Single Step Catalytic Process For The Conversion Of N-Paraffins And Naphtha To Diesel Range Hydrocarbons (United States Patent Application 20150284643 Council of Scientific and Industrial Research, New Delhi, India)

Single Step Catalytic Process For The Conversion Of N-Paraffins And Naphtha To Diesel Range Hydrocarbons (United States Patent Application 20150284643 Council of Scientific and Industrial Research, New Delhi, India)
October 8, 2015
Assignee: Council of Scientific and Industrial Research, New Delhi, India
Abstract
The present invention discloses a single step catalytic process for the conversion of n-paraffins and naphtha to diesel range hydrocarbons. A bi-metallic Pt--Sn/ZSM-5 catalyst has been developed for the direct conversion of n-heptane as well as naphtha into diesel range hydrocarbons in a single step process.
FIELD OF INVENTION
[0001] The present invention relates to a single step catalytic process for the conversion of n-paraffins and naphtha to diesel range hydrocarbons. Particularly the invention relates to a process for the preparation of a solid acid catalyst suitable for the effective conversion of n-paraffins and light naphtha in a single reaction (once-through) operation into diesel range hydrocarbons along with gasoline range hydrocarbons, Liquefied Petroleum Gas (LPG) and light olefins (C.sub.2-C.sub.4) as valuable bi-products. Further, a considerable amount of hydrogen is also produced during the process from the dehydrogenation reaction of paraffins and naphthenes. More particularly, the present invention relates to the preparation of a solid acid catalyst suitable for the effective conversion of light naphtha.
BACKGROUND OF THE INVENTION
[0002] The availability of naphtha at refineries has been encouraging its value addition through its effective conversion to various hydrocarbon products. Traditionally gasoline is produced from such feedstocks, where the hydrocarbons such as aromatics, alkyl aromatics and isoparaffins are produced without changing the carbon number of the reactant molecule. Traditionally, lower olefins such as hexene and heptane are converted to diesel through simple oligomerization. But the conversion of n-paraffins was reported to need four-reactor system with at least three catalysts work in sequential reactions of paraffin dehydrogenation, oligomerization and saturation for the production of diesel. Currently the increasing demand for diesel compared to gasoline inspiring refineries to look for new processes that can convert light naphtha directly into diesel range hydrocarbons, which requires a catalyst that can not only facilitate the reforming of the molecule but also increase the carbon number so as to convert low boiling range naphtha into high boiling range diesel. Chemically, the catalyst needs to have active component to facilitate oligomerization reaction to join smaller hydrocarbon molecules to grow up to the range of diesel. The oligomerization reaction is easily occur when the reactant molecules have at least some olefins and most of the recent research is focused on converting olefins such as hexene, heptanes and octenes into diesel range products. For the conversion of paraffin-rich naphtha into diesel range products, there needs additional reaction steps such as paraffin dehydrogenation and it is challenging for a chemist to establish high temperature favored dehydrogenation and low temperature favored oligomerization reactions on a single catalyst system.
[0003] Thus the present study explores the possibility developing a zeolite based solid acid catalyst for facilitating the effective conversion of n-heptane into diesel range hydrocarbons. Further, the catalyst explored for the conversion of industrial naphtha cut into diesel range products. The process also produced considerable amount of gasoline, light olefins, LPG and hydrogen as valuable bi-products on the designed catalyst.
[0004] References may be made to US 2011/0114538A1 describes a process for the production of kerosene and diesel along with hydrogen from a saturated light cut by using sequential reactors containing molecular sieves and three different catalysts for separation of n-paraffins from isoparaffins followed by dehydrogenation of n-paraffins, oligomerization of olefins and saturation of oligomers in the final reactor to obtain the diesel range product. It involves three catalysts and four reactor system for step wise conversion of naphtha.
[0005] Reference may be made to WO 2011/075523A2 describes a catalytic process for production of diesel and other distillates by oligomerization of olefins followed by alkylation of oligomers with the aromatics such as benzene. It was meant for olefin conversion and not suitable for hydrocarbon of paraffins and naphtha range to diesel product.
[0006] Reference may be made to U.S. Pat. No. 7,741,526 B2 describes a catalytic process for the production of diesel and jet fuels from a mixture of olefinic streams such as butene, pentene, hexene, butadiene and pentadienes. It was meant for olefin conversion and not suitable for hydrocarbon of paraffins and naphtha range to diesel product.
[0007] Reference may be made to U.S. Pat. No. 6,914,165B2 describes the process for the production of diesel cut fuel by sequential reaction steps of oligomerization of C.sub.2-C.sub.10 olefins followed by selective hydrogenation of C.sub.12-C.sub.24 oligomers stream. It was meant for olefin conversion and not suitable for hydrocarbon of paraffins and naphtha range to diesel product.
[0008] Reference may be made to EP 1249486 B1 describes the process for the production of diesel cut fuel from the sequential reaction steps of oligomerization of C.sub.2-C.sub.4 olefins, separation of C.sub.12-C.sub.24 distillate followed by its saturation to produce the final product. It was meant for olefin conversion and not suitable for hydrocarbon of paraffins and naphtha range to diesel product.
[0009] Reference may be made to U.S. Pat. No. 6,281,401 B1 describes oligomerization between smaller olefin (less than C.sub.5) and higher olefin (larger than C.sub.5) to obtain C.sub.11.sup.+ oligomers falling in the diesel range hydrocarbons. Alkylation of smaller olefins with longer olefins is used for diesel production. It was meant for olefin conversion. It is not suitable for hydrocarbon of paraffins and naphtha range to diesel product
[0010] Reference may be made to U.S. Pat. No. 4,740,648 describes a catalytic process for the conversion of C.sub.2 to C.sub.12 linear and branched olefins to liquid motor fuel falling in jet and diesel range. It was meant for olefin conversion and not suitable for hydrocarbon of paraffins and naphtha range to diesel product.
[0011] Reference may be made to U.S. Pat. No. 721,304 B2 describes a catalytic process for the production of diesel fuels by oligomerization of short and branched olefins having the chain length from three to eight carbon atoms. The process is not aimed to obtain the diesel range hydrocarbons from paraffins and naphtha range hydrocarbons.
[0012] Reference may be made to WO/2006/09/091986 describes catalytic conversion of C.sub.3-C.sub.5 olefins to diesel and gasoline range fuels. The process is not aimed to obtain the diesel range hydrocarbons from paraffins and naphtha range hydrocarbons.
[0013] Reference may be made to US 2006/0217580 describes a catalytic process for the conversion of C.sub.3-C.sub.8 olefins through oligomerization to produce hydrocarbon composition suitable for jet fuel and diesel applications. The process is not aimed to obtain the diesel range hydrocarbons from paraffins and naphtha range hydrocarbons.
[0014] Reference may be made to U.S. Pat. No. 5,780,703 describes a catalytic process for the production of low aromatic diesel fuel with high cetane index from the feedstock containing the mixture of one olefinic component such as propylene and butenes and one iso-paraffinic component such as isobutene or iso-pentane. Process is for the reaction between isoparaffins and olefins. Not suitable for hydrocarbon of paraffins and naphtha range to diesel product
[0015] Reference may be made to US 2012/0209046A1 described a catalytic process for the production of diesel turbine range hydrocarbons by sequential steps of alcohol dehydration followed by oligomerization of the resultant olefins and hydro-finishing. Process uses alcohol as source for olefin production followed by oligomerization. Not suitable for hydrocarbon of paraffins and naphtha range to diesel product
[0016] Till date no information is available on single step conversion of n-paraffins such as n-heptane and paraffin containing feedstocks such as naphtha into diesel range products. Most of the references are dealt with the conversion of olefins and mixed olefin feedstocks, or combination of olefins and isoparaffins into diesel range hydrocarbons. Since, n-paraffins and n-paraffin containing feedstocks such as naphtha are cheaply available for value addition, conversion of these feedstocks directly into diesel gains importance in terms of reduced cost of the process and consumption of olefins. The refineries having only paraffins but not olefins, can also process the feedstock through the direct conversion of n-paraffins to diesel. Hence, the present invention relates to provide a single step catalytic process for the conversion of n-paraffins and naphtha to diesel range hydrocarbons. Which obviates the drawbacks of the hitherto known prior art as detailed above for the direct conversion of n-paraffins and naphtha into diesel.
[0017] Conversion of paraffins into diesel in a single step process is first of its kind and the process also produces valuable bi-products such as gasoline range hydrocarbons, LPG, light olefins and hydrogen. The catalyst exhibits high yield diesel range hydrocarbons of about 15 wt %, highest gasoline yield of about 74 wt % with iso-paraffins and aromatics as major components. Moreover, considerable amount of the Liquefied Petroleum Gas (LPG) (18 wt %) and light olefins (10.7 wt %) are also formed as bi-product that adds value to the process. The study reveals the effective conversion of naphtha to high octane gasoline. The catalyst also exhibits the stability in activity for the studied period of 40 h.
[0018] The problems solved by the present invention are as follows: [0019] 1. Development of a catalyst bearing active site components suitable for facilitating the various hydrocarbon conversion steps such as dehydrogenation of n-paraffins, oligomerization of olefins and saturation of oligomers for the direct production of higher range hydrocarbons from the short chain n-paraffins or mixed feedstocks like naphtha. [0020] 2. Single reactor and single catalyst system for simplicity in process operation and to reduce process cost [0021] 3. Unlike other similar processes, there is no requirement of olefins in the feedstock. The paraffin rich (olefin-free) hydrocarbons can be directly used as feedstocks so as to check the performance of the catalyst for the value addition of n-paraffins or naphtha into diesel range hydrocarbons.
OBJECT OF THE INVENTION
[0022] The main object of the present invention is to provide a single step catalytic process for the conversion of n-paraffins and naphtha to diesel range hydrocarbons.
[0023] Another object of the present invention is to provide a single step process for the conversion of n-paraffins such as n-heptane and naphtha (90-14.0.degree. C.) into diesel range hydrocarbons.
[0024] Yet another object of the present invention is to provide process suitable for the production of valuable bi-products gasoline blending stock along with negligible concentration of benzene.
[0025] Yet another object of the present invention is to provide a process suitable for production of light olefins as valuable bi-product.
[0026] Yet another object of the present invention is to provide a process suitable for production of Liquefied Petroleum Gas (LPG) range hydrocarbons as co-bi product along with hydrogen.
[0027] Still another object of the present invention is to provide a process for the preparation of Pt--Sn-ZSM-5 catalyst.
SUMMARY OF THE. INVENTION
[0028] Accordingly, the present invention provides a single step catalytic process for the conversion of n-paraffins and naphtha (90-1400 C) to diesel range hydrocarbons using Pt--Sn-ZSM-5 catalyst, wherein the said process comprises loading of Pt--Sn-ZSM-5 catalyst in a reactor followed by reducing the catalyst using the hydrogen at 500-6000 C for 6-10 h with 6-16 l/h hydrogen gas flow further, introducing the feed in a continuous flow rate 2-10 h-1 WHSV (weight hourly space velocity) at temperatures ranging between 400.degree. C.-450.degree. C. with a carrier gas, preferably, nitrogen gas at flow rate 5-50 l/h at pressure ranging between 2-30 bar to obtain liquid products containing gasoline and diesel collected from downstream and gas product collected from upstream. A considerable amount of hydrogen is also produced during the process from the dehydrogenation reaction of paraffins and naphthenes.
[0029] In the present invention the percentage of Pt and Sn in Pt--Sn-ZSM-5 catalyst is in the range of 0.1- to 1.0 wt % and 0.2 wt % to-1.6-wt % respectively and the catalyst bed was sandwiched between two layers of alpha alumina (inert binder material) for the mechanical support. In the present invention the Si/Al ratio in ZSM-5 is in the range of 15 to 200 and the yield of diesel is in the range of 2 to 15 wt % and gasoline is in the range of 50 wt % to 80 wt %. The valuable bi-products are LPG, olefins and hydrogen and the catalyst exhibits stability in activity in terms of diesel yield for the minimum reaction time period of 40 h.
Brief Description of the Graph and Tables
[0030] Graph 1 represents a plot of the reaction time vs diesel yield over the promising catalyst (NTDZSM-5) described in example 9.
[0031] Table 1 is indicating the detailed components and D-86 analysis of naphtha (90-140.degree. C.) feed described in example 3.
[0032] Table 2 is indicating the overall performance of PT-SN-ZSM-5 catalyst for conversion of naphtha to diesel described in example 3.
[0033] Table 3 is indicating the overall olefins distribution on various reaction temperatures described in example 6.
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