Process for the selective adsorption of para-xylene

A process for preparing a stream enriched in para-xylene from a mixture of para-xylene with other aromatic hydrocarbons which comprises contacting the mixture with a particular modified crystalline silicate and subsequently desorbing the para-xylene enriched stream from the silicate.

FIELD OF THE INVENTION 
This invention relates to a process for producing a stream rich in 
para-xylene from a mixture consisting substantially of aromatic 
hydrocarbons with six to nine carbon atoms in the molecule and including 
at least some para-xylene and some ethyl benzene by contacting the mixture 
with a modified crystalline silicate and subsequently desorbing a 
para-xylene enriched stream from the silicate. 
BACKGROUND OF THE INVENTION 
Para-xylene is an important base material in the chemical industry. It is 
generally required substantially free from other aromatic hydrocarbons and 
in particular from the isomeric compounds, ortho-xylene, meta-xylene, and 
ethylbenzene often produced during its manufacture. Since the four 
isomeric compunds closely resemble each other as regards their physical 
and chemical properties, the separation of para-xylene from such a mixture 
presents a particular problem. 
While it is known from U.S. Pat. No. 3,729,523 to use crystalline silicates 
for the separation of para-xylene from the said mixtures, in practice a 
large quantity of ethyl benzene is also adsorbed by the silicate. The 
present invention seeks to improve the selectivity of the crystalline 
silicate for para-xylene over ethyl benzene. 
It has now been found that the selectivity for para-xylene over ethyl 
benzene can be improved by using a modified crystalline silicate. 
SUMMARY OF THE INVENTION 
In a process for selectively adsorbing para-xylene from a mixture of 
aromatic hydrocarbons of six to nine carbon atoms including para-xylene 
and ethyl benzene utilizing a crystalline silicate, the adsorption 
selectivity of para-xylene over ethyl benzene is improved by modifying the 
siicate by bringing it into contact with a solution of concentration m (in 
gion/l) of a salt of a polyvalent cation of charge density (e/r) (in 
nm.sup.-1) wherein (e/r)m is at least 45 after which it is filtered, 
washed and dried at an elevated temperature so that the salt decomposes to 
leave the metal cation in the crystalline silicate. After contacting the 
silicate with the mixture a stream rich in para-xylene over ethylbenzene 
is desorbed from the silicate. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Crystalline silicates are characterized as a class of compounds by their 
thermal stability, their crystallinity which follows from the fact that 
they all show a clear X-ray powder diffraction pattern, their adsorption 
behavior, and their overall composition. 
In this specification the term crystalline silicate will be used to refer 
to crystalline silicates which after calcining for one hour in air at 
500.degree. C. display the following characteristics: 
(a) They are thermally stable up to at least 600.degree. C. In this 
specification, "thermally stable up to t.degree.C." shall mean that after 
heating the crystalline silicate to t.degree.C. its X-ray powder 
diffraction pattern is not changed. 
(b) They have an X-ray powder diffraction pattern showing iner alia the 
reflections given in Table A below. 
TABLE A 
______________________________________ 
Source Cu-K.alpha. 
Wave length 0.15418nm 
2.theta. Relative intensity 
______________________________________ 
7.9- 8.2 S 
8.7- 9.1 M 
11.8-12.1 W 
12.4-12.7 W 
14.6-14.9 W 
15.4-15.7 W 
15.8-16.1 W 
17.6-17.9 W 
19.2-19.5 W 
20.2-20.6 W 
20.7-21.1 W 
23.1-23.4 VS 
23.8-24.1 VS 
24.2-24.8 S 
29.7-30.1 M 
______________________________________ 
In which the letters have the following significance: 
VS = very strong; 
S = strong; 
M = moderate; 
W = weak. 
Q is the angle according to Bragg's law. 
(c) In their so-called "H-form" after evacuation to 2.times.10.sup.-9 bar 
at a temperature of 400.degree. C. for 16 hours and measured at a 
hydrocarbon pressure of 8.times.10.sup.-2 bar at a temperature of 
100.degree. C. they have an adsorption of n-hexane (n-C.sub.6) of at least 
0.8 mmol/g and an adsorption of 2,2 dimethyl butane (2,2 DMB) of at least 
0.5 mmol/g, and the ratio 
##EQU1## 
should be at least 1.5. 
(d) Their chemical formula is: 
EQU y(1.0.+-.0.3)M.sub.2 O.y(aFe.sub.2 O.sub.3.bAl.sub.2 O.sub.3).SiO.sub.2 
Where: 
M is H and an alkali metal 
a+b=1; 
a.gtoreq.0; 
b.gtoreq.0 
O.ltoreq.y.ltoreq.0.1 
For the adsorption measurements under paragraph (c) the silicate must be in 
its so-called "H-form" as described below. 
A modified crystalline silicate shall mean a crystalline silicate which has 
been brought into contact with solution of a salt of a polyvalent metal 
cation, filtered, washed and dried or calcined preferably at between 
400.degree. C. and 600.degree. C., so that the salt decomposes leaving the 
metal cation in the silicate. The solution is conveniently, though not 
necessarily an aqueous solution. 
The salt conveniently can be one of an organic acid such as a formate or an 
oxalate, which readily decomposes on heating, or alternatively of an 
inorganic acid, such as a nitrate which also decomposes without leaving 
traces of undesirable compounds or elements in the modified crystalline 
silicate. 
In order to obtain the increase in the selectivity for para-xylene over 
ethyl benzene in accordance with the invention, the cation should have 
such a charge density (being the quotient of the charge e and the ion 
radius R) in nm.sup.-1 and a concentration m in gion/l that the product of 
the charge density and the concentration amounts to at least 45. Compared 
with conventional processes, application of the present invention yields a 
desorbate which is richer in para-xylene, which may in some cases obviate 
the need for further purification steps, or certainly render any such 
steps, for example crystallisation, more efficient. 
Where the valency of the metal cation is 2, (e/R)m is preferably in excess 
of 60 in order to obtain a significant increase in the selectivity for 
para-xylene to ethyl benzene S.sub.PX/EB. At values of (e/R)m in excess of 
100 a 50 percent increase in the selectivity S.sub.PX/EB can be obtained 
at a temperature of 80.degree. C. 
While the invention produces a valuable increase in the selectivity 
S.sub.PX/EB where metal cations of a valency of two are employed, a still 
greater improvement can be obtained where the metal cation has a valency 
of three. In this case, an improvement in the selectivity S.sub.PX/EB of 
20 percent is obtained where (e/R)m is greater than 45 and as much as 100 
percent improvement when (e/R)m is greater than 115 at a temperature of 
80.degree. C. 
At lower temperatures, for example, in the liquid phase a selectivity 
S.sub.PX/EB in excess of five may be found. These values have been 
established with respect to a silicate in the Na-form. 
However, while such increases in the selectivity S.sub.PX/EB are very 
encouraging, it has been found that a pretreatment of the crystalline 
silicate can still further increase its selectivity. Such a pretreatment 
involves substitution of hydrogen ions for M ions present in the 
originally prepared and calcined silicate, which are often sodium ions. 
(Such a silicate is said to be in the "H-form"). This may conveniently be 
performed by bringing the crystals into contact with an ammonium salt, or 
a weak acid. The crystals are then washed and dried. Where an ammonium 
salt is used they are also heated until the ammonium has decomposed to 
leave hydrogen ions in the crystal structure. While this pretreatment will 
in itself increase the selectivity for para-xylene, its combination with 
the modification in accordance with the invention, whereby a metal cation 
is fixed in the crystalline structure, produces a substantial further 
improvement in the desired selectivity of some 10 percent in the case of a 
crystalline aluminum silicate with a low Al content to more than 70 
percent for a crystalline iron silicate with a high Fe content. 
For modifying the crystalline silicate, suitable metal cations may be 
selected from the alkaline earth metals, rare earth metals, the iron 
group, manganese, aluminum and gallium. Of these magnesium and calcium, 
are preferred, and iron, aluminum and lanthanum are most preferred. 
The salt of the metal cation should decompose on heating to leave only the 
metal cation in the crystalline silicate. Particularly suitable salts are 
nitrates and oxalates which decompose without depositing any side products 
which might adversely influence the performance of the crystalline 
silicate. 
Best results are found when the solution of the salt is made as 
concentrated as possible, say from a two molar solution to one of the 
maximum solubility of the salt in question. 
The unmodified and untreated crystalline silicate preferably has an X-ray 
diffraction pattern substantially as set out in Table B below: 
TABLE B 
______________________________________ 
Wave length 0.15418nm 
Source Cu--K.alpha. 
Relative intensity 
description 
2.theta. (100 . I/I.sub.o) 
of the reflection 
______________________________________ 
8.00 55 SP 
8.90 36 SP 
9.10 20 SR 
11.95 7 NL 
12.55 3 NL 
13.25 4 NL 
13.95 10 NL 
14.75 9 BD 
15.55 7 BD 
15.95 9 BD 
17.75 5 BD 
19.35 6 NL 
20.40 9 NL 
20.90 10 NL 
21.80 4 NL 
22.25 8 NL 
23.25 100* SP 
23.95 45 SP 
24.40 27 SP 
25.90 11 BD 
26.70 9 BD 
27.50 4 NL 
29.30 7 NL 
29.90 11 BD 
31.25 2 NL 
32.75 4 NL 
34.40 4 NL 
36.05 5 BD 
37.50 4 BD 
45.30 9 BD 
______________________________________ 
*I.sub.o = intensity of the strongest separated reflection occurring in 
the pattern. 
The abbreviations used in Table B to describe the reflections have the 
following meanings: 
SP = sharp; 
SR = shoulder; 
NL = normal; 
BD = broad. 
.theta. is the angle according to Bragg's law. 
The pores of the crystalline silicate are generally substantially 
elliptical in shape and their diameter is between 5 and 6 A. 
In general terms this invention defines a process for preparing a stream 
enriched in para-xylene from a mixture consisting substantially of 
aromatic hydrocarbons with six to nine carbon atoms in the molecule 
including para-xylene and ethyl benzene which process comprises contacting 
the mixture with the crystalline silicate described herein which 
selectively adsorbs the para-xylene and subsequently desorbing the 
para-xylene enriched stream from the silicate. The para-xylene enriched 
stream may be desorbed from the silicate by any of several alternative 
procedures. Thus, heating the silicate, reducing the partial pressure of 
the sorbed material in the vapor or liquid surrounding the silicate, 
lowering the total pressure of the system or purging with a suitable inert 
gas or liquid effect suitable desorption of the para-xylene enriched 
stream. 
The invention will now be further described by way of example. First the 
preparation of a number of candidate crystalline silicates will be 
described: 
Silicate A 
A crystalline silicate was prepared from a mixture of Fe(NO.sub.3).sub.3, 
SiO.sub.2, NaOH and [(C.sub.3 H.sub.7).sub.4 ]OH in water with a molar 
composition as follows: 
EQU 25SiO.sub.2.1/4Fe.sub.2 O.sub.3.3[(C.sub.3 H.sub.7).sub.4 N]OH.Na.sub.2 
O.450H.sub.2 O 
The mixture was heated to 150.degree. C. in an autoclave under autogeneous 
pressure, at which temperature it was maintained for 24 hours after which 
it was filtered and washed until its pH was approximately eight. After 
drying the resulting crystals were calcined for eight hours at 500.degree. 
C. This crystalline iron silicate will be referred to as Silicate A. 
(a) Silicate A was thermally stable to above 600.degree. C. 
(b) It had an X-ray powder diffraction pattern showing the reflections 
given in Table B above. 
(c) In the "H-form" at 100.degree. C. it has an adsorption of n-C.sub.6 of 
1.22 mmol/g and of 2,2 DMB of 0.60 mmol/g. 
(d) Its chemical formula was 
EQU 0.011Na.sub.2 O.0.011(0.97Fe.sub.2 O.sub.3.0.03Al.sub.2 O.sub.3).SiO.sub.2. 
The occurrence of Al.sub.2 O.sub.3 in the formula can be explained by the 
presence of up to 500 ppm Al in the SiO.sub.2 used in its preparation. Up 
to 240 ppm Al is also found in the Fe(NO.sub.3).sub.3 used. 
Silicate B 
Silicate A was contacted with a 1 molar NH.sub.4 NO.sub.3 solution at 
100.degree. C. for 10 hours (2.times.5 hr). The crystals were filtered, 
washed and then dried for 15 hours at 120.degree. C. This treated 
crystalline iron silicate will be referred to as Silicate B. 
Silicate C 
Silicate A was contacted with a 4 molar solution of La(NO.sub.3).sub.3 at 
100.degree. C. for 10 hours (2.times.5 hr). The crystals were filtered, 
washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline iron silicate will be referred to as Silicate C. 
Silicate D 
Silicate B was contacted with a 4 molar solution of La(NO.sub.3).sub.3 at 
100.degree. C. for 10 hours (2.times.5 hr). The crystals were filtered, 
washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline iron silicate will be referred to as Silicate D. 
Silicate E 
A reaction mixture was prepared from SiO.sub.2, NaNO.sub.3 and [(C.sub.3 
H.sub.7).sub.4 N]OH in water with a molar composition as follows: 
EQU 29.1SiO.sub.2.3.0[(C.sub.3 H.sub.7).sub.4 N]OH.1Na.sub.2 O.430H.sub.2 O 
The mixture was heated to 150.degree. C. in an autoclave under autogenous 
pressure, for 24 hours, then filtered and washed until its pH was below 9. 
After drying at 120.degree. C., the crystals were calcined at 500.degree. 
C. for three hours. This crystalline silicate 
(a) was thermally stable to above 600.degree. C.; 
(b) had an X-ray powder diffraction pattern showing inter alia the 
reflections given in Table B above; 
(c) in the H-form at 100.degree. C. it has an adsorption of n-C.sub.6 of 
1.29 mmol/g and of 2,2 DMB of 0.67 mmol/g; 
(d) its chemical formula was 
EQU 0.0003Na.sub.2 O.0.0003Al.sub.2 O.sub.3.SiO.sub.2. 
The occurrence of Al.sub.2 O.sub.3 in the final formula can be explained by 
the presence of up to 500 ppm Al in the SiO.sub.2 used in its preparation. 
It was then contacted with a 1 molar solution of NH.sub.4 NO.sub.3 for two 
hours (2.times.1 hr) at 100.degree. C. which was followed by drying and at 
120.degree. C. for 15 hours. This crystalline silicate will be referred to 
as Silicate E. 
Silicate F 
Silicate E was contacted with a 1 molar solution of RbNO.sub.3 for 10 hours 
(2.times.5 hrs) at 100.degree. C. The crystals were filtered and washed 
before drying for 15 hours at 400.degree. C. This modified crystalline 
silicate will be referred to as Silicate F. 
Silicate G 
Silicate E was contacted with a 1 molar solution of La(NO.sub.3).sub.3 for 
10 hours (2.times.5 hrs) at 100.degree. C. After filtering and washing it 
was dried for 15 hours at 400.degree. C. This modified crystalline 
silicate will be referred to as Silicate G. 
Silicate H 
Silicate E was contacted with a 4 molar solution of La(NO.sub.3).sub.3 for 
10 hours (2.times.5 hrs) at 100.degree. C. After filtering and washing it 
was dried for 14 hours at 400.degree. C. This modified crystalline 
silicate will be referred to as Silicate H. 
Silicate I 
Silicate B was contacted with a 4 molar solution of Ca(NO.sub.3).sub.2 for 
10 hours (2.times.5 hrs) at 100.degree. C. After filtering and washing it 
was dried for 15 hours at 400.degree. C. This modified crystalline 
silicate will be referred to as Silicate I. 
Silicate J 
Silicate B was contacted with a 2.5 molar solution of Ca(NO.sub.3).sub.2 
for 10 hours (2.times.5 hrs) at 100.degree. C. After filtering and 
washing, it was dried for 15 hours at 400.degree. C. This modified 
crystalline silicate will be referred to as Silicate J. 
Silicate K 
A crystalline silicate was prepared from a mixture of Al(NO.sub.3).sub.3, 
SiO.sub.2, NaOH and [(C.sub.3 H.sub.7).sub.4 N]OH in water with a solar 
composition as follows: 
EQU 25SiO.sub.2.1/8Al.sub.2 O.sub.3.3[(C.sub.3 H.sub.7).sub.4 N]OH.Na.sub.2 
O.450H.sub.2 O 
The mixture was heated to 150.degree. C. in a autoclave under autogenous 
pressure, at which temperature it was maintained for 24 hours after which 
it was filtered and washed until its pH was approximately 8. The resulting 
crystalline silicate after drying and calcining at 500.degree. C. for 
three hours will be referred to as Silicate K. 
(a) Silicate K was thermally stable to above 600.degree. C.; 
(b) It had an X-ray powder diffraction pattern showing the reflections 
given in Table B above. 
(c) In the H-form its adsorption of n-C.sub.6 was 1.25 mmol/g and that of 
2,2 DMB was 0.62 mmol/g. 
(d) Its chemical formula was 0.006 Na.sub.2 O.0.006Al.sub.2 
O.sub.3.SiO.sub.2. 
Silicate L 
Silicate K was contacted with a 1 molar NH.sub.4 NO.sub.3 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered, 
washed and then dried for 15 hours at 120.degree. C. This treated silicate 
will be referred to as Silicate L. 
Silicate M 
Silicate L was contacted with a 0.8 molar Mg(NO.sub.3).sub.2 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate M. 
Silicate N 
Silicate L was contacted with a 2.5 molar Mg(NO.sub.3).sub.2 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate N. 
Silicate O 
Silicate L was contacted with a 1 molar Fe(NO.sub.3).sub.3 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate O. 
Silicate P 
Silicate L was contacted with a 6 molar Ca(NO.sub.3).sub.2 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate P. 
Silicate Q 
A crystalline silicate was prepared from a mixture of Al(NO.sub.3).sub.3, 
Fe(NO.sub.3).sub.3, SiO.sub.2, NaOH and [(C.sub.3 H.sub.7).sub.4 N]OH in 
water with a molar composition as follows: 
EQU 25SiO.sub.2.5/64Fe.sub.2 O.sub.3.3/64Al.sub.2 O.sub.3.3.0[(C.sub.3 
H.sub.7).sub.4 N]OH.Na.sub.2 O.450H.sub.2 O. 
The mixture was heated to 150.degree. C. in an autoclave under autogenous 
pressure, at which temperature it was maintained for 24 hours after which 
it was filtered and washed until the pH was 8. After drying the resulting 
crystals were calcined for eight hours at 500.degree. C. This crystalline 
silicate will be referred to as Silicate Q. 
(a) Silicate Q was thermally stable to above 600.degree. C. 
(b) It had an X-ray powder diffraction pattern showing the reflections 
given in Table B above. 
(c) In the H-form its adsorption of n-C.sub.6 was 1.27 mmol/g and that of 
2,2 DMB was 0.63 mmol/g. 
(d) Its chemical formula was 
EQU 0.0044Na.sub.2 O.0.0044(0.64Fe.sub.2 O.sub.3.0.34Al.sub.2 
O.sub.3).SiO.sub.2. 
Silicate R 
Silicate Q was contacted with a 1 molar La(NO.sub.3).sub.3 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate R. 
Silicate S 
Silicate Q was contacted with a 4 molar La(NO.sub.3).sub.3 solution at 
100.degree. C. for 10 hours (2.times.5 hrs). The crystals were filtered 
and washed and then dried at 400.degree. C. for 15 hours. This modified 
crystalline silicate will be referred to as Silicate S.

EXAMPLE I 
Samples of 100 g of each of Silicates A to H inclusive, J and L to O 
inclusive were brought into contact with a nitrogen stream at 80.degree. 
C. containing para-xylene and ethyl benzene in equal molar proportions, 
the C.sub.8 aromatics having a combined partial pressure of 45 m bar. 
After equilibrium was reached the samples were weighed, and the ratio of 
para-xylene to ethyl benzene established. 
The following results were obtained. 
______________________________________ 
Silicate 
##STR1## Para-xylene and ethyl benzene absorbed (% 
Ratio PX/EB 
______________________________________ 
A -- 8.1 0.8 
B -- 9.5 1.7 
C 118 8.3 1.3 
D 118 10.8 3.4 
E -- 8.9 1.2 
F 7 9.5 1.0 
G 30 9.5 1.3 
H 118 10.5 2.4 
J 51 10.0 1.9 
L -- 9.5 1.5 
M 24 9.5 1.4 
N 76 10.1 1.9 
O 47 10.1 2.0 
______________________________________ 
Note: 
"Ratio PX/EB" is the ratio of paraxylene adsorbed to ethyl benzene 
adsorbed. In the case where the composition of the gas stream remains 
constant and the quantities of paraxylene and ethyl benzene in the stream 
are equal the ratio PX/EB is equivalent to the selectivity S.sub.PX/EB fo 
paraxylene over ethyl benzene for the crystalline silicate. 
Commentary 
Comparing Silicate C to Silicate A it will be seen, that the modification 
of Silicate C in accordance with the invention has improved the ratio 
PX/EB substantially. Similarly, taking Silicate D a similar improvement 
over Silicate B is demonstrated. Where the product (e/R)m is smaller the 
effect is less marked, as with Silicate J, although still useful. 
Taking Silicate E it is seen that the modifications resulting in Silicates 
F and G do not lead to any marked improvement-the product (e/R)m is too 
small, and in the case of Silicate F, Rb is monovalent. Silicate H in 
accordance with the invention, however, shows a significant improvement. 
Starting from Silicate L, Silicates N and O, which are in accordance with 
the invention show a significant improvement, whereas Silicate 
M[(e/R)m=24] does not. 
EXAMPLE II 
Samples of 100 g of each of Silicates A, B, D, I, J, L, and N to S 
inclusive were brought separately into contact with a solution of 
2,2,4-trimethylpentane at 25.degree. C. containing 4% w of para-xylene and 
ethyl benzene in a ratio of para-xylene to ethyl benzene of 1. After 
equilibrium was reached the solution was analyzed and the ratio of 
para-xylene to ethyl benzene adsorbed by the samples thus established. The 
following results were obtained. 
______________________________________ 
Para-xylene 
Liquid- and ethyl 
Silicate 
##STR2## 
solids ratio 
benzene adsorbed (% w) 
Ratio PX/EB 
S.sub.PX/EB 
______________________________________ 
A -- 10.0 10.3 2.7 3.7 
B -- 10.1 10.4 3.7 5.7 
D 118 13.0 11.8 5.6 9.0 
I 81 11.8 10.6 5.2 7.8 
J 51 10.2 10.9 4.2 6.6 
L -- 10.2 10.3 3.5 5.1 
N 76 10.3 10.7 4.2 6.3 
O 47 10.5 10.6 4.0 6.3 
P 121 9.8 11.2 4.6 7.3 
Q -- 10.0 9.3 2.7 3.5 
R 30 10.0 9.4 2.7 3.6 
S 118 10.2 11.0 5.1 7.0 
______________________________________ 
Note: 
"Ratio PX/EB" is the ratio of paraxylene adsorbed to ethyl benzene 
adsorbed. "S.sub.PX/EB " is the selectivity for paraxylene over ethyl 
benzene taking account of the reduced proportion of paraxylene in the 
solution under equilibrium conditions, i.e.; 
##STR3## 
- 
Commentary 
A substantial improvement is found in the selectivity S.sub.PX/EB for 
Silicate D, I, and J over Silicates A and B from which they were derived. 
Similarly, Silicates N, O, and P showed an improvement over Silicate L. 
Moreover, Silicate R [(e/R)m=30] showed hardly any increase over Silicate 
Q whereas Silicate S [(e/R)m=118] showed a marked increase. It should be 
noted that Silicates D, I, J, N, O, P, and S are in accordance with the 
invention.