KR910010095B1 - Process for preparation of an isomerization process feedstock containing light hydrocarbons - Google Patents

Abstract

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Description

Pretreatment method of isomerization method of light hydrocarbon raw material

1 is a chromatographic analysis of sulfur compounds present in untreated light naphtha feedstock.

Figure 2 is a chromatographic analysis of sulfur compounds contained in the light naphtha raw material after treatment with molecular sieves.

The present invention relates to a process for pretreating light hydrocarbons to remove sulfur, water and oxygen containing compounds. In particular, the present invention relates to sending a light hydrocarbon feed containing a C ₄ -C ₈ hydrocarbon into a first adsorption zone in which molecular sieves are present and then into a second adsorption zone in which activated alumina is present. The present invention provides a use as a pretreatment method for a light hydrocarbon isomerization process.

The removal of sulfur compounds, water, and oxygen-containing compounds from light hydrocarbons is suitable for a number of reasons, depending in part on the intended use of the purified final product. In many cases, light hydrocarbons can be treated through catalysis, such as isomerization, to produce other hydrocarbons, increase octane number, or easily improve product value. Reactions using catalyst complexes are very sensitive to contaminants such as sulfur, water and oxygen-containing compounds. These contaminants reduce catalyst life by inactivating or damaging the catalyst, increasing catalyst regeneration or in some cases completely replacing the catalyst.

Techniques have been developed to remove contaminants from hydrocarbon streams using various sorbents, including zeolites, alumina, carbon and molecular sieves. For example, US Pat. No. 4,098,684 teaches a process for removing only sulfur compounds from paraffin-containing raw materials using two different adsorbents in the adsorption zone. The primary material contains zeolitic molecular sieves and the secondary material contains zeolite A. However, there is no mention of removing water or oxygen-containing compounds. U.S. Patent No. 3,931,350 describes that the oxygen-containing compounds can be selectively removed from the n-paraffin stock by using liquid or solid sorbents.

The reference does not suggest the use of two adsorption zones, nor does it teach the removal of water or sulfur compounds.

References to the multi-step removal of impurities from hydrocarbon feedstocks include US Pat. Nos. 4,313,821 and 4,374,654. The “Solvent Refined Coal” method of US Pat. Contaminant removal is carried out by primary contact with an ion exchange resin followed by secondary contact with zeolite. In US Pat. No. 654, a two-stage low temperature adsorptive separation method was found to be used to remove HCl and H ₂ S from the reformer exhaust gas. The first step uses molecular sieves to adsorb HCl and the second step uses zinc oxide to remove H ₂ S.

Although the above-described prior art takes into account the advantages of the present invention, it is known so far that the prior art refers to the use as a procedure for pretreatment of raw materials in a contaminant sensitive isomerization method using a special combination of adsorption zones. There was nothing.

The present invention relates to a two-stage pretreatment method for removing impurities such as sulfur compounds, water, and oxygen-containing compounds from hydrocarbon conversion processes used in the hydrogen conversion process. These feedstocks contain 4-8 carbon atoms per molecule. In particular, the pretreatment method consists of the following steps. Sending the raw material to the primary adsorption zone containing molecular sieves; Sending the eluate from the primary adsorption zone into a secondary adsorption zone containing activated alumina; The eluate is recovered from the secondary adsorption zone in which sulfur compounds, oxygen-containing compounds and water are substantially free.

In particular, the present invention relates to a pretreatment method of a light hydrocarbon conversion method, wherein the raw material is light naphtha containing 4 to 6 carbon atoms of paraffin hydrocarbon per molecule. The present invention eliminates the need for conventional hydrotreating of raw materials and saves equipment costs and use.

The present invention relates to a method for pretreatment of raw materials used in a hydrocarbon conversion process. Removal of impurities such as sulfur compounds, oxygen-containing compounds and water from C ₄ -C ₈ hydrocarbon-containing raw materials is carried out by a process containing two adsorption zones. The primary zone contains molecular sieves for removing water and sulfur compounds other than carbon disulfide, and the secondary zone contains activated alumina for removing carbon disulfide and oxygen containing compounds. Among these impurities, when the impurities are removed by the specific combination of the adsorption bands as described above, the hydrocarbon conversion process can be improved by using the raw materials thus treated. Raw materials treated by the process of the present invention are bicyclic paraffins and cyclic naphthenes as light hydrocarbons having 4-8 carbon atoms per molecule. Further examples of the raw material include n-butane, n-pentane, n-hexane, n-heptane, n-octane, 2-methylpentane, 3-methylpentane, 3-ethylpentane and the like as linear or partially branched paraffins. In addition, small amounts of aromatic compounds benzene and toluene may also be present. Cyclo paraffins such as alkylcyclopentane, cyclohexane, methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane and dimethylcyclohexane may be present in the raw materials. The raw materials consist of a mixture of paraffins and / or naphthenes, which include the selective fractional distillation of natural gasoline and naphtha. Preferred raw materials are hard naphtha containing 4 to 6 carbon atoms per molecule containing paraffin hydrocarbons.

The present invention relates to a method for removing impurity components from raw materials and should include contaminants in a measurable amount. Such contaminants include sulfur compounds, water and / or oxygen containing compounds. "Sulfur compound" means any compound containing sulfur, whether in elemental or compound form. Examples of this include hydrogen sulfide, mercaptan, carbonyl sulfide and carbon disulfide. Sulfur compounds are present in the feed in amounts of about 0.5 to about 300 weight ppm, calculated as sulfur atoms. Water and its precursors are present in the raw materials in amounts of 5-250 ppm by weight, as measured in ppm. The contaminants may also be oxidized hydrocarbon compounds known as oxygen containing compounds such as alcohols, ethers, ketones and acids. Specific examples of such oxygen-containing compounds are ethanol, methanol, tertiary butyl alcohol, dimethyl ether and methyl tertiary butyl ether. Generally, the amount of compound present in the raw materials is about 0.1- about 10,000 ppm by weight. In addition, the present invention can remove the oxygen-containing material in the raw material, such as carboxide. The raw material may or may not undergo conventional hydrotreating before being used in the pretreatment process of the present invention.

According to the invention, the raw material is subjected to primary adsorption treatment containing molecular sieves. As used herein, "molecular sieve" is defined as a class of adsorptive desiccants, which are naturally crystalline forms obtained from amorphous materials such as gamma-alumina. Preferred forms of molecular sieves within the crystalline adsorbent fraction are known as zeolites as aluminosilicate materials.

The term “zeolite” generally refers to a group of natural and synthetic hydrated metal aluminosilicates of mainly structure to be determined. However, there are significant differences between synthesis and nature in physical properties such as chemical composition, crystal structure and X-ray powder diffraction pattern.

The structure of crystalline zeolite molecular sieves can be described as open conformations such as SiO ₄ and AlO ₄ tetrahedra. The tetrahedral structure is crosslinked by oxygen atoms so that the weight ratio of oxygen atoms: aluminum and silicon atoms is 2, that is, O / (Al + Si) = 2. The cations of alkali metals and alkaline earth metals, such as sodium, potassium, calcium and magnesium ions, are contained in the crystals, thereby equilibrating by the anionic electron valence of the tetrahedron containing aluminum. One cation can be exchanged for another cation by ion exchange.

Zeolites can be activated by releasing all of the water of the hydration reaction. The space in the crystals after the activation reaction is useful for the adsorption of absorbed molecules. These spaces, which are not filled by the reduced constituent metal atoms, are adsorbed by molecules of suitable size and shape and the energy that the adsorbed molecules can enter the molecular sieve pores.

Zeolites are either produced as fine crystalline aggregates or synthesized into fine powders and are preferably purified or pelletized to be suitable for large scale adsorption applications. The pelletization method is very satisfactory. This is because the adsorption characteristics of the zeolite are substantially unchanged in comparison with the selectivity and capacity.

The pore size of the zeolite molecular sieve can be modified by using various metal cations. For example, sodium zeolite A has a pore size of about 4 mm 3 units, while calcium zeolite A has a pore size of about 5 mm 3 units.

13X molecular sieve is used in the primary adsorption phase. The general formula of the commercially available molecular sieve composition as form 13X is as follows; 0.83 ± 0.05 Na ₂ O 1.00 Al ₂ O ₃ 2.48 ± 0.038 The water of SiO ₂ and hydrogen reaction, form 13X, is a cubic structure. The structure is characterized by a three-dimensional mesh with pores capable of passing molecules up to 10 microns in size and interconnecting internal crystalline pores. The pore volume is 51% by volume of the zeolite and all adsorption takes place in the crystalline pores.

The primary adsorption zone removes water present in the feed and also removes sulfur compounds but does not adsorb carbon disulfide in a detectable amount. Similarly, hard oxygen-containing compounds such as CO ₂ are not removed by the primary adsorption zone.

The eluate from the primary adsorption zone is passed through a secondary adsorption zone containing activated alumina. The use of secondary adsorption zones solves the problems caused by the inability of primary adsorption zones to efficiently remove carbon disulfide and light oxygen-containing compounds. The activated alumina used in the secondary adsorption zone is aluminum oxide having a high porosity and high surface area alumina oxide of at least 90% by weight of Al ₂ O ₃ based on the absence of volatiles. Activated alumina can be obtained by removing water components from various hydrated aluminas by controlled heating. The heating is carried out very rapidly at 400-800 ° C. in air or other gases to produce alumina exhibiting chi- and gamma-shaped amorphous X-ray diffraction images, which are weak at combustion at temperatures of 250-1200 ° C. Reduce 5% by weight volatiles. Activated alumina also contains small amounts of SiO ₂ , Na ₂ O and Fe ₂ O _{3 of up} to 1% by weight and has a bulk density of 0.5-0.9 g / cc. The total surface area of the activated alumina is 200-500 m 2 / g and the pore volume is 0.20-0.75 cc / g. The most preferred properties contain a surface area of about 325 m 2 / g, a total pore volume of about 0.5 cc / g and a bulk density of about 0.75 g / cc.

Activated alumina includes modified compounds to improve the efficiency for removing carbon disulfide, a sulfur compound. Preferred kinds of modifiers include lithium, sodium, potassium, rubidium and cesium as group IA alkali metals. Sodium is a preferred modifier. Activated alumina contains up to 10% by weight, preferably 1-5% by weight, of modifier based on amounts excluding volatiles. Although the efficiency of activated alumina is independent of the shape of the material, useful forms are spherical and cylindrical in diameter 1 / 16-1 / 14 inch (1.6-5.6 mm).

The amount of contaminants present in the eluate in the secondary adsorption zone differs depending on the amount and characteristics of the contaminants present in the raw materials introduced into the primary adsorption zone. In addition, the time taken for the pretreatment process affects the removal efficiency of contaminants. Sulfur compounds, oxygen-containing compounds and water are substantially liberated in the secondary adsorption zone eluent when the pretreatment process is primary on-stream. Preferably, this eluate contains less than 1 ppm by weight of sulfur compound, oxygen-containing compound and water.

The adsorption conditions required for the two zones are determined by factors such as the amount of adsorbent used and the contaminants removed from the raw materials. The general range of suitable adsorption conditions is that although high pressure may be used, when an ultrahigh pressure of about 3448 kPa (ga) or less is used, the temperature is about 150 ° C. An hourly liquid space velocity of less than 10 hr ⁻¹ is used. The preferred range of adsorption conditions for the two zones is 101-1379 kPa (ga), temperature 25-100 ° C., space velocity 1-5 vol% of raw material / hour / adsorption band volume.

The raw material is continuously passed through a pretreatment process and carried out until the capacity of one or both of the two adsorbents is reached. The presence of significant amounts of contaminants in the eluate of the secondary adsorption zones means that the capacity is exhausted. At this point, it is necessary to desorb or regenerate the adsorption zone. Before the regeneration step, the raw material is switched from the two adsorption zones that require regeneration to the two newly regenerated adsorption zones. The regeneration step is performed by passing a hot, almost non-adsorbable purge gas into the zone at a temperature of 175-315 ° C. Suitable purge gases include natural gas, methane, hydrogen, nitrogen and carbon monoxide. It is also possible to regenerate with nonadsorbable liquid hydrocarbons or hydrocarbon mixtures. For example, when the present invention is used as a pretreatment process in the isomerization of light hydrocarbons, a stream from the bottom of the stabilizer column containing pentane and hexene can be used.

As mentioned above, the present invention is preferably used as a raw material pretreatment process before the hydrocarbon conversion process. The term "hydrocarbon conversion process" includes all reactions that modify the physical or chemical composition of a hydrocarbon. Preferred hydrocarbon conversion processes are catalytic isomerization of light hydrocarbons. Among the groups of light hydrocarbons that may be included are saturated hydrocarbons, in particular straight or partially branched chain paraffins containing at least 4 carbon atoms per molecule. The isomerization reaction is carried out over a wide range of temperatures from about 93 to about 427 ° C. The isomerized hydrocarbon liquid volume / hour / volume of the catalyst composite of about 0.25 to about 5 preferably has a pressure in the reaction zone within about 690 to about 6900 kPa (ga). A detailed description of the isomerization of light naphtha hydrocarbons is taught in US Pat. No. 4,665,272. Particular preference is given to carrying out the isomerization reaction preferably in the presence of about 0.05 to about 5 moles of H ₂ against one mole of isomerized hydrocarbon. The function of hydrogen is to improve the life of the catalyst, which improves the life of the catalyst and prevents the polymerization of the reaction intermediates to be precipitated. It is not necessary to use purified hydrogen, and a hydrogen-containing gas is suitable. Isomerization methods, such as catalytic conversion of naphtha or other product separation solubility, are gaseous sources with high H ₂ , which contain lower hydrocarbons (C ₁ -C ₃ ) and may also contain other compounds such as sulfur. It is suitable.

The invention is embodied by the following examples. The examples described below are not intended to limit the present invention, which is intended to be specific only.

EXAMPLE

An untreated feed consisting of a mixture of C ₅ and C ₆ paraffin hydrocarbons containing about 158 ppm of sulfur compound (analyzed by sulfur element) is contacted in an adsorption zone containing 13X molecular sieves. Adsorption zone process conditions include a temperature of about 25 ° C., a pressure of about 2413 kPa (ga), and a liquid speed velocity of about 1.0 hr ⁻¹ .

1 graphically illustrates various sulfur compounds in untreated raw materials. 2 shows the sulfur compounds present in the eluate. It has been found that substantially all sulfur compounds are removed except carbonyl disulfide, which yields a sulfur concentration of about 6 ppm by weight.

About 20 ppm by weight of carbon disulfide is added to a secondary feed consisting of C ₅ and C ₆ paraffinic hydrocarbons. The raw material representing the eluate discharged from the primary adsorption zone containing 13X type molecular sieve was passed through the adsorption zone containing activated alumina. Adsorption zone process conditions include a temperature of about 175 ° C., a pressure of about 2413 kPa (ga), and a liquid speed velocity of 1.0. Sulfur analysis of the eluate from this adsorption zone showed 1 wt. ppm or less was shown.

Claims (1)

Per molecule isomerized using sulfur-, oxygen-containing and water-sensitive catalyst systems when isomerizing the feed in the reaction zone where isomerization catalysts exist under isomerization conditions to produce products with increased octane numbers compared to the feed. A process for catalytic isomerization of 4-6 carbon number raw hydrocarbons, comprising: (a) a hard naphtha containing hydrocarbon stream containing sulfur compounds, oxygen containing compounds, water or mixtures thereof at a temperature of 25-100 ° C., 3448 kPa; (ga) countercurrent flow into a 13X zeolite-containing primary adsorption zone maintained at a pressure of less than or equal to 1-5 volumes of naphtha / hour / primary adsorption zone volume; (b) Secondary activated alumina-containing eluate discharged from the primary adsorption zone is maintained at a temperature of 25-100 ° C., a pressure of up to 3448 kPa (ga), and a space velocity of 1-5 volumes of raw material / hour / secondary adsorption zone volume. Passing backflow into the adsorption zone; (c) recovering the eluate from the secondary adsorption zone containing less than 1 ppm of sulfur compound, oxygen-containing compound and water, and then treating the raw material hydrocarbon by a pretreatment method including passing the eluate through the reaction zone. Catalytic isomerization method of raw hydrocarbon.

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