JPH06154610A - Catalyst for residual oil having high metal content, method for its production and process for its use - Google Patents

Abstract

PURPOSE: To obtain a catalyst composition having improved catalytic service life and metal removing ability for the hydrodesulfurization of metal-containing heavy oil feedstock by using a carrier having a prescribed pore volume, a prescribed grain density and a specified pore distribution. CONSTITUTION: The catalyst composition has an alumina carrier and groups VIB and VIII components selected from the group consisting of metals, oxides and sulfides of groups VIB and VIII elements. The carrier has about 0.5-1.1 cm<3> /g pore volume, a grain density of <1.0 and a pore distribution in which pores having 110-190 Ådiameter account for at least 70% of the total pore volume, pores having >=500 Å diameter account for <5% and <2% of the pores have >=1,000 Å pore diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst carrier, a hydrocarbon desulfurization catalyst produced using this carrier, and a method for hydrodesulfurizing a hydrocarbon feedstock using the above catalyst.
More specifically, the present invention is a porous material which is substantially free of macropores (those having a diameter of 1000 Å or more) and which contains at least one type 6B and 8 group metal and / or metal compound. It relates to the production of catalysts. More specifically, the present invention provides an alumina-based carrier that is substantially free of macropores, has a specific pore size distribution, and contains the aforementioned metals and / or metal compounds. Relates to a catalyst to be included. The invention also relates to a hydrocarbon hydrodesulfurization process using the catalyst.

It is well known that there is an urgent need to desulfurize the hydrocarbons obtained from petroleum processing processes. When such oils are burned as fuel in the usual way, the sulfur present in the hydrocarbons becomes a significant pollutant in the atmosphere in the form of sulfur oxide gases.

Typical operating conditions for the hydrodesulfurization process are: reaction zone temperature 600 ° F to 900 ° F, pressure 2
Includes catalysts such as nickel or cobalt and molybdenum or tungsten supported on a porous refractory support at 0 to 3000 psig, a hydrogen feed rate of 500 to 15000 SCF per feed barrel.

[0004]

BACKGROUND OF THE INVENTION The problems that have been recognized in the case of hydrodesulfurization of heavy oils are that, especially when the heavy oils contain organometallic compounds, impurities such as dissolved nickel and dissolved vanadium. It means that the effective catalytic activity decreases relatively rapidly when the content of such metals is about 10 to 20 ppm or more. These metal impurities are said to deposit on the surface of the hydrodesulfurization catalyst and in its pores.

One of the approaches to this problem, that is, the problem of deactivation of hydrodesulfurization catalysts due to metallic impurities, has been to change the pore structure of the catalyst. However, the answer to the question of what kind of pore structure is best has not been easily obtained, and in fact, there are some inconsistencies in the solutions suggested by the conventional technology. is there. U.S. Pat. No. 4,066,574, 4,
Nos. 113,661 and 4,341,625 are referred to below as the Tamm '574 patent and the Tam', respectively.
No. 661 patent and Tam '625 patent, the disclosures of which are incorporated herein by reference in their entirety, but in these patent specifications, contradictions in the art are discussed, and the solution is also Has been suggested.

According to the disclosure of the Tam patent, metal-containing heavy oil feedstocks, especially residual oil feedstocks, contain alumina containing at least 70% of the pore volume of the carrier having pores having a diameter of 80-150Å. It is hydrodesulfurized using a catalyst prepared by impregnating a support with Group 6B and Group 8 metals or metal compounds. A hydrodesulfurization catalyst that is particularly excellent in that it has an extremely low deactivation rate can be obtained by using an alumina carrier having the above pore size distribution.

In the Tam '661 patent, the catalyst is 50
It is produced by using a main component of alpha-alumina monohydrate having a size in the range of 0 micron or less and treating it with a specific amount of a monobasic acid. The acid and the resulting mixture are then at least partially neutralized by combining with an aqueous solution of a nitrogenous base such as an aqueous ammonia solution. The solution contains 0.6 to 1.2 equivalents of base per equivalent of acid. The treated and neutralized product is converted to the catalyst support by shaping, drying and calcining as desired. Finally, the catalyst support is impregnated with the metals mentioned above.

It would be advantageous if the catalysts and processes of the Tam '574 patent, the Tam' 661 patent, and the Tam '625 patent could be improved to give catalysts used for residual oil treatment a longer life. .

[0009]

The present invention is summarized. According to the present invention, there is provided a process for hydrodesulfurizing a metal-containing hydrocarbon feedstock, wherein the feedstock is at least 70% of the pore volume of the carrier under hydrogenation conditions of at least 70%.
Contacting with a catalyst prepared by impregnating an alumina-containing support having pores having a diameter of 0 to 190Å with a Group 6B and Group 8 metal or metal compound.
The total pore volume of this carrier is about 0.5 to about 1.1 cm ³ / g.
, Less than 5% of this pore volume is occupied by pores having a diameter of 500 Å or more, and 2% of this pore volume.
Less than 1% is occupied by pores having a diameter of 1000Å or more.

The present invention is based on the discovery that a catalyst with unexpectedly long life can be obtained by slightly changing the pore size distribution. In another aspect of the present invention, a clear pore distribution is obtained by improving the method of making the catalyst support. In particular, the carrier is treated in the following step: (a) about 3.0-4.5 by mixing a peptizable granular solid containing alpha-alumina monohydrate as a major component with an acidic aqueous solution. Treating the solid to a pH in the range of: (b) an aqueous solution of a nitrogenous base containing an amount of base in the range of about 0.6 to 1.0 equivalents per equivalent of the acid treated as above. Neutralizing at least a portion of the mixed acid by blending into a solid; (c) shaping the neutralized or partially neutralized solid; and (d) about Drying the molded solid at a temperature in the range of 150 ° F to 1700 ° F and calcining to complete the carrier. Manufactured by.

In another aspect of the invention, the peptizing acid nitrogen during reverse neutralization is used to produce larger pore catalysts having higher metal capacities than prior art catalysts during residual oil conversion. Increasing the number of base equivalents and also raising the calcination temperature. This is particularly useful for feedstocks with relatively high metal content.

The preferred embodiment of the present invention will be described in detail.
The contact process of the present invention is basically applied to a residual oil feedstock different from a gas oil feedstock. Residual oils typically contain more than 10 ppm metal, while light oils usually have less than 10 ppm metal. Therefore, a typical raw material of the present invention is a bottom oil of a crude oil atmospheric distillation column (reduced crude oil or atmospheric tower residual oil) or a bottom oil of a vacuum distillation column (vacuum residual oil). The metal is believed to be present as an organometallic compound, presumably in a porphyrin or chelate type structure, but the concentration of the metal referred to herein is to be calculated as ppm of pure metal. To do.

Alumina is the preferred support material for the catalyst used in the process of the present invention, although alumina may be combined with other refractory support materials such as silica and magnesia.

The alpha-alumina monohydrate preferably used in the present invention is commercially available from many commercial sources such as Catapal.
Commercially available from (Catapal) or Versal. This material can also be prepared as described in the Tam '661 patent.

The alumina-containing support material must have the aforementioned pore size distribution in order to produce a catalyst that meets the requirements of the present invention. The pore size distribution for the alumina support used to form the final catalyst is substantially the same as the pore size distribution of the final catalyst. This is because there is almost no change in the pore size distribution when the carrier is impregnated with the Group 6B or Group 8 metal compound. Relatively pure alumina is spray dried
It is available as amorphous or crystalline hydrate powder from several sources. These materials are suitable for extrusion with mixing with water after the addition of molding aids. Two commonly used auxiliaries are strong mineral acids or combustible organic lubricants. When the former is used, a high-density extrusion molded product is usually obtained, and when the latter is used, a pore size distribution containing a considerable micropore volume is obtained, so that the residual oil hydrodesulfurization catalyst of the present invention can be obtained. Not acceptable for carriers. In the Tam patent cited herein above,
A method is disclosed in which such materials can be used to obtain medium to low density alumina having a pore volume of greater than 97%, usually greater than 99% in the micropore region. This is in the range of pore sizes less than about 500Å.

In the present invention, the process of the Tam patent is improved by a special method of improving the manufacturing method, in which the pore size distribution is such that 70% of the pore volume is pores having a diameter of 80 to 150Å. Therefore, 70% of the pore volume is 110
It is intended to shift to a pore size distribution which is a pore having a particle size of ˜190Å. As pointed out in the Tam '661 patent, the acid-treated solid particulate alumina monohydrate has a base amount in the range of about 0.6 to 1.2 equivalents per equivalent of previously added acid. It is partially neutralized by combining the aqueous solution of the nitrogenous base it contains with the acid-treated solids. This process is sometimes known as "back titration". About 0.6 to 1. per equivalent of the previously added acid.
It is an aspect of this invention to perform this back titration using an aqueous solution of a nitrogenous base containing an amount of base in the range of 2 equivalents.

In order to produce an alumina support or carrier having the pore size distribution required by the present invention, the alumina should be a suitable monobasic acid, preferably nitric acid, or as described in (Tamm Patent '661). Must be treated with the corresponding acids, such as hydrochloric acid, hydrofluoric acid and hydrobromic acid.

It has been recognized that acid-treated alumina is satisfactory for producing a final support that is substantially free of macropores. However, this is unsatisfactory for producing a catalyst support having a pore volume suitable for use in producing a residual oil desulfurization catalyst. A satisfactory residual oil desulfurization catalyst support and catalyst itself should be at least about 0.5 cc /
It should have a pore volume of g, preferably at least about 0.65 cc / g. Generally, as long as the distribution of micropores and the content of macropores are satisfied, the higher the pore volume ratio, the longer the life of the catalyst. In order to achieve a useful pore volume and provide the suitable pore distribution needed for the final support and catalyst,
A significant portion of the mixed acid in the processed raw material is
It must be neutralized with a nitrogenous base which is thoroughly mixed into the raw material by vigorous stirring.

As used herein, "nitrogen base" refers to the formula: R ₃ N and the corresponding hydroxyl group R ₃ HNOH.
(Wherein the R groups are the same or different and are hydrogen and 1-3
Selected from the group consisting of alkyl groups having 1 carbon atom). Aqueous ammonia solution is preferred.

The prior art recommends that "generally at least about 0.6 equivalents of base are required for each equivalent of acid used in the treatment". The assertion of the prior art is that the use of relatively large amounts of base for neutralization, to some point, becomes increasingly advantageous. After that point it is undesirable to use a relatively large amount of base. According to the Tam '661 patent, excellent results are generally obtained for the final carrier when the relative amount of base in aqueous solution per equivalent of acid is in the range of about 0.6 to 1.2, and this ratio is about At 1.6, the carrier obtained is usually unsatisfactory.

What has been found during the present invention is that in order to obtain an improved highly active residual oil catalyst, the relative amount of base in the neutralized aqueous solution per equivalent of acid is It should be in the range of about 0.6 to 1.0 equivalents, preferably more than about 0.55.

The properties of the mixture resulting from the neutralization of the treated alumina vary according to its volatile content.
The mixture can be a flowable solid or a viscous paste. In the preferred form required for use as a raw material for extrusion molding,
This mixture is a flowable solid with a volatile content in the range of 50 to 70% by weight. As used herein, the term “volatile component” refers to a substance that volatilizes at elevated temperatures of 900 ° F. and above. Various molding methods may be used to form the catalyst support precursor from the treated and neutralized solids. This molding is preferably performed by extrusion molding. In the manufacture of the final carrier, the drying and calcination steps of the method of the invention are generally carried out at temperatures in the range of about 150 ° F to 1700 ° F. Drying process is typically about 150 ° F
˜500 ° F., with this drying followed by calcination at about 500 ° F. to 1700 ° F., preferably 10 ° F.
It is carried out in a dry or wet atmosphere at temperatures in the range of 50 ° F to 1700 ° F, most preferably above 1500 ° F.

According to the method of the present invention, a method for producing a medium- to low-density alumina-based catalyst carrier is obtained, which carrier preferably has a pore volume in the micropore region of about about 3. Have a volume greater than 98%, and especially 1
Pores having a pore size in the range of 10 to 190Å have at least 70% of the total pore volume, pores having a diameter of 500Å or greater have less than 5% of the total pore volume, and 1000
It has less than 2% of pores having a pore diameter of Å or more. Table 1 shows a typical distribution of pore volume between the pore sizes in the prior art catalysts described in the Tam '661,' 574 and '625 patents. Table 2 shows a typical pore volume distribution between the pore sizes of the catalyst of the present invention.

The pore volume described in this specification is the volume of the liquid adsorbed to the pore structure of the sample at the saturated vapor pressure, and the adsorbed liquid has the same density as the initial density of the liquid. I'm assuming. The liquid used for this analysis is liquid nitrogen. The procedure for measuring the pore volume by physical adsorption of nitrogen is described by DH Everett and Stone (F.
S. Stone) disclosed in more detail (Academic Press, Bristol, UK, March 1958)
ess) Published Proceedings of the Tenth Symposium of t
he Colstrom Research Society, pp. 109-110).

[0025]

[Table 1] Table 1 Pore size Cumulative pore volume Pore volume (estimated) (Å) (%) (cc / g) 1000.00 0.009 0.0001 900.00 0.029 0.0002 800.00 0.065 0.0005 700.00 0.119 0.0010 600.00 0.192 0.0015 500.00 0.295 0.0024 400.00 0.410 0.0033 300.00 0.717 0.0058 250.00 1.021 0.0082 240.00 1.111 0.0090 230.00 1.230 0.0099 220.00 1.436 0.0116 210.00 1.705 0.0137 200.00 2.129 0.0172 190.00 2.680 0.0216 180.00 3.548 0.0286 170.00 6.088 0.0491 160.00 12.180 0.0982 150.00 23.636 0.1905 140.00 39.950 0.3220

[Table 2] Table 1 (continued) Pore size Cumulative pore volume Pore volume (estimated) (Å) (%) (cc / g) 130.00 57.483 0.4634 120.00 71.144 0.5735 110.00 80.589 0.6496 100.00 87.513 0.7054 95.00 90.229 0.7273 90.00 92.480 0.7455 85.00 94.451 0.7614 80.00 96.096 0.7746 75.00 97.430 0.7854 70.00 98.426 0.7934 65.00 99.166 0.7994 60.00 99.708 0.8038 55.00 100.146 0.8073 50.00 100.430 0.8096 45.00 100.564 0.8107 40.00 100.640 0.8113 35.00 100.686 0.8116 30.00 100.535 0.8104 25.00 100.359 0.8090

[0026]

[Table 3] Table 2 Pore size Cumulative pore volume Pore volume (estimate) (Å) (%) (cc / g) 1000.00 0.007 0.0001 900.00 0.032 0.0003 800.00 0.090 0.0008 700.00 0.173 0.0015 600.00 0.254 0.0022 500.00 0.387 0.0034 400.00 0.595 0.0052 300.00 1.052 0.0092 250.00 1.621 0.0142 240.00 1.818 0.0159 230.00 2.063 0.0180 220.00 2.439 0.0213 210.00 2.900 0.0253 200.00 3.797 0.0332 190.00 6.357 0.0556 180.00 12.723 0.1112 170.00 26.368 0.2304 160.00 44.063 0.3850 150.00 58.600 0.5121 140.00 69.041 0.6033 130.00 77.690 0.6789 120.00 90.84.781 0.7408 0.8225

[Table 4] Table 2 (continued) Pore size Cumulative pore volume Pore volume (estimated) (Å) (%) (cc / g) 95.00 95.594 0.8353 90.00 96.870 0.8465 85.00 97.970 0.8561 80.00 98.831 0.8636 75.00 99.476 0.8692 70.00 99.970 0.8736 65.00 100.311 0.8765 60.00 100.551 0.8786 55.00 100.722 0.8801 50.00 100.808 0.8809 45.00 100.829 0.8811 40.00 100.779 0.8806 35.00 100.688 0.8798 30.00 100.547 0.8786 25.00 100.338 0.8768

The hydrocarbon hydrodesulfurization catalyst of the present invention contains at least one hydrogenating agent, and preferably contains a combination of two kinds of such hydrogenating agents. Metals and / or metal compounds of the elements Group 6B (especially molybdenum and tungsten) and Group 8 (especially cobalt and nickel), especially sulphides and oxides, are generally satisfactory catalyst agents and are prepared by the process of the invention. , Shall be used for a carrier substantially free of macropores. A combination of cobalt, nickel and molybdenum catalysts is preferred.

The catalyst agent required for the catalyst composition of the present invention can be supported on the calcined carrier by a suitable method, in particular, an impregnation method generally used in the catalyst manufacturing art. Not only does the alumina used have the pore size distribution required for the present invention, but it is also possible to catalyze the catalyst in a one-step impregnation process of alumina using a solution of a cobalt salt or nickel salt and a heteropolymolybdic acid such as phosphomolybdic acid. A particularly good catalyst is produced when produced.

[0029]

EXAMPLES The method for producing the catalyst of the present invention will be described below with reference to examples. Example A Preparation of catalyst carrier Alumina raw material consisting of 60% of catapal alumina and 40% of Versal 250 alumina was peptized with 7.6% nitric acid and reverse neutralized with 71% ammonium hydroxide. % Present. In detail, 1260 g of Catapal and Versal 8 on the basis of not including volatile components.
40 g was maintained at a temperature of 130 ° F-140 ° F and mixed together with 228 g of concentrated nitric acid and 1515 g of deionized water at a rate of about 150 cc / min in the mixer for 15 minutes or until pasty. 109 g of concentrated ammonium hydroxide (58% by weight ammonium hydroxide) was added to deionized water 109
Mix with 0 g and add to the mixer at a rate of about 150 cc / min, then mix for an additional 15 minutes. The content of volatile components was 63.6% by weight. The temperature of the resulting paste is 1
It was 44 ° F. This paste was extrusion molded in a 2 inch extrusion machine using a 0.039 inch cylindrical die. Air dry the extrudate, and 2
Heated in oven at 250 ° F for time. Then another 2
Heated at 400 ° F for hours. Recovered weight is 1,95
It was 8 g. The dried extrudate is 1500
Calcination was carried out for 1 hour at ° F and dry air at an air velocity of 1 cubic foot / hour. The obtained particles had the following properties. That is, particle diameter: 0.0322 inch; particle density: 0.8730 g / cc; total pore volume: 0.
8046 cc / g; surface area: 180 m ² / g. The support material was then impregnated with nickel and molybdenum by the following procedure.
A mixture of molybdenum oxide dissolved in ammonium hydroxide was acidified with phosphoric acid to pH 3.53 and more nickel nitrate hexahydrate was added to a final pH of 2.55. The resulting catalyst was dried at 250 ° F for 2 hours and 400 ° F for 6 hours. Then dry air at 20 ft / hr for 4 hours at 450 ° F, 4 hours at 750 ° F, and 9 more
It was calcined at 50 ° F for 5 hours. The final finished catalyst contained 8.12 wt% molybdenum, 2.91 wt% nickel, and 1.79 wt% phosphorus. The median pore size was 154 Å, which was greater than the prior art catalysts. The surface area was 154 m ² / g. See FIG.

Example B The catalyst of Example A was tested in a standard life test in the same manner as in the prior art catalyst (Table 1 and FIG. 2-Tamm '574 patent,'
625 patent, '661 patent). In this test, a desulfurization conversion catalyst was loaded under a bed of standard commercial demetallization catalyst and both catalysts were pre-sulphurized with dimethyl disulfide. Then 650 ° F + Maya 35% by weight and 72
0.46 LHSV and a total pressure of 2 with the blended raw material containing 0 ° F + 65% by weight of Arabian heavy residual oil and this two-layer catalyst system.
It was contacted under the condition of hydrogen circulation rate of 5000 SCF / bbl under 200 psig. The hydrogen partial pressure was maintained above 1800 psig by using a controlled withdrawal stream for the recycle stream. The reaction temperature is based on the MCR content of the raw material and the MCR conversion rate is 5
It was controlled to maintain 5%. Residual fine carbon (MCR) is A
It is defined in STM D4530-85. The test run was over when the required reaction temperature exceeded 800 ° F. and the catalyst was considered completely fouled. Figure 3 shows MCR conversion 55
Indicates the temperature required to maintain the%. According to the results shown in FIG. 3, the catalyst of the present invention maintained useful activity for a significantly longer period than the reference catalyst.

[Brief description of drawings]

FIG. 1 is a diagram showing a pore size distribution of a catalyst of the present invention.

FIG. 2 is a diagram showing a pore size distribution of a conventional catalyst.

[Figure 3] Maya atmospheric residual oil 1/3 (by weight) and Arabian
A diagram showing the temperature required to maintain a residual fine carbon (MCR) of 55% by supplying a mixture of heavy atmospheric residual oil 2/3 (weight) at 0.46 liquid space velocity (LHSV). is there.

Claims (13)

[Claims] 1. A catalyst composition having improved demetallization capability in hydrodesulfurization of heavy oils, comprising: an alumina support, and a group consisting of metals, oxides and sulfides of Group 6B and Group 8 elements. A catalyst composition comprising a Group 6B component and a Group 8 component selected from: wherein the support has a pore volume in the range of about 0.5 to about 1.1 cm ³ / g, particles less than 1.0. Pores having a density and having a diameter of 110 to 190Å occupy at least 70% of the pore volume, pores having a diameter of 500 Å or more occupy less than 5% of the pore volume, and The catalyst composition, wherein less than 2% has a pore size of 1000Å or more. 2. A porous support is impregnated with an aqueous solution containing at least one catalyst agent or catalyst agent precursor selected from the group consisting of Group 6B and Group 8 compounds, the compound being thermally decomposable to a metal oxide. And impregnating the resulting impregnated support after impregnation, and calcining.
A method for producing a catalyst having improved demetallization capacity in hydrodesulfurization of heavy oil, the carrier comprising: (a) a peptizable granular solid comprising alpha-alumina monohydrate as a main component. Treating the solids to a pH in the range of about 3.0 to 4.5 by combining the acid with an acidic aqueous solution; (b) in the range of about 0.6 to 1.0 equivalents per equivalent of the acid. Neutralizing at least a portion of the combined acid by mixing an aqueous solution of a nitrogenous base containing a base amount to the treated solid; (c) neutralizing or partially medium Forming the hydrated solid; and (d) drying the formed solid at a temperature in the range of about 150 ° F to 1700 ° F and calcining to complete the carrier. And the carrier is 100
110% to 190% of the pores having a pore size of 0Å or more are less than 2% and the carrier has a pore volume of at least 0.5.
Improved demetallization catalyst wherein pores having a pore diameter in the range of Å make up at least 70% of the pore volume and pores having a diameter of 500 Å or more make up less than 5% of the pore volume. Manufacturing method. 3. A heavy oil under hydrodesulfurization conditions, (a) an alumina support, and (b) a 6B group selected from the group consisting of metals, oxides and sulfides of 6B and 8 elements. a hydrodesulfurization process of heavy oil comprising contacting the catalyst with the components and improved metal capabilities include 8-group component, wherein the support is about 0.5 to about 1.1 cm ³ Pore volume in the range of / g, with a particle density of less than 1.0, and a diameter of 1
Pores having a diameter of 10 to 190Å account for at least 70% of the pore volume, pores having a diameter of 500Å or more account for less than 5% of the pore volume, and less than 2% of the pores account for 1%.
The heavy oil hydrodesulfurization process having a pore size of 000 Å or more. 4. The carrier has a diameter of 110 to 190Å
The catalyst, method or process according to claim 1, 2 or 3, wherein the pores having occupy at least 80% of the pore volume. 5. The catalyst, method or process of claim 1, 2 or 3 wherein said catalyst is selected from the group consisting of cobalt, nickel and molybdenum where the Group 6B and 8 compounds are. 6. The catalyst, method or process according to claim 1, 2 or 3, wherein less than 5% of the pore volume is pores having a diameter greater than 220Å. 7. The catalyst, method or process according to claim 1, 2 or 3, wherein pores having a diameter of 1000 Å or more occupy less than 1% of the pore volume. 8. The method of claim 2 wherein the acidic solution is selected from the acidic solutions of nitric acid, hydrochloric acid, hydrofluoric acid and hydrobromic acid. 9. The method of claim 2, wherein the alpha alumina monohydrate is sized to a range of about 500 microns or less. 10. The nitrogenous base has the formula: R ₃ N or R ₃ HNOH.
(Wherein all groups are the same or different, hydrogen and 1
3. The method according to claim 2, having from 3 to 4 carbon atoms selected from the group consisting of alkyl groups having 3 carbon atoms. 11. The method according to claim 2, wherein said aqueous solution is a solution of cobalt or nickel and heteropolymolybdic acid, and said impregnation is carried out in a one-step process. 12. The catalyst comprises nickel and molybdenum in amounts of about 3 and 9% by weight, respectively.
The catalyst, method or process according to 2 or 3. 13. The method of claim 2 wherein said solution of nitrogenous base contains less than about 0.95 equivalents of base per equivalent of said acid.