CN109207192B

CN109207192B - Adsorption desulfurization method for catalytically cracked gasoline

Info

Publication number: CN109207192B
Application number: CN201811347239.0A
Authority: CN
Inventors: 陈开龙; 庄琴珠
Original assignee: Shanghai Youhao Technology Co ltd
Current assignee: SHANGHAI YOUHAO TECHNOLOGY Co.,Ltd.
Priority date: 2018-11-13
Filing date: 2018-11-13
Publication date: 2020-12-18
Anticipated expiration: 2038-11-13
Also published as: CN109207192A

Abstract

The invention relates to an adsorption desulfurization method of catalytic cracking gasoline, which adopts a fixed bed reactor, wherein the gasoline is contacted with an adsorption desulfurization catalyst, and the catalyst comprises the following components in percentage by weight: 25.0-50.0 wt% of zinc oxide, 0.5-25.0 wt% of nickel oxide, 2.0-55.0 wt% of ZSM-5 molecular sieve, 20.0-50.0 wt% of macroporous alumina and 1.0-25.0 wt% of cerium-zirconium solid solution; the reaction process conditions are as follows: the reaction temperature is 280 ℃ and 400 ℃, the reaction pressure is 0.4-2.5MPa, and the volume space velocity is 3-8h^‑1The volume ratio of hydrogen to oil is 1-50. The catalyst has high sulfur penetration capacity, small octane value loss and good regeneration and reduction stability.

Description

Adsorption desulfurization method for catalytically cracked gasoline

Technical Field

The invention relates to an adsorption desulfurization method for catalytically cracked gasoline.

Background

The gasoline adsorption desulfurization technology becomes an important means for upgrading the quality of oil products, and the technology has the characteristics of high sulfur selectivity, small octane value loss and low investment and operation cost. Most of the existing adsorbents are desulfurization adsorbents prepared by using a silicon/aluminum material as a carrier and zinc oxide/active metal (such as nickel) as an active component, and the adsorption activity is reduced due to the formation of carbon deposit, zinc sulfide, zinc silicate and zinc aluminate in the reaction process, so that the regeneration reduction is needed to recover the activity of the adsorbent. The octane number loss is large due to the occurrence of olefin saturation.

The existing gasoline adsorption desulfurization method mainly comprises the following steps: (1) and (3) desulfurization treatment: mixing and contacting sulfur-containing hydrocarbon and hydrogen donor with an adsorbent to obtain desulfurized sulfur-containing hydrocarbon and a sulfur-carrying spent catalyst; (2) regeneration treatment: mixing and contacting the sulfur-carrying spent regenerant with oxygen-containing regeneration gas to obtain a regenerant; (3) reduction treatment: mixing and contacting the regenerant with a reducing gas to obtain a reducing regenerant which is recycled as an adsorbent; and refluxing the reduction regenerant obtained in the step (3) as an adsorbent to the step (1) to form an adsorbent circulating flow path. With continuous cyclic reduction and regeneration of the adsorbent, the adsorbent often has the problems of fragmentation (strength reduction) and activity reduction, and further the desulfurization efficiency is reduced.

CN103657709A discloses a reactive adsorption desulfurization-aromatization reaction process and a catalyst thereof. The catalyst not only has the function of reaction adsorption desulfurization when the catalytic cracking gasoline raw material is hydrotreated, but also can be coupled with the reaction adsorption desulfurization reaction and the aromatization reaction, so that the octane number of the product is not obviously reduced while deep desulfurization can be achieved when the developed process and the catalyst thereof modify the catalytic cracking gasoline raw material. The FCC gasoline with the sulfur content of 300-800ppm is used as the raw material, the S content of the product gasoline is less than 10ppm, the olefin content is reduced by 10 percent, the RON loss is less than 1, and the gasoline yield is more than 95 percent. CN101905161A relates to a catalytic gasoline adsorption desulfurization catalyst and preparation and application thereof; the weight percentage composition is as follows: 10-85% of active zinc oxide, 5-80% of white carbon black, 5-30% of alumina and 4-45% of nickel oxide; (1) carrying out pyrolysis on titanium tetrachloride at 1400 ℃ under hydrogen atmosphere to obtain fumed silica; (2) mixing active zinc oxide, fumed silica, alumina and nickel salt uniformly to form slurry; (3) spraying the mixture into balls or injecting oil into balls; (4) drying the particles in the step (3), wherein the drying temperature is 110-150 ℃; (5) roasting the microspheres obtained in the step (4) at the roasting temperature of 300-550 ℃; the prepared adsorption desulfurization catalyst has the advantages of good strength, high wear resistance, good desulfurization activity, small octane number loss and low operation cost, and is very suitable for a moving bed adsorption desulfurization process.

CN108018069A discloses a sulfur-containing hydrocarbon adsorption desulfurization method and device, the method comprises: and (3) desulfurization treatment: mixing and contacting sulfur-containing hydrocarbon and hydrogen donor with an adsorbent to obtain desulfurized sulfur-containing hydrocarbon and a sulfur-carrying spent catalyst; regeneration treatment: mixing and contacting the sulfur-carrying spent regenerant with oxygen-containing regeneration gas to obtain a regenerant; reduction treatment: mixing and contacting the regenerant with a reducing gas to obtain a reducing regenerant which is recycled as an adsorbent; the adsorbent contains active metal monomers, and the reaction conditions of the reduction treatment comprise: taking a gas mixture containing non-hydrogen reducing gas as reducing gas, wherein the reducing temperature is 250-420 ℃, the reducing pressure is 0-3 MPa, and the volume space velocity of the reducing gas is 50-1000 h^-1The reduction time is 0.5-3 h. The method suppresses the formation of zinc silicate in the reduction reaction and desulfurization reaction, thereby improving the activity and strength of the regenerant. CN201310292325.7 discloses a method for adsorption desulfurization of catalytically cracked gasoline, which comprises the steps of using the catalytic gasoline subjected to selective hydrodesulfurization as a raw material (the sulfur content is less than 150 mu g/g), and performing cutting fractionation by a fractionating tower to obtain light gasoline and heavy gasoline. The light gasoline enters a fixed bed reactor to be subjected to non-hydrogenation physical adsorption desulfurization, the olefin content is not reduced by the physical adsorption desulfurization, and the octane number of the product is not lost; heavy gasoline enters a fixed bed reactor for carrying outThe hydro-adsorption desulfurization is carried out, and the reaction product is blended with the light gasoline physical adsorption desulfurization product to obtain the clean gasoline product which can meet the Euro V sulfur index requirement. The prior catalyst has the problems that the sulfur capacity is possibly low, zinc silicate and zinc aluminate are easily formed during regeneration and reduction, the adsorption activity is reduced, the octane number loss is large due to the occurrence of olefin saturation reaction, and the like. Therefore, it is necessary to develop a catalyst and a desulfurization process thereof, which have high breakthrough sulfur capacity, small octane number loss, good regeneration and reduction stability, and high adsorption desulfurization activity.

Disclosure of Invention

The invention provides an adsorption desulfurization method for catalytically cracked gasoline, which has the advantages of high sulfur capacity of a catalyst, small octane value loss, good regeneration and reduction stability and high adsorption desulfurization activity.

A catalytic cracking gasoline adsorption desulfurization method adopts a fixed bed reactor, gasoline is contacted with an adsorption desulfurization catalyst, and the catalyst comprises the following components in percentage by weight: 25.0-50.0 wt% of zinc oxide, 0.5-25.0 wt% of nickel oxide, 2.0-55.0 wt% of ZSM-5 molecular sieve, 20.0-50.0 wt% of macroporous alumina and 1.0-25.0 wt% of cerium-zirconium solid solution; the reaction process conditions are as follows: the reaction temperature is 280 ℃ and 400 ℃, the reaction pressure is 0.4-2.5MPa, and the volume space velocity is 3-8h^-1The volume ratio of hydrogen to oil is 1-50.

The gasoline adsorption desulfurization method provided by the invention has the advantages that the fixed bed reactor can be a fixed bed adiabatic reactor or a fixed bed isothermal reactor, and is preferably the fixed bed adiabatic reactor; further preferably, the reaction process conditions are as follows: the reaction temperature is 280 plus 360 ℃, the reaction pressure is 0.5-2.0MPa, and the volume space velocity is 5-8h^-1The volume ratio of hydrogen to oil is 1-40.

A preparation method of a catalytic cracking gasoline adsorption desulfurization catalyst comprises the following steps: (1) dissolving nickel salt and zinc salt in nitric acid, and adding a pore-expanding agent to obtain acid liquor containing the nickel salt and the zinc salt; (2) preparing an acid solution containing a pore-expanding agent, adding a ZSM-5 molecular sieve, macroporous alumina and a cerium-zirconium solid solution into the acid solution containing the pore-expanding agent, and uniformly stirring to obtain a mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution, wherein the mass percentage of the pore-expanding agent in the acid solution containing nickel and zinc is more than 2 times higher than that of the pore-expanding agent in the mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution in terms of oxides; adding an acid solution containing nickel salt and zinc salt into the slurry obtained in the step (2), and then adding an alkaline solution to perform a precipitation reaction; after the reaction is finished, the catalyst is obtained by filtering, washing, drying, forming and roasting.

In the preparation method of the catalyst, the addition amount of the pore-expanding agent in the step (1) accounts for 1-35% of the total mass of the nickel-zinc oxide.

The catalyst is further improved by dissolving nickel salt and zinc salt in deionized water, impregnating the surface of the catalyst, drying and roasting to obtain the catalyst, wherein the catalyst is controlled to contain 25.0-50.0 wt% of zinc oxide and 0.5-25.0 wt% of nickel oxide. The mass percentage content of nickel oxide and zinc oxide on the surface of the catalyst is 0.1-2.0 times higher than that of the nickel oxide and the zinc oxide in the catalyst. Is favorable for improving the adsorption desulfurization activity and selectivity of the catalyst, and has high adsorption desulfurization rate. The desulfurization activity and selectivity of the catalyst after 8-10 times of regeneration are higher than those of the catalyst without surface modification by nickel oxide and zinc oxide.

The catalytic gasoline adsorption desulfurization catalyst has the mass percentage content of nickel oxide and zinc oxide on the surface of the catalyst being 0.1-2.0 times higher than that of the nickel oxide and the zinc oxide in the catalyst.

Further preferably, the catalytic cracking gasoline adsorption desulfurization catalyst comprises the following components in percentage by weight: 25.0-45.0 wt% of zinc oxide, 0.5-20.0 wt% of nickel oxide, 10.0-55.0 wt% of ZSM-5 molecular sieve, 20.0-40.0 wt% of macroporous alumina and 1.0-20.0 wt% of cerium-zirconium solid solution.

The alkaline solution comprises: one or more of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, sodium hydroxide and ammonia water. The catalyst calcination temperature is 450-650 ℃.

Preparation of cerium-zirconium solid solution: weighing cerium nitrate and zirconium nitrate according to a stoichiometric ratio, placing the weighed cerium nitrate and zirconium nitrate into a beaker to prepare a mixed solution, adding a pore-expanding agent, dropwise adding ammonia water or a sodium carbonate solution into the mixed solution under the condition of continuously stirring, carrying out coprecipitation reaction, carrying out suction filtration, drying, roasting at 800-950 ℃ for 4-8 hours, and then crushing and grinding into powder. The addition amount of the pore-expanding agent accounts for 1-30% of the mass of the cerium-zirconium solid solution.

The pore-expanding agent is methyl cellulose, active carbon, polyvinyl alcohol, urea or sodium polyacrylate; polyacrylic acid; one or more of ammonium polyacrylate, preferably sodium polyacrylate.

The pore-expanding agent is added into the catalyst step by step, the catalyst has a mesoporous and macroporous structure, and the mass percentage of the pore-expanding agent in the acid solution containing nickel and zinc is higher than that of the pore-expanding agent in the mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution by more than 2 times in terms of metal oxide, so that the penetration sulfur capacity of the adsorption desulfurization catalyst is favorably improved, the olefin saturation rate of the catalyst is low, and the octane number loss is low.

The catalyst of the invention comprises: 25.0-50.0 wt% of zinc oxide, 0.5-25.0 wt% of nickel oxide, 2.0-55.0 wt% of ZSM-5 molecular sieve, 20.0-50.0 wt% of macroporous alumina and 1.0-25.0 wt% of cerium-zirconium solid solution, especially the introduction of cerium-zirconium solid solution (adding pore expanding agent in the mixing process of cerium-zirconium solid solution, ZSM-5 molecular sieve and macroporous alumina), effectively inhibits the generation of zinc aluminate/zinc silicate in the high-temperature reduction and regeneration process, and improves the reduction and regeneration stability of the catalyst. The method is suitable for removing sulfur in the catalytically cracked gasoline, the sulfur capacity of the adsorption desulfurization catalyst is reduced by 2-7% after the adsorption desulfurization catalyst is regenerated for 8 times, and the catalyst has good stability.

The present invention will be further illustrated by way of examples to illustrate the measurement method of the present invention, but the present invention is not limited to these examples.

Detailed Description

All starting materials for the present invention are commercially available.

Example 1

Preparation of cerium-zirconium solid solution: weighing 38.8g of cerium nitrate and 33.9g of zirconium nitrate according to a stoichiometric ratio, placing the cerium nitrate and the zirconium nitrate into a beaker to prepare a mixed solution, adding 4g of sodium polyacrylate, dropwise adding ammonia water or a sodium carbonate solution into the mixed solution under the condition of continuous stirring for coprecipitation reaction, then carrying out suction filtration, drying, roasting at 840 ℃ for 6 hours, crushing and grinding into powder.

Preparation of the catalyst: (1) dissolving 67.4g of nickel nitrate and 136g of zinc nitrate in nitric acid, and adding 16g of sodium polyacrylate to obtain acid liquor containing nickel and zinc; (2) preparing an acid solution containing 5.5g of sodium polyacrylate, adding 23g of ZSM-5 molecular sieve, 17g of macroporous alumina and 5.7g of cerium-zirconium solid solution into the acid solution containing sodium polyacrylate, and uniformly stirring to obtain a mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution; and then adding acid liquor containing nickel salt and zinc salt into the mixture slurry, adding sodium carbonate and ammonia water solution, carrying out precipitation reaction, raising the temperature of the obtained reaction product to 90 ℃, aging for 5 hours, filtering, washing, drying, molding and roasting to obtain the catalyst. The composition of the catalyst is shown in table 1.

Example 2

The preparation of cerium zirconium solid solution was the same as in example 1, the catalyst was prepared in the same manner as in example 1, the pore-expanding agent in the acid solution containing nickel and zinc was contained in an amount of 3.2 times by mass as the metal oxide as compared with the pore-expanding agent in the slurry of the mixture containing ZSM-5 molecular sieve, macroporous alumina and cerium zirconium solid solution, and the composition of the catalyst is shown in table 1.

Example 3

The preparation of the cerium zirconium solid solution is the same as that of example 1, the preparation steps of the catalyst are the same as that of example 1, and the mass percentage of the pore-expanding agent in the acid solution containing nickel and zinc is 3.8 times higher than that of the pore-expanding agent in the mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium zirconium solid solution calculated by oxides. After obtaining the catalyst, preparing nickel salt and zinc salt to be dissolved in deionized water, impregnating the surface of the catalyst, and then drying and roasting to obtain the catalyst with modified nickel and zinc surfaces. The mass percentage content of nickel oxide and zinc oxide on the surface of the catalyst is 0.9 times higher than that of the nickel oxide and the zinc oxide in the catalyst. The composition of the catalyst is shown in table 1.

Example 4

The preparation of the cerium zirconium solid solution is the same as that of example 3, the preparation steps of the catalyst are the same as that of example 3, and the mass percentage content of nickel oxide and zinc oxide on the surface of the catalyst is 1.5 times higher than that of the nickel oxide and zinc oxide in the catalyst. The composition of the catalyst is shown in table 1.

Table 1 example/comparative catalyst composition/wt%

Examples/comparative examples	Zinc oxide	Nickel oxide	ZSM-5	Macroporous aluminium oxide	Cerium zirconium solid solution
						Example 1	37	17.3	23	17	5.7
Example 2	46	16	20	13	5.0
						Example 3	29	20	33	13.5	4.5
Example 4	31	23	19	23.5	3.5

Comparative example 1

Preparation of the catalyst: (1) dissolving 67.4g of nickel nitrate and 136g of zinc nitrate in nitric acid, and adding 16g of sodium polyacrylate to obtain acid liquor containing nickel and zinc; (2) preparing an acid solution containing 5.5g of sodium polyacrylate, adding 23g of ZSM-5 molecular sieve and 17g of macroporous alumina into the acid solution containing sodium polyacrylate, and uniformly stirring to obtain a mixture slurry containing the ZSM-5 molecular sieve and the macroporous alumina; and adding an acid solution containing nickel salt and zinc salt into the mixture slurry, adding sodium carbonate and an ammonia water solution, carrying out precipitation reaction, raising the temperature of the obtained reaction product to 90 ℃, aging for 5 hours, filtering, washing, drying, molding and roasting to obtain the comparative catalyst 1.

Comparative example 2

Preparation of the catalyst: (1) dissolving 67.4g of nickel nitrate and 136g of zinc nitrate in nitric acid, and adding 21.5g of sodium polyacrylate to obtain acid liquor containing nickel and zinc; (2) adding 23g of ZSM-5 molecular sieve, 17g of macroporous alumina and 5.7g of cerium-zirconium solid solution into acid liquor containing nickel and zinc, uniformly stirring, adding sodium carbonate and ammonia water solution, carrying out precipitation reaction, raising the temperature of an obtained reaction product to 90 ℃, aging for 5 hours, filtering, washing, drying, forming and roasting to obtain the comparative catalyst 2.

Full-fraction FCC gasoline is adopted to evaluate the adsorption desulfurization catalyst and the comparative catalyst, and the gasoline raw material has olefin content of 38.5 v%, sulfur content of 127ppm and octane number of 91.1.

The evaluation is carried out by adopting a 100ml adiabatic bed, the catalyst or a comparative catalyst is firstly reduced by hydrogen under the pressure of 1.8MPa, the temperature of the bed layer is firstly increased to 360 ℃ and stays for 5 hours, and then the temperature of the bed layer is increased to 460 ℃ and stays for 8 hours to finish the reduction. Catalyst evaluation process conditions: the inlet temperature of the reactor is 330 ℃, the pressure is 1.3MPa, and the space velocity is 5.5h^-1The hydrogen-oil volume ratio was 1.3, and the evaluation results are shown in Table 2. The desulfurization rate of the catalyst is more than 90.8 percent, the octane number loss is less than 0.4, the penetrating sulfur capacity is more than 27 percent, and the olefin saturation rate is less than 15 percent. The comparative catalyst 1 has large octane number loss, the comparative catalyst 2 has low desulfurization rate, large octane number loss and low penetrating sulfur capacity. After the adsorbed sulfur capacity reaches saturation, the catalyst or the comparative catalyst is regenerated, and the process conditions are as follows: heating to 260 ℃ at a heating rate of 35 ℃/h in a nitrogen atmosphere, and staying for 7 h; and then regenerating the catalyst, wherein the used regeneration gas is a mixed gas of oxygen and nitrogen, and the volume content of the oxygen accounts for 7 percent of the total gas.

TABLE 2 catalyst and comparative catalyst reaction results

The regenerated catalysts 1 and 3, comparative examples 1 and 2, have the reactor inlet temperature of 330 ℃, the pressure of 1.3MPa and the space velocity of 5.5h^-1The evaluation results are shown in Table 3, with a hydrogen-oil volume ratio of 1.3. The desulfurization effect of the catalyst can be basically recovered to the level of a fresh agent, and the high temperature reduction can be effectively inhibitedThe generation of zinc silicate and zinc aluminate in the original and regeneration processes improves the reduction and regeneration stability of the catalyst. Compared with catalysts 1 and 2, the activity is reduced after regeneration, the octane number loss is large, and the penetration sulfur capacity is reduced. After 8 times of regeneration, the desulfurization rate of the catalyst in the embodiment 1 is 84.1 percent, and the sulfur capacity is reduced by 6 percent; in example 3, the desulfurization rate of the catalyst is 87.5 percent, and the sulfur capacity is reduced by 3 percent.

TABLE 3 catalyst and comparative catalyst reaction results

	Desulfurization rate/%)	Loss of octane number	Penetration of sulfur capacity/%)
				Example 1	91.1	0.3	29
Example 3	92.4	0.3	31
				Comparative example 1	86.1	2.4	23
Comparative example 2	76.9	1.6	14

Claims

1. A catalytic cracking gasoline adsorption desulfurization method is characterized in that a fixed bed reactor is adopted, gasoline is contacted with an adsorption desulfurization catalyst, and the catalyst comprises the following components in percentage by weight: 25.0-50.0 wt% of zinc oxide, 0.5-25.0 wt% of nickel oxide, 2.0-55.0 wt% of ZSM-5 molecular sieve, 20.0-50.0 wt% of macroporous alumina and 1.0-25.0 wt% of cerium-zirconium solid solution; the mass percentage content of nickel oxide and zinc oxide on the surface of the catalyst is 0.1-2.0 times higher than that of the nickel oxide and the zinc oxide in the catalyst; the reaction process conditions are as follows: the reaction temperature is 280 ℃ and 400 ℃, the reaction pressure is 0.4-2.5MPa, and the volume space velocity is 3-8h^-1Hydrogen-oil volume ratio is 1-50; the catalytic cracking gasoline adsorption desulfurization method comprises the following steps: (1) dissolving nickel salt and zinc salt in nitric acid, and adding a pore-expanding agent to obtain acid liquor containing the nickel salt and the zinc salt; (2) preparing an acid solution containing a pore-expanding agent, adding a ZSM-5 molecular sieve, macroporous alumina and a cerium-zirconium solid solution into the acid solution containing the pore-expanding agent, and uniformly stirring to obtain a mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution, wherein the mass percentage of the pore-expanding agent in the acid solution containing nickel and zinc is more than 2 times higher than that of the pore-expanding agent in the mixture slurry containing the ZSM-5 molecular sieve, the macroporous alumina and the cerium-zirconium solid solution in terms of oxides; adding an acid solution containing nickel salt and zinc salt into the slurry obtained in the step (2), and then adding an alkaline solution to perform a precipitation reaction; after the reaction is finished, filtering, washing, drying, forming and roasting to obtain a catalyst; the catalyst was then further modified: dissolving nickel salt and zinc salt in deionized water, dipping the surface of the catalyst, drying and roasting to obtain the finished catalyst, wherein the catalyst comprises 25.0-50.0 wt% of zinc oxide and 0.5-25.0 wt% of nickel oxide.

2. The catalytically cracked gasoline of claim 1The adsorption desulfurization method is characterized in that the adsorption desulfurization reaction process conditions are as follows: the reaction temperature is 280 plus 360 ℃, the reaction pressure is 0.5-2.0MPa, and the volume space velocity is 5-8h^-1The volume ratio of hydrogen to oil is 1-40.

3. The adsorptive desulfurization method for catalytically cracked gasoline according to claim 1, wherein the fixed bed reactor is a fixed bed adiabatic reactor or a fixed bed isothermal reactor.

4. The catalytic cracked gasoline adsorption desulfurization method of claim 1, wherein the cerium-zirconium solid solution is prepared as follows: weighing cerium nitrate and zirconium nitrate according to a stoichiometric ratio, placing the weighed cerium nitrate and zirconium nitrate into a beaker to prepare a mixed solution, adding a pore-expanding agent, dropwise adding ammonia water or a sodium carbonate solution into the mixed solution under the condition of continuously stirring, carrying out coprecipitation reaction, carrying out suction filtration, drying, roasting at 800-950 ℃ for 4-8 h, crushing and grinding into powder.

5. The catalytic cracked-gasoline adsorptive desulfurization method of claim 1, wherein the alkaline solution comprises: one or more of sodium bicarbonate, ammonium bicarbonate, sodium carbonate, sodium hydroxide and ammonia water.

6. The catalytic gasoline adsorption desulfurization method of claim 1, wherein the pore-expanding agent is added in the step (1) in an amount of 1-35% of the total mass of the nickel-zinc oxide.

7. The adsorptive desulfurization method for catalytically cracked gasoline according to claim 1, wherein the pore-expanding agent is one or more of sodium polyacrylate, polyacrylic acid and ammonium polyacrylate.