Method for producing ethylene and propylene from naphtha

Abstract

The subject matter of the present disclosure relates to a method for producing ethylene and propylene by catalytic steam cracking of naphtha using an HZSM-5 catalyst. An exemplary method may include providing a naphtha feedstock, providing steam, and providing an HZSM-5 catalyst. The method may further include preparing the HZSM-5 catalyst by titanium modification or alkali treatment followed by phosphorus modification. The method may further include feeding the naphtha feedstock and steam into a reactor containing the catalyst and removing an effluent from the reactor having a total yield of ethylene and propylene greater than about 45 wt%.

Description

[0001] This application is a divisional application of the invention patent application with the application date of December 13, 2016, application number 202110270964.8, and invention title "Method for Producing Ethylene and Propylene from Naphtha". The invention patent application with the application number 202110270964.8 is a divisional application of the invention patent application with the application date of December 13, 2016, application number 201680075632.1, and invention title "Method for Producing Ethylene and Propylene from Naphtha". Technical Field

[0002] The subject matter of the present disclosure relates to a method for producing ethylene and propylene from naphtha. Background Art

[0003] Naphtha can be a low-value petroleum chemical stream found in petroleum distillate streams from refining processes. Naphtha from fractions of crude oil distillation stills, i.e., straight-run naphtha, can contain various components depending on the composition of the crude oil source. Straight-run naphtha typically contains a large amount of straight-chain and branched-chain alkanes and may also contain olefins and / or aromatics.

[0004] With the growing demand for petrochemical products, there is an increasing interest in converting low-value naphtha streams into high-value petrochemical products, including ethylene and propylene. Some techniques for producing light olefins such as ethylene and propylene are known in the art, such as by fluid catalytic cracking (FCC), deep catalytic cracking (DCC), advanced catalytic olefins (ACO) process, steam cracking, propane dehydrogenation, and olefin metathesis.

[0005] For example, European Patent No. 1117750 discloses a catalytic naphtha cracking process for producing olefins using a zeolite catalyst containing phosphorus and a promoter metal. U.S. Patent Publication No. 2007 / 0082809 discloses a hydrothermally stable porous molecular sieve catalyst that can be used in catalytic cracking reactions, including the production of light olefins from naphtha. U.S. Patent Publication No. 2007 / 0010699 discloses a method for producing light olefins from hydrocarbon feeds using a porous molecular sieve catalyst having a water-insoluble metal salt and a phosphate compound. International Patent Publication No. WO 2011 / 162717 discloses a method for producing olefins by dehydrating alcohols using a metal-modified zeolite. U.S. Patent Publication No. 2007 / 0209969 discloses a catalyst for cracking heavy feeds to produce light olefins, which may include an alkali-treated zeolite having a silica-to-alumina ratio of less than 45.

[0006] However, there is still a need for a method for producing ethylene and propylene in high yields from naphtha. Summary of the Invention

[0007] The subject matter of the present disclosure provides a method for producing ethylene and propylene from naphtha using an HZSM-5 catalyst.

[0008] In certain embodiments, an exemplary method includes providing a naphtha feedstock and steam, providing a catalyst comprising phosphorus-modified titanium-containing HZSM-5, feeding the naphtha feedstock and steam to a reactor containing the catalyst, and removing an effluent from the reactor having a total yield of ethylene and propylene greater than about 45 wt%.

[0009] In certain embodiments, the naphtha feedstock can include light straight-run naphtha. The steam can be co-fed with the naphtha feedstock. The catalyst can have a Si / Al2 ratio of about 27 to about 30. The catalyst can comprise about 1.0 wt% to about 5.0 wt% of titanium (Ti) and about 1.0 wt% to about 10.0 wt% of phosphoric anhydride (P2O5). In certain embodiments, the catalyst is prepared by titanium modification followed by phosphorus modification. The phosphorus modification can use monoammonium phosphate.

[0010] In certain embodiments, the coke deposition on the catalyst can be less than about 5 wt% 6 hours after the naphtha feedstock is first fed to the reactor. In certain embodiments, the catalyst is not steamed before the naphtha feedstock is fed to the reactor.

[0011] The subject matter of the present disclosure also provides a method that includes providing a naphtha feedstock and steam, providing a catalyst comprising phosphorus-modified mesoporous HZSM-5, feeding the naphtha feedstock and steam to a reactor containing the catalyst, and removing an effluent from the reactor having a total yield of ethylene and propylene greater than about 45 wt%.

[0012] In certain embodiments, the naphtha feedstock can include light straight-run naphtha. The steam can be co-fed with the naphtha feedstock. The catalyst can have a Si / Al2 ratio of about 27 to about 30. The catalyst can comprise about 1.0 wt% to about 5.0 wt% of Ti and about 1.0 wt% to about 10.0 wt% of P2O5. The catalyst can be treated with 0.5M NaOH. The catalyst is prepared by alkali treatment followed by phosphorus modification. In certain embodiments, the phosphorus modification uses monoammonium phosphate. In certain embodiments, the coke deposition on the catalyst can be less than about 5 wt% 6 hours after the naphtha feedstock is first fed to the reactor. In certain embodiments, the catalyst is not steamed before the naphtha feedstock is fed to the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A method for producing ethylene and propylene by catalytic steam cracking of naphtha according to an exemplary embodiment of the disclosed subject matter is described.

[0014] Figure 2 A method for producing ethylene and propylene by catalytic steam cracking of naphtha according to another exemplary embodiment of the disclosed subject matter is described. DETAILED DESCRIPTION

[0015] The disclosed subject matter provides a method for producing ethylene and propylene from naphtha. In certain embodiments, the disclosed subject matter relates to a method for catalytic steam cracking of naphtha to light olefins such as ethylene and propylene using an HZSM-5 catalyst. For purposes of illustration and not limitation, Figure 1 and Figure 2 are schematic diagrams of methods according to non-limiting embodiments of the disclosed subject matter.

[0016] Referring to Figure 1 and Figure 2 , in certain embodiments, methods 100, 200 include providing a naphtha feedstock 101, 201. The naphtha for the disclosed subject matter can be sourced from various sources, including natural gas condensate, petroleum fractions, coal tar fractions, and / or peat. The naphtha for the disclosed subject matter can be light straight-run naphtha.

[0017] In certain embodiments, the naphtha feedstock contains normal paraffins and isoparaffins. The naphtha feedstock can also contain other components, such as naphthenes and / or aromatics. For example, the naphtha feedstock can contain from about 20 wt% to about 90 wt%, from about 30 wt% to about 80 wt%, from about 40 wt% to about 70 wt%, or from about 50 wt% to about 60 wt% of normal paraffins. The naphtha feedstock can contain from about 5 wt% to about 75 wt%, from about 15 wt% to about 65 wt%, from about 25 wt% to about 55 wt%, or from about 35 wt% to about 45 wt% of isoparaffins. The naphtha feedstock can contain less than about 10 wt% of naphthenes and less than about 2 wt% of aromatics.

[0018] As used herein, the term "about" or "approximately" means within an acceptable error range of a particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can refer to a range of up to 20%, up to 12%, up to 10%, up to 5%, and / or up to 1% of the given value.

[0019] In certain embodiments, the initial boiling point of the naphtha feedstock is from about 30 °C to about 65 °C, from about 40 °C to about 55 °C, or from about 45 °C to about 50 °C. The final boiling point of the naphtha feedstock can be from about 70 °C to about 130 °C, from about 80 °C to about 110 °C, or from about 85 °C to about 90 °C. The saturated vapor pressure (at 20 °C) of the naphtha feedstock can be from about 50 kPa to about 90 kPa, from about 60 kPa to about 80 kPa, or from about 65 kPa to about 75 kPa.

[0020] In certain embodiments, methods 100, 200 further include providing an HZSM-5 catalyst. The HZSM-5 catalyst can be a zeolite having a silica to alumina ratio (Si / Al₂) of from about 10 to about 50, from about 20 to about 40, from about 25 to 35, or from about 27 to 30. The HZSM-5 catalyst can be mesoporous, i.e., can have a pore diameter of from about 2 to about 50 nanometers.

[0021] In certain non-limiting embodiments, method 100 can include preparing a catalyst 102 comprising HZSM-5 by titanium (Ti) modification. For example, an HZSM-5 catalyst can be prepared by treating with a Ti compound. The Ti compound can be titanium tetrachloride, titanium oxychloride, titanium methoxide, titanium ethoxide, titanium isopropoxide, titanium butoxide, or a mixture thereof. In a specific embodiment, the Ti compound is titanium oxychloride. In certain embodiments, the Ti compound can be present in a solvent. The solvent for the methods of the present disclosure can be any solvent suitable for dissolving the Ti compound. Such solvents include, but are not limited to, water, alcohols, organic sulfoxides or sulfones, carboxylic acids, and / or esters.

[0022] In certain embodiments, a Ti-modified HZSM-5 catalyst is prepared by treating an HZSM-5 catalyst with a solution comprising a Ti compound. The method can further include removing the solvent from the Ti-modified HZSM-5 catalyst by filtration and / or evaporation. The method can further include calcining the Ti-modified HZSM-5 catalyst. The Ti-modified HZSM-5 catalyst can contain from about 0.1 wt% to about 20 wt%, from about 0.5 wt% to about 10 wt%, or from about 1 wt% to about 5 wt% of Ti. In a specific embodiment, the HZSM-5 catalyst can contain about 2 wt% of Ti.

[0023] In other non-limiting embodiments, method 200 can include preparing a catalyst 202 comprising HZSM-5 by alkali treatment. The alkali treatment can result in an increase in the mesoporosity and dealumination of the HZSM-5 catalyst. The alkali treatment can include preparing an alkaline solution containing the HZSM-5 catalyst. The alkaline solution can contain NaOH. The NaOH can be present in the alkaline solution at a concentration of from about 0.02 M to about 0.20 M. The method can further include removing the solvent from the alkali-treated HZSM-5 catalyst by filtration and / or evaporation. The method can further include calcining the alkali-treated HZSM-5 catalyst.

[0024] In certain embodiments, phosphorus modification can be carried out after Ti modification and / or alkali treatment. For example, the method can include treating the HZSM-5 catalyst with a source of phosphate ions. The source of phosphate ions can be monoammonium phosphate. In certain embodiments, the method can include treating the HZSM-5 catalyst with a solution containing phosphate ions. The method can further include removing the solvent from the phosphorus-modified HZSM-5 catalyst by filtration and / or evaporation. The method can further include calcining the phosphorus-modified HZSM-5 catalyst. The phosphorus-modified HZSM-5 catalyst can contain from about 0.1 wt% to about 20 wt%, from about 0.5 wt% to about 15 wt% or from about 1 wt% to about 10 wt% of phosphorus oxide. The phosphorus oxide can be phosphoric anhydride (P2O5). In certain embodiments, the HZSM-5 catalyst contains about 5 wt% of P2O5.

[0025] It should be noted that in the method according to the disclosed subject matter, it is not necessary to steam the HZSM-5 catalyst before feeding it to the reactor, since catalytic steam cracking is carried out in the presence of steam. Thus, compared to some other methods, the method according to the disclosed subject matter can eliminate the need for steaming and improve efficiency.

[0026] In certain embodiments, methods 100, 200 further include feeding a naphtha feedstock to reactors 103, 203 containing a catalyst. The reactor can be any reactor type known to be suitable for catalytic steam cracking of naphtha. By way of example and not limitation, the reactor can be a fixed bed reactor such as a tubular fixed bed reactor or a multitubular fixed bed reactor, a fluidized bed reactor such as an entrained fluidized bed reactor or a fixed fluidized bed reactor, or a slurry bed reactor such as a three-phase slurry bubble column, or a ebullated bed reactor. The size and structure of the reactors according to the disclosed subject matter can vary depending on the capacity of the reactor. The capacity of the reactor can be determined by the reaction rate, the stoichiometric amounts of the reactants, and / or the feed flow rate.

[0027] In certain embodiments, the method further includes catalytic steam cracking of naphtha to form ethylene and propylene. The method can include providing steam to the reactor. The ratio of steam provided to the reactor to naphtha can be from about 0.25 to about 0.75, from about 0.35 to about 0.65 or from about 0.4 to about 0.6. In a specific embodiment, the ratio of steam fed to the reactor to naphtha is about 0.5. The reaction can be carried out at a temperature of from about 400 °C to about 900 °C, from about 500 °C to about 800 °C, from about 550 °C to about 750 °C or from about 600 °C to about 700 °C. The reaction can be carried out at a pressure of from about atmospheric pressure to about 30 psig. The reaction can be carried out at a weight hourly space velocity of from about 5 to about 7 per hour of naphtha feedstock.

[0028] In certain embodiments, methods 100, 200 further include removing effluent 104, 204 from the reactor. The effluent can contain ethylene and propylene. For example, the effluent can contain from about 5 wt% to about 35 wt%, from about 10 wt% to about 30 wt%, or from about 15 wt% to about 25 wt% ethylene. The effluent can contain from about 10 wt% to about 50 wt%, from about 20 wt% to about 40 wt%, or from about 25 wt% to about 35 wt% propylene. The effluent can also contain other components such as higher carbon olefins, alkanes, and / or aromatic hydrocarbons such as benzene, toluene, and / or xylene. For example, the effluent can contain from about 5 wt% to about 10 wt% higher carbon olefins, from about 0.1 wt% to about 5 wt% aromatic hydrocarbons, from about 20 wt% to about 30 wt% C1 - C4 alkanes, and / or from about 15 wt% to about 30 wt% higher carbon alkanes.

[0029] In certain embodiments, the total yield of ethylene and propylene in the effluent is greater than about 30 wt%, greater than about 35 wt%, greater than about 40 wt%, or greater than about 45 wt%.

[0030] The methods of the present disclosure can provide advantages over some of the prior art. Exemplary advantages include elimination of catalyst steaming prior to use, superior run - time stability, and high ethylene and propylene yields.

[0031] The following examples are merely illustrative of the present disclosure and should not be construed as limiting in any way.

[0032] Examples

[0033] Example 1: Naphtha Feedstock

[0034] Catalytic steam cracking of light straight - run naphtha to lower - carbon olefins was carried out using a series of catalysts (Examples 2 - 9 below).

[0035] Catalytic steam cracking was carried out at a reaction temperature of 650 °C and a time - on - stream (TOS) of 6 hours. The ratio of steam to naphtha in the feed was 0.5. The weight hourly space velocity (WHSV) of the reaction was about 6.1 per hour. Table 1 shows the physical properties of the naphtha feedstock.

[0036] Table 1: Physical Properties of Light Straight - Run Naphtha

[0037]

[0038] Example 2: Unmodified HZSM - 5 Catalyst

[0039] Calcine commercially available HZSM-5 (Zeolyst, NH4 form, CBV3024E) with a Si / Al2 ratio of 27 at 550 °C at a heating rate of 3 °C / minute and a holding time of 5 hours. Table 2 shows the catalytic performance of unmodified HZSM-5 in the catalytic steam cracking process of Example 1.

[0040] Table 2: Catalytic performance of unmodified HZSM-5 catalyst

[0041]

[0042] Example 3: HZSM-5 catalyst with added titanium and alkali-treated HZSM-5 catalyst

[0043] Ti / HZSM-5 catalyst

[0044] Stir 1.0 g of HZSM-5 zeolite with a Si / Al2 ratio of 27 in a solution containing a Ti precursor (titanium oxychloride). Calibrate the amount of titanium oxychloride in the solution to produce a 2.0 wt% metal loading. Stir the mixture for 3 hours. Filter off the solvent. Then dry the product overnight at 90 °C and subsequently calcine it at 650 °C (heating rate 3 °C / minute, holding time 5 hours).

[0045] Alkali-treated HZSM-5 catalyst

[0046] In a flask connected to a reflux and a water bath, heat 60 mL of 0.05 M alkaline NaOH solution to about 65 °C to about 75 °C. Add 1.0 g of HZSM-5 zeolite with a Si / Al2 ratio of 30 to the heated solution and stir the solution at a constant temperature for 2 hours. Immediately cool the zeolite suspension in an ice bath and then separate it by suction filtration. Wash the product thoroughly with deionized water to a neutral pH. Then dry the product at ambient temperature and subsequently dry it overnight at 110 °C. Calcinate the sample in static air at 550 °C (heating rate 3 °C / minute, holding time 5 hours). Convert the Na + -containing zeolite to the ammonium form by performing two ion exchanges with 2.20 M NH4Cl at 80 °C for a total of 5 hours, with no calcination between the two ion exchange processes. The ion exchange is carried out at a concentration of 1.0 g zeolite / 50 mL NH4Cl solution. Then dry the sample and subsequently calcine it to produce the H-form.

[0047] Table 3 shows the catalytic performance of Ti / HZSM-5 and alkali-treated HZSM-5 compared to unmodified HZSM-5 of Example 2 after undergoing the catalytic steam cracking process of Example 1.

[0048] Table 3: Catalytic performance of Ti / HZSM-5, alkali-treated HZSM-5, and unmodified HZSM-5 catalysts

[0049]

[0050] As shown by the data in Table 3, compared with the unmodified HZSM-5 catalyst, the titanium-modified HZSM-5 catalyst and the alkali-treated HZSM-5 catalyst according to the disclosed subject matter provide increased total yields of ethylene and propylene. In addition, compared with the unmodified HZSM-5 catalyst, titanium modification and alkali treatment increase the naphtha conversion rate.

[0051] Example 4: Phosphorus-modified HZSM-5 catalyst

[0052] Prepare a slurry containing 35 wt% of the solid unmodified HZSM-5 of Example 2. Add monoammonium phosphate (MAP) to the slurry such that the slurry contains 5 wt% of P2O5. Heat the solution to 95 °C and stir continuously for 1 hour. Then remove the water by slow evaporation. Dry the product overnight at 90 °C and then calcine it at 650 °C (heating rate of 3 °C / minute, holding time of 3 hours). Table 4 shows the catalytic performance of phosphorus-modified HZSM-5 compared with the unmodified HZSM-5 of Example 2 after undergoing the catalytic steam cracking process of Example 1.

[0053] Table 4: Catalytic performance of unmodified HZSM-5 and HZSM-5-P2O5 catalysts

[0054]

[0055] As shown by the data in Table 4, compared with the unmodified HZSM-5 catalyst, the total yields of ethylene and propylene are not increased by phosphorus modification of the HZSM-5 catalyst alone. In addition, compared with the unmodified HZSM-5 catalyst, the conversion rate of naphtha is not increased by phosphorus modification alone.

[0056] Example 5: Phosphorus-modified alkali-treated HZSM-5 catalyst

[0057] Prepare a slurry containing 35 wt% of the solid alkali-treated HZSM-5 of Example 3. Add monoammonium phosphate (MAP) to the slurry such that the slurry contains 5 wt% of P2O5. Heat the solution to 95 °C and stir continuously for 1 hour. Then remove the water by slow evaporation. Dry the product overnight at 90 °C and then calcine it at 650 °C (heating rate of 3 °C / minute, holding time of 3 hours). Table 5 shows the catalytic performance of phosphorus-modified alkali-treated HZSM-5 compared with the alkali-treated HZSM-5 of Example 3 after undergoing the catalytic steam cracking process of Example 1.

[0058] Table 5: Catalytic performance of alkali-treated HZSM-5 and alkali-treated HZSM-5-P2O5 catalysts

[0059]

[0060] As shown by the data in Table 5, compared with the alkali-treated HZSM-5 catalyst, the phosphorus modification of the alkali-treated HZSM-5 catalyst according to the disclosed subject matter increased the total yield of ethylene and propylene. In addition, compared with the alkali-treated HZSM-5 catalyst, the phosphorus modification increased the naphtha conversion rate.

[0061] Example 6: Phosphorus-modified Ti / HZSM-5 catalyst

[0062] Prepare a slurry containing 35 wt% of the solid Ti / HZSM-5 of Example 3. Add ammonium dihydrogen phosphate (MAP) to the slurry such that the slurry contains 5 wt% of P2O5. Heat the solution to 95 °C and continuously stir for 1 hour. Then remove the water by slow evaporation. Dry the product overnight at 90 °C and then calcine it at 650 °C (heating rate: 3 °C / minute, holding time: 3 hours).

[0063] Table 6 shows the catalytic performance of phosphorus-modified Ti / HZSM-5 compared with Ti / HZSM-5 of Example 3 after undergoing the catalytic steam cracking process of Example 1.

[0064] Table 6: Catalytic performance of Ti / HZSM-5 and Ti / HZSM-5-P2O5 catalysts

[0065]

[0066] As shown by the data in Table 6, compared with the Ti / HZSM-5 catalyst, the phosphorus modification of the Ti / HZSM-5 catalyst according to the disclosed subject matter increased the total yield of ethylene and propylene. In addition, compared with the Ti / HZSM-5 catalyst, the phosphorus modification increased the naphtha conversion rate.

[0067] Example 7: Steamed HZSM-5 and HZSM-5-P2O5 catalysts

[0068] 1.0 g of the unmodified HZSM-5 of Example 2 was subjected to steam treatment at 700 °C for 3 hours (100% steam, heating rate 10 °C / min). The steamed catalyst was dried overnight at 100 °C. 1.0 g of the phosphorus-modified HZSM-5-P2O5 of Example 4 was also subjected to steam treatment and dried in the same manner. Table 7 shows the catalytic performance of the steamed HZSM-5 and the steamed HZSM-5-P2O5 compared to the unmodified HZSM-5 of Example 2 and the HZSM-5-P2O5 of Example 4 after undergoing the catalytic steam cracking process of Example 1.

[0069] Table 7: Catalytic performance of steamed and unsteamed HZSM-5 and HZSM-5-P2O5 catalysts

[0070]

[0071] As the data in Table 7 show, steaming the HZSM-5 catalyst prior to the catalytic steam cracking reaction unexpectedly did not consistently increase the total yield of ethylene and propylene or the conversion of naphtha compared to the unsteamed HZSM-5 catalyst.

[0072] Example 8: Steamed alkali-treated HZSM-5 and HZSM-5-P2O5 catalysts

[0073] 1.0 g of the alkali-treated HZSM-5 of Example 3 was subjected to steam treatment at 700 °C for 3 hours (100% steam, heating rate 10 °C / min). The steamed catalyst was dried overnight at 100 °C. 1.0 g of the phosphorus-modified alkali-treated HZSM-5-P2O5 of Example 5 was also subjected to steam treatment and dried in the same manner. Table 8 shows the catalytic performance of the steamed alkali-treated HZSM-5 and the steamed alkali-treated HZSM-5-P2O5 compared to the alkali-treated HZSM-5 of Example 3 and the alkali-treated HZSM-5-P2O5 of Example 5 after undergoing the catalytic steam cracking process of Example 1.

[0074] Table 8: Catalytic performance of steamed and unsteamed alkali-treated HZSM-5 and HZSM-5-P2O5 catalysts

[0075]

[0076] As the data in Table 8 show, steaming the alkali-treated HZSM-5 catalyst prior to the catalytic steam cracking reaction unexpectedly did not increase the total yield of ethylene and propylene or the conversion of naphtha.

[0077] Example 9: Steamed Ti / HZSM-5 and Ti / HZSM-5-P2O5 Catalysts

[0078] 1.0 g of the Ti / HZSM-5 of Example 3 was subjected to steaming at 700 °C for 3 hours (100% steam, heating rate 10 °C / min). The steamed catalyst was dried overnight at 100 °C. 1.0 g of the phosphorus-modified Ti / HZSM-5-P2O5 of Example 6 was also subjected to steaming and dried in the same manner. Table 9 shows the catalytic performance of the steamed Ti / HZSM-5 and the steamed Ti / HZSM-5-P2O5 compared to the Ti / HZSM-5 of Example 3 and the Ti / HZSM-5-P2O5 of Example 6 after undergoing the catalytic steam cracking process of Example 1.

[0079] Table 9: Catalytic Performance of Steamed and Unsteamed Ti / HZSM-5 and Ti / HZSM-5-P2O5 Catalysts

[0080]

[0081] As the data in Table 9 show, steaming the Ti / HZSM-5 catalyst prior to the catalytic steam cracking reaction unexpectedly did not increase the total yield of ethylene and propylene or the conversion of naphtha compared to the unsteamed Ti / HZSM-5 catalyst.

[0082] Example 10: Coke Deposition on HZSM-5 Catalysts

[0083] Catalytic steam cracking of light straight-run naphtha to lower olefins was carried out using a series of catalysts (Examples 2 to 9 above). Table 10 shows the coke deposition (carbide deposition) on the catalyst surfaces of Examples 2 to 9 after undergoing the catalytic steam cracking process of Example 1 for 6 hours.

[0084] Table 10: Coke Deposition on the Catalysts of Examples 1 to 9

[0085] Catalyst Weight % of coke Example 2: Unmodified HZSM-5 5.41 Example 3: Alkali-treated HZSM-5 6.68 Example 3: Ti / HZSM-5 7.11 <![CDATA[Example 4: HZSM-5-P2O5]]> 3.39 <![CDATA[Example 5: Alkali-treated HZSM-5-P2O5]]> 4.32 <![CDATA[Example 6: Ti / HZSM-5-P2O5]]> 3.88 Example 7: Steamed HZSM-5 4.72 <![CDATA[Example 7: Steamed HZSM-5-P2O5]]> 4.78 Example 8: Steamed alkali-treated HZSM-5 6.31 <![CDATA[Example 8: Steamed alkali-treated HZSM-5-P2O5]]> 4.11 Example 9: Steamed Ti-HZSM-5 4.52 <![CDATA[Example 9: Steam-treated Ti-HZSM-5-P2O5]]> 3.41

[0086] As the data in Table 10 show, the phosphorus modification according to the disclosed subject matter reduced coke deposition after 6 hours of catalytic steam cracking. The phosphorus-modified HZSM-5 catalyst showed less coke deposition (by weight percentage) compared to the unmodified HZSM-5 catalyst. The phosphorus-modified alkali-treated HZSM-5 catalyst showed less coke deposition (by weight percentage) compared to the alkali-treated HZSM-5 catalyst. The phosphorus-modified Ti / HZSM-5 catalyst showed less coke deposition (by weight percentage) compared to the Ti / HZSM-5 catalyst.

[0087] In addition to the various embodiments depicted and claimed, the disclosed subject matter also relates to other embodiments having other combinations of the features disclosed and claimed herein. Thus, the specific features presented herein can be combined with each other in other ways within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to the embodiments disclosed.

[0088] It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Accordingly, the disclosed subject matter is intended to embrace modifications and variations that fall within the scope of the appended claims and their equivalents.

[0089] Various patents and patent applications are cited herein, the contents of which are incorporated herein by reference in their entirety.

Claims

1. A method for producing ethylene and propylene by catalytic steam cracking of naphtha, the method comprising: (a) providing a naphtha feedstock; (b) providing steam; (c) providing a catalyst comprising phosphorus-modified Ti-containing HZSM-5; (d) feeding the naphtha feedstock and steam into a reactor containing the catalyst, thereby producing an effluent comprising ethylene and propylene; and (e) removing the effluent from the reactor, the effluent having a total yield of ethylene and propylene greater than 45% by weight; wherein, 6 hours after the naphtha feedstock and steam are first fed into the reactor, based on the weight of the deactivated catalyst, the deactivated catalyst contains less coke deposition than an unphosphorus-modified Ti-containing HZSM-5 catalyst, wherein the deactivated catalyst contains the catalyst and coke deposition, wherein the catalyst contains 1.0% to 10.0% by weight of P2O5, and wherein the catalyst contains 1.0% to 5.0% by weight of Ti.

2. The method according to claim 1, wherein the naphtha feedstock comprises light straight-run naphtha.

3. The method according to claim 1, wherein the steam is co-fed with the naphtha feedstock.

4. The method according to claim 1, wherein the phosphorus-modified Ti-containing HZSM-5 has a Si / Al2 ratio of 27 to 30.

5. The method according to claim 1, wherein the catalyst is not steamed before the naphtha feedstock is fed into the reactor.

6. A method for producing ethylene and propylene by catalytic steam cracking of naphtha, the method comprising: (a) providing a naphtha feedstock; (b) providing steam; (c) providing a catalyst comprising phosphorus-modified Ti-containing HZSM-5; (d) feeding the naphtha feedstock and steam into a reactor containing the catalyst, thereby producing an effluent comprising ethylene and propylene; and (e) removing the effluent from the reactor, the effluent having a total yield of ethylene and propylene greater than 45% by weight, wherein, 6 hours after the naphtha feedstock and steam are first fed into the reactor, based on the weight of the deactivated catalyst, the deactivated catalyst contains less coke deposition than an unphosphorus-modified Ti-containing HZSM-5 catalyst, wherein the deactivated catalyst contains the catalyst and coke deposition.

7. The method according to claim 6, wherein the phosphorus modification uses monoammonium phosphate.

8. The method according to claim 6, wherein the naphtha feedstock comprises light straight-run naphtha.

9. The method according to claim 6, wherein the steam is co-fed with the naphtha feedstock.

10. The method according to claim 6, wherein the phosphorus-modified Ti-containing HZSM-5 has a Si / Al2 ratio of 27 to 30.

11. The method according to claim 6, wherein the catalyst contains 0.1% to 5.0% by weight of Ti.

12. The method according to claim 6, wherein the catalyst is prepared by titanium modification followed by phosphorus modification.

13. The method according to claim 12, wherein the phosphorus modification uses monoammonium phosphate.

14. The method according to claim 6, wherein the catalyst comprises 1.0 wt% to 10.0 wt% of P2O5, and wherein the catalyst is prepared by titanium modification followed by phosphorus modification.

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