CA1061740A - Continuous turpentine purification - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the continuous purification of crude sulphate turpentine to remove odour and colour in which the crude turpentine product is intensely agitated with an alkali metal or alkaline earth metal hypochlorite in a first reactor vessel having a high speed impeller therein, subsequently subjecting the turpentine-hypochlorite mixture to a high velocity stream of water vapour in a steam ejector and equilibrating the resulting mixture in a second reaction vessel, and finally separating a purified vapour phase containing turpentine from a liquid phase containing impurities.

Description

This invention relates to the purification of crude sulphate turpentine which is produced and recovered during the manufacture of kraft wood pulp from pine.
Crude sulphate turpentine as a by-product of the kraft process is characterized by a disagreeable odour and dark coloration which are due to the presence of sulphur compounds such as mercaptans, di- and poly-sulphides, cyclic sulphur compounds and possibly some elemental sulphur.
Because of the odour and colour, crude sulphate turpentine has little commercial value except as an important source of terpènes, mostly pinenes.
Many commercial pro~ssesfor producing purified sul-ph~te turpentine have been proposed and these usually consist of two treatments: (a) fractional and/or steam distillation, and (b) chemical treatment. A considerable portion of the sulphur bearing impurities can be removed by distillation, as most of the sulphur compounds have lower boiling points than the other constituents of the turpentine.
However, chemical treatment, before or after distillation, is normally necessary for complete removal of the impurities which cause the malodour and undesirable colour. These pro-cesses are, of course, costly, not only to operate but also in view of the capital equipment requirements, time-consuming and not without their attendant difficulties. Efforts have, therefore, been made to simplify the purification process for sulphate turpentine and hence provide a less costly alternative. One such process is described in United States Patent 3,778,485, issued December 11, 1973, in the name of ra/ - 1 -.. . ' . :.; .
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Oldrich Prochazka and assigned to the assignee of the present application, in which the curde turpentine is intensely agitated with a hypochlorite bleach solution so that the distillation step previously required is avoided. The resultant turpentine from such a hypochlorite agitation process has the characteristic odour of wood turpentine, is normally straw-yellowish in colour (Saybolt Standard 18-19) and is suitable for most commercial purposes. However, there are certain applications which require a still lighter colour in the turpentine (Saybolt 19-22), and it is an object of the present invention to improve the colour properties of the purified turpentine obtained by the process described in the aforesaid patent.
A further object of the present invention is to provide a prc^ess amenable to continuous operation at high throughput with attendant savings in time and labour cost.
By one aspect of this invention there is provided in a process for treating crude sulphate turpentine in which said crude sulphate turpentine is intensely agitated with an oxidizing solution containinq an alkali metal or alkaline earth hypochlorite, in a first reaction vessel, the improve-ment comprising continuously passing the agitated turpentine-hypochlorite mixture through a high velocity steam ejector to thereby mix with steam at a flow of 5.0-8.0 lbs. of steam per gallon of turpentine, equilibrating the steam treated mixture in a second reaction vessel and separating a vapour phase containing purified turpentine.

We have found that a remarkable decoloration of the final product can be effected by mixing a stream of the turpentine-hypochlorite mixture which need not be agitatéd for such a long period as in the aforesaid patent with a high velocity stream of water vapour, preferably in a steam ejector, equilibrating the steam and product mixture in a reaction vessel and subsequently separating a vapour phase, containing purified turpentine, and a liquid phase containing impurities.
The steam flow is sufficient to provide 5.0-8.0 lbs. steam per gallon of turpentine.
The invention will be described in more detail herein-/ after by reerence`to the drawings in which the sole figure is a flow sheet of the process according to the present invention.
In the first stage of the process of the present invention, a hypochlorite solution, selected from alkali metal and alkaline earth metal-hypochlorites and preferably sodium or calcium hypochlorite, is mixed in a reaction vessel 1 with crude turpentine. Reaction vessel 1 is provided with agitat-ing means, such as a high shear turbine impeller (not shown) ~ ~ qnd ~q,7~a~0~7 to ensure intense mixingAof the~hypochlorite and crude turpen-tine. Preferably the hypochlorite ànd crude turpentine are mixed in a volume ratio of 1:1 to 1:2, but any volume ratio may be used that permits sufficient contact between the two solutions for the economic removal of the sulphur-containing impurities. Volume ratios from 0.1:1 to 10:1, hypochlorite to turpentine have been successfully used, depending upon the amount of coloured impurities in the turpentine. Reaction temperatures are not critical but from 30C-75C has been .. : . . .: , , : ~

'7~() found to be a most suitable range.
The pH of the reaction solution depends on the presence of excess alkali. Preferably, the pH should be in the range 8.0-13Ø
A specific feature of the process according to the aforesaid patent resides in the agitation of the mixture and preferably a high shear turbineimpeller is used with a "Tip speed" as high as 2800 ft/min. Agitator tip speed in ft/min is commonly used as a measure of the degree of agitation in a liquid mixing system. It is defined as: Tip speed = ~ D x rpm where D is the diameter of the agitator in feet and rpm is ~the rotational speed in revs per minute. A high or intense degree of agitation is defined as a Tip speed in excess of llO0 ft/min, and which is necessary to assure proper mixing of the turpentine and hypochlorite. The residence time in the reaction vessel l is, of course, a functic~n of the Tip speed, the available chlorine, the amount of impurities in the turpentine and the temperature, and may vary up to about one hour. In contrast to the process according to the afore-2Q said patent, a residence time of 5-20 minutes is all that is usually required prior to the steam treatment of the present invention. A short residence time is, of course, advantageous as it minimizes side reactions. It has been found that in ~he present continuous process the "heavy-ènds" range from l.0-1~5% in contrast to a batch process according to the aforesaid patent which averages about 2.7~ heavy ends for a 4-hQur mixing time. The intensely agitated hypochlorite-~urpentine mixture is then introduced and dispersed into a .

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l()ti,1'740 high velocity stream of steam passing through a steam ejector 2. The inlet steam pressure to the ejector is usually between 40 and 100 psi~ and we have found that between 5.0 and 8.0 lbs. of steam per gallon of turpentine are required. The steam ejector ensures even more thorough mixir.g and reaction of the hypochlorite and turpentine and initiates a substantially instantaneous steam distillation to separate the turpentine from the non-volatile components.
Since steam distillation is used, there is no requirement for washing and total fresh water usage is reduced by 3 gals/gal of turpentine as compared to the` batch process.
Following the steam ejector 2, the steam-turpentine-hypochlorite mixture is passed through an equilibration vessel 3. The mixture has a residence time in vessel 3 of the order of 0.1 secs up to 10 seconds, which permits completion of the required hypochlorite reaction and also provides the substantially equilibrium distillation conditions which are preferred for separating turpentine from contaminants.
The mixture is then passed to a tangential entry separator ~0 4 to separate a turpentine-containing vapour phase and a contaminant and heavy-end-containing liquid phase. The vapour phase is then condensed in condenser 5, to an aqueous phase which is decanted in decanter 6 and discarded, and a turpentine phase which is collected as the desired product.
~ A conversion yield of 93-99% is achieved.

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- -111~174~) Examp~le 1 Crude sulphate turpentine, containing 3% by vol.
contaminants, and calcium hypochlorite (7~ active chlorine, based on turpentine) were pumped into a 20 gal reaction vessel in a 1:1 ratio at 73F, and pH 12-12.5. The mixture was agitated for 12.5 minutes at an agitator tip speed o~
2550 fpm, and the reaction temperature reached 125F. It was found that the agitator power required was 3 HP for 1 I.G.P.M. ~n a reaction vessel having an agitator diameter/
vessel diameter ratio of 1:3. After the 12.5 minute retention in the reaction vessel the agitated mixture of crude turpentine and hypochlorite was withdrawn through a 1.5" diameter steam ejector. Inlet steam pressure was 85 psig and sufficient steam was passed through the ejector to provide a flow of 6.5 lbs. of steam per gallon of turpen-tine. The steam/hypochlorite/turpentine mixture was then equilibrated in a second vessel. Residence time in the second vessel was calculated at 0.1 secs. The phases were then separated and the vapour phase condensed. Purified ~0 turpentine was then decanted from the condensed vapour phase.
The conversion yield was 95%, and the turpentine produced had the following properties:
ASTM Standard Colour (Saybolt) 19-22min. 11-19 Refractive Index ~20C) 1.469 1.465-1.474 Specific gravity ~15.5C)0.866 0.860-0.875 Odour Excellent "

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1'74() Example 2 The procedure of Example 1 was repeated except that the steam was merely mixed in line, without use of the ejector. The odour of the purified product was unacceptable and the colour was in the range 13~15. This indicates that mere mixing with steam, using the short agitation times of the present invention, is insufficient to produce an acceptable product.
Example 3 The procedure of Example 1 was repeated except that the equilibration in the second reaction vessel was omitted.
The purified turpentine produced had excellent odour but the colour was only in the range of 13-17, again indicating that insufficient reaction between the turpentine and the hypochlorite had occurred.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for treating crude sulphate turpentine in which said crude sulphate turpentine is intensely agitated with an oxidizing solution containing an alkali metal or alkaline earth hypochlorite, in a first reaction vessel, the improvement comprising continuously passing the agitated turpentine-hypochlorite mixture through a high velocity steam ejector to thereby mix with steam at a flow of 5.0-8.0 lbs of steam per gallon of turpentine, equilibrating the steam treated mixture in a second reaction vessel and separating a vapour phase containing purified turpentine.

2. The process as defined in claim 1 wherein said steam is injected to provide about 6.5 lbs of steam per gallon of turpentine.

3. The process of claim 1 wherein said steam treated mixture is equilibrated for a period in the range of 0.1 to 10 seconds.

4. The process as defined in claim 1 wherein said agitation is effected in said first reaction vessel with an impeller with a tip speed in the range 1200 to 3000 ft/min.

5. The process as defined in claim 4 wherein said tip speed is 2550 ft/min.

6. The process as claimed in claim 4 wherein the pH
of said turpentine-hypochlorite mixture is in the range 8.0-13Ø

7. The process as defined in claim 4, 5 or 6 wherein said first reaction vessel is at a temperature in the range 120-140°F.

8. The process as defined in claim 4, 5 or 6 wherein the residence time of said turpentine-hypochlorite mixture in said first reaction vessel is in the range 5-20 minutes.

9. A process as claimed in claim 1 or 4 wherein said alkali metal hypochlorite is sodium hypochlorite.