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O-Ksilenin otoksidasyonu ve ürünlerinin analizi

Başlık çevirisi mevcut değil.

  1. Tez No: 75469
  2. Yazar: NİHAL COŞKUN
  3. Danışmanlar: DOÇ. DR. BİRSEN DEMİRATA ÖZTÜRK
  4. Tez Türü: Yüksek Lisans
  5. Konular: Kimya, Chemistry
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1998
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Kimya Ana Bilim Dalı
  12. Bilim Dalı: Kimyagerlik Bilim Dalı
  13. Sayfa Sayısı: 77

Özet

Bu çalışmada o-ksilenin hava oksijeni kullanılarak otoksidasyonu ve ürünlerinin analizi yapılmıştır. O-ksilenin otoksidasyonu ile ftalik anhidrit üretimine ait çok sayıda araştırma yapılmaktadır. Ftalik anhidrit özellikle plastifiyan olarak kullanılmaktadır. Bu araştırmalarda kullanılan katalizörler yüksek ve düşük sıcaklık katalizörleri olmak üzere iki tiptir ve kullanılan katalizörün esasını çoğunlukla V2O5 teşkil etmektedir. Yine bu araştırmalarda görüldüğü gibi yüksek dönüşüm oranına erişmek için ya yüksek sıcaklık yada baskı altında çalışılmıştır. Bu konuda ilgili firmalarca birçok araştırmalar yapılmış ve binlerce patent alınmıştır. Bu çalışmada %70 V2O5 ve %30 A1203 mol oranındaki karışım katalizör olarak kullanılıp, reaksiyon hem sıvı fazda, hem de buhar fazında yapılmıştır. Çalışmanın temel amacı, düşük sıcaklıkta olabildiğince yüksek dönüşüm oranına ve verimine sahip bir reaksiyon gerçekleştirmektir. Gaz fazında o-ksilenin yükseltgenmesiyle ftalik anhidrit üretimi değişik araştırma grupları ile hala çalışılmaktadır. Bu çalışmalarda katalizör karekteristiğine bağlı olarak, o-tolualdehit, ftalit ve maleik anhidritin yan ürün olduğu görülmüştür. Elde edilen ürünlerin analizleri çeşitli analitik yöntemlerle (kalitatif ve kantitatif olmak üzere aletli ve yaş yöntemlerle) yapılarak reaksiyon şartlan belirlenmiştir. Ülkemizde ftalik anhidrit ve tuzlarının tüketimi oldukça fazladır. Bu çalışma, bundan sonraki aşamada uygun bir proses şekline getirildiğinde ftalik anhidritin ucuz yolla üretimi yapılabilir.

Özet (Çeviri)

The phthalic anhydride is produced by a vapour phase catalytic oxidation process of aromatic hydrocarbons. Naphthalene was a basic feedstock for this process. O-xylene which until then was only a substitue material, became a principal feedstock. Technology for oxidation of o-xylene was further developed in the 70's. Each year the utilization of naphthalene for the manufacture of phthalic anhydride was reduced. This trend could be also noticed in 1979-1991. Modern plants can process both o-xylene and napthalene, depending on what is available at the moment. This flexibility together with yet another possibility to process mixtures thereof is very important on a tight phthalic market. Phthalic anhydride plants utilizing coal-derived napthalene are situated close to big metallurgical complexes. Table 1 Capacities of O-xylene Against Capacities of Phthalic Anhydride in 1990- 1991 (Thousands Mg/year) According to the American forecasts, the production of naphthalene is expected to increase and to reach the level of 1960, yet this will chiefly be relatively expensive petrochemical naphthalene. This material could compensate for missing o- xylene which is consumed in the isomerization process yielding p-xylene. Today, the supply of o-xylene completely satisfies the demand. Nowadays this subject can be discussed only with reference to one manufacturing method employed to obtain phthalic anhydride. gaseous phase oxidation of o-xylene and/or napthalene on a catalyst fixed bed. Other two known methods : gaseous phase oxidation of naphthalene with the use of a catalytic fluidized bed and liquid phase oxidation of o-xylene can be called“historical ones”. Liquid phase oxidation was ceased long ago, while catalytic fluidized bed turned out less competetive compared to catalytic fixed bed. This is one of basic reasons for reduced utilization of naphthalene.The fixed method for oxidation of o-xylene was developed principally in Europe, though plants were also built on other continents based on licenced from Von Heyden and from BASF. In 1994, the production of phthalic anhydride is still employing the improved process from mid-60's. Processes developed in Germany remain dominant, von Heyden/Wacker Chemie granted licences to about 50 companies having 50% of total capacity. A method for the manufacture of phthalic anhydride by vapour phase oxidation of aromatic hydrocarbons (o-xylene and/or napthalene), with the use molecular oxygen and fixed bed of suitable catalyst, comprises a few stages: a) preparation of a hydrocarbon/air mixture b) oxidation of hydrocarbon to yield phthalic anhydride in a reactor filled with a catalyst c) separation of phthalic from reaction gases-desublimation d) purification of vent gases e) conditioning of phthalic anhydride to obtain a commercial product Table 2 Flow Diagram For Oxidation Of O-Xylene and/or Naphtalane Yielding Phthalic Anhydride L 1 o-vylene T naphthalene Homogenization - vapor gas reaction mixture Oxidation reaction Desublimation crude_jjrûducL 1 Purification Removal of impurities commercial product to atmosphereThe basic design of a reactor suggested many years ago has not changed much until today. The trend observed in the past to increase plant capacity by increasing reactor volume was abandoned. This was caused chiefly by a catalyst which can accept the load of above 200 g o-xylene/dm3 and higher concentration of hydrocarbons in the reaction mixture. In this year, the capacity of existing and new reactors can reach the level of 25000-50000 Mg/year. Any construction if bigger units is a risky business : respectively low savings in investment outlay is obtainable against increased costs of planned and emergency shut-downs. The reactor-heat exchanger design, with its tubes of catalytic internal side having the diameter of 20-25 mm and cooled by melted circulated salts outside the tubes, is still the best design. Catalyst is a factor certifying the level of technology for phthalic anhydride plant. It is obvious that the proses equipment and auxiliary facilities must be able to take full advantage of the catalyst employed. Catalyst basic component- V205-has been used for 75 years already. For 25 years the catalyst basic composition has been V2O5-TİO2 what still attracting attention of scientists. Successive improved formulations of vanadium catalyst offer better selectivity, higher load acceptable, higher thermal resistance,etc. The phthalic anhydride desublimation unit, in its shape operated today, was designed and implement in the 60's. The so-called box condensers were then replaced by radiator type desublimators. initially, the heating cooling system employed steam and water. Now, it utilizes hot and cold oils. Theory and practical experience for this proses was provided by Kassat from GEA. High efficiency of employed apparatus allows for recovery of over 98% of produced anhydride, but this results from numerous tests and failures involving directly commercial plants. The acquired experience contributed to optimized design of desublimators allowing for much longer their life time, better heat transfer factors and automated operating cycles. Concentrations of by-products in reaction gases and first of all those for phthalide, benzoic acid and tolualdehyde, influence the structure of phthalic anhydride crystals. And this is critical for losses of phthalic anhydride due to entrained anhydride dust. Chemical treatment has numerous disadvantages, e.g.decarboxylation of phthalic anhydride and build up of tar-like substances. The choice is : higher temperature profile for basic reaction with purposeful lowered yield of phthalic anhydride or optimized parameters offering highest yield of phthalic anhydride and often longer catalyst life time with difficult purification process. Limited application of phthalic anhydride to alkyd resins, polyesters and as a PVC plastifier (esters), resulting from unsteady consumption, gives no reasons for optimistic forecasts. There are no new outlets capable of increasing sales. Also, nobody expects some significant break in technology for the manufacture of phthalic anhydride and hence some change in this situation. So, all the possibilities for the development of present technology should be kept in mind, with subsequent maintaining the position of phthalic anhydride among the basic products of chemical industry. Catalyst should have a satisfactory selectivity and efficiency and should be active in the oxidation prosess involving o-xylene, naphthalene and any mixtures thereof. It should be expected that physical forms offered catalyst will be modified to reduce pressure drop along the catalytic bed, and to reduce time needed for loading tha catalyts into any reactor and for emptying the reactor. The yield reached, 80% mole for o-xylene can certainly be increased.Reduction of the total exothermic effect will allow to increase concentrations of utilized hydrocarbons in the reaction mixture and hence to increase plant capacity. This was achieved by a) liquid phase oxidation of o-xylene to o-toluil acid with a cobalt naphthenate catalyst present b) vapour phase oxidation of this acid to phthalic anhydride in the presence of conventional catalyst American scientists insist on developing a fludized bed prosess for oxidation of o-xylene. Some investigations were carried out in Europe, too. SİO2 was found not to make a suitable catalyst carrier while mechanical properties of anatase are too poor. The future brings another problem to be solved by phthalic anhydride producers-reduced emissions of carbon dioxide to atmosphere. In this study, at low conversion, o-tolualdehyde was found as the main product on all vanadia containing catalysts, its selectivity decreased rapidly with increasing conversion. At medium conversion, phthalic anhydride was the main reaction product and phthalide was formed as a by-product. At high conversions, maleic anhydride was also formed (up to 8%). The total oxidation products CO and C02 were formed over the whole temperature range investigated. The selectivitiy of total oxidation remained almost constant up to 80% conversion. Then it increased rapidly, causing a sudden drop of the selectivity to phthalic anhydride. The rapid increase of the phthalic anhydride surface concentration with temperature, measured using FT-IR and the observed increase in phthalic anhydride production with increasing conversion, both support the generally accepted consequtive reaction model. Analyses of o-xylene, phthalic anhydride and side products o-tolualdehyde and phthalide are performed by using this techniques : Analytical methods: 1- Phthalic anhydride (PA) : (determined from the difference between the total acidity and acidity contributed by maleic anhdride(MA) and sitrasonic anhydride) TITRATION 2- Maleic anhydride (MA) : REDOX TITRATION 3- Citrasonic anhydride (CA) : GAS CHROMATOGRAPHY 4- O-tolualdehyde (TA) : GAS CHROMATOGRAPHY 5- Phthalide (PD) : GAS CHROMATOGRAPHY 6- unreacted o-xylene : GAS CHROMATOGRAPHY 7- CO,C02 : GAS CHROMATOGRAPHY DETERMINATION OF TOTAL ACIDITY : 10 ml of distillate is pipette out into conical flask and 10 ml of distilled water is added. This mixed solution titrated by alkaline solution (0.2 N NaOH) with indicator.DETERMINATION OF ORTOTOLUALDEHYDE: 5 ml is pipetted out into conical flask and 10 ml NaHS03 solution is added. Excess amaount of NaHSOî was titrated with iodine solution by using starch indicators. To collect other by products, the condition are given to study GSMS. Volumetric and GCMS results are used to find yields. Following table shows the experimental results at different conditions. Table 3 Experimental Results

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