W A S T E W A T E R

I N D U S T R Y

T R E A T M E N T IN T H E P E T R O C H E M I C A L

A. G. N e m c h e n k o , L . M. S a m o i l o v a , O. V o M a m o n t o v a , ]~. V. R u b i n s k a y a , a nd V. L . V a i n e r

UDC 665~

At the present time, the traditional biological method of wastewater treatment is no longer satisfying the increasingly more stringent requirements for the protection of quality of water supplies. We are feeling an acute need for the development and introduction of new, highly effective, local methods for the treatment of wastewaters from petrochemical plants, particularly for methods to eliminate aromatic hydrocarbons, toxic nitrogen-, chlorine-, and sulfur-containing organic compounds, and high-molecular-weight substances that are diffcult to decompose biologically, as the content of these substances in wastewaters is showing a con- tinuous increase.

At VNIINeftekhim, we have developed a desorpt ion- adsorption method for the treatment of industrial water to remove aromatic hydrocarbons. In Fig. 1 we show a simplified flow plan for a unit to t reat industrial water by this method.

�9 The original water, containing aromatic hydrocarbons, is fed from the separator 1 by the pump 2 through the heat exchanger 3 (where it is heated with exhaust steam if necessary) and then to the upper part of the desorber 4. Simultaneously, air is fed from the blower 9 to the lower part of the desorber .

The hydrocarbon-saturated air is cooled in the heat exchanger 5 and then passes to the absorber 6 (two absorbers are provided, operating alternately), which is packed with activated carbon; here the aromatic hydrocarbons are removed from the air . The purified air is vented to the atmosphere. The activated carbon, after saturation with aromatic hydrocarbons, is subjected to regeneration by live steam, which is condensed in the heat exchanger 7 andthenpasses to the separator 1, where it separates into a water layer and an organic layer . The organic layer is picked up by the pump 10 and t ransferred to processing; the water layer is mixed with the original water and returned to the desorber 4. After regeneration of the carbon with live steam has been completed, it is dried with air, which is supplied by the blower 9 through the heat exchanger 8.

The water, now free of aromatic hydrocarbons, is directed to biochemical treatment.

The basic process parameters are as follows:

Specific capacity of desorber for water, m3/m 2 Temperature , ~ Air consumption, gm3/m 3 water Degree of aromatic hydrocarbon removal, Specific capacity of adsorber for air, m3/(m 2 .min) Temperature, ~

Adsorption Regeneration of carbon

Time, h Adsorption Regeneration Drying of carbon

10-50 20-40

40 99.8-100

5-10

20-35 100-110

24 1 1

All-Union Scientific-Research Institute of Petrochemical Processes (VNIINeftekhim). Translated from Khimiya i Tekhnologiya Topilv i Masel, No. 11, pp. 23-26, November, 1976.

This material is protected by copyright registered in the name of Plenum Publishing Corporation, 227 West 17th Street, New York, N.Y. 10011. No part I [of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, I [ microfilming, recording or otherwise, without written permission o f the publisher. A copy of this arHcle is available from the publisher for $ Z 50. J

846

i / i7 z

Fig. 1. Simplif ied flow plan of unit for deso rp t ion -adsorp t ion t r ea tmen t of industr ial wa te r containing a romat i c hydrocarbons : 1) s e p a r a t o r ; 2 ) p u m p ; 3, 5, 7, 8) heat ex- changers ; 4) d e s o r b e r ; 6) a d s o r b e r s ; 9) a i r b lower ; t0) pump; I) a roma t i c hydroca rbons ; II) or iginal water ; III) t rea ted water ; I V ) s t e a m ; V) a i r to a tmosphe re ; VI) a i r .

Cooling of ca rbon 1 Act ivi ty of carbon,% 12-25" S team consumption in r egenera t ing t kg of carbon, kg 0.4

A i r consumption, kg In drying 1 kg of ca rbon 0.4 In cooling 1 kg of carbon 0 A

L o s s e s of act ivated carbon per me t r i c ton of a roma t i c hydrocarbons ex t rac ted , kg 0.5-1

With a capaci ty of 100,000 m3/y r for the unit, the use of this method will provide a saving of more than 20,000 r u b l e s y r in compar i son with an analogous unit for s t e a m - s t r i p p i n g the a romat ic hydrocarbons .

Fo r the t r e a t m e n t of was tewa te r s to r emove toxic n i t rogen- , ch lor ine- , and sul fur -conta in ing compounds and organic compounds that a re difficult to decompose biologically, we have developed a new and or iginal method of ozonizat ion with subsequent b iochemica l a f t e r t r e a t m e n t in the genera l plant t rea t ing fac i l i t ies . A s impl i f ied flow plan of this unit is shown in Fig. 2.

A tmosphe r i c a i r through the d r i e r 1 and f i l ter 2 is fed to the ozonizer 3, where it is subjected to the action of a weak e l ec t r i c d ischarge at a vol tage of 7-10 kV, and ozone is genera ted . The o z o n e / a i r mix ture (OAM) pas se s to the lower par t of the ozoaizat ion r eac to r 4 (through a s p a r g e r ) . The was tewa te r is fed f rom the working tank 6 by means of the pump 5 to the upper pa r t of the r e ac to r . Simultaneously, a 20% NaOH solution is added to the was t ewa te r . The spent OAM f rom the r eac to r 5 is vented to the a tmosphere , and the was tewate r a f ter ozonizat ioa is d i rec ted to b iochemica l t r ea tment .

It has been found that when the was tewa te r s a re ozonized, the toxic and biological ly unoxidizable sub- s tances in the was tewate r s a re decomposed to l ow-molecu la r -we igh t monocarboxyl ic and dicarboxyl ie acids and the cor responding mine ra l acids . Here the main fac tor de termining the degree of puri f icat ion of the wa te r and the composi t ion of the oxidation products is the quantity (dose) of absorbed ozone.

The degree of puri f icat ion of the water and the composi t ion of the oxidation products a re shown in r e l a - tion to the ozone dose in Fig. 3. It will be noted that the degree of water purif icat ion i nc rea se s with increas ing ozone dose. Fo r example , with an ozone dose of 0.5-0.6 g / g COD, the polyhydric alcohols p re sen t as HBBP (high-boiling byproducts) a re comple te ly decomposed . The max imum quantity of s t eam-d i s t i l l ab t e acids is fo rmed with an ozone dose of 0.3-0.4 g / g COD.

It is in te res t ing to note that the m a x i m u m degree of b iochemical purif icat ion is also achieved af ter t r ea tmen t of the wa te r with this dose of ozone.

The opt imal conditions for the ozonization of was tewa te r s containing toxic and difficultly biooxidizable organic compounds are as follows:

*Depends on content of a roma t i c hydrocarbons in v a p o r / a i r mix tu re .

847

Fig. 2, Simplified flow plan of unit for oxidation of wastewaters by ozone: 1) d r i e r ; 2) f i l ter ; 3) ozonizer i 4) r eac to r ; 5) pump; 6) tank; I) a i r ; II) spent ozone / a i r mixture ; III) NaOH solution; IV) original wastewater ; V) ozonized wastewater to biological t r ea tment ,

�9 L)

g.6 TM w

~ 28O

~

~J o,# 68 z,g z,# z# Ozone dose, g/g COD

Fig. 3. Degree of water purif icat ion and composit ion of oxidation products as functions of ozone dose (O 3 12 mg/ l i te r , caust ic consumption 0.333 g /g COD}: 1) content of HBBP; 2) content of volat i le acids; 3) degree of wate r purif icat ion in ozonization stage; 4 )de- g ree of purif ication ofozonized water in aera t ion tanks.

Tempera tu re , ~ Caustic consumption, g /g COD Ozone dose, g /g COD Ozoaizat ion period, min Degree of ozone conversion,~c Water feed rate, m3/(m2-.h)

20-70 0.5-0.6 0.4-0.5 20-30

100 5

Here it must be acted that improvements in ozonizer design and inc reases in s ingle-unit ozonizer capaci ty will lead to a continuous reduction in the cost of ozone. In the future, it will become the most readi ly available and cheapest oxidant. Hence the ozonization method is finding the widest application for the local t rea tment of was tewate rs .

Calculat ions have shown that, by putting this method into use at the Nizhnekamsk Pe t rochemica l Combine, replacing the combustion of i soprene production wastewater in cyclone furnaces , the savings will amount to about 1 million r u b l e s / y r .

A number of pe t rochemica l manufacturing p rocesses give wastewaters containing mineral sal ts . Hence the select ion and introduction of a technologically and economical ly justified method for desalting wastewaters can give ve r y marked reduct ions in both the discharge of minera l compounds to r e s e r v o i r s and wa te rcourses and the total quantity of wastewaters formed, since the desal ted waters can be reused in production.

848

TABLE 1. Resul ts f r o m Studies of Desal t ing of Biological ly T rea t ed Was tewa te r s f r o m P e t r o c h e m i c a l Combine

Content, mg/liter I orgarde

Wastewater salts cl-X so~-2 NO~-t ca+2 Mr NH +i substances (based on COD)

Untreated waste Filtrate

2285 73,5 (96,8)

594 33 (94,4)

708 I 18 45 28 !

5 (99,3) I 0 (i00) 0,38(99,1)t0,15(99,5 ) 3o

o 0oo)

Note. Values in pa ren theses indicate degree of pur i f ica t ion (in %).

t78 12 (93,2)

Fig. 4. Simplified flow plan of unit for desal t ing was tewa te r s f rom p e t r o c h e m - ical production by r e v e r s e o smos i s meth- od.

In the USSR and in o ther countr ies , use is a l ready being made of the r e v e r s e o s m o s i s method for desal t ing sea wa te r and b rack i sh water ; this method is based on the f i l t ra t ion of water through s e m i p e r m e a b l e m e m - b ranes under a p r e s s u r e exceeding the osmot ic p r e s s u r e [2-4]. The advantage of this method over o ther desal t ing methods cu r r en t ly avai lable is that it does not requi re high t e m p e r a t u r e s ; also, it is s imple in equip- ment design, readi ly control lable , and can be automated.

In Fig. 4 we show a s impl i f ied flow plan of a unit for desal t ing was tewa te r s by r e v e r s e o s m o s i s .

Sal t -containing wate r f r o m the rece iv ing tank 1 pa s se s through the m e c h a n i c a l - t r e a t m e n t f i l te r 2 and is fed by the me te r ing pump 3 under a p r e s s u r e of 35-100 kg f / cm ~ to the desal t ing v e s s e l through the tu rbu l ize r 5 to the s e m i p e r m e a b l e m e m b r a n e 6o The f i l t ra te , pass ing through the porous backing 7, is col lected in the r e c e i v e r 11; the concent ra te is drawn off to the r e c e i v e r 10. Constant p r e s s u r e in the s y s t e m is mainta ined by means of the regulat ing valve 9.

As the f i l te r ma te r i a l , we tes ted ce l lu lose acetate m e m b r a n e s of the "Vladipor" type, with a se lec t iv i ty of 96% with r e spe c t to NaC1 and a throughput capaci ty of 150-350 l i t e r s / ( m ~ "day).

These studies showed that, s ince the was tewate r s contain va r ious c l a s s e s of organic compounds along with the mine ra l sa l t s , the desal t ing can be p e r f o r m e d mos t effect ively a f t e r phys icoehemica l and biological t r e a tmen t .

The r e su l t s obtained in s tudies of the desal t ing of biologically t r ea t ed was tewa te r s f r o m the pe t ro - chemica l combine are l i s ted in Table 1.

By r e v e r s e o smos i s , we can not only reduce the sa l t content of the was tewater by 95-98%, but also effect comple te r e m o v a l of the h igh -molecu la r -we igh t o r g a n i c subs tances p r e sen t in the wa te r . The s e l e c - t ivity of the m e m b r a n e s r e m a i n s unchanged over extended per iods .

In view of the growth of the USSR mach ine ry cons t ruc t ion indust ry and the expansion of production of h igh-capac i ty s e m i p e r m e a b l e m e m b r a n e s , we may cons ider that this method will be finding widespread ap- pl icat ions in was tewa te r desal t ing.

Approx imate calcula t ions have shown that the savings through rea l iza t ion of the r e v e r s e - o s m o s i s desal t ing of was t ewa te r s f rom pe t rochemica l production, in c o m p a r i s o n with the ion exchange method (Salavat P e t r o c h e m i c a l Combine), will amount to about 1.3 mill ion r u b l e s / y r .

849

L I T E R A T U R E C I T E D

1. USSR Inventor ' s Cer t i f ica te 346,235, Byull . Izobret . , No. 23 (1972). 2. I . D . Rodzi l ler and Yu. N. Golovenkov, Zh. Vses . Khim. O-va, 17, No. 2, 184 (1972). 3. Yu. I. Dytnerski i et al., Wastewater T rea tm en t by Reverse Osmosis and Ult raf i l t ra t ion [in Russian},

NIITEkhim, Moscow (1973). 4. A . A . Yasimov et at., Khim. P rom. , No. 3, 23-29 (1974).

E X P E R I E N C E IN L O C A L T R E A T M E N T O F

W A S T E W A T E R S F R O M P E T R O C H E M I C A L P R O D U C T I O N

Vo V . A m o s . v , A . G. Z i l ' b e r m a n , E . I . K u c h e r y a v y k h , l~. I . S o r k i n , L . Y a . T s a r i k , S . A . ] ~ p p e l ' , V~ E . T i m o s h e k , a n d I . P . T i t o v

UDC 628.443.1 : 665,65

T R E A T M E N T O F S U L F I D E - C O N T A I N I N G W A S T E W A T E R S

In the course of refining crude oil, the wastewaters that are formed may contain hydrogen sulfide, sodium and ammonium sulfides, and phenols. The total quantity of sulfur compounds may vary f rom 0.5 to 10 g a i t e r . Var ious methods are used to detoxify such wastewaters , the main methods being desorpt ion and oxidation of the sulfur compounds.

At "Angarsknef teorgs in tez ," a unit is in operat ion for the purging of hydrogen sulfide with carbon dioxide [1]. This method, with a r a the r large CO 2 consumption (50 m3/m 3 of wastewater) , will remove f rom the water not only the f ree hydrogen sulfide, but also sulfide sulfur, through the format ion of the corresponding carbonates . Disadvantages of the method are the la rge demand for carbon dioxide compress ion and the formation of purge gas with a low content of hydrogen sulfide. The uti l ization of such gas for sulfuric acid manufacture is not at all des i rable , so that it must be f lared, with resul tant pollution of the a tmosphere with sulfur oxides.

If no CO~ is available in the plant, the desorpt ion of sulfur compounds f rom the wastewater is usually c a r r i e d out at e levated t empera tu re (85-95~ The higher t empera tu res favor dissociat ion of the sulfides and the i r desorpt ion f rom the water . Flue gas containing 10-15% CO 2 is normal ly used for purging in this situation.

Recent ly coming into use is the physical desorpt ion method, essent ia l ly a t r ea tment of the wastewater with a hydrocarbon gas [2]. This does not produce conditions for any extensive decomposit ion of sulfides (as does take place upon carbonation); however, the advantage of the physical desorpt ioa method is the possibil i ty of utilizing the sulfur and eliminating a tmospher ic pollution, as the waste gases may be p rocessed in a common sulfur removal unit.

Of the oxidative methods, the best known is t rea tment of the wastewater with ai r at 90-95~ under a p r e s s u r e of 4 kgf /cm 2. Under these conditions, the sulfides are oxidized mainly to thiosulfates [3]. The disadvantage of the method is the re ta rda t ion of the oxidation process by dissolved pe t ro leum products, as well as the considerable consumption of compres sed a i r (at l eas t 30 m3/m 3 of wastewater) .

With the aim of acce lera t ing the oxidation of sulf ide-containing wastewaters and simplifying the me- chanical design of the equipment for the p rocess , the Institute of Catalysis of the Siberian Branch of the USSR Academy of Sciences (in Novosibirsk) has proposed the use of homogeneous catalyt ic oxidation. The p rocess goes forward at 20-30~ with only a smal l consumption of a i r (10 m3/m 3 of waste) and does not pollute the

"Angarsknef teorgs in tez" (a production associat ion for pe t rochemica l and organic synthesis , located at Angarsk) . Institute of Pe t rochemica l and Coa l -Ta r Chemical Synthesis, at the Zhdanov Irkutsk State Univers i ty . Trans la ted f rom Khimiya i Tekhnologiya Topliv i Masel, No. 11, pp. 26-28, November, 1976.

I T his material is protected by copyright registered in the name of Plenum Publishing Corporation, 227 West 17th Street, New York, iV. Y. 10011. No part I of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission of the publisher. A copy of this article is available from the publisher for $7.50. .J

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