How do non-universalists account for these passages talking about the salvation of all?

Once one logically considers the relevant extant documents (by the genuine methodology of truly scientific textual criticism) ; once one has accurately translated these same documents ; once one has examined them hermeneutically ; once one has given attention to the context of the wording ; and once one has balanced all the information throughout all of the scripture, comparing 'spiritual things with spiritual things', these particular texts (and many others like them) are found to refer to 'all' that are under headship.

The question is, Which Headship ?

1. First Corinthians 15:22 "for as all in Adam all die, so also in Christ shall all be made alive".

This expresses that under Adam's headship, all his progeny die. And it expresses that under Christ's headship, all live.

It does not state that all under Adam are also under Christ. We know, from other places, that repentance and faith are essential to pass from death (under Adam) to life (under Christ).

2. Romans 5:18 "as one man's trespass lead to the condemnation of all men, so one man's act leads to the acquittal and life for all men".

This is a bad translation. The literal reads 'as by one offence unto all humanity unto condemnation so also by one demonstrated righteousness unto all humanity unto justification of life' (1).

This expresses that one offence brought all humanity (under the one who committed that offence) into condemnation. It also expresses that by one demonstrated righteousness (the righteousness of God upon his own Son) all of the humanity under Christ's headship was brought into justification.

But we know, from other places, that justification is only by (and never without) faith.

3. Corinthians 1:19-20

You would need to tell us to which of the two epistles you refer.

Please see @Anne 's answer regarding Colossians 1:19-20.

4. Romans 11:32 "For God has imprisoned all in disobedience so that he may be merciful to all."

The context is from verse 26 : so all Israel shall be saved. But we know from another place, Romans 9:6, that they are not all Israel who are of Israel.

Paul is writing of the true Israel of God in this place, not Israel after the flesh. Again, this is a matter of headship and progeny.

5. 1 John 2:2 "He is the propitiation for our sins, and not for ours only but also for the sins of the whole world."

This is a bad translation. The literal reads and he the propitiation is for the sins of us but not for that of us only but also for that of the whole world.(2)

The three words, 'the sins of' (the whole world), are not in the original Greek Text of John's words.

We know from other places that Jesus Christ not only suffered (before death) for sins not his own, which has an effect on those chosen of God (for God placed their sins upon Christ in the hours of darkness upon the cross) but he was also, by God, 2 Corinthians 5:21, effected sin (itself) and - dying - he took sin (itself) out of the world, which has an effect on humanity generally.

There are two significant parts to the doctrine, which Paul teaches as separate matters. One is specific (one's own personal sinful deeds) and one is generic (the matter of the entrance of sin into the world, by deed of serpent, woman and man).

These two should not be confused together.

All of the above is clearly taught in such as Calvin's Institutes (1536) and the Westminster Confession (1646) ; and in such systematic theologies as that of William Huntington (1745-1813) J C Philpot (1802-1869) and John Metcalfe (1931 to the present day).

(1) and (2) are from The Englishman's Greek New Testament of 1870 (the interlinear English being translated from Stephanus' Greek Text of 1550).

Translation Note on Romans 5:18

(1) The EGNT renders δικαιώματος, dikaiomatos, as an 'accomplished' righteousness, but it is clear from the usage of this word, in the apostolic writings of the New Testament, that this is actually a 'demonstrated' righteousness, in the context of active judgment.

That is to say it is the demonstrated righteousness of God (not sparing his own Son, but delivering him up for us all) not the (conjectured) 'accomplished' righteousness (supposedly by legal works on earth) attributed (by some) to Jesus Christ, acting in humanity.

Calling it an 'accomplished' righteousness is clearly the wishful thinking of those who want to conform to the idea of 'active' and 'passive' righteousness, which Dr John Owen added to the Savoy Declaration of 1658, it being not present in the Westminster Confession of 1647.