Production process for refined hydrogen iodide

A process for producing refined hydrogen iodide having organic components of 0.2 ppm by volume or less and water of 0.1 ppm by volume or less by contacting crude hydrogen iodide with a zeolite is disclosed. Crude hydrogen iodide is obtained by reducing iodine with a hydrogenated naphthalene, wherein all of the iodine is dissolved in advance in a portion of the hydrogenated naphthalene to prepare an iodine solution, and the reaction is carried out while adding continuously or intermittently the iodine solution to the balance of the hydrogenated naphthalene. The same operation may be repeated in succession using unreacted hydrogenated naphthalene and fresh iodide. The zeolite is contacted in advance with crude hydrogen iodide, the amount of which is at least 1/3 (weight ratio) relative to the amount of the zeolite, to convert impurities of sulfur components contained in the zeolite to hydrogen sulfide, thereby removing the sulfur components. Further, an activated carbon may be combined with the zeolite at the rear stage thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a production process for hydrogen iodide, 
more specifically to a process in which iodine of a raw material is 
efficiently reacted to obtain crude hydrogen iodide at a good yield, and 
then the crude hydrogen iodide is refined to produce high purity hydrogen 
iodide. 
Hydrogen iodide is used as a synthetic raw material for various iodides, 
medical intermediates or a reducing agent. Further, in recent years, it is 
specially spotlighted as an etching agent in a semiconductor field and is 
an industrially useful substance. Hydrogen halides are widely utilized as 
the etching agent. Among them, hydrogen iodide is paid attention in terms 
of the high etching performance thereof. 
The process of the present invention is used, for example, for obtaining 
hydrogen iodide used in a semiconductor production field. 
2. Description of the Related Art 
In recent years, it is particularly recognized in a semiconductor field 
that hydrogen iodide is a substance having a very good etching 
performance. Hydrogen iodide to be used in such field is required to have 
a purity as high as 99.99 to 99.999 and to have no possibility of 
containing phosphorus and sulfur unlike reagents for ordinary chemical 
reactions. 
Conventional making methods of hydrogen iodide are disclosed in Mellors 
Comprehensive Treatise on Inorganic and Theoretical Chemistry, Supplement 
2, Part 1 edited by J. W. Mellor, p. 170 (1960), published by Longmans 
Co., Ltd. Among them is a method in which phosphorus or a phosphorus 
compound is used as a reducing agent to convert iodine to hydrogen iodide. 
In this method, there is a possibility that the phosphorus compound would 
be mixed in the product. In another method, iodine is reduced with 
hydrogen sulfide in the presence of water. This method has a defect in 
that a lot of water is mixed in the product because it uses an aqueous 
reaction system. 
In addition to the above methods, available are a method of reducing iodine 
in phosphinic acid or sulfur dioxide-water system (U.S. Pat. No. 
4,089,940) and a method in which iodine is hydrogenated in the presence of 
rhodium or iridium used as a catalyst (Japanese Patent Publication No. 
54-43480). However, every method employs an aqueous reaction system, and 
therefore a lot of water is mixed in a hydrogen iodide gas. In a 
non-aqueous reaction system in which a platinum catalyst is used to 
hydrogenate catalytically iodine (E. R. Caley, M. G. Burforal, Inorganic 
Synthesis Vol. 1, p. 159 (1939), and the preceding publication edited by 
J. W. Mellor), the reaction temperature is as high as 300.degree. to 
500.degree. C. In addition thereto, this method has a defect in that the 
reaction is slow and the conversion rate to hydrogen iodide and the yield 
thereof are low, and therefore it is not so suitable as an industrial 
production process for hydrogen iodide. 
On the other hand, a process for industrially producing high purity 
hydrogen iodide includes a process in which iodine is reduced with organic 
reducing agents. 
A literature in which a process for producing hydrogen iodide with organic 
reducing agents such as tetrahydronaphthalene is disclosed includes, for 
example, C. J. Hoffman, Inorganic Syntheses Collective Vol. VII, p. 180 
(1963). It is described that in this process iodine is added 1/37 times as 
less equivalent as tetrahydronaphthalene at 200.degree. C. or higher to 
react with tetrahydronaphthalene, whereby hydrogen iodide can be prepared 
at a yield of 90%. 
However, according to research made by the present inventors, this process 
involves some problems. That is, since a lot of iodine vapor besides 
hydrogen iodide is generated from the liquid during the reaction, iodine 
of the raw material is not only liable to be lost but also iodine is mixed 
in the resulting hydrogen iodide to reduce the purity of the product, and 
in view of the industrial production facilities, the large-scaled treating 
facilities for preventing a harmful iodine vapor from diffusing to the 
outside of the system are required to be installed. 
Further, in this reaction vapor is generated and it is very difficult to 
control the amount of a hydrogen iodide gas generating from the reaction 
liquid, so that there is a possible risk that the reaction runs away to 
generate a lot of hydrogen iodide for short time. 
Further, since overexcessive tetrahydronaphthalene is used (37 times as 
much equivalent as iodine), a waste liquid containing a lot of unreacted 
tetrahydronaphthalene remains after the reaction. That is, only a part of 
a lot of tetrahydronaphthalene is consumed in this process, and a volume 
efficiency is very poor and uneconomical. Further, since a waste liquid 
containing unreacted tetrahydronaphthalene is inevitably required to be 
treated, it is difficult to employ the process as it is for producing 
hydrogen iodide industrially. 
Even if these problems would be solved, resulting hydrogen iodide is 
usually crude hydrogen iodide containing at least about 0.5% of impurities 
such as water and organic components and is inadequate for using in a 
semiconductor field. Accordingly, it has to be refined furthermore. 
However, techniques for removing impurities contained in hydrogen iodide to 
obtain hydrogen iodide having a high purity have not been known at all up 
to now. 
With respect to a method of refining gas other than hydrogen iodide, for 
example, only the following methods are disclosed. 
That is, there are disclosed in Japanese Patent Laid-Open No. 61-209902, a 
method in which nitrogen contained in hydrogen is removed with a mordenite 
type zeolite subjected to calcium ion treatment; in U.S. Pat. No. 
4,557,921, a refining method of silicon tetrafluoride, in which a 
mordenite type zeolite is used to remove impurities such as sulfur dioxide 
and hydrogen halides; in Japanese Patent Publication No. 3-29003, a 
refining method of silicon hydride, in which a 5A type zeolite is used to 
remove impurities such as phosphines; in U.S. Pat. No. 5,051,117, a method 
of removing halosilanes contained in hydrogen with a zeolite; in Japanese 
Patent Laid-Open No. 4-330916, a method in which a synthetic zeolite 
subjected to hydrophobicity treatment is used to remove organic components 
contained in air; and in Japanese Patent Laid-Open No. 6-32601, a refining 
method of hydrogen bromide, in which a zeolite is used to remove 
impurities such as carbon dioxide, hydrogen chloride, oxygen, and 
nitrogen. 
SUMMARY OF THE INVENTION 
The present invention provides not only a process free of the defects in 
the conventional processes described above in producing hydrogen iodide, 
but also a process in which impurities contained in hydrogen iodide are 
removed to render the hydrogen iodide useful in a semiconductor field and 
which is industrially suitable for obtaining high purity hydrogen iodide. 
Intensive investigations made by the present inventors in order to achieve 
the subjects described above have resulted in finding that it is very 
effective to carry out the reaction while adding continuously or 
intermittently iodine to tetrahydronaphthalene instead of reacting with 
heating a mixed liquid or a suspended liquid of iodine and 
tetrahydronaphthalene as is the case with the conventional processes 
described above, and further that the reaction goes on almost in the same 
way even when not only tetrahydronaphthalene but also other hydrogenated 
naphthalene are used. 
In addition, it has been found that when iodine is added again to the 
reaction liquid after the preceding reaction, hydrogen iodide 
corresponding to the amount of iodine added is produced. 
Further, it has been found that almost all of the tetrahydronaphthalene 
initially charged can be effectively used for producing hydrogen iodide 
without reducing the purity and the yield of resulting hydrogen iodide 
even when the operation described above is repeated many times in the same 
manner. 
Also, it has been found that when thus produced hydrogen iodide containing 
impurities (water and organic components such as tetrahydronaphthalene and 
naphthalene as main impurities) is contacted with a zeolite in a gaseous 
phase, the impurities are adsorbed very well on the zeolite. 
Further, it has been found that since contacting a zeolite with hydrogen 
iodide reduces sulfur components contained in the zeolite to hydrogen 
sulfide, which is mixed in hydrogen iodide as an impurity, treating the 
zeolite in advance with hydrogen iodide eliminates the sulfur. 
It has been found that the integration of a series of these operations 
enables to provide high purity hydrogen iodide with ease and at high 
efficiency. Thus, the present invention has come to be completed. 
That is, the present invention is characterized in that crude hydrogen 
iodide obtained by reducing iodine with a hydrogenated naphthalene is 
contacted with a zeolite in a gaseous phase to produce high purity 
hydrogen iodide. 
When this process is used, hydrogen iodide of a required amount can readily 
be obtained at a required time by storing the liquid after the reaction. 
This production process does not discharge a lot of a waste liquid and is 
notably advantageous in terms of an economy of raw materials. Accordingly, 
it is reasonable to say that this process is an industrially very 
preferable production process. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First of all, a production process of crude hydrogen iodide will be 
explained. 
In general, when iodine is added in one lot to a hydrogenated naphthalene 
such as tetrahydronaphthalene in producing hydrogen iodide by reducing 
iodine, a vapor of iodine is generated from the reaction liquid in large 
quantities while a hydrogen iodide gas is violently generated from the 
reaction liquid. This phenomenon takes place almost similarly when a 
hydrogenated naphthalene is added to iodine or when the hydrogenated 
naphthalene is added to a solution or suspended liquid containing a lot of 
iodine. 
However, in the case where iodine or a iodine solution in a hydrogenated 
naphthalene is continuously or intermittently added to a hydrogenated 
naphthalene and the reaction is initiated almost at the same time as this 
addition as is the case with the process of the present invention 
described below, iodine added is very rapidly reduced to produce hydrogen 
iodide, and therefore iodine vapor can be effectively prevented from being 
generated. Accordingly, if only a prescribed amount of iodine is added to 
react with the hydrogenated naphthalene, hydrogen iodide having a high 
purity can be produced at a good yield. 
The hydrogenated naphthalene used in the process of the present invention 
is a substance having a structure in which 2 or 4 hydrogen atoms are added 
to naphthalene and, to be concrete, includes tetrahydronaphthalene and 
dihydronaphthalene. They may be used singly or in combination of two 
kinds. Here, tetrahydronaphthalene is a substance called tetralin or 
1,2,3,4-tetrahydronaphthalene. Dihydronaphthalene includes the substances 
in which hydrogens are added to a 1- and 2-positions and 1- and 
4-positions. Each of the above compounds may be used in the present 
invention and provides sufficiently good results. 
In the process of the present invention, among the substances described 
above, tetrahydronaphthalene is more preferably used and gives the very 
notable effects that it is not only easy to control a progress of the 
reaction by temperature but also a loss of iodine can be greatly reduced 
obtaining high purity hydrogen iodide at a good yield. 
An amount of the hydrogenated naphthalene used in the process of the 
present invention will be an equivalent time or more relative to iodine 
used for the reaction. The amount of less than an equivalent time is not 
preferred since unreacted iodine is liable to be present in the 
hydrogenated naphthalene in the course of the reaction and iodine vapor as 
well as hydrogen iodide is possibly generated. When the hydrogenated 
naphthalene is used in relatively large quantity, no problems are involved 
in achieving the objects. 
In the production process of the present invention, the reaction is carried 
out while adding iodine to the hydrogenated naphthalene. The reaction 
pressure can suitably be selected without being specifically restricted. 
Usually, ordinary pressures are used in many cases because of an easier 
operation. The reaction temperature falls in a range of 120.degree. C. to 
the boiling point of the reaction liquid (for example, about 210.degree. 
C. when tetrahydronaphthalene is used), preferably 150.degree. C. to the 
boiling point of the reaction liquid. In this case, a temperature of less 
than 120.degree. C. retards a progress in the reaction, and when the 
reaction is carried out at a temperature over a boiling point of the 
reaction liquid, it is difficult to produce hydrogen iodide under ordinary 
pressures. In addition, hydrogen iodide obtained is liable to be 
contaminated with hydrogenated naphthalene. At a temperature near the 
boiling point of the reaction liquid, the hydrogenated naphthalene 
vaporizes from the reaction liquid in addition to the generation of 
hydrogen iodide. These can be sufficiently separated by such well-known 
methods as passing resulting mixed gas through a cold trap. 
In the process of the present invention, iodine may be either continuously 
or intermittently added to the hydrogenated naphthalene. The adding rate 
thereof depends largely on the amount and the kind of the hydrogenated 
naphthalene used, a manner of addition operation, a reaction temperature, 
a production amount of hydrogen iodide and the shape of a reactor, and can 
not easily be determined. Usually, the objects of the present invention 
can be achieved if the rate is such that the color of a gaseous phase at 
the upper part of the reaction liquid does not assume a brown or purple 
color. 
Further, in adding iodine to the hydrogenated naphthalene, iodine may be 
added in a solid form such as powder, particle and flake, or it may be 
charged into the liquid in a gaseous phase. 
After finishing the addition of iodine, the reaction liquid is preferably 
left standing to ripen, whereby the reaction is completed. The time needed 
for this ripening depends on the temperature thereof and is not fixed. 
Usually, it is 10 minutes or more, preferably 1 hour or more. The degree 
of the ripening can easily be judged not only by the lapse of time but 
also by observing the reaction liquid. That is, the ripening can be 
regarded as being completed if a brown or purple color of the reaction 
liquid disappears and hydrogen iodine is no longer generated thereafter 
(Examples 1 to 6 and Comparative Examples 1 to 2). 
Next, in the process for producing crude hydrogen iodide according to the 
present invention, after dissolving all of iodine in advance in a part of 
the hydrogenated naphthalene to prepare an iodine solution, the reaction 
is carried out while adding the resulting solution to the balance of the 
hydrogenated naphthalene. 
In this process, the reaction can be carried out under tight sealing, and 
therefore air can be prevented from mixing and also iodine can be 
prevented from sticking to or clogging a feed pipe to the reactor. 
Accordingly, this process is preferred very much. The solution of iodine 
and the hydrogenated naphthalene is saturated with iodine (20 weight 
%/20.degree. C.) or has a lower concentration. 
In this case, a reaction pressure, a reaction temperature, a manner of 
addition of the solution of iodine and the hydrogenated naphthalene and 
adding rate is the same as for with adding the hydrogenated naphthalene to 
iodine. And ripening of the reaction liquid is carried out in the same 
manner. 
Further, in the production process of the present invention, a liquid 
remaining after the reaction described above is divided into two portions, 
and additional iodine is dissolved in one of these portions to prepare a 
new solution. Then the reaction is carried out while adding the solution 
to the other portion of the divided liquid and the same operation is 
repeated in succession. 
In this process, the liquid remaining after the preceding reaction is 
divided into two portions in a weight ratio falling in a range of (10 to 
40):(90 to 60), and the smaller portion of the divided liquids is 
maintained at temperatures of 120.degree. C. to a boiling point of the 
liquid (about 210.degree. C.), preferably 150.degree. C. to a boiling 
point of the liquid (about 210.degree. C.). The reaction is carried out 
while adding an iodine solution of about 20 to 40 weight % (saturated 
solution or lower concentration) prepared by dissolving iodine in the 
other larger portion to the small portion described above. In this case, 
if the preceding liquids were divided in a ratio out of the range 
described above, the amount of iodine capable of being dissolved decreases 
to deteriorate the productivity of hydrogen iodide, and besides, it 
becomes difficult to maintain the temperature during the reaction. 
In the process of the present invention, also when the liquid remaining 
after the reaction is repeatedly used to carry out the reaction many 
times, the yield of hydrogen iodide based on iodine added and the purity 
thereof are very rarely lowered, and almost all of the hydrogenated 
naphthalene initially charged can effectively be consumed for producing 
hydrogen iodide (Examples 7 to 8). 
Secondly, a refining process for crude hydrogen iodide will be explained. 
The kind of a zeolite capable of being used for the refining includes, for 
example, an A type and a mordenite type. They include various forms such 
as powder, sphere and pellet, and a zeolite of every form may be used. 
A zeolite includes those which are commercially available in the market as 
Molecular Sieves (trade name manufactured by U.S. Union Carbide Co., 
Ltd.), and to give the examples thereof, 3A, 4A and 5A of A types, and 
AW-300 of a mordenite type are commercialized. 
In the process of the present invention, a zeolite is required to be 
subjected to heat treatment at a temperature falling in a range of 
200.degree. to 400.degree. C. to activate it. In the heat treatment, it is 
more effective to carry out it under a reduced pressure. The zeolite after 
the heat treatment has to be prevented from contacting with air. Because 
after this treatment the contact of the zeolite with air causes the 
zeolite to absorb moisture and markedly damages an ability to adsorb 
impurities contained in hydrogen iodide. Usually, the zeolite after the 
heat treatment is handled in an inert gas such as nitrogen gas. 
In the refining process of the present invention, the zeolite described 
above is subjected to pretreatment, wherein the zeolite is contacted in 
advance with crude hydrogen iodide to convert impurities of sulfur 
components contained in the zeolite to hydrogen sulfide, thereby removing 
the sulfur components. 
The contact of the zeolite with crude hydrogen iodide allows sulfur 
components contained in the zeolite to be notably reduced by a strong 
reducing strength of hydrogen iodide particularly at high temperatures of 
50.degree. C. or higher to form hydrogen sulfide. The zeolite is 
preferably subjected to pretreatment, wherein the zeolite is heated to 
50.degree. to 500.degree. C., preferably 80.degree. to 200.degree. C. 
under a pressure of ordinary pressure to 20 atmospheric pressure, and 
crude hydrogen iodide is passed through it at a flow rate falling in a 
range of 300 to 1500 hr.sup.-1 in terms of a space velocity based on the 
mixed gas of dry nitrogen and crude hydrogen iodide (hereinafter 
abbreviated as SV) to remove sulfur components contained in the zeolite in 
a state of hydrogen sulfide. It is suitable that the flow amount of 
hydrogen iodide is 1/3 or more by weight, preferably 1/2 or more by weight 
relative to the amount of the zeolite charged. 
An amount less than 1/3 provides the possibility that the sulfur components 
contained in the zeolite remain without being sufficiently removed 
(Examples 9 to 12 and Comparative Example 3). 
The refining of hydrogen iodide in the process of the present invention is 
not restricted to a specific system. Usually, a tower or column packed 
with a zeolite is used, and crude hydrogen iodide is passed through it in 
a gaseous phase to carry out the refining. 
In the refining process of the present invention, crude hydrogen iodide is 
passed through the zeolite subjected to the pretreatment described above, 
so that impurities such as moisture and organic substances contained in 
crude hydrogen iodide can sufficiently be removed. 
In this process, a tower or a column packed with the zeolite is used. 
Operation is carried out under a pressure within a range of ordinary 
pressure to 20 atmospheric pressure, at a temperature of -30.degree. C. to 
100.degree. C., preferably -30.degree. C. to 50.degree. C. and at SV of 
300 to 1500.sup.-1 based on the mixed gas of dry nitrogen and crude 
hydrogen iodide. Temperatures and pressures outside the above range are 
not preferred, because an effect to adsorb impurities with the zeolite is 
reduced. 
The use of the present invention can reduce impurities, for example, 
moisture to 1 ppm or less by volume and organic substances to 0.5 ppm or 
less by volume. 
A zeolite to be used is preferably an A type zeolite having an average pore 
diameter of 3 to 5 angstrom, and the use thereof can reduce moisture 
contained in refined hydrogen iodide to 1 ppm or less by volume. More 
preferably, the A type zeolite having an average pore diameter of 4 
angstrom is used. The use thereof can reduce moisture contained in refined 
hydrogen iodide to 0.1 ppm or less by volume (Examples 14 to 17). 
It is sufficiently possible to reuse the zeolite used as an adsorbing agent 
by regenerating with well-known methods such as thermal swing, pressure 
swing, purge gas stripping and displacement after it is used to the break 
point. Generally thermal swing cycle is employed. 
Further, in the refining process of the present invention, organic 
substances can be removed more preferably by combining a zeolite with an 
activated carbon, thereby reducing the concentration of the organic 
substances contained in refined hydrogen iodide to 0.2 ppm or less. 
The contact of activated carbon with hydrogen iodide causes sulfur 
components contained in the activated carbon to be reduced by a strong 
reducing strength of hydrogen iodide to form hydrogen sulfide as in the 
case with zeolite. Accordingly, activated carbon is subjected to 
pretreatment which is effectuated by heating it at 50.degree. to 
500.degree. C., preferably 80.degree. to 200.degree. C. under ordinary 
pressure to 20 atmospheric pressure, and passing hydrogen iodide through 
it at SV of 300 to 1500 hr.sup.-1 based on the mixed gas of dry nitrogen 
and crude hydrogen iodide. The suitable flow amount of crude hydrogen 
iodide is 1/3 or more by weight, more preferably 1/2 or more by weight 
based on the amount of the activated carbon charged. The amount outside 
the above range provides the possibility that the sulfur components 
contained in the activated carbon remain without being sufficiently 
removed (Example 13). 
In the present invention, the operation is carried out in the conditions 
described above, whereby impurities such as moisture and organic 
substances contained in crude hydrogen iodide can sufficiently be removed, 
and a particularly notable effect to obtain hydrogen iodide having a high 
purity is given. 
Refined hydrogen iodide produced by the process of the present invention is 
useful as a dry etching agent in the field of electronic devices 
represented by semiconductors and liquid crystals.

EXAMPLES 
The present invention will be explained below in conjunction with examples 
and comparative examples. There will be described, "the production process 
of crude hydrogen iodide" in Examples 1 to 8 and Comparative Examples 1 
and 2, "pretreatment of a zeolite or activated carbon with crude hydrogen 
iodide" in Examples 9 to 13 and Comparative Example 3, and "refining 
process of crude hydrogen iodide" in Examples 14 to 18, respectively. 
Hereinafter, "%" is by weight, and "ppm" is by volume. The yield of 
hydrogen iodide is a value calculated based on the amount of iodine newly 
used in the formation reaction thereof. Determined were moisture with a 
dew-point hygrometer, organic components with a high-performance liquid 
chromatography (HPLC) and hydrogen sulfide with a gas detecting tube, 
respectively. 
Example 1 
A flask of 500 ml was charged with tetrahydronaphthalene of 100 g and 
heated to 210.degree. C. while stirring. Flaky solid iodine of 20.0 g was 
continuously added thereto over a period of one hour while maintaining the 
above temperature to react them. Gas generated as the reaction went on was 
solidified by passing through cold traps cooled to -30.degree. C. and 
-60.degree. C. or lower to obtain crude hydrogen iodide. After finishing 
the addition of iodine, the reaction liquid was left standing at 
210.degree. C. for 15 minutes to ripen. The color of the reaction liquid 
which had been purple disappeared during that time, and it was confirmed 
that almost all amount of iodine had been consumed. Crude hydrogen iodide 
of 19.7 g was obtained. The purity thereof was 99.5% or more, and the 
yield thereof was 97.8%. The results thereof are summarized in Table 1. 
Example 2 
A flask of 100 ml was charged with flaky solid iodine of 20.0 g, and 
gaseous iodide was generated by heating at 120.degree. C. A flask of 500 
ml was charged with tetrahydronaphthalene of 100 g and heated to 
200.degree. C. while stirring. The gaseous iodine was continuously 
introduced thereinto over a period of 2 hours while maintaining the above 
temperature to react them. Gas generated as the reaction went on was 
solidified by passing through the cold traps cooled to -30.degree. C. and 
-60.degree. C. or lower to obtain crude hydrogen iodide. After finishing 
the introduction of iodine, the reaction liquid was left standing at 
200.degree. C. for 15 minutes to ripen. Crude hydrogen iodide of 19.8 g 
was obtained. The purity thereof was 99.5% or more, and the yield thereof 
was 98.0%. The results thereof are summarized in Table 1. 
Example 3 
The same operation that carried out in Example 1 was repeated to obtain 
crude hydrogen iodide, except that the reaction temperature and the 
ripening temperature of the reaction liquid were changed to 200.degree. 
C., respectively. The amount of the crude hydrogen iodide was 19.8 g. The 
purity thereof was 99.5% or more, and the yield thereof was 98.0%. The 
results thereof are summarized in Table 1. 
Example 4 
Flaky solid iodine of 20.0 g was dissolved in tetrahydronaphthalene of 100 
g charged in a flask of 500 ml at 40.degree. C. to prepare a 
tetrahydronaphthalene solution of iodine. A flask of 500 ml was charged 
with tetrahydronaphthalene of 100 g and heated to 200.degree. C. while 
stirring. The iodine solution prepared above was continuously added 
thereto over a period of 2 hours while maintaining the above temperature 
to react them. Gas generated as the reaction went on was solidified by 
passing through the cold traps cooled to -30.degree. C. and -60.degree. C. 
or lower to obtain crude hydrogen iodide. After finishing the addition of 
the iodine solution, the reaction liquid was left standing at 200.degree. 
C. for 15 minutes to ripen. Crude hydrogen iodide of 19.8 g was obtained. 
The purity thereof was 99.5% or more, and the yield thereof was 98.0%. The 
results thereof are summarized in Table 1. 
Example 5 
The same operation that was carried out in Example 1 was repeated to obtain 
crude hydrogen iodide, except that solid iodine of 20.0 g was divided into 
five portions of each 4.0 g and added intermittently five times. The 
amount of the crude hydrogen iodide was 19.6 g. The purity thereof was 
99.5% or more, and the yield thereof was 97.2%. The results thereof are 
summarized in Table 1. 
TABLE 1 
______________________________________ 
Example 
1 2 3 4 5 
______________________________________ 
Tetrahydro- (g) 100 100 100 200 100 
naphthalene (mole) 0.76 0.76 0.76 1.52 0.76 
Iodine (g) 20 20 20 20 4 .times. 5 
(mole) 0.079 0.079 
0.079 
0.079 0.079 
Phase Solid Gas Solid 
Solution 
Solid 
Addition manner Cont. Cont. 
Cont. 
Cont. Int.* 
Reaction temperature 
(.degree.C.) 
210 200 200 200 210 
Reaction time 
(hrs) 1 2 1 2 1 
Hydrogen iodide 
Purity (%) 99.5 % or more 
Yield (%) 97.8 98.0 98.0 98.0 97.2 
______________________________________ 
Cont.: Continuously, 
Int.: Intermittently 
*: 5 times 
Example 6 
The same operation that was carried out in Example 1 was repeated to obtain 
crude hydrogen iodide, except that tetrahydronaphthalene was replaced with 
dihydronaphthalene. The amount of the crude hydrogen iodide was 19.7 g. 
The purity thereof was 99.5% or more, and the yield thereof was 97.7%. The 
results thereof are summarized in Table 2. 
Comparative Example 1 
Flaky solid iodine of 20.0 g was dissolved in tetrahydronaphthalene of 100 
g charged in a flask of 500 ml at 40.degree. C. to prepare a 
tetrahydronaphthalene solution of iodine. This iodine solution was heated 
up to 210.degree. C. to react them for one hour. Resulting gas was 
solidified by passing through the cold traps cooled at -30.degree. C. and 
-60.degree. C. or lower to obtain crude hydrogen iodide. Gas generated 
during this reaction was purple, and iodine was observed to be accompanied 
therewith. Further, iodine sticked to the inside of a gas discharging 
tube, and clogging was apt to take place. The amount of resulting crude 
hydrogen iodide was 14.2 g. The purity thereof was 82.5% or more, and the 
yield was 70.3%. The results thereof are summarized in Table 2. 
Comparative Example 2 
The same operation that was carried out in Example 4 was repeated to obtain 
crude hydrogen iodide, except that instead of adding the iodine solution 
of 40.degree. C. to tetrahydronaphthalene of 200.degree. C., the latter 
kept at room temperature was added intermittently by 1/10 portions to the 
former ten times while maintaining 160.degree.-200.degree. C. in contrast 
with the above manner. During the reaction iodine was observed to be 
accompanied therewith. Further, iodine sticked to the inside of a gas 
discharging tube and was apt to clog the tube. The amount of resulting 
crude hydrogen iodide was 16.0 g. The purity thereof was 85.5% or more, 
and the yield was 79.4%. The results thereof are summarized in Table 2. 
Example 7 
Flaky solid iodine of 40 g was dissolved in tetrahydronaphthalene of 160 g 
charged in a flask of 500 ml at 40.degree. C. to prepare a 
tetrahydronaphthalene solution of iodine. A flask of 500 ml was charged 
with tetrahydronaphthalene of 40 g and heated to 200.degree. C. while 
stirring. The iodine solution prepared above was continuously added 
thereto over a period of 2 hours while maintaining the above temperature 
to react them. Crude hydrogen iodide gas generated as the reaction went on 
was introduced into a 10% sodium hydroxide aqueous solution of 1 liter to 
absorb the whole amount thereof. A weight change in this aqueous solution 
was measured with the lapse of time, and the end point of the first 
reaction was set at the point where the change thereof was not observed. 
The yield of the crude hydrogen iodide was 94.6%, and the purity thereof 
was 99.5% or more. The concentrations of organic components and water 
contained therein were 200 ppm and 30 ppm, respectively. The 
concentrations of tetrahydronaphthalene and naphthalene contained in the 
liquid remaining after the reaction were 94.1% and 5.2%, respectively. The 
results thereof are summarized in Table 2 and Table 3. 
Next, the second reaction was carried out, wherein the liquid remaining 
after the first reaction described above was divided into two portions by 
1:4 (weight ratio); the smaller portion was maintained at 200.degree. C.; 
and a solution prepared by adding new iodine of 40 g to the liquid of the 
other large portion was continuously added the small portion over a period 
of 2 hours to react them. Resulting hydrogen iodide gas was treated in the 
same manner as in the first reaction to determine the yield and measure 
the concentration of a liquid remaining after this second reaction. The 
results thereof are summarized in Table 3. 
Further, the liquid remaining after the reactions was still used to repeat 
the operation in the same manner as described above, and the third to 
eighth reactions were carried out. The yields of crude hydrogen iodide 
thus obtained and the concentrations of the liquids remaining after the 
reactions are summarized in Table 3. 
Example 8 
The same operation that was carried out in Example 7 was repeated to carry 
out the first to eighth reactions, except that the reaction temperature 
was changed from 200.degree. C. to 170.degree. C. (Table 2). The yields of 
resulting crude hydrogen iodide and the concentrations of the liquids 
remaining after the reactions are summarized in Table 3. 
TABLE 2 
______________________________________ 
Comparative 
Example example 
6 7 8 1 2 
______________________________________ 
Tetrahydro- 
(g) -- 200 200 100 200 
naphthalene 
(mole) -- 1.52 1.52 0.76 1.52 
Dihydro- (g) 100 -- -- -- -- 
naphthalene 
(mole) 0.77 -- -- -- -- 
Iodine (g) 20 40 40 20 20 
(mole) 0.079 0.16 0.16 0.079 0.079 
Phase Solid Solution 
Solution 
Solution 
Solution 
Addition manner Cont. Cont. Cont. One lot 
Int.* 
Reaction (.degree.C.) 
210 200 170 210 160.about. 
temperature 200 
Reaction time 
(hrs) 1 2 2 1 2 
Hydrogen iodide 
Purity (%) 
99.5 % or more 82.5 85.5 
Yield (%) 97.7 94.6 97.5 70.3 79.4 
______________________________________ 
Cont.: Continuously, 
Int: Intermittently 
*10 times 
TABLE 3 
______________________________________ 
Liquid concentration after reaction (%) 
Yield of Tetrahydro- 
Reaction 
HI (%) naphthalene 
Naphthalene 
Total 
times 7 8 7 8 7 8 7 8 
______________________________________ 
1 94.6 97.5 94.1 94.3 5.2 4.8 99.3 99.1 
2 95.5 97.2 91.4 89.1 8.5 9.6 99.9 98.7 
3 96.9 98.0 86.1 83.8 13.5 14.3 99.6 98.1 
4 97.5 98.0 78.9 78.5 20.3 18.6 99.2 97.1 
5 96.5 97.9 73.4 72.6 25.4 22.2 98.8 94.8 
6 96.6 97.6 68.6 67.2 30.7 26.2 99.3 93.4 
7 97.4 97.4 63.2 56.9 35.6 33.9 98.8 90.8 
8 96.6 96.3 55.0 52.3 38.8 37.4 93.8 89.7 
______________________________________ 
Example 9 
The pretreatment of a zeolite was carried out in the following manner. 
Used were crude hydrogen iodide which had been obtained in the first 
reaction of Example 7 (purity: 99.5% or more, organic components: 200 ppm, 
and moisture: 30 ppm) and zeolite which had been obtained by drying 
Molecular Sieves 4A (trade name, manufactured by Union Showa Co., Ltd.). 
Equipped in series were a glass-made column (inner diameter: 25 mm) filled 
with the zeolite of 20 g and an absorbing bottle charged with 
demineralized water of 400 ml. 
First, crude hydrogen iodide of 10 g (crude hydrogen iodide/zeolite: 1/2 
weight ratio) was passed through this column at a temperature of 
100.degree. C. and SV of 300 hr.sup.-1. Then, gas dissolved in the aqueous 
solution contained in the absorbing bottle was expelled by bubbling dry 
nitrogen to collect the gas in a gas sampling bag (1 liter). The 
concentration of hydrogen sulfide in the resulting mixed gas was 120 ppm 
based on crude hydrogen iodide. 
Next, crude hydrogen iodide of 10 g was again passed through the column 
through which crude hydrogen iodide was once passed as described above at 
room temperature and SV of 300 hr.sup.-1. Then gas dissolved in the 
aqueous solution contained in the absorbing bottle was expelled by 
bubbling dry nitrogen to collect the mixed gas. The concentration of 
hydrogen sulfide in the gas was 1 ppm or less based on crude hydrogen 
iodide. 
The zeolite treated by crude hydrogen iodide as described above is used in 
Example 14 and Example 18, respectively. 
Examples 10 to 13 
The same operation as carried out in Example 9 was repeated to collect two 
kinds of mixed gas, except that the kind of the zeolite was changed to 
Molecular Sieves 3A (trade name, manufactured by Union Showa Co., Ltd.) 
(Example 10) and Molecular Sieves 5A (ditto) (Example 11), or AW-300 
(ditto) (Example 12), or the zeolite was changed to an activated carbon 
(trade name: 4GS-S, manufactured by Tsurumi Coal Co., Ltd.) (Example 13). 
The concentrations of hydrogen sulfide contained in these mixed gases were 
130 ppm and 1 ppm or less in Example 10, 120 ppm and 1 ppm or less in 
Example 11, 150 ppm and 1 ppm or less in Example 12, and 250 ppm and 1 ppm 
or less in Example 13, respectively, based on crude hydrogen iodide. 
Three kinds of the zeolite and one kind of the activated carbon each 
treated in the foregoing manners are used in Examples 15 to 18, 
respectively. 
Comparative Example 3 
The same operation as carried out in Example 9 was repeated to collect two 
kinds of mixed gas, except that the amount of crude hydrogen iodide was 
changed to 5 g, that is, crude hydrogen iodide/zeolite=1/4 (weight ratio). 
The concentrations of hydrogen sulfide contained in these mixed gases were 
120 ppm and 15 ppm, respectively, based on crude hydrogen iodide. 
Examples 14 to 17 
Used were crude hydrogen iodide which had been obtained in the first 
reaction of Example 7 (purity: 99.5% or more, organic components: 200 ppm, 
and moisture: 30 ppm) and the zeolite which had been treated with crude 
hydrogen iodide in Examples 9 to 12. Equipped in series were a glass-made 
column (inner diameter: 25 mm) filled with the zeolite of 50 g and an 
absorbing bottle charged with demineralized water of 400 ml. 
Crude hydrogen iodide of 20 g (crude hydrogen iodide/zeolite: 2/5 weight 
ratio) accompanied by dry nitrogen was passed through this column at a 
temperature of 30.degree. C., ordinary pressure, and SV of 600 hr.sup.-1. 
The concentrations of impurities (organic components and moisture) based 
on crude hydrogen iodide were as follows at the column exit during that 
time. That is, the organic components were 0.5 ppm or less and the 
moisture was 0.1 ppm or less in Example 14; and the organic components 
were 0.5 ppm or less and the moisture was 1 ppm or less in Examples 15 to 
17. Hydrogen sulfide was not detected in every case. 
Example 18 
Used were crude hydrogen iodide which had been obtained in the first 
reaction of Example 7 (purity: 99.5% or more, organic components: 200 ppm, 
and moisture: 30 ppm), the zeolite which had been treated with crude 
hydrogen iodide in Example 9, and the activated carbon which had been 
treated with crude hydrogen iodide in Example 13. Equipped in series were 
a glass-made column (inner diameter: 25 mm) of the first stage filled with 
the zeolite of 50 g, a glass-made column (inner diameter: 25 mm) of the 
second stage filled with the activated carbon of 10 g, and an absorbing 
bottle charged with demineralized water of 400 ml. 
Crude hydrogen iodide of 20 g (crude hydrogen iodide/zeolite: 2/5 weight 
ratio, and crude hydrogen iodide/activated carbon: 1/5 weight ratio) 
accompanied by dry nitrogen was passed through from the column inlet of 
the first stage at a temperature of 30.degree. C., ordinary pressure, and 
SV of 600 hr.sup.-1. The concentrations of impurities were 0.2 ppm or less 
for the organic components and 0.1 ppm or less for the moisture based on 
crude hydrogen iodide, at the column exit of the second stage during the 
above operation.