CA1131247A

CA1131247A - Sulfonation of alkylated aromatic hydrocarbons

Info

Publication number: CA1131247A
Application number: CA327,572A
Authority: CA
Inventors: Burton Brooks; Thomas W. Marson
Original assignee: Chemithon Corp
Current assignee: Chemithon Corp
Priority date: 1978-06-12
Filing date: 1979-05-14
Publication date: 1982-09-07
Also published as: IT7968257A0; DE2923510A1; JPS59502B2; GB2023138A; GB2023138B; IT1118773B; JPS554376A; DE2923510C2

Abstract

ABSTRACT
Alkylated aromatic hydrocarbons are sulfonated with SO3 gas, and an anhydrous low molecular weight carboxylic acid is added to the hydrocarbon before sulfonation to improve the color and lower the H2SO4 content of the sulfonic acid reaction product. The hydrocarbon is sulfonated in an atomized condition to provide a reaction mixture which is quenched by, and agglomerated in, cooled, recycled reaction product.

Description

~3~ 7 BACKGROUND OF THE INVENTION
The present invention relates generally to the sulfonation of alkylated aromatic hydrocarbons, such as alkyl benzene, and more particularly to the sulfonation of such hydrocarbons using sulfur trioxide as a sulfonating agent.
In a typical sulfonating operation in which alkyl benzene is the alkylated aromatic hydrocarbon undergoing sulfonation, the alkyl benzene is reacted with a sulfonating agent, such as sulfur trioxide gas in an air carrier, to form a sulfonic acid which is then neutralized with an alkali metal hydroxide, such as sodium hydroxide, to form a sulfonate. During the sulfonation operation, side reactions may occur which form sulfuric acid (H2SO4), and during the subsequent neutralization step, the sulfuric acid is converted to an alkali metal sulfate (e.g., Na2SO4). The neutralized product, typically consisting essentially of sodium sulfonate, is used primarily for detergent. The sodium sulfate in the end product is undesirable for detergent purposes.
It is also desirable to maintain the color of the end product as good as possible. On a Klett color scale (5%
solution, 40 mm path), the lower the Klett number, the better the color; and a Klett number of 50 or below indicates increasingly excellent color.
In the sulfonation of unalkylated aromatic hydrocarbons, such as toluene, benzene, xylene and the like, there are formed undesirable side reaction products called sulfones.
The sulfone content resulting from the sulfonation of unalkylated aromatic hydrocarbons may be reduced by adding a low molecular weight carboxylic acid such as acetic acid, " ~

~3~

propionic acid, butyric acid, valeric acid, cuproic or caprylic acid (see Gilbert et al. U.S. Patent No. 2,704,295).
Sulfone formation is generally not a problem in the sulfonation of alkylated aromatic hydrocarbons, such as alkyl benzene.
However, Norwood et al. U.S. Patent 2,831,020 discloses the -sulfonation of aromatic hydrocarbons, including alkyl benzene among others, with SO3 gas dissolved in liquid SO2 and the addition thereto of 0.25-1% of an organic carboxylic acid (e.g., acetic, malonic, azelaic or benzoic acids) to reduce the sulfone content. Norwood et al. also states that the formation of sulfones reduces the efficiency of the process by wasting reagent.
In Benson et al. U.S. Patent No. 3,681,443 there is disclosed a process for the sulfonation of alkyl benzene with SO3 gas, or SO3 dissolved in liquid SO2, to form sulfonic acid to which is added 0.25-2.5% of an alpha, beta-unsaturated carboxylic acid (e.g., fumaric, maleic, citraconic or mesaconic acids), with the carboxylic acid being added to the sulfonic acid after the latter has been formed. According to Benson et al., the objectives of adding these carboxylic acids to the sulfonic acid are to retard color degradation of the sulfonic acid and to retard acid or pH drift of the sulfonic acid.
As part of the disclosure, Benson et al. refers to Norwood et al. '020, discussed above, and acknowledges that Norwood et al. teaches the use of certain carboxylic acids for inhibiting the formation of sulfones in the sulfonation of alkylated aromatic hydrocarbons using sulfur trioxide (SO3) dissolved in li~uid sulfur dioxide (SO2). However, Benson et al. goes on to say that the carboxylic acids,

2~

disclosed in Norwood et al. as useful in preventing the formation of sulfones, are unsatisfactory and ineffective to achieve the objectives of ~enson et al., namely re-tarding color degradation and acid drift in the sulfonic acid after the latter has been formed. Sulfones are relatively colorless and do not affect the color of the sulfonic acid to any substantial degree.
SUM~ARY OF_THE INVENTION
In a sulfonation process in accordance with the present invention, an alkylated aromatic hydrocarbon is sulfonated with SO3 gas, the color of the sulfonic acid is improved, and the sulfuric acid content of the product resulting from the sulfonation reaction is reduced (thereby reducing the sodium sulfate content in the final sodium sulfonate product). These two improvements are accomplished by adding to the alkylated aromatic hydrocarbon a low molecular weight, anhydrous carboxylic acid such as acetic acid, benzoic acid or propionic acid. These are among the very acids which Benson et al. stated would not prevent color degradation when added to the sulfonic acid after the latter was formed.
In accordance with the present invention, these carboxylic acids are added to the alkylated aromatic hydrocarbon (e.g., alkyl ben~ene~ prior to the reaction thereof with the sulfur trioxide gas. The sulfur trioxide gas is the sole sulfonating agent used in the reaction.
; In addition to improving the color and reducing the amount of sulfuric acid formed, the addition of acetic acid, for example, to the alkylated hydrocarbon increases the active content (e.g., above 96.5%) and reduces the free ~L~3~Z~7 oil content (e.g., below 1.5~) of the sulfonation product.
The acetic acid addition prevents color degradation not only during the initial sulfonation reaction but also during the digestion period which normally follows the initial reaction period. This permits operating at a higher digestion temperature without degrading the color (e.g., 125-130F versus 115F maximum without acetic acid).
Operating at a higher diges-tion temperature in turn drives the reaction further toward completion, thus depleting the free oil content.
Typical sulfonation processing and operating conditions and procedures and a typical apparatus for sulfonating alkylated aromatic hydrocarbons useful in connection with an embodiment of the present invention are described in the copending application of the present applicant, No. 277,481 filed May 3, 1977.
In brief, in the sulfonation process of said application no. 277,481, the alkylated aromatic hydrocarbon is atomized and, in its atomized condition, reacted with the SO3 in a venturi-type reactor or venturi section.
The resulting reaction mixture is quenched~ in a quenching section immediately downstream of the venturij with a cooling liquid comprising cooled, recycled sulfonic acid, and the particles of liquid in the reaction mixture are agglomerated into the cooling liquid by flowing the particles between parallel streams of the cooling liquid.
At least part of the liquid, into which the liquid particles have been agglomerated, is cooled and recycled as the cooling ,.~,

3~

liquid, and the other part is withdrawn from the recycle loop and digested and neutralized.
Other features and advantages are inherent in the structure claimed and disclosed or will become apparent to those skilled in the art from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Flg. 1 is a fragmentary sectional view of an apparatus for sulfonating an alkylated aromatic hydrocarbon in accordance with an embodiment of the present invention;
and Fig. 2 is a flow diagram illustrating an embodiment of a method in accordance with the present invention.
DETAILED DESCRIPTION
The organic reactants to which the present invention is applicable are alkylated aromatic hydrocarbons with a side chain having 11 to 25 carbon atoms, 11 to 15 carbon atoms in the side chain being preferred. Examples of such hydrocarbons are alkyl benzene or alkyl toluene.
The sulfonating agent in accordance with the present invention is sulfur trioxide gas (SO3) in an air carrier, as more fully described in the abo~e-noted earlier n~ ~ ~7 ?, ~/~
application er~
The neutralizing agent for neutralizing the sulfonic acid formed from the reaction of the SO3 gas with the alkylated aromatic hydrocarbons is an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide or -ammonium hydroxide.
Examples of low molecular weight, anhydrous carboxylic acids which are useful in accordance with the ~3~

present invention for improving the color and reducing the sulfuric acid content of the sulfonic acid are acetic acid (the preferred material in most cases), benzoic acid, propionic acid, malonic acid, azelaic acid, butyric acid, valeric acid, cuproic acid and caprylic acid. Acetic acid is effective on both linear and branched chain alkyl benzene.
Propionic acid is slightly more effective on linear then on branched chain.
When acetic acid is neutralized, it forms, e.g., sodium acetate which is an acceptable ingredient sometimes intentionally added to cosmetic and detergent grade sulfonates as a buffering agent to prevent pH drift. Thus, the addition of acetic acid further upstream, to the organic reactant, does not introduce to the neutralized sulfonate end-product an unwanted ingredient.
The carboxylic acid should be added in an amount in the range 0.03-0.3% of the weight of the alkylated aromatic hydrocarbon (alkyl benzene) to which the carboxylic acid is added. Above 0.3% there is no significant improve-ment compared to 0.3%, although there is also no harm tousing amounts above 0.3%. A preferred range is 0.1-0~2%
when used with alkyl benzene.
Referring initially to Fig. l, indicated generally at 7 is a reactor including a venturi indicated generally at 8 and comprisin~, in downstream sequence, an upstream end 9, an approach zone 11 having side walls converging in a downstream direction, a throat 12, a recovery zone 13 having side walls diverging in a downstream direction and a down-stream end 10. A first conduit 16 communicates with venturi approach zone 11 and is axially aligned therewith. Conduit ~L~3~7 16 includes an inlet 17 extending to one side of conduit 16, and ports 18, 19 for inserting temperature and pressure measuring devices.
A second conduit indicated generally at 20 includes an upstream portion 21 communicating with downstream end 10 of venturi 8 and axially aligned with the venturi immediately downstream thereof.
Located concentrically within first conduit 16 is a third conduit 22 terminating at fluid injection means 23 located within venturi approach zone 11. Third conduit 22 includes an inlet 24 at the upstream end thereof.
Located concentrically within the upstream portion 21 of second conduit 20 is a fourth conduit 26 terminating at liquid outlet means 27 adjacent downstream end 10 of venturi 8. Outlet means 27 may extend into venturi recovery zone 13. Located at the opposite end of fourth conduit 26 is a liquid inlet 28.
Referring now to both Figs. 1 and 2, second conduit 20 has an outlet 29 communicating with one end of a line 30 having another end leading into a liquid cyclone separator 31. Communicating with the top of cyclone sepa- -rator 31 is a vent line 32, and communicating with the bottom of cyclone separator 31 is an outlet line 33 com-municating with a pump 3~ from which extends a line 35 leading to a heat exchanger 36 from which extends a line 37 leading to inlet 28 in faurth conduit 26.
~lso extending from pump outlet line 35 is another line 38 from which extends a branch line 39 leading back to cyclone separator 31.
First conduit 16, through which the gaseous ~33L%~

sulfonating agent is introduced into the venturi, preferably has a straight length of approximately 10 pipe diameters upstream of venturi 8. This is desirable to smooth out the flow and distribution of the gas, following movement of the gas around a curve or elbow or corner such as at inlet 17.
Injection means 23, through which liquid organic reactant is injected into the gas stream at venturi approach zone 11, usually comprises a plurality of small holes around the periphery of a tube perfectly centered within venturi approach zone 11 (although only one hole is shown in Fig.
1) .
In a -typical operation utilizing the reactor 7, gaseous sulfonating agent (sulfur trioxide gas plus air) is introduced through inlet 17 into first conduit 16. Si-multaneously, the alkylated aromatic hydrocarbon or liquid reactant is introduced through inlet 24 into third conduit 22. The anhydrous, low molecular weight carboxylic acid is added to the liquid hydrocarbon upstream of inlet 24.
The gaseous sulfonating agent flows downstream through conduit 16 into venturi approach zone 11, and the liquid organic reactant is injected into the stream of gaseous sulfonating agent in venturi approach zone 11 through injecting means 23.
Upon injection of the organic reactant into the gaseous sulfonating agent at approach zone 11, the organic reactant is atomized by the high speed gas into a fine mist which absorbs and reacts with the sulfur trioxide in the gaseous sulfonating agent. The reaction mixture thus formed continues to move through and out of the venturi 8 in a downstream direction.

~3~ 7 Atomization may also be accomplished by injecting the liquid organic reactant as a film at the periphery of the venturi (e.y., through a peripheral slit in the approach zone) and providing a gas velocity sufficiently high (e.g., 350 feet per second or higher) to assure atomization.
After leaving venturi 8, the reaction mixture is flowed along a confined pathr downstream of the venturi, defined by conduit 20. The reaction mixture is quenched, to cool the mixture, no later than immediately after the mixture leaves venturi 8. The reaction mixture, at the start of the quenching step, is in the form of fine par-ticles of liquid (including particles of sulfonic acid) in a gaseous carrying medium. In other words, the reaction mixture liquid is present as a discontinuous phase. Quenching is accomplished by contacting the reaction mixture with a moving volume or mass of cooled, recycled liquid reaction product comprising sulfonic acid and introduced into the reactor through fourth conduit 26 via outlet means 27 at the terminal end of conduit 26. In other words, the quenching liquid is provided as a continuous phase at outlet means 27.
A stream o~ cooled liquid reaction product contacts the reaction mixture at downstream end 10 of venturi 8 or slightly upstream thereof. The quenching liquid then flows through conduit 20 along a path coinciding with the flow path of the reaction mixture coming from the venturi, with the quenching liquid assuming the form of a film along the outside walls of fourth conduit 26 and a film along the inside walls o~ second conduit 20. The quenching liquid for the latter film may be introduced through a peripheral slit 40 in venturi recovery zone 13 supplied by a branch line 41 ~3~2~

communicating with recycle line 37.
By flowing the quenching liquid as a film along a path parallel to and adjacent that of the reaction mixture, there is provided repeated contact between the fine par-ticles of reaction product and the film of cooled liquid reaction product thereby causing the fine particles to agglomerate. A factor in the continuous contacting of the fine particles of liquid reaction product with the film of cooled liquid reaction product is the presence, in conduit 20, of gas eddies which repeatedly impinge the fine particles a~ainst the recycled quenching liquid flowing down the walls of conduits 20 and 26.
The mixture of liquid and spent gas leaves second conduit 20 through outlet 29 and flows through line 30 into cyclone separator 31 where the gas is separated from the liquid, the gas being withdrawn through vent line 32 and the liquid (consisting essentially of reaction product, i.e., sulfonic acid) being removed through line 33.
The effluent gas removed through vent line 32 has a lower sulfur dioxide content ~SO2 gas) when low molecular weight carboxylic acid is added to the liquid hydrocarbon in accordance with the present invention (e.g., 100-150 parts per million (ppm) versus 200-300 ppm without such an addition).
Reduced SO2 content in the effluent gas indicates a reduction in certain reactions which accompany poorer color. The addition of the low molecular weight carboxylic acid retards these reactions which form color bodies.
Part of the liquid removed from the bottom of cyclone separator 31 through line 33 is pumped by pump 34 through line 35 to heat exchanger 36 from which cooled ~3~4~
liquid reaction product is recycled through line 37 back to fourth conduit 26, as quenching liquid. Another part of the liquid removed Erom the bottom of cyclone separator 31 is pumped through a line 38 to additional processing stages including digestion and neutralization. A portion of the liquid reaction product moving through line 38 is recycled through branch line 39 back to cyclone separator 31 to wash the walls of cyclone separator 31 and prevent the buildup thereon of over-reacted material.
Only part of the reaction usually occurs in venturi 8. Additional reaction takes place in conduit 20, the recycle loop (30, 31, 33-37) illustrated in Fig. 2 and downstream thereof.
A more detailed discussion of the processing and operating conditions and procedures and apparatus described above is contained in Canadian application no. 277,481 referred to above.
Following is a summary of examples of typical operating conditions for the venturi and quenching sections.
Ven-tur-i Sect-ion Liquid organic reactant injection through multiple holes.

Actual gas velocity at liquid injection point --100 feet/second.

Actual gas velocity at venturi throat -- 400-550 feet/second.
Temperature at venturi throat -- 120-160F.
Pressure drop through venturi - 4-7 psig.

~31 3~

Quenching Section Actual gas velocity at upstream end -- 110 feet/second minimum.
~ctual gas velocity at downstream end -- 130 feet/second mlnimum.
Liquid to gas ratio, by weight -- 30/1.
by volume -- 1/25.
Recycle ratio [(a) recycled liquid to (b) organic reactant feed plus sulfur trioxide feed] -- 35/1.
Estimated film thickness -- 0.12-0.2".
Pressure drop -- 3-4 psig.
Calculated Reynolds No. of liquid film -- 100-200.
Follo~ing is an example of the processing conditions in a sulfonation process in accordance with the present in~ention (except for the addition of the carboxylic acid, examples of which are described subsequently).
Organic Reactant - Linear dodecyl benzene Organic Reactant Flow Rate - 600#~hr.
SO3 Flow Rate - 216#/hr.
SO3 Concentration - 6.5 vol. %
Air Flow Rate - 250 SCFM
Venturi Diameter at Throat - 1"
Reaction Path Length - 8"
Gas Pressure at Upstream End of Venturi - 10-13 PSIG
Pressure at Venturi Throat - 6 PSIG
Approximate Gas Velocity at Venturi Throat -550 Ft./Sec.
Approximate Gas Velocity at Organic Reactant Injection Point - 160 Ft./Sec.
Ratio of Recycle Quench to Reactants - 40 to 1 Quenching Liquid Temperature - 115F.

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Gas Velocity in Agglomeration Section -130 Ft./Sec.
Digestion Time Following Recycle Loop - 30 minutes As noted above, in accordance with the present invention, an anhydrous, low molecular weight carboxylic acid is added to the alkylated aromatic hydrocarbon prior to the reaction thereof with the sulfur trioxide gas, and examples comparing (a) the present invention, utilizing said carboxylic acid addition, and (b) a process otherwise the same except for the absence of said carboxylic acid addition are listed in the following table.

7.

TABLE I

Example No. 1 2 3 Mol ratio of SO3 1.06 1.04 1.04 to linear alkyl benzene Acetic acid -- 0.1% 0.25%
addition (alkyl benzene weight basis) Free oil, 1.8% 1.0% 0.7%
petroleum ether ; extract procedure (active ingredient basis) _ ; Na2S 4 2.5% 2.0% 1~5%

Klett color 35-40 30 30 (5% solution, ; 40 mm. path) From the table it will be noted that there is an improvement in color, up to 25%, when comparing a process with a carboxylic acid addition in accordance with the present invention (Examples 2-3) with a process in which there was no such addition. In addition, in a process in accordance with the present invention, there is a reduction in sodium sulfate content, in the sodium sulfonate product, of up to 40%, this being a reflection of a reduction of the sulfuric acid produced as a side reaction product in the sulfonation reaction of the alkyl benzene. Moreover, the sodium sulfate content is reduced by 20% and 40% respectively in Examples 2 and 3 while the mol ratio of SO3 to alkyl benzene was reduced less than 2%. The free oil contents in Examples 2 and 3 are reduced to 55% and 38% respectively of that in Example 1.
Additional Examples 4-6 are reflected in the following table. Standard operating conditions were employed using a sulfonating process of the type described above and illustrated in Fig. 2. The organic reactant employed was an alkyl benzene having a molecular weight of 238. Examples 5 and 6 employed acetic acid while Example 4 did not. Example 5 reflects a liquid detergent formulation while Example 6 reflects a powder deter~ent formulation.
TABLE II

Example_No. 4 5 6_ Mol ratio of SO3 l.G5-1.06 1.02-1.03 1.04-1.06 to alkyl benzene SO3 concentrate 7-8% 7-8% 7-8%

(volume %) .
Temperature of 110-115F 100-110F 115-130F

recycle liquid ,, .

Acetic acid -- 0.1% 0.1-0.4%
addition (alkyl benzene weight basis Active ingredient 95.5-96.0% 97.0-97.5% 96.8-97.2%
wt. % (Hyamine titration procedure) Free oil, 1.8-2.0% 1.0-1.3% 0.5-0.7%
petroleum ether extract procedure (active ingredient basis) Sulfuric acid 2.0-2.2% 1.3-1.5% 1~5-2.2%
(before neutraliæation) wt. %

Water, wt. % 0.1-0.2% 0.1-0.2% 0.1-0.2%

_ Klett color (5% 40-50 20-30 35-50 solution, 40 mm path) -30Comparing Examples 4 and 5, it is seen that adding aeetie aeid (Example 5) inereases the active ingredient ~3~

content even wlth a reduced mol ratio of SO3, decreases the free oil content, decreases the sulfuric acid content and improves the color. Comparing Examples 4 and 6, it is seen that, at recycle liquid (digestion) temperatures above 115F, with an acetic acid addition there is no color degradation while improvements in active ingredient and free oil content are substantial.
Thus, an acetic acid addition in accordance with the present invention permits greater flexibility in the operating conditions of the sulfonating process. It allows a higher digestion temperature without adversely affecting color, or it allows a lower mol ratio of SO3 to hydrocarbon reactant without decreasing the amount of active ingredient formed or increasing the amount of free oil; and it forms a product of improved color, with less sulfuric acid, less free oil and more active ingredient with less SO3 required to perform the reaction.
The foregoing examples of the process have been described in connection with a jet reactor (Fig. 1) for performing the sulfonation operation, but the present invention is not limited to jet reactors and may also be useful with other types of reactors (e.g., film reactors) as are conventional in the sul~onation of organic reactants with SO3.
The foregoing detailed description has been given for clearness of understand only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. In a process wherein an alkylated aromatic hydrocarbon with a side chain having 11 to 25 carbon atoms is reacted with a sulfonating agent to form sulfonic acid and spent gas and said sulfonic acid is separated from said spent gas and neutralized with an alkali metal hydroxide to form a product comprising an alkali metal sulfonate, with the corresponding alkali metal sulfate as a by-product, a method for improving the color of said product, said method comprising the steps of:
providing sulfur trioxide gas as the sole sulfonating agent;
initiating contact between said alkylated aromatic hydrocarbon and said sulfonating agent at a predetermined location without further introduction of the sulfonating agent downstream of said predetermined location;
and preventing a substantial increase in the sulfur dioxide content of said spent gas by adding 0.03-0.3 wt.%
of a low molecular weight, anhydrous carboxylic acid to said hydrocarbon before the reaction thereof with said sulfur trioxide gas.

2. In a process as recited in Claim 1 wherein:
the amount of said low molecular weight carboxylic acid added is 0.1-0.2 wt.%.

3. In a process as recited in Claim 1 wherein:
said low molecular weight carboxylic acid comprises at least one of the group comprising acetic acid, benzoic acid, propionic acid, malonic acid, azelaic acid, butyric acid, valeric acid, cuproic acid, and caprylic acid.

4. In a process as recited in Claim 1 wherein:
said alkylated aromatic hydrocarbon is alkyl ben-zene or alkyl toluene.

5. In a process as recited in Claim 1 wherein:
said alkylated aromatic hydrocarbon has a side chain with 11-15 carbon atoms.

6. In a process as recited in Claim 1 wherein:
the alkali metal sulfate content of said product is reduced by said method.

7. In a process as recited in Claim 6 wherein:
said alkali metal sulfate content is reduced by at least 20%.

8. In a process as recited in Claim 1 and further comprising the steps of:
atomizing said alkylated aromatic hydrocarbon;
reacting said hydrocarbon with said sulfur trioxide gas when the hydrocarbon is in said atomized condition to form a reaction mixture comprising liquid particles of said sulfonic acid quenching said reaction mixture with a quenching liquid comprising cooled, recycled sulfonic acid;
agglomerating said liquid particles of sulfonic acid into said quenching liquid;
and cooling and recycling, as said quenching liquid, at least part of the liquid into which said particles of sulfonic acid have been agglomerated.

9. In a process as recited in Claim 8 wherein:
said sulfonic acid undergoes digestion before it is neutralized, said digestion being conducted at a tem-perature greater than 115°F up to about 130°F;
and said sulfonic acid has a Klett color no greater than 50.

10. In a process as recited in Claim 1 wherein the active ingredient content is increased by said method to greater than 96.5% (hyamine titration procedure) and the free oil content is reduced to less than 1.5% (petroleum ether extract procedure).

11. In a process as recited in Claim 1 wherein said sulfonic acid has a Klett color of 20-30.

12. In a process as recited in claim 1 wherein:
said adding step prevents a substantial increase in sulfur dioxide content above about 150 ppm.

13. In a process as recited in Claim 12 wherein:
said adding step prevents an increase in sulfur dioxide content into the range 200-300 ppm and provides a sulfur dioxide content in the range of about 100-150 ppm.