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Effect of aromatic hydrocarbons on liquid-phase oxidation of paraffins in the presence of boric acid
EFFECT OF AROMATIC HYDROCARBONS ON LIQUID-PHASE OXIDATION OF PARAFFINS IN THE PRESENCE OF BORIC ACID * A. N. BASHKIROV, L. A. GILYAROVSKAYA, YE. S. ALENT'EVA, R. V. KOZLENKOVA a n d A. K. KUROCHKINA M. V. Lomonosov Institute of Fine Chemical Technology, Moscow A. V. Topchiov Institute for Petrochemical Synthesis, U.S.S.R. Academy of Sciences (Received 9 January 1964)
DURING liquid-phase oxidation of paraffins in the presence of boric acid, we have repeatedly observed the retarding effect of aromatic hydrocarbons. A content of the latter of more than 0 . 5 ~ markedly retards oxidation [1]. In using liquid petroleum paraffins as racy material for the production of higher aliphatic alcohols b y direct oxidation, these paraffins have to be additionally purified from aromatic hydrocarbons. This equally concerns all liquid paraffins separated b y the urea method or by a method of direct cr~'stallization from petroleum fractions since, in almost all cases, liquid paraffins contain more than 0.5 ~ of aromatic hydrocarbons. This paper gives new data to facilitate quantitative evaluation of the effect of aromatic hydrocarbons in liquid petroleum paraffins and also of certain individual aromatic hydrocarbons on controlled oxidation to alcohols. Paraffins were oxidized under the conditions previously described [2]. In all experiments the oxygen content in the nitrogen-oxygen mixture was 3-5%; reaction temperature, 165-170°; the proportioll of boric acid 5~o; oxidation time 4 hours. A colorimetric method was used to determine small amounts of aromatic hydrocarbons in liquid paraffins. This is based on the well-kno~m Nastyukov reaction, according to which the increase of concentration of aromatic h)'drocarbons, the intensity of colouration increases in reaction with formaldehyde in the presence of concentrated sulphnric acid. Colour intensity was determfiled b y a F E K - M photocolorimeter. Two liquid petroleum paraffin fractions (240-350 ° and 270-320 °) containing from 0 to 4 ~ aromatic hydrocarbons, were oxidized. These fractions were separated from diesel fuel obtained by urea purifications from Tartar petroleum mixtures. * _Neftekhimiya 4, No. 5, 777-779, 1964. 292
Liquid-phase oxidation of paraffins
293
The oxidates, after saponification with water of the boric acid esters were subjected to functional analysis by conventional methods. The results of the investigation are shown in Fig. 1. Curve 1 refers to the fraction boiling within the range of 270-320 °, curve 2 to the fraction evaporating within the range 240-350 °. The hydroxyl numbers of the oxidate are shown on the curves for each experiment after 4 hours oxidation with different aromatic hydrocarbon contents. The curves inidcate the retarding effect of these hydrocarbons on oxidation. If, in the presence of aromatic hydrocarbons the hydroxyl number reaches 90 units, with the same oxidation time and 1 ~oo content of aromatic hydrocarbons, the hydroxyl nmnber sharply decreases to 40 units. In the presence of 0"5~o aromatic hydrocarbons, alcohol formation noticeably decreases, if their content exceeds 1 ~ , oxidation hardly takes place and is accompanied by strong resinification and darkening of the hydrocarbons oxidized. Neither does an increase of oxidation time to 6-7 hours promote the process. In this ease, on the contrary, a reduction of hydroxyl numbers and an even more intensive darkening of the oxidate are observed.
700
8o
c6o 4o
~2o
O
I
I
05
~
I
/.0
i
t
~5
~
2
0/
t
i
25
i
310
J
J
35
Aromatic hgdpocarbon~ , % :FIG. 1. E f f e c t o f a r o m a t i c h y d r o c a r b o n content on the oxidation of liquid leum paraffin fractions: 1--270-320 ° fraction; 2--240-350 ° fraction.
petro-
Experiments on the study of the effect on oxidation of individual aromatic hydrocarbons were carried out with a synthol fraction in the boiling range of 275-320 ° . Various amounts of aromatic hydrocarbons were added to this fraction: decylbenzene, butylnaphthalene, naphthalene, tetralin, diphenyl and ditolylmethane. Oxidation conditions were as described above. The oxidates obtained, with an aromatic hydrocarbon content of over 0 . 5 ~ were liquid, dark-coloured products with resinous impurities, of which the amount and colour
294
A . N . BASttKIRO¥ et al.
intensity increased with the increase of the content of aromatic hydrocarbons added to the synthol fraction. The results of experiments are shown in Fig. 2. Here, as in Fig. 1, the hydroxyl numbers obtained after 4 hours oxidation are sho~. The retarding effect of individual aromatic hydrocarbons on oxidation is of the same order as in the first case. However, as could be expected, their effect differs according to the aromatic hydrocarbon structure. Butylnaphthalene has the strangest inhibiting effect. Thus, with a content of 0.15~, the hydroxyl numbers decrease from 93 (synthol fraction) to 40 units. Tetralin has a lesser inhibiting effect. 85
@
80\
~80
7o!
k
3O 10 0.150200-25 0-50 0"75 1"00 Arornat/c hgdrocapbons , % b.u weighf
FIG. 2.
0
025 J5 Butylnaphthalene , % FIG. 3.
FIG. 2. Effect of aromatic hydrocarbons on the liquid phase oxidation of synthol in the presence of boric acid. Tetralin (•); diphenyl (2); ditolylmethane (3); decylbenzene (4); naphthalene (5); butylnaphthalene (6). :FIG. 3. Effect of butylnaphthalene on oxidation of paraffin hydrocarbons. H y d roxyl number (•); carbonyl number (2); ester number (3); acid number (4).
Simultaneously with the decrease of hydroxyl numbers, during oxidation of paraffins in the presence of aromatic hydrocarbons, a reduced content is observed of all the other functional groups which is reflected in the acid, ester and carbonyl numbers. This can be demonstrated by the example of oxidation of a syathol fraction in the presence of various amounts of butynapthalene (Fig. 3). Finally, it should be noted that the retarding effect observed of small amounts of aromatic hydrocarbons on the liquid phase oxidation of paraffins
Liquid-phase oxidation of paraffins
295
is apparent only in the presence of boric acid. Without boric acid, the aromatic hydrocarbons studied (even in large quantities) do not inhibit oxidation at 165-170 ° in practice. SUMMARY
1. Aromatic hydrocarbons present in liquid petroleum paraffins markedly inhibit liquid phase oxidation of paraffins in the presence of boric acid. In the presence of aromatic hydrocarbons in proportions exceeding 0 . 5 ~ oxidation does not take place. Marked darkening and resinification of hydrocarbons oxidized occur. 2. A study has beed made of the effect of certain aromatic hydrocarbons on liquid phase oxidation of paraffins in the presence of boric acid. Nephthalene and butylnaphthalene have the strongest inhibiting effects. Translated by E. SE~ERE REFERENCES
1. A. N. BASHKIROY and V. V. KAMZOLKIN, Khim. nauka i prom-st' 4, 607, 1959 2. A. N. BASHKIROV, Khim. nauka i prom-st' 1, 273, 1956
DURING liquid-phase oxidation of paraffins in the presence of boric acid, we have repeatedly observed the retarding effect of aromatic hydrocarbons. A content of the latter of more than 0 . 5 ~ markedly retards oxidation [1]. In using liquid petroleum paraffins as racy material for the production of higher aliphatic alcohols b y direct oxidation, these paraffins have to be additionally purified from aromatic hydrocarbons. This equally concerns all liquid paraffins separated b y the urea method or by a method of direct cr~'stallization from petroleum fractions since, in almost all cases, liquid paraffins contain more than 0.5 ~ of aromatic hydrocarbons. This paper gives new data to facilitate quantitative evaluation of the effect of aromatic hydrocarbons in liquid petroleum paraffins and also of certain individual aromatic hydrocarbons on controlled oxidation to alcohols. Paraffins were oxidized under the conditions previously described [2]. In all experiments the oxygen content in the nitrogen-oxygen mixture was 3-5%; reaction temperature, 165-170°; the proportioll of boric acid 5~o; oxidation time 4 hours. A colorimetric method was used to determine small amounts of aromatic hydrocarbons in liquid paraffins. This is based on the well-kno~m Nastyukov reaction, according to which the increase of concentration of aromatic h)'drocarbons, the intensity of colouration increases in reaction with formaldehyde in the presence of concentrated sulphnric acid. Colour intensity was determfiled b y a F E K - M photocolorimeter. Two liquid petroleum paraffin fractions (240-350 ° and 270-320 °) containing from 0 to 4 ~ aromatic hydrocarbons, were oxidized. These fractions were separated from diesel fuel obtained by urea purifications from Tartar petroleum mixtures. * _Neftekhimiya 4, No. 5, 777-779, 1964. 292
Liquid-phase oxidation of paraffins
293
The oxidates, after saponification with water of the boric acid esters were subjected to functional analysis by conventional methods. The results of the investigation are shown in Fig. 1. Curve 1 refers to the fraction boiling within the range of 270-320 °, curve 2 to the fraction evaporating within the range 240-350 °. The hydroxyl numbers of the oxidate are shown on the curves for each experiment after 4 hours oxidation with different aromatic hydrocarbon contents. The curves inidcate the retarding effect of these hydrocarbons on oxidation. If, in the presence of aromatic hydrocarbons the hydroxyl number reaches 90 units, with the same oxidation time and 1 ~oo content of aromatic hydrocarbons, the hydroxyl nmnber sharply decreases to 40 units. In the presence of 0"5~o aromatic hydrocarbons, alcohol formation noticeably decreases, if their content exceeds 1 ~ , oxidation hardly takes place and is accompanied by strong resinification and darkening of the hydrocarbons oxidized. Neither does an increase of oxidation time to 6-7 hours promote the process. In this ease, on the contrary, a reduction of hydroxyl numbers and an even more intensive darkening of the oxidate are observed.
700
8o
c6o 4o
~2o
O
I
I
05
~
I
/.0
i
t
~5
~
2
0/
t
i
25
i
310
J
J
35
Aromatic hgdpocarbon~ , % :FIG. 1. E f f e c t o f a r o m a t i c h y d r o c a r b o n content on the oxidation of liquid leum paraffin fractions: 1--270-320 ° fraction; 2--240-350 ° fraction.
petro-
Experiments on the study of the effect on oxidation of individual aromatic hydrocarbons were carried out with a synthol fraction in the boiling range of 275-320 ° . Various amounts of aromatic hydrocarbons were added to this fraction: decylbenzene, butylnaphthalene, naphthalene, tetralin, diphenyl and ditolylmethane. Oxidation conditions were as described above. The oxidates obtained, with an aromatic hydrocarbon content of over 0 . 5 ~ were liquid, dark-coloured products with resinous impurities, of which the amount and colour
294
A . N . BASttKIRO¥ et al.
intensity increased with the increase of the content of aromatic hydrocarbons added to the synthol fraction. The results of experiments are shown in Fig. 2. Here, as in Fig. 1, the hydroxyl numbers obtained after 4 hours oxidation are sho~. The retarding effect of individual aromatic hydrocarbons on oxidation is of the same order as in the first case. However, as could be expected, their effect differs according to the aromatic hydrocarbon structure. Butylnaphthalene has the strangest inhibiting effect. Thus, with a content of 0.15~, the hydroxyl numbers decrease from 93 (synthol fraction) to 40 units. Tetralin has a lesser inhibiting effect. 85
@
80\
~80
7o!
k
3O 10 0.150200-25 0-50 0"75 1"00 Arornat/c hgdrocapbons , % b.u weighf
FIG. 2.
0
025 J5 Butylnaphthalene , % FIG. 3.
FIG. 2. Effect of aromatic hydrocarbons on the liquid phase oxidation of synthol in the presence of boric acid. Tetralin (•); diphenyl (2); ditolylmethane (3); decylbenzene (4); naphthalene (5); butylnaphthalene (6). :FIG. 3. Effect of butylnaphthalene on oxidation of paraffin hydrocarbons. H y d roxyl number (•); carbonyl number (2); ester number (3); acid number (4).
Simultaneously with the decrease of hydroxyl numbers, during oxidation of paraffins in the presence of aromatic hydrocarbons, a reduced content is observed of all the other functional groups which is reflected in the acid, ester and carbonyl numbers. This can be demonstrated by the example of oxidation of a syathol fraction in the presence of various amounts of butynapthalene (Fig. 3). Finally, it should be noted that the retarding effect observed of small amounts of aromatic hydrocarbons on the liquid phase oxidation of paraffins
Liquid-phase oxidation of paraffins
295
is apparent only in the presence of boric acid. Without boric acid, the aromatic hydrocarbons studied (even in large quantities) do not inhibit oxidation at 165-170 ° in practice. SUMMARY
1. Aromatic hydrocarbons present in liquid petroleum paraffins markedly inhibit liquid phase oxidation of paraffins in the presence of boric acid. In the presence of aromatic hydrocarbons in proportions exceeding 0 . 5 ~ oxidation does not take place. Marked darkening and resinification of hydrocarbons oxidized occur. 2. A study has beed made of the effect of certain aromatic hydrocarbons on liquid phase oxidation of paraffins in the presence of boric acid. Nephthalene and butylnaphthalene have the strongest inhibiting effects. Translated by E. SE~ERE REFERENCES
1. A. N. BASHKIROY and V. V. KAMZOLKIN, Khim. nauka i prom-st' 4, 607, 1959 2. A. N. BASHKIROV, Khim. nauka i prom-st' 1, 273, 1956