Chemistry of hydrocarbon compounds – Saturated compound synthesis – By isomerization
Reexamination Certificate
1998-03-04
2001-03-06
Utech, Benjamin L. (Department: 1764)
Chemistry of hydrocarbon compounds
Saturated compound synthesis
By isomerization
C585S740000, C585S750000, C502S061000, C502S064000, C502S073000, C502S074000
Reexamination Certificate
active
06198015
ABSTRACT:
PRIOR ART
High quality lubricants are of fundamental importance for proper operation of modern machines, cars and trucks. However, the quantity of paraffins originating directly from petroleum, which have not been treated, and with properties which are suitable for good lubricants is very low with respect to the increasing demand in this sector.
Treatment of heavy petroleum fractions with high concentrations of linear or slightly branched paraffins is necessary to obtain good quality lubricant stock in the best possible yields, using a dewaxing operation which aims to eliminate linear or very slightly branched paraffins from feeds which are then used as lubricant stock or kerosine or jet fuel. High molecular weight paraffins which are linear or very slightly branched and which are present in oils or in kerosine or jet fuel result in high pour points and thus coagulation on low temperature use. In order to reduce the pour points, such linear paraffins which are not or very slightly branched must be completely or partially eliminated.
The dewaxing operation can be carried out by extraction using solvents such as propane or methyl ethyl ketone, known as propane or methyl ethyl ketone (MEK) dewaxing. However, such techniques are expensive, long and not always easy to carry out.
Catalytic dewaxing, so named to differentiate it from solvent dewaxing, is cheaper and can produce products with the desired physico-chemical properties. This is achieved by selective cracking of the longest linear paraffin chains leading to the formation of lower molecular weight compounds, part of which can be eliminated by distillation.
Zeolites are among the most widely used dewaxing catalysts because of their shape selectivity. The concept behind their use is that zeolitic structures exist with pore openings which allow long linear or very slightly branched paraffins to enter their micropores but which exclude branched paraffins, naphthenes and aromatics. This phenomenon results in selective cracking of linear or very slightly branched paraffins.
Catalysts based on zeolites with intermediate pore sizes such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 have been described for their use in processes for catalytic dewaxing by cracking.
Processes using such zeolites enable dewaxing by cracking feeds containing less than 50% by weight of linear or very slightly branched paraffins. However, with feeds containing larger quantities of such compounds, it appears that cracking thereof results in the formation of large quantities of lower molecular weight products such as butane, propane, ethane and methane, which considerably reduces the yield of desired products.
In order to overcome these disadvantages, we have concentrated our research resources on developing catalysts (preferably not ZSM) which can isomerise such compounds.
A number of patents exist in this field, for example International patent application WO 92/01657 describes and claims a process for dewaxing feeds by means of an isomerisation reaction in the presence of a group VIII metal, a hydrogen pressure in the range 100 KPa to 21000 KPa and a catalyst with a pore opening in the range 0.48 nm to 0.71 nm and in which the crystallite size is less than 0.5 &mgr;m. The performance of that catalyst was improved in terms of yield, compared with the prior art.
AIM OF THE INVENTION
The invention provides a catalyst comprising a matrix, at least 5% of at least one hydro-dehydrogenating element selected from the group formed by non noble GVIII metals, GVIB metals, and niobium, and at least one molecular sieve with a one- or two-dimensional pore network, the accessible pore openings of which being delimited by 10 oxygen atoms, and a distance termed the bridging distance between the pores being less than 0.70 nm, and the zeolite is such that the catalyst constituted by the zeolite and 0.5% by weight of platinum when subjected to a standard n-heptadecane isomerisation test has a selectivity for isomerised products of at least 70% for a conversion of 95%.
The invention also provides a process for selective hydroisomerisation of compounds with at least one n-alkane chain containing more than 10 carbon atoms, in which the compound to be treated is brought into contact with a catalyst of the invention.
This process can advantageously convert a feed with a high pour point to a mixture with a lower pour point and a high viscosity index.
The feed includes, inter alia, linear and/or slightly branched paraffins containing at least 10 carbon atoms, preferably 15 to 50 carbon atoms, advantageously 15 to 40 carbon atoms.
The process comprises using a catalyst comprising at least one molecular sieve with at least one pore type in which the opening is delimited by 10 oxygen atoms and which are the largest pores in the structure which are accessible from the exterior. The pore network of the zeolite is one- or two-dimensional, preferably one-dimensional.
The bridging distance between two pore openings (with 10 oxygen atoms), as defined above, is less than 0.70 nm (1 nm=10
−9
nm), preferably in the range 0.50 nm to 0.68 nm, more preferably in the range 0.52 nm to 0.65 nm. The crystallite size is preferably less than 2 &mgr;m (1&mgr;m=10
−6
m), advantageously less than 1 &mgr;m, and preferably 0.4 &mgr;m.
The zeolite is such that the catalyst constituted by the zeolite and 0.5% of platinum results in, for a conversion of the order of 95% by weight of n-heptadecane (n-C17), a selectivity for isomerised products of 70% or more, preferably at least 80%, under standard isomerisation test (SIT) conditions for n-C17 which are defined below. The isomerised products generally contain between about 65% and 80% by weight of single-branched products and between about 20% and 35% by weight of multi-branched products, essentially two-branched products. The term “single-branched products” means linear paraffins containing a single methyl group, and the term “two-branched products” means linear paraffins containing two methyl groups which are not carried by the same carbon atom. Multi-branched products are defined by extension. The hydroisomerisation is thus selective.
The catalyst comprises at least one hydro-dehydrogenating function provided by at least one hydro-dehydrogenating element selected from the group formed by non noble group VIII metals, group VIB metals, and niobium, and the reaction is carried out under the conditions described below.
We have surprisingly discovered that one of the determining factors for obtaining high selectivities for isomerised products is the use of molecular sieves which are characterized in that
the largest pore openings are delimited by 10 oxygen atoms;
the bridging distance must be less than 0.70 nm, preferably in the range 0.50 nm to 0.68 nm, more preferably in the range 0.52 nm to 0.65 nm.
This latter point in particular is in contrast to that claimed in the prior art patents cited above such as WO 92/01657 which cites as an essential feature a range of pore sizes for obtaining good yields of isomerised products.
The bridging distance was measured using a drawing and molecular modelling tool such as Hyperchem or Biosym, which allows the surface of the molecular sieves in question to be constructed and, using the ionic radii of the elements present in the framework of the sieve, allows the bridging distance to be measured.
The use of such molecular sieves of the invention under the conditions described above can in particular enable the production of products with a low pour point and high viscosity index in good yields.
DETAILED DESCRIPTION OF THE INVENTION
The molecular sieves of the invention which can be used for isomerising linear or slightly branched paraffin hydrocarbons are zeolites, crystalline aluminosilicates such as Theta-1, NU-10, NU-23, EU-13, in which the Si/Al ratio is that which is best suited for the desired application. The zeolites of the invention include NU-87 which, of course, contains pores delimited by 10 and 12 oxygen atoms, but accessibility to the latter is via 10 oxygen atom pore
Benazzi Eric
George-Marchal Nathalie
Marcilly Christian
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Nguyen Tam M.
Utech Benjamin L.
LandOfFree
Catalyst based on a molecular sieve and a process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst based on a molecular sieve and a process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst based on a molecular sieve and a process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2533651