Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By addition of extraneous agent – e.g. – solvent – etc.
Reexamination Certificate
2001-10-15
2003-12-16
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By addition of extraneous agent, e.g., solvent, etc.
C585S808000, C585S807000
Reexamination Certificate
active
06664433
ABSTRACT:
FIELD OF TECHNOLOGY
This invention relates to a process for purifying aromatic hydrocarbons containing impurities such as aromatic heterocyclic compounds to obtain purified aromatic hydrocarbons, for example, high-purity naphthalene, and, more particularly, to a process for preparing high-purity naphthalene with a less offensive odor and good flavoring quality.
BACKGROUND TECHNOLOGY
Aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, naphthalene, methylnaphthalene, anthracene, acenaphthene, and phenanthrene are obtained from coal tar- or petroleum-derived raw materials. As these raw materials contain a variety of compounds, they go through a step for separation such as extraction, distillation and crystallization before they are made into final products.
For example, naphthalene occurs relatively abundantly in the middle fraction (boiling approximately in the range 200-250° C.) of petroleum- and coal-derived oil and it is recovered from this fraction by distillation and the like. Typically, naphthalene is prepared from a coal source as follows: coal tar is distilled to take out the middle fraction, acidic and basic components such as phenol and quinoline are extracted, and the remainder is distilled further or crystallized to recover naphthalene. The product obtained in this manner is crude naphthalene with a purity of 95% or so.
Crude naphthalene is generally purified by distillation or crystallization and, in the case of the latter process, recrystallization or continuous crystallization is adopted (JP58-46322 (1983)A1). A process based on a combination of azeotropic distillation and crystallization is proposed in JP03-2128 (1991)B2. Naphthalene purified by the aforementioned processes has a purity of nearly 100% and is used as an insecticide; even in a case such as this, the product is desirably as little colored and odorous as possible. On the other hand, where naphthalene is used as a raw material in the synthesis of pharmaceuticals, it desirably contains as little sulfur compounds impurities as possible because sulfur compounds act as catalyst poison. The aforementioned middle oil fraction, however, is known to contain a large number of impurities boiling close to one another and it is extremely difficult to remove those impurities completely.
Commercially available aromatic hydrocarbons other than naphthalene are also known to contain impurities which boil at points near those of the aromatic hydrocarbons in question. Typical impurities are sulfur-containing aromatic heterocyclic compounds such as thiophene and benzothiophene and nitrogen-containing heterocyclic compounds such as pyridine, quinoline and isoquinoline. When such other aromatic hydrocarbons are used as chemical raw materials, the impurities contained therein often act as catalyst poisons and their maximal removal is desirable. The impurities are also known to be emitters of an offensive odor.
For this reason, a variety of processes for purification by hydrogenation such as hydrodesulfurization have been proposed and adopted. However, such a process requires a high-pressure reactor or incurs a high processing cost.
The specification of JP04-327543 (1992)A1 points out the problems associated with the conventional desulfurization processes and proposes a process for purifying aromatic hydrocarbons by desulfurization, feasible in a relatively simple apparatus at a high efficiency, which comprises adding olefins to an aromatic hydrocarbon oil, effecting polymerization in the presence of an acid catalyst, and removing the sulfur-containing polymerization products by distillation. This process faces a problem in the treatment of polymerization products.
There often appears a demand for a high-purity aromatic hydrocarbon with a purity of 99.5 wt % or more, preferably 99.9 wt % or more. For example, naphthalene is used as an insecticide; the so-called naphthalene odor is shunned in this use and a perfume is often added for flavoring. In the case of flavoring, naphthalene is required to be free of an offensive odor and have an exceptionally low content of odorous impurities.
Known processes for preparing high-purity naphthalene on a commercial scale include 1) a combination of distillation and crystallization, 2) a combination of hydrogenation, compression, clay treatment and distillation and 3) a combination of hydrogenation, distillation and crystallization. Process 1) cannot separate naphthalene from impurity benzothiophene because the two not only boil at points close to each other but also form a solid solution. Processes 2) and 3) yield tetralin as a by-product which is difficult to separate. Thus, none of the three processes gives a satisfactory product.
An object of this invention is to provide a process for purifying aromatic hydrocarbons which is feasible in a simple apparatus at a high efficiency. Another object of this invention is to provide highly purified aromatic hydrocarbons. A further object of this invention is to provide purified naphthalene which is free of an offensive odor and suitable for use as an insecticide after flavoring with a perfume. A still further object of this invention is to provide a highly efficient desulfurization process which employs a relatively simple apparatus and procedure.
DISCLOSURE OF THE INVENTION
The present inventors have conducted studies to solve the aforementioned problems, found that those impurities which are present in raw material aromatic hydrocarbons and difficult to separate by such operation as distillation and crystallization can be separated efficiently by turning the impurities into heavy matters and distilling them, and arrived at this invention.
This invention relates to a process for purifying an aromatic hydrocarbon which comprises treating an aromatic hydrocarbon containing impurities with an aldehyde selected from formaldehyde and compounds generating formaldehyde in the reaction system such as paraformaldehyde or with said aldehyde and a phenol in the presence of an acid catalyst to form oligomers and recovering the unreacted aromatic hydrocarbon from the reaction mixture by evaporation or distillation.
An aromatic hydrocarbon containing impurities to be used as feedstock in this invention is a monocyclic aromatic hydrocarbon such as benzene, toluene, xylene and ethylbenzene or a polycyclic aromatic hydrocarbon such as naphthalene, methylnaphthalene, anthracene, acenaphthene and fluorene, although a polycyclic aromatic hydrocarbon containing two to three rings is preferable. The feedstock may contain two kinds or more of aromatic hydrocarbons, but it is advisable to adjust the content of the hydrocarbon at 70 wt % or more, preferably at 90 wt % or more, in advance by distillation or the like.
Impurities are contained in commercially available aromatic hydrocarbons and the purifying process of this invention is effective for those compounds which are difficult to separate by distillation, for example, sulfur compounds and nitrogen compounds. Typical sulfur compounds are sulfur-containing heterocyclic aromatic compounds such as thiophene and benzothiophene and their methyl- or ethyl-substituted derivatives while typical nitrogen compounds are nitrogen-containing heterocyclic aromatic compounds such as pyridine, indole, quinoline, isoquinoline and carbazole and their methyl- or ethyl-substituted derivatives. Normally, sulfur compounds contain 100-10,000 wt ppm of sulfur while nitrogen compounds contain 10-5,000 wt ppm of nitrogen.
The feedstock aromatic hydrocarbon oil may contain aliphatic hydrocarbons and phenols, but it is better to remove bases and components harming the activity of a catalyst in advance. A suitable aromatic hydrocarbon is the one or a fraction containing it separated from petroleum or coal tar, preferably the one or a fraction thereof obtained from coal tar. For example, crude naphthalene or a naphthalene oil containing 10 wt % or more of naphthalene or methylnaphthalene is advantageous as feedstock.
In case the target is high-purity naphthalene, crude naphthalene to be used as feedstock is adjusted to have
Imamura Takahiro
Noguchi Katsuhide
Senzaki Toshihide
Takayama Takeshi
Birch & Stewart Kolasch & Birch, LLP
Dang Thuan D.
Nippon Steel Chemical Co. Ltd.
LandOfFree
Process for the purification of aromatic hydrocarbons and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the purification of aromatic hydrocarbons and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the purification of aromatic hydrocarbons and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3110019