clogged regularly after such a short period of operation. These occlusions were found to be associated with coking. However, coking within the catalyst particles is a common problem in hydrocarbon processing, but the extent and rate of clogging of the coke other than the catalyst particles associated with this special device is far beyond expectations. It was a thing.
Disclosure of the invention
Accordingly, one object of the present invention is to avoid the above-mentioned problems found with low sulfur processes, such as a short operation period, in hydrocarbon reforming processes under low sulfur conditions. Is to give you a way.
Another object of the present invention is to lengthen the operation period. It is to provide a reactor device for hydrocarbon reforming under low sulfur conditions.
Detailed analysis and study of the coke blockage of the low sulfur reactor apparatus found it surprising that they contained metal droplets and particles in the particle size range up to several microns. This observation has led to the surprising recognition that there is a new and critical problem that is not a problem with conventional reforming processes where the amount of process sulfur and water is significantly higher. In particular, it has been discovered that there are problems that compromise the effective and economical operability of the device as well as the physical integrity of the device. Also, it has been discovered that these problems occur due to low sulfur conditions and occur due to a small amount of water.
For the last 40 years, catalytic reforming reactor equipment has been used in conventional mild steel (eg 2¹/_FourCr, 1 Mo). Experience has since shown that these devices can work well for about 20 years without losing much physical strength. However, the discovery of metal particles and droplets in plugged coke eventually led to a study of the physical properties of the reactor apparatus. Quite surprisingly, the cause of the potential severe physical degradation of all reactor equipment, including furnace tubes, piping, reactor walls, and other perimeters such as iron containing catalysts and metal mesh in the reactor The condition to become was discovered. Eventually, it was discovered that this problem was accompanied by excessive carbonization of the steel, which caused the steel to become brittle by injecting process carbon into the metal. Perhaps it can result in catastrophic physical destruction of the reactor system.
In conventional reforming processes, mere carbonization has not become a problem or concern and has not seemed to exist in modern low sulfur / low water content devices. It was also assumed that conventional process equipment could be used. However, it is clear that the sulfur present in conventional equipment effectively prevents carbonization. In conventional methods, process sulfur somewhat inhibits the carbonization reaction. However, in systems with very low sulfur content, this inherent protection no longer exists.
FIG. 1A is a photomicrograph of a portion of the interior (processing side) of a mild steel furnace tube of a commercial reformer. The tube has been exposed to conventional reforming conditions for about 19 years. This picture shows that even after the tube surface has been exposed to hydrocarbons at high temperatures for a long time, the tube structure remains normal and essentially unchanged (the black part of the photo is the background). Is).
FIG. 1B is a photomicrograph of a portion of a mild steel specimen that has been placed in the reactor of a low sulfur / low moisture test plant for only 13 weeks. This photo shows the corroded surface of the sample where metal dusting occurred (contrast with the black background). The dark gray veins indicate carbonization around the steel, which causes carbonization and embrittlement deeper than 1 mm deep.
Of course, the problems associated with carbonization only occur with the carbonization of physical devices. Carbonization of the steel wall causes “metal granulation” and liberation of molten metal droplets due to catalytically active particles and metal corrosion.
Active metal granules provide additional sites for coke formation in the equipment. While catalyst deactivation by coking is a problem that must generally be addressed by reforming, this new critical coke formation source has created a new clogging problem with coke, which is aggravating the problem. . In fact, it has been found that mobile active metal particulates and coke particles generally transfer coking throughout the apparatus. Active metal particles actually induce coke formation on their own and wherever they accumulate in the device, resulting in coke clogging and a hot zone of exothermic demethanation reaction Result. As a result, an uncontrollable coke blockage of the reactor unit occurs, which will shut down the unit several weeks after startup. However, these problems can be solved by using the method and reactor apparatus of the present invention.
Thus, the first aspect of the present invention has resistance to carbonization and metal granulation, which is an improvement over conventional mild steel reactor equipment under low sulfur conditions, often low sulfur and low water content conditions. The resistance when reformed is less than about 2.5 mm / year of weakening due to carbonization, preferably less than 1.5 mm / year, more preferably less than 1 mm / year, most preferably 0.1 mm Reforming catalyst containing alkali or alkaline earth metal and one or more Group VIII metals, preferably an air-hole zeolite catalyst and hydrocarbon, in a reactor apparatus having a resistance of less than 1 year The present invention relates to a hydrocarbon reforming process comprising contacting Preventing embrittlement to such an extent would allow operation over longer periods of time by significantly reducing metal granulation and coking in the reactor apparatus.
Another aspect of the present invention is to reform hydrocarbons using a reforming catalyst, such as an atmospheric pore zeolite catalyst that includes an alkaline earth metal and is provided with one or more Group VIII metals under low sulfur conditions. The method is an improvement over conventional mild steel equipment, with resistance to carbonization and metal granulation, the resistance being less than about 2.5 mm / year, preferably less than 1.5 mm / year, More preferably, it relates to a reactor apparatus comprising means for providing a resistance of less than 1 mm / year, most preferably less than 0.1 mm / year.
Among many factors, the present invention is based on the discovery that there are significant carbonization, metal granulation, and coking problems with low sulfur and low sulfur, low water reforming processes. Such problems are not as serious as in conventional reforming processes where higher levels of sulfur are present. This discovery has led to an enormous amount of research and development to solve these problems, a solution that is novel for low sulfur reforming and a resistant material for low sulfur reforming equipment. Judgment and selection, effective use and application of these resistant materials, carbonization, metal granulation and coking additives (other than sulfur), and various to effectively address the above problems The present invention relates to process modification and configuration, and combinations thereof.
In particular, due to its discovery, resistance materials for low sulfur reformers, preferably reactor walls, furnace tubes and their networks, such as certain alloys, which have been previously unnecessary in conventional reformers Studies for the identification and selection of stainless steel, aluminized and chromated materials, and certain ceramic materials have been conducted. It has also been discovered that other special materials applied as plating, cladding, paint, etc. can also be effectively made resistant. These materials include copper, tin, arsenic, antimony, brass, lead, bismuth, chromium, their intermetallic compounds, their alloys, as well as silica and silicon-based coatings. In one preferred embodiment of the present invention, a novel resistive tin-containing paint is provided.
In addition, as a result of the above discovery, the following mentions as essential carbon-free and anti-coking agents which are essentially sulfur-free, preferably completely sulfur-free, which are new to reformation, as essential: It was decided to develop an additive. Such additives include organic tin compounds, organic antimony compounds, organic bismuth compounds, organic arsenic compounds, and organic lead compounds.
In addition, due to the problems associated with low sulfur reforming, certain process modifications and forms have been developed that were previously unnecessary in conventional reforming. These include certain temperature control methods, the use of superheated hydrogen between reactors, more frequent catalyst regeneration, the use of staged heaters and tubes, the use of staged temperature zones, the use of superheated feeds, larger diameters Use of tubes and / or higher tube speeds is included.
[Brief description of the drawings]
As mentioned above, FIG. 1A is a photomicrograph of a portion of the interior (processing side) of a mild steel furnace tube from a commercial reformer used for about 19 years.
FIG. 1B is a photomicrograph of a portion of a mild steel specimen placed for only 13 weeks inside the reactor of a low sulfur / low water test plant, also as described above.
FIG. 2 is a schematic diagram of a reforming reactor apparatus suitable for use in the present invention.
Detailed description of preferred embodiments
As used herein, metallurgical terms have their general metallurgical meaning as described in “THE METALS HANDBOOK” (American Society of Metals). For example, “carbon steel” has no specified minimum amount for any alloying element (other than the generally accepted amounts of manganese, silicon, and copper); carbon, silicon, manganese, copper, A steel that contains only elements, other than sulfur and phosphorus, in only incidental amounts. “Mild steel” refers to carbon steel containing up to about 0.25% carbon. Alloy steels have a certain amount of alloying elements (carbon and generally acceptable amounts other than manganese, copper, silicon, sulfur and phosphorous) within the scope recognized as structural alloy steels, mechanical or physical properties. It is steel added to change the content. The alloy steel will contain less than 10% chromium. The stainless steel can be any of several types of steel containing at least 10%, preferably 12-30% chromium as the principal alloying element.
Thus, in general, one object of the present invention is to use a reforming catalyst, particularly an air hole zeolite catalyst, containing an alkali or alkaline earth metal and imparting one or more sulfur-sensitive Group VIII metals. It is to provide an improved method for reforming hydrocarbons under sulfur conditions. Of course, such a process should be more resistant to carbonization than conventional low sulfur reforming processes.
One solution to the problem addressed by the present invention is to improve the resistance to carbonization and metal granulation during reforming using a reforming catalyst such as the aforementioned sulfur sensitive atmospheric pore zeolite catalyst under low sulfur conditions. It is to provide a novel reactor apparatus comprising one or more of various means for doing so.
As used herein, “reactor system” includes at least one reforming reactor and a corresponding furnace mechanism and piping. FIG. 2 illustrates a typical reforming reactor apparatus suitable for practicing the present invention. It may comprise a plurality of reforming reactors (10), (20) and (30). Each reactor contains a catalyst bed. The apparatus also includes a plurality of furnaces (11), (21) and (31); a heat exchanger (12); and a separator (13).
Through research accompanying the present invention, it has been discovered that the above problems for low sulfur reforming can be effectively addressed by selecting appropriate reactor equipment materials that contact the hydrocarbons being processed. Typically, the reforming reactor apparatus was made of mild steel or a typical alloy steel such as chrome steel and did not cause much carbonization or granulation. For example, 2 for standard reforming conditions¹/_Four Cr furnace tube can last 20 years. However, these steels have been found to be inappropriate under low sulfur reforming conditions. They quickly become brittle due to carbonization within about a year. For example, 2¹/₂ Cr 1 Mo steel has been found to carbonize and become brittle faster than 1 mm / year.
Furthermore, it has been found that materials considered to be resistant to coking and carbonization by standard metallurgical practices do not necessarily become resistant under low sulfur reforming conditions. For example, nickel rich alloys such as Incoloy 800 and 525; Inconel 600; Marcel and Haynes 230 are unacceptable because they exhibit excessive coking and granulation.
However, 300 series stainless steels, preferably 304, 316, 321 and 347, are acceptable as materials for at least the parts of the reactor apparatus in contact with the hydrocarbon. They have been found to have greater carbonization resistance than mild steel and nickel rich alloys.
Initially, aluminized materials such as those sold by Allon Corp. ("Alonized Steel") are suitable for carbonization with the reforming reactor apparatus and method of the present invention. It was thought that protection would not be given. However, carbonization and metal granules under low sulfur reforming conditions can then be applied by applying a thin aluminum or alumina coating on the metal surface of the reforming reactor apparatus or simply using aronized steel during manufacture. It has been discovered that surfaces can be provided that are sufficiently resistant to oxidation. However, such materials are relatively expensive and resistant to carbonization and metal granulation, but tend to crack and exhibit a substantial reduction in tensile strength. The crack exposes the underlying base metal and makes it susceptible to carbonization and metal granulation under low sulfur reforming conditions.
Aluminized materials have been used to prevent carbonization in ethylene steam cracking processes, but such processes are operated at temperatures much higher than reforming, where carbonization is expected to occur. Simple carbonization and metal granulation have not been a problem with conventional reforming methods.
Thus, another solution to the problem of carbonization and metal granulation involves applying a thin aluminum or alumina coating or using an aluminized material as at least a portion of the metal surface in the reactor apparatus. . Indeed, metal surfaces that are particularly susceptible to carbonization and metal granulation can be provided in such a manner. Such metal surfaces include but are not limited to reactor walls, furnace tubes, and hearths.
When applying an aluminum or alumina film, thermal expansion similar to the coefficient of thermal expansion of the metal surface to which it is applied (eg mild steel) so that it can withstand the thermal shocks and repeated temperature cycles that occur during reforming It is preferable to have a coefficient. This prevents cracking or peeling of the coating that would expose the underlying metal surface to a carbonization-induced hydrocarbon environment.
In addition, the coating should have a thermal conductivity that is similar to or greater than that of metals conventionally used in the manufacture of reforming reactor devices. Furthermore, the aluminum or alumina membrane must not degrade in the reforming environment or the oxidizing environment associated with catalyst regeneration and should not result in the decomposition of hydrocarbons in the reactor apparatus.
Suitable methods for applying an aluminum or alumina film to a metal surface such as mild steel include well known deposition methods. Preferred methods include powder and vapor diffusion methods such as the “Aronization” method commercially available by Alon Processing, Inc. of Teritown, Pa.
In essence, “alonization” is a high temperature diffusion process in which aluminum is alloyed into the surface of the metal being treated, for example, commercial grade mild steel. In this method, a metal (eg, mild steel) is placed in a retort and surrounded by a mixture of mixed aluminum powders. The retort is then sealed secretly and placed in an atmosphere control furnace. At elevated temperatures, aluminum diffuses deeply into the metal being processed, producing an alloy. After cooling the furnace, the substrate is removed from the retort to remove excess powder. Next, straightening, trimming, chamfering, and other secondary operations can be performed as needed. By this method, the treated (alonized) metal can be made resistant to carbonization and metal granulation under low sulfur reforming conditions according to the present invention.
In order to make the surface resistant to carbonization and metal agglomeration under low sulfur reforming conditions, a thin chromium or chromium oxide film can also be applied to the metal surface of the reactor apparatus. Similar to using alumina and aluminum films and aluminized materials, chromium or chromium oxide coated metal surfaces have not been used to address the carbonization problem under low sulfur reforming conditions.
Chromium or chromium oxide can also be applied to metal surfaces that are susceptible to carbonization and metal granulation, such as reactor walls, furnace linings, and furnace tubes. However, any surface in the device that exhibits signs of carbonization and metal granulation under low sulfur reforming conditions will benefit from applying a thin film of chromium or chromium oxide.
When a chromium or chromium oxide film is applied, the chromium or chromium oxide film preferably has a thermal expansion coefficient similar to that of the metal to which it is applied. In addition, the chromium or chromium oxide film should be able to withstand repeated thermal shock and temperature cycling that typically occurs during modification. This can prevent cracking or peeling of the chromium or chromium oxide film that would potentially expose the underlying metal surface to the carbonization-inducing environment. In addition, the chromium or chromium oxide film should have a thermal conductivity similar to or greater than the materials conventionally used in reforming reactor equipment (especially mild steel) so that efficient heat transfer can be maintained. It is. Chromium or chromium oxide membranes should also not degrade in the reforming environment or the oxidizing environment associated with catalyst regeneration and should not induce hydrocarbon decomposition in the reactor unit.
For example, suitable methods for applying a chromium or chromium oxide film to a surface such as mild steel include well known deposition methods. Preferred methods include powder packs and vapor diffusion methods such as the “chromation” method that is commercially available by Alloy Surfaces, Inc. of Wilmington, Delaware.
The “chromation” method is essentially a vapor diffusion method (similar to the “alonization method” above) in which chromium is applied to the metal surface. The method involves contacting the metal to be coated with a chromium powder followed by a thermal diffusion step. This actually results in an alloy of the treated metal and chromium, making the surface extremely resistant to carbonization and metal granulation under low sulfur reforming conditions.
In certain areas of the reactor apparatus, the local temperature may become excessively high during reforming (eg, 900-1250 ° F.). This is particularly the case when exothermic demethanization reactions occur in the coke balls that normally occur in the furnace tube and catalyst bed, resulting in localized high temperature regions. Mild steel and nickel-rich alloys are still preferred, but the 300 series stainless steel shows some coking and granulation at about 1000 ° F. Thus, 300 series stainless steel is useful but not the most preferred material for use in the present invention.
Chromium-rich stainless steels such as 446 and 430 have greater resistance to carbonization than 300 series stainless steels. However, these steels are not desirable for heat resistance (they tend to be brittle).
Preferred resistive materials over the 300 series stainless steel used in the present invention include copper, tin, arsenic, antimony, bismuth, chromium, and brass, and their intermetallic compounds and alloys [e.g., Cu-Sn alloys, Cu-Sb alloy, stannide, antimonide, bismuthide, etc.). Even steel and nickel-rich alloys containing these metals can show reduced carbonization. In preferred embodiments, these materials are applied to the substructure material as a plating, cladding, paint (eg, oxide paint), or other coating. This is particularly advantageous. This is because conventional structural materials such as mild steel can still be used with only the surface in contact with the treated hydrocarbon. Of these, tin is particularly preferred. This is because it reacts with the surface to have excellent high temperature carbonization resistance and provides a coating that is less prone to stripping and flaking. The tin-containing layer may be as thin as 1/10 μm, and it is still considered that carbonization can be prevented.
In practice, these resistant materials are preferably applied to new or existing reactor equipment as paint-like formulations (hereinafter “paints”). Such paint can be applied by spraying, brushing, casting, etc. to the surface of a reactor apparatus such as mild steel or stainless steel. Such paints are degradable reactive tin-containing paints that are reduced to reactive tin when heated in a reducing atmosphere to form metal stannates (eg, iron stannate and nickel / iron stannate). Is most preferred.
Most preferably, the aforementioned paint comprises at least four components (or functional equivalents thereof); (i) a hydrogen decomposable tin compound, (ii) a solvent system, (iii) finely divided tin metal, and ( iv) Reducing sponge / dispersion / tin oxide as binder. The paint should contain finely divided solids to minimize settling and should not contain non-reactive materials that would interfere with the reaction of the reactor apparatus surface with reactive tin.
As the hydrogen decomposable tin compound, tin octoate is particularly useful. Commercial blends of the compound itself are available, and when partially dried on the steel surface, it becomes an almost chewing gum layer. The layer does not crack and / or split. This property is necessary for any coating composition used in the present invention. This is because the coated material is believed to be stored for several months before being treated with hydrogen. Also, if the parts are coated before assembly, they must be resistant to chipping during assembly. As mentioned above, tin octoate is commercially available. It is reasonably priced and breaks down smoothly into a reactive tin layer, which forms iron stannate in hydrogen at temperatures as low as 600 ° F.
However, octanoic acid should not be used alone in the paint. It is insufficiently viscous. Even if the solvent is evaporated from there, the remaining liquid will drip and flow over the surface of the coating. In practice, for example, if such is used to coat a horizontal furnace tube, it will accumulate at the bottom of the tube.
Component (iv), Tin Oxide Sponge / Dispersion / Binder, is a porous tin-containing compound that can absorb organometallic tin compounds and still be reduced to active tin in a reducing atmosphere be able to. In addition, tin oxide can be processed by a colloid mill to produce very fine particles that are difficult to settle rapidly. The addition of tin oxide gives a paint that feels dry and difficult to flow.
Unlike typical paint thickeners, component (iv) is selected to be the reactive portion of the coating when reduced. It is not as inert as formed silica, a typical paint thickener that leaves a non-reactive surface coating after processing.
Finely ground tin metal, component (iii), is added so that it can be used to react with the surface to be coated with metallic tin at the lowest possible temperature, even in a non-reducing atmosphere. The particle size of the tin is preferably 1 to 5 μ, so that the surface to be coated can be covered very well with tin metal. Non-reducing conditions may occur during paint drying and pipe joint welding. The presence of metallic tin ensures that the tin metal is present and reacts to form the desired stannate layer even when a portion of the coating is not fully reduced.
The solvent should be non-toxic and effective to allow the paint to be sprayed and spread as desired. It should also evaporate rapidly and be solvent compatible with hydrogen decomposable tin compounds. Isopropyl alcohol is most preferred, but hexane and pentane can be used if necessary. However, acetone tends to precipitate organotin compounds.
In one embodiment, using 20% Tin-Cem (stannous octoate in octanoic acid), stannous dioxide, tin metal powder and isopropyl alcohol tin paint. it can.
Tin paint can be applied in many ways. For example, the furnace tubes of the reactor apparatus can be applied individually or as a module. The reforming reactor apparatus according to the present invention has various numbers of furnace tubes of appropriate width, length and height (eg, about 10 feet long, about 4 feet wide, and about 40 feet high). Modules (eg, about 24 furnace tube modules) can be included. Typically, each module includes two headers of a suitable diameter, preferably about 2 feet in diameter, which are about 4 to 10 in a suitable length (eg, about 42 feet long). Connected by u-tube. Thus, the total surface area to be applied in the module varies very widely, for example, in one embodiment it is about 16,500 ft.²May be.
It is advantageous to apply the tubes as modules rather than individually, in at least four respects; (i) Thermal destruction of the tin paint can be avoided by applying the modules rather than the individual tubes. Because the components of the module are usually heat treated at extremely elevated temperatures during manufacture; (ii) applying the module is faster, cheaper and cheaper than applying the tubes individually; (Iii) Applying the module is more efficient when scheduling production; and (iv) Applying the module allows application of welds.
However, by applying the modules, it is not possible to completely coat the tubes with paint as if the tubes were applied individually. If the coating is insufficient, the tubes can be coated individually.
The paint is preferably sprayed into the tube and header. Sufficient paint should be applied to completely cover the tube and header. After spraying the module, it may be left to dry for about 24 hours, and then a slow stream of heated nitrogen may be applied (eg, about 24 hours at about 150 ° F.). Thereafter, a second paint coating is preferably applied and also dried by the procedure described above. After applying the paint, it is preferable to keep the modules under a slight nitrogen pressure and should not be exposed to temperatures above about 200 ° F. prior to installation and expose them to water except during the hydrogenation test. Should not.
Iron-containing reactive paints are also useful in the present invention. Such iron-containing reactive paints would preferably include various tin compounds to which iron was added in an amount up to 1/3 by weight of Fe / Sn.
For example, the addition of iron is Fe₂O_ThreeIt can be done in the form of Significant advantages are provided by adding iron to the tin-containing paint; in particular, (i) it accelerates the reaction of the paint forming the iron stannate, thereby acting as a flux; (ii) it is in the stannate layer Dilute the nickel concentration of the iron, thereby providing better protection against coking; and (iii) it results in a paint that provides anti-coking protection of iron stannate even when the underlying surface does not react well .
Yet another means for preventing carbonization, coking, and metal granulation in low sulfur reactor equipment consists of applying a metal coating or cladding to the chromium rich steel contained in the reactor equipment. These metallizations or claddings may consist of tin, antimony, bismuth or arsenic. Tin is particularly preferred. These coatings or claddings can be applied by methods including electrodeposition, vapor deposition, and immersion of chromium rich steel in a molten metal bath.
In reforming reactor equipment where carbonization, coking and metal granulation are particularly problematic, it has been found that coating a nickel-rich steel rich in chromium with a tin layer actually results in a double protective layer. Has been. This results in a chromium-rich inner layer that is less susceptible to carbonization, coking, and metal granulation and an outer tin layer that is also less susceptible to carbonization, coking, and metal granulation. This occurs because when chromium-rich tin-coated steel is exposed to typical reforming temperatures, for example, about 1200 ° F., it reacts with the steel to form iron nickel stannate. Thereby nickel leaches preferentially from the surface of the steel, leaving a layer of steel rich in chromium. In some cases it may be desirable to remove the iron nickel stannate layer from the stainless steel to expose the chromium rich steel layer.
For example, when tin clad is applied to grade 304 stainless steel and heated at about 1200 ° F., it is a chromium-rich steel layer comparable to grade 430 stainless steel that contains about 17% chromium and is essentially nickel free. Has been found to yield a result.
When applying a tin metal coating or cladding to a chromium rich steel, it may be desirable to vary the thickness of the metal coating or cladding to achieve the desired resistance to carbonization, coking, and metal atomization. . This can be done, for example, by adjusting the length of time that the steel rich in chromium is immersed in the molten tin bath. This will also affect the thickness of the resulting chromium-rich steel layer. It may also be desirable to change the composition of the coated chromium-rich steel or to change the operating temperature in order to adjust the chromium concentration in the resulting chromium-rich steel layer.
In addition, the tin-coated steel is made from a thin oxide coating, preferably Cr.₂O_ThreeIt has been found that post-treatment steps including application of chromium oxide such as can provide further protection from carbonization, metal granulation, and coking. This coating will be as thin as a few μm. The application of such chromium oxide will protect steels coated with aluminum as well as tin such as aronized steels under low sulfur reforming conditions.
The chromium oxide layer can be applied by a variety of methods including: a method of applying a chromate or dichromate paint followed by a reduction step; steam treatment with an organic chromium compound; or chromium A method of oxidizing the resulting chrome-plated steel after applying metal plating.
Examination of the tin electrodeposited steel subjected to low sulfur reforming conditions for a substantial period of time reveals that if the chromium oxide layer is formed on or under the stannate layer, the chromium oxide layer It has been found that it does not cause layer degradation but appears to make the steel more resistant to carbonization, coking, and metal granulation. Therefore, applying a chromium oxide layer to tin or aluminum coated steel results in a steel that is more resistant to carbonization and coking under low sulfur reforming conditions. This post-treatment process is particularly applicable for treating tin or aluminum coated steels that need repair after being exposed to low sulfur reforming conditions for a long time.
Aluminized, eg, “alonized” steels that are resistant to carbonization under current low sulfur reforming conditions are more resistant by post-treating the aluminized steel with a tin coating. It has further been found that it can be made. This results in a steel that is more difficult to carbonize. This is because the cumulative effect of carbonization resistance is obtained from both the aluminum coating and the tin coating. This post-treatment provides an additional advantage in that it will repair defects or cracks in the aluminum, eg, the aronized coating. Such post-processing will also give lower costs. This is because a thinner aluminum coating may be applied to the steel surface post-treated with a tin coating. Furthermore, this post-treatment will protect the underlying steel layer exposed by bending of the aluminized steel, which will crack the aluminum layer and expose the steel to carbonization induced under reforming conditions. Will. This post-treatment step also prevents coke formation on the treated steel surface and also prevents coke formation that occurs behind cracks that appear in steel that is aluminized but not coated with tin. .
It has been found that a sample of aronized steel coated with tin on one side shows black coke deposits only on the untreated side under low sulfur reforming conditions. The coke formed on the aluminized surface is good quality coke resulting from cracks on the acidic alumina sites. It cannot induce additional coke adhesion. Thus, the post-treatment of applying a tin coating to the aluminized steel can further reduce the problems of carbonization, coking and metal granulation that occur in reactor devices operated under the reforming conditions according to the present invention.
Without wishing to be bound by theory, it is believed that the stability of the various materials of the present invention can be selected and classified according to their responsiveness to the carbonized atmosphere. For example, iron, cobalt, and nickel form relatively unstable carbides that are later carbonized, coked, and granulated. Elements such as chromium, niobium, vanadium, tungsten, molybdenum, tantalum and zirconium form stable carbides that are more resistant to carbonization, coking and granulation. Elements such as tin, antimony and bismuth do not form carbides or coke. And these compounds may form stable compounds under the modifying conditions with many metals such as iron, nickel and copper. Tindes, antimonides, bismuths, and compounds of lead, mercury, arsenic, germanium, indium, tellurium, selenium, thallium, sulfur and oxygen are also resistant. The last category of materials includes elements such as silver, copper, gold, platinum, and refractory oxides such as silica and alumina. These materials are resistant, do not form carbides, and do not react with other metals in a carbonized atmosphere under reforming conditions.
As mentioned above, the selection of suitable metals that are resistant to carbonization and metal granulation, and their use as a coating material for the metal surface of the reactor apparatus is This is one way to prevent problems. However, carbonization and metal granulation occur widely with a wide variety of metals, and metals that are difficult to carbonize are more common than conventional materials (eg, mild steel) used in the production of reforming reactor equipment. The price is high or special. Therefore, it is desirable to use a ceramic material for the reactor apparatus of the present invention for at least a portion of the metal surface of the reactor apparatus that does not form carbides under typical reforming conditions and is therefore less susceptible to carbonization. For example, at least a portion of the furnace tube, hearth lining, or both can be made of a ceramic material.
When selecting a ceramic material for use in the present invention, it is preferred that the ceramic material has a thermal conductivity greater than or equal to that of materials conventionally used in the manufacture of reforming reactor devices. Furthermore, the ceramic material should have sufficient structural strength at the temperatures that occur in the reforming reactor apparatus. Furthermore, the ceramic material should be able to withstand repeated thermal shocks and temperature cycles that occur during operation of the reactor apparatus. When a ceramic material is used in the manufacture of a furnace backing, the ceramic material should have a coefficient of thermal expansion that is approximately the same as the coefficient of thermal expansion of the metal outer surface with which the backing is in intimate contact. This prevents abnormal stresses occurring at the joint during the temperature cycle that occurs during start and stop. Furthermore, the ceramic surface should not be subject to degradation in a hydrocarbon or oxidizing environment that occurs during catalyst regeneration. The ceramic material selected should not promote the degradation of hydrocarbons in the reactor apparatus.
Suitable ceramic materials include, but are not limited to materials such as silicon carbide, silicon oxide, silicon nitride, and aluminum nitride. Of these, silicon carbide and silicon nitride are particularly preferred. Because they appear to be able to give full protection to the reactor equipment under low sulfur reforming conditions.
At least a portion of the metal surface of the reactor apparatus can be coated with a silicon or silica film. In particular, metal surfaces that can be coated include, but are not limited to, reactor walls, furnace tubes, and furnace linings. However, the metal surface of the reactor apparatus that shows signs of carbonization and metal granulation under low sulfur reforming conditions will benefit from the application of a thin film of silicon or silica.
Conventional methods can be used to apply a silicon or silica film to a metal surface and coat it. Silica or silicon can be applied by chemical vapor deposition and electrodeposition of alkoxysilanes in a water vapor carrier gas. The silicon or silica film preferably has a coefficient of thermal expansion that is approximately the same as that of the metal surface on which it is coated. Furthermore, the silicon or silica film should be able to withstand the thermal shock and temperature cycling that occurs during modification. This prevents cracking or peeling of the silicon or silica film and prevents potential exposure of the underlying metal surface to the carbonization-induced hydrocarbon environment. Also, the silica or silicon film should have a thermal conductivity that is approximately equal to or greater than that of metals conventionally used in reforming reactor equipment so that sufficient heat transfer can be maintained. is there. The silicon or silica film should not degrade in the reforming environment or the oxidizing environment associated with catalyst regeneration, and it should not cause the hydrocarbon itself to decompose.
Since different areas of the reactor apparatus of the present invention (eg, different areas in the furnace) may be exposed to a wide range of temperatures, the choice of material should be in the area that receives the highest temperature in the apparatus. The material may be stepped to use a material having a higher carbonization resistance.
With regard to material selection, it has been discovered that oxidized surfaces of Group VIII metals such as iron, nickel and cobalt are more active against coking and carbonization than their unoxidized ones. . For example, an air roasted sample of 347 stainless steel has been found to be significantly more active than an unoxidized sample of the same steel. This is believed to be due to the re-reduction of the oxidized steel resulting in very fine particles of iron and / or nickel metal. Such metals are particularly active against carbonization and coking. Therefore, it is desirable to avoid using these materials as much as possible during the oxidative regeneration process, such as those typically used in catalytic reforming. However, air-roasted 300 series stainless steel coated with tin can provide coking and carbonization resistance similar to the unbaked samples of 300 series stainless steel with the same tin coating. Is known.
Furthermore, it has been recognized that the functionality of the catalyst to sulfur is not a problem and oxidation is a problem in equipment where sulfur is used to immobilize the metal surface. If the sulfur level in such a system is insufficient, the metal sulfide formed on the metal surface is reduced to a finely divided metal after oxidation and reduction. This metal is very reactive to coking and carbonization. This could potentially cause catastrophic failure of metallurgy, or most coking problems.
As noted above, when the exothermic demethanization reaction in the coke balls produces a localized hot zone, an excessively high temperature is generated in the catalyst bed. These high hot spots also cause problems with conventional reforming reactor equipment (as well as other areas of chemical and petrochemical processing).
For example, it has been observed that the central pipe network of the reformer is locally aged and perforated, eventually resulting in catalyst migration. In conventional reforming processes, the temperature during formation and combustion in the coke balls is clearly high enough to exceed the ability of process sulfur to disable coking, carbonization, and granulation. Thus, the metal screen is carbonized and more susceptible to wear due to interparticle oxidation (a type of corrosion) during regeneration. The mesh becomes larger and has holes.
The teachings of the present invention can be applied to other areas of chemical and petrochemical processing as well as conventional reforming. For example, the plating, cladding and coating described above can be used in the manufacture of a central pipe network to prevent excessive hole formation and catalyst migration. Furthermore, their teachings undergo carbonization, coking and metal granulation. It can be applied to any furnace tube such as a furnace tube in a coke oven.
In addition, the techniques described herein can be used to control carbonization, coking, and metal granulation at excessively high temperatures so that they operate in a cracking furnace operating at about 1400 to about 1700 ° F. Can be used. For example, steel degradation that occurs in cracking furnaces operating at these temperatures can be controlled by applying various metallizations. These metal coatings can be applied by melting, electrodeposition and coating. Application is particularly preferred.
For example, antimony coatings applied to iron-containing steels protect these steels from carbonization, coking, and metal granulation under the described cracking conditions. Indeed, antimony paint applied to iron-containing steel provides protection against carbonization, coking and metal granulation at 1600 ° F.
A coating of bismuth applied to a nickel rich steel alloy (eg, Inconel 600) can protect these steels against carbonization, coking, and metal granulation under cracking conditions. This is illustrated at temperatures up to 1600 ° F.
Bismuth coatings can also be applied to iron-containing steels to provide protection against carbonization, metal granulation and coking under cracking conditions. A metal coating made of a combination of bismuth, antimony and / or tin can also be used.
Looking again at the low sulfur reformation, other methods can be used to address the problems discovered by the present invention. They can be used in conjunction with a suitable material selection for the reactor apparatus, or they can be used alone. Preferred among these alternative techniques is the addition of non-sulfur carbonization and coking agents (one or many) during the reforming process. These agents may be added continuously during the process and serve to interact with the surface of the reactor apparatus in contact with the hydrocarbons, or they may be applied as a pretreatment to the reactor apparatus.
Although not wishing to be bound by theory, these agents interact with the surface of the reactor apparatus by decomposition and erode the surface, such as stannates, antimonides, bismuthides, plumbides, arsenides, etc. It is believed to form such iron and / or nickel intermetallic compounds. Such intermetallic compounds are resistant to carbonization, coking and granulation and can protect the underlying metallurgical part.
Intermetallic compounds are also used to immobilize metals.₂It is believed to be more stable than metal sulfides formed in devices using S. These compounds are not reduced by hydrogen like metal sulfides. As a result, they are less likely to exit the device than metal sulfides. Thus, the continuous addition of carbonization inhibitor performed with the feed can be minimized.
Preferred non-sulfur carbonization and coking inhibitors include organometallic compounds such as organotin compounds, organoantimony compounds, organobismuth compounds, organoarsenic compounds, and organolead compounds. Suitable organic lead compounds include tetraethyl lead and tetramethyl lead. Particularly preferred are organotin compounds such as tetrabutyltin and trimethyltin hydride.
Other specific organometallic compounds include bismuth neodecanoate, chromium octoate, copper naphthenate, manganese carboxylate, palladium neodecanoate, silver neodecanoate, tetrabutylgermanium, tributylantimony, triphenylantimony, triphenyl Arsine and zirconium octoate are included.
Where and how these agents are added to the reactor apparatus is not a problem and will depend primarily on the design characteristics of the particular process. For example, they may be added continuously with the feed or discontinuously.
However, the addition of these drugs to the feed is not preferred because they tend to accumulate in the first part of the reactor apparatus. This does not provide adequate protection in other areas of the device.
These agents are preferably provided as a coating before manufacture, before start-up, or in situ (ie, for existing devices). If added in situ, it should be done immediately after catalyst regeneration. A very thin coating can be applied. For example, when an organic tin compound is used, it is considered that a thin iron stannate coating of about 0.1 μm is also effective.
A preferred method of coating the agents on existing or new reactor surfaces, or new or existing furnace tubes, is to decompose the organometallic compound in a hydrogen atmosphere at a temperature of about 900 ° F. For example, in the case of an organic tin compound, this produces reactive metal tin on the tube surface. At these temperatures, the tin further reacts with the surface metal and immobilizes it.
The optimum coating temperature will depend on the particular organometallic compound or, if an alloy is desired, on the mixture of those components. Typically, excess organometallic coating can be pulsed into the tube at a high hydrogen flow rate so that the coating can be carried in a mist throughout the apparatus. The flow rate is then reduced so that the coated metal mist coats and reacts with the furnace tube or reactor surface. Alternatively, the compound is introduced as a vapor that can be decomposed in a reducing atmosphere to react with the hot walls of the tube or reactor.
As described above, a reformer apparatus that is susceptible to carbonization, metal granulation, and coking, a reactor apparatus that is most susceptible to carbonization, with a degradable coating containing a decomposable organometallic tin compound. It is possible to process by applying to the area. Such a method is particularly successful in a temperature controlled furnace.
However, such control does not necessarily exist. There are “hot spots” that occur in the reactor apparatus, particularly in the furnace tube, where the organometallic compound decomposes to form deposits. Accordingly, another aspect of the present invention resides in a method that does not cause such deposition in a reforming reactor apparatus that cannot control the temperature accurately and that exhibits a hot, hot spot region.
Such a method involves preheating the entire reactor apparatus with a hot stream of hydrogen gas to a temperature of 750-1150 ° F., preferably 900-1100 ° F., most preferably about 1050 ° F. . A reactor apparatus preheated with a preheated cold gas stream containing a vaporized organometallic tin compound and hydrogen gas at a temperature of 400-800 ° F., preferably 500-700 ° F., most preferably about 550 ° F. Introduce into. This gas mixture can be introduced upstream to give a cracked “wave” that travels throughout the entire reactor apparatus.
This method is essentially effective. This is because the hot hydrogen gas produces a uniformly heated surface that decomposes the cold organometallic gas as it travels as waves throughout the reactor apparatus. A cold gas containing an organometallic tin compound decomposes on the hot surface and coats the surface. The organometallic tin vapor will continue to travel as waves treating the hotter surface downstream of the reactor unit. Thereby, the entire reactor apparatus can have a uniform coating of the organometallic tin compound. It may also be desirable to perform these high-low temperature cycles several times to ensure that the entire reactor apparatus is uniformly coated with the organometallic tin compound.
In operation of the reforming reactor apparatus according to the present invention, naphtha is reformed to form aromatics. The naphtha feed is a light hydrocarbon, preferably a hydrocarbon boiling in the range of about 70 ° F to 450 ° F, more preferably about 100 to 350 ° F. The naphtha feed will contain aliphatic or paraffinic hydrocarbons. These aliphatics are at least partially converted into aromatics within the reforming reaction zone.
In the “low sulfur” system of the present invention, the sulfur content of the feed will preferably be less than 100 ppb, more preferably less than 50 ppb. If necessary, a slight excess of sulfur can be removed using a sulfur scrubber.
Preferred reforming process conditions include a temperature of 700-1050 ° F, more preferably 850-125 ° F; and a pressure of 0-400 psig, more preferably 15-150 psig; 0.1-20, more preferably 0.5-10, A recycle hydrogen rate sufficient to produce a hydrogen to hydrocarbon molar ratio for the feed to the reforming reaction zone; and for a hydrocarbon feed on the reforming catalyst of 0.1 to 10, more preferably 0.5 to 5. Of liquid space per hour.
In order to achieve a suitable reformer temperature, it is often necessary to heat the furnace tube to a high temperature. These temperatures often range from 600 to 1800 ° F, usually from 850 to 1250 ° F, and more often from 900 to 1200 ° F.
As noted above, low sulfur system carbonization, coking, and metal granulation problems have been found to be associated with excessively high local process temperatures in the reactor equipment, This is particularly noticeable in furnace tubes for devices characterized by high temperatures. Conventional reforming processes where high levels of sulfur are present typically result in furnace tube surface temperatures of up to 1175 ° F at the end of operation. However, excessive carbonization, coking, and metal granulation have not been observed. However, it has been discovered that in low sulfur systems, rapid and excessive carbonization, coking and metal granulation occur in CrMo steels above 950 ° F and stainless steels above 1025 ° F. Yes.
Accordingly, another aspect of the present invention is to reduce the temperature of the reformer furnace tube, transfer piping and / or metal surface inside the reactor below the above level. For example, temperature can be detected and monitored using thermocouples installed at various locations within the reactor apparatus. In the case of a furnace tube, the thermocouple can be mounted on its outer wall, preferably at the hottest point of the furnace (usually near the furnace outlet). If necessary, adjustments during the processing operation can be made to maintain the temperature at the desired level.
There are other ways to reduce the exposure of the device surface to undesirably high temperatures as well. For example, a heat transfer zone with a resistive (usually more expensive) tube can be used at the final stage where the temperature is usually highest.
Furthermore, superheated hydrogen can be added between the reactors of the reformer. In addition, a larger catalyst introduction amount can be used. Also, the catalyst may be regenerated more frequently. In the case of catalyst regeneration, it can best be achieved using a moving bed process where the catalyst is removed from the final bed, regenerated and introduced into the first bed.
Carbonization and metal granulation can be minimized with certain other new equipment configurations and process conditions in the low sulfur reforming reactor apparatus of the present invention. For example, the reactor apparatus can be constructed using staged heaters and / or tubes. In other words, the heater or tube that is subjected to the most extreme temperature conditions in the reactor apparatus is a material that has a greater resistance to carbonization than the materials conventionally used in the manufacture of reforming reactor apparatus, It can be made from the materials mentioned above. A heater or tube that is not subjected to extreme temperatures may be made directly from conventional materials.
By using such a staged design for the reactor apparatus, the overall cost of the system is still provided while still providing a reactor apparatus that is sufficiently resistant to carbonization and metal granulation under low sulfur reforming conditions. (Because carbonized resistant materials are generally more expensive than conventional materials). In addition, this should facilitate the refit of existing reforming reactor devices such that they are resistant to carbonization and metal granulation under low sulfur operating conditions. . This is because a smaller portion of the reactor apparatus need only be replaced or modified with a staged design.
The reactor apparatus can be operated using at least two temperature zones. That is, a higher temperature region and a lower temperature region. This method is based on the observation that metal granulation has the highest and lowest temperatures, and above and below it the least. Thus, “higher” temperatures mean that they are higher than those conventionally used in reforming reactor equipment and higher than the highest temperature for granulation. “Lower” temperature means that the temperature is at or near the temperature at which the reforming process is routinely performed and below the temperature at which granulation is a problem.
Operating the reactor unit portion at different temperature zones should reduce metal granulation because fewer reactor unit portions are at temperatures that cause metal granulation. Another advantage of such a design also includes improved heat transfer efficiency and equipment scale reduction capability because operation of certain parts of the equipment is performed at higher temperatures. However, operating the reactor unit at a level below and above the level at which metal granulation occurs is not completely eliminated, only by reducing the temperature range at which metal granulation occurs. This is unavoidable. This is due to temperature fluctuations that occur during daily operation of the reforming reactor apparatus, particularly when the process fluid is heated in the reactor apparatus, when the apparatus is shut down and started, when it is repeated, and when the process fluid is heated in the reactor apparatus. This is because temperature fluctuations occur.
Another way of minimizing metal granulation involves using a superheated feed (such as hydrogen) to heat the equipment, thereby minimizing the need to heat hydrocarbons through the furnace wall.
Yet another process design method involves providing a larger tube diameter and / or a higher tube speed to the existing reforming reactor apparatus. By using a larger tube diameter and / or a higher tube speed, the heating surface in the reactor apparatus is least exposed to hydrocarbons.
As mentioned above, catalytic reforming is well known in petrochemistry and involves treating the naphtha fraction to improve octanation by aromatic formation. More important hydrocarbon reactions that occur during reforming operations include cyclohexane to aromatic dehydrogenation, alkylcyclopentane to aromatic dehydroisomerization, and acyclic hydrocarbon to aromatic dehydration. Includes cyclization. In addition, many other reactors occur, including dealkylation of alkylbenzenes, paraffin isomerization, and hydrocracking reactions that produce light gaseous hydrocarbons such as methane, ethane, propane and butane. These hydrocracking reactions should reduce as much as possible during reforming because they reduce the yield of gasoline boiling products and hydrogen. Thus, as used herein, “reforming” refers to one or more aromatic production reactions to provide a product rich in aromatics (ie, a product having a higher aromatic content than in the feed). Is used to treat the hydrocarbon feed.
The present invention is primarily concerned with catalytic reforming, but will generally be useful for producing aromatic hydrocarbons from various hydrocarbon feeds under low sulfur conditions. That is, catalytic reforming typically refers to the conversion of naphtha, but other feeds can be treated to give products that are similarly rich in aromatics. Thus, although conversion of naphtha is a preferred embodiment, the present invention relates to paraffinic hydrocarbons, olefinic hydrocarbons, acetylene hydrocarbons, cyclic paraffinic hydrocarbons, cyclic olefinic hydrocarbons, and mixtures thereof, particularly saturated hydrocarbons. It is also useful for the conversion or aromatization of various feedstocks.
Examples of paraffin hydrocarbons are those having 6-10 carbon atoms such as n-hexane, methylpentane, n-heptane, methylhexane, dimethylpentane, and n-octane. Examples of acetylene hydrocarbons are those having 6-10 carbon atoms such as hexyne, heptin, and octyne. Examples of acyclic paraffin hydrocarbons are those having 6 to 10 carbon atoms such as methylcyclopentane, cyclohexane, methylcyclohexane, and dimethylcyclohexane. Typical examples of cyclic olefin hydrocarbons are those having 6-10 carbon atoms such as methylcyclopentene, cyclohexene, methylcyclohexene, and dimethylcyclohexene.
The present invention is also useful for reforming under low sulfur conditions using a variety of different reforming catalysts. Such catalysts include Group VIII noble metals on refractory inorganic oxides such as platinum on alumina, Pt / SN on alumina, and Pt / Re on alumina; Group VIII noble metals on zeolite such as Pt on zeolites such as L-zeolite, ZSM-5, silicates and β, Pt / SN and Pt / Re; including Group VIII noble metals on alkali and alkaline earth metal exchanged L-zeolites, including It is not limited.
Preferred embodiments of the present invention include the use of an atmospheric pore zeolite catalyst containing an alkali or alkaline earth metal and having one or more Group VIII metals added thereto. Most preferred is an embodiment where such a catalyst is used to reform a naphtha feed.
The term “atmospheric zeolite” generally refers to a zeolite having an effective pore diameter of 6-15 mm. Preferred atmospheric porous crystalline zeolites useful in the present invention include L-type zeolite, zeolite X, zeolite Y and faujasite. These have an apparent pore diameter of about 7 to 9 mm. Most preferred is zeolite, L-type zeolite.
The composition of the L-type zeolite expressed in terms of the molar ratio of the oxide can be expressed by the following formula:
(0.9-1.3) M_{2 / n}O: Al₂O_Three(5.2-6.9) SiO₂: YH₂O
In the above formula, M represents a cation, n represents the valence of M, and y can be a value from 0 to about 9. Zeolite L, its X-ray diffraction pattern, its properties, and its preparation are described in detail, for example, in US Pat. No. 3,216,789, the contents of which are hereby incorporated by reference. The actual formula can be changed without changing the crystal structure. For example, the molar ratio of silicon to aluminum (Si / Al) can be varied in the range of 1.0 to 3.5.
The chemical formula for zeolite Y expressed in terms of the molar ratio of oxides can be written as:
(1.7-1.1) Na₂O: Al₂O_Three: XSiO₂: YH₂O
In the above equation, x is a value greater than 3 and up to about 6. y is a value up to about 9. Zeolite Y has a characteristic powder X-ray diffraction image that can be used with the above formula for identification. Zeolite Y is described in more detail in US Pat. No. 3,130,007, the contents of which are hereby incorporated by reference.
Zeolite X is a synthetic crystalline zeolite molecular sieve that can be represented by the following formula:
(1.7-1.1) M_{2 / n}O: Al₂O_Three: (2.0-3.0) SiO₂: YH₂O
Where M is a metal, especially alkali and alkaline earth metals, n is the valence of M, and y is a value up to about 8 depending on the type of M and the degree of hydration of the crystalline zeolite. Have. Zeolite X, its X-ray diffraction pattern, its properties, and its preparation are described in detail in US Pat. No. 2,882,244, the contents of which are hereby incorporated by reference.
The atmosphere pore zeolite preferably contains an alkali or alkaline earth metal. The alkaline earth metal may be barium, strontium or calcium, but barium is preferred. Alkaline earth metals can be blended into the zeolite by synthesis, impregnation, or ion exchange. Barium is preferred over other alkaline earth metals because it results in a somewhat less acidic catalyst. Strong acidity is undesirable for the catalyst because it promotes cracking and results in low selectivity.
Alternatively, at least a portion of the alkali metal can be exchanged for barium using ion exchange methods known for zeolites. This is an excess of Ba⁺⁺Contacting the zeolite with a solution containing ions. In this embodiment, barium preferably comprises 0.1% to 35% by weight of zeolite.
At least one Group VIII metal such as nickel, ruthenium, rhodium, palladium, iridium or platinum is added to the atmospheric pore zeolite catalyst used in the present invention. Preferred Group VIII metals are iridium and especially platinum. They are more selective with respect to dehydrocyclization and are more stable under dehydrocyclization reaction conditions than other Group VIII metals. If used, the preferred weight percent of platinum in the catalyst is 0.1% to 5%.
Group VII metals are introduced into the pore zeolite by synthesis, impregnation, or exchange of an appropriate salt in an aqueous solution. If it is desired to introduce two Group VIII metals into the zeolite, the operation can be carried out simultaneously or sequentially.
In order that this invention be more fully understood, the following examples are set forth which illustrate certain aspects of the invention. However, it is to be understood that the invention is not limited to the specific conditions described therein.
Example 1
Experiments were conducted to show the effect of sulfur and water on carbonization in the reforming reactor.
In these tests, carbonization and embrittlement of 347 stainless steel wire were studied using a copper tube 8 inches long and 1/4 inch outside diameter as the reactor. Three of these stainless steel wires having a diameter of 0.035 inches were inserted into the tube and the 4 inch portion of the tube was maintained at a uniform temperature of 1250 ° F. by the furnace. The system pressure was maintained at 50 psig. Hexane is introduced into the reactor at a flow rate of 25 μl / min (1.5 ml / hr) and a hydrogen flow rate of about 25 cc / min (H₂The ratio of HC to HC is 5: 1. The presence of an exothermic methane reaction was determined by measuring methane in the effluent product.
A control experiment was performed using essentially pure hexane with a sulfur content of less than 0.2 ppm. After only 3 hours, the tube was found to be completely filled with carbon. This not only stopped the flow of hydrogen and hexane feed, but carbon growth actually ruptured the tube and caused swells in the reactor. Methane in the effluent product approached 60-80% by weight before plugging.
Another experiment was performed using essentially the same conditions, except that 10 ppm of sulfur was added. The experiment lasted 50 hours and was stopped to examine the wire. No increase in methane was observed during the experiment. It remained constant at about 16% by weight due to pyrolysis. No blockage due to coke was found, and no carbonization of the steel wire was observed.
A similar experiment was conducted except that only 1 ppm of sulfur was added (1/10 of the previous experiment). This experiment showed little methane formation or blockage after 48 hours. Examination of the steel wire showed a small amount of surface carbon, but no band-like carbon.
Another experiment was performed except that 1000 ppm of water (0.1%) was added to hexane as methanol. Sulfur was not added. The experiment lasted 16 hours, but no blockage occurred in the reactor. However, when the tube was opened, it was discovered that about 50% of the tube was filled with carbon. However, the carbon accumulation was not as bad as the control experiment.
Example 2
Materials suitable for use in low-sulfur reforming reactor equipment; tests were conducted to determine materials with better resistance to carbonization than mild steel conventionally used in low-sulfur reforming processes .
In these tests, an apparatus including a Lindberg alumina tube furnace was used, and the temperature was controlled within 1 degree with a thermocouple placed outside the tube in the heating zone. The furnace tube had an inner diameter of 5 / 8in. High heat area of the tube

Several experiments were performed at an applied temperature of 1200 ° F. using a thermocouple suspended within. The internal thermocouple measured a constant 0-10 ° F. lower than the external thermocouple.
Mild steel (C steel and 2¹/_FourCr) samples and 300 series stainless steel samples are tested for 24 hours at 1100 ° F, 1150 ° F and 1200 ° F, exposing the material under low sulfur reforming conditions for 90 hours at 1100 ° F. Were tested under similar conditions. Samples of various materials were placed in open quartz boats in the hot zone of the furnace tube. The boats were 1in long and 1 / 2in wide and fit well within the hot zone of 2in of the tube. These boats were attached to silica glass rods and moved in and out. An internal thermocouple was not used when the boat was placed inside the tube.
Prior to initiation, the tube was flushed with nitrogen for several minutes. About 1% toluene was introduced into the feed gas mixture by bubbling carbonizing gas, a commercially available mixture of 7% propane in hydrogen, through a 1 l flask of toluene at room temperature. A gas flow of 25-30 cc / min and atmospheric pressure was maintained in the apparatus. The sample was brought to operating temperature at a rate of 144 ° F./min.
After exposing the material to the carbonizing gas at the desired temperature for the desired time, the apparatus was quenched with a stream of air applied to the outside of the tube. When the device was cool enough, the hydrocarbons were purged with nitrogen and the boat was removed for analysis.
Prior to initiation, the test material was cut into a size and shape suitable for macroscopic observation. After pre-treatment such as cleaning or roasting, the sample was weighed. Most samples were less than 300 mg. Typically, each experiment was performed with 3-5 samples in a boat. A sample of 347 stainless steel was present as an internal standard in each experiment.
At the end of each experiment, the condition of the boat and each material was carefully observed. Typically, a picture of the boat was taken. Each sample was then weighed with care to maintain coke deposits with the appropriate substrate material to determine the change. The sample was then attached to an epoxy resin and polished to make samples for petrological and scanning electron microscopy analysis to determine the changes to coking, metal granulation, and carbonization of each material.
If necessary, the residence time of the carbonizing gas used in these tests was much longer than in typical commercial operations. Therefore, the experimental conditions are considered to be more severe than the commercial conditions. Some of the materials that fail in these tests are actually considered commercially reliable. Nevertheless, this test provides a reliable indication of the relative resistance of the material to coking, carbonization and metal granulation.
The results are listed in the table below.

Of course, the above results are quantitative and depend on the surface morphology, ie the microscopic roughness of the metal. The increase in carbon weight is an indication of surface coking that is self-touching.
Example 3
Using the same method as used above again, a broad classification selection test of the material was performed at a temperature of 1200 ° F. for 16 hours. Results are shown below. Each group represents a side-by-side comparison in a single boat under similar conditions.

Example 4
Additional materials were tested using the method described in Example 2 again (unless stated otherwise).
Samples of 446 stainless steel and 347 stainless steel were placed in a sample boat and tested simultaneously for a total of two weeks on a 1100 ° F. carbonizer. 446 stainless steel had a thin coke coating, but no other changes were detected. 347 stainless steel, on the other hand, had large local coke deposits with holes deeper than 4 mils from which coke and metal granules spouted.
Samples of carbon steel mesh electroplated with tin, silver, copper, and chromium were tested. The sample had a coating of about 0.5 mil. After conducting a carbonization screening test at 1200 ° F. for 16 hours, no coke was formed on the tin plating net and the chrome plating net. Coke was formed on the silver plating net and the copper plating net, but only where the plating was peeled off. The unplated carbon steel mesh tested simultaneously with the plated mesh showed severe coking, carbonization and metal granulation. A sample of 304 stainless steel mesh was tested. Each sample was electroplated with one type of tin, silver, copper, and chromium. The samples had a coating thickness of about 0.5 mil. After performing a carbonization screening test at 1200 ° F. for 16 hours, no coke was formed on any of the plated meshes, except for the local areas where the copper plating mesh was foamed and peeled off. A thin coke coating was observed on the unplated sample of 304 stainless steel tested at the same time as the plated net.
A sample of 304 stainless steel mesh was tested. Each sample was electrodeposited with either tin or chromium. These samples were tested in a 1100 ° F. carbonization test with a 446 stainless steel sample. Samples were exposed for 5 weeks. Each week, the sample was cooled to room temperature and recorded for observation and photography. They were then reheated to 1100 ° F. The tinned net had no coke. The chrome-plated net also had no coke except in the local areas where the chrome plating was peeled off. The 446 stainless steel pieces were uniformly coated with coke.
Samples of uncoated Inconel 600 (75% Ni) and tin-coated (electrodeposited) Inconel 600 (75% Ni) were tested at 1200 ° F. for 16 hours. Tin-plated samples were coked and granulated, but not as well as uncoated samples.
Example 5
The following experiment was conducted to study the exothermic methanation reaction that occurs due to the formation and combustion of coke balls during reforming under low sulfur conditions. In addition, tin was studied as an additive to reduce methane formation.
Coke deposits containing molten iron particles have been found in low sulfur reforming reactor equipment. It is believed that this molten iron formation that occurs during reforming at temperatures between 900 and 1200 ° F. is due to a very exothermic reaction that occurs during the reforming. The only route to generate such a temperature appears to be by highly exothermic methane formation. The high temperature is particularly surprising. This is because reforming generally has endothermic properties and actually tends to cool the reactor apparatus. These high temperatures are generated within a well-insulated coke ball where hydrogen diffuses into the internal catalytic iron powder sites where they catalyze the formation of methane from coke and hydrogen.
In this experiment, steel wool was used to study methane formation in a micropilot plant. A 1/4 inch stainless steel tube was filled with 0.14 g of steel wool and placed in a 1175 ° F. tube. Hexane and hydrogen were sent over the iron and the resulting stream was analyzed for feed and product. Steel wool was pretreated in hydrogen for 24 hours before introducing hexane. Next, hexane was introduced into the reactor at a flow rate of 25 μl / min, and the hydrogen flow rate was about 25 cc / min.
Initially methane formation was low, but continued to rise as the experiment progressed and finally reached 4.5%. Next, 0.1 cc of tetrabutyltin dissolved in 2 cc of hexane was injected into the pure feed stream before the iron. Methane formation decreased to about 1% and remained at 1% over the next 3 hours. The data is summarized in the table below.

From the above results, it can be seen that the addition of tin to steel wool stops the promotion of methane formation and reduces it to an acceptable level in the product.
Example 6
Further tests were performed using steel wool previously coated with tetrabutyltin. In particular, as in Example 5, 0.1 cc of tetrabutyltin dissolved in 2 cc of hexane was injected three times into a 1/4 inch stainless steel tube containing 0.15 g of steel wool. The solution was carried on a steel wool in a 900 ° F. hydrogen stream.
The hydrocarbon feed was then introduced at 1175 ° F. with a hydrocarbon flow rate of 25 μl / min and the hydrogen flow rate was about 25 cc / min. The gas coming out was analyzed for methane and remained below 1% for 24 hours. The reactor was then stopped and the reactor tube was opened and inspected. Steel wool had very little carbonization.
In contrast, a control experiment was performed in which no pretreatment with tetrabutyltin was performed. It was performed for 1 day under the same conditions as described above. After 24 hours, no hydrogen or feed was detected at the tube outlet. The inlet pressure increased from the first 50 lb to 300 lb. When the reactor tube was opened and inspected, it was found that the coke was completely clogged.
Therefore, it can be seen that the organotin compound can prevent carbonization of steel wool under the modifying conditions.
Example 7
In order to investigate the effect of carbonization conditions on stainless steel wire coated with tin in a gold plated reactor tube, an experiment similar to the control experiment of Example 1 was further performed. The only difference from the control experiment was that a higher hydrogen flow rate of 100 ml / min was used.
The experiment was conducted for 8 hours with no clogging or excessive methane formation. When the tube was opened and analyzed, no obstruction or carbon band was observed. Only one black carbon streak was seen on one wire. This is probably due to improper coating.
This experiment shows that tin can protect stainless steel from carbon in a manner similar to sulfur. However, unlike sulfur, it need not be continuously injected into the feed. Sulfur must be continuously injected into the feed to maintain the hydrogen sulfide partial pressure in the system in an amount sufficient to maintain the sulfide surface on the steel. When sulfur is removed from the feedstock, carbonization begins after the sulfur is expelled from the reactor unit. This usually occurs within 10 hours after sulfur termination.
Although the present invention has been described above with reference to preferred embodiments, it should be understood that various changes and modifications can be made as will be appreciated by those skilled in the art. For example, steel parts in the reactor apparatus can be coated with niobium, zirconium, silica, ceramic, tungsten or chromium (chromation), but these techniques are very difficult to implement or use and are expensive. It will not be available too. Alternatively, as few heat exchangers can be used as possible to heat the hydrocarbons to the reaction temperature. Heat can also be provided by superheated hydrogen. Alternatively, the exposure of the heated surface to hydrocarbons can be reduced by using a larger tube diameter and a larger tube speed. Accordingly, there are many variations or modifications to the preferred embodiment that should be readily apparent to those skilled in the art and are considered to be within the scope of the invention as defined by the following claims.

Claims (19)

In a catalytic hydrocarbon reforming process for producing an aromatic-rich hydrocarbon stream while increasing resistance to carbonization and metal granulation of at least a portion of a reforming reactor apparatus, less than 50 ppb as hydrocarbon A hydrocarbon having a sulfur content of less than 1000 ppm and contacting with the reforming catalyst in the reforming reactor apparatus, wherein at least a portion of the reforming reactor apparatus in contact with the hydrocarbon is metal clad thereon, a metal coating or a metal paint, tin, intermetallic tin compound, the metal cladding containing at least one selected from the group consisting of tin alloy and mixtures thereof, have a metal coating or a metal paint, reforming A method for catalytic reforming of hydrocarbons, characterized in that the catalytic reforming reaction in the reactor apparatus is carried out at a temperature between 700-1050 ° F (371-566 ° C) . The method of claim 1, wherein the reforming contact contains a zeolite catalyst . The process of claim 1 wherein the reforming catalyst comprises an atmospheric pore zeolite containing at least one of an alkali or alkaline earth metal and a Group VIII metal . The process according to claim 3 , wherein the reforming catalyst further contains a platinum atmosphere pore zeolite . The method of claim 1 , wherein the reforming reactor apparatus comprises a furnace having a plurality of furnace tubes; and a reactor having a catalyst bed; a portion of the reactor having at least one of the plurality of furnace tubes. . The method of claim 1, wherein the resistance to carbonization and metal granulation is that the weakening is less than about 2.5 mm / year . The method of claim 1, wherein the metal paint further comprises a reducible tin paint and the reducible tin paint is further heated under reducing conditions . The method of claim 1 , wherein the tin-containing paint forms an iron stannate . Tin-containing paint, further hydrogen decomposable tin compound, a solvent system, finely divided tin metal, and containing tin oxide, the method according to claim 1. The method of claim 9 , wherein the finely divided tin metal has a particle size in the range of about 1 to 5 microns . The method of claim 1 , wherein the tin-containing paint comprises a tin-containing compound and an iron compound, and the iron: tin ratio is less than about 1: 3 by weight . Iron compound contains Fe ₂ O _3, The method of claim 11. The method of claim 1 , wherein the metal paint comprises a tin oxide paint . The metal clad, metal coating or metal paint further comprises copper, arsenic, antimony, brass, lead, bismuth, chromium, any intermetallic compound or alloy of these metals, copper-tin alloy, or copper-antimony alloy The method according to claim 1 , comprising at least one selected from : The method of claim 1 , wherein the metal coating is further combined with a layer comprising aluminum or chromium oxide . The method of claim 1 , wherein at least a portion of the reforming reactor apparatus comprises silica . The method of claim 1 , wherein the metal cladding, metal coating, or metal paint contains a metal stannate . The method of claim 1 , wherein at least a portion of the reforming reactor apparatus comprises air roasted tin coated 300 stainless steel . In a process for producing aromatics by catalytically reforming a hydrocarbon stream for a sufficiently long period of time with a sulfur-sensitive reforming catalyst loaded with at least one Group VIII metal without severely clogging the coke,
Reducing the sulfur concentration of the hydrocarbon stream to less than 50 ppb and lowering the moisture to less than 1000 ppm to provide a low sulfur and low moisture hydrocarbon-containing stream;
A low sulfur, low moisture, hydrocarbon-containing stream is heated between 700-1050 ° F. (371-566 ° C.), which is a catalytic reforming temperature in a furnace having a plurality of furnace tubes, A portion in contact with a low sulfur, low moisture, hydrocarbon-containing stream, the portion being a metal cladding, metal coating or metal paint, the group consisting of tin, intermetallic tin compounds, tin alloys and mixtures thereof The metal clad, metal coating or metal paint comprising at least one selected from
Contacting a low-sulfur, low-moisture hydrocarbon-containing stream with a sulfur-sensitive reforming catalyst to produce aromatics
A process for producing an aromatic comprising a step .

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